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Interplanetary spaceflight

Interplanetary spaceflight or interplanetary travel is the crewed or uncrewed travel between stars and planets, usually within a single planetary system. In practice, spaceflights of this type are confined to travel between the planets of the Solar System. Uncrewed space probes have flown to all the observed planets in the Solar System as well as to dwarf planets Pluto and Ceres, and several asteroids. Orbiters and landers return more information than fly-by missions. Crewed flights have landed on the Moon and have been planned, from time to time, for Mars, Venus and Mercury. While many scientists appreciate the knowledge value that uncrewed flights provide, the value of crewed missions is more controversial. Science fiction writers propose a number of benefits, including the mining of asteroids, access to solar power, and room for colonization in the event of an Earth catastrophe.

A number of techniques have been developed to make interplanetary flights more economical. Advances in computing and theoretical science have already improved some techniques, while new proposals may lead to improvements in speed, fuel economy, and safety. Travel techniques must take into consideration the velocity changes necessary to travel from one body to another in the Solar System. For orbital flights, an additional adjustment must be made to match the orbital speed of the destination body. Other developments are designed to improve rocket launching and propulsion, as well as the use of non-traditional sources of energy. Using extraterrestrial resources for energy, oxygen, and water would reduce costs and improve life support systems.

Any crewed interplanetary flight must include certain design requirements. Life support systems must be capable of supporting human lives for extended periods of time. Preventative measures are needed to reduce exposure to radiation and ensure optimum reliability.

Current achievements in interplanetary travel
Remotely guided space probes have flown by all of the observed planets of the Solar System from Mercury to Neptune, with the New Horizons probe having flown by the dwarf planet Pluto and the Dawn spacecraft currently orbiting the dwarf planet Ceres. The most distant spacecraft, Voyager 1 and Voyager 2 have left the Solar System as of 8 December 2018 while Pioneer 10, Pioneer 11, and New Horizons are on course to leave it.

In general, planetary orbiters and landers return much more detailed and comprehensive information than fly-by missions. Space probes have been placed into orbit around all the five planets known to the ancients: The first being Venus (Venera 7, 1970), Mars (Mariner 9, 1971), Jupiter (Galileo, 1995), Saturn (Cassini/Huygens, 2004), and most recently Mercury (MESSENGER, March 2011), and have returned data about these bodies and their natural satellites.

The NEAR Shoemaker mission in 2000 orbited the large near-Earth asteroid 433 Eros, and was even successfully landed there, though it had not been designed with this maneuver in mind. The Japanese ion-drive spacecraft Hayabusa in 2005 also orbited the small near-Earth asteroid 25143 Itokawa, landing on it briefly and returning grains of its surface material to Earth. Another ion-drive mission, Dawn, has orbited the large asteroid Vesta (July 2011 – September 2012) and later moved on to the dwarf planet Ceres, arriving in March 2015.

Remotely controlled landers such as Viking, Pathfinder and the two Mars Exploration Rovers have landed on the surface of Mars and several Venera and Vega spacecraft have landed on the surface of Venus, with the latter deploying balloons to the planet's atmosphere. The Huygens probe successfully landed on Saturn's moon, Titan.

No crewed missions have been sent to any planet of the Solar System. NASA's Apollo program, however, landed twelve people on the Moon and returned them to Earth. The American Vision for Space Exploration, originally introduced by U.S. President George W. Bush and put into practice through the Constellation program, had as a long-term goal to eventually send human astronauts to Mars. However, on February 1, 2010, President Barack Obama proposed cancelling the program in Fiscal Year 2011. An earlier project which received some significant planning by NASA included a crewed fly-by of Venus in the Manned Venus Flyby mission, but was cancelled when the Apollo Applications Program was terminated due to NASA budget cuts in the late 1960s.

Reasons for interplanetary travel
The costs and risk of interplanetary travel receive a lot of publicity—spectacular examples include the malfunctions or complete failures of probes without a human crew, such as Mars 96, Deep Space 2, and Beagle 2 (the article List of Solar System probes gives a full list).

Many astronomers, geologists and biologists believe that exploration of the Solar System provides knowledge that could not be gained by observations from Earth's surface or from orbit around Earth. However, they disagree about whether human-crewed missions justify their cost and risk. Critics of human spaceflight argue that robotic probes are more cost-effective, producing more scientific knowledge per dollar spent; robots do not need costly life-support systems, can be sent on one-way missions, and are becoming more capable as artificial intelligence advances. Others argue that either astronauts or spacefaring scientists, advised by Earth-based scientists, can respond more flexibly and intelligently to new or unexpected features of whatever region they are exploring.

Some members of the general public mainly value space activities for whatever tangible benefits they may deliver to themselves or to the human race as a whole. So far the only benefits of this type have been "spin-off" technologies which were developed for space missions and then were found to be at least as useful in other activities (NASA publicizes spin-offs from its activities). However, public support, at least in the US, remains higher for basic scientific research than for human space flight; a 2023 survey found that Americans rate basic research as their third-highest priority for NASA, after monitoring Earth-endangering asteroids and understanding climate change. Support for scientific research is about four times higher than for human flight to the Moon or Mars.

Besides spinoffs, other practical motivations for interplanetary travel are more speculative. But science fiction writers have a fairly good track record in predicting future technologies—for example geosynchronous communications satellites (Arthur C. Clarke) and many aspects of computer technology (Mack Reynolds).

Many science fiction stories feature detailed descriptions of how people could extract minerals from asteroids and energy from sources including orbital solar panels (unhampered by clouds) and the very strong magnetic field of Jupiter. Some claim that such techniques may be the only way to provide rising standards of living without being stopped by pollution or by depletion of Earth's resources (for example peak oil).

There are also non-scientific motives for human spaceflight, such as adventure or the belief that humans have a spiritually fated destiny in space.

Finally, establishing completely self-sufficient colonies in other parts of the Solar System could, if feasible, prevent the human species from being exterminated by several possible events (see Human extinction). One of these possible events is an asteroid impact like the one which may have resulted in the Cretaceous–Paleogene extinction event. Although various Spaceguard projects monitor the Solar System for objects that might come dangerously close to Earth, current asteroid deflection strategies are crude and untested. To make the task more difficult, carbonaceous chondrites are rather sooty and therefore very hard to detect. Although carbonaceous chondrites are thought to be rare, some are very large and the suspected "dinosaur-killer" may have been a carbonaceous chondrite.

Some scientists, including members of the Space Studies Institute, argue that the vast majority of mankind eventually will live in space and will benefit from doing so.

Economical travel techniques
One of the main challenges in interplanetary travel is producing the very large velocity changes necessary to travel from one body to another in the Solar System.

Due to the Sun's gravitational pull, a spacecraft moving farther from the Sun will slow down, while a spacecraft moving closer will speed up. Also, since any two planets are at different distances from the Sun, the planet from which the spacecraft starts is moving around the Sun at a different speed than the planet to which the spacecraft is travelling (in accordance with Kepler's Third Law). Because of these facts, a spacecraft desiring to transfer to a planet closer to the Sun must decrease its speed with respect to the Sun by a large amount in order to intercept it, while a spacecraft traveling to a planet farther out from the Sun must increase its speed substantially. Then, if additionally the spacecraft wishes to enter into orbit around the destination planet (instead of just flying by it), it must match the planet's orbital speed around the Sun, usually requiring another large velocity change.

Simply doing this by brute force – accelerating in the shortest route to the destination and then matching the planet's speed – would require an extremely large amount of fuel. And the fuel required for producing these velocity changes has to be launched along with the payload, and therefore even more fuel is needed to put both the spacecraft and the fuel required for its interplanetary journey into orbit. Thus, several techniques have been devised to reduce the fuel requirements of interplanetary travel.

As an example of the velocity changes involved, a spacecraft travelling from low Earth orbit to Mars using a simple trajectory must first undergo a change in speed (also known as a delta-v), in this case an increase, of about 3.8 km/s. Then, after intercepting Mars, it must change its speed by another 2.3 km/s in order to match Mars' orbital speed around the Sun and enter an orbit around it. For comparison, launching a spacecraft into low Earth orbit requires a change in speed of about 9.5 km/s.

