Their next task was the first of two firings of the big OMS engines to establish Columbia in her correct orbit. This began 10.5 minutes after launch and lasted 90 seconds; it was described by Flight Director Jay Greene as ''normal''. The crew agreed: ''We're looking good.'' A second OMS burn at apogee, about 35 minutes later, circularised the orbit. Although the burns were satisfactory, the instruments providing quantity readings for the OMS pods turned out to be erroneous. They showed sporadic propellant quantities throughout the flight, often staying constant for some seconds, then changing at faster-than-expected rates.
None of this had been seen in ground tests. Nevertheless, all evaluations of the system during STS-1 - using both thrusters in unison and singly - were performed without incident. To test an emergency procedure, Young and Crippen even successfully fired the right-hand OMS engine using propellant from the left-hand tank.
After establishing themselves in a stable, circular orbit around Earth, Young and Crippen turned their attention to opening Columbia's 18.2-m-long clamshell doors and expose the cavernous payload bay to space for the first time. The bay was empty for this first mission, but on subsequent flights it was expected that it would be crammed with commercial satellites, scientific instruments, laboratories - the most important of which was the European-built Spacelab - and major astronomical observatories. For STS-1, it carried sensors to record Columbia's performance and the stresses and strains endured at key points in the mission.
It was essential that the doors were opened within the first hours after reaching orbit, so that radiators attached to their inside panels could dump excess heat into space. If, for whatever reason, the crew had been unable to open the doors, flight rules dictated that they return to Earth at the end of their fifth orbit. Although extra systems were carried to dissipate heat, they could be used for a day at most. If, at the other extreme, difficulties were encountered closing the doors at the end of the mission, Crippen was spacewalk-trained to secure them manually.
Early plans called for STS-1 to fly with the doors closed throughout the mission -relying on Columbia's flash evaporators rather than the radiators - but it was soon realised that opening them was essential to dissipate her heat load.
Had a spacewalk been necessary, the entire cabin pressure would have been reduced from the normal 14.7 psi to 9.0 psi and after nine hours of 'pre-breathing', Crippen would have suited up and entered the payload bay. By lowering the pressure in this way, the crew's 'day' would have been shortened by two hours, and Young pre-breathed in case he needed to go outside to assist Crippen.
Fortunately, Crippen opened the doors perfectly at the end of Columbia's second orbit. He gingerly unlatched the starboard door first - ''Here comes the right door and, boy, that is really beautiful out there'' - then closed it again to verify the satisfactory performance of its seal. ''All the latches work just fine,'' he told Mission Control, ''and the door looks like she's doing her thing.'' Both doors would be opened and closed on several occasions during the next two days to evaluate not only the seals, but also their latches and actuators.
Throughout this procedure, the astronauts worked at the rear of the cockpit, facing a pair of small square windows overlooking the payload bay; they reported that they could work there quite comfortably without needing any kind of foot restraints. Looking into the pristine white, insulation-enshrouded payload bay, there was not a great deal to see. There were no payloads to deploy and not much in the way of experiments to perform. In fact, the only real 'payloads' were the small, unassuming -yet vitally important - boxes of measuring devices, detectors and sensors.
It was known as the Development Flight Instrumentation (DFI), and although it was mainly destined to be used during the first four test flights, several of its components remained on board Columbia during later missions. Weighing 9,290 kg, it provided the first 'real' measurements of the Shuttle's performance and the stresses she endured during launch, ascent, in space and during re-entry and landing. Previous data had only been available through computer simulations and the DFI data was expected to provide the first hard details. It stored this information on three magnetic tape recorders, which were analysed after landing.
Other devices mounted on the DFI pallet were microphones to acquire acoustic data and an array of six different materials - including Teflon and gold - to assess their level of degradation in the harsh low-Earth-orbit environment.
Two more experiments were also carried on STS-1; one of which included actual hardware, and the other which took advantage of Columbia's re-entry flight path. The Aerodynamic Coefficient Identification Package (ACIP) complemented the DFI by collecting data during all flight phases, but particularly during the hypersonic, supersonic and transonic periods of re-entry, in order to help to validate wind-tunnel predictions. As well as helping to advance engineers' understanding of the thermal and structural dynamics of the Shuttle during its glide back to Earth, ACIP measured the positions of each flight surface and gathered about four hours of data.
The second experiment was a wholly passive one, known as the Infrared Imagery of Shuttle (IRIS). It featured nothing in the way of onboard equipment and involved NASA's Kuiper Airborne Observatory taking high-resolution infrared pictures of Columbia's belly and sides as she re-entered the atmosphere.
Young and Crippen had little direct involvement in any of these experiments, which operated autonomously throughout the mission. In any case, they had their hands full with the many engineering tests planned. It was during the first day of the flight, while Crippen was busy evaluating the performance of the payload bay doors, that they noticed several missing thermal protection tiles from one of the OMS pods.
''Okay,'' Young told Mission Control, ''what camera are y'all looking at now, do you know?''
''We're looking out the forward camera,'' replied the Capcom.
''Okay. We want to tell y'all here we do have a few tiles missing off the starboard pod. Basically, it's got what appears to be three tiles and some smaller pieces; and off the port pod - looks like - I can see one full square and looks like a few little triangular shapes that are missing and we are trying to put that on the TV right now.'' Young's observations highlighted, for the first time, a problem that would become almost commonplace on Shuttle missions: tiles coming off certain areas of the vehicle during the violent climb into orbit.
He also commented, after a visual inspection, that no tiles seemed to be missing from Columbia's wings, vertical stabiliser or nose. However, it was impossible to determine if tiles had been lost from her belly. Back on Earth, managers watched the transmissions, but decided that none of the missing tiles was in a 'critical' area that might pose a hazard to the Shuttle's re-entry. The most that could happen, they said, was that after landing a patch of aluminium skin underneath some tiles may need replacing. Yet, even at this early stage, a potentially lethal problem with their integrity had reared its head.
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