Apollo 9 launched March 3, 1969, with a crucial mission: to fly the lunar module for the first time. The spacecraft had been tested successfully during the unmanned Apollo 5 mission. This would be the first time a crew would be aboard the spacecraft.
The crew spent 10 days in low Earth orbit testing the lunar module's engines, navigation systems and docking maneuvers, as well as backpack life support systems. And while the module performed well, the crew had to scrap a spacewalk after one of the astronauts fell ill during the flight.
Commander Jim McDivitt began his flying career in the Air Force both in combat and as a test pilot, and joined NASA for the Gemini program. He was aboard Gemini 4 during Ed White's famous spacewalk – the first of the U.S. program – and took pictures that still are widely circulated today.
Dave Scott, also an Air Force pilot and Apollo 9's command module pilot, had one mission of spaceflight experience under his belt. He was co-pilot on the Gemini 8 mission, which experienced a malfunction when the thruster stuck open and began spinning the spacecraft so quickly that the astronauts feared losing consciousness. Scott's commander, Neil Armstrong, stabilized the ship and the two had an early, but safe landing. Scott later commanded the Apollo 15 mission.
Fellow Air Force flier Russell Schweickart also had a strong theoretical background: he graduated from the Massachusetts Institute of Technology with experience in upper atmosphere physics and tracking stars. Apollo 9 would be his only flight in space.
Flying in Earth orbit
After the triumph of Apollo 8 orbiting the moon, Apollo 9's mission was no less ambitious. Perhaps it did not have the glamour of circling another world, but it was an important step to getting to the moon.
Future crews had to be comfortable with docking and undocking the spacecraft to link up with the orbiting command module and head back home.
Although the astronauts were serious about their work, they had a note of whimsy when naming the spacecraft: the command module was called Gumdrop, and the lunar module Spider, because that's what the modules resembled.
The first few days went relatively smoothly. The astronauts docked the two spacecraft successfully on the first day. Gumdrop fired its engines several times with Spider attached, proving it could handle the mass of the lunar module when doing orbital maneuvers.
On Flight Day 4, NASA wanted to test an astronaut's ability to climb from one spacecraft to the other if for some reason, the lunar module and command module refused to dock with each other in lunar orbit. In that case, a spacewalk to the command module would be the crew's only ticket home.
Unfortunately for the crew's plans, Schweickart had been nauseous since almost the beginning of the mission. According to flight director Chris Kraft, McDivitt waited until almost the last minute to inform Mission Control about the situation.
"If he reported on Schweickart a few days earlier, the flight surgeons would probably have prescribed medications that could have eliminated his symptoms," Kraft recalled in his autobiography, "Flight: My Life in Mission Control."
Adapting on the fly
That said, a space mission is often about adapting plans as you go, and the crew pressed on. McDivitt and Schweickart performed their assigned tests of Spider's engine, showing that it could easily maneuver the spacecraft.
Then came the spacewalk. Schweickart carefully suited up and climbed out on the front "porch" of Spider to pick up some science samples on the outside. He was then supposed to clamber over to Gumdrop. However, Schweickart began to tire and McDivitt decided to cancel that climb. Mission Control agreed with the decision and called it a day.
Flight Day 5 brought the hardest and most exciting part of the mission: undocking the two spacecraft and flying the lunar module by itself. McDivitt and Schweickart flew Spider more than 100 miles away. Scott, remaining in Gumdrop, watched in wonder as Spider got smaller and smaller, appearing like a bright star in the distance, and then disappeared.
Spider's crew then turned on their "ascent" stage to simulate rising again from the moon, while men in Mission Control waited anxiously to see if it worked. The engine fired flawlessly and Spider eventually docked with Gumdrop safely.
The crew remained in orbit until March 13, and splashed down about three miles from their recovery ship in the Atlantic Ocean. Apollo 9's tests of Spider proved the lunar module could work in space. With that established, now NASA could turn to the tricky problem of testing it near the surface of the moon.
— Elizabeth Howell, SPACE.com Contributor