Hohmann transfers
For many years economical interplanetary travel meant using the Hohmann transfer orbit. Hohmann demonstrated that the lowest energy route between any two orbits is an elliptical "orbit" which forms a tangent to the starting and destination orbits. Once the spacecraft arrives, a second application of thrust will re-circularize the orbit at the new location. In the case of planetary transfers this means directing the spacecraft, originally in an orbit almost identical to Earth's, so that the aphelion of the transfer orbit is on the far side of the Sun near the orbit of the other planet. A spacecraft traveling from Earth to Mars via this method will arrive near Mars orbit in approximately 8.5 months, but because the orbital velocity is greater when closer to the center of mass (i.e. the Sun) and slower when farther from the center, the spacecraft will be traveling quite slowly and a small application of thrust is all that is needed to put it into a circular orbit around Mars. If the manoeuver is timed properly, Mars will be "arriving" under the spacecraft when this happens.

The Hohmann transfer applies to any two orbits, not just those with planets involved. For instance it is the most common way to transfer satellites into geostationary orbit, after first being "parked" in low Earth orbit. However, the Hohmann transfer takes an amount of time similar to ½ of the orbital period of the outer orbit, so in the case of the outer planets this is many years – too long to wait. It is also based on the assumption that the points at both ends are massless, as in the case when transferring between two orbits around Earth for instance. With a planet at the destination end of the transfer, calculations become considerably more difficult.

Gravitational slingshot
The gravitational slingshot technique uses the gravity of planets and moons to change the speed and direction of a spacecraft without using fuel. In typical example, a spacecraft is sent to a distant planet on a path that is much faster than what the Hohmann transfer would call for. This would typically mean that it would arrive at the planet's orbit and continue past it. However, if there is a planet between the departure point and the target, it can be used to bend the path toward the target, and in many cases the overall travel time is greatly reduced. A prime example of this are the two crafts of the Voyager program, which used slingshot effects to change trajectories several times in the outer Solar System. It is difficult to use this method for journeys in the inner part of the Solar System, although it is possible to use other nearby planets such as Venus or even the Moon as slingshots in journeys to the outer planets.

This maneuver can only change an object's velocity relative to a third, uninvolved object, – possibly the “centre of mass” or the Sun. There is no change in the velocities of the two objects involved in the maneuver relative to each other. The Sun cannot be used in a gravitational slingshot because it is stationary compared to rest of the Solar System, which orbits the Sun. It may be used to send a spaceship or probe into the galaxy because the Sun revolves around the center of the Milky Way.

Powered slingshot
A powered slingshot is the use of a rocket engine at or around closest approach to a body (periapsis). The use at this point multiplies up the effect of the delta-v, and gives a bigger effect than at other times.

Fuzzy orbits
Computers did not exist when Hohmann transfer orbits were first proposed (1925) and were slow, expensive and unreliable when gravitational slingshots were developed (1959). Recent advances in computing have made it possible to exploit many more features of the gravity fields of astronomical bodies and thus calculate even lower-cost trajectories. Paths have been calculated which link the Lagrange points of the various planets into the so-called Interplanetary Transport Network. Such "fuzzy orbits" use significantly less energy than Hohmann transfers but are much, much slower. They aren't practical for human crewed missions because they generally take years or decades, but may be useful for high-volume transport of low-value commodities if humanity develops a space-based economy.

Aerobraking
Aerobraking uses the atmosphere of the target planet to slow down. It was first used on the Apollo program where the returning spacecraft did not enter Earth orbit but instead used a S-shaped vertical descent profile (starting with an initially steep descent, followed by a leveling out, followed by a slight climb, followed by a return to a positive rate of descent continuing to splash-down in the ocean) through Earth's atmosphere to reduce its speed until the parachute system could be deployed enabling a safe landing. Aerobraking does not require a thick atmosphere – for example most Mars landers use the technique, and Mars' atmosphere is only about 1% as thick as Earth's.

Aerobraking converts the spacecraft's kinetic energy into heat, so it requires a heatshield to prevent the craft from burning up. As a result, aerobraking is only helpful in cases where the fuel needed to transport the heatshield to the planet is less than the fuel that would be required to brake an unshielded craft by firing its engines. This can be addressed by creating heatshields from material available near the target.

Improved technologies and methodologies
Several technologies have been proposed which both save fuel and provide significantly faster travel than the traditional methodology of using Hohmann transfers. Some are still just theoretical, but over time, several of the theoretical approaches have been tested on spaceflight missions. For example, the Deep Space 1 mission was a successful test of an ion drive. These improved technologies typically focus on one or more of:
 * Space propulsion systems with much better fuel economy. Such systems would make it possible to travel much faster while keeping the fuel cost within acceptable limits.
 * Using solar energy and in-situ resource utilization to avoid or minimize the expensive task of shipping components and fuel up from the Earth's surface, against the Earth's gravity (see "Using non-terrestrial resources", below).
 * Novel methodologies of using energy at different locations or in different ways that can shorten transport time or reduce cost per unit mass of space transport

Besides making travel faster or cost less, such improvements could also allow greater design "safety margins" by reducing the imperative to make spacecraft lighter.

Improved rocket concepts
All rocket concepts are limited by the Tsiolkovsky rocket equation, which sets the characteristic velocity available as a function of exhaust velocity and mass ratio, of initial (M0, including fuel) to final (M1, fuel depleted) mass. The main consequence is that mission velocities of more than a few times the velocity of the rocket motor exhaust (with respect to the vehicle) rapidly become impractical, as the dry mass (mass of payload and rocket without fuel) falls to below 10% of the entire rocket's wet mass (mass of rocket with fuel).

Nuclear thermal and solar thermal rockets
In a nuclear thermal rocket or solar thermal rocket a working fluid, usually hydrogen, is heated to a high temperature, and then expands through a rocket nozzle to create thrust. The energy replaces the chemical energy of the reactive chemicals in a traditional rocket engine. Due to the low molecular mass and hence high thermal velocity of hydrogen these engines are at least twice as fuel efficient as chemical engines, even after including the weight of the reactor.

The US Atomic Energy Commission and NASA tested a few designs from 1959 to 1968. The NASA designs were conceived as replacements for the upper stages of the Saturn V launch vehicle, but the tests revealed reliability problems, mainly caused by the vibration and heating involved in running the engines at such high thrust levels. Political and environmental considerations make it unlikely such an engine will be used in the foreseeable future, since nuclear thermal rockets would be most useful at or near the Earth's surface and the consequences of a malfunction could be disastrous. Fission-based thermal rocket concepts produce lower exhaust velocities than the electric and plasma concepts described below, and are therefore less attractive solutions. For applications requiring high thrust-to-weight ratio, such as planetary escape, nuclear thermal is potentially more attractive.

Electric propulsion
Electric propulsion systems use an external source such as a nuclear reactor or solar cells to generate electricity, which is then used to accelerate a chemically inert propellant to speeds far higher than achieved in a chemical rocket. Such drives produce feeble thrust, and are therefore unsuitable for quick maneuvers or for launching from the surface of a planet. But they are so economical in their use of reaction mass that they can keep firing continuously for days or weeks, while chemical rockets use up reaction mass so quickly that they can only fire for seconds or minutes. Even a trip to the Moon is long enough for an electric propulsion system to outrun a chemical rocket – the Apollo missions took 3 days in each direction.

NASA's Deep Space One was a very successful test of a prototype ion drive, which fired for a total of 678 days and enabled the probe to run down Comet Borrelly, a feat which would have been impossible for a chemical rocket. Dawn, the first NASA operational (i.e., non-technology demonstration) mission to use an ion drive for its primary propulsion, successfully orbited the large main-belt asteroids 1 Ceres and 4 Vesta. A more ambitious, nuclear-powered version was intended for a Jupiter mission without human crew, the Jupiter Icy Moons Orbiter (JIMO), originally planned for launch sometime in the next decade. Due to a shift in priorities at NASA that favored human crewed space missions, the project lost funding in 2005. A similar mission is currently under discussion as the US component of a joint NASA/ESA program for the exploration of Europa and Ganymede.

