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Flying the Shuttle - Launch: Difference between revisions
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{{Note|This article refers to the {{AircraftHangar|aircraft=SpaceShuttle}} in the FGAddon repository.}} | |||
This mission phase can directly be started using <code>--aircraft=SpaceShuttle-launch</code> on the command line. | |||
This mission phase can directly be started using < | |||
== What are we trying to do? == | == What are we trying to do? == | ||
The launch phase of the Shuttle lasts from ignition of the main engines until the shuttle reaches orbit. This is a surprisingly short time, all in all just about eight minutes. During this time, an enormous amount of propellant is spent accelerating the orbiter to Mach 26 at an altitude of 150 km. The complete launch stack consists of the orbiter, mounted on the external tank (ET) which supplies propellant for the Space Shuttle Main Engines (SSMEs), assisted by two solid rocket boosters (SRBs). | |||
The first two minutes of the flight pass through the atmosphere, during this time the SRBs provide most of the thrust. The SRBs can not be throttled, once on, they burn till they are spent. At an altitude of about 150,000 ft the SRBs are disconnected and the shuttle accelerates only using the main engines fed from the ET which is disconnected just before reaching orbit. | |||
The first two minutes of the flight pass through the atmosphere, during this time the SRBs provide most of the thrust. The SRBs can not be throttled, once on, they burn till they are spent. At an altitude of about 150 | |||
* | The tasks are hence: | ||
* | * Bring the orbiter safely through the atmosphere | ||
* | * Steer towards a launch course corresponding to an orbit with the desired inclination | ||
* Accelerate to orbital speed outside the atmosphere | |||
[[File:Shuttle FG03.jpg|600px|Space Shuttle Launch]] | [[File:Shuttle FG03.jpg|600px|Space Shuttle Launch]] | ||
== How it feels in FG == | == How it feels in FG == | ||
The launch dynamics in FG is, if we neglect the noise and the shaking of the real thing (which is described as 'driving down a rough gravel road without any suspension, a shaking so hard the eyes cannot properly focus' as long as the SRBs are burning) probably fairly realistic. | The launch dynamics in FG is, if we neglect the noise and the shaking of the real thing (which is described as 'driving down a rough gravel road without any suspension, a shaking so hard the eyes cannot properly focus' as long as the SRBs are burning) probably fairly realistic. | ||
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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. | 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. | |||
At around 150 | |||
[[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]] | ||
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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. | 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) | 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 | 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). | ||
<b>What should not happen is that the trajectory drops below 265.000 ft | <b>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.</b> | ||
At this stage, the thrust vector is not very aligned with the shuttle axis | 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. | 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. | ||
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Good luck, you're ready to do orbital maneuvering. | Good luck, you're ready to do orbital maneuvering. | ||