The countdown for the Apollo 9 mission began on Feb. 26, 1969, for a planned launch two days later. However, the crew of Commander James A. McDivitt, Command Module Pilot (CMP) David R. Scott, and Lunar Module Pilot (LMP) Russell L. Schweickart, developed sore throats and nasal congestion so NASA halted the countdown and rescheduled the launch for Mar. 3 to give the astronauts time to recover. Apollo 9 was the most complex piloted mission attempted by NASA to that point and the crew needed to be healthy to accomplish all the difficult tasks planned for their 10-day flight. The most critical tasks were scheduled for the first five days of the mission to maximize the chances of accomplishing them, should an anomaly force an early end to the flight.
The Apollo 9 mission called for a complete checkout of the LM’s systems in Earth orbit, performing as many of the same operations as possible in Earth orbit as on a lunar landing mission. The first major activity after reaching orbit was to undock the CM, nicknamed Gumdrop, from the rocket’s third stage, where the LM, nicknamed Spider, was carried into space. The crew then was to turn Gumdrop around and dock with Spider and extract it from the third stage. McDivitt and Schweickart were to enter the LM to thoroughly check out all its systems including extending its landing legs. Schweickart and Scott planned to conduct the first extravehicular activity of the Apollo program, the only one scheduled before the spacewalk on the Moon’s surface, to test the reliability of the Apollo A-7L space suit and the Portable Life Support System (PLSS) backpack. The most complex activity was for McDivitt and Schweickart to undock Spider and fly it up to 100 miles from Gumdrop, fire both the descent and ascent stage engines, and rendezvous and dock with Scott in the CM. They would then jettison the LM and continue in orbit for five more days, conducting Earth observation experiments useful for future projects like Landsat and Skylab. Their mission complete, the Apollo 9 crew planned to splashdown in the Atlantic Ocean and be recovered by the prime recovery ship, the landing platform-helicopter USS Guadalcanal.