A NASA multi-center Technology Applications Assessment Team led from the Johnson Spaceflight Center, has as of January 2011 described "Nautilus-X", a concept study for a multi-mission space exploration vehicle useful for missions beyond low Earth orbit (LEO), of up to 24 months duration for a crew of up to six. Although Nautilus-X is adaptable to a variety of mission-specific propulsion units of various low-thrust, high specific impulse (Isp) designs, nuclear ion-electric drive is shown for illustrative purposes. It is intended for integration and checkout at the International Space Station (ISS), and would be suitable for deep-space missions from the ISS to and beyond the Moon, including Earth/Moon L1, Sun/Earth L2, near-Earth asteroidal, and Mars orbital destinations. It incorporates a reduced-g centrifuge providing artificial gravity for crew health to ameliorate the effects of long-term 0g exposure, and the capability to mitigate the space radiation environment.

Fission powered rockets
The electric propulsion missions already flown, or currently scheduled, have used solar electric power, limiting their capability to operate far from the Sun, and also limiting their peak acceleration due to the mass of the electric power source. Nuclear-electric or plasma engines, operating for long periods at low thrust and powered by fission reactors, can reach speeds much greater than chemically powered vehicles.

Fusion rockets
Fusion rockets, powered by nuclear fusion reactions, would "burn" such light element fuels as deuterium, tritium, or 3He. Because fusion yields about 1% of the mass of the nuclear fuel as released energy, it is energetically more favorable than fission, which releases only about 0.1% of the fuel's mass-energy. However, either fission or fusion technologies can in principle achieve velocities far higher than needed for Solar System exploration, and fusion energy still awaits practical demonstration on Earth.

One proposal using a fusion rocket was Project Daedalus. Another fairly detailed vehicle system, designed and optimized for crewed Solar System exploration, "Discovery II", based on the D3He reaction but using hydrogen as reaction mass, has been described by a team from NASA's Glenn Research Center. It achieves characteristic velocities of >300 km/s with an acceleration of ~1.7•10−3 g, with a ship initial mass of ~1700 metric tons, and payload fraction above 10%.

Fusion rockets are considered to be a likely source of interplanetary transport for a planetary civilization.

Exotic propulsion
See the spacecraft propulsion article for a discussion of a number of other technologies that could, in the medium to longer term, be the basis of interplanetary missions. Unlike the situation with interstellar travel, the barriers to fast interplanetary travel involve engineering and economics rather than any basic physics.

Solar sails
Solar sails rely on the fact that light reflected from a surface exerts pressure on the surface. The radiation pressure is small and decreases by the square of the distance from the Sun, but unlike rockets, solar sails require no fuel. Although the thrust is small, it continues as long as the Sun shines and the sail is deployed.

The original concept relied only on radiation from the Sun – for example in Arthur C. Clarke's 1965 story "Sunjammer". More recent light sail designs propose to boost the thrust by aiming ground-based lasers or masers at the sail. Ground-based lasers or masers can also help a light-sail spacecraft to decelerate: the sail splits into an outer and inner section, the outer section is pushed forward and its shape is changed mechanically to focus reflected radiation on the inner portion, and the radiation focused on the inner section acts as a brake.

Although most articles about light sails focus on interstellar travel, there have been several proposals for their use within the Solar System.

Currently, the only spacecraft to use a solar sail as the main method of propulsion is IKAROS which was launched by JAXA on May 21, 2010. It has since been successfully deployed, and shown to be producing acceleration as expected. Many ordinary spacecraft and satellites also use solar collectors, temperature-control panels and Sun shades as light sails, to make minor corrections to their attitude and orbit without using fuel. A few have even had small purpose-built solar sails for this use (for example Eurostar E3000 geostationary communications satellites built by EADS Astrium).

Cyclers
It is possible to put stations or spacecraft on orbits that cycle between different planets, for example a Mars cycler would synchronously cycle between Mars and Earth, with very little propellant usage to maintain the trajectory. Cyclers are conceptually a good idea, because massive radiation shields, life support and other equipment only need to be put onto the cycler trajectory once. A cycler could combine several roles: habitat (for example it could spin to produce an "artificial gravity" effect); mothership (providing life support for the crews of smaller spacecraft which hitch a ride on it). Cyclers could also possibly make excellent cargo ships for resupply of a colony.

Space elevator
A space elevator is a theoretical structure that would transport material from a planet's surface into orbit. The idea is that, once the expensive job of building the elevator is complete, an indefinite number of loads can be transported into orbit at minimal cost. Even the simplest designs avoid the vicious circle of rocket launches from the surface, wherein the fuel needed to travel the last 10% of the distance into orbit must be lifted all the way from the surface, requiring even more fuel, and so on. More sophisticated space elevator designs reduce the energy cost per trip by using counterweights, and the most ambitious schemes aim to balance loads going up and down and thus make the energy cost close to zero. Space elevators have also sometimes been referred to as "beanstalks", "space bridges", "space lifts", "space ladders" and "orbital towers".

A terrestrial space elevator is beyond our current technology, although a lunar space elevator could theoretically be built using existing materials.

Skyhook
A skyhook is a theoretical class of orbiting tether propulsion intended to lift payloads to high altitudes and speeds. Proposals for skyhooks include designs that employ tethers spinning at hypersonic speed for catching high speed payloads or high altitude aircraft and placing them in orbit. In addition, it has been suggested that the rotating skyhook is "not engineeringly feasible using presently available materials".

Launch vehicle and spacecraft reusability
The SpaceX Starship is designed to be fully and rapidly reusable, making use of the SpaceX reusable technology that was developed during 2011–2018 for Falcon 9 and Falcon Heavy launch vehicles.

SpaceX CEO Elon Musk estimates that the reusability capability alone, on both the launch vehicle and the spacecraft associated with the Starship will reduce overall system costs per tonne delivered to Mars by at least two orders of magnitude over what NASA had previously achieved.

Staging propellants
When launching interplanetary probes from the surface of Earth, carrying all energy needed for the long-duration mission, payload quantities are necessarily extremely limited, due to the basis mass limitations described theoretically by the rocket equation. One alternative to transport more mass on interplanetary trajectories is to use up nearly all of the upper stage propellant on launch, and then refill propellants in Earth orbit before firing the rocket to escape velocity for a heliocentric trajectory. These propellants could be stored on orbit at a propellant depot, or carried to orbit in a propellant tanker to be directly transferred to the interplanetary spacecraft. For returning mass to Earth, a related option is to mine raw materials from a solar system celestial object, refine, process, and store the reaction products (propellant) on the Solar System body until such time as a vehicle needs to be loaded for launch.

On-orbit tanker transfers
As of 2019, SpaceX is developing a system in which a reusable first stage vehicle would transport a crewed interplanetary spacecraft to Earth orbit, detach, return to its launch pad where a tanker spacecraft would be mounted atop it, then both fueled, then launched again to rendezvous with the waiting crewed spacecraft. The tanker would then transfer its fuel to the human crewed spacecraft for use on its interplanetary voyage. The SpaceX Starship is a stainless steel-structure spacecraft propelled by six Raptor engines operating on densified methane/oxygen propellants. It is 55 m-long, 9 m-diameter at its widest point, and is capable of transporting up to 100 tonne of cargo and passengers per trip to Mars, with on-orbit propellant refill before the interplanetary part of the journey.

Propellant plant on a celestial body
As an example of a funded project currently under development, a key part of the system SpaceX has designed for Mars in order to radically decrease the cost of spaceflight to interplanetary destinations is the placement and operation of a physical plant on Mars to handle production and storage of the propellant components necessary to launch and fly the Starships back to Earth, or perhaps to increase the mass that can be transported onward to destinations in the outer Solar System.

The first Starship to Mars will carry a small propellant plant as a part of its cargo load. The plant will be expanded over multiple synods as more equipment arrives, is installed, and placed into mostly-autonomous production.

The SpaceX propellant plant will take advantage of the large supplies of carbon dioxide and water resources on Mars, mining the water (H2O) from subsurface ice and collecting CO2 from the atmosphere. A chemical plant will process the raw materials by means of electrolysis and the Sabatier process to produce oxygen (O2) and methane (CH4), and then liquefy it to facilitate long-term storage and ultimate use.

