Page "STS-2" Paragraph 22

Although the STS-2 mission had been planned for a duration of five days, with a few hours a day spent testing the Canadarm, the flight was cut short when one of the three fuel cells that produce electricity and drinking water failed.

The mission was shortened to two days, and the Canadarm tests were canceled.

The crew stayed awake during a scheduled sleep period and tested the arm anyway, working during the Loss-Of-Signal ( LOS ) periods when they were not in contact with Mission Control.

The deorbit and reentry phase of this mission differed from STS-1, in that while the first shuttle entry was flown as a " middle of the road " test of the automatic guidance, the success of that mission allowed for the STS-2 crew to explore the stability margins of the vehicle's performance.

Twenty-nine planned Programmed Test Inputs ( PTIs ) were manually flown in the Control Stick Steering ( CSS ) mode, with Engle making use of his past manual hypersonic flying experience in the X-15.

These PTIs provided useful data for subsequent engineering modifications.