8,564
edits
Flying the Shuttle - Launch: Difference between revisions
Jump to navigation
Jump to search
m
Fix internal wiki links + wiki formatting
m (cat sort) |
m (Fix internal wiki links + wiki formatting) |
||
| Line 3: | Line 3: | ||
Once you feel confident, you can move on more advanced tutorial with more steps to do with Very Close to real operations and Checklists | Once you feel confident, you can move on more advanced tutorial with more steps to do with Very Close to real operations and Checklists | ||
[ | [[Flying_the_Shuttle_-_Launch_And_Post_Insertion_Advanced#Prelaunch_procedure|Pre Launch T-9 mn until MECO advanced tutorial]]}} | ||
{{Note|This article refers to the {{AircraftHangar|aircraft=SpaceShuttle}} in the FGAddon repository.}} | {{Note|This article refers to the {{AircraftHangar|aircraft=SpaceShuttle}} in the FGAddon repository.}} | ||
{{Space Shuttle navigation}} | {{Space Shuttle navigation}} | ||
| Line 37: | Line 37: | ||
For this reason, a launch trajectory always has two parts. The first part is near-vertical and lifts the spacecraft out of the atmosphere, the second part is near horizontal and accelerates to orbital speed. | For this reason, a launch trajectory always has two parts. The first part is near-vertical and lifts the spacecraft out of the atmosphere, the second part is near horizontal and accelerates to orbital speed. | ||
From an energetic perspective, the vertical part is wasteful and should be over as soon as possible. Imagine you have one g of thrust - it just allows you to overcome gravity and hover, but once your propellant is spent, you will fall down. This is the reason the SRBs are part of the launch stack - they generate a lot of thrust to get the shuttle out of the atmosphere as quickly as possible. It follows that it is wasteful if you want to reach an orbit of 600 km altitude to fly upwards to 600 km altitude and accelerate to orbital speed there - it costs far less energy to fly to 150 km altitude, accelerate to orbital speed there and later raise the orbit so that no energy is wasted fighting against gravity. For this reason, good launch tracks go out of the atmosphere but then stay low above it (of course, the spacecraft should not drop | From an energetic perspective, the vertical part is wasteful and should be over as soon as possible. Imagine you have one g of thrust - it just allows you to overcome gravity and hover, but once your propellant is spent, you will fall down. This is the reason the SRBs are part of the launch stack - they generate a lot of thrust to get the shuttle out of the atmosphere as quickly as possible. It follows that it is wasteful if you want to reach an orbit of 600 km altitude to fly upwards to 600 km altitude and accelerate to orbital speed there - it costs far less energy to fly to 150 km altitude, accelerate to orbital speed there and later raise the orbit so that no energy is wasted fighting against gravity. For this reason, good launch tracks go out of the atmosphere but then stay low above it (of course, the spacecraft should not drop ''back'' into the atmosphere...). | ||
As the acceleration depends both on thrust and the remaining mass of the stack (once the propellant is spent, the acceleration grows), the shuttle is initially highly maneuverable as long as the SRBs are burning, then thrust reduces dramatically and slowly grows towards the end as the ET depletes. Vertical launch trajectory management hence utilizes the enormous upward push of the SRBs to bridge the time till the main engine acceleration is strong enough to stabilize the trajectory vertically. In other words, after SRB separation vertical speed is initially high, then reduces due to gravity to even below zero (i.e. the tranjectory falls slightly) till the SSME and the centrifugal force push it up again, at which point it should be managed to near zero once injecting into orbit. | As the acceleration depends both on thrust and the remaining mass of the stack (once the propellant is spent, the acceleration grows), the shuttle is initially highly maneuverable as long as the SRBs are burning, then thrust reduces dramatically and slowly grows towards the end as the ET depletes. Vertical launch trajectory management hence utilizes the enormous upward push of the SRBs to bridge the time till the main engine acceleration is strong enough to stabilize the trajectory vertically. In other words, after SRB separation vertical speed is initially high, then reduces due to gravity to even below zero (i.e. the tranjectory falls slightly) till the SSME and the centrifugal force push it up again, at which point it should be managed to near zero once injecting into orbit. | ||
| Line 62: | Line 62: | ||
At about 35 seconds into the flight, dynamical pressure (qbar) will rise rapidly as the stack goes supersonic. This is a dangerous phase of the flight. The stack is very top-heavy (as the heavy oxygen is stored in the tip of the ET and the light hydrogen in the bottom), so once it starts toppling, it won't come back. In addition, aerodynamical forces are very strong. In fact the very reason we do this phase in inverted flight is to reduce the wing loading. At the callout, reduce throttle of the main engines to 65% to minimize the pressure spike. | At about 35 seconds into the flight, dynamical pressure (qbar) will rise rapidly as the stack goes supersonic. This is a dangerous phase of the flight. The stack is very top-heavy (as the heavy oxygen is stored in the tip of the ET and the light hydrogen in the bottom), so once it starts toppling, it won't come back. In addition, aerodynamical forces are very strong. In fact the very reason we do this phase in inverted flight is to reduce the wing loading. At the callout, reduce throttle of the main engines to 65% to minimize the pressure spike. | ||
