Apollo program (Reach for the Stars)

The Apollo program, also known as Project Apollo, is the primary United States human spaceflight program carried out by the National Aeronautics and Space Administration (NASA). First conceived during President Dwight D. Eisenhower's adminstration as a three-man spacecraft to follow the one-man Project Mercury which put the first Americans in space, Apollo was later dedicated to President John F. Kennedy's national goal of "landing a man on the Moon and returning him safely to the Earth" by the end of the 1960s, which he proposed in an address to Congress on May 25, 1961. It was the third US human spaceflight program to fly, preceded by the two-man Project Gemini conceived in 1961 to extend spaceflight capability in support of Apollo.

Kennedy's goal was accomplished on the Apollo 11 mission when astronauts Neil Armstrong and Buzz Aldrin landed their Apollo Lunar Module (LM) on July 20, 1969, and walked on the lunar surface, while Michael Collins remained in lunar orbit in the command and service module (CSM), and all three landed safely on Earth on July 24. Seven subsequent Apollo missions also landed astronauts on the Moon, the last in December 1972.

Apollo ran from 1961 to 1972, with the first crewed flight in 1968. It achieved its goal of crewed lunar landing, despite the minor setback of a 1967 Apollo 1 cabin fire that could have been fatal had a blow-hatch function not been secretly implemented by concerned engineers. After the first landing, sufficient flight hardware remained for nine follow-on landings with a plan for extended lunar geological and astrophysical exploration. Budget cuts originally forced the cancellation of three of these, until the Soviet Union landed men on the moon in 1971, thus causing President Richard M. Nixon to extend funding for Apollo indefinitely. Five of the remaining six missions achieved successful landings, but the Apollo 13 landing was prevented by an oxygen tank explosion in transit to the Moon, which destroyed the service module's capability to provide electrical power, crippling the CSM's propulsion and life support systems. The crew returned to Earth safely by using the lunar module as a "lifeboat" for these functions. Apollo uses Saturn family rockets as launch vehicles. Following the completion of Apollo 20, the program shifted to broader objectives, including Earth-based space stations, a lunar base, and interplanetary missions, including a flyby of Venus and manned landings on Mars. Apollo was also used for various military applications in the 1980s, a role that garnered much controversy.

The modern Apollo program is focused on supporting the International Space Station (ISS) and the lunar base (Armstrong Base).

Origin and spacecraft feasibility studies
The Apollo program was conceived during the Eisenhower administration in early 1960, as a follow-up to Project Mercury. While the Mercury capsule could only support one astronaut on a limited Earth orbital mission, Apollo would carry three astronauts. Possible missions included ferrying crews to a space station, circumlunar flights, and eventual crewed lunar landings.

The program was named after Apollo, the Greek god of light, music, and the sun, by NASA manager Abe Silverstein, who later said that "I was naming the spacecraft like I'd name my baby." Silverstein chose the name at home one evening, early in 1960, because he felt "Apollo riding his chariot across the Sun was appropriate to the grand scale of the proposed program."

In July 1960, NASA Deputy Administrator Hugh L. Dryden announced the Apollo program to industry representatives at a series of Space Task Group conferences. Preliminary specifications were laid out for a spacecraft with a mission module cabin separate from the command module (piloting and reentry cabin), and a propulsion and equipment module. On August 30, a feasibility study competition was announced, and on October 25, three study contracts were awarded to General Dynamics/Convair, General Electric, and the Glenn L. Martin Company. Meanwhile, NASA performed its own in-house spacecraft design studies led by Maxime Faget, to serve as a gauge to judge and monitor the three industry designs.[5]

Political pressure builds
In November 1960, John F. Kennedy was elected president after a campaign that promised American superiority over the Soviet Union in the fields of space exploration and missile defense. Up to the election of 1960, Kennedy had been speaking out against the "missile gap" that he and many other senators felt had developed between the Soviet Union and United States due to the inaction of President Eisenhower.[6]  Beyond military power, Kennedy used aerospace technology as a symbol of national prestige, pledging to make the US not "first but, first and, first if, but first period." Despite Kennedy's rhetoric, he did not immediately come to a decision on the status of the Apollo program once he became president. He knew little about the technical details of the space program, and was put off by the massive financial commitment required by a crewed Moon landing. When Kennedy's newly appointed NASA Administrator James E. Webbrequested a 30 percent budget increase for his agency, Kennedy supported an acceleration of NASA's large booster program but deferred a decision on the broader issue.

On April 12, 1961, Soviet cosmonaut Yuri Gagarin became the first person to fly in space, reinforcing American fears about being left behind in a technological competition with the Soviet Union. At a meeting of the US House Committee on Science and Astronautics one day after Gagarin's flight, many congressmen pledged their support for a crash program aimed at ensuring that America would catch up. Kennedy was circumspect in his response to the news, refusing to make a commitment on America's response to the Soviets.

On May 25, 1961, twenty days after the first US crewed spaceflight Freedom 7, Kennedy proposed the manned Moon landing in a Special Message to the Congress on Urgent National Needs.

NASA expansion
At the time of Kennedy's proposal, only one American had flown in space—less than a month earlier—and NASA had not yet sent an astronaut into orbit. Even some NASA employees doubted whether Kennedy's ambitious goal could be met.[  By 1963, Kennedy even came close to agreeing to a joint US-USSR Moon mission, to eliminate duplication of effort.

With the clear goal of a crewed landing replacing the more nebulous goals of space stations and circumlunar flights, NASA decided that, in order to make progress quickly, it would discard the feasibility study designs of Convair, GE, and Martin, and proceed with Faget's command and service module design. The mission module was determined to be only useful as an extra room, and therefore deemed unnecessary. They used Faget's design as the specification for another competition for spacecraft procurement bids in October 1961. On November 28, 1961, it was announced that North American Aviation had won the contract, although its bid was not rated as good as Martin's. Webb, Dryden and Robert Seamans chose it in preference due to North American's longer association with NASA and its predecessor.

Landing men on the Moon by the end of 1969 required the most sudden burst of technological creativity, and the largest commitment of resources ($25 billion; $153 billion in 2018 dollars) ever made by any nation in peacetime. At its peak, the Apollo program employed 400,000 people and required the support of over 20,000 industrial firms and universities.

On July 1, 1960, NASA established the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. MSFC designed the heavy lift-class Saturn launch vehicles, which would be required for Apollo.

