Johnson Space Center, Houston — Delta-winged shuttle Challenger, which rode a thundering tower of flame on its first launch into space April 4, glided gracefully back to a perfect touchdown April 9.
With Challenger, as with the world's first reusable shuttle, Columbia, split-second precision in accomplishing each mission objective has confirmed how well the Space Transportation System (STS) has been designed to cope with the tremendous extremes of space flight.
The only disappointment marring Challenger's inaugural STS-6 mission happened far offstage. After a perfect launch from the shuttle's cargo bay, a giant communications satellite veered off course due to a misfiring booster rocket. But National Aeronautics and Space Administration (NASA) officials expect to nudge the misplaced satellite into its proper orbit by firing its own small thruster rockets in a carefully programmed sequence over the next month.
Ironically, the shuttle program's two-year string of remarkable successes may conceal the magnitude of what has been achieved.
Gordon Fullerton, the NASA astronaut who piloted Columbia on its STS-3 mission and is more than ready for his next shuttle flight, explains that ''it's almost impossible for anyone not intimately connected with the space program to understand the complexity of the shuttle system.''
A quick glance at the shuttle cockpit's vast display of control panels gives a hint of the endless stream of information and interactive options available to each shuttle crew. But even a full understanding of the shuttle's maze of electrical and mechanical systems leaves out a wealth of operational complexity.
STS-6's successful four-hour spacewalk, for instance, demonstrated an astronaut's ability to move freely in space and carry out a variety of tasks. But the importance of this achievement is that it is part of a long-term series of steps leading up to carrying out repairs in space. The next step will come with Challenger's STS-7 mission in June. On that flight, the first US woman astronaut, Sally Ride, will use the shuttle's Canadian-built manipulator arm first to put a West German satellite into orbit and then to retrieve the satellite and place it back inside the shuttle. If each successive test goes according to plan, the crew of STS-13 will be ready to repair the damaged Solar Max satellite early in 1984.
John F. Guilmartin, a Rice University military historian in charge of compiling a chronological history of the space-shuttle program, insists that the shuttle's ''immense complexity'' represents far more than simply a breakthrough in aerospace engineering.
From the perspective of an experienced US Air Force officer decorated for service in Vietnam and Laos, former Lieutenant Colonel Guilmartin explains that the shuttle itself is a unique accomplishment. ''The shuttle's reusable rocket boosters on their own represent an integral system which is up to the level of our most complex World War II bombers.''
The shuttle's complexity has created tremendous reliability challenges, according to Guilmartin. When a number of sophisticated systems are interconnected, as in the shuttle, he says, each component must be virtually 100 percent reliable. He explains that with the shuttle's thousands of interconnections, stringing as few as 25 components together results in an ''unacceptably low level of cumulative reliability,'' even if each component operates perfectly 99 percent of the time.
Along with most other Johnson Space Center workers from janitors to top management, Guilmartin shows his appreciation for the shuttle by decorating his office with a large shuttle poster. But with his historian's perspective, he concludes that the greatest STS achievement may not be the $1 billion spacecraft itself. Instead, he says, ''it is incredible to me that NASA has been able to overcome not only the technical problems, but also all the political pressures and budgetary obstacles that have surrounded the shuttle program throughout its development.''
Guilmartin says that the STS has faced a complex array of opposition ''in sharp contrast with our Apollo program, where there was something approaching a national mandate to get a man on the moon.
''NASA's skill in shepherding the shuttle program through a political minefield has been remarkable, a case study in how this can be done in a democracy,'' he explains.