Using extraterrestrial resources
Current space vehicles attempt to launch with all their fuel (propellants and energy supplies) on board that they will need for their entire journey, and current space structures are lifted from the Earth's surface. Non-terrestrial sources of energy and materials are mostly a lot further away, but most would not require lifting out of a strong gravity field and therefore should be much cheaper to use in space in the long term.

The most important non-terrestrial resource is energy, because it can be used to transform non-terrestrial materials into useful forms (some of which may also produce energy). At least two fundamental non-terrestrial energy sources have been proposed: solar-powered energy generation (unhampered by clouds), either directly by solar cells or indirectly by focusing solar radiation on boilers which produce steam to drive generators; and electrodynamic tethers which generate electricity from the powerful magnetic fields of some planets (Jupiter has a very powerful magnetic field).

Water ice would be very useful and is widespread on the moons of Jupiter and Saturn:
 * The low gravity of these moons would make them a cheaper source of water for space stations and planetary bases than lifting it up from Earth's surface.
 * Non-terrestrial power supplies could be used to electrolyse water ice into oxygen and hydrogen for use in bipropellant rocket engines.
 * Nuclear thermal rockets or Solar thermal rockets could use it as reaction mass. Hydrogen has also been proposed for use in these engines and would provide much greater specific impulse (thrust per kilogram of reaction mass), but it has been claimed that water will beat hydrogen in cost/performance terms despite its much lower specific impulse by orders of magnitude.
 * A spacecraft with an adequate water supply could carry the water under the hull, which could provide a considerable additional safety margin for the vessel and its occupants:
 * The water would absorb and conduct solar energy, thus acting as a heat shield. A vessel traveling in the inner Solar System could maintain a constant heading relative to the Sun without overheating the side of the spacecraft facing the Sun, provided the water under the hull was constantly circulated to evenly distribute the solar heat throughout the hull;
 * The water would provide some additional protection against ionizing radiation;
 * The water would act as an insulator against the extreme cold assuming it was kept heated, whether by the Sun when traveling in the inner Solar System or by an on board power source when traveling further away from the Sun;
 * The water would provide some additional protection against micrometeoroid impacts, provided the hull was compartmentalized so as to ensure any leak could be isolated to a small section of the hull.

Oxygen is a common constituent of the Moon's crust, and is probably abundant in most other bodies in the Solar System. Non-terrestrial oxygen would be valuable as a source of water ice only if an adequate source of hydrogen can be found. Possible uses include:

 * In the life support systems of space ships, space stations and planetary bases.
 * In rocket engines. Even if the other propellant has to be lifted from Earth, using non-terrestrial oxygen could reduce propellant launch costs by up to 2/3 for hydrocarbon fuel, or 85% for hydrogen. The savings are so high because oxygen accounts for the majority of the mass in most rocket propellant combinations.

Unfortunately hydrogen, along with other volatiles like carbon and nitrogen, are much less abundant than oxygen in the inner Solar System.

Scientists expect to find a vast range of organic compounds in some of the planets, moons and comets of the outer Solar System, and the range of possible uses is even wider. For example, methane can be used as a fuel (burned with non-terrestrial oxygen), or as a feedstock for petrochemical processes such as making plastics. And ammonia could be a valuable feedstock for producing fertilizers to be used in the vegetable gardens of orbital and planetary bases, reducing the need to lift food to them from Earth.

Even unprocessed rock may be useful as rocket propellant if mass drivers are employed.

Life support
Life support systems must be capable of supporting human life for weeks, months or even years. A breathable atmosphere of at least 35 kPa must be maintained, with adequate amounts of oxygen, nitrogen, and controlled levels of carbon dioxide, trace gases and water vapor.

In October 2015, the NASA Office of Inspector General issued a health hazards report related to human spaceflight, including a human mission to Mars.

Radiation
Once a vehicle leaves low Earth orbit and the protection of Earth's magnetosphere, it enters the Van Allen radiation belt, a region of high radiation. Beyond the Van Allen belts, radiation levels generally decrease, but can fluctuate over time. These high energy cosmic rays pose a health threat. Even the minimum levels of radiation during these fluctuations is comparable to the current annual limit for astronauts in low-Earth orbit.

Scientists of Russian Academy of Sciences are searching for methods of reducing the risk of radiation-induced cancer in preparation for the mission to Mars. They consider as one of the options a life support system generating drinking water with low content of deuterium (a stable isotope of hydrogen) to be consumed by the crew members. Preliminary investigations have shown that deuterium-depleted water features certain anti-cancer effects. Hence, deuterium-free drinking water is considered to have the potential of lowering the risk of cancer caused by extreme radiation exposure of the Martian crew.

In addition, coronal mass ejections from the Sun are highly dangerous, and are fatal within a very short timescale to humans unless they are protected by massive shielding.

Reliability
Any major failure to a spacecraft en route is likely to be fatal, and even a minor one could have dangerous results if not repaired quickly, something difficult to accomplish in open space. The crew of the Apollo 13 mission survived despite an explosion caused by a faulty oxygen tank (1970).

Launch windows
For astrodynamics reasons, economic spacecraft travel to other planets is only practical within certain time windows. Outside these windows the planets are essentially inaccessible from Earth with current technology. This constrains flights and limits rescue options in the case of an emergency.

title: Interplanetary spaceflight


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Wave interference

In physics, interference is a phenomenon in which two coherent waves are combined by adding their intensities or displacements with due consideration for their phase difference. The resultant wave may have greater intensity (constructive interference) or lower amplitude (destructive interference) if the two waves are in phase or out of phase, respectively. Interference effects can be observed with all types of waves, for example, light, radio, acoustic, surface water waves, gravity waves, or matter waves as well as in loudspeakers as electrical waves.

Etymology
The word interference is derived from the Latin words inter which means "between" and fere which means "hit or strike", and was used in the context of wave superposition by Thomas Young in 1801.

Mechanisms

The principle of superposition of waves states that when two or more propagating waves of the same type are incident on the same point, the resultant amplitude at that point is equal to the vector sum of the amplitudes of the individual waves. If a crest of a wave meets a crest of another wave of the same frequency at the same point, then the amplitude is the sum of the individual amplitudes—this is constructive interference. If a crest of one wave meets a trough of another wave, then the amplitude is equal to the difference in the individual amplitudes—this is known as destructive interference. In ideal mediums (water, air are almost ideal) energy is always conserved, at points of destructive interference, the wave amplitudes cancel each other out, and the energy is redistributed to other areas. For example, when two pebbles are dropped in a pond, a pattern is observable; but eventually waves continue, and only when they reach the shore is the energy absorbed away from the medium.

Constructive interference occurs when the phase difference between the waves is an even multiple of $\pi$ (180°), whereas destructive interference occurs when the difference is an odd multiple of π. If the difference between the phases is intermediate between these two extremes, then the magnitude of the displacement of the summed waves lies between the minimum and maximum values.

Consider, for example, what happens when two identical stones are dropped into a still pool of water at different locations. Each stone generates a circular wave propagating outwards from the point where the stone was dropped. When the two waves overlap, the net displacement at a particular point is the sum of the displacements of the individual waves. At some points, these will be in phase, and will produce a maximum displacement. In other places, the waves will be in anti-phase, and there will be no net displacement at these points. Thus, parts of the surface will be stationary—these are seen in the figure above and to the right as stationary blue-green lines radiating from the centre.

Interference of light is a unique phenomenon in that we can never observe superposition of the EM field directly as we can, for example, in water. Superposition in the EM field is an assumed phenomenon and necessary to explain how two light beams pass through each other and continue on their respective paths. Prime examples of light interference are the famous double-slit experiment, laser speckle, anti-reflective coatings and interferometers.

In addition to classical wave model for understanding optical interference, quantum matter waves also demonstrate interference.

