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Apollo 1

Apollo 1, initially designated AS-204, was planned to be the first crewed mission of the Apollo program, the American undertaking to land the first man on the Moon. It was planned to launch on February 21, 1967, as the first low Earth orbital test of the Apollo command and service module. The mission never flew; a cabin fire during a launch rehearsal test at Cape Kennedy Air Force Station Launch Complex 34 on January 27 killed all three crew members—Command Pilot Gus Grissom, Senior Pilot Ed White, and Pilot Roger B. Chaffee—and destroyed the command module (CM). The name Apollo 1, chosen by the crew, was made official by NASA in their honor after the fire.

Immediately after the fire, NASA convened an Accident Review Board to determine the cause of the fire, and both chambers of the United States Congress conducted their own committee inquiries to oversee NASA's investigation. The ignition source of the fire was determined to be electrical, and the fire spread rapidly due to combustible nylon material and the high-pressure pure oxygen cabin atmosphere. Rescue was prevented by the plug door hatch, which could not be opened against the internal pressure of the cabin. Because the rocket was unfueled, the test had not been considered hazardous, and emergency preparedness for it was poor.

During the Congressional investigation, Senator Walter Mondale publicly revealed a NASA internal document citing problems with prime Apollo contractor North American Aviation, which became known as the Phillips Report. This disclosure embarrassed NASA Administrator James E. Webb, who was unaware of the document's existence, and attracted controversy to the Apollo program. Despite congressional displeasure at NASA's lack of openness, both congressional committees ruled that the issues raised in the report had no bearing on the accident.

Crewed Apollo flights were suspended for twenty months while the command module's hazards were addressed. However, the development and uncrewed testing of the lunar module (LM) and Saturn V rocket continued. The Saturn IB launch vehicle for Apollo1, AS-204, was used for the first LM test flight, Apollo 5. The first successful crewed Apollo mission was flown by Apollo1's backup crew on Apollo 7 in October 1968.

Apollo crewed test flight plans

AS-204 was to be the first crewed test flight of the Apollo command and service module (CSM) to Earth orbit, launched on a Saturn IB rocket. AS-204 was to test launch operations, ground tracking and control facilities and the performance of the Apollo-Saturn launch assembly and would have lasted up to two weeks, depending on how the spacecraft performed.

The CSM for this flight, number 012 built by North American Aviation (NAA), was a Block I version designed before the lunar orbit rendezvous landing strategy was chosen; therefore it lacked the capability of docking with the lunar module. This was incorporated into the Block II CSM design, along with lessons learned in Block I. Block II would be test-flown with the LM when the latter was ready.

Director of Flight Crew Operations Deke Slayton selected the first Apollo crew in January 1966, with Grissom as Command Pilot, White as Senior Pilot, and rookie Donn F. Eisele as Pilot. But Eisele dislocated his shoulder twice aboard the KC-135 weightlessness training aircraft, and had to undergo surgery on January 27. Slayton replaced him with Chaffee, and NASA announced the crew selection on March 21, 1966. James McDivitt, David Scott and Russell Schweickart were named as the backup crew.

On September 29, Walter Schirra, Eisele, and Walter Cunningham were named as the prime crew for a second Block I CSM flight, AS-205. NASA planned to follow this with an uncrewed test flight of the LM (AS-206), then the third crewed mission would be a dual flight designated AS-278 (or AS-207/208), in which AS-207 would launch the first crewed Block II CSM, which would then rendezvous and dock with the LM launched uncrewed on AS-208.

In March, NASA was studying the possibility of flying the first Apollo mission as a joint space rendezvous with the final Project Gemini mission, Gemini 12 in November 1966. But by May, delays in making Apollo ready for flight just by itself, and the extra time needed to incorporate compatibility with the Gemini, made that impractical. This became moot when slippage in readiness of the AS-204 spacecraft caused the last-quarter 1966 target date to be missed, and the mission was rescheduled for February 21, 1967.

Mission background
In October 1966, NASA announced the flight would carry a small television camera to broadcast live from the command module. The camera would also be used to allow flight controllers to monitor the spacecraft's instrument panel in flight. Television cameras were carried aboard all crewed Apollo missions.

Insignia
Grissom's crew received approval in June 1966 to design a mission patch with the name Apollo1 (though the approval was subsequently withdrawn pending a final decision on the mission designation, which was not resolved until after the fire). The design's center depicts a command and service module flying over the southeastern United States with Florida (the launch point) prominent. The Moon is seen in the distance, symbolic of the eventual program goal. A yellow border carries the mission and astronaut names with another border set with stars and stripes, trimmed in gold. The insignia was designed by the crew, with the artwork done by North American Aviation employee Allen Stevens.

Spacecraft and crew preparation

The Apollo command and service module was much bigger and far more complex than any previous crewed spacecraft. In October 1963, Joseph F. Shea was named Apollo Spacecraft Program Office (ASPO) manager, responsible for managing the design and construction of both the CSM and the LM. In a spacecraft review meeting held with Shea on August 19, 1966 (a week before delivery), the crew expressed concern about the amount of flammable material (mainly nylon netting and Velcro) in the cabin, which both astronauts and technicians found convenient for holding tools and equipment in place. Although Shea gave the spacecraft a passing grade, after the meeting they gave him a crew portrait they had posed with heads bowed and hands clasped in prayer, with the inscription: "It isn't that we don't trust you, Joe, but this time we've decided to go over your head." Shea gave his staff orders to tell North American to remove the flammables from the cabin, but did not supervise the issue personally.

North American shipped spacecraft CM-012 to Kennedy Space Center on August 26, 1966, under a conditional Certificate of Flight Worthiness: 113 significant incomplete planned engineering changes had to be completed at KSC. That was not all; an additional 623 engineering change orders were made and completed after delivery. Grissom became so frustrated with the inability of the training simulator engineers to keep up with the spacecraft changes that he took a lemon from a tree by his house and hung it on the simulator.

The command and service modules were mated in the KSC altitude chamber in September, and combined system testing was performed. Altitude testing was performed first uncrewed, then with both the prime and backup crews, from October 10 through December 30. During this testing, the environmental control unit in the command module was found to have a design flaw, and was sent back to the manufacturer for design changes and rework. The returned ECU then leaked water/glycol coolant, and had to be returned a second time. Also during this time, a propellant tank in another service module had ruptured during testing at NAA, prompting the removal from the KSC test chamber of the service module so it could be tested for signs of the tank problem. These tests were negative.

In December the second Block I flight AS-205 was canceled as unnecessary; Schirra, Eisele and Cunningham were reassigned as the backup crew for Apollo1. McDivitt's crew was now promoted to prime crew of the Block II/LM mission, re-designated AS-258 because the AS-205 launch vehicle would be used in place of AS-207. A third crewed mission was planned to launch the CSM and LM together on a SaturnV (AS-503) to an elliptical medium Earth orbit (MEO), to be crewed by Frank Borman, Michael Collins and William Anders. McDivitt, Scott and Schweickart had started their training for AS-258 in CM-101 at the NAA plant in Downey, California, when the Apollo1 accident occurred.

Once all outstanding CSM-012 hardware problems had been fixed, the reassembled spacecraft completed a successful altitude chamber test with Schirra's backup crew on December 30. According to the final report of the accident investigation board, "At the post-test debriefing the backup flight crew expressed their satisfaction with the condition and performance of the spacecraft." This would appear to contradict the account given in the 1994 book Lost Moon: The Perilous Voyage of Apollo13 by Jeffrey Kluger and astronaut James Lovell, that "When the trio climbed out of the ship,... Schirra made it clear that he was not pleased with what he had seen," and that he later warned Grissom and Shea that "there's nothing wrong with this ship that I can point to, but it just makes me uncomfortable. Something about it just doesn't ring right," and that Grissom should get out at the first sign of trouble.

After the successful altitude tests, the spacecraft was removed from the altitude chamber on January 3, 1967, and mated to its Saturn IB launch vehicle on pad 34 on January 6.

Grissom said in a February 1963 interview that NASA could not eliminate risk despite precautions:

"An awful lot of people have devoted more effort than I can describe to [make] Project Mercury and its successors, as safe as humanly possible ... But we also recognize that there remains a great deal of risk, especially in initial operations, regardless of planning. You just can't forecast all the things that could happen, or when they could happen."

"I suppose that someday we are going to have a failure. In every other business there are failures, and they are bound to happen sooner or later", he added. Grissom was asked about the fear of potential catastrophe in a December 1966 interview:

"You sort of have to put that out of your mind. There's always a possibility that you can have a catastrophic failure, of course; this can happen on any flight; it can happen on the last one as well as the first one. So, you just plan as best you can to take care of all these eventualities, and you get a well-trained crew and you go fly."

Plugs-out test

The launch simulation on January 27, 1967, on pad 34, was a "plugs-out" test to determine whether the spacecraft would operate nominally on (simulated) internal power while detached from all cables and umbilicals. Passing this test was essential to making the February 21 launch date. The test was considered non-hazardous because neither the launch vehicle nor the spacecraft was loaded with fuel or cryogenics and all pyrotechnic systems (explosive bolts) were disabled.