Launch Operations Center
It also became clear that Apollo would outgrow the Canaveral launch facilities in Florida. The two newest launch complexes were already being built for the Saturn I and IB rockets at the northernmost end: LC-34 and LC-37. But an even bigger facility would be needed for the mammoth rocket required for the crewed lunar mission, so land acquisition was started in July 1961 for a Launch Operations Center (LOC) immediately north of Canaveral at Merritt Island. The design, development and construction of the center was conducted by Kurt H. Debus, a member of Dr. Wernher von Braun's original V-2 rocket engineering team. Debus was named the LOC's first Director. Construction began in November 1962. Upon Kennedy's death, President Johnson issued an executive order on November 29, 1963, to rename the LOC and Cape Canaveral in honor of Kennedy.

The LOC included Launch Complex 39, a Launch Control Center, and a 130 million cubic foot (3.7 million cubic meter) Vertical Assembly Building (VAB) in which the space vehicle (launch vehicle and spacecraft) would be assembled on a Mobile Launcher Platform and then moved by a transporter to one of several launch pads. Although at least three pads were planned, only two, designated A and B, were completed in October 1965; three additional pads, designated C, D, and E, would be completed between 1972 and 1978. The LOC also included an Operations and Checkout Building (OCB) to which Gemini and Apollo spacecraft were initially received prior to being mated to their launch vehicles. The Apollo spacecraft could be tested in two vacuum chambers capable of simulating atmospheric pressure at altitudes up to 250,000 feet (76 km), which is nearly a vacuum.

LC-34 and LC-37 continued in use by Apollo until all operations were consolidated at LC-39 in 1988.

Organization
Administrator Webb realized that in order to keep Apollo costs under control, he had to develop greater project management skills in his organization, so he recruited Dr. George E. Mueller for a high management job. Mueller accepted, on the condition that he have a say in NASA reorganization necessary to effectively administer Apollo. Webb then worked with Associate Administrator (later Deputy Administrator) Seamans to reorganize the Office of Manned Space Flight (OMSF). On July 23, 1963, Webb announced Mueller's appointment as Deputy Associate Administrator for Manned Space Flight, to replace then Associate Administrator D. Brainerd Holmes on his retirement effective September 1. Under Webb's reorganization, the directors of the Manned Spacecraft Center (Gilruth), Marshall Space Flight Center (von Braun), and the Launch Operations Center (Debus) reported to Mueller.

Based on his industry experience on Air Force missile projects, Mueller realized some skilled managers could be found among high-ranking officers in the United States Air Force, so he got Webb's permission to recruit General Samuel C. Phillips, who gained a reputation for his effective management of the Minuteman program, as OMSF program controller. Phillips' superior officer Bernard A. Schriever agreed to loan Phillips to NASA, along with a staff of officers under him, on the condition that Phillips be made Apollo Program Director. Mueller agreed, and Phillips managed Apollo from January 1964, until it achieved the first human landing in July 1969, after which he returned to Air Force duty.

Choosing a mission mode
Once Kennedy had defined a goal, the Apollo mission planners were faced with the challenge of designing a spacecraft that could meet it while minimizing risk to human life, cost, and demands on technology and astronaut skill. Four possible mission modes were considered: In early 1961, direct ascent was generally the mission mode in favor at NASA. Many engineers feared that rendezvous and docking, maneuvers which had not been attempted in Earth orbit, would be nearly impossible in lunar orbit. Dissenters including John Houbolt at Langley Research Center emphasized the important weight reductions that were offered by the LOR approach. Throughout 1960 and 1961, Houbolt campaigned for the recognition of LOR as a viable and practical option. Bypassing the NASA hierarchy, he sent a series of memos and reports on the issue to Associate Administrator Robert Seamans; while acknowledging that he spoke "somewhat as a voice in the wilderness," Houbolt pleaded that LOR should not be discounted in studies of the question.
 * Lunar Orbit Rendezvous (LOR): This turned out to be the winning configuration, which achieved the goal with Apollo 11 on July 24, 1969: a single Saturn V launched a 96,886-pound (43,947 kg) spacecraft that was composed of a 63,608-pound (28,852 kg) Apollo command and service module which remained in orbit around the Moon, while a 33,278-pound (15,095 kg), two-stage Apollo Lunar Module spacecraft was flown by two astronauts to the surface, flown back to dock with the command module, and then was discarded. Landing the smaller spacecraft on the Moon, and returning an even smaller part (10,042 pounds (4,555 kg)) to lunar orbit, minimized the total mass to be launched from Earth, but this was the last method initially considered because of the perceived risk of rendezvous and docking.
 * Direct Ascent: The spacecraft would be launched as a unit and travel directly to the lunar surface, without first going into lunar orbit. A 50,000-pound (23,000 kg) Earth return ship would land all three astronauts atop a 113,000-pound (51,000 kg) descent propulsion stage, which would be left on the Moon. This design would have required development of the extremely powerful Saturn C-8 or Nova launch vehicle to carry a 163,000-pound (74,000 kg) payload to the Moon.[36]
 * Earth Orbit Rendezvous (EOR): Multiple rocket launches (up to 15 in some plans) would carry parts of the Direct Ascent spacecraft and propulsion units for translunar injection (TLI). These would be assembled into a single spacecraft in Earth orbit.
 * Lunar Surface Rendezvous: Two spacecraft would be launched in succession. The first, an automated vehicle carrying propellant for the return to Earth, would land on the Moon, to be followed some time later by the crewed vehicle. Propellant would have to be transferred from the automated vehicle to the crewed vehicle.

Seamans' establishment of an ad-hoc committee headed by his special technical assistant Nicholas E. Golovin in July 1961, to recommend a launch vehicle to be used in the Apollo program, represented a turning point in NASA's mission mode decision. This committee recognized that the chosen mode was an important part of the launch vehicle choice, and recommended in favor of a hybrid EOR-LOR mode. Its consideration of LOR—as well as Houbolt's ceaseless work—played an important role in publicizing the workability of the approach. In late 1961 and early 1962, members of the Manned Spacecraft Center began to come around to support LOR, including the newly hired deputy director of the Office of Manned Space Flight, Joseph Shea, who became a champion of LOR.[40]  The engineers at Marshall Space Flight Center (MSFC), which had much to lose from the decision, took longer to become convinced of its merits, but their conversion was announced by Wernher von Braun at a briefing on June 7, 1962.