If you ascent is too flat in this phase, maximum qbar will be violated, or you may lose control of the stack beyond the point the thrust vectoring can recover. If the orbiter is not in inverted flight at this point, the wing bending moment will grow too large, ripping the wings of the orbiter, resulting in a catastrophic loss of vehicle. | If you ascent is too flat in this phase, maximum qbar will be violated, or you may lose control of the stack beyond the point the thrust vectoring can recover. If the orbiter is not in inverted flight at this point, the wing bending moment will grow too large, ripping the wings of the orbiter, resulting in a catastrophic loss of vehicle. '''Do not attempt to cross max. qbar with positive AoA!''' | ||
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. | 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. | ||
| Line 82: | Line 82: | ||
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). | 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: | 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: | ||
| Line 119: | Line 119: | ||
Once you feel confident, you can move on more advanced tutorial with more steps to do with Close to real operations and Checklists | Once you feel confident, you can move on more advanced tutorial with more steps to do with Close to real operations and Checklists | ||
[[Flying the Shuttle - Launch And Post Insertion Advanced#Prelaunch procedure]] | |||
| Line 127: | Line 127: | ||
''In this tutorial, you'll learn how to program a launch into the Shuttle's guidance system, what happens during a launch and how to monitor ascent into orbit.'' | |||
* Start Flightgear with the commandline options | * Start Flightgear with the commandline options | ||
| Line 137: | Line 137: | ||
[[File:On_the_pad_1.jpg|800px|Ready to go]] | [[File:On_the_pad_1.jpg|800px|Ready to go]] | ||
''If you toy with the idea that specifying a heading is silly, be warned - it's crucial for the launch guidance to find a viable solution that the tail fin of the Shuttle points into the Eastern hemisphere - keep this in mind if you want to launch from somewhere else in the world.'' | |||
* Now, in reality the launch has been in planning for months if not years, and all guidance information is already loaded and cross checked at this point. FG doesn't (yet) support mission files or similar, so we need to tell the computer where we want to go. Open | * Now, in reality the launch has been in planning for months if not years, and all guidance information is already loaded and cross checked at this point. FG doesn't (yet) support mission files or similar, so we need to tell the computer where we want to go. Open '''SpaceShuttle -> Launch guidance''', select a target inclination of 51.5 degrees or so (that'd be required for a launch to ISS), leave the branch and target apoapsis as they are (you'll go to a 320 km orbit) and press '''Activate'''. The guidance now knows where to go. | ||
Next, tell the Shuttle that you want the flight on autopilot by selecting the PITCH AUTO and ROLL/YAW AUTO pushbuttons on the forward panel (circled in red, underneath the transparent checklist). | Next, tell the Shuttle that you want the flight on autopilot by selecting the PITCH AUTO and ROLL/YAW AUTO pushbuttons on the forward panel (circled in red, underneath the transparent checklist). | ||
| Line 145: | Line 145: | ||
[[File:Setting_apu_guidance.jpg|800px|Working through the checklist]] | [[File:Setting_apu_guidance.jpg|800px|Working through the checklist]] | ||
Flying the Shuttle manually into orbit isn't actually difficult at all - if you know what you have to do, because you need to anticipate a few things and that's what we're out to learn here. But if you want to take over from the automatic guidance at any point, push the CSS pushbutton for the channel (you can just take control of pitch and let the DAP handle yaw/roll for instance). | Flying the Shuttle manually into orbit isn't actually difficult at all - if you know what you have to do, because you need to anticipate a few things and that's what we're out to learn here. But if you want to take over from the automatic guidance at any point, push the CSS pushbutton for the channel (you can just take control of pitch and let the DAP handle yaw/roll for instance). ''' After activating CSS in-flight, do not attempt to hand control back to the AP - this will not work!'''. | ||
* There's also real-world stuff you need to do in cockpit. Open | * There's also real-world stuff you need to do in cockpit. Open '''Help -> Aircraft Checklists''' and study what we have to do for launch. Engine controllers need to be powered (obviously) - they should already be. APUs need to be running and supplying hydraulic power to gimbal the engines. That we still need to do. Open '''Space Shuttle -> APU and hydraulics''' and follow the items in the checklist to start all three APUs and bring hydraulic pressure to 3000 psi (hint: the sequence in which you work actually matters). | ||
Okay, there's a few other items which you can't yet perform on the list (it's the original from the Shuttle's Crew manual), so we're good to launch as soon as engines ignite. | Okay, there's a few other items which you can't yet perform on the list (it's the original from the Shuttle's Crew manual), so we're good to launch as soon as engines ignite. | ||