At 1:00 pm EST (1800 GMT) on January 27, first Grissom, then Chaffee, and White entered the command module fully pressure-suited, and were strapped into their seats and hooked up to the spacecraft's oxygen and communication systems. Grissom immediately noticed a strange odor in the air circulating through his suit which he compared to "sour buttermilk", and the simulated countdown was put on hold at 1:20 pm, while air samples were taken. No cause of the odor could be found, and the countdown was resumed at 2:42 pm. The accident investigation found this odor not to be related to the fire.

Three minutes after the count was resumed the hatch installation was started. The hatch consisted of three parts: a removable inner hatch which stayed inside the cabin; a hinged outer hatch which was part of the spacecraft's heat shield; and an outer hatch cover which was part of the boost protective cover enveloping the entire command module to protect it from aerodynamic heating during launch and from launch escape rocket exhaust in the event of a launch abort. The boost hatch cover was partially, but not fully, latched in place because the flexible boost protective cover was slightly distorted by some cabling run under it to provide the simulated internal power (the spacecraft's fuel cell reactants were not loaded for this test). After the hatches were sealed, the air in the cabin was replaced with pure oxygen at 16.7 psi, 2 psi higher than atmospheric pressure.

Movement by the astronauts was detected by the spacecraft's inertial measurement unit and the astronauts' biomedical sensors, and also indicated by increases in oxygen spacesuit flow, and sounds from Grissom's stuck-open microphone. The stuck microphone was part of a problem with the communications loop connecting the crew, the Operations and Checkout Building, and the Complex 34 blockhouse control room. The poor communications led Grissom to remark: "How are we going to get to the Moon if we can't talk between two or three buildings?"

The simulated countdown was put on hold again at 5:40 pm while attempts were made to troubleshoot the communications problem. All countdown functions up to the simulated internal power transfer had been successfully completed by 6:20 pm, and at 6:30 the count remained on hold at T minus 10 minutes.

The fire

The crew members were using the time to run through their checklist again, when a momentary increase in AC Bus2 voltage occurred. Nine seconds later (at 6:31:04.7), one of the astronauts (some listeners and laboratory analysis indicate Grissom) exclaimed "Hey!", "Fire!", or "Flame!"; this was followed by two seconds of scuffling sounds through Grissom's open microphone. This was immediately followed at 6:31:06.2 (23:31:06.2 GMT) by someone (believed by most listeners, and supported by laboratory analysis, to be Chaffee) saying, "[I've, or We've] got a fire in the cockpit." After 6.8 seconds of silence, a second, badly garbled transmission was heard by various listeners (who believed this transmission was made by Chaffee ) as: The transmission lasted 5.0 seconds and ended with a cry of pain.
 * "They're fighting a bad fire—Let's get out... Open 'er up",
 * "We've got a bad fire—Let's get out... We're burning up", or
 * "I'm reporting a bad fire... I'm getting out..."

Some blockhouse witnesses said that they saw White on the television monitors, reaching for the inner hatch release handle as flames in the cabin spread from left to right.

The heat of the fire fed by pure oxygen caused the pressure to rise to 29 psi, which ruptured the command module's inner wall at 6:31:19 (23:31:19 GMT, initial phase of the fire). Flames and gases then rushed outside the command module through open access panels to two levels of the pad service structure. The intense heat, dense smoke, and ineffective gas masks designed for toxic fumes rather than smoke, hampered the ground crew's attempts to rescue the men. There were fears the command module had exploded, or soon would, and that the fire might ignite the solid fuel rocket in the launch escape tower above the command module, which would have likely killed nearby ground personnel, and possibly have destroyed the pad.

As the pressure was released by the cabin rupture, the rush of gases within the module caused flames to spread across the cabin, beginning the second phase. The third phase began when most of the oxygen was consumed and was replaced with atmospheric air, essentially quenching the fire, but causing high concentrations of carbon monoxide and heavy smoke to fill the cabin, and large amounts of soot to be deposited on surfaces as they cooled. It took five minutes for the pad workers to open all three hatch layers, and they could not drop the inner hatch to the cabin floor as intended, so they pushed it out of the way to one side. Although the cabin lights remained on, they were unable to see the astronauts through the dense smoke. As the smoke cleared they found the bodies, but were not able to remove them. The fire had partly melted Grissom's and White's nylon space suits and the hoses connecting them to the life support system. Grissom had removed his restraints and was lying on the floor of the spacecraft. White's restraints were burned through, and he was found lying sideways just below the hatch. It was determined that he had tried to open the hatch per the emergency procedure, but was not able to do so against the internal pressure. Chaffee was found strapped into his right-hand seat, as procedure called for him to maintain communication until White opened the hatch. Because of the large strands of melted nylon fusing the astronauts to the cabin interior, removing the bodies took nearly 90 minutes. The bodies were only able to be removed after 7.5 hours from the time the incident took place, due to the gasses and toxins present which prevented medical personnel from entering initially.

Deke Slayton was possibly the first NASA official to examine the spacecraft's interior. His testimony contradicted the official report concerning the position of Grissom's body. Slayton said of Grissom and White's bodies, "it is very difficult for me to determine the exact relationships of these two bodies. They were sort of jumbled together, and I couldn't really tell which head even belonged to which body at that point. I guess the only thing that was real obvious is that both bodies were at the lower edge of the hatch. They were not in the seats. They were almost completely clear of the seat areas."

Investigation

As a result of the in-flight failure of the Gemini 8 mission on March 17, 1966, NASA Deputy Administrator Robert Seamans wrote and implemented Management Instruction 8621.1 on April 14, 1966, defining Mission Failure Investigation Policy And Procedures. This modified NASA's existing accident procedures, based on military aircraft accident investigation, by giving the Deputy Administrator the option of performing independent investigations of major failures, beyond those for which the various Program Office officials were normally responsible. It declared, "It is NASA policy to investigate and document the causes of all major mission failures which occur in the conduct of its space and aeronautical activities and to take appropriate corrective actions as a result of the findings and recommendations."

Immediately after thefire NASA Administrator James E. Webb asked President Lyndon B. Johnson to allow NASA to handle the investigation according to its established procedure, promising to be truthful in assessing blame, and to keep the appropriate leaders of Congress informed. Seamans then directed establishment of the Apollo 204 Review Board chaired by Langley Research Center director Floyd L. Thompson, which included astronaut Frank Borman, spacecraft designer Maxime Faget, and six others. On February 1, Cornell University professor Frank A. Long left the board, and was replaced by Robert W. Van Dolah of the U.S. Bureau of Mines. The next day North American's chief engineer for Apollo, George Jeffs, resigned as well.

Seamans ordered all Apollo1 hardware and software impounded, to be released only under control of the board. After thorough stereo photographic documentation of the CM-012 interior, the board ordered its disassembly using procedures tested by disassembling the identical CM-014 and conducted a thorough investigation of every part. The board also reviewed the astronauts' autopsy results and interviewed witnesses. Seamans sent Webb weekly status reports of the investigation's progress, and the board issued its final report on April 5, 1967.

Cause of death
According to the Board, Grissom suffered severe third-degree burns on more than one-third of his body and his spacesuit was almost completely destroyed. White suffered third-degree burns on almost half of his body and a quarter of his spacesuit had melted away. Chaffee suffered third-degree burns on almost a quarter of his body and a small portion of his spacesuit was damaged. The autopsy report determined that the primary cause of death for all three astronauts was cardiac arrest caused by high concentrations of carbon monoxide. Burns suffered by the crew were not believed to be major factors, and it was concluded that most of them had occurred postmortem. Asphyxiation occurred after the fire melted the astronauts' suits and oxygen tubes, exposing them to the lethal atmosphere of the cabin.

Major causes of accident
The review board identified several major factors which combined to cause the fire and the astronauts' deaths:
 * An ignition source most probably related to "vulnerable wiring carrying spacecraft power" and "vulnerable plumbing carrying a combustible and corrosive coolant"
 * A pure oxygen atmosphere at higher than atmospheric pressure
 * A cabin sealed with a hatch cover which could not be quickly removed at high pressure
 * An extensive distribution of combustible materials in the cabin
 * Inadequate emergency preparedness (rescue or medical assistance, and crew escape)

Ignition source
The review board determined that the electrical power momentarily failed at 23:30:55 GMT, and found evidence of several electric arcs in the interior equipment. They were unable to conclusively identify a single ignition source. They determined that the fire most likely started near the floor in the lower left section of the cabin, close to the Environmental Control Unit. It spread from the left wall of the cabin to the right, with the floor being affected only briefly.

The board noted that a silver-plated copper wire, running through an environmental control unit near the center couch, had become stripped of its Teflon insulation and abraded by repeated opening and closing of a small access door.