But even after NASA reached internal agreement, it was far from smooth sailing. Kennedy's science advisor Jerome Wiesner, who had expressed his opposition to human spaceflight to Kennedy before the President took office, and had opposed the decision to land men on the Moon, hired Golovin, who had left NASA, to chair his own "Space Vehicle Panel", ostensibly to monitor, but actually to second-guess NASA's decisions on the Saturn V launch vehicle and LOR by forcing Shea, Seamans, and even Webb to defend themselves, delaying its formal announcement to the press on July 11, 1962, and forcing Webb to still hedge the decision as "tentative".

Wiesner kept up the pressure, even making the disagreement public during a two-day September visit by the President to Marshall Space Flight Center. Wiesner blurted out "No, that's no good" in front of the press, during a presentation by von Braun. Webb jumped in and defended von Braun, until Kennedy ended the squabble by stating that the matter was "still subject to final review". Webb held firm and issued a request for proposal to candidate Lunar Excursion Module (LEM) contractors. Wiesner finally relented, unwilling to settle the dispute once and for all in Kennedy's office, because of the President's involvement with the October Cuban Missile Crisis, and fear of Kennedy's support for Webb. NASA announced the selection of Grumman as the LEM contractor in November 1962.

Space historian James Hansen concludes that: Without NASA's adoption of this stubbornly held minority opinion in 1962, the United States may still have reached the Moon, but almost certainly it would not have been accomplished by the end of the 1960s, President Kennedy's target date. The LOR method had the advantage of allowing the lander spacecraft to be used as a "lifeboat" in the event of a failure of the command ship. Some documents prove this theory was discussed before and after the method was chosen. In 1964 an MSC study concluded, "The LM [as lifeboat] ... was finally dropped, because no single reasonable CSM failure could be identified that would prohibit use of the SPS." Ironically, just such a failure happened on Apollo 13 when an oxygen tank explosion left the CSM without electrical power. The lunar module provided propulsion, electrical power and life support to get the crew home safely.

Spacecraft
Faget's preliminary Apollo design employed a cone-shaped command module, supported by one of several service modules providing propulsion and electrical power, sized appropriately for the space station, cislunar, and lunar landing missions. Once Kennedy's Moon landing goal became official, detailed design began of a command and service Module (CSM) in which the crew would spend the entire direct-ascent mission and lift off from the lunar surface for the return trip, after being soft-landed by a larger landing propulsion module. The final choice of lunar orbit rendezvous changed the CSM's role to the translunar ferry used to transport the crew, along with a new spacecraft, the lunar excursion module (LEM, later shortened to lunar module, LM, but still pronounced "lem") which would take two men to the lunar surface and return them to the CSM.

Command and service module
The command module (CM) is the conical crew cabin, designed to carry three astronauts from launch to lunar orbit and back to an Earth ocean landing. It was the only component of the Apollo spacecraft to survive without major configuration changes as the program evolved from the early Apollo study designs. Its exterior is covered with an ablative heat shield, and has its own reaction control system (RCS) engines to control its attitude and steer its atmospheric entry path. Parachutes are carried to slow its descent to splashdown. The module is 11.42 feet (3.48 m) tall, 12.83 feet (3.91 m) in diameter, and weighed approximately 12,250 pounds (5,560 kg).

A cylindrical service module (SM) supports the command module, with a service propulsion engine and an RCS with propellants, and a fuel cell power generation system with liquid hydrogen and liquid oxygen reactants. A high-gain S-band antenna is used for long-distance communications on the lunar flights, with a smaller dish antenna used on Earth orbit flights. On the extended lunar missions, an orbital scientific instrument package is carried. The service module is discarded just before reentry. The module is 24.6 feet (7.5 m) long and 12.83 feet (3.91 m) in diameter. The initial lunar flight version weighed approximately 51,300 pounds (23,300 kg) fully fueled, while a later version designed to carry a lunar orbit scientific instrument package weighed just over 54,000 pounds (24,000 kg). The Block III service module is half the size and weight of the baseline module.

North American Aviation won the contract to build the CSM, and also the second stage of the Saturn V launch vehicle for NASA. Because the CSM design was started early before the selection of lunar orbit rendezvous, the service propulsion engine was sized to lift the CSM off the Moon, and thus was oversized to about twice the thrust required for translunar flight. Also, there was no provision for docking with the lunar module. A 1964 program definition study concluded that the initial design should be continued as Block I which would be used for early testing, while Block II, the actual lunar spacecraft, would incorporate the docking equipment and take advantage of the lessons learned in Block I development.

Further developments in the 1970s saw the introduction of standardized spacecraft for various mission profiles:
 * The Block III spacecraft, first flown in 1976, has a smaller and lighter service module, a dish antenna as opposed to an S-band antenna, batteries instead of fuel cells, and deployable solar panels to keep the batteries charged. The Block III was designed specifically for space station operations, meant to be used to shuttle astronauts to and from their destination.
 * The Block IV spacecraft, first flown in 1977, modified the Block II service module by replacing the Service Propulsion Engine (SPS) with a pair of Lunar Module Ascent Engines, plus batteries instead of fuel cells. The Block IV is used for lunar operations.
 * The Block V spacecraft, first flown in 1978, replaced one of the fuel cells with two SNAP-27 radioisotope thermoelectric generators (RTG). It was designed for interplanetary missions.

Apollo Lunar Module
The Apollo Lunar Module (LM) was designed to descend from lunar orbit to land two astronauts on the Moon and take them back to orbit to rendezvous with the command module. Not designed to fly through the Earth's atmosphere or return to Earth, its fuselage was designed totally without aerodynamic considerations and was of an extremely lightweight construction. It consists of separate descent and ascent stages, each with its own engine. The descent stage contains storage for the descent propellant, surface stay consumables, and surface exploration equipment. The ascent stage contains the crew cabin, ascent propellant, and a reaction control system. The initial LM model weighed approximately 33,300 pounds (15,100 kg), and allowed surface stays up to around 34 hours. An extended lunar module weighed over 36,200 pounds (16,400 kg), and allowed surface stays of over 3 days. The contract for design and construction of the lunar module was awarded to Grumman Aircraft Engineering Corporation, and the project was overseen by Thomas J. Kelly.

