Flying the Shuttle - Entry: Difference between revisions

Entry preparations begin in orbit - it is important to work through the entry preparation checklists, in particular payload bay door and ET umbilical doors need to be closed or the Shuttle will have incomplete thermal protection and burn up. APUs need to be running to provide hydraulic power for the aerodynamical control surfaces.

 

Another important aspect is CoG management - during entry, the CoG should ideally be at 66% of the vehicle length - check this in the propellant dialog. There is about a 1 % margin around this value in which the orbiter gets progressively more difficult to manage, but for instance an entry with full OMS tanks is not survivable, the elevons can not hold the Shuttle in such a tail-heavy configuration.

 

Forward RCS fuel should be dumped for safety reasons, the forward RCS will not be used any more (usually it is burned up by firing left and right-firing thrusters at the same time - {{Key press|Control|f}} toggles this). Excess OMS fuel should be burned by orienting the Shuttle perpendicular to the motion vector (i.e. a normal or anti-normal burn) which will change the entry trajectory very little. In the unlikely case that there is excess aft RCS fuel, this can also be burned by a normal burn in translational mode.

 

If there is insufficient RCS fuel in one or both of the rear pods, pre-entry preparations are a good time to set up RCS to RCS or OMS to RCS crossfeeding.

Pitch up and wait for the atmosphere to grab the shuttle. This will be felt initially by a very slow drift of the attitude, trying to reduce pitch. Apply thrusters to keep the nose up. The thrust level needed to hold the 40 degrees will increase with increasing qbar, and eventually the controls will revert to aerodynamical surfaces for roll (qbar = 10 psf) and pitch (qbar = 40 psf). Using the <b>RCS ROT ENTRY DAP</b> steering characteristics changes quite drastically - initially it is probably easier to make minute thruster adjustments with the keyboard, in the later phase a stick or mouse is a much better option. With the <b>Aerojet</b> DAP, the change will hardly be felt as the rate controller logic adapts automatically to all changes in qbar and Mach number.

Once the Shuttle is under aerodynamical control, watch descent rate slow and reverse. Once the rate comes back up to about -50 m/s, you can initiate the first careful high-bank roll. Do it gently in order not to lose the AoA if you're flying by hand! If you're maneuvering with automatic pitch axis control, aim for about 6 deg/s roll rate. Watch the response of nose cone temperature and acceleration and the slow drift in course. The descent rate will fall again, don't let it fall too fast, or you'll get too hot. Allow for some lag, get a feeling for how the trajectory responds to what you're doing. This is actually piloting, and you can influence a lot of what is happening here. With the <b>Aerojet</b> DAP flight characteristics are very stable and the vehicle holds attitude and AoA automatically, which means you can use roll to control sinkrate very precisely - flying by hand, that may not work so well. Once deviation to target azimuth exceeds 10 degrees, do a roll reversal.