This weak point in the wiring also ran near a junction in an ethylene glycol/water cooling line that had been prone to leaks. Electrolysis of ethylene glycol solution with the silver anode of the wire was discovered at the Manned Spacecraft Center on May 29, 1967, to be a hazard capable of causing a violent exothermic reaction, igniting the ethylene glycol mixture in the Command Module's pure oxygen atmosphere. Experiments at the Illinois Institute of Technology confirmed the hazard existed for silver-plated wires, but not for copper-only or nickel-plated copper. In July, ASPO directed both North American and Grumman to ensure no silver or silver-coated electrical contacts existed in the vicinity of possible glycol spills in the Apollo spacecraft.

Pure oxygen atmosphere
The plugs-out test had been run to simulate the launch procedure, with the cabin pressurized with pure oxygen at the nominal launch level of 16.7 psi, 2 psi above standard sea level atmospheric pressure. This is more than five times the 3 psi partial pressure of oxygen in the atmosphere, and provides an environment in which materials not normally considered flammable will be highly flammable and burst into flame.

The high-pressure oxygen atmosphere was similar to that which had been used successfully in the Mercury and Gemini programs. The pressure before launch was deliberately greater than ambient in order to drive out the nitrogen-containing air and replace it with pure oxygen, and also to seal the plug door hatch cover. During the launch, the pressure would have been gradually reduced to the in-flight level of 5 psi, providing sufficient oxygen for the astronauts to breathe while reducing the fire risk. The Apollo1 crew had successfully tested this procedure with their spacecraft in the Operations and Checkout Building altitude (vacuum) chamber on October 18 and 19, 1966, and the backup crew of Schirra, Eisele and Cunningham had repeated it on December 30. The investigation board noted that, during these tests, the command module had been fully pressurized with pure oxygen four times, for a total of six hours and fifteen minutes, two and a half hours longer than it had been during the plugs-out test.

Flammable materials in the cabin
The review board cited "many types and classes of combustible material" close to ignition sources. The NASA crew systems department had installed 34 sqft of Velcro throughout the spacecraft, almost like carpeting. This Velcro was found to be flammable in a high-pressure 100% oxygen environment. Astronaut Buzz Aldrin states in his book Men From Earth that the flammable material had been removed per the crew's August 19 complaints and Joseph Shea's order, but was replaced before the August 26 delivery to Cape Kennedy.

Hatch design

The inner hatch cover used a plug door design, sealed by higher pressure inside the cabin than outside. The normal pressure level used for launch (2 psi above ambient) created sufficient force to prevent removing the cover until the excess pressure was vented. Emergency procedure called for Grissom to open the cabin vent valve first, allowing White to remove the cover, but Grissom was prevented from doing this because the valve was located to the left, behind the initial wall of flames. Also, while the system could easily vent the normal pressure, its flow capacity was utterly incapable of handling the rapid increase to 29 psi caused by the intense heat of the fire.

North American had originally suggested the hatch open outward and use explosive bolts to blow the hatch in case of emergency, as had been done in Project Mercury. NASA did not agree, arguing the hatch could accidentally open, as it had on Grissom's Liberty Bell 7 flight, so the Manned Spacecraft Center designers rejected the explosive design in favor of a mechanically operated one for the Gemini and Apollo programs. Before the fire, the Apollo astronauts had recommended changing the design to an outward-opening hatch, and this was already slated for inclusion in the Block II command module design. According to Donald K. Slayton's testimony before the House investigation of the accident, this was based on ease of exit for spacewalks and at the end of flight, rather than for emergency exit.

Emergency preparedness
The board noted that the test planners had failed to identify the test as hazardous; emergency equipment (such as gas masks) were inadequate to handle this type of fire; that fire, rescue, and medical teams were not in attendance; and that the spacecraft work and access areas contained many hindrances to emergency response such as steps, sliding doors, and sharp turns.

Choice of pure oxygen atmosphere
When designing the Mercury spacecraft, NASA had considered using a nitrogen/oxygen mixture to reduce the fire risk near launch, but rejected it based on a number of considerations. First, a pure oxygen atmosphere is comfortably breathable by humans at 5 psi, greatly reducing the pressure load on the spacecraft in the vacuum of space. Second, nitrogen used with the in-flight pressure reduction carried the risk of decompression sickness (known as "the bends"). But the decision to eliminate the use of any gas but oxygen was criticized when a serious accident occurred on April 21, 1960, in which McDonnell Aircraft test pilot G. B. North passed out and was seriously injured when testing a Mercury cabin / spacesuit atmosphere system in a vacuum chamber. The problem was found to be nitrogen-rich (oxygen-poor) air leaking from the cabin into his spacesuit feed. North American Aviation had suggested using an oxygen/nitrogen mixture for Apollo, but NASA overruled this. The pure oxygen design was judged to be safer, less complicated, and lighter in weight. In his monograph Project Apollo: The Tough Decisions, Deputy Administrator Seamans wrote that NASA's worst mistake in engineering judgment was not running a fire test on the command module before the plugs-out test. In the first episode of the 2009 BBC documentary series NASA: Triumph and Tragedy, Jim McDivitt said that NASA had no idea how a 100% oxygen atmosphere would influence burning. Similar remarks by other astronauts were expressed in the 2007 documentary film In the Shadow of the Moon.

Other oxygen incidents
Several fires in high-oxygen test environments had occurred before the Apollo fire. In 1962, USAF Colonel B. Dean Smith was conducting a test of the Gemini space suit with a colleague in a pure oxygen chamber at Brooks Air Force Base in San Antonio, Texas, when a fire broke out, destroying the chamber. Smith and his partner narrowly escaped. On November 17, 1962, a fire broke out in a chamber at the Navy's Air Crew Equipment Laboratory during a pure oxygen test. The fire was started because a faulty ground wire arced onto nearby insulation. After attempts to extinguish the fire by smothering it, the crew escaped the chamber with minor burns across large parts of their bodies. On February 16, 1965, United States Navy Divers Fred Jackson and John Youmans were killed in a decompression chamber fire at the Experimental Diving Unit in Washington, D.C., shortly after additional oxygen was added to the chamber's atmospheric mix.

In addition to fires with personnel present, the Apollo Environmental Control System experienced several accidents from 1964 to 1966 due to various hardware malfunctions. Notable is the April 28, 1966, fire, as the subsequent investigation found that several new measures should be taken to avoid fires, including improved selection of materials and that ESC and Command Module circuits have a potential for arcing or short circuits.

Other oxygen fire occurrences are documented in reports archived in the National Air and Space Museum, such as:
 * Selection of Space Cabin Atmospheres. Part II: Fire and Blast Hazards [sic] in Space Cabins. (Emanuel M. Roth; Dept of Aeronautics Medicine and Bioastronautics, Lovelace Foundation for Medical Education and Research. c. 1964–1966)
 * "Fire Prevention in Manned Spacecraft and Test Chamber Oxygen Atmospheres". (Manned Spacecraft Center. NASA General Working Paper 10 063. October 10, 1966)

Incidents had also occurred in the Soviet space program, but due to the Soviet government's policy of secrecy, these were not disclosed until well after the Apollo1 fire. Cosmonaut Valentin Bondarenko died on March 23, 1961, from burns sustained in a fire while participating in a 15-day endurance experiment in a high-oxygen isolation chamber, less than three weeks before the first Vostok crewed space flight; this was disclosed on January 28, 1986.

During the Voskhod 2 mission in March 1965, cosmonauts Pavel Belyayev and Alexei Leonov could not completely seal the spacecraft hatch after Leonov's historic first walk in space. The spacecraft's environmental control system responded to the leaking air by adding more oxygen to the cabin, causing the concentration level to rise as high as 45%. The crew and ground controllers worried about the possibility of fire, remembering Bondarenko's death four years earlier.

On January 31, 1967, four days after the Apollo1 fire, United States Air Force airmen William F. Bartley Jr. and Richard G. Harmon were killed in a flash fire while tending laboratory rabbits in the Two Man Space Environment Simulator, a pure oxygen chamber at the School of Aerospace Medicine at Brooks Air Force Base. Like the Apollo1 fire, the School fire was caused by an electrical spark in a pure oxygen environment. The widows of the Apollo1 crew sent condolence letters to Bartley and Harmon's families.

Political fallout

Committees in both houses of the United States Congress with oversight of the space program soon launched investigations, including the Senate Committee on Aeronautical and Space Sciences, chaired by Senator Clinton P. Anderson. Seamans, Webb, Manned Space Flight Administrator Dr. George E. Mueller, and Apollo Program Director Maj Gen Samuel C. Phillips were called to testify before Anderson's committee.

In the February 27 hearing, Senator Walter F. Mondale asked Webb if he knew of a report of extraordinary problems with the performance of North American Aviation on the Apollo contract. Webb replied he did not, and deferred to his subordinates on the witness panel. Mueller and Phillips responded they too were unaware of any such "report".