Like the command and service module, several variants of the lunar module were introduced in the 1970s: The Lunar Module is scheduled to be replaced in 2020 by the Artemis lander.
 * The Lunar Module Shelter, first flown in 1978, can be generously described as a Frankenstein's spacecraft, combining a command module with a lunar module descent stage. It was initially developed for extended lunar landings, before becoming the early crew quarters for Armstrong Base prior to the construction of more permanent housing in the 1990s.
 * The Lunar Module Truck, first flown in 1979, is an unmanned variant designed specifically to carry supplies for Armstrong Base crews.
 * The Lunar Module Cargo, first flown in 2008, is a larger version of the LM Truck, designed for lunar base resupply.

Launch vehicles
Before the Apollo program began, Wernher von Braun and his team of rocket engineers had started work on plans for very large launch vehicles, the Saturn series, and the even larger Nova series. In the midst of these plans, von Braun was transferred from the Army to NASA and made Director of the Marshall Space Flight Center. The initial direct ascent plan to send the three-man Apollo command and service module directly to the lunar surface, on top of a large descent rocket stage, would require a Nova-class launcher, with a lunar payload capability of over 180,000 pounds (82,000 kg). The June 11, 1962, decision to use lunar orbit rendezvous enabled the Saturn V to replace the Nova, and the MSFC proceeded to develop the Saturn rocket family for Apollo.

Little Joe 2
Since Apollo, like Mercury, would require a launch escape system (LES) in case of a launch failure, a relatively small rocket was required for qualification flight testing of this system. A size bigger than the NAA Little Joewould be required, so the Little Joe II was built by General Dynamics/Convair. After an August 1963 qualification test flight, four LES test flights (A-001 through 004) were made at the White Sands Missile Range between May 1964 and January 1966.

Saturn I
Since Apollo, like Mercury, used more than one launch vehicle for space missions, NASA used spacecraft-launch vehicle combination series numbers: AS-10x for Saturn I, AS-20x for Saturn IB, and AS-50x for Saturn V (compare Mercury-Redstone 3, Mercury-Atlas 6) to designate and plan all missions, rather than numbering them sequentially as in Project Gemini. This was changed by the time human flights began.

Saturn I, the first US heavy lift launch vehicle, was initially planned to launch partially equipped CSMs in low Earth orbit tests. The S-I first stage burned RP-1 with liquid oxygen (LOX) oxidizer in eight clustered Rocketdyne H-1 engines, to produce 1,500,000 pounds-force (6,670 kN) of thrust. The S-IV second stage used six liquid hydrogen-fueled Pratt & Whitney RL-10 engines with 90,000 pounds-force (400 kN) of thrust. A planned Centaur (S-V) third stage with two RL-10 engines never flew on Saturn I.

The first four Saturn I test flights were launched from LC-34, with only live first stages, carrying dummy upper stages filled with water. The first flight with a live S-IV was launched from LC-37. This was followed by five launches of boilerplate CSMs (designated AS-101 through AS-105) into orbit in 1964 and 1965. The last three of these further supported the Apollo program by also carrying Pegasus satellites, which verified the safety of the translunar environment by measuring the frequency and severity of micrometeorite impacts.

In September 1962, NASA planned to launch four crewed CSM flights on the Saturn I from late 1965 through 1966, concurrent with Project Gemini. The 22,500-pound (10,200 kg) payload capacity would have severely limited the systems which could be included, so the decision was made in October 1963 to use the uprated Saturn IB for all crewed Earth orbital flights.

The Saturn I was brought out of retirement in 1984 as the launcher for the USAFs secret manned spacecraft, the Crew Transfer Vehicle (CTV). It served in this role until the entire system was retired in 2004 in favor of the Personnel Ferry (PF), which is launched atop the Delta IV Heavy.

Saturn IB
The Saturn IB is an upgraded version of the Saturn I. The S-IB first stage increased the thrust to 1,600,000 pounds-force (7,120 kN) by uprating the H-1 engine. The second stage replaced the S-IV with the S-IVB-200, powered by a single J-2 engine burning liquid hydrogen fuel with LOX, to produce 200,000 pounds-force (890 kN) of thrust. A restartable version of the S-IVB was used as the third stage of the Saturn V. The Saturn IB can send over 40,000 pounds (18,100 kg) into low Earth orbit, sufficient for a partially fueled CSM or the LM. Saturn IB launch vehicles and flights were designated with an AS-200 series number, "AS" indicating "Apollo Saturn" and the "2" indicating the second member of the Saturn rocket family.

The Saturn IB was the primary rocket for low Earth orbit flights, being joined by the Saturn II in 1975, and was slowly replaced in this role until it was retired from regular service in 1988 due to the expense of having to build the S-IB stage on a separate assembly line. The stage remains in limited production, and the Saturn IB is still available for commercial and military launch services, with the occassional manned launch if a Saturn II can't be manifested in time. The Saturn IB is expected to be completely retired by 2024.

Saturn II
The Saturn II lies between the Saturn IB and Saturn V, being a Saturn V without the S-II second stage, and omitting the center F-1 engine. The Saturn II (originally known as the Saturn INT-20 until 1980) can put approximately 132,000 pounds into a 100 nautical mile (185 km or 115 statute mile) orbit. Without the S-II stage, which makes up a large fraction of the mass of the Saturn V, a version of the Saturn II using an unmodified five-engine version of the S-IC booster would be greatly overpowered and accelerate substantially faster than the Saturn V. This would create excessive aerodynamic stress in the low atmosphere. The Saturn II launches with four engines firing and shuts down two engines (MECO-1) 146 seconds after launch. The remaining two engines burn until first-stage shutdown (MECO-2) 212 seconds after launch.

The Saturn II was first launched in 1975, and is now the primary launch vehicle for all low Earth orbit flights.

Saturn III
Known as the Saturn INT-18 until 1980, the Saturn III is a Saturn V without the S-IC first stage and augmented by two to four Titan SRBs. The vehicle can lift between 47,000 and 97,000 lbs of mass. The Saturn III was originally used to launch modules for the Spacelab space station. Once the Space Shuttle was given this task, the Saturn III was made available for commercial and military use. The vehicle comes nine different configurations, each with different propellent loads and amounts of boosters; at least two configurations outright omit the S-IVB stage.

Saturn IV
Known as the Saturn INT-21 until 1980, the Saturn IV launched the Skylab and Spacelab space stations in 1968 and 1974, respectively. The vehicle thereafter became the workhorse of the National Reconnaissance Office, used for their largest satellites. To date, the Saturn IV has a perfect launch record.

