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Flying the Shuttle - Entry: Difference between revisions
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As soon as guidance is active, the FG native HUD should show a few new figures, among them the distance to destination. | As soon as guidance is active, the FG native HUD should show a few new figures, among them the distance to destination. | ||
Now, let's take a minute to consider our situation. The red trajectory line is a ballistic trajectory, and it's endpoint is where the Shuttle would hit the surface <i>if there wasn't an atmosphere.</i> Since there is an atmosphere however, we may end up somewhere else - which is the whole point of entry trajectory control. | |||
Since the Shuttle is an aerodynamical object, it can (within limits) control its lift and drag and thus change the trajectory (shorten, lengthen or extend laterally) around the ballistic impact point - by a good 1085 miles in fact (that's technically known as 'cross range capability'). So we will aim such that the actual point where we hit the lower atmosphere is some 60 miles away from Vandenberg (at which point TAEM guidance takes over and this tutorial ends). | |||
* We have a few minutes time before we really reach the dense atmosphere, so we can configure the cockpit to our needs. Bring up a DPS screen in GNC mode (it should show the ENTRY TRAJ 1) before you, next to it the PFD might be handy, and the APU/HYD and the SPI displays to your right. You may find the information from the FG-native HUD useful, though if you want to be realistic, switch the layer off (before you do so, check that the DAP selection in the upper left reads 'Aerojet' - if not, you'll be in big trouble...) | * We have a few minutes time before we really reach the dense atmosphere, so we