However, in late 1965, just over a year before the accident, Phillips had headed a "tiger team" investigating the causes of inadequate quality, schedule delays, and cost overruns in both the Apollo CSM and the Saturn V second stage (for which North American was also prime contractor). He gave an oral presentation (with transparencies) of his team's findings to Mueller and Seamans, and also presented them in a memo to North American president John L. Atwood, to which Mueller appended his own strongly worded memo to Atwood.

During Mondale's 1967 questioning about what was to become known as the "Phillips Report", Seamans was afraid Mondale might actually have seen a hard copy of Phillips' presentation, and responded that contractors have occasionally been subjected to on-site progress reviews; perhaps this was what Mondale's information referred to. Mondale continued to refer to "the Report" despite Phillips' refusal to characterize it as such, and, angered by what he perceived as Webb's deception and concealment of important program problems from Congress, he questioned NASA's selection of North American as prime contractor. Seamans later wrote that Webb roundly chastised him in the cab ride leaving the hearing, for volunteering information which led to the disclosure of Phillips' memo.

On May 11, Webb issued a statement defending NASA's November 1961 selection of North American as the prime contractor for Apollo. This was followed on June9 by Seamans filing a seven-page memorandum documenting the selection process. Webb eventually provided a controlled copy of Phillips' memo to Congress. The Senate committee noted in its final report NASA's testimony that "the findings of the [Phillips] task force had no effect on the accident, did not lead to the accident, and were not related to the accident", but stated in its recommendations: "Notwithstanding that in NASA's judgment the contractor later made significant progress in overcoming the problems, the committee believes it should have been informed of the situation. The committee does not object to the position of the Administrator of NASA, that all details of Government/contractor relationships should not be put in the public domain. However, that position in no way can be used as an argument for not bringing this or other serious situations to the attention of the committee."

Freshman Senators Edward W. Brooke III and Charles H. Percy jointly wrote an Additional Views section appended to the committee report, chastising NASA more strongly than Anderson for not having disclosed the Phillips review to Congress. Mondale wrote his own, even more strongly worded Additional View, accusing NASA of "evasiveness,... lack of candor,... patronizing attitude toward Congress... refusal to respond fully and forthrightly to legitimate Congressional inquiries, and... solicitous concern for corporate sensitivities at a time of national tragedy".

The potential political threat to Apollo blew over, due in large part to the support of President Lyndon B. Johnson, who at the time still wielded a measure of influence with the Congress from his own Senatorial experience. He was a staunch supporter of NASA since its inception, had even recommended the Moon program to President John F. Kennedy in 1961, and was skilled at portraying it as part of Kennedy's legacy.

Relations between NASA and North American deteriorated over the assignment of blame. North American argued unsuccessfully it was not responsible for the fatal error in spacecraft atmosphere design. Finally, Webb contacted Atwood, and demanded either he or Chief Engineer Harrison A. Storms resign. Atwood elected to fire Storms.

On the NASA side, Joseph Shea resorted to barbiturates and alcohol in order to help him cope. NASA administrator James Webb became increasingly worried about Shea's mental state. Shea was asked to take an extended voluntary leave of absence, but Shea refused, threatening to resign rather than take leave. As a compromise, he agreed to meet with a psychiatrist and to abide by an independent assessment of his psychological fitness. This approach to remove Shea from his position was also unsuccessful. Finally, six months after the fire, Shea's superiors reassigned him to NASA headquarters in Washington, D.C. Shea felt that his new post was a "non-job," and left after only two months.

Program recovery
Gene Kranz called a meeting of his staff in Mission Control three days after the accident, delivering a speech which has subsequently become one of NASA's principles. Speaking of the errors and overall attitude surrounding the Apollo program before the accident, he said: "We were too 'gung-ho' about the schedule and we blocked out all of the problems we saw each day in our work. Every element of the program was in trouble and so were we." He reminded the team of the perils and mercilessness of their endeavor, and stated the new requirement that every member of every team in mission control be "tough and competent", requiring nothing less than perfection throughout NASA's programs. In 2003, following the Space Shuttle Columbia disaster, NASA administrator Sean O'Keefe quoted Kranz's speech, applying it to the Columbia crew.

Command module redesign
After the fire, the Apollo program was grounded for review and redesign. The command module was found to be extremely hazardous and, in some instances, carelessly assembled (for example, a misplaced wrench socket was found in the cabin).

It was decided that the remaining Block I spacecraft would be used only for uncrewed Saturn V test flights. All crewed missions would use the Block II spacecraft, to which many command module design changes were made:
 * The cabin atmosphere at launch was adjusted to 60% oxygen and 40% nitrogen at sea-level pressure: 14.7 psi. During ascent the cabin rapidly vented down to 5 psi, releasing approximately 2/3 of the gas originally present at launch. The vent then closed and the environmental control system maintained a nominal cabin pressure of 5 psi as the spacecraft continued into vacuum. The cabin was then very slowly purged (vented to space and simultaneously replaced with 100% oxygen), so the nitrogen concentration gradually fell off to zero over the next day. Although the new cabin launch atmosphere was significantly safer than 100% oxygen, it still contained almost three times the amount of oxygen present in ordinary sea-level air (20.9% oxygen). This was necessary to ensure a sufficient partial pressure of oxygen when the astronauts removed their helmets after reaching orbit. (60% of five psi is three psi, compared to 60% of 14.7 psi which is 8.8 psi at launch, and 20.9% of 14.7 psi which is 3.07 psi in sea-level air.)
 * The environment within the astronauts' pressure suits was not changed. Because of the rapid drop in cabin (and suit) pressures during ascent, decompression sickness was likely unless the nitrogen had been purged from the astronauts' tissues before launch. They would still breathe pure oxygen, starting several hours before launch, until they removed their helmets on orbit. Avoiding the "bends" was considered worth the residual risk of an oxygen-accelerated fire within a suit.
 * Nylon used in the Block I suits was replaced in the Block II suits with Beta cloth, a non-flammable, highly melt-resistant fabric woven from fiberglass and coated with Teflon.
 * Block II had already been planned to use a completely redesigned hatch which opened outward, and could be opened in less than five seconds. Concerns of accidental opening were addressed by using a cartridge of pressurized nitrogen to drive the release mechanism in an emergency, instead of the explosive bolts used on Project Mercury.
 * Flammable materials in the cabin were replaced with self-extinguishing versions.
 * Plumbing and wiring were covered with protective insulation. Aluminum tubing was replaced with stainless steel tubing that used brazed joints when possible.

Thorough protocols were implemented for documenting spacecraft construction and maintenance.

New mission naming scheme
The astronauts' widows asked that Apollo 1 be reserved for the flight their husbands never made, and on April 24, 1967, Mueller, as Associate Administrator for Manned Space Flight, announced this change officially: AS-204 would be recorded as Apollo1, "first manned Apollo Saturn flight – failed on ground test". Even though three uncrewed Apollo missions (AS-201, AS-202, and AS-203) had previously occurred, only AS-201 and AS-202 carried spacecraft. Therefore, the next mission, the first uncrewed Saturn V test flight (AS-501) would be designated Apollo4, with all subsequent flights numbered sequentially in the order flown. The first three flights would not be renumbered, and the names Apollo2 and Apollo3 would officially go unused. Mueller considered AS-201 and AS-202, the first and second flights of the Apollo Block I CSM, as Apollo2 and3 respectively.

The crewed flight hiatus allowed work to catch up on the Saturn V and lunar module, which were encountering their own delays. Apollo4 flew in November 1967. Apollo1's (AS-204) Saturn IB rocket was taken down from Launch Complex 34, later reassembled at Launch complex 37B and used to launch Apollo5, an uncrewed Earth orbital test flight of the first lunar module, LM-1, in January 1968. A second uncrewed Saturn V AS-502 flew as Apollo6 in April 1968, and Grissom's backup crew of Wally Schirra, Don Eisele, and Walter Cunningham, finally flew the orbital test mission as Apollo7 (AS-205), in a Block II CSM in October 1968.

Memorials

Gus Grissom and Roger Chaffee were buried at Arlington National Cemetery. Ed White was buried at West Point Cemetery on the grounds of the United States Military Academy in West Point, New York. NASA officials attempted to pressure Pat White, Ed White's widow, into allowing her husband also to be buried at Arlington, against what she knew to be his wishes; their efforts were foiled by astronaut Frank Borman. The names of the Apollo 1 crew are among those of multiple astronauts who have died in the line of duty, listed on the Space Mirror Memorial at the Kennedy Space Center Visitor Complex in Merritt Island, Florida. President Jimmy Carter awarded the Congressional Space Medal of Honor posthumously to Grissom on October 1, 1978. President Bill Clinton awarded it to White and Chaffee on December 17, 1997.

An Apollo 1 mission patch was left on the Moon's surface after the first crewed lunar landing by Apollo11 crew members Neil Armstrong and Buzz Aldrin. The Apollo15 mission left on the surface of the Moon a tiny memorial statue, Fallen Astronaut, along with a plaque containing the names of the Apollo1 astronauts, among others including Soviet cosmonauts, who perished in the pursuit of human space flight.