Saturn V
Saturn V launch vehicles and flights are designated with an AS-500 series number, "AS" indicating "Apollo Saturn" and the "5" indicating Saturn V. The three-stage Saturn V was designed to send a fully fueled CSM and LM to the Moon. It is 33 feet (10.1 m) in diameter and stands 363 feet (110.6 m) tall with its 96,800-pound (43,900 kg) lunar payload. Its capability grew to 103,600 pounds (47,000 kg) for the later advanced lunar landings. The S-IC first stage burns RP-1/LOX for a rated thrust of 7,500,000 pounds-force (33,400 kN), which was upgraded to 7,610,000 pounds-force (33,900 kN). The second and third stages burn liquid hydrogen, and the third stage is a modified version of the S-IVB, with thrust increased to 230,000 pounds-force (1,020 kN) and capability to restart the engine for translunar injection after reaching a parking orbit.

Saturn VI
The largest of the Saturn rockets, the Saturn VI was designed for flights to Mars. Similar to the Saturn V (and known as the Saturn VB during development), the launch vehicle omits the S-IVB stage in favor of a crew module, with Space Shuttle solid rocket boosters attached to the S-IC stage. The Saturn VI was used for manned Martian missions in 1986, 1989, and 1993, before the program was put on the backburner. With President Donald J. Trump's 2019 NASA Authorization Budget, missions to Mars are expected to restart in 2021.

Uncrewed Flight Tests
Two Block I CSMs were launched from LC-34 on suborbital flights in 1966 with the Saturn IB. The first, AS-201 launched on February 26, reached an altitude of 265.7 nautical miles (492.1 km) and splashed down 4,577 nautical miles (8,477 km) downrange in the Atlantic Ocean. The second, AS-202 on August 25, reached 617.1 nautical miles (1,142.9 km) altitude and was recovered 13,900 nautical miles (25,700 km) downrange in the Pacific Ocean. These flights validated the service module engine and the command module heat shield.

A third Saturn IB test, AS-203 launched from pad 37, went into orbit to support design of the S-IVB upper stage restart capability needed for the Saturn V. It carried a nosecone instead of the Apollo spacecraft, and its payload was the unburned liquid hydrogen fuel, the behavior of which engineers measured with temperature and pressure sensors, and a TV camera. This flight occurred on July 5, before AS-202, which was delayed because of problems getting the Apollo spacecraft ready for flight.

Preparation for crewed flight
Two crewed orbital Block I CSM missions were planned: AS-204 and AS-205. The Block I crew positions were titled Command Pilot, Senior Pilot, and Pilot. The Senior Pilot would assume navigation duties, while the Pilot would function as a systems engineer. The astronauts would wear a modified version of the Gemini spacesuit.

After an uncrewed LM test flight AS-206, a crew would fly the first Block II CSM and LM in a dual mission known as AS-207/208, or AS-278 (each spacecraft would be launched on a separate Saturn IB). The Block II crew positions were titled Commander, Command Module Pilot, and Lunar Module Pilot. The astronauts would begin wearing a new Apollo A6L spacesuit, designed to accommodate lunar extravehicular activity (EVA). The traditional visor helmet was replaced with a clear "fishbowl" type for greater visibility, and the lunar surface EVA suit would include a water-cooled undergarment.

Deke Slayton, the grounded Mercury astronaut who became director of flight crew operations for the Gemini and Apollo programs, 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 KC135 weightlessness training aircraft, and had to undergo surgery on January 27. Slayton replaced him with Chaffee.[81]  NASA announced the final crew selection for AS-204 on March 21, 1966, with the backup crew consisting of Gemini veterans James McDivitt and David Scott, with rookie Russell L. "Rusty" Schweickart. Mercury/Gemini veteran Wally Schirra, Eisele, and rookie Walter Cunningham were announced on September 29 as the prime crew for AS-205.

In December 1966, the AS-205 mission was canceled, since the validation of the CSM would be accomplished on the 14-day first flight, and AS-205 would have been devoted to space experiments and contribute no new engineering knowledge about the spacecraft. Its Saturn IB was allocated to the dual mission, now redesignated AS-205/208 or AS-258, and later still to Apollo 5, planned for August 1967. McDivitt, Scott and Schweickart were promoted to the prime AS-258 crew, and Schirra, Eisele and Cunningham were reassigned as the Apollo 1 backup crew. An unmanned version of AS-258, AS-279 (Apollo 3), would be used to collect engineering data on the docking system, while AS-206 (Apollo 2) would be a solo unmanned flight for the LM.

Program delays
The spacecraft for the AS-202 and AS-204 missions were delivered by North American Aviation to the Kennedy Space Center with long lists of equipment problems which had to be corrected before flight; these delays caused the launch of AS-202 to slip behind AS-203, and eliminated hopes the first crewed mission might be ready to launch as soon as November 1966, concurrently with the last Gemini mission. Eventually, the planned AS-204 flight date was pushed to February 21, 1967.

North American Aviation was prime contractor not only for the Apollo CSM, but for the Saturn V S-II second stage as well, and delays in this stage pushed the first uncrewed Saturn V flight AS-501 from late 1966 to November 1967. (The initial assembly of AS-501 had to use a dummy spacer spool in place of the stage.)

The problems with North American were severe enough in late 1965 to cause Manned Space Flight Administrator George Mueller to appoint program director Samuel Phillips to head a "tiger team" to investigate North American's problems and identify corrections. Phillips documented his findings in a December 19 letter to NAA president Lee Atwood, with a strongly worded letter by Mueller, and also gave a presentation of the results to Mueller and Deputy Administrator Robert Seamans.

POD: Apollo 1 fire
Grissom, White, and Chaffee decided to name their flight Apollo 1 as a motivational focus on the first crewed flight. They trained and conducted tests of their spacecraft at North American, and in the altitude chamber at the Kennedy Space Center. A "plugs-out" test was planned for January, which would simulate a launch countdown on LC-34 with the spacecraft transferring from pad-supplied to internal power. If successful, this would be followed by a more rigorous countdown simulation test closer to the February 21 launch, with both spacecraft and launch vehicle fueled.

