Apollo 9 was the third spaceflight in NASA's Apollo program, the second crewed Apollo mission, and the first flight of the full Apollo spacecraft, which included the Lunar Module (LM) with the command and service module (CSM). The primary goal of the Apollo 9 mission was to qualify the LM for lunar orbit operations in preparation for future lunar landings. The mission demonstrated its descent and ascent propulsion systems, showing that its crew could fly it independently and its rendezvous and dock capability with the CSM, which was necessary for a lunar landing. Firing the LM descent engine as a backup mode to propel the spacecraft stack, something that would be incredibly valuable during Apollo 13, and the use of the portable life support system backpack outside the LM cabin were secondary flight objectives.
Apollo 9 had a three-person crew, Commander James McDivitt, Command Module Pilot David Scott, and Lunar Module Pilot Rusty Schweickart. During their ten-day mission, the astronauts tested systems and procedures that would prove critical to landing on the Moon, including backpack life support systems, docking maneuvers, navigation systems, and the LM engines.
The launch was initially scheduled for February 28, 1969. However, it was postponed because all three astronauts had colds. NASA didn't want to risk how that could affect the mission. Around-the-clock labor shifts were necessary to keep the spacecraft ready; the delay cost $500,000. Launch occurred on March 3, well within the initial launch window. Vice President Spiro Agnew was present in the firing control room was on behalf of the new Nixon administration. McDivitt reported it was a smooth ride during the launch, although there was some vibration.
The crew began their first significant orbital task when the CSM separated from the S-IVB nearly 3 hours into the mission. They had to turn around and dock with the LM on the end of the S-IVB. After this, the combined spacecraft separated from the rocket. If a docking like this could not be accomplished, future lunar landings could not take place. Scott, who was responsible for flying the CSM, completed a successful docking. McDivitt and Schweickart then inspected the tunnel connecting the CM and LM, and then the joined spacecraft separated from the S-IVB. The next task was to maneuver the two docked spacecrafts with one engine. The burn took place 6 hours into the mission and was performed with the Service Propulsion System (SPS). Scott then excitedly reported the LM was still in place. The S-IVB was then fired again, and the stage was sent into solar orbit.
The highlight of the next day was three SPS burns. The initial burn lasted 110 seconds and including gimbaling the engine to see if the autopilot could lessen the sway, which it did within five seconds. The engine and spacecraft passed every test, sometimes proving more robust than expected. The plan for the third day in space was to have the commander and lunar module pilot check out the LM's systems and use the LM descent engine to move the entire spacecraft. The descent engine served as backup to the SPS, which was critical during Apollo 13.
However, the flight plan reconsidered when Schweickart and McDivitt became ill. They were suffering from space adaptation sickness, and Schweickart vomited, while McDivitt felt queasy. They had been avoiding sudden movements, but the act of putting on their spacesuits for the LM checkout caused them to feel sick. The experience of McDivitt and Schweickart taught the doctors how to avoid this sickness for lunar landings. However, at the time, Schweickart feared his vomiting might endanger Kennedy's goal of landing on the Moon. However, they felt well enough to move forward with the plan and entered the LM. This transfer between vehicles marked the first-ever transfer for the US space program and was the first-ever transfer without a spacewalk. The spacewalk was unnecessary because of the internal connection between the two modules. The hatches between the CM and the LM were closed, and they operated as though the modules were separated, even though they remained docked for the time being. This showed that Spider's life support systems and communications would work even when separated from Gumdrop. As they would for landing on the Moon on command, the landing legs sprang into position, ensuring the LM was fully operational. They finished the LM checkout, including the descent engine's successful firing, and returned to Scott in Gumdrop. The burn simulated the throttle pattern used during the landing on the Moon. A fifth firing of the SPS occurred after they returned to prepare the rendezvous.
On the fourth day, Schweickart exited the hatch on the LM and made his way around the outside of the spacecraft to the hatch of the CM, where Scott was standing by to assist. The purpose of this was to demonstrate what could be done in the event of an emergency. Schweickart wore the life support backpack or PLSS during his EVA and seeing as it was the only one scheduled, it was the singular opportunity to test the PLSS in space. McDivittthe EVA initially canceled the EVA Schweickart's illness. However, considering he felt better, McDivitt allowed Schweickart to exit the LM and move around the LM exterior using the handholds. Both Scott and Schweickart photographed each other and retrieved experiments from their vehicles' exterior. He found moving around in space easier than the simulations had been. Both Schweickart and Scott were confident that he could have completed the exterior transfer, but they considered it unnecessary.
The mission's key event took place on the fifth day: the separation and rendezvous of the LM and the CM. McDivitt and Schweickart entered the LM Spider without wearing their helmets and gloves, having obtained permission to do so because it was easier to set up the LM without them. In the CM Gumdrop, Scott attempted to release the LM, but it remained stuck on the docking probe latches, but Scott hit the release again, and Spider was cleared. After spending 45 minutes near Gumdrop, Spider went into a slightly higher orbit, making the two crafts separate over time with Gumdrop ahead. Over the next few hours, McDivitt continued to fire the LM's descent engine, moving through several throttle settings. The LM was thoroughly test-flown by the end of the day. Spider was then put into a lower orbit to catch up with Gumdrop. This process would take over two hours, and the descent stage was jettisoned.
The approach and rendezvous were then conducted, and to demonstrate that either craft could perform rendezvous, Spider was the active participant during the maneuver, with Gumdrop taking the passive role. Spider was brought close to Gumdrop by McDivitt, who then maneuvered the LM to show Scott each side, allowing him to inspect for any damage. Then, McDivitt docked the craft. Due to glare from the Sun, McDivitt had trouble doing this, and Scott guided him in. During the later missions, docking the two spacecraft in lunar orbit would fall to the command module pilot. McDivitt and Schweickart returned to Gumdrop, and Spider was jettisoned, and its engine was fired remotely by Mission Control to deplete the fuel entirely as part of further engine testing. This simulated the ascent stage's climb from the lunar surface. The only primary lunar module system not thoroughly tested was the landing radar, as this could not be done in Earth orbit.
Apollo 9 was scheduled to remain in space for about ten days to check how the CSM would perform over the time required for a lunar mission. Most significant events had been scheduled for the first days in case the flight needed to be ended early. The remaining days in orbit were more leisurely. With the mission's main goals accomplished, the hatch window was used for special photography of Earth. Four identical Hasselblad cameras coupled together and film sensitive to different parts of the electromagnetic spectrum were used. This allowed for various surface features of Earth to appear. For example, water pollution as it exited rivers into the sea was tracked, and agricultural areas using infrared were highlighted. This photographing system was a prototype that would pave the way for the Earth Resources Technology Satellite, a predecessor to the Landsat series. The CSM was tested at length during this time, but this was mostly Scott's responsibility, which allowed McDivitt and Schweickart time to observe Earth leisurely. They did alert Scott of anything noteworthy, which allowed him to leave his work for a moment to look at Earth.
On March 13, during the mission's tenth-day, the service module was jettisoned. Due to unfavorable weather in the primary landing zone, the landing was delayed one orbit. Apollo 9 splashed down in the Atlantic ocean, around 160 nautical miles (300 km) east of the Bahamas, with the USS Guadalcanal recovery carrier, just over 3 miles (4.8 km) away. The mission lasted 10 days, 1 hour, 54 seconds. Apollo 9 was the last spacecraft to splashdown in the Atlantic Ocean until the Crew Dragon Demo-1 mission in 2019.