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Legend Airlines

Legend Airlines was an airline headquartered at Dallas Love Field in Dallas, Texas, United States. Legend operated nonstop flights from its Love Field hub to Washington, D.C.; Las Vegas; Los Angeles; and New York City, the first carrier to fly from Love Field to destinations beyond the Wright Amendment five-state region after the opening of Dallas/Fort Worth International Airport in 1974. Legend's aircraft were limited to 56 passenger seats by the Wright Amendment, so the aircraft were outfitted in a spacious all-business class layout, aiming at the lucrative business travel market.

Legend's initial flights were substantially delayed by lobbying to persuade Congress to modify the Wright Amendment, court battles instigated by American Airlines and the city of Fort Worth, and by difficulties obtaining operational approval from the Federal Aviation Administration (FAA). Flights began in April 2000, but were suspended indefinitely in December 2000 due to mounting losses, with the airline filing for bankruptcy. Efforts to secure additional financing and restart flights came to naught; the airline surrendered its air operator's certificate and was liquidated in mid-2001.

The airline's private Love Field terminal—which was independently owned and leased to the carrier—was condemned under eminent domain and the gates razed after the 2006 Wright Amendment repeal imposed a 20-gate cap at the airport. These events triggered a series of lawsuits that were not fully settled until 2016.

Background
By the early 1960s, Love Field was reaching the limits of its capacity, and efforts to share Greater Southwest International Airport (GSW) in Fort Worth had proven unsuccessful. The situation was inefficient, and in 1964, the Civil Aeronautics Board (CAB) ordered Dallas and Fort Worth to establish a new joint regional airport. The cities and airlines ultimately agreed, signing a 1968 bond ordinance obligating all existing carriers to move to the new regional airport and prohibiting the operation of competing municipal airports. The effort culminated in the demolition of GSW, the 1974 opening of Dallas/Fort Worth International Airport (DFW), the closure of Love Field to certified air carriers, and a corresponding effort to redevelop Love for general aviation.

Southwest Airlines was founded after the 1968 bond ordinance; it was not a party to the agreement and felt that its business model would be affected by the long drive to the new airport. Dallas and Fort Worth sued Southwest but were unsuccessful in dislodging the airline from Love Field. After the Airline Deregulation Act in 1978, Southwest announced plans to begin interstate service in 1979. However, Texas officials—particularly those from Fort Worth—thought that increased traffic at Love Field could draw flights away from DFW Airport and threaten its financial stability. Acting on their behalf, Jim Wright, member of the U.S. House of Representatives serving Fort Worth, sponsored and helped pass an amendment to the International Air Transportation Act of 1979 in Congress that restricted passenger service out of Love Field in the following ways:
 * Service using larger mainline airliners could be provided from Love Field only to airports within Texas or to four neighboring U.S. states: Arkansas, Louisiana, New Mexico and Oklahoma.
 * Airlines could not offer connecting flights, through service on another airline, or through ticketing beyond the five-state region.
 * Flights to other states were allowed only on aircraft with 56 seats or fewer, in an attempt to prohibit mainline passenger service outside of the five-state region.

By the mid-1990s, Southwest Airlines' business within the five-state region had burgeoned, but no carrier had seriously attempted to exploit the 56-seat exemption. Factions in Dallas had begun to view the Wright Amendment as anti-competitive and harmful to local business interests, but its restrictions were backed by Fort Worth and American Airlines to protect DFW Airport, and by local property owners who wanted to reduce jet noise and street traffic around Love Field. Attempts to modify the restrictions had become mired in lawsuits and controversy.

Founding and early history
Legend Airlines was the brainchild of T. Allan McArtor, former Federal Aviation Administration (FAA) Administrator, Federal Express executive and a U.S. Air Force pilot who had been a member of the Air Force precision flying team, the Thunderbirds. McArtor served as airline's President and chief executive officer (CEO).

In 1996, Dallas aviation company and Legend partner Dalfort Aviation announced that Legend would fly from Love Field using jets with 56 seats—the maximum number allowed for long-haul flights under Wright. Dalfort would refurbish older McDonnell Douglas DC-9s or Boeing 727s—aircraft that normally carried 90 or more passengers—with an all-first class configuration. McArtor and Dalfort CEO Bruce Leadbetter claimed that buying new regional jets with 56 or fewer seats was too expensive and would not provide Dalfort with much-needed overhaul business. However, the United States Department of Transportation ruled in September 1996 that the 56-seat restriction applied to the "designed capacity" of an airliner rather than to the number of seats actually installed, prompting Legend to seek a change in the law; at Legend's behest, Texas Rep. Joe Barton was soon calling for the U.S. House of Representatives to change the 56-seat requirement.

By July 1997, McArtor had enlisted the help of Senator Richard Shelby of Alabama, who proposed to change the Wright restrictions to allow Legend to use reconfigured aircraft. On 7 October 1997, despite fierce opposition from the Texas congressional delegation, the United States Senate passed a transportation funding bill including Shelby's amendment to allow nationwide flights using reconfigured 56-seat aircraft and add three U.S. states to the Wright Amendment region. On 9 October 1997, the U.S. House overwhelmingly approved the bill.

Within a month, Fort Worth was suing Legend and the city of Dallas, arguing for upholding the 1968 DFW bond agreement; Dallas and Legend argued that it could no longer be enforced. American Airlines joined Fort Worth in suing Dallas to stop the Shelby Amendment from taking effect, and McArtor accused American of quietly orchestrating the entire effort in order to block Legend. By February 1998, Southwest Airlines joined the Dallas lawsuit at the behest of Legend.

McArtor argued that Fort Worth was also violating the bond agreement by allowing Mesa Airlines and FedEx Express to operate from Meacham Field and the recently-constructed Fort Worth Alliance Airport respectively. In October 1998, Legend sued Fort Worth, accusing the city of a "double standard" in its simultaneous support for Alliance and opposition to expansion at Love. However, State District Judge Bob McCoy dismissed the suit later that month on the grounds that Legend was not a party to the 1968 DFW bond agreement and thus lacked standing to sue.

Service begins
On 5 April 2000, after further legal battles against Fort Worth and American Airlines and delays in gaining operating approval from the FAA, Legend began the first long-haul service from Love Field since 1974 with a flight to Washington Dulles International Airport (IAD). Legend Airlines soon operated nonstop service to IAD, Las Vegas McCarran International Airport (LAS) and Los Angeles International Airport (LAX). LaGuardia Airport (LGA) in New York City was then added as a fourth destination.

Despite continuing to argue in court that long-haul service from Love Field should be blocked, American Airlines, in a competitive move, reconfigured several of its Fokker 100 jets with 56 seats in a similar business class-like configuration and operated nonstop service from Love Field starting on 1 May 2000 to Chicago O'Hare Airport (ORD), LAX, and LGA.

On 29 June 2000, the United States Supreme Court declined to review a federal appeals court decision allowing long-haul flights from Love, effectively ending the last attempt by Fort Worth, the D/FW Airport Board, and American Airlines to stop Legend in the courts.

Demise
Legend spent more than most new airlines prior to starting flights; figures range from $21 million to $29 million. Its aircraft had languished on the ground for three years. Although its flights to New York and Washington averaged almost two-thirds capacity, the airline lost $25 million during its first six months of operation, being afflicted by high start-up costs, high fuel costs, and intense competition from other airlines.

Legend suspended flights indefinitely on 3 December 2000 after failing to secure additional financing, and announced that it would be filing for Chapter 11 bankruptcy protection. In early 2001, Legend laid off all of its Dallas employees, surrendered its air operator's certificate, and announced that it would enter Chapter 7 liquidation. In May, McArtor left Legend to head the North American unit of Airbus, and the airline's physical assets were auctioned in June 2001, including an estimated $1 million in DC-9 spares, but not the aircraft themselves, which were leased. By late 2002, two of the airline's former DC-9s were being operated by Southeast Airlines, one had been purchased by the Columbus Blue Jackets hockey team, and the other four had been mothballed in Kingman, Arizona, awaiting new buyers.

In 2016, journalist Robert Wilonsky described the airline's downfall as the result of a conspiracy by American Airlines, Southwest Airlines, the D/FW Airport Board, and the cities of Dallas and Fort Worth to "break Legend before it ever got off the ground."

Despite its failure to establish a viable aviation business, industry observers credited Legend Airlines with engineering the first substantive change to the controversial Wright Amendment and with introducing competition to Southwest Airlines at Love Field; when Legend ceased operation, American, Continental Express, and Delta Connection affiliate Atlantic Southeast Airlines had all begun operating from the airport to compete with the startup carrier. Legend's activities prompted other aviation interests to seriously consider using regional jets on long-haul flights from Love Field and to more openly back changes to the Wright Amendment, ideas that seemed infeasible beforehand. The Wright Amendment region was subsequently expanded again in 2005, and the law was partially repealed in 2006 and fully repealed in 2014.