Launch Complex 34
After the Apollo 1 fire, Launch Complex 34 was subsequently used only for the launch of Apollo7 and later dismantled down to the concrete launch pedestal, which remains at the site (28.52182°N, -80.56126°W) along with a few other concrete and steel-reinforced structures. The pedestal bears two plaques commemorating the crew. The "Ad Astra per aspera" plaque for "the crew of Apollo 1" is seen in the 1998 film Armageddon. The "Dedicated to the living memory of the crew of the Apollo 1" plaque is quoted at the end of Wayne Hale's Requiem for the NASA Space Shuttle program. Each year the families of the Apollo1 crew are invited to the site for a memorial, and the Kennedy Space Center Visitor Complex includes the site during the tour of the historic Cape Canaveral launch sites.

In January 2005, three granite benches, built by a college classmate of one of the astronauts, were installed at the site on the southern edge of the launch pad. Each bears the name of one of the astronauts and his military service insignia.

Stars, landmarks on the Moon and Mars

 * Apollo astronauts frequently aligned their spacecraft inertial navigation platforms and determined their positions relative to the Earth and Moon by sighting sets of stars with optical instruments. As a practical joke, the Apollo1 crew named three of the stars in the Apollo catalog after themselves and introduced them into NASA documentation. Gamma Cassiopeiae became Navi – Ivan (Gus Grissom's middle name) spelled backwards. Iota Ursae Majoris became Dnoces – "Second" spelled backwards, for Edward H. White II. And Gamma Velorum became Regor – Roger (Chaffee) spelled backwards. These names quickly stuck after the Apollo1 accident and were regularly used by later Apollo crews.
 * Craters on the Moon and hills on Mars are named after the three Apollo1 astronauts.

Civic and other memorials

 * Three public schools in Huntsville, Alabama (home of George C. Marshall Space Flight Center and the U.S. Space & Rocket Center): Virgil I. Grissom High School, Ed White Middle School, and the Chaffee Elementary School.
 * Ed White II Elementary e-STEM (Elementary-Science, Technology, Engineering and Math) Magnet school in El Lago, Texas, near the Johnson Space Center. White lived in El Lago (next door to Neil Armstrong).
 * There are Grissom or Virgil I. Grissom middle schools in Mishawaka, Indiana, Sterling Heights, Michigan, and Tinley Park, Illinois.
 * Virgil Grissom Elementary School in Princeton, Iowa, and the Edward White Elementary School in Eldridge, Iowa, are both part of the North Scott Community School District also naming the other three elementary schools after astronauts Neil Armstrong, John Glenn, and Alan Shepard.
 * School #7 in Rochester, New York, is also known as the Virgil I. Grissom School.
 * In the early 1970s, three streets in Amherst, New York, were named for Chaffee, White and Grissom. By 1991, when no homes had been built on Grissom Drive, the area was repurposed as commercial property; the Grissom street sign was removed and the street renamed Classics V Drive for the banquet hall that occupied the land.
 * The THUMS Islands, four man-made oil drilling islands in the harbor off Long Beach, California, are named Grissom, White, Chaffee and Theodore Freeman.
 * The Roger B. Chaffee Planetarium is located at the Grand Rapids Public Museum.
 * Roger B. Chaffee Memorial Boulevard in Wyoming, Michigan, the largest suburb of Grand Rapids, Michigan, which is today an industrial park, but exists on the site of the former Grand Rapids Airport. A large portion of the north-south runway is used today as the roadway of the Roger B. Chaffee Memorial Boulevard.
 * Roger B. Chaffee Scholarship Fund in Grand Rapids, Michigan, each year in memory of Chaffee honors one student who intends to pursue a career in engineering or the sciences
 * Three adjacent parks in Fullerton, California, are each named for Grissom, Chaffee and White. The parks are located near a former Hughes Aircraft research and development facility. A Hughes subsidiary, Hughes Space and Communications Company, built components for the Apollo program.
 * Two buildings on the campus of Purdue University in West Lafayette, Indiana, are named for Grissom and Chaffee (both Purdue alumni). Grissom Hall houses the School of Industrial Engineering (and was home to the School of Aeronautics and Astronautics before it moved into the new Neil Armstrong Hall of Engineering). Chaffee Hall, constructed in 1965, is the administration complex of Maurice J. Zucrow Laboratories where combustion, propulsion, gas dynamics, and related fields are studied. The Chaffee Hall contains a 72-seat auditorium, offices, and administrative staff.
 * A tree for each astronaut was planted in NASA's Astronaut Memorial Grove at the Johnson Space Center in Houston, Texas, not far from the Saturn V building, along with trees for each astronaut from the Challenger and Columbia disasters. Tours of the space center pause briefly near the grove for a moment of silence, and the trees can be seen from nearby NASA Road 1.
 * In 1968, Bunker Hill Air Force Base near Peru, Indiana was renamed Grissom Air Force Base. The three-letter code for the VOR air navigation beacon at the base is GUS.
 * All three Apollo 1 astronauts are memorialized in Jacksonville, Florida: Edward H. White High School, Chaffee Road, and Grissom Drive.

Remains of CM-012

The Apollo 1 command module has never been on public display. After the accident, the spacecraft was removed and taken to Kennedy Space Center to facilitate the review board's disassembly in order to investigate the cause of the fire. When the investigation was complete, it was moved to the NASA Langley Research Center in Hampton, Virginia, and placed in a secured storage warehouse. On February 17, 2007, the parts of CM-012 were moved approximately 90 ft to a newer, environmentally controlled warehouse. Only a few weeks earlier, Gus Grissom's brother Lowell publicly suggested CM-012 be permanently entombed in the concrete remains of Launch Complex 34.

On January 27, 2017, the 50th anniversary of the fire, NASA put the hatch from Apollo1 on display at the Saturn V Rocket Center at Kennedy Space Center Visitors Complex. KSC's Visitor Complex also houses memorials that include parts of Challenger and Columbia, located in the Space Shuttle Atlantis exhibit. "This is way, way, way long overdue. But we're excited about it," said Scott Grissom, Gus Grissom's older son.

In popular culture

 * The accident and its aftermath are the subject of episode2, "Apollo One", of the 1998 HBO miniseries From the Earth to the Moon.
 * The mission and accident are covered in the 2015 ABC television series The Astronaut Wives Club, episodes8 "Rendezvous" and9 "Abort" from the point of view of Grissom's widow Betty.
 * The incident is the subject of the Public Service Broadcasting track "Fire in the Cockpit" from their 2015 album The Race for Space.
 * The incident is featured in the 2018 movie First Man.
 * A short dramatization of the accident is featured at the beginning of the 1995 film Apollo 13.
 * The accident and a subsequent emphasis on safety within NASA are the subject of investigation in the first two episodes of the Apple TV+ series For All Mankind.

title: Apollo 1


text:
Apollo 10

Apollo 10 (May 18–26, 1969) was the fourth human spaceflight in the United States' Apollo program and the second to orbit the Moon. NASA, the mission's operator, described it as a "dress rehearsal" for the first Moon landing (Apollo 11, two months later). It was designated an "F"mission, intended to test all spacecraft components and procedures short of actual descent and landing.

After the spacecraft reached lunar orbit, astronaut John Young remained in the Command and Service Module (CSM) while astronauts Thomas Stafford and Gene Cernan flew the Apollo Lunar Module (LM) to within 7.8 nmi of the lunar surface, the point at which powered descent for landing would begin on a landing mission. After four orbits they rejoined Young in the CSM and, after the CSM completed its 31st orbit of the Moon, they returned safely to Earth.

While NASA had considered attempting the first crewed lunar landing on Apollo 10, mission planners ultimately decided that it would be prudent to have a practice flight to hone the procedures and techniques. The crew encountered some problems during the flight: pogo oscillations during the launch phase and a brief, uncontrolled tumble of the LM ascent stage in lunar orbit during its solo flight. However, the mission accomplished its major objectives. Stafford and Cernan observed and photographed Apollo 11's planned landing site in the Sea of Tranquility. Apollo 10 spent 61 hours and 37 minutes orbiting the Moon, for about eight hours of which Stafford and Cernan flew the LM apart from Young in the CSM, and about eight days total in space. Additionally, Apollo 10 set the record for the highest speed attained by a crewed vehicle: 39,897 km/h (11.08 km/s or 24,791 mph) on May 26, 1969, during the return from the Moon.

The mission's call signs were the names of the Peanuts characters Charlie Brown for the CSM and Snoopy for the LM, who became Apollo 10's semi-official mascots. Peanuts creator Charles Schulz also drew mission-related artwork for NASA.