Real-valued wave functions
The above can be demonstrated in one dimension by deriving the formula for the sum of two waves. The equation for the amplitude of a sinusoidal wave traveling to the right along the x-axis is $$W_1(x,t) = A\cos(kx - \omega t)$$ where $$A$$ is the peak amplitude, $$k = 2\pi/\lambda$$ is the wavenumber and $$\omega = 2\pi f$$ is the angular frequency of the wave. Suppose a second wave of the same frequency and amplitude but with a different phase is also traveling to the right $$W_2(x,t) = A\cos(kx - \omega t + \varphi)$$ where $$\varphi$$ is the phase difference between the waves in radians. The two waves will superpose and add: the sum of the two waves is $$W_1 + W_2 = A[\cos(kx - \omega t) + \cos(kx - \omega t + \varphi)].$$ Using the trigonometric identity for the sum of two cosines: $\cos a + \cos b = 2\cos\left({a-b \over 2}\right)\cos\left({a+b \over 2}\right),$ this can be written $$W_1 + W_2 = 2A\cos\left({\varphi \over 2}\right)\cos\left(kx - \omega t + {\varphi \over 2}\right).$$ This represents a wave at the original frequency, traveling to the right like its components, whose amplitude is proportional to the cosine of $$\varphi/2$$.
 * Constructive interference: If the phase difference is an even multiple of π: $$\varphi = \ldots,-4\pi, -2\pi, 0, 2\pi, 4\pi,\ldots$$ then $$\left|\cos(\varphi/2)\right| = 1$$, so the sum of the two waves is a wave with twice the amplitude $$W_1 + W_2 = 2A\cos(kx - \omega t)$$
 * Destructive interference: If the phase difference is an odd multiple of π: $$\varphi = \ldots,-3\pi,\, -\pi,\, \pi,\, 3\pi,\, 5\pi,\ldots$$ then $$\cos(\varphi/2) = 0\,$$, so the sum of the two waves is zero $$W_1 + W_2 = 0$$

Between two plane waves
A simple form of interference pattern is obtained if two plane waves of the same frequency intersect at an angle. One wave is travelling horizontally, and the other is travelling downwards at an angle θ to the first wave. Assuming that the two waves are in phase at the point B, then the relative phase changes along the x-axis. The phase difference at the point A is given by

$$ \Delta \varphi = \frac {2 \pi d} {\lambda} = \frac {2 \pi x \sin \theta} {\lambda}.$$

It can be seen that the two waves are in phase when

$$ \frac {x \sin \theta} {\lambda} = 0, \pm 1, \pm 2, \ldots ,$$

and are half a cycle out of phase when

$$ \frac {x \sin \theta} {\lambda} = \pm \frac {1}{2}, \pm \frac {3}{2}, \ldots $$

Constructive interference occurs when the waves are in phase, and destructive interference when they are half a cycle out of phase. Thus, an interference fringe pattern is produced, where the separation of the maxima is

$$ d_f = \frac {\lambda} {\sin \theta}$$

and $d_{f}$ is known as the fringe spacing. The fringe spacing increases with increase in wavelength, and with decreasing angle $θ$.

The fringes are observed wherever the two waves overlap and the fringe spacing is uniform throughout.

Between two spherical waves

A point source produces a spherical wave. If the light from two point sources overlaps, the interference pattern maps out the way in which the phase difference between the two waves varies in space. This depends on the wavelength and on the separation of the point sources. The figure to the right shows interference between two spherical waves. The wavelength increases from top to bottom, and the distance between the sources increases from left to right.

When the plane of observation is far enough away, the fringe pattern will be a series of almost straight lines, since the waves will then be almost planar.

Multiple beams
Interference occurs when several waves are added together provided that the phase differences between them remain constant over the observation time.

It is sometimes desirable for several waves of the same frequency and amplitude to sum to zero (that is, interfere destructively, cancel). This is the principle behind, for example, 3-phase power and the diffraction grating. In both of these cases, the result is achieved by uniform spacing of the phases.

It is easy to see that a set of waves will cancel if they have the same amplitude and their phases are spaced equally in angle. Using phasors, each wave can be represented as $$A e^{i \varphi_n}$$ for $$N$$ waves from $$n=0$$ to $$n = N-1$$, where $$\varphi_n - \varphi_{n-1} = \frac{2\pi}{N}.$$

To show that $$\sum_{n=0}^{N-1} A e^{i \varphi_n} = 0$$

one merely assumes the converse, then multiplies both sides by $$ e^{i \frac{2\pi}{N}}.$$

The Fabry–Pérot interferometer uses interference between multiple reflections.

A diffraction grating can be considered to be a multiple-beam interferometer; since the peaks which it produces are generated by interference between the light transmitted by each of the elements in the grating; see interference vs. diffraction for further discussion.

Complex valued wave functions
Mechanical and gravity waves can be directly observed: they are real-valued wave functions; optical and matter waves cannot be directly observed: they are complex valued wave functions. Some of the differences between real valued and complex valued wave interference include:

The interference involves different types of mathematical functions: A classical wave is a real function representing the displacement from an equilibrium position; an optical or quantum wavefunction is a complex function. A classical wave at any point can be positive or negative; the quantum probability function is non-negative. Any two different real waves in the same medium interfere; complex waves must be coherent to interfere. In practice this means the wave must come from the same source and have similar frequencies Real wave interference is obtained simply by adding the displacements from equilibrium (or amplitudes) of the two waves; In complex wave interference, we measure the modulus of the wavefunction squared.

Optical wave interference

Because the frequency of light waves (~1014 Hz) is too high for currently available detectors to detect the variation of the electric field of the light, it is possible to observe only the intensity of an optical interference pattern. The intensity of the light at a given point is proportional to the square of the average amplitude of the wave. This can be expressed mathematically as follows. The displacement of the two waves at a point $r$ is:

$$U_1 (\mathbf r,t) = A_1(\mathbf r) e^{i [\varphi_1 (\mathbf r) - \omega t]}$$ $$U_2 (\mathbf r,t) = A_2(\mathbf r) e^{i [\varphi_2 (\mathbf r) - \omega t]}$$

where $A$ represents the magnitude of the displacement, $φ$ represents the phase and $ω$ represents the angular frequency.

The displacement of the summed waves is

$$U (\mathbf r,t) = A_1(\mathbf r) e^{i [\varphi_1 (\mathbf r) - \omega t]}+A_2(\mathbf r) e^{i [\varphi_2 (\mathbf r) - \omega t]}.$$

The intensity of the light at $r$ is given by

$$ I(\mathbf r) = \int U (\mathbf r,t) U^* (\mathbf r,t) \, dt \propto A_1^2 (\mathbf r)+ A_2^2 (\mathbf r) + 2 A_1 (\mathbf r) A_2 (\mathbf r) \cos [\varphi_1 (\mathbf r)-\varphi_2 (\mathbf r)]. $$

This can be expressed in terms of the intensities of the individual waves as

$$ I(\mathbf r) = I_1 (\mathbf r)+ I_2 (\mathbf r) + 2 \sqrt{ I_1 (\mathbf r) I_2 (\mathbf r)} \cos [\varphi_1 (\mathbf r)-\varphi_2 (\mathbf r)].$$

Thus, the interference pattern maps out the difference in phase between the two waves, with maxima occurring when the phase difference is a multiple of 2π. If the two beams are of equal intensity, the maxima are four times as bright as the individual beams, and the minima have zero intensity.

Classically the two waves must have the same polarization to give rise to interference fringes since it is not possible for waves of different polarizations to cancel one another out or add together. Instead, when waves of different polarization are added together, they give rise to a wave of a different polarization state.

Quantum mechanically the theories of Paul Dirac and Richard Feynman offer a more modern approach. Dirac showed that every quanta or photon of light acts on its own which he famously stated as "every photon interferes with itself". Richard Feynman showed that by evaluating a path integral where all possible paths are considered, that a number of higher probability paths will emerge. In thin films for example, film thickness which is not a multiple of light wavelength will not allow the quanta to traverse, only reflection is possible.

Light source requirements
The discussion above assumes that the waves which interfere with one another are monochromatic, i.e. have a single frequency—this requires that they are infinite in time. This is not, however, either practical or necessary. Two identical waves of finite duration whose frequency is fixed over that period will give rise to an interference pattern while they overlap. Two identical waves which consist of a narrow spectrum of frequency waves of finite duration (but shorter than their coherence time), will give a series of fringe patterns of slightly differing spacings, and provided the spread of spacings is significantly less than the average fringe spacing, a fringe pattern will again be observed during the time when the two waves overlap.