In-flight services
Aiming for the lucrative full-fare business travel market, Legend Airlines provided a high level of service, with all seats in a business class configuration. Two wide seats were installed on each side of the generous center aisle (known as a 2-2 arrangement), and legroom was ample due to the removal of several entire rows of seats from its DC-9 airliners, which usually carried 100 or more passengers in a 2-3 arrangement. Fresh flowers adorned aircraft interiors and the executive terminal at Love Field; the latter was set up so passengers could exit their aircraft and board a taxi in less than a minute. Legend was the first airline to offer live in-flight television on seat-back monitors; the DirecTV service was soon offered by JetBlue as well, but Legend offered it for free rather than charging travelers $5 to use it. Seats were also equipped with an AT&T Airfones and laptop computer charging ports. The lavish meals, described as "celebrity-chef crafted", were commissioned from several Dallas-area chefs and were served on real china with silverware, fresh fruit, and individual pats of real butter, rather than the plastic trays, plastic utensils, and packaged condiments and fruit generally offered by other carriers. Meals came with a ribbon-tied box of chocolate truffles and wines selected to complement the food. All of these amenities were offered for fares comparable to rival airlines' coach-class tickets.

Executive terminal
Legend operated a separate executive passenger terminal at the perimeter of Love Field, at 7777 Lemmon Avenue near Lovers Lane, rather than using the primary central passenger terminal. The Legend terminal's compact size and efficient layout allowed passengers to board flights only a few minutes after arriving at curbside. The terminal cost $20 million to construct and reflected the airline's upscale image, with leather seats, fresh flowers, and gates designed to resemble private executive clubs.

The complex was built by and leased from a private investment group loosely affiliated with Legend and Dalfort but not directly controlled by either company. Upon Legend's collapse, the owners immediately sought new tenants, subleasing one gate to Atlantic Southeast Airlines and entering into talks with American and Continental Express, who were then sharing the only two gates in the main terminal that were not controlled by Southwest Airlines. Despite the owner's efforts, the gates were vacant by the summer of 2002, although some office and parking garage space had been leased to non-aviation businesses.

In late 2005, the owners were publicly backing an effort to repeal the Wright Amendment, hoping to boost the lease value of the still-vacant gates; however, Dallas mayor Laura Miller was openly campaigning for the structure to be torn down. In June 2006, the cities of Dallas and Fort Worth, DFW Airport, Southwest Airlines, and American Airlines executed a complex agreement as a condition of their mutual support for the repeal of the Wright Amendment. Among other provisions, the agreement imposed a permanent 20-gate cap at Love Field and obligated Dallas to revise its airport master plan and demolish all gates in excess of that number "as soon as practical". After the partial repeal of the Wright Amendment became effective in October 2006, the Dallas City Council immediately approved using eminent domain to seize and raze the Legend gates to comply with the cap. This effectively ended negotiations to sell the facility to Pinnacle Airlines, and the gates were subsequently condemned by the federal government and torn down, with the owners receiving nothing in return.

The owners filed a lawsuit challenging the Wright Amendment repeal on antitrust grounds but the suit was thrown out by the federal courts in late 2007. However, the owners filed another suit in 2008 accusing the federal government of having condemned the structure without just compensation, and in April 2016, Federal Claims Judge Margaret M. Sweeney sided with owners Love Terminal Partners and Virginia Aerospace, ordering the government to pay them $133 million plus interest for having destroyed the property's economic value.

Fleet

 * 7 McDonnell Douglas DC-9-32 - seven (7) aircraft in fleet, all obtained secondhand from other airlines and configured with 56 seats

Destinations
Legend Airlines served the following destinations during its existence:

 * Dallas, Texas: Love Field (DAL) - airline headquarters and hub
 * Las Vegas, Nevada: McCarran International Airport (LAS)
 * Los Angeles, California: Los Angeles International Airport (LAX)
 * New York City, New York: LaGuardia Airport (LGA)
 * Washington, D.C.: Washington Dulles International Airport (IAD)

title: Legend Airlines


text:
Kožený

Kožený is a Czech surname. Kožená is the female form and Kozeny the German form. Notable people with the surname include:

 * Josef Kozeny (1889–1967), Austrian physicist
 * Magdalena Kožená (born 1973), Czech opera singer
 * Viktor Kožený (born 1963), Czech-born fugitive financier

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Kožený


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User talk:Sparky8181

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User talk:Pme~enwiki

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Image copyright problem with Image:Skando.jpg
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Your account will be renamed
Hello,

The developer team at Wikimedia is making some changes to how accounts work, as part of our on-going efforts to provide new and better tools for our users like cross-wiki notifications. These changes will mean you have the same account name everywhere. This will let us give you new features that will help you edit and discuss better, and allow more flexible user permissions for tools. One of the side-effects of this is that user accounts will now have to be unique across all 900 Wikimedia wikis. See the announcement for more information.

Unfortunately, your account clashes with another account also called Pme. To make sure that both of you can use all Wikimedia projects in future, we have reserved the name Pme~enwiki that only you will have. If you like it, you don't have to do anything. If you do not like it, you can pick out a different name. If you think you might own all of the accounts with this name and this message is in error, please visit Special:MergeAccount to check and attach all of your accounts to prevent them from being renamed.

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Renamed
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title: User talk:Pme~enwiki


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User talk:Forcenewearl

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User talk:Honi2sweet

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User talk:Fem

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Images
If you continue to upload copyrighted images to Wikipedia under misleading licences you will be blocked from editing.--nixie 08:08, 28 December 2005 (UTC)

title: User talk:Fem


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User talk:Catz28

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title: User talk:Catz28


text:
Talk:Osteophyte

Names
Suggested template for Orthopaedic Conditions (see Talk:Orthopedic surgery) is Name Definition Synonyms Incidence Pathogenesis Pathology Stages Classification Natural History/Untreated Prognosis Clinical Features Investigation Non-Operative Treatment Risks of Non-Operative Treatment Prognosis following Non-Operative Treatment Operative Treatment (Note that each operations should have its own wiki entry) Risks of Operative Treatment Prognosis Post Operation Complications Management Prevention History --Mylesclough 05:21, 8 October 2005 (UTC)

From article page
osteophytes of the knee

Xray diagnosis of my knee swelling and pain indicated osteophytes of the knee, further diagnosis will be a knee scan with dye and an MRI. I have read taping can reduce pain and improve movement over time so I am wrapping my knee with an ace bandage. Please include your treatment experience of knee pain in this article. thanks

 * I moved this here because it is a question. JFW | T@lk  12:51, 11 December 2005 (UTC)

Replacement rate and such
The article says "In an adult, 20 percent of bone calcium is withdrawn from bones and replaced each year. Thus, every five years the bones are renewed." This is not true. Perhaps 20% of bone calcium is withdrawn and replaced each year (although this does need a citation), but this does not mean that every five years the bones are completely renewed. Only faulty reasoning leads from one to the other; the same reasoning would lead one to think that a radioactive sample will have completely decayed after two half-lives. Not so. After five years, about 33% of bone calcium will still be in place. Reason is that some of the 20 percent that gets replaced this year is the same calcium that got replaced last year. I'm removing the sentence "Thus, every five years..." to this page. 24.162.120.52 01:54, 8 May 2007 (UTC)

Possible plagarism
The "Cause" section is nearly identical with the "What Causes" section of this commercial page: http://www.bonespur.com/bone-spur-surgery.html Somebody is using somebody else's work without attribution. Also, source number 4, Neurosurgery Today, says nothing about eruptions being a source of bone spurs. —The preceding unsigned comment was added by Jcatkeson (talk • contribs).

Merger Proposal
Bone spur and Osteophyte pages contain virtually the same content. Most referenced sources for each typically reference a bone spur thus: Bone spur (Osteophyte). I propose merging the two pages retaining the most complete work from each. Particlebry (talk) 09:15, 7 April 2009 (UTC)

I agree. Bone spur is synonymous with osteophyte. Corta (talk) 04:58, 21 April 2009 (UTC)

Strongly Agree --Daydreamer302000 (talk) 08:09, 9 July 2009 (UTC)

Absolutely Hananekosan (talk) 08:12, 11 September 2009 (UTC)
 * It looks like this has been resolved and done. I removed the merge template. -- B.S. Lawrence (talk) 18:42, 30 October 2009 (UTC)

Where they form
I added clarification to the intro that osteophytes do not only form at joints as they can actually form anywhere on the body. They do usually form at joints, but not exclusively. Hananekosan (talk) 08:10, 11 September 2009 (UTC)

Opening contradiction re: "bone spur" and "osteophyte"
The article opens with "Osteophytes, also known as bone spurs ..." The sentence immediately following, however, is, "There is a great difference between osteophytes and bone spurs."

