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Flying the Shuttle - Launch: Difference between revisions
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[[File:Launch tutorial03.jpg|600px|More useful information]] | [[File:Launch tutorial03.jpg|600px|More useful information]] | ||
There's plenty of useful information displayed here, all items worth monitoring during ascent marked with red dots. While the Shuttle displays velocities in ft/sec and orbital altitudes in miles, you may find the option of getting some parameters displayed in metric units helpful (if you have a science background for instance). | |||
In particular, this layer is the only way you can currently monitor orbital inclination, apoapsis, periapsis and dynamical pressure at the moment, so if you're launching manually into a particular orbit, you need this information. | |||
* Okay, we're good to go. When you feel ready, move throttle to full. In real life, the Shuttle's engines would be ignited by remote command from mission control, but we have to work this in a different way. Make sure you really move throttle to full - if the engine controllers do not detect > 90% thrust three seconds after ignition for all engines, there will be a launchpad abort. | |||
You can actually watch the show from outside by using tower view. If you've done everything according to plan, the SRBs ignite three seconds after the main engine, and at that point Atlantis lifts off. | |||
[[File:Launch tutorial04.jpg|600px|And... we have liftoff. Atlantis is on her way!]] | [[File:Launch tutorial04.jpg|600px|And... we have liftoff. Atlantis is on her way!]] | ||
[[File:Launch tutorial06.jpg|600px| | * If you stay in-cockpit view, what happens next feels and looks decidedly weird - as soon as the (currently not modeled, you remember?) launch gantry is cleared, the orbiter rotates and yaws to get onto the launch course, and then pitches down into inverted flight. That's right, you ride into orbit head-down. | ||
[[File:Launch tutorial05.jpg|600px|Punching through the cloud layer]] | |||
One of the main reasons is the wing bending moment. While in terms of thermal stresses, entry is far more dangerous than launch, in terms of forces acting on the frame, launch is a good factor two more serious. If we would launch in upright position, the wings would be ripped off cleanly. The lowest stress on the wings occurs for negative AoA, so we pass the region of max. qbar (i.e. highest aerodynamical stresses) at the optimum alpha for the wings. | |||
There are other reasons to keep the attitude later - one of them is in the event of a PFD failure, you have visuals of Earth early on in inverted flight but not in upright attitude. Another reason is keeping a direct com connection to mission control for as long as possible. | |||
* Okay, enough with sightseeing. Some 30 seconds into the flight there should be a callout to throttle down (that's as qbar peaks somewhere close to 700 psi - you can monitor it on the native HUD layer). The engines get throttled down to relieve the stress. | |||
Look at the engine status. | |||
[[File:Launch tutorial06.jpg|600px|Engine status]] | |||
The lower right shows chamber pressure of all three main engines. During max. qbar they get throttled back, otherwise they should show (at least) 100% of rated power. In the case of an engine loss, it's possible to throttle the remaining ones up to 109% of rated power via the override display, but perhaps let's just not try this right now. Above are helium regulator and storage tank pressures. What's that for? | |||
The Shuttle's main engines use a pre-burner to drive the turbo-pumps which bring the fuel into the combustion chamber. But that means that liquid oxygen and hydrogen are on the same turbine shaft at some point - if they ever get in contact, the engine explodes. To avoid that, the gap is purged with high-pressure helium while the engine is running. So the depletion of helium tells how long the engine has been running, and if the regulator pressure ever drops into the red, the engine needs to be off immediately or you might lose all three. | |||
Right now, everything should be nominal, and you should see the engines throttling up to full rated power just after max. qbar is over, and then slowly pitch down further. | |||
* Let's take a look at the ascent trajectory: | |||
[[File:Shuttle avionics ascent1.jpg|600px|ASCENT TRAJ 1 display of the Space Shuttle]] | [[File:Shuttle avionics ascent1.jpg|600px|ASCENT TRAJ 1 display of the Space Shuttle]] | ||
This is a plot of ground-relative velocity vs. altitude. The Shuttle is the yellow triangle climbing along the line, and there's a predictor which tells us where the Shuttle is expected to be 20 seconds from now - if there's no change in attitude or thrust. | |||
That's important when flying manually. The Shuttle reacts very different from an airplane, which responds to changes almost instantaneously. Launch is a near-ballistic trajectory - if you have a large velocity component, say, upward, you'll go upward no matter how you maneuver for a minute or two, and anything you do right now will be felt afterward. So you need to know what the Shuttle will do if you do nothing for the next minute to know what you should be doing. | |||
It'll become clearer in a minute. As the triangle climbs to the upper edge of the line, you can switch to outside view and watch the SRBs separating. If you can't run 300+ km visibility in FG, this would also be a good altitude to switch to Earthview orbital rendering. | |||
* After SRB separation, the ascent trajectory display changes to this: | |||
[[File:Shuttle avionics ascent2.jpg|600px|ASCENT TRAJ 2 display of the Space Shuttle]] | [[File:Shuttle avionics ascent2.jpg|600px|ASCENT TRAJ 2 display of the Space Shuttle]] | ||
What's the state of the spacecraft now? The SRBs are very powerful devices, we've been rising with close to 3 g for two minutes. Now they're gone, and the remaining thrust is not even enough to hold the Shuttle with the near-full ET against gravity. But it doesn't need to, we're climbing with almost a kilometer per second vertically. Even if we had no thrust, we'd go above 100 km altitude now. | |||
[[File:Launch tutorial08.jpg|600px|Launch tutorial 1]] | [[File:Launch tutorial08.jpg|600px|Launch tutorial 1]] | ||