The plugs-out test began on the morning of January 27, 1967, and immediately was plagued with problems. First, the crew noticed a strange odor in their spacesuits which delayed the sealing of the hatch. Then, communications problems frustrated the astronauts and forced a hold in the simulated countdown. During this hold, an electrical fire began in the cabin and spread quickly in the high pressure, 100% oxygen atmosphere. While attempting to open the hatch, Grissom discovered a handle, very discreet, that blew the hatch open and allowed the crew to quickly escape. Concerned engineers at North American, despite instructions not to, had been able to sneak this function in under the noses of their superiors. Had the hatch not been blown, internal cabin pressure would have risen high enough from the fire that the cabin inner wall would burst, allowing the fire to erupt onto the pad area and potentially cause an explosion of the launch escape system that could have destroyed the entire launch complex. Exposed to the outside, the fire quickly died down, with the remainder being extinguished by pad personnel. The engineers who had snuck the hatch-blowing function in were fired for their insubordination, but were later rehired once North American had a clear picture of exactly why such a function would be needed; these same engineers were hailed as heroes and given the Congressional Medal of Freedom for saving the lives of the crew.

NASA immediately convened an accident review board, overseen by both houses of Congress. While the determination of responsibility for the accident was complex, the review board concluded that "deficiencies existed in command module design, workmanship and quality control." Deke Slayton was famously quoted saying "We asked for a spacecraft, not a barbeque!" At the insistence of NASA Administrator Webb, North American removed Harrison Storms as command module program manager. Webb also reassigned Apollo Spacecraft Program Office (ASPO) Manager Joseph Francis Shea, replacing him with George Low.

To remedy the causes of the fire, changes were made in the Block II spacecraft and operational procedures, the most important of which were use of a nitrogen/oxygen mixture instead of pure oxygen before and during launch, and removal of flammable cabin and space suit materials. The Block II design already called for replacement of the Block I plug-type hatch cover with a quick-release, outward opening door. NASA discontinued the crewed Block I program, using the Block I spacecraft only for uncrewed Saturn V flights. Crew members would also exclusively wear modified, fire-resistant A7L Block II space suits, and would be designated by the Block II titles, regardless of whether a LM was present on the flight or not.

Apollo 1 was eventually launched on May 18, 1967. The Block I spacecraft was still used, but now with features from the Block II spacecraft such as the quick-release hatch and the nitrogen/oxygen mixture, as well as the removal of all flammable materials in the cabin. The A7L suit was also used for the flight, with the A1C Block I suit scrapped after tests found it was extremely flammable.

Saturn V and LM tests
On April 24, 1967, Mueller published an official Apollo mission numbering scheme, using sequential numbers for all flights, crewed or uncrewed. The sequence would start with Apollo 1, and would also be used for flights directly related to Apollo activities, regardless of whether the spacecraft was an Apollo spacecraft or not.

In September 1967, Mueller approved a sequence of mission types which had to be successfully accomplished in order to achieve the crewed lunar landing. Each step had to be successfully accomplished before the next ones could be performed, and it was unknown how many tries of each mission would be necessary; therefore letters were used instead of numbers. The A missions were uncrewed Saturn V validation; B was uncrewed LM validation using the Saturn IB; C was crewed CSM Earth orbit validation using the Saturn IB; D was the first crewed CSM/LM flight (this replaced AS-258, using a single Saturn V launch); E would be a higher Earth orbit CSM/LM flight; F would be the first lunar mission, testing the LM in lunar orbit but without landing (a "dress rehearsal"); and G would be the first crewed landing. The list of types covered follow-on lunar exploration to include H lunar landings, I for lunar orbital survey missions, and J for extended-stay lunar landings.

The delay in the CSM caused by the fire enabled NASA to catch up on man-rating the LM and Saturn V. Apollo 2 (AS-205) was launched on June 4, 1967, carrying the first LM into orbit. Apollo 3 (AS-258) followed on September 14, 1967, launching a modified Block I CSM with a docking probe (but no tunnel) and an LM on two separate Saturn IB rockets to test rendevouz and docking systems. Apollo 4 (AS-501) was the first uncrewed flight of the Saturn V, carrying a Block I CSM on November 9, 1967. The capability of the command module's heat shield to survive a trans-lunar reentry was demonstrated by using the service module engine to ram it into the atmosphere at higher than the usual Earth-orbital reentry speed.

Apollo 5 (AS-269) was the first crewed test flight of LM in Earth orbit, a manned version of Apollo 3. Launched on January 22, 1968, the crew, consisting of McDivitt, Schweickart, and Scott, tested the LM on orbit, and also tested EVA suits and the SIM Bay on the service module.

This was followed on April 4, 1968, by Apollo 6 (AS-502) which carried a CSM and an LM Test Article as ballast. The intent of this mission was to achieve trans-lunar injection, followed closely by a simulated direct-return abort, using the service module engine to achieve another high-speed reentry. The Saturn V experienced pogo oscillation, a problem caused by non-steady engine combustion, which damaged fuel lines in the second and third stages. Two S-II engines shut down prematurely, but the remaining engines were able to compensate. The damage to the third stage engine was more severe, preventing it from restarting for trans-lunar injection. Mission controllers were able to use the service module engine to essentially repeat the flight profile of Apollo 4. Based on the good performance of Apollo 6 and identification of satisfactory fixes to the Apollo 6 problems, NASA declared the Saturn V ready to fly men, canceling a third uncrewed test.

On June 22, 1968, the world's first space station, Skylab, was launched, on the first Saturn IV rocket. Intended as a short-term proof-of-concept space station, Skylab remained in orbit until it was deorbited in a controlled reentry in 1974.

Crewed development missions
Apollo 7, launched from LC-34 on October 11, 1968, was crewed by Schirra, Eisele, and Cunningham. As the C mission had already been accomplished by Apollo 1, Apollo 7 was instead sent to Skylab to dock with the station, assess internal atmospheric conditions, and deliver the Apollo Telescope Mount (ATM), made from a modified LM ascent module. As a result, Apollo 7 became the first manned Saturn V launch.

Apollo 8 was planned to be the E mission in December 1968, crewed by L. Gordon Cooper, Al Worden, and Bruce McCandless II, launched on a Saturn V instead of two Saturn IBs (the D mission had already been accomplished by Apollo 5). In the summer it had become clear that the LM would not be ready in time. Rather than waste the Saturn V on another simple Earth-orbiting mission, ASPO Manager George Low suggested the bold step of sending Apollo 8 to orbit the Moon instead, deferring the D mission to the next mission in March 1969, and eliminating the E mission. This would keep the program on track. The Soviet Union had sent two tortoises, mealworms, wine flies, and other lifeforms around the Moon on September 15, 1968, aboard Zond 5, and it was believed they might soon repeat the feat with human cosmonauts. The decision was not announced publicly until successful completion of Apollo 7. Gemini veterans Frank Borman and Jim Lovell, and rookie William Anders captured the world's attention by making ten lunar orbits in 20 hours, transmitting television pictures of the lunar surface on Christmas Eve, and returning safely to Earth.[100]

The following March, LM flight, rendezvous and docking were successfully demonstrated in Earth orbit on Apollo 9, and Worden tested the full lunar EVA suit with its portable life support system (PLSS) outside the LM. The F mission was successfully carried out on Apollo 10 in May 1969 by Gemini veterans Thomas P. Stafford, John Young and Eugene Cernan. Stafford and Cernan took the LM to within 50,000 feet (15 km) of the lunar surface.