Well, which is it? Somebody who understands these things should clear this up.

Mark —Preceding unsigned comment added by 24.5.131.32 (talk) 04:07, 12 January 2010 (UTC)

reference link #2 leads to a 404
subject says all.

reference link #2 gives a 404 not found

More images.
Well, I have bone spurs at the proximal joints of several fingers, and at various carpal bones, and on both elbows. If I can find old Xrays of them, would they be of any value on this page? There's only one pic so far and it's not very clear. — Preceding unsigned comment added by 121.212.64.150 (talk) 03:21, 28 February 2018 (UTC)

title: Talk:Osteophyte


text:
User talk:Bubaib 98

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title: User talk:Bubaib 98


text:
Man of the Century

Man of the Century is a 1999 American comedy film directed by Adam Abraham and written by Abraham and Gibson Frazier. The film stars Frazier, Cara Buono, Susan Egan, Dwight Ewell and Anthony Rapp. It is a farce about the attitudes, values, and slang displayed in the popular culture of the 1920s (and, to some extent, the early 1930s). Man of the Century was filmed in black and white. Its working title was "Johnny Twennies".

Characters
The main characters include:
 * Johnny Twennies – (Gibson Frazier) A lovable, good-looking, fast-talking newspaper reporter whose manner is similar to that of a 1920s pulp character.
 * Virginia Clemens - (Cara Buono) A sweet girl who has an innocent school-girl crush on Johnny.
 * Samantha Winter - (Susan Egan) Johnny's modern girlfriend.

title: Man of the Century


text:
Wikipedia:Articles for deletion/88face

 * The following discussion is an archived debate of the proposed deletion of the article below. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or on a Votes for Undeletion nomination).  No further edits should be made to this page.

The result of the debate was speedy deleted.  Grue  17:48, 10 October 2005 (UTC)

88face
Article is for a neosmileyface. Non-notable, newly created, article fails to assert any notability, yet a tragic oversight in WP:CSD forces this to be an AFD. C HAIRBOY (☎) 05:22, 8 October 2005 (UTC)
 * Delete per nomination. C HAIRBOY (☎) 05:22, 8 October 2005 (UTC)

The 88face is a valid symbol and has been in wide use for a considerable amount of time. Therefore, this article should not be deleted, as it is extremely relevant and accurate. - Unsigned by 69.248.86.170

 * Delete per the nomination Jtkiefer  T - 05:25, 8 October 2005 (UTC)
 * Delete as per nom. MCB 06:58, 9 October 2005 (UTC)

 * The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or in an undeletion request). No further edits should be made to this page.

title: Wikipedia:Articles for deletion/88face


text:
User talk:Hitmanmj3

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title: User talk:Hitmanmj3


text:
Talk:U.S. Route 112

Merge from M-112
I disagree with the suggestion to merge M-112 (Michigan highway) with US 112. M-112 was a different road with a distintive history that only coincidentally happened to connect with US 112. older ≠ wiser
 * Just merge and redirect M112, M-16 (Michigan highway) was recently redirected and merged to U.S. Route 16 since M-16 is another state highway that later became part of a US highway with the same number. --Nintendude userpage 09:56, 20 May 2006 (UTC)
 * That was very different because the route of M-16 actually became US-16. M-112 was a different route from US 112 that only happenned to have its endpoints on 112. older ≠ wiser 10:39, 20 May 2006 (UTC)

Assessment
Although the RD is lacking, the article has all the "big four", so it's at C-class. CL — 04:05, 28 July 2008 (UTC)
 * Needs some extra referencing. –Juliancolton Tropical Cyclone  02:46, 5 September 2008 (UTC)
 * Both are no longer valid concerns. I have merged this into U.S. Route 12 in Michigan, its successor designation to eliminate the redundancy.  Imzadi 1979  →   18:59, 21 May 2012 (UTC)

title: Talk:U.S. Route 112


text:
User talk:Irockster

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User talk:Not Being A Child

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Talk:WPBO-TV

 * Do you think that this article should be merged with the WOSU-TV article? TomStike 05:21, 8 October 2005 (UTC)

title: Talk:WPBO-TV


text:
User talk:Nameer~enwiki

Welcome
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Wikipedia:Articles for deletion/E-space

 * The following discussion is an archived debate of the proposed deletion of the article below. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or on a Votes for Undeletion nomination).  No further edits should be made to this page.

The result of the debate was Delete. --Ryan Delaney talk 02:33, 15 October 2005 (UTC)

E-space
Weak delete, close to being nn fancruft, but not completely sure it cannot be expanded. Tito xd (?!?) 05:22, 8 October 2005 (UTC)
 * Speedy This is patent nonsense. Qaz  ( talk ) 06:54, 8 October 2005 (UTC)
 * Delete either way, be it as nn fancruft or nonsene. -- Egil 15:55, 8 October 2005 (UTC)
 * Delete nonesense --Rogerd 17:53, 8 October 2005 (UTC)

 * The above discussion is preserved as an archive of the debate. Please do not modify it. Subsequent comments should be made on the appropriate discussion page (such as the article's talk page or in an undeletion request). No further edits should be made to this page.

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Electrodynamic tether

Electrodynamic tethers (EDTs) are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy. Electric potential is generated across a conductive tether by its motion through a planet's magnetic field.

A number of missions have demonstrated electrodynamic tethers in space, most notably the TSS-1, TSS-1R, and Plasma Motor Generator (PMG) experiments.

Tether propulsion
As part of a tether propulsion system, craft can use long, strong conductors (though not all tethers are conductive) to change the orbits of spacecraft. It has the potential to make space travel significantly cheaper. When direct current is applied to the tether, it exerts a Lorentz force against the magnetic field, and the tether exerts a force on the vehicle. It can be used either to accelerate or brake an orbiting spacecraft.

In 2012 Star Technology and Research was awarded a $1.9 million contract to qualify a tether propulsion system for orbital debris removal.

Uses for ED tethers
Over the years, numerous applications for electrodynamic tethers have been identified for potential use in industry, government, and scientific exploration. The table below is a summary of some of the potential applications proposed thus far. Some of these applications are general concepts, while others are well-defined systems. Many of these concepts overlap into other areas; however, they are simply placed under the most appropriate heading for the purposes of this table. All of the applications mentioned in the table are elaborated upon in the Tethers Handbook. Three fundamental concepts that tethers possess, are gravity gradients, momentum exchange, and electrodynamics. Potential tether applications can be seen below:

ISS reboost
EDT has been proposed to maintain the ISS orbit and save the expense of chemical propellant reboosts. It could improve the quality and duration of microgravity conditions.

Electrodynamic tether fundamentals
The choice of the metal conductor to be used in an electrodynamic tether is determined by a variety of factors. Primary factors usually include high electrical conductivity, and low density. Secondary factors, depending on the application, include cost, strength, and melting point.

An electromotive force (EMF) is generated across a tether element as it moves relative to a magnetic field. The force is given by Faraday's Law of Induction:

 * $$ V_\mathrm{emf} = \int_0^L \left( \vec{v}_\mathrm{orb} \times \vec{B} \right) d\vec{L}. $$

Without loss of generality, it is assumed the tether system is in Earth orbit and it moves relative to Earth's magnetic field. Similarly, if current flows in the tether element, a force can be generated in accordance with the Lorentz force equation

 * $$ \vec{F} = \int_0^L I(L) \, d\vec{L} \times \vec{B}. $$

In self-powered mode (deorbit mode), this EMF can be used by the tether system to drive the current through the tether and other electrical loads (e.g. resistors, batteries), emit electrons at the emitting end, or collect electrons at the opposite. In boost mode, on-board power supplies must overcome this motional EMF to drive current in the opposite direction, thus creating a force in the opposite direction, as seen in below figure, and boosting the system.

Take, for example, the NASA Propulsive Small Expendable Deployer System (ProSEDS) mission as seen in above figure. At 300 km altitude, the Earth's magnetic field, in the north-south direction, is approximately 0.18–0.32 gauss up to ~40° inclination, and the orbital velocity with respect to the local plasma is about 7500 m/s. This results in a Vemf range of 35–250 V/km along the 5 km length of tether. This EMF dictates the potential difference across the bare tether which controls where electrons are collected and / or repelled. Here, the ProSEDS de-boost tether system is configured to enable electron collection to the positively biased higher altitude section of the bare tether, and returned to the ionosphere at the lower altitude end. This flow of electrons through the length of the tether in the presence of the Earth's magnetic field creates a force that produces a drag thrust that helps de-orbit the system, as given by the above equation. The boost mode is similar to the de-orbit mode, except for the fact that a High Voltage Power Supply (HVPS) is also inserted in series with the tether system between the tether and the higher positive potential end. The power supply voltage must be greater than the EMF and the polar opposite. This drives the current in the opposite direction, which in turn causes the higher altitude end to be negatively charged, while the lower altitude end is positively charged(Assuming a standard east to west orbit around Earth).