Conventional light sources emit waves of differing frequencies and at different times from different points in the source. If the light is split into two waves and then re-combined, each individual light wave may generate an interference pattern with its other half, but the individual fringe patterns generated will have different phases and spacings, and normally no overall fringe pattern will be observable. However, single-element light sources, such as sodium- or mercury-vapor lamps have emission lines with quite narrow frequency spectra. When these are spatially and colour filtered, and then split into two waves, they can be superimposed to generate interference fringes. All interferometry prior to the invention of the laser was done using such sources and had a wide range of successful applications.

A laser beam generally approximates much more closely to a monochromatic source, and thus it is much more straightforward to generate interference fringes using a laser. The ease with which interference fringes can be observed with a laser beam can sometimes cause problems in that stray reflections may give spurious interference fringes which can result in errors.

Normally, a single laser beam is used in interferometry, though interference has been observed using two independent lasers whose frequencies were sufficiently matched to satisfy the phase requirements. This has also been observed for widefield interference between two incoherent laser sources.

It is also possible to observe interference fringes using white light. A white light fringe pattern can be considered to be made up of a 'spectrum' of fringe patterns each of slightly different spacing. If all the fringe patterns are in phase in the centre, then the fringes will increase in size as the wavelength decreases and the summed intensity will show three to four fringes of varying colour. Young describes this very elegantly in his discussion of two slit interference. Since white light fringes are obtained only when the two waves have travelled equal distances from the light source, they can be very useful in interferometry, as they allow the zero path difference fringe to be identified.

Optical arrangements
To generate interference fringes, light from the source has to be divided into two waves which then have to be re-combined. Traditionally, interferometers have been classified as either amplitude-division or wavefront-division systems.

In an amplitude-division system, a beam splitter is used to divide the light into two beams travelling in different directions, which are then superimposed to produce the interference pattern. The Michelson interferometer and the Mach–Zehnder interferometer are examples of amplitude-division systems.

In wavefront-division systems, the wave is divided in space—examples are Young's double slit interferometer and Lloyd's mirror.

Interference can also be seen in everyday phenomena such as iridescence and structural coloration. For example, the colours seen in a soap bubble arise from interference of light reflecting off the front and back surfaces of the thin soap film. Depending on the thickness of the film, different colours interfere constructively and destructively.

Quantum interference
Quantum interference – the observed wave-behavior of matter – resembles optical interference. Let $$\Psi (x, t)$$ be a wavefunction solution of the Schrödinger equation for a quantum mechanical object. Then the probability $$P(x)$$ of observing the object at position $$x$$ is $$P(x) = |\Psi (x, t)|^2 = \Psi^* (x, t) \Psi (x, t)$$ where * indicates complex conjugation. Quantum interference concerns the issue of this probability when the wavefunction is expressed as a sum or linear superposition of two terms $$\Psi (x, t) = \Psi_A (x, t) + \Psi_B (x, t)$$: $$P(x) = |\Psi (x, t)|^2 = |\Psi_A (x, t)|^2 + |\Psi_B (x, t)|^2 + (\Psi_A^* (x, t) \Psi_B (x, t) + \Psi_A (x, t) \Psi_B^* (x, t))$$

Usually, $$\Psi_A (x, t)$$ and $$\Psi_B (x, t)$$ correspond to distinct situations A and B. When this is the case, the equation $$\Psi (x, t) = \Psi_A (x, t) + \Psi_B (x, t)$$ indicates that the object can be in situation A or situation B. The above equation can then be interpreted as: The probability of finding the object at $$x$$ is the probability of finding the object at $$x$$ when it is in situation A plus the probability of finding the object at $$x$$ when it is in situation B plus an extra term. This extra term, which is called the quantum interference term, is $$\Psi_A^* (x, t) \Psi_B (x, t) + \Psi_A (x, t) \Psi_B^* (x, t)$$ in the above equation. As in the classical wave case above, the quantum interference term can add (constructive interference) or subtract (destructive interference) from $$|\Psi_A (x, t)|^2 + |\Psi_B (x, t)|^2$$ in the above equation depending on whether the quantum interference term is positive or negative. If this term is absent for all $$x$$, then there is no quantum mechanical interference associated with situations A and B.

The best known example of quantum interference is the double-slit experiment. In this experiment, matter waves from electrons, atoms or molecules approach a barrier with two slits in it. One slit becomes $$\Psi_A (x, t)$$ and the other becomes $$\Psi_B (x, t)$$. The interference pattern occurs on the far side, observed by detectors suitable to the particles originating the matter wave. The pattern matches the optical double slit pattern.

Beat
In acoustics, a beat is an interference pattern between two sounds of slightly different frequencies, perceived as a periodic variation in volume whose rate is the difference of the two frequencies.

With tuning instruments that can produce sustained tones, beats can be readily recognized. Tuning two tones to a unison will present a peculiar effect: when the two tones are close in pitch but not identical, the difference in frequency generates the beating. The volume varies like in a tremolo as the sounds alternately interfere constructively and destructively. As the two tones gradually approach unison, the beating slows down and may become so slow as to be imperceptible. As the two tones get further apart, their beat frequency starts to approach the range of human pitch perception, the beating starts to sound like a note, and a combination tone is produced. This combination tone can also be referred to as a missing fundamental, as the beat frequency of any two tones is equivalent to the frequency of their implied fundamental frequency.

Optical interferometry
Interferometry has played an important role in the advancement of physics, and also has a wide range of applications in physical and engineering measurement.

Thomas Young's double slit interferometer in 1803 demonstrated interference fringes when two small holes were illuminated by light from another small hole which was illuminated by sunlight. Young was able to estimate the wavelength of different colours in the spectrum from the spacing of the fringes. The experiment played a major role in the general acceptance of the wave theory of light. In quantum mechanics, this experiment is considered to demonstrate the inseparability of the wave and particle natures of light and other quantum particles (wave–particle duality). Richard Feynman was fond of saying that all of quantum mechanics can be gleaned from carefully thinking through the implications of this single experiment.

The results of the Michelson–Morley experiment are generally considered to be the first strong evidence against the theory of a luminiferous aether and in favor of special relativity.

Interferometry has been used in defining and calibrating length standards. When the metre was defined as the distance between two marks on a platinum-iridium bar, Michelson and Benoît used interferometry to measure the wavelength of the red cadmium line in the new standard, and also showed that it could be used as a length standard. Sixty years later, in 1960, the metre in the new SI system was defined to be equal to 1,650,763.73 wavelengths of the orange-red emission line in the electromagnetic spectrum of the krypton-86 atom in a vacuum. This definition was replaced in 1983 by defining the metre as the distance travelled by light in vacuum during a specific time interval. Interferometry is still fundamental in establishing the calibration chain in length measurement.

Interferometry is used in the calibration of slip gauges (called gauge blocks in the US) and in coordinate-measuring machines. It is also used in the testing of optical components.

Radio interferometry
In 1946, a technique called astronomical interferometry was developed. Astronomical radio interferometers usually consist either of arrays of parabolic dishes or two-dimensional arrays of omni-directional antennas. All of the telescopes in the array are widely separated and are usually connected together using coaxial cable, waveguide, optical fiber, or other type of transmission line. Interferometry increases the total signal collected, but its primary purpose is to vastly increase the resolution through a process called Aperture synthesis. This technique works by superposing (interfering) the signal waves from the different telescopes on the principle that waves that coincide with the same phase will add to each other while two waves that have opposite phases will cancel each other out. This creates a combined telescope that is equivalent in resolution (though not in sensitivity) to a single antenna whose diameter is equal to the spacing of the antennas farthest apart in the array.

Acoustic interferometry
An acoustic interferometer is an instrument for measuring the physical characteristics of sound waves in a gas or liquid, such velocity, wavelength, absorption, or impedance. A vibrating crystal creates ultrasonic waves that are radiated into the medium. The waves strike a reflector placed parallel to the crystal, reflected back to the source and measured.