Background
By 1967, NASA had devised a list of mission types, designated by letters, that needed to be flown before a landing attempt, which would be the "G" mission. The early uncrewed flights were considered "A" or "B" missions, while Apollo 7, the crewed-flight test of the Command and Service Module (CSM), was the "C" mission. The first crewed orbital test of the Lunar Module (LM) was accomplished on Apollo 9, the "D" mission. Apollo 8, flown to the Moon's orbit without an LM, was considered a "C-prime" mission, but its success gave NASA the confidence to skip the "E" mission, which would have tested the full Apollo spacecraft in medium or high Earth orbit. Apollo 10, the dress rehearsal for the lunar landing, was to be the "F" mission.

NASA considered skipping the "F" mission as well and attempting the first lunar landing on Apollo 10. Some with the agency advocated this, feeling it senseless to bring astronauts so close to the lunar surface, only to turn away. Although the lunar module intended for Apollo 10 was too heavy to perform the lunar mission, the one intended for Apollo 11 could be substituted by delaying Apollo 10 a month from its May 1969 planned launch. NASA official George Mueller favored a landing attempt on Apollo 10; he was known for his aggressive approach to moving the Apollo program forward. However, Director of Flight Operations Christopher C. Kraft and others opposed this, feeling that new procedures would have to be developed for a rendezvous in lunar orbit and that NASA had incomplete information regarding the Moon's mass concentrations, which might throw off the spacecraft's trajectory. Lieutenant General Sam Phillips, the Apollo Program Manager, listened to the arguments on both sides and decided that having a dress rehearsal was crucial.

Crew and key Mission Control personnel
On November 13, 1968, NASA announced the crew members of Apollo 10. Thomas P. Stafford, the commander, was 38 years old at the time of the mission. A 1952 graduate of the Naval Academy, he was commissioned in the Air Force. Selected for the second group of astronauts in 1962, he flew as pilot of Gemini 6A (1965) and command pilot of Gemini 9A (1966). John Young, the command module pilot, was 38 years old and a commander in the Navy at the time of Apollo 10. A 1952 graduate of Georgia Tech who entered the Navy after graduation and became a test pilot in 1959, he was selected as a Group 2 astronaut alongside Stafford. He flew in Gemini 3 with Gus Grissom in 1965, becoming the first American not of the Mercury Seven to fly in space. Young thereafter commanded Gemini 10 (1966), flying with Michael Collins. Eugene Cernan, the lunar module pilot, was a 35-year-old commander in the Navy at the time of Apollo 10. A 1952 graduate of Purdue University, he entered the Navy after graduation. Selected for the third group of astronauts in 1963, Cernan flew with Stafford on Gemini 9A before his assignment to Apollo 10. With five prior flights among them, the Apollo 10 crew was the most experienced to reach space until the Space Shuttle era, and the first American space mission whose crew were all spaceflight veterans.

The backup crew for Apollo 10 was L. Gordon Cooper Jr as commander, Donn F. Eisele as command module pilot, and Edgar D. Mitchell as lunar module pilot. By the normal crew rotation in place during Apollo, Cooper, Eisele, and Mitchell would have flown on Apollo 13, but Cooper and Eisele never flew again. Deke Slayton, Director of Flight Crew Operations, felt that Cooper did not train as hard as he could have. Eisele was blackballed because of incidents during Apollo 7, which he had flown as CMP and which had seen conflict between the crew and ground controllers; he had also been involved in a messy divorce. Slayton only assigned the two as backups because he had few veteran astronauts available. Cooper and Eisele were replaced by Alan Shepard and Stuart Roosa respectively. Feeling they needed additional training time, George Mueller rejected the Apollo 13 crew. The crew was switched to Apollo 14, which saw Shepard and Mitchell walk on the Moon.

For projects Mercury and Gemini, a prime and a backup crew had been designated, but for Apollo, a third group of astronauts, known as the support crew, was also designated. Slayton created the support crews early in the Apollo program on the advice of McDivitt, who would lead Apollo 9. McDivitt believed that, with preparation going on in facilities across the U.S., meetings that needed a member of the flight crew would be missed. Support crew members were to assist as directed by the mission commander. Usually low in seniority, they assembled the mission's rules, flight plan, and checklists, and kept them updated. For Apollo 10, they were Joe Engle, James Irwin, and Charles Duke.

Flight directors were Gerry Griffin, Glynn Lunney, Milt Windler, and Pete Frank. Flight directors during Apollo had a one-sentence job description: "The flight director may take any actions necessary for crew safety and mission success." CAPCOMs were Duke, Engle, Jack Lousma, and Bruce McCandless II.

Call signs and mission insignia

The command module was given the call sign "Charlie Brown" and the lunar module the call sign "Snoopy". These were taken from the characters in the comic strip, Peanuts, Charlie Brown and Snoopy. These names were chosen by the astronauts with the approval of Charles Schulz, the strip's creator, who was uncertain it was a good idea, since Charlie Brown was always a failure. The choice of names was deemed undignified by some at NASA, as were the choices for Apollo 9's CM and LM ("Gumdrop" and "Spider"). Public relations chief Julian Scheer urged a change for the lunar landing mission. But for Apollo 10, according to Cernan, "The P.R.-types lost this one big-time, for everybody on the planet knew the klutzy kid and his adventuresome beagle, and the names were embraced in a public relations bonanza." Apollo 11's call signs were "Columbia" for the command module and "Eagle" for the lunar module.

Snoopy, Charlie Brown's dog, was chosen for the call sign of the lunar module since it was to "snoop" around the landing site, with Charlie Brown given to the command module as Snoopy's companion. Snoopy had been associated for some time with the space program, with workers who performed in an outstanding manner awarded silver "Snoopy pins", and Snoopy posters were seen at NASA facilities, with the cartoon dog having traded in his World War I aviator's headgear for a space helmet. Stafford stated that, given the pins, "the choice of Snoopy [as call sign] was a way of acknowledging the contributions of the hundreds of thousands of people who got us there". The use of the dog was also appropriate since, in the comic strip, Snoopy had journeyed to the Moon the year before, thus defeating, according to Schulz, "the Americans, the Russians, and that stupid cat next door".

The shield-shaped mission insignia shows a large, three-dimensional Roman numeral X sitting on the Moon's surface, in Stafford's words, "to show that we had left our mark". Although it did not land on the Moon, the prominence of the number represents the contributions the mission made to the Apollo program. A CSM circles the Moon as an LM ascent stage flies up from its low pass over the lunar surface with its engine firing. The Earth is visible in the background. On the mission patch, a wide, light blue border carries the word APOLLO at the top and the crew names around the bottom. The patch is trimmed in gold. The insignia was designed by Allen Stevens of Rockwell International.

Training and preparation
Apollo 10, the "F" mission or dress rehearsal for the lunar landing, had as its primary objectives to demonstrate crew, space vehicle and mission support facilities performance during a crewed mission to lunar orbit, and to evaluate the performance of the lunar module there. In addition, it was to attempt photography of Apollo Landing Site 2 (ALS-2) in the Sea of Tranquillity, the contemplated landing site for Apollo 11. According to Stafford, "Our flight was to take the first lunar module to the moon. We would take the lunar module, go down to within about ten miles above the moon, nine miles above the mountains, radar map, photo map, pick out the first landing site, do the first rendezvous around the moon, pick out some future landing sites, and come home."

Apollo 10 was to adhere as closely as possible to the plans for Apollo 11, including its trajectory to and from lunar orbit, the timeline of mission events, and even the angle of the Sun at ALS-2. However, no landing was to be attempted. ALS-1, given that number because it was the furthest to the east of the candidate sites, and also located in the Sea of Tranquility, had been extensively photographed by Apollo 8 astronauts; at the suggestion of scientist-astronaut Harrison Schmitt, the launch of Apollo 10 had been postponed a day so ALS-2 could be photographed under proper conditions. ALS-2 was chosen as the lunar landing site since it was relatively smooth, of scientific interest, and ALS-1 was deemed too far to the east. Thus, when Apollo 10's launch date was announced on January 10, 1969, it was shifted from its placeholder date of May 1 to May 17, rather than to May 16. On March 17, 1969, the launch was slipped one day to May 18, to allow for a better view of ALS-3, to the west of ALS-2. Another deviation from the plans for Apollo 11 was that Apollo 10 was to spend an additional day in lunar orbit once the CSM and LM rendezvoused; this was to allow time for additional testing of the LM's systems, as well as for photography of possible future Apollo landing sites.

The Apollo 10 astronauts undertook five hours of formal training for each hour of the mission's eight-day duration. This was in addition to the normal mission preparations such as technical briefings, pilot meetings and study. They took part in the testing of the CSM at the Downey, California, facility of its manufacturer, North American Rockwell, and of the LM at Grumman in Bethpage, New York. They visited Cambridge, Massachusetts, for briefings on the Apollo Guidance Computer at the Massachusetts Institute of Technology Instrumentation Laboratory. They each spent more than 300 hours in simulators of the CM or LM at the Manned Spacecraft Center (MSC) in Houston and at Kennedy Space Center (KSC) in Florida. To train for the high-acceleration conditions they would experience in returning to Earth's atmosphere, they endured MSC's centrifuge.