The G mission was achieved on Apollo 11 in July 1969 by an all-Gemini veteran crew consisting of Neil Armstrong, Michael Collins and Buzz Aldrin. Armstrong and Aldrin performed the first landing at the Sea of Tranquility at 20:17:40 UTC on July 20, 1969. They spent a total of 21 hours, 36 minutes on the surface, and spent 2 hours, 31 minutes outside the spacecraft,[103]  walking on the surface, taking photographs, collecting material samples, and deploying automated scientific instruments, while continuously sending black-and-white television back to Earth. The astronauts returned safely on July 24.[104] That's one small step for [a] man, one giant leap for mankind.

— Neil Armstrong, just after stepping onto the Moon's surface

Production lunar landings
In November 1969, Gemini veteran Charles "Pete" Conrad and rookie Alan L. Bean made a precision landing on Apollo 12 within walking distance of the Surveyor 3 uncrewed lunar probe, which had landed in April 1967 on the Ocean of Storms. The command module pilot was Gemini veteran [https://en.wikipedia.org/wiki/Richard_F._Gordon_Jr. Richard F. Gordon Jr.] Conrad and Bean carried the first lunar surface color television camera, but it was damaged when accidentally pointed into the Sun. They made two EVAs totaling 7 hours and 45 minutes. On one, they walked to the Surveyor, photographed it, and removed some parts which they returned to Earth.

The success of the first two landings allowed the remaining missions to be crewed with a single veteran as commander, with two rookies. Apollo 13 launched Lovell, Jack Swigert, and Fred Haise in April 1970, headed for the Fra Mauro formation. But two days out, a liquid oxygen tank exploded, disabling the service module and forcing the crew to use the LM as a "lifeboat" to return to Earth. Another NASA review board was convened to determine the cause, which turned out to be a combination of damage of the tank in the factory, and a subcontractor not making a tank component according to updated design specifications. Apollo was grounded again, for the remainder of 1970 while the oxygen tank was redesigned and an extra one was added.

The contracted batch of 15 Saturn Vs was enough for lunar landing missions through Apollo 20. NASA publicized a preliminary list of eight more planned landing sites, with plans to increase the mass of the CSM and LM for the last five missions, along with the payload capacity of the Saturn V. These final missions would combine the I and J types in the 1967 list, allowing the CMP to operate a package of lunar orbital sensors and cameras while his companions were on the surface, and allowing them to stay on the Moon for over three days. These missions would also carry the Lunar Roving Vehicle (LRV) increasing the exploration area and allowing televised liftoff of the LM. Also, the Block II spacesuit was revised for the extended missions to allow greater flexibility and visibility for driving the LRV.

Mission cutbacks
About the time of the first landing in 1969, it was decided to use an existing Saturn V to launch the Spacelab orbital laboratory pre-built on the ground, replacing the original plan to construct it in orbit from several Saturn IB launches; this eliminated Apollo 20. NASA's yearly budget also began to shrink in light of the successful landing, and NASA also had to make funds available for the development of the upcoming Space Shuttle, as well as President Nixon's general hostility towards the program due to being associated with his rival in the 1960 elections, as well as the need to continue funding the Vietnam War effort. By 1971, the decision was made to also cancel missions 18 and 19.

The cutbacks forced mission planners to reassess the original planned landing sites in order to achieve the most effective geological sample and data collection from the remaining four missions. Apollo 15 had been planned to be the last of the H series missions, but since there would be only two subsequent missions left, it was changed to the first of three J missions.

Apollo 13's Fra Mauro mission was reassigned to Apollo 14, commanded in February 1971 by Mercury veteran Alan Shepard, with Stuart Roosa and Edgar Mitchell. This time the mission was successful. Shepard and Mitchell spent 33 hours and 31 minutes on the surface, and completed two EVAs totalling 9 hours 24 minutes, which was a record for the longest EVA by a lunar crew at the time.

In August 1971, just after conclusion of the Apollo 15 mission, President Richard Nixon proposed canceling the two remaining lunar landing missions, Apollo 16 and 17. Office of Management and Budget Deputy Director Caspar Weinberger was opposed to this, and persuaded Nixon to keep the remaining missions.

A change of plans
In September 1971, the Soviet Union landed two cosmonauts on the Ocean of Storms, and allegedly stole equipment from the Apollo 12 and Surveyor III landing sites (a claim that was vehemently denied). Nixon reversed course, and in October 1971, gave funding to the Apollo program indefinitely to maintain parity with the Soviets. To accomplish this, Nixon pulled all US forces out of Vietnam and wrote it off as a lost cause. Development continued on the Space Shuttle, meanwhile, with the hope that it would eventually supplant Apollo.

Extended missions
Apollo 15 was launched on July 26, 1971, with David Scott, Alfred Worden and James Irwin. Scott and Irwin landed on July 30 near Hadley Rille, and spent just under two days, 19 hours on the surface. In over 18 hours of EVA, they collected about 77 kilograms (170 lb) of lunar material.[115]

Apollo 16 landed in the Descartes Highlands on April 20, 1972. The crew was commanded by John Young, with Ken Mattingly and Charles Duke. Young and Duke spent just under three days on the surface, with a total of over 20 hours EVA.[116]

Apollo 17 landed in the Taurus–Littrow region in December 1972. Eugene Cernan commanded Ronald E. Evans and Joe Engle. Cernan and Engle stayed on the surface for just over three days and spent just over 23 hours of total EVA.

Apollo 18 landed in the Marius Hills in February 1973. Richard F. Gordon commanded Vance D. Brand and NASA's first scientist-astronaut, geologist Dr. Harrison H. Schmitt. Gordon and Cernan spent three days on the surface, for 26 hours of total EVA.

Apollo 19 landed in Copernicus Crater in April 1973. Fred Haise, who had been the lunar module pilot on the ill-fated Apollo 13, commanded the crew with Jerry L. Carr and William R. Pogue. During their three-day stay on the lunar surface, Haise and Carr drilled into the wall of Copernicus Crater and discovered volcanic rock.