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

title: Wave interference


text:
Talk:Interplanetary spaceflight

Venus orbiter misleading
The article contains a list showing what are implied to be the first spacecraft placed into orbit around each planet. But for Venus, shouldn't it show Venera 9? (sdsds - talk) 04:39, 9 May 2011 (UTC)
 * I have already corrected this. --D.M. from Ukraine (talk) 14:03, 24 December 2011 (UTC)

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On-orbit tanker transfers: Presumably a composition error.
"SpaceX is currently developing a new spacecraft design that will, on all Earth-away launches, utilize the long-duration spacecraft (tanker or spaceship) to play a role briefly as the second stage of the launch vehicle to provide acceleration to orbital velocity. This approach is an unusual design approach launch vehicles designed prior to the 2010s."

My guess the second sentence was intended to be 'This approach is an unusual design compared to launch vehicles conceived prior to the 2010s.' or similar.

In light of the previous "Staging propellants" section which already describes the basic concept, may I suggest the following replacement for both sentences?:

'SpaceX is currently developing a system in which a reusable first stage vehicle would transport a manned interplanetary spacecraft to earth orbit, detach, return to its launch pad where a tanker spacecraft would be mounted atop it, then both fueled, then launched again to rendezvous with the waiting manned spacecraft. The tanker would then transfer its fuel to the manned spacecraft for use on its interplanetary voyage.'

I omitted the comment about this SpaceX system being relatively novel in part because I don't know how the concept evolved, and thus how much original inventiveness is attributable to SpaceX as opposed to others. And my sense is that it's not an appropriate subject to try to parse in the context of the Interplanetary spaceflight article anyway.

Comments and refinements eagerly welcome of course. If none after a few days I'll invoke the change. --H Bruce Campbell (talk) 23:34, 14 July 2017 (UTC)

Since no objections appeared I edited the article as described. But comments and refinements remain eagerly welcome of course. --H Bruce Campbell (talk) 08:46, 24 July 2017 (UTC)

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Another "Economical Travel Technique": the Interplanetary Transport Network
The Interplanetary Transport Network could have use in robotic/AI satellite exploration and for shipping supplies to human colonies on the planets. It may even have some use for human exploration/settlement with "sleeper ships."

I'll leave it to folks who know more than I to add it to the main article. Phantom in ca (talk) 22:48, 11 November 2018 (UTC)

Proposed merge of Interplanetary mission into Interplanetary spaceflight
Obvious overlap with two concepts. Soumya-8974 talk contribs subpages 06:05, 13 August 2020 (UTC)

The article Interplanetary mission has no references at all and would be WP:OR and without valid sources for claims made in the Interplanetary mission article it should probably be deleted and made a redirect. Interplanetary spaceflight already mentions multiple of the missions while figures appear to be "close" and imprecise in the Interplanetary mission article. Example: for the Mariner 2 mission it claims: "in December 1962 when it collected data within 35,000 km (22,000 mi) of Venus." whereas the actual values are: "its closest distance of 34,773 km at 19:59:28 UT 14 December 1962." Terasail [Talk] 22:13, 15 September 2020 (UTC)

. I concur. A redirect of interplanetary mission to interplanetary spaceflight is the correct option. I am going to redirect the article now. I don't plan on merging any of the information. I wouldn't object to other editors adding in information, but only selectively - not a block copy. Desertarun (talk) 16:46, 5 December 2020 (UTC)

Extended the lead
I will remove the 'lead too short' template in a week or so if nobody objects. Redwidgeon (talk) 20:07, 31 December 2020 (UTC)
 * Since there have been no objections, I removed the lead-too-short template. — Preceding unsigned comment added by Redwidgeon (talk • contribs) 20:00, 12 February 2021 (UTC)

"SpaceX Mars propellant plant" listed at Redirects for discussion
The redirect [//en.wikipedia.org/w/index.php?title=SpaceX_Mars_propellant_plant&redirect=no SpaceX Mars propellant plant] has been listed at redirects for discussion to determine whether its use and function meets the redirect guidelines. Readers of this page are welcome to comment on this redirect at  until a consensus is reached. Jay 💬 15:22, 18 April 2024 (UTC)

Advocacy in "Reasons for interplanetary travel" section
The "Reasons for interplanetary travel" section reads like it was written by an enthusiast from a space colonization organization. It does not sound like a dispassionate overview of the relevant controversies. Specifics:

1) Where mention is made of the controversy "about whether human-crewed missions make a useful scientific contribution" to exploration of the Solar System, (a) a reference is given only for the pro-human-spaceflight view and (b) the controversy itself is presented in a straw-man form; the actual debate is not around whether humans can be "useful" in space (of course they can), but whether they are cost-effective in space.

2) The section cites science fiction as if it were an indicator of what is possible or desirable in actual space activities. This is inappropriate for an encyclopedia and the argument, such as it is, is poorly grounded: the author claims that SF has a "fairly good track record in predicting future technologies" but this is debatable given that many (perhaps most) SF speculations have not predicted actual technologies, e.g. telepathy, weather control, faster-than-light travel, time travel, force fields, antigravity, tractor beams, matter transporters, cities located aloft (or underground or undersea or in orbit), etc.

3) The public view of space priorities is mischaracterized: "Those who pay for such missions (primarily in the public sector) are more likely to be interested in benefits for themselves or for the human race as a whole [than in scientific knowledge]." No source is cited for this claim about public opinion. Looking into the question, I immediately see counterevidence: e.g., a 2023 Pew survey in 2023 finds that Americans' highest priorities for NASA are, in descending order, (1) asteroid monitoring, (2) climate change monitoring, and (3) "basic scientific research." Sending astronauts to the Moon or Mars is at the bottom of the list (each garnering about 1/4 as much support as "basic scientific research to increase knowledge of space"). Thus the US public, at least, is _not_ "more likely to be interested in [tangible] benefits" like spinoffs, or in human spaceflight, than in scientific knowledge return:  https://www.pewresearch.org/science/2023/07/20/americans-views-of-space-u-s-role-nasa-priorities-and-impact-of-private-companies/

I have not deleted any significant chunks of the existing text, but I have added some balancing text and references on the cost-effectiveness debate and the state of public opinion. The text could still use improvement. Right now it still emits a strong whiff of human spaceflight advocacy.

Specifically, I move that we delete the two science-fiction paragraphs, i.e. the text from "Other practical motives" to "peak oil." They lack references for their claims, e.g. that "some point out" (who?) that asteroid mining "may be the only way to provide rising standards of living" on Earth, and arguing from fantasy to reality doesn't belong in an encyclopedia in any case.

I also suggest deleting the last paragraph of the section, about the "vast majority" of humans perhaps someday living in space and "benefit[ing] from doing so." It is both vague (how would they "benefit"?) and one-sided; only a pro view is mentioned or referenced.

Sincere regards,

Larry Lgilman909 (talk) 16:48, 22 June 2024 (UTC)

title: Talk:Interplanetary spaceflight


text:
Indictable offence

In many common law jurisdictions (e.g. England and Wales, Ireland, Canada, Hong Kong, India, Australia, New Zealand, Malaysia, Singapore), an indictable offence is an offence which can only be tried on an indictment after a preliminary hearing to determine whether there is a prima facie case to answer or by a grand jury (in contrast to a summary offence). A similar concept in the United States is known as a felony, which for federal crimes, also requires an indictment. In Scotland, which is a hybrid common law jurisdiction, the procurator fiscal will commence solemn proceedings for serious crimes to be prosecuted on indictment before a jury.

Australia
In Australia, an indictable offence is more serious than a summary offence, and one where the defendant has the right to trial by jury. They include crimes such as murder, rape, and threatening or endangering life. The system is underpinned by various state and territory acts and the Commonwealth Crimes Act 1914.

In South Australia, New South Wales, and Queensland, indictable offences are further split into two categories: major indictable offences (including murder, rape, and threatening or endangering life) are heard in the state's Supreme Court, while minor indictable offences are heard in the District Court. In South Australia, minor indictable offences are generally heard in magistrates courts, although the defendant may elect to be heard in the District Court.

Canada
In Canada, an indictable offence is a crime that is more serious than a summary offence. Examples of indictable offences include theft over $5,000, breaking and entering, aggravated sexual assault, and murder. Maximum penalties for indictable offences are different depending on the crime and can include life in prison. There are minimum penalties for some indictable offences.