To further emphasize the de-boosting phenomenon, a schematic sketch of a bare tether system with no insulation (all bare) can be seen in below figure.

The top of the diagram, point A, represents the electron collection end. The bottom of the tether, point C, is the electron emission end. Similarly, $$V_\mathrm{anode}$$ and $$V_\mathrm{cathode}$$ represent the potential difference from their respective tether ends to the plasma, and $$V - V_p$$ is the potential anywhere along the tether with respect to the plasma. Finally, point B is the point at which the potential of the tether is equal to the plasma. The location of point B will vary depending on the equilibrium state of the tether, which is determined by the solution of Kirchhoff's voltage law (KVL)
 * $$ V_\mathrm{anode} + \int_A^C I(y) \, dR_t + R_\mathrm{load} I_C + V_\mathrm{emit} + V_\mathrm{cathode} = V_\mathrm{emf} $$

and Kirchhoff's current law (KCL)
 * $$ I_{AB} = I_{BC} + I_C $$

along the tether. Here $$I_{AB}$$, $$I_{BC}$$, and $$I_C$$ describe the current gain from point A to B, the current lost from point B to C, and the current lost at point C, respectively.

Since the current is continuously changing along the bare length of the tether, the potential loss due to the resistive nature of the wire is represented as $$\textstyle\int_A^C I(y)\,dR_t$$. Along an infinitesimal section of tether, the resistance $$dR_t$$ multiplied by the current $$I(y)$$ traveling across that section is the resistive potential loss.

After evaluating KVL & KCL for the system, the results will yield a current and potential profile along the tether, as seen in above figure. This diagram shows that, from point A of the tether down to point B, there is a positive potential bias, which increases the collected current. Below that point, the $$V - V_p$$ becomes negative and the collection of ion current begins. Since it takes a much greater potential difference to collect an equivalent amount of ion current (for a given area), the total current in the tether is reduced by a smaller amount. Then, at point C, the remaining current in the system is drawn through the resistive load ($$R_\mathrm{load}$$), and emitted from an electron emissive device ($$V_\mathrm{emit}$$), and finally across the plasma sheath ($$V_\mathrm{cathode}$$). The KVL voltage loop is then closed in the ionosphere where the potential difference is effectively zero.

Due to the nature of the bare EDTs, it is often not optional to have the entire tether bare. In order to maximize the thrusting capability of the system a significant portion of the bare tether should be insulated. This insulation amount depends on a number of effects, some of which are plasma density, the tether length and width, the orbiting velocity, and the Earth's magnetic flux density.

Tethers as generators

An electrodynamic tether is attached to an object, the tether being oriented at an angle to the local vertical between the object and a planet with a magnetic field. The tether's far end can be left bare, making electrical contact with the ionosphere. When the tether intersects the planet's magnetic field, it generates a current, and thereby converts some of the orbiting body's kinetic energy to electrical energy. Functionally, electrons flow from the space plasma into the conductive tether, are passed through a resistive load in a control unit and are emitted into the space plasma by an electron emitter as free electrons. As a result of this process, an electrodynamic force acts on the tether and attached object, slowing their orbital motion. In a loose sense, the process can be likened to a conventional windmill- the drag force of a resistive medium (air or, in this case, the magnetosphere) is used to convert the kinetic energy of relative motion (wind, or the satellite's momentum) into electricity. In principle, compact high-current tether power generators are possible and, with basic hardware, tens, hundreds, and thousands of kilowatts appears to be attainable.

Voltage and current
NASA has conducted several experiments with Plasma Motor Generator (PMG) tethers in space. An early experiment used a 500-meter conducting tether. In 1996, NASA conducted an experiment with a 20,000-meter conducting tether. When the tether was fully deployed during this test, the orbiting tether generated a potential of 3,500 volts. This conducting single-line tether was severed after five hours of deployment. It is believed that the failure was caused by an electric arc generated by the conductive tether's movement through the Earth's magnetic field.

When a tether is moved at a velocity (v) at right angles to the Earth's magnetic field (B), an electric field is observed in the tether's frame of reference. This can be stated as:

 * E = v * B = vB

The direction of the electric field (E) is at right angles to both the tether's velocity (v) and magnetic field (B). If the tether is a conductor, then the electric field leads to the displacement of charges along the tether. Note that the velocity used in this equation is the orbital velocity of the tether. The rate of rotation of the Earth, or of its core, is not relevant. In this regard, see also homopolar generator.

Voltage across conductor
With a long conducting wire of length L, an electric field E is generated in the wire. It produces a voltage V between the opposite ends of the wire. This can be expressed as:

 * $$V = \mathbf{E}\cdot\mathbf{L} = EL \cos \tau = vBL \cos \tau$$

where the angle τ is between the length vector (L) of the tether and the electric field vector (E), assumed to be in the vertical direction at right angles to the velocity vector (v) in plane and the magnetic field vector (B) is out of the plane.

Current in conductor
An electrodynamic tether can be described as a type of thermodynamically "open system". Electrodynamic tether circuits cannot be completed by simply using another wire, since another tether will develop a similar voltage. Fortunately, the Earth's magnetosphere is not "empty", and, in near-Earth regions (especially near the Earth's atmosphere) there exist highly electrically conductive plasmas which are kept partially ionized by solar radiation or other radiant energy. The electron and ion density varies according to various factors, such as the location, altitude, season, sunspot cycle, and contamination levels. It is known that a positively charged bare conductor can readily remove free electrons out of the plasma. Thus, to complete the electrical circuit, a sufficiently large area of uninsulated conductor is needed at the upper, positively charged end of the tether, thereby permitting current to flow through the tether.

However, it is more difficult for the opposite (negative) end of the tether to eject free electrons or to collect positive ions from the plasma. It is plausible that, by using a very large collection area at one end of the tether, enough ions can be collected to permit significant current through the plasma. This was demonstrated during the Shuttle orbiter's TSS-1R mission, when the shuttle itself was used as a large plasma contactor to provide over an ampere of current. Improved methods include creating an electron emitter, such as a thermionic cathode, plasma cathode, plasma contactor, or field electron emission device. Since both ends of the tether are "open" to the surrounding plasma, electrons can flow out of one end of the tether while a corresponding flow of electrons enters the other end. In this fashion, the voltage that is electromagnetically induced within the tether can cause current to flow through the surrounding space environment, completing an electrical circuit through what appears to be, at first glance, an open circuit.

Tether current
The amount of current (I) flowing through a tether depends on various factors. One of these is the circuit's total resistance (R). The circuit's resistance consist of three components: In addition, a parasitic load is needed. The load on the current may take the form of a charging device which, in turn, charges reserve power sources such as batteries. The batteries in return will be used to control power and communication circuits, as well as drive the electron emitting devices at the negative end of the tether. As such the tether can be completely self-powered, besides the initial charge in the batteries to provide electrical power for the deployment and startup procedure.
 * 1) the effective resistance of the plasma,
 * 2) the resistance of the tether, and
 * 3) a control variable resistor.

The charging battery load can be viewed as a resistor which absorbs power, but stores this for later use (instead of immediately dissipating heat). It is included as part of the "control resistor". The charging battery load is not treated as a "base resistance" though, as the charging circuit can be turned off at any time. When off, the operations can be continued without interruption using the power stored in the batteries.

Current collection / emission for an EDT system: theory and technology
Understanding electron and ion current collection to and from the surrounding ambient plasma is critical for most EDT systems. Any exposed conducting section of the EDT system can passively ('passive' and 'active' emission refers to the use of pre-stored energy in order to achieve the desired effect) collect electron or ion current, depending on the electric potential of the spacecraft body with respect to the ambient plasma. In addition, the geometry of the conducting body plays an important role in the size of the sheath and thus the total collection capability. As a result, there are a number of theories for the varying collection techniques.

The primary passive processes that control the electron and ion collection on an EDT system are thermal current collection, ion ram collection effects, electron photoemission, and possibly secondary electron and ion emission. In addition, the collection along a thin bare tether is described using orbital motion limited (OML) theory as well as theoretical derivations from this model depending on the physical size with respect to the plasma Debye length. These processes take place all along the exposed conducting material of the entire system. Environmental and orbital parameters can significantly influence the amount collected current. Some important parameters include plasma density, electron and ion temperature, ion molecular weight, magnetic field strength and orbital velocity relative to the surrounding plasma.

Then there are active collection and emission techniques involved in an EDT system. This occurs through devices such as hollow cathode plasma contactors, thermionic cathodes, and field emitter arrays. The physical design of each of these structures as well as the current emission capabilities are thoroughly discussed.

