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Flying the Shuttle - Launch: Difference between revisions
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If you ascent is too flat in this phase, maximum qbar will be violated, or more likely, you'll lose control of the stack beyond the point the thrust vectoring can recover. | If you ascent is too flat in this phase, maximum qbar will be violated, or more likely, you'll lose control of the stack beyond the point the thrust vectoring can recover. | ||
About 20 seconds later, max. qbar is over and the stack becomes much more controllable. | About 20 seconds later, max. qbar is over and the stack becomes much more controllable. Throttle up to full and reduce pitch to about 60 degrees (still inverted) and keep rising. | ||
[[File:Shuttle launch01.jpg|600px|Launch track of the Space Shuttle]] | [[File:Shuttle launch01.jpg|600px|Launch track of the Space Shuttle]] | ||
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[[File:Shuttle SRBsep03.jpg|600px|SRB separation]][[File:Shuttle SRBsep04.jpg|600px|SRB separation]] | [[File:Shuttle SRBsep03.jpg|600px|SRB separation]][[File:Shuttle SRBsep04.jpg|600px|SRB separation]] | ||
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. | |||
Outside of the atmosphere, handling characteristics are much improved, but there's now no friction, so every motion has to be explicitly canceled. Time to fine-tune the launch course - watch inclination in the HUD to insert into an orbit at a given inclination now. | |||
Pitch should be gradually reduced to about 30 deg, still in inverted flight. The reason for this is communication (not implemented in FG) - at this point the Shuttle has contact to ground stations in the Caribbean for a proper launch trajectory. Watch vertical velocity and adjust pitch to get it to zero out at about 150 km altitude. Watch launch course and don't allow large deviations any more - they will reduce your reserves to make orbit. | |||
You will almost inevitably drop in altitude for a bit from there - that's normal, and it'll recover once the ET gets light when all the fuel is spent and thrust increases. Roll out of inverted flight about 5 minutes into the launch to be realistic (the shuttle makes now communication via the satellite network and no longer directly with the ground). | |||
What should not happen is that the trajectory drops below 265.000 ft - the reason is ET heat load. The ET is equipped with an ablator to take care of the worst of friction heat, but if you go too fast too low, the heat shield will fail and the ET will explode. | |||
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: | |||
[[File:Shuttle FG5.jpg|600px|Final stage in the flight to orbit]] | [[File:Shuttle FG5.jpg|600px|Final stage in the flight to orbit]] | ||
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 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. | |||
In reality, propellant is calculated rather closely to the needs. In FG, without a payload, especially launching due east, you may arrive in orbit with some leftover propellant, potentially enabling to reach a rather high orbit. Take on a heavy payload and launch on a high inclination, and that may change. | |||
Good luck, you're ready to do orbital maneuvering. | |||
== Further reading == | == Further reading == | ||