England and Wales
In relation to England and Wales, the expression indictable offence means an offence which, if committed by an adult, is triable on indictment, whether it is exclusively so triable or triable either way; and the term indictable, in its application to offences, is to be construed accordingly. In this definition, references to the way or ways in which an offence is triable are to be construed without regard to the effect, if any, of section 22 of the Magistrates' Courts Act 1980 on the mode of trial in a particular case.

An either-way offence allows the defendant to elect between trial by jury on indictment in the Crown Court and summary trial in a magistrates' court. However, the election may be overruled by the magistrates' court if the facts suggest that the sentencing powers of a magistrates' court would be inadequate to reflect the seriousness of the offence.

In relation to some indictable offences, for example criminal damage, only summary trial is available unless the damage caused exceeds £5,000.

A youth court has jurisdiction to try all indictable offences with the exception of homicide and certain firearms offences, and will normally do so provided that the available sentencing power of two years' detention is adequate to punish the offender if found guilty.

History
See section 64 of the Criminal Law Act 1977.

Grand juries were abolished in 1933.

Offences triable only on indictment
Some offences such as murder and rape are considered so serious that they can only be tried on indictment at the Crown Court where the widest range of sentencing powers is available to the judge.

The expression indictable-only offence was defined by section 51 of the Crime and Disorder Act 1998, as originally enacted, as an offence triable only on indictment. Sections 51 and 52 of, and Schedule 3 to, that Act abolished committal proceedings for such offences and made other provisions in relation to them.

When the accused is charged with an indictable-only offence, he or she will be tried in the Crown Court. The rules are different in England and Wales in respect of those under 18 years of age.

See also section 14(a) of the Criminal Law Act 1977.

New Zealand
Similarly in New Zealand, a rape or murder charge will be tried at the High Court, while less serious offences such as theft will be tried at the District Court. However, the District Court can hold both jury and summary trials.

United States
In the United States, federal felonies always require an indictment from a grand jury before proceeding to trial. In contrast, while misdemeanours may proceed to trial on indictment; this is not required, as they may also proceed on information or complaint. Different states have different policies; since the requirement of an indictment by grand jury is not incorporated against the states, in many states, an indictment is not required for a felony case to proceed. However, some states do still use grand jury indictments for felony-level offenses and may use other terminology. For instance, in New Jersey, whose constitution requires all "crimes" to be charged by indictment but allows lesser "offenses" not to be, felony-level offenses are commonly called "indictable offenses", including in the New Jersey Penal Code, to avoid confusion between the narrow technical definition of the word "crime" from the state's constitutional jurisprudence and the broader sense.

title: Indictable offence


text:
Talk:Indictment

Untitled
Just an observer, but reading through the article, it has severe (whether intentional or not) prejudices toward the jury concept. A few examples:

 "Most common law jurisdictions (except for much of the United States) have abolished grand juries"

'' "In many (though not all) U.S. jurisdictions retaining the grand jury. . ." ''

'' "Notwithstanding the existence of the right to jury trial, the vast majority of criminal cases in the U.S. are resolved by the plea bargaining process. . ." ''

These, especially the first two, seem unnecessary to the article's overall purpose.

Article read:
 * Alternatively an indictment may be issued by a court, following arraignment, at a preliminary hearing.

According to arraignment, this is when the plea is enterred; isn't indictment an earlier process than arraignment? -- Simon J Kissane

I currently have my civics book open and it agrees with you. The order of process that it states is, Preliminary Hearing, Indictment, Arraignment, Trial, Sentancing.Rudraksha 02:48, 4 October 2006 (UTC)

The pronunciation of this word should be listed somewhere on this article as the word sounds little like how it is spelt.

Yo! The explanation of R v Smith has been given as R versus Smith. In English law the 'v' stands for 'and'. It is in the US (and i am not sure where else) that stands for versus. I had changed this yesterday but it has been chnaged back... Come let us inform people correctly and not change it again. —Preceding unsigned comment added by 82.35.115.185 (talk • contribs) on 5 July 2007.

- It only stands for "and" in civil cases, I believe 172.189.53.141 (talk) 01:22, 22 February 2008 (UTC)

The abbreviation "v" stands for "versus" ("against") in both English law and U.S. law, in both civil and criminal cases. The "v" does not stand for "and." Famspear (talk) 15:07, 22 February 2008 (UTC)

The correct pronunciation (at least in the UK) is "against" in criminal cases and "and" in civil cases - see the article and the book that I have cited in it. James500 (talk) 20:43, 20 November 2008 (UTC)

Charging document
Presently charging document redirects to this article. Are the one and they same thing? I thought an information (law) was another type of charging document, distinct from an indictment. Thanks,  Tisane  talk/stalk 16:00, 15 July 2010 (UTC)

United States

 * There is a problem with the wording in the 2nd paragraph that states "...a judge determines whether there was probable cause to arrest the suspect who is in custody. This should be worded "probable cause to formally charge and if bail can not be made remand the suspect who is in custody".
 * If a person is in custody (deprived of liberty) they are "arrested" (seized) if they can not willing leave. An exception to this is being "detained" for a reasonable amount of time for identification Stop and identify statutes (currently around half the states) and certain questioning by an officer of the peace. A contentious practice of detaining as a material witness has shown that there can be ramifications against the authority for False imprisonment and/or False arrest (Ashcroft v. al-Kidd; held 16 days). Otr500 (talk) 18:17, 27 December 2014 (UTC)

Yes Chiyere (talk) 14:44, 11 September 2017 (UTC)

"Jurisdictions that use the concept of felonies"
In the article top, a distinction is made between "jurisdictions that use the concept of felonies" and "jurisdictions that do not use the concept of felonies". Most of the subsequent discussion seems to concern juridical terminology in English-speaking countries. I have two questions: If the answer of the first question is "mainly term", and the answer to the second one is "No", then the distinction should be stated to be primarily between US and other 'Anglo-Saxon' jurisdictions. It may also have effects on some articles with "felony" in their names. JoergenB (talk) 00:36, 13 April 2015 (UTC)
 * 1) Is this really related to the concept felony, or mainly to the term?
 * 2) Is there any other jurisdiction than that/those in the US which still uses the term "felony"?

Neglect
Can cps give you neglect. If the indictment is undisposed and there was no grand jury to decide if there was probable cause against the accused? This indictment is not a true bill and the accused did not waive his rights and plead guilty. He is actually on the run and in California of which is out of the jurisdiction I recently live in. But cps is saying since the accused "sexually abused" my boyfriends son and since his son had no counseling right away. That by law they are they allowed to give him neglect. His son's mom which is a active drug user and has been so for many of year(s) brought this attention to the police. she made the statement that all 3 of her children two of which are not my boyfriends kids went on a camping trip (which is true) and was all 3 sexually abused. But she did not put her third oldest child in this report. I don't know if she manipulated the truth and brain washed her 3 kids into making them give the police officers false facts. My boyfriend grew up with this guy and he never was sexually abused by this man and he practically helped raise him like a dad. Being that his biological father was not in his life. Honestly, I am lost for words and I know you should never not believe a child when they say "someone sexually abused them." I do believe the children. But as for the mom I do not believe her. Being that the third child is not in the report. The investigators have picture of all three of the boys at the camp grounds. My question is it illegal to give someone a child abuse and neglect charge for not getting counseling for the son based on accusations. — Preceding unsigned comment added by 98.28.43.177 (talk) 08:29, 20 January 2018 (UTC)

Article top is poorly written
"An indictment (/ɪnˈdaɪtmənt/ in-DYT-mənt) is a criminal accusation that a person has committed a crime. In jurisdictions that use the concept of felonies, the most serious criminal offence is a felony; jurisdictions that do not use the concept of felonies often use that of an indictable offence—an offence that requires an indictment."

Does a poor job of actually explaining the concept of an indictment, appears slightly condescending.

This part as well: "In jurisdictions that use the concept of felonies, the most serious criminal offence is a felony; " Is simply poorly written. — Preceding unsigned comment added by 212.10.113.229 (talk) 19:47, 16 October 2018 (UTC)

title: Talk:Indictment