Doing The Twist

The ascent, though picture-perfect, was unusual, as it featured the first use of a novel 'heads-up' manoeuvre about six minutes after launch. In effect, the onboard GPCs commanded the main engines, over a 20-second period, to roll Columbia 180 degrees from a 'belly-up' to a 'belly-down' orientation, enabling the crew to communicate with Mission Control through the TDRS network two-and-a-half minutes sooner than had previously been possible. As well as eliminating the need for a ground-tracking station at Bermuda - the use of which had required the Shuttle to ascend belly-up - the move saved NASA $5 million per year.

The computers pulled off the manoeuvre effortlessly and Columbia rolled left at 5 degrees per second, resulting in a minimal 15-second communications loss with Mission Control. ''In the roll, we transitioned from ground station telemetry to TDRS telemetry,'' said Shuttle launch integration manager Don McMonagle, himself a former astronaut. ''That transition occurred in less than 15 seconds, which is precisely as we expected. We're very satisfied that that unique aspect of this ascent trajectory went as planned.'' The manoeuvre, which was to be used on future flights on an easterly heading, allowed Columbia's cockpit antennas to 'lock-on' to the overhead TDRS.

''Nice roll,'' radioed Capcom Scott Horowitz from Mission Control.

''Copy and concur,'' Kregel replied simply. The entire manoeuvre was controlled by the onboard computers, and the crew did not even know if they would roll to the left or the right until it actually happened; that decision was made in real-time, based on incoming velocity and orientation data. Telemetry indicated the manoeuvre, which took place 480 km downrange of KSC and at an altitude of about 110 km, went smoothly, although unfortunately it was not visible on long-range tracking cameras. ''We do not characterise this as a risky manoeuvre,'' McMonagle told journalists. ''This was analysed so we would make this roll to heads-up after we're outside the atmosphere, so the concerns about aerodynamic loads on the vehicle are not a problem. This occur[red] six minutes into the launch, so we're well out of the atmosphere and the roll to heads-up is completely unaffected by air. To quote Kevin Kregel, he expects it to be an E-ticket ride, but it's predictable and completely certified.''

''We had to do a fair amount of analysis to ensure that we weren't doing something dumb,'' said Flight Director Wayne Hale. ''One thing we didn't want to perturb was the [RTLS] abort mode,'' which Kregel would perform in the event of an emergency early in the ascent. ''That [the RTLS] is a fairly intricate manoeuvre, it's been analysed to death and we spent a lot of money making sure it would work if we ever had to do that and it is based on a heads-down trajectory. So we picked a time [for the roll] that was after negative return [to KSC].'' The analysis concluded that, even with electrical failures or two main engines shutting down, ''it never goes what you would call 'out of control' ''.

''It'll be pretty neat to see from a piloting perspective,'' said Horowitz before the launch, ''because here you are, upside-down, and then you're going to roll to right-side-up. It may actually make the ride a little bit more comfortable.'' To be safe, the manoeuvre was carried out before Columbia was out of range of the Air Force's Eastern Test Range tracking radars, to enable Mission Control to maintain contact with the crew throughout, until TDRS-supported communications commenced.

''The whole sequence is very fast,'' Chawla said of her first Shuttle launch. ''I was doing the photography [of the jettisoned External Tank] and was disoriented because I didn't know where my legs were! You only have two-and-a-half minutes [to photograph it] because after that it is not going to be visible. During the time it was in view, I took 40 pictures. The people on the ground were happy because it showed them the sequence for how the venting was taking place. They hadn't seen it on previous flights. NASA did a lot of analysis to see if this could become a problem on another day and they concluded that it wasn't.''

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