Bare conductive tethers
The concept of current collection to a bare conducting tether was first formalized by Sanmartin and Martinez-Sanchez. They note that the most area efficient current collecting cylindrical surface is one that has an effective radius less than ~1 Debye length where current collection physics is known as orbital motion limited (OML) in a collisionless plasma. As the effective radius of the bare conductive tether increases past this point then there are predictable reductions in collection efficiency compared to OML theory. In addition to this theory (which has been derived for a non-flowing plasma), current collection in space occurs in a flowing plasma, which introduces another collection effect. These issues are explored in greater detail below.

Orbit motion limited (OML) theory
The electron Debye length is defined as the characteristic shielding distance in a plasma, and is described by the equation

 * $$ \lambda_\mathrm{De} \cong \sqrt{ \frac{ \varepsilon_0 T_e }{ q n_0 } }.$$

This distance, where all electric fields in the plasma resulting from the conductive body have fallen off by 1/e, can be calculated. OML theory is defined with the assumption that the electron Debye length is equal to or larger than the size of the object and the plasma is not flowing. The OML regime occurs when the sheath becomes sufficiently thick such that orbital effects become important in particle collection. This theory accounts for and conserves particle energy and angular momentum. As a result, not all particles that are incident onto the surface of the thick sheath are collected. The voltage of the collecting structure with respect to the ambient plasma, as well as the ambient plasma density and temperature, determines the size of the sheath. This accelerating (or decelerating) voltage combined with the energy and momentum of the incoming particles determines the amount of current collected across the plasma sheath.

The orbital-motion-limit regime is attained when the cylinder radius is small enough such that all incoming particle trajectories that are collected are terminated on the cylinder's surface are connected to the background plasma, regardless of their initial angular momentum (i.e., none are connected to another location on the probe's surface). Since, in a quasi-neutral collisionless plasma, the distribution function is conserved along particle orbits, having all “directions of arrival” populated corresponds to an upper limit on the collected current per unit area (not total current).

In an EDT system, the best performance for a given tether mass is for a tether diameter chosen to be smaller than an electron Debye length for typical ionospheric ambient conditions (Typical ionospheric conditions in the from 200 to 2000 km altitude range, have a T_e ranging from 0.1 eV to 0.35 eV, and n_e ranging from 10^10 m^-3 to 10^12 m^-3 ), so it is therefore within the OML regime. Tether geometries outside this dimension have been addressed. OML collection will be used as a baseline when comparing the current collection results for various sample tether geometries and sizes.

In 1962 Gerald H. Rosen derived the equation that is now known as the OML theory of dust charging. According to Robert Merlino of the University of Iowa, Rosen seems to have arrived at the equation 30 years before anyone else.

Deviations from OML theory in a non-flowing plasma
For a variety of practical reasons, current collection to a bare EDT does not always satisfy the assumption of OML collection theory. Understanding how the predicted performance deviates from theory is important for these conditions. Two commonly proposed geometries for an EDT involve the use of a cylindrical wire and a flat tape. As long as the cylindrical tether is less than one Debye length in radius, it will collect according to the OML theory. However, once the width exceeds this distance, then the collection increasingly deviates from this theory. If the tether geometry is a flat tape, then an approximation can be used to convert the normalized tape width to an equivalent cylinder radius. This was first done by Sanmartin and Estes and more recently using the 2-Dimensional Kinetic Plasma Solver (KiPS 2-D) by Choiniere et al.

Flowing plasma effect
There is at present, no closed-form solution to account for the effects of plasma flow relative to the bare tether. However, numerical simulation has been recently developed by Choiniere et al. using KiPS-2D which can simulate flowing cases for simple geometries at high bias potentials. This flowing plasma analysis as it applies to EDTs have been discussed. This phenomenon is presently being investigated through recent work, and is not fully understood.

Endbody collection
This section discusses the plasma physics theory that explains passive current collection to a large conductive body which will be applied at the end of an ED tether. When the size of the sheath is much smaller than the radius of the collecting body then depending on the polarity of the difference between the potential of the tether and that of the ambient plasma, (V – Vp), it is assumed that all of the incoming electrons or ions that enter the plasma sheath are collected by the conductive body. This 'thin sheath' theory involving non-flowing plasmas is discussed, and then the modifications to this theory for flowing plasma is presented. Other current collection mechanisms will then be discussed. All of the theory presented is used towards developing a current collection model to account for all conditions encountered during an EDT mission.

Passive collection theory
In a non-flowing quasi-neutral plasma with no magnetic field, it can be assumed that a spherical conducting object will collect equally in all directions. The electron and ion collection at the end-body is governed by the thermal collection process, which is given by Ithe and Ithi.

Flowing plasma electron collection mode
The next step in developing a more realistic model for current collection is to include the magnetic field effects and plasma flow effects. Assuming a collisionless plasma, electrons and ions gyrate around magnetic field lines as they travel between the poles around the Earth due to magnetic mirroring forces and gradient-curvature drift. They gyrate at a particular radius and frequency dependence upon their mass, the magnetic field strength, and energy. These factors must be considered in current collection models.

Flowing plasma ion collection model
When the conducting body is negatively biased with respect to the plasma and traveling above the ion thermal velocity, there are additional collection mechanisms at work. For typical Low Earth Orbits (LEOs), between 200 km and 2000 km, the velocities in an inertial reference frame range from 7.8 km/s to 6.9 km/s for a circular orbit and the atmospheric molecular weights range from 25.0 amu (O+, O2+, & NO+) to 1.2 amu (mostly H+), respectively. Assuming that the electron and ion temperatures range from ~0.1 eV to 0.35 eV, the resulting ion velocity ranges from 875 m/s to 4.0 km/s from 200 km to 2000 km altitude, respectively. The electrons are traveling at approximately 188 km/s throughout LEO. This means that the orbiting body is traveling faster than the ions and slower than the electrons, or at a mesosonic speed. This results in a unique phenomenon whereby the orbiting body 'rams' through the surrounding ions in the plasma creating a beam like effect in the reference frame of the orbiting body.

Porous endbodies
Porous endbodies have been proposed as a way to reduce the drag of a collecting endbody while ideally maintaining a similar current collection. They are often modeled as solid endbodies, except they are a small percentage of the solid spheres surface area. This is, however, an extreme oversimplification of the concept. Much has to be learned about the interactions between the sheath structure, the geometry of the mesh, the size of the endbody, and its relation to current collection. This technology also has the potential to resolve a number of issues concerning EDTs. Diminishing returns with collection current and drag area have set a limit that porous tethers might be able to overcome. Work has been accomplished on current collection using porous spheres, by Stone et al. and Khazanov et al.

It has been shown that the maximum current collected by a grid sphere compared to the mass and drag reduction can be estimated. The drag per unit of collected current for a grid sphere with a transparency of 80 to 90% is approximately 1.2 – 1.4 times smaller than that of a solid sphere of the same radius. The reduction in mass per unit volume, for this same comparison, is 2.4 – 2.8 times.

Other current collection methods
In addition to the electron thermal collection, other processes that could influence the current collection in an EDT system are photoemission, secondary electron emission, and secondary ion emission. These effects pertain to all conducting surfaces on an EDT system, not just the end-body.

Space charge limits across plasma sheaths
In any application where electrons are emitted across a vacuum gap, there is a maximum allowable current for a given bias due to the self repulsion of the electron beam. This classical 1-D space charge limit (SCL) is derived for charged particles of zero initial energy, and is termed the Child-Langmuir Law. This limit depends on the emission surface area, the potential difference across the plasma gap and the distance of that gap. Further discussion of this topic can be found.

Electron emitters
There are three active electron emission technologies usually considered for EDT applications: hollow cathode plasma contactors (HCPCs), thermionic cathodes (TCs), and field emission cathodes (FEC), often in the form of field emitter arrays (FEAs). System level configurations will be presented for each device, as well as the relative costs, benefits, and validation.

Thermionic cathode (TC)
Thermionic emission is the flow of electrons from a heated charged metal or metal oxide surface, caused by thermal vibrational energy overcoming the work function (electrostatic forces holding electrons to the surface). The thermionic emission current density, J, rises rapidly with increasing temperature, releasing a significant number of electrons into the vacuum near the surface. The quantitative relation is given in the equation

 * $$ J_{the} = A_R T^2 e^{-\phi / (kt)}.$$

This equation is called the Richardson-Dushman or Richardson equation. (ф is approximately 4.54 eV and AR ~120 A/cm2 for tungsten).

Once the electrons are thermionically emitted from the TC surface they require an acceleration potential to cross a gap, or in this case, the plasma sheath. Electrons can attain this necessary energy to escape the SCL of the plasma sheath if an accelerated grid, or electron gun, is used. The equation

 * $$ \Delta V_{tc} = \left[\frac{\eta \cdot I_t}{\rho}\right]^{2/3}$$

shows what potential is needed across the grid in order to emit a certain current entering the device.