Lunar landing capability
While Apollo 10 was meant to follow the procedures of a lunar landing mission to the point of powered descent, Apollo 10's LM was not capable of landing and returning to lunar orbit. The ascent stage was loaded with the amount of fuel and oxidizer it would have had remaining if it had lifted off from the surface and reached the altitude at which the Apollo 10 ascent stage fired; this was only about half the total amount required for lift off and rendezvous with the CSM. The mission-loaded LM weighed 30735 lb, compared to 33278 lb for the Apollo 11 LM which made the first landing. Additionally, the software necessary to guide the LM to a landing was not available at the time of Apollo 10.

Craig Nelson wrote in his book Rocket Men that NASA took special precaution to ensure Stafford and Cernan would not attempt to make the first landing. Nelson quoted Cernan as saying "A lot of people thought about the kind of people we were: 'Don't give those guys an opportunity to land, 'cause they might!' So the ascent module, the part we lifted off the lunar surface with, was short-fueled. The fuel tanks weren't full. So had we literally tried to land on the Moon, we couldn't have gotten off." Mueller, NASA's Associate Administrator for Manned Space Flight, stated, "There had been some speculation about whether or not the crew might have landed, having gotten so close. They might have wanted to, but it was impossible for that lunar module to land. It was an early design that was too heavy for a lunar landing, or, to be more precise, too heavy to be able to complete the ascent back to the command module. It was a test module, for the dress rehearsal only, and that was the way it was used."

Equipment
The descent stage of the LM was delivered to KSC on October 11, 1968, and the ascent stage arrived five days later. They were mated on November 2. The Service Module (SM) and Command Module (CM) arrived on November 24 and were mated two days later. Portions of the Saturn V launch vehicle arrived during November and December 1968, and the complete launch vehicle was erected in the Vehicle Assembly Building (VAB) on December 30. After being tested in an altitude chamber, the CSM was placed atop the launch vehicle on February 6, 1969. The completed space vehicle was rolled out to Launch Complex 39B on March 11, 1969—the fact that it had been assembled in the VAB's High Bay 2 (the first time it had been used) required the crawler to exit the rear of the VAB before looping around the building and joining the main crawlerway, proceeding to the launch pad. This rollout, using Mobile Launch Platform-3 (MLP-3), happened eight days after the launch of Apollo 9, while that mission was still in orbit.

The launch vehicle for Apollo 10 was a Saturn V, designated AS-505, the fifth flight-ready Saturn V to be launched and the third to take astronauts to orbit. The Saturn V differed from that used on Apollo 9 in having a lower dry weight (without propellant) in its first two stages, with a significant reduction to the interstage joining them. Although the S-IVB third stage was slightly heavier, all three stages could carry a greater weight of propellant, and the S-II second stage generated more thrust than that of Apollo 9.

The Apollo spacecraft for the Apollo 10 mission was composed of Command Module 106 (CM-106), Service Module 106 (SM-106, together with the CM known as CSM-106), Lunar Module 4 (LM-4), a spacecraft-lunar module adapter (SLA), numbered as SLA-13A, and a launch escape system. The SLA was a mating structure joining the Instrument Unit on the S-IVB stage of the Saturn V launch vehicle and the CSM, and acted as a housing for the LM, while the Launch Escape System (LES) contained rockets to propel the CM to safety if there was an aborted launch. At about 76.99 metric tons, Apollo 10 would be the heaviest spacecraft to reach orbit to that point.

Launch and outbound trip
Apollo 10 launched from KSC on May 18, 1969, at 12:49:00 EDT (16:49:00 UT), at the start of a 4.5-hour launch window. The launch window was timed to secure optimal lighting conditions at Apollo Landing Site 2 at the time of the LM's closest approach to the site days later. The launch followed a countdown that had begun at 21:00:00 EDT on May 16 (01:00:00 UT on May 17). Because preparations for Apollo 11 had already begun at Pad 39A, Apollo 10 launched from Pad 39B, becoming the only Apollo flight to launch from that pad and the only one to be controlled from its Firing Room 3.

Problems that arose during the countdown were dealt with during the built-in holds, and did not delay the mission. On the day before launch, Cernan had been stopped for speeding while returning from a final visit with his wife and child. Lacking identification and under orders to tell no one who he was, Cernan later attested in his autobiography that he had feared being arrested. Launch pad leader Gunther Wendt, who had pulled over nearby after recognizing Cernan, explained the situation to the police officer, who then released Cernan despite the officer's skepticism that Cernan was an astronaut.

The crew experienced a somewhat rough ride on the way to orbit due to pogo oscillations. About 12 minutes after liftoff, the spacecraft entered a low Earth orbit with a high point of 100.32 nmi and a low point of 99.71 nmi. All appeared to be normal during the systems review period in Earth orbit, and the crew restarted the S-IVB third stage to achieve trans-lunar injection (TLI) and send them towards the Moon. The vehicle shook again while executing the TLI burn, causing Cernan to be concerned that they might have to abort. However, the TLI burn was completed without incident. Young then performed the transposition, docking, and extraction maneuver, separating the CSM from the S-IVB stage, turning around, and docking its nose to the top of the lunar module (LM), before separating from the S-IVB. Apollo 10 was the first mission to carry a color television camera inside the spacecraft, and mission controllers in Houston watched as Young performed the maneuver. Soon thereafter, the large television audience was treated to color views of the Earth. One problem that was encountered was that the mylar cover of the CM's hatch had pulled loose, spilling quantities of fiberglass insulation into the tunnel, and then into both the CM and LM. The S-IVB was fired by ground command and sent into solar orbit with a period of 344.88 days.

The crew settled in for the voyage to the Moon. They had a light workload, and spent much of their time studying the flight plan or sleeping. They made five more television broadcasts back to Earth, and were informed that more than a billion people had watched some part of their activities. In June 1969, the crew would accept a special Emmy Award on behalf of the first four Apollo crews for their television broadcasts from space. One slight course correction was necessary; this occurred at 26:32:56.8 into the mission and lasted 7.1 seconds. This aligned Apollo 10 with the trajectory Apollo 11 was expected to take. One issue the crew encountered was bad-tasting food, as Stafford apparently used a double dose of chlorine in their drinking water, which had to be placed in their dehydrated food to reconstitute it.

Arrival and initial operations
At 75:55:54 into the mission, 95.1 nmi above the far side of the Moon, the CSM's service propulsion system (SPS) engine was fired for 356.1 seconds to slow the spacecraft into a lunar orbit of 170.0 by. This was followed, after two orbits of the Moon, with a 13.9-second firing of the SPS to circularize the orbit to 61.0 by at 80:25:08.1. Within the first couple of hours after the initial lunar orbit insertion burn and following the circularization burn, the crew turned to tracking planned landmarks on the surface below to record observations and take photographs. In addition to ALS-1, ALS-2, and ALS-3, the crew of Apollo 10 observed and photographed features on the near and far sides of the Moon, including the craters Coriolis, King, and Papaleksi. Shortly after the circularization burn, the crew partook in a scheduled half-hour color-television broadcast with descriptions and video transmissions of views of the lunar surface below.

About an hour after the second burn, the LM crew of Stafford and Cernan entered the LM to check out its systems. They were met with a blizzard of fiberglass particles from the earlier problem, which they cleaned up with a vacuum cleaner as best they could. Stafford had to help Cernan remove smaller bits from his hair and eyebrows. Stafford later commented that Cernan looked like he just came out of a chicken coop, and that the particles made them itch and got into the air conditioning system, and they were scraping it off the filter screens for the rest of the mission. This was merely an annoyance, but the particles may have gotten into the docking ring joining the two craft and caused it to misalign slightly. Mission Control determined that this was still within safe limits.

The flight of Snoopy
After Stafford and Cernan checked out Snoopy, they returned to Charlie Brown for a rest. Then they re-entered Snoopy and undocked it from the CSM at 98:29:20. Young, who remained in the CSM, became the first person to fly solo in lunar orbit. After undocking, Stafford and Cernan deployed the LM's landing gear and inspected the LM's systems. The CSM performed an 8.3-second burn with its RCS thrusters to separate itself from the LM by about 30 feet, after which Young visually inspected the LM from the CSM. The CSM performed another separation burn, this time separating the two spacecraft by about 2 nmi. The LM crew then performed the descent orbit insertion maneuver by firing their descent engine for 27.4 seconds at 99:46:01.6, and tested their craft's landing radar as they approached the 50000 ft altitude where the subsequent Apollo 11 mission would begin powered descent to land on the Moon. Previously, the LM's landing radar had only been tested under terrestrial conditions. While the LM executed these maneuvers, Young monitored the location and status of the LM from the CSM, standing by to rescue the LM crew if necessary. Cernan and Stafford surveyed ALS-2, coming within 8.4 nmi of the surface at a point 15 degrees to its east, then performed a phasing burn at 100:58:25.93, thrusting for just under 40 seconds to allow a second pass at ALS-2, when the craft came within 7.8 nmi of the Moon, its closest approach. Reporting on his observations of the site from the LM's low passes, Stafford indicated that ALS-2 seemed smoother than he had expected and described its appearance as similar to the desert surrounding Blythe, California; but he observed that Apollo 11 could face rougher terrain downrange if it approached off-target. Based upon Apollo 10's observations from relatively low altitude, NASA mission planners became comfortable enough with ALS-2 to confirm it as the target site for Apollo 11.

