Space shuttle Challenger's four crew members kept ahead of schedule on their third day in orbit Wednesday as they worked through a long list of vehicle checks and scientific experiments while preparing for a scheduled Thursday spacewalk and a Saturday landing.
Adding to the astronauts' enthusiasm was word from Houston that their mission's chief objective - putting the first of three $75 million tracking and data relay satellites (TDRS) into orbit - almost certainly will be accomplished, despite some unexpected problems.
It may be weeks before detailed analysis pinpoints the exact cause of a malfunction that left the 2.5-ton communications satellite temporarily out of control and out of contact with National Aeronautics and Space Administration controllers. But Robert E. Smylie, NASA's associate administrator for space tracking and data systems, predicts that space agency will be able to use TDRS's own small thruster rockets to push the misplaced satellite into the desired orbit. The latest estimate of how long this will take is six to seven days.
According to a US Air Force spokesman, ''some problem occurred'' with the 16 -ton inertial upper stage rocket system developed by the Air Force for lifting satellites from the shuttle's 175-mile orbit into higher orbits. But the spokesman explained that putting TDRS into service despite a major systems failure demonstrates the effectiveness of the close working relationships that link the Air Force, NASA, and private-contractor personnel within the US space program.
The cooperative effort propelling America's shuttle program extends beyond US borders.
Robert Shutak, vice-president of France's Arianespace Inc., is trying hard to talk more American companies into using its Ariane rocket to carry their commercial satellites into orbit. Yet he insists that ''Arianespace hopes the shuttle is a great success, because its success will make everyone more confident about venturing into space, and I believe there is enough room for all of us up there.''
Mr. Shutak adds that Challenger's 10-week delay to correct engine leaks, following last September's Ariane failure, in which two commercial satellites along with the unmanned single-use French rocket were destroyed, ''has caused customers to rethink their space satellite plans.''
Arianespace estimates that it can make a profit for its shareholders by capturing a 30-percent share of the 258 satellite launches it projects for the 1985-91 period. ''The shuttle is a heavy-lift vehicle, while Ariane is limited to launching smaller spacecraft,'' Shutak says, ''so there is room for both the Ariane and the shuttle because we provide alternatives.''
Shutak says that Ariane's September failure, which has delayed its sixth launch until June 3, has led to proof that NASA and Arianespace can cooperate. To help Ariane get back on schedule, NASA will launch the European Space Agency's scientific Exosat payload in late May on a Delta rocket. ''This helps show that, yes, we are competitors,'' says aeronautics engineer and lawyer Shutak, ''but we are also in a space venture which is a cooperative space venture.''
One reason that the shuttle might lose customers to Ariane, Shutak explains, is that Ariane can offer long-term financing through a network of European banks. To meet this particular challenge, the US Congress may consider legislation this year which would offer shuttle customers the same option, of flying now and paying later.
One private-industry executive adds the warning that no matter how flawlessly US shuttles perform, they will lose customers unless the Reagan administration makes a commitment to expand the program. He urges backing for a fifth orbiter and support for a permanent manned space station. Without assurances that flights will go up on time, and that commercial cargoes will not be ''bumped'' by Defense Department requirements, the shuttle will lose customers to Ariane, he says.
According to this space specialist, the shuttle program needs to sign up more commercial customers to develop a ''lower cost, higher volume, higher efficiency operation'' able to provide frequent and dependable service.
This contrasts with a 1982 letter from Budget Director David A. Stockman to NASA administrator James M. Beggs, stating that ''it should not be assumed that the US government should have responsibility to fund an operational system with sufficient capacity to meet non-US government needs once the shuttle technology has been developed.''
Congress may decide to support an expanded program. A recent House subcommittee report favors spending $1.5 billion for a fifth shuttle.