Flying the Shuttle - Launch: Difference between revisions

As part of the pre-launch preparations, the APU and hydraulics subsystems has to be started to enable thrust vector control of the main engines during ascent. If this is not done, the Shuttle will cease to be maneuverable after SRB separation. The procedure is outlined in a checklist:

As soon as the throttle is moved to 65%, the main engines ignite. This is the starting signal for SRB ignition, the SRBs will follow three seconds later, and once they burn, there is no going back. The SRBs can not be throttled and will burn till exhausted, and they have enough thrust to lift the stack even if the main engine is switched off.

Upon ascent, the shuttle is controlled by thrust vectoring of both the SRBs and the SSME. About ten seconds after liftoff while the dynamical pressure is still small, roll the shuttle to the desired launch course, then pull slightly down to a pitch of 80-85 degrees of inverted flight (the journey into orbit is flown with the head hanging down). You should now verify that you are approximately (within 10-20 degrees) on your launch course. Don't worry about details, they can be fixed later.

About 20 seconds later, max. qbar is over and the stack becomes much more controllable. Throttle up to full and gradually reduce pitch to about 60 degrees (still inverted) and keep rising.

Seen from the ground, the smoke trail of the launch shows clearly the point at which the shuttle departs from vertical ascent and reduces pitch.

At around 150,000 ft altitude, the SRBs separate. They're still burning for a while, but they won't generate any thrust. While they seem to fall back, they actually continue to rise - just the shuttle accelerates away from them at a faster pace.

With the SRBs gone and most of the fuel still in the tank, thrust is down from abut 2.5 g to less than 1 g - which means that the stack no longer gains vertical velocity. Nevertheless, there's still a tremendous vertical velocity left, so the shuttle will continue to rise until this is depleted.

At this stage, the thrust vector is not very aligned with the shuttle axis – note how the SSME pointed out of the axis push through the ETs top-heavy CoG:

Once the ET depletes, thrust builds up. Watch acceleration and throttle back to keep it below 3 g (which is the structural limit of the stack on ascent). Manging vertical velocity should be easy at this point, there's plenty of thrust so that pitch has an immediate and strong effect on vertical speed. Keep it close to zero and maintain 150 km altitude. Keep an eye on the perigee counter now - once you are close to orbital velocity, it moves fast. Reduce thrust as soon as it comes above zero, cut thrust once the apogee reaches the desired value and drop the external tank. The RCS will fire automatically in translational mode to separate the orbiter from the tank.

The final push into orbit is done by the orbital maneuvering system (OMS). The reaction control system (RCS) will come on automatically, enabling you to null any remaining rotation of the orbiter.