Here, η is the electron gun assembly (EGA) efficiency (~0.97 in TSS-1), ρ is the perveance of the EGA (7.2 micropervs in TSS-1), ΔVtc is the voltage across the accelerating grid of the EGA, and It is the emitted current. The perveance defines the space charge limited current that can be emitted from a device. The figure below displays commercial examples of thermionic emitters and electron guns produced at Heatwave Labs Inc.

TC electron emission will occur in one of two different regimes: temperature or space charge limited current flow. For temperature limited flow every electron that obtains enough energy to escape from the cathode surface is emitted, assuming the acceleration potential of the electron gun is large enough. In this case, the emission current is regulated by the thermionic emission process, given by the Richardson Dushman equation. In SCL electron current flow there are so many electrons emitted from the cathode that not all of them are accelerated enough by the electron gun to escape the space charge. In this case, the electron gun acceleration potential limits the emission current. The below chart displays the temperature limiting currents and SCL effects. As the beam energy of the electrons is increased, the total escaping electrons can be seen to increase. The curves that become horizontal are temperature limited cases.

Field emission cathode (FEC)

In field electron emission, electrons tunnel through a potential barrier, rather than escaping over it as in thermionic emission or photoemission. For a metal at low temperature, the process can be understood in terms of the figure below. The metal can be considered a potential box, filled with electrons to the Fermi level (which lies below the vacuum level by several electron volts). The vacuum level represents the potential energy of an electron at rest outside the metal in the absence of an external field. In the presence of a strong electric field, the potential outside the metal will be deformed along the line AB, so that a triangular barrier is formed, through which electrons can tunnel. Electrons are extracted from the conduction band with a current density given by the Fowler−Nordheim equation

 * $$J_{the} = A_{FN} \cdot E_{FN}^2 \cdot e^{-B_{FN}/E_{FN}}.$$

AFN and BFN are the constants determined by measurements of the FEA with units of A/V2 and V/m, respectively. EFN is the electric field that exists between the electron emissive tip and the positively biased structure drawing the electrons out. Typical constants for Spindt type cathodes include: AFN = 3.14 x 10-8 A/V2 and BFN = 771 V/m. (Stanford Research Institute data sheet). An accelerating structure is typically placed in close proximity with the emitting material as in the below figure. Close (micrometer scale) proximity between the emitter and gate, combined with natural or artificial focusing structures, efficiently provide the high field strengths required for emission with relatively low applied voltage and power.

A carbon nanotube field-emission cathode was successfully tested on the KITE Electrodynamic tether experiment on the Japanese H-II Transfer Vehicle.

Field emission cathodes are often in the form of Field Emitter Arrays (FEAs), such as the cathode design by Spindt et al. The figure below displays close up visual images of a Spindt emitter.

A variety of materials have been developed for field emitter arrays, ranging from silicon to semiconductor fabricated molybdenum tips with integrated gates to a plate of randomly distributed carbon nanotubes with a separate gate structure suspended above. The advantages of field emission technologies over alternative electron emission methods are:

 * 1) No requirement for a consumable (gas) and no resulting safety considerations for handling a pressurized vessel
 * 2) A low-power capability
 * 3) Having moderate power impacts due to space-charge limits in the emission of the electrons into the surrounding plasma.

One major issue to consider for field emitters is the effect of contamination. In order to achieve electron emission at low voltages, field emitter array tips are built on a micrometer-level scale sizes. Their performance depends on the precise construction of these small structures. They are also dependent on being constructed with a material possessing a low work-function. These factors can render the device extremely sensitive to contamination, especially from hydrocarbons and other large, easily polymerized molecules. Techniques for avoiding, eliminating, or operating in the presence of contaminations in ground testing and ionospheric (e.g. spacecraft outgassing) environments are critical. Research at the University of Michigan and elsewhere has focused on this outgassing issue. Protective enclosures, electron cleaning, robust coatings, and other design features are being developed as potential solutions. FEAs used for space applications still require the demonstration of long term stability, repeatability, and reliability of operation at gate potentials appropriate to the space applications.

Hollow cathode
Hollow cathodes emit a dense cloud of plasma by first ionizing a gas. This creates a high density plasma plume which makes contact with the surrounding plasma. The region between the high density plume and the surrounding plasma is termed a double sheath or double layer. This double layer is essentially two adjacent layers of charge. The first layer is a positive layer at the edge of the high potential plasma (the contactor plasma cloud). The second layer is a negative layer at the edge of the low potential plasma (the ambient plasma). Further investigation of the double layer phenomenon has been conducted by several people. One type of hollow cathode consists of a metal tube lined with a sintered barium oxide impregnated tungsten insert, capped at one end by a plate with a small orifice, as shown in the below figure. Electrons are emitted from the barium oxide impregnated insert by thermionic emission. A noble gas flows into the insert region of the HC and is partially ionized by the emitted electrons that are accelerated by an electric field near the orifice (Xenon is a common gas used for HCs as it has a low specific ionization energy (ionization potential per unit mass). For EDT purposes, a lower mass would be more beneficial because the total system mass would be less. This gas is just used for charge exchange and not propulsion.). Many of the ionized xenon atoms are accelerated into the walls where their energy maintains the thermionic emission temperature. The ionized xenon also exits out of the orifice. Electrons are accelerated from the insert region, through the orifice to the keeper, which is always at a more positive bias.

In electron emission mode, the ambient plasma is positively biased with respect to the keeper. In the contactor plasma, the electron density is approximately equal to the ion density. The higher energy electrons stream through the slowly expanding ion cloud, while the lower energy electrons are trapped within the cloud by the keeper potential. The high electron velocities lead to electron currents much greater than xenon ion currents. Below the electron emission saturation limit the contactor acts as a bipolar emissive probe. Each outgoing ion generated by an electron allows a number of electrons to be emitted. This number is approximately equal to the square root of the ratio of the ion mass to the electron mass.

It can be seen in the below chart what a typical I-V curve looks like for a hollow cathode in electron emission mode. Given a certain keeper geometry (the ring in the figure above that the electrons exit through), ion flow rate, and Vp, the I-V profile can be determined. [111-113].

The operation of the HC in the electron collection mode is called the plasma contacting (or ignited) operating mode. The “ignited mode” is so termed because it indicates that multi-ampere current levels can be achieved by using the voltage drop at the plasma contactor. This accelerates space plasma electrons which ionize neutral expellant flow from the contactor. If electron collection currents are high and/or ambient electron densities are low, the sheath at which electron current collection is sustained simply expands or shrinks until the required current is collected.

In addition, the geometry affects the emission of the plasma from the HC as seen in the below figure. Here it can be seen that, depending on the diameter and thickness of the keeper and the distance of it with respect to the orifice, the total emission percentage can be affected.

Plasma collection and emission summary
All of the electron emission and collection techniques can be summarized in the table following. For each method there is a description as to whether the electrons or ions in the system increased or decreased based on the potential of the spacecraft with respect to the plasma. Electrons (e-) and ions (ions+) indicates that the number of electrons or ions are being increased (↑) or reduced (↓). Also, for each method some special conditions apply (see the respective sections in this article for further clarification of when and where it applies).

 * {| class="wikitable"

! Passive e− and ion emission/collection ! V − Vp < 0 ! V − Vp > 0 ! Active e− and ion emission
 * Bare tether: OML
 * ions+ ↑
 * e− ↑
 * Ram collection
 * ions+ ↑
 * 0
 * Thermal collection
 * ions+ ↑
 * e− ↑
 * Photoemmision
 * e− ↓
 * e− ↓,~0
 * Secondary electron emission
 * e− ↓
 * e− ↓
 * Secondary ion emission
 * ions+ ↓,~0
 * 0
 * Retardation regieme
 * e− ↑
 * ions+ ↑, ~0
 * Secondary ion emission
 * ions+ ↓,~0
 * 0
 * Retardation regieme
 * e− ↑
 * ions+ ↑, ~0
 * ions+ ↑, ~0
 * colspan="2"| Potential does not matter
 * Thermionic emission
 * colspan="2"| e− ↓
 * Field emitter arrays
 * colspan="2"| e− ↓
 * Hollow cathodes
 * e− ↓
 * e− ↑
 * }
 * e− ↓
 * e− ↑
 * }

For use in EDT system modeling, each of the passive electron collection and emission theory models has been verified by reproducing previously published equations and results. These plots include: orbital motion limited theory, Ram collection, and thermal collection, photoemission, secondary electron emission, and secondary ion emission.

Electrodynamic tether system fundamentals
In order to integrate all the most recent electron emitters, collectors, and theory into a single model, the EDT system must first be defined and derived. Once this is accomplished it will be possible to apply this theory toward determining optimizations of system attributes.