The next action was to prepare to separate the LM ascent stage from the descent stage, to jettison the descent stage, and fire the Ascent Propulsion System to return the ascent stage towards the CSM. As Stafford and Cernan prepared to do so, the LM began to gyrate out of control. Alarmed, Cernan exclaimed, "Son of a bitch!" into a hot mic being broadcast live, which, combined with other language used by the crew during the mission, generated some complaints back on Earth. Stafford discarded the descent stage about five seconds after the tumbling began and fought to regain control manually, suspecting that there might have been an "open thruster", or a thruster stuck firing. He did so in time to orient the spacecraft to rejoin Charlie Brown. The problem was traced to a switch controlling the mode of the abort guidance system; it was to be moved as part of the procedure, but both of the crew members switched it, thus returning it to the original position. Had they fired Snoopy in the wrong direction, they might have missed the rendezvous with Charlie Brown or crashed into the Moon. Once Stafford had regained control of the LM ascent stage, which took about eight seconds, the pair fired the ascent engine at the lowest point of the LM's orbit, mimicking the orbital insertion maneuver after launch from the lunar surface in a later landing mission. Snoopy coasted on that trajectory for about an hour before firing the engine once more to further fine-tune its approach to Charlie Brown.

Snoopy rendezvoused with and re-docked with Charlie Brown at 106:22:02, just under eight hours after undocking. The docking was telecast live in color from the CSM. Once Cernan and Stafford had re-entered Charlie Brown, Snoopy was sealed off and separated from Charlie Brown. The rest of the LM's ascent-stage engine fuel was burned to send it on a trajectory past the Moon and into a heliocentric orbit.

It was the only Apollo LM to meet this fate. The Apollo 11 ascent stage would be left in lunar orbit to crash, while post-Apollo 11 ascent stages were steered into the Moon to obtain readings from seismometers placed on the surface, with two exceptions: Apollo 13's ascent stage, which the crew used as a "life boat" to get safely back to Earth before releasing it to burn up in Earth's atmosphere, and Apollo 16's, which NASA lost control of after jettison.

Return to Earth
After ejecting the LM ascent stage, the crew slept and performed photography and observation of the lunar surface from orbit. Though the crew located 18 landmarks on the surface and took photographs of various surface features, crew fatigue necessitated the cancellation of two scheduled television broadcasts. Thereafter, the main Service Propulsion System engine of the CSM re-ignited for about 2.5 minutes to set Apollo 10 on a trajectory towards Earth, achieving such a trajectory at 137:39:13.7. As it departed lunar orbit, Apollo 10 had orbited the Moon 31 times over the span of about 61 hours and 37 minutes.

During their journey back to Earth, the crew performed some observational activities which included star-Earth horizon sightings for navigation. The crew also performed a scheduled test to gauge the reflectivity of the CSM's high-gain antenna and broadcast six television transmissions of varying durations to show views inside the spacecraft and of the Earth and Moon from the crew's vantage point. Cernan reported later that he and his crewmates became the first to "successfully shave in space" during the return trip, using a safety razor and thick shaving gel, as such items had been deemed a safety hazard and prohibited on earlier flights. The crew fired the engine of the CSM for the only mid-course-correction burn required during the return trip at 188:49:58, a few hours before separation of the CM from the SM. The burn lasted about 6.7 seconds.

As the spacecraft rapidly approached Earth on the final day of the mission, the Apollo 10 crew traveled faster than any humans before or since, relative to Earth: 39,897 km/h (11.08 km/s or 24,791 mph). This is because the return trajectory was designed to take only 42 hours rather than the normal 56. The Apollo 10 crew also traveled farther than any humans before or since from their (Houston) homes: 408950 km (though the Apollo 13 crew was 200 km farther away from Earth as a whole). While most Apollo missions orbited the Moon at 111 km from the lunar surface, the distance between the Earth and Moon varies by about 43000 km, between perigee and apogee, throughout each lunar month, and the Earth's rotation makes the distance to Houston vary by at most another 11000 km each day. The Apollo 10 crew reached the farthest point in their orbit around the far side of the Moon at about the same time Earth's rotation put Houston nearly a full Earth diameter farther away.

At 191:33:26, the CM (which contained the crew) separated from the SM in preparation for reentry, which occurred about 15 minutes later at 191:48:54.5. Splashdown of the CM occurred about 15 minutes after reentry in the Pacific Ocean about 400 nmi east of American Samoa on May 26, 1969, at 16:52:23 UTC and mission elapsed time 192:03:23. The astronauts were recovered by USS Princeton (CV-37). They spent about four hours aboard, during which they took a congratulatory phone call from President Richard Nixon. As they had not made contact with the lunar surface, Apollo 10's crew were not required to quarantine like the first landing crews would be. They were flown to Pago Pago International Airport in Tafuna for a greeting reception, before boarding a C-141 cargo plane to Ellington Air Force Base near Houston.

Aftermath
Orbital operations and the solo maneuvering of the LM in partial descent to the lunar surface paved the way for the successful Apollo 11 lunar landing by demonstrating the capabilities of the mission hardware and systems. The crew demonstrated that the checkout procedures of the LM and initial descent and rendezvous could be accomplished within the allotted time, that the communication systems of the LM were sufficient, that the rendezvous and landing radars of the LM were operational in lunar orbit, and that the two spacecraft could be adequately monitored by personnel on Earth. Additionally, the precision of lunar orbital navigation improved with Apollo 10 and, combined with data from Apollo 8, NASA expected that it had achieved a level of precision sufficient to execute the first crewed lunar landing. After about two weeks of Apollo 10 data analysis, a NASA flight readiness team cleared Apollo 11 to proceed with its scheduled July 1969 flight. On July 16, 1969, the next Saturn V to launch carried the astronauts of Apollo 11: Neil Armstrong, Buzz Aldrin, and Michael Collins. On July 20, Armstrong and Aldrin landed on the Moon, and four days later the three astronauts returned to Earth, fulfilling John F. Kennedy's challenge to Americans to land astronauts on the Moon and return them safely to Earth by the end of the 1960s.

In July 1969, Stafford replaced Alan Shepard as Chief Astronaut, and then became deputy director of Flight Crew Operations under Deke Slayton. In his memoirs, Stafford wrote that he could have put his name back in the flight rotation, but wanted managerial experience. In 1972, Stafford was promoted to brigadier general and assigned to command the American portion of the Apollo–Soyuz Test Project, which flew in July 1975. He commanded the Air Force Flight Test Center at Edwards Air Force Base in California, and retired in November 1979 as a lieutenant general. Young commanded the Apollo 16 lunar landing mission flown in April 1972. From 1974 to 1987, Young served as Chief Astronaut, commanding the STS-1 (1981) and STS-9 (1983) Space Shuttle missions in April 1981 and November 1983, respectively, and retired from NASA's Astronaut Corps in 2004. Gene Cernan commanded the final Apollo lunar mission, Apollo 17, flown in December 1972. Cernan retired from NASA and the Navy as a captain in 1976.

Hardware disposition
The Smithsonian has been accountable for the command module Charlie Brown since 1970. The spacecraft was on display in several countries until it was placed on loan to the London Science Museum in 1978. Charlie Brown's SM was jettisoned just before re-entry and burned up in the Earth's atmosphere, its remnants scattering in the Pacific Ocean.

After translunar injection, the Saturn V's S-IVB third stage was accelerated past Earth escape velocity to become space debris;, it remains in a heliocentric orbit.

The ascent stage of the Lunar Module Snoopy was jettisoned into a heliocentric orbit. Snoopy's ascent stage orbit was not tracked after 1969, and its whereabouts were unknown. In 2011, a group of amateur astronomers in the UK started a project to search for it. In June 2019, the Royal Astronomical Society announced a possible rediscovery of Snoopy, determining that small Earth-crossing asteroid 2018 AV2 is likely to be the spacecraft with "98%" certainty. It is the only once-crewed spacecraft known to still be in outer space without a crew.

Snoopy's descent stage was jettisoned in lunar orbit; its current location is unknown, though it may have eventually crashed into the Moon as a result of orbital decay. Phil Stooke, a planetary scientist who studied the lunar crash sites of the LM's ascent stages, wrote that the descent stage "crashed at an unknown location", and another source stated that the descent stage "eventually impact(ed) within a few degrees of the equator on the near side". Richard Orloff and David M. Harland, in their sourcebook on Apollo, stated that "the descent stage was left in the low orbit, but perturbations by 'mascons' would have caused this to decay, sending the stage to crash onto the lunar surface".

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title: Apollo 10