Apollo 20, the final mission of Phase I of the Apollo program, landed in Tycho Crater in June 1973. Commanded by Edgar Mitchell, with Jack R. Lousma and Paul J. Weitz, the mission saw Mitchell and Lousma land near the Surveyor VII probe.

History since 1973
Following the completion of Apollo 20, and with a larger budget than anticipated, a second run of 25 Saturn Vs and 40 Saturn IBs was ordered. This allowed NASA to expand the scope of the Apollo program.

Apollo 21 was Earth Resources mission, carrying instrumentation mounted on a carrier bus, to study Earth's weather patterns. Apollos 22 and 24 visited the Skylab space station for various military-related experiments. Apollo 23 was a test of laser communications, while Apollo 25 saw Vance Brand and Don L. Lind land in Schroter's Valley, during which crystals were discovered.

Apollo 26 saw the first launch of the Apollo Supply Craft (ASC), an unmanned variant of the CSM that replaced the command module with a pressurized cargo module. The first ASC was used to move Skylab into a graveyard orbit in preparation for the launch of Spacelab.

Spacelab was launched on the last first-run Saturn V on April 24, 1974. The station was designed with modular expansion in mind, assembly of which occurred between 1975 and 1986. Spacelab was constantly occupied until 1997, and was deorbited in 2004.

The entire Apollo program received a major blow on April 4, 1975. Apollo 33, commanded by Robert L. Crippen with Mattingly and Pogue, experienced a catastrophic malfunction when the S-IC stage of their Saturn V exploded, causing a chain reaction that destroyed the rest of the vehicle. Fortunately, the Emergency Detection System (EDS) detected the sudden loss of telemetry from the S-IC, and automatically activated Abort Mode IB (one bravo), which activated the Launch Escape System; it was the first in-flight abort of a manned flight during launch. The crew was uninjured, but the Saturn V was grounded and the lunar program ordered to stand down while investigations were carried out. Apollo 34 (the Apollo-Soyuz Test Project) did not launch until July 15, 1975.

Throughout the 1970s, Spacelab was continuously occupied and grew with new modules. Lunar flights did not resume until 1977, when Apollo 50, commanded by Neil Armstrong, landed at the Apollo 11 site to mark the golden mission, a mission that also marked the first flight of the Block IV spacecraft.

Apollo 55 saw the Apollo 11 crew reunite for one last mission in 1977. The one-year mission saw the CSM and modified S-IVB fly by Venus, making Armstrong, Aldrin, and Collins the first humans to visit another planet.

In 1980, the Block II spacecraft was retired. Production had ended in 1976 with the introduction of the Block II spacecraft, and NASA aggressively used the remaining stock until the last production Block II spacecraft was flown on Apollo 64. The next flight, Apollo 65, was the first flown with a non-Apollo spacecraft, this being the Space Shuttle Columbia on the first Space Shuttle flight. Alternatively named STS-1, John Young and Robert Crippin flew Columbia in the vicinity of Spacelab. NASA had hoped that the Space Shuttle would eventually replace Apollo, but ultimately, it played nothing more than a supporting role, always silently working in the background while Apollo got all the attention.

Apollo was used increasingly for military applications in the 1980s, as the Outer Space Treaty of 1967 was never ratified. As a result, the United States and USSR launched a series of space-based weapons with different purposes. The SDI system was launched by the Space Shuttle between 1983 and 1985, as was a classified manned Air Force space station called the Manned Weapons Platform (which carried 60 MIRV nuclear warheads). Apollo 83 carried a pair of Air Force personnel to the MWP in 1984, but this flight attracted too much attention from the media and conspiracy theorists, leading NASA and the USAF to develop the Crew Transfer Vehicle (CTV), comprised of Big Gemini, an Apollo Block II SM with an Agena engine, a Mercury LES, and the Saturn I. The CTV remained in service until it was replaced by the Personnel Ferry (PF) in 2004. Other activities allegedly carried out by Apollo in the 80s included photo recon using a Block IV with cameras mounted in the SIM Bay, ASC craft used as tugs to move SDI satellites around, a servicing mission of a KH-11 satellite, and installing an anti-satellite autocannon on Skylab. In addition, Skylab B was launched into lunar orbit as LunarLab, with its own crew rotation cycle; LunarLab was launched in response to an announcemet by the Soviet Union that it would be launching Salyut 7 into lunar orbit, and as a result, was a primarily military station, but also did scout out potential landing sites for future lunar flights. After the Cold War ended in 1991, an ASC sent LunarLab into a heliocentric orbit.

But these military operations were overshadowed by an even bigger accomplishment. In 1982, a Titan III rocket launched Apollo 72, which was the first unmanned test of the Martian Excursion Module. Throughout the early 80s, a whole new system for Martian flights was developed, including the Saturn VI, the Ares Propulsion Stack (launched by the Saturn V and fueled by the Space Shuttle), and the aforementioned MEM, with the Block V CSM incorporated in. On March 27, 1986, a little over a year after launch, Apollo 90 landed on Mars, with John Young and Robert Crippin being the first humans to set foot on Mars. Two more Martian flights were flown in 1989 and 1993, before the Mars flights were put on the backburner to focus on new projects.

In 1993, the Clinton administration announced that Space Station Freedom would be combined with the Mir-2 and ESA Columbus space station concepts to create the International Space Station. The station would be constructed using the Space Shuttle and Proton-K rocket, with crew rotation provided by multiple nations; initially, the Apollo Block III and Soyuz were to be the only crew transfer craft, before the ESA developed the Hermes shuttle, Russia resumed development of the Buran program, and private aerospace firm Johnson Aerospace developed the Antares spacecraft. Resupply was initially provided by the ASC and Progress, later joined by the Shuttle-C and ESA Automated Transfer Vehicle (ATV), and commercial spacecraft such as the Johnson Aerospace Verrezzano and SpacePlanes Eridanus and Esperia, SpaceX Dragon, and Orbital ATK Antares; in future, additional commercial manned spacecraft will service the station, these being the SpaceX Dragon 2 and Boeing CST-100 Starliner. Originally, it was planned to incorporate Spacelab into the new station, before NASA sent a crew to assertain Spacelab's condition, coming to the conclusion that it would be cheaper to just build a new station, resulting Spacelab's deorbiting in 2004.

Missions
The following is the missions of the program.