There are a number of derivations that solve for the potentials and currents involved in an EDT system numerically. The derivation and numerical methodology of a full EDT system that includes a bare tether section, insulating conducting tether, electron (and ion) endbody emitters, and passive electron collection is described. This is followed by the simplified, all insulated tether model. Special EDT phenomena and verification of the EDT system model using experimental mission data will then be discussed.

Bare tether system derivation
An important note concerning an EDT derivation pertains to the celestial body which the tether system orbits. For practicality, Earth will be used as the body that is orbited; however, this theory applies to any celestial body with an ionosphere and a magnetic field.

The coordinates are the first thing that must be identified. For the purposes of this derivation, the x- and y-axis are defined as the east-west, and north-south directions with respect to the Earth's surface, respectively. The z-axis is defined as up-down from the Earth's center, as seen in the figure below. The parameters – magnetic field B, tether length L, and the orbital velocity vorb – are vectors that can be expressed in terms of this coordinate system, as in the following equations:

 * $$\mathbf{B} = B_x \hat{x} + B_y \hat{y} + B_z \hat{z}$$ (the magnetic field vector),

 * $$ \mathbf{L} = L \cos \alpha_\mathrm{out} \sin \alpha_\mathrm{in} \hat{x} + L \sin \alpha_\mathrm{out} \hat{y} + L \cos\alpha_\mathrm{out} \cos \alpha_\mathrm{in} \hat{z}$$  (the tether position vector), and

 * $$\mathbf{v}_\mathrm{orb} = v_\mathrm{orb} \cos \lambda_\mathrm{out} \sin \lambda_\mathrm{in} \hat{x} + v_\mathrm{orb} \sin \lambda_\mathrm{out} \hat{y} + v_\mathrm{orb} \cos\lambda_\mathrm{out} \cos \lambda_\mathrm{in} \hat{z}$$  (the orbital velocity vector).

The components of the magnetic field can be obtained directly from the International Geomagnetic Reference Field (IGRF) model. This model is compiled from a collaborative effort between magnetic field modelers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world. For this derivation, it is assumed that the magnetic field lines are all the same angle throughout the length of the tether, and that the tether is rigid.

Realistically, the transverse electrodynamic forces cause the tether to bow and to swing away from the local vertical. Gravity gradient forces then produce a restoring force that pulls the tether back towards the local vertical; however, this results in a pendulum-like motion (Gravity gradient forces also result in pendulous motions without ED forces). The B direction changes as the tether orbits the Earth, and thus the direction and magnitude of the ED forces also change. This pendulum motion can develop into complex librations in both the in-plane and out-of-plane directions. Then, due to coupling between the in-plane motion and longitudinal elastic oscillations, as well as coupling between in-plane and out-of-plane motions, an electrodynamic tether operated at a constant current can continually add energy to the libration motions. This effect then has a chance to cause the libration amplitudes to grow and eventually cause wild oscillations, including one such as the 'skip-rope effect', but that is beyond the scope of this derivation. In a non-rotating EDT system (A rotating system, called Momentum Exchange Electrodynamic Reboost [MXER]), the tether is predominantly in the z-direction due to the natural gravity gradient alignment with the Earth.

Derivations
The following derivation will describe the exact solution to the system accounting for all vector quantities involved, and then a second solution with the nominal condition where the magnetic field, the orbital velocity, and the tether orientation are all perpendicular to one another. The final solution of the nominal case is solved for in terms of just the electron density, n_e, the tether resistance per unit length, R_t, and the power of the high voltage power supply, P_hvps.

The below figure describes a typical EDT system in a series bias grounded gate configuration (further description of the various types of configurations analyzed have been presented ) with a blow-up of an infinitesimal section of bare tether. This figure is symmetrically set up so either end can be used as the anode. This tether system is symmetrical because rotating tether systems will need to use both ends as anodes and cathodes at some point in its rotation. The V_hvps will only be used in the cathode end of the EDT system, and is turned off otherwise.

In-plane and out-of-plane direction is determined by the orbital velocity vector of the system. An in-plane force is in the direction of travel. It will add or remove energy to the orbit, thereby increasing the altitude by changing the orbit into an elliptical one. An out-of-plane force is in the direction perpendicular to the plane of travel, which causes a change in inclination. This will be explained in the following section.

To calculate the in-plane and out-of-plane directions, the components of the velocity and magnetic field vectors must be obtained and the force values calculated. The component of the force in the direction of travel will serve to enhance the orbit raising capabilities, while the out-of-plane component of thrust will alter the inclination. In the below figure, the magnetic field vector is solely in the north (or y-axis) direction, and the resulting forces on an orbit, with some inclination, can be seen. An orbit with no inclination would have all the thrust in the in-plane direction.

There has been work conducted to stabilize the librations of the tether system to prevent misalignment of the tether with the gravity gradient. The below figure displays the drag effects an EDT system will encounter for a typical orbit. The in-plane angle, α_ip, and out-of-plane angle, α_op, can be reduced by increasing the endmass of the system, or by employing feedback technology. Any deviations in the gravity alignment must be understood, and accounted for in the system design.

Interstellar travel
An application of the EDT system has been considered and researched for interstellar travel by using the local interstellar medium of the Local Bubble. It has been found to be feasible to use the EDT system to supply on-board power given a crew of 50 with a requirement of 12 kilowatts per person. Energy generation is achieved at the expense of kinetic energy of the spacecraft. In reverse the EDT system could be used for acceleration. However, this has been found to be ineffective. Thrustless turning using the EDT system is possible to allow for course correction and rendezvous in interstellar space. It will not, however, allow rapid thrustless circling to allow a starship to re-enter a power beam or make numerous solar passes due to an extremely large turning radius of 3.7*1013 km (~3.7 lightyears).

title: Electrodynamic tether


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Bactrocera tryoni

Bactrocera tryoni, the Queensland fruit fly, is a species of fly in the family Tephritidae in the insect order Diptera. B. tryoni is native to subtropical coastal Queensland and northern New South Wales. They are active during the day, but mate at night. B. tryoni lay their eggs in fruit. The larvae then hatch and proceed to consume the fruit, causing the fruit to decay and drop prematurely. B. tryoni are responsible for an estimated $28.5 million a year in damage to Australian crops and are the most costly horticultural pest in Australia. Up to 100% of exposed fruit can be destroyed due to an infestation of this fly species. Previously, pesticides were used to eliminate B. tryoni from damaging crops. However, these chemicals are now banned. Thus, experts devoted to B. tryoni control have transitioned to studying this pests' behaviors to determine a new method of elimination.

Identification
Adult B. tryoni flies are reddish brown in color, have distinct yellow markings and are typically 5–8 mm in length. Adults hold their wings horizontally when walking and flick them in a specific, characteristic manner. The wingspan of B. tryoni ranges from 4.8 to 6.3 mm. B. tryoni may be mistaken for wasps as they appear wasp-like.

Complex and sister species
They are part of a species complex, or a group of morphologically similar but biologically distinct species. These are called sibling species. B. tryoni has three sibling species: B. neohumeralis, B. aquilonis, and B. melas. All of these flies are sympatric, meaning that they inhabit the same territory, except B. aquilonas, which inhabits a different geographical area in northwest Australia. Genetic data has suggested that B. aquilonas is simply an allopatric population of B. tryoni. Additionally, B. tryoni mate at night, while B. neohumeralis mate during the day. More pertinently, B. neohumeralis are not pests; they do not destroy crops. Despite this behavioral difference, B. neohumeralis and B. tryoni are nearly genetically identical: the two species are only differentiable based on newly developed microsatellite technology. The evolutionary relationship between the species within the B. tryoni complex is unknown.

Distribution and habitat
B. tryoni prefer humid and warm climates. Thus, they are most widespread in eastern Australia, as well as New Caledonia, French Polynesia, the Pitcairn Islands, and the Cook Islands. Commercial fruit production has increased in Australia, increasing the geographical area in which B. tryoni can reside, extending as far inland as central Queensland and New South Wales. Occasionally, there are outbreaks of B. tryoni in southern and western Australia; however, the coastal areas of Australia are relatively isolated from one another due to harsh, dry weather conditions in intervening regions that are unsuitable for B. tryoni. Therefore, other regions of Australia typically remain free of this pest as long as infested fruit is not transported between regions.

Egg
After passing through a two-week pre-oviposition stage following emergence from the pupae, adult females deposit around seven eggs in a fruit puncture, and may deposit up to 100 eggs per day. Fruit punctures are holes in the skin of the fruit that allow the females to access the nutrient-rich interior. Females often oviposit in punctures made by other fruit flies, such as the Mediterranean fruit fly (Ceratitis capitata), which results in many eggs occurring in a single cavity. Additionally, B. tryoni females can create their own puncture to oviposit in the fruit, called a "sting".

Maggot (larva)
Eggs hatch into white larvae in 2–4 days under favorable weather conditions. These larvae, or maggots, eat toward the center of the fruit with their cutting jaws, causing it to rot. The maggots may reach up to 9 mm in length; larval development is completed in 10-31 days. At this point, the fruit has likely fallen to the ground. Up to 40 larvae can be reared from a single piece of fruit.

Pupal
The maggot chews its way out of the remaining fruit and enters the soil, where it enters the pupal stage of development. Pupal development requires various temperature ranges from one week in warmer weather to one month in cooler conditions. The flexible amount of time needed for pupal development has resulted in B. tryoni relative adaptiveness to different environments.

Adult
After the pupal stage is complete, adults emerge from the soil. This typically occurs near the end of the summer season. Unlike other fly pests, B. tryoni does not breed continuously, but spends the winter in the adult stage. Adult females live many months, and up to four or five overlapping generations may occur annually. Adults may live for a year or longer.

Host selection
B. tryoni have been found to infect almost all commercial fruit crops as hosts, including abiu, apple, avocado, babaco, capsicum, carambola, casimiroa, cherry, citrus, custard apple, granadilla, grape, guava, kiwifruit, mango, nectarine, papaya, passionfruit, peach, pear, persimmon, plum, pomegranate, prune, quince, loquat, santol, sapodilla, tamarillo, tomato, and wax jambu, with the exception of pineapples. B. tryoni strongly prefer to oviposit into rotting fruit, although some evidence suggests that they will oviposit into under-ripe fruit as well. B. tryoni prefer to select fruits that have an outer layer that is able to be punctured or has already been lesioned. The majority of research on B. tryoni host selection has included just a few, economically important crops.

Adult feeding behavior
Larvae feed only on the flesh of fruit until they mature into adulthood. Adult flies, however, rely on leaf surface bacteria as a major source of protein. There is some evidence suggesting that the bacteria and flies co-evolved, but other data suggest that this symbiosis does not occur as the presence of protein-providing bacteria is not consistent throughout B. tryoni populations. Due to this dependence on protein originating from bacteria, it is possible to control the population by providing flies with artificial protein mixed with insecticide.

Mating behavior
B. tryoni flies mate at dusk. This is pertinent to control efforts because it is one of the few characteristics that distinguish it from sister species, B. neohumeralis, which are not a highly destructive species, even though the two are very closely related genetically and evolutionarily.

Cue-lure in males
B. tryoni males exhibit behavior termed cue-lure, meaning that they are strongly attracted to a specific scent. While this scent is artificially made, it is closely related to compounds occurring in nature. Male B. tryoni respond most greatly to the lure in the morning, likely because this is their peak of foraging time; however, an evolutionary reason for the cue-lure is not fully known. Cue-lure is only exhibited in sexually mature males, indicating that mate finding is related to the cue-lure behavior. However, other Bactrocera species have been identified as means of enhancing male competitiveness, or to afford protection from predation.

Ovipositional behavior
B. tryoni lay their eggs in fruit. Females prefer to lay their eggs in fruit that is sweet, juicy, and not acidic. The presence of other female flies in pre- or post- oviposition on a piece of fruit was found to have no bearing on another female's likeliness to land on the fruit; however, female flies were more likely to bore into a piece of fruit that other female flies were currently ovipositing into, therefore increasing the density of larvae within a single piece of fruit. This is an example of reciprocal altruism as larvae are at an advantage at higher densities.

Movement and dispersal
B. tryoni have evolved to disperse widely, which was greatly influenced their ability to cause damage to farms. When fruit is available, the flies often do not disperse far distances (only a few hundred meters to a kilometer), but they have been found to travel large distances in the absence of fruit. In addition to lack of resources, adult flies may also move to locate overwintering sites or avoid dry or cold weather.

Genomic studies
The genome of B. tryoni has been sequenced and published by a group at the University of New South Wales, Australia. While the coding regions are mostly completely sequenced, about one-third of the genome appears to consist of highly repetitive sequences.

Control efforts
B. tryoni has been the subject of extensive control regimens. One of these regimens is a Fruit Fly Exclusion Zone (FFEZ), where transporting fruit into certain regions of Australia and Polynesia is illegal. In May 2012, January 2013, February 2015, and February 2019, the fly was found in Auckland, posing a risk to horticulture and leading to a quarantine (see Biosecurity in New Zealand).

Lure-and-kill tactics
Farmers in effected regions are encouraged to use a lure and kill tactic to combat the presence of B. tryoni. Lure and kill tactics include the use of some sort of bait that attracts the pest, or a lure. This can include semiochemical lures such as pheromones, food attractants, host mimics, or color attractants. The killing mechanism often involves pesticides, liquid traps in which the pest drowns, or sticky traps that the pest cannot escape from. At low densities of B. tryoni, lure and kill tactics are most effective as a mechanism to monitor the frequency of B. tryoni; at high densities, they effectively combat the pest via population reduction. Two of the most common lure and kill approaches for B. tryoni are the male annihilation technique (MAT) and the protein-bait spray (PBS).

Protein-bait spray
Both male and female B. tryoni require proteins produced by bacteria found on the leaves of plants in order to reach sexual maturity. The protein-bait spray takes advantage of this behavior by combining necessary proteins normally acquired from leaf bacteria with deadly insecticides. The combination of protein and insecticide attracts B. tryoni of both sexes, resulting in elimination of adult flies. Neither the effectiveness of this technique, nor the scientific underpinnings of what protein exactly attracts B. tryoni to the spray, are well investigated.

Male annihilation technique
B. tryoni sexually mature males are strongly responsive to specific scents that may be associated with mating, or a cue-lure. A specific cue-lure, Willson's lure, was found to be incredibly effective at attracting sexually mature B. tryoni males. When combined with insecticides, artificially developed cue lures may be an effective elimination method of sexually mature males. While extensive research has suggested this is an effective strategy in other fly species, very few controlled experiments have been conducted to determine the effectiveness of the male annihilation technique in B. tryoni.

Pesticides
Control efforts include submerging post-harvest fruit and treating fields of fruit trees with the chemicals dimethoate and fenthion. As of October 2011, the use of these chemicals was under review by the Australian Pesticides and Veterinary Medicines Authority. As a result, dimethoate was suspended from use. As of 2014, fenthion was no longer commercially available in Australia.

Sterile insect technique (SIT)
Containment efforts have included irradiating pupae in order to induce sterility. A study testing the viability of this technique found that sterility was dose independent, meaning that a single ionizing event was enough to render the male sperm sterile. Additionally, it was found that emergence and flight ability remained unaffected by the ionizing event. This indicates that males sterilized via a low dosage of radiation were equally as competitive as males that were not irradiated.

The white locus
A popular method for controlling populations of invasive or destructive species of flies involves producing a strain of fly that is incapable of reproducing. If this can be accomplished, this strain can be mass-produced and released into the wild without necessitating repeated exposure to irradiation as required in methods such as the sterile insect technique (SIT). If they have the same sexual competitiveness as wild type males, then the species' overall population will presumably decrease. In order to accomplish developing such a strain in B. tryoni, molecular tools capable of genetically transforming B. tryoni must be implemented. One such strain of a genetically compatible fly has been developed in Drosophila melanogaster. The phenotypic marker for the presence of an efficient vector for gene transfer is white eye color. Development of a genetically engineered B. tryoni strain that is compatible with gene transfer was successful; however, scientists have yet to develop a sterile strain that can be released into the wild.

Climate change
While this species is native to northeastern Australia, rising temperatures due to climate change has allowed the species to spread to other regions of Australia and Polynesia. B. tryoni are able to tolerate extremely high temperatures but have a minimum necessary temperature to breed; therefore, global warming has fostered their spread across Australia and Polynesia. Although B. tryoni have a minimum temperature requirement for survival, extreme plasticity and adaptation has been observed in adult B. tryoni. This adaptation has allowed them to survive in cooler temperatures and at higher altitudes. This behavior, combined with global warming, indicates that damage due to these insects will continue to increase as the temperatures continue to rise. One study predicted that farm damage due to Queensland fruit flies will increase by $3.1, $4.7, and $12.0 million with temperature increases of 0.5, 1 and 2 °C, respectively.

Simulations of climate change
Rising CO2 levels may influence the distribution of B. tryoni . Based upon recent studies which utilize computer programs to simulate B. tryoni distribution in the event of rising temperatures, it was predicted that there will be an overall increase in Queensland fruit fly damage, but the fruit flies will re-localize to more southerly locations as northern and central Queensland will begin to exceed the maximum habitable temperature of B. tryoni. However, these simulations may not accurately predict the future distributions of B. tryoni as they have exhibited an immense capability to adapt to various conditions. The prediction is also complicated by the uncertainty of how the relative humidity will change in regions across Australia as temperature increases, and B. tryoni survival is heavily dependent upon a humid climate.

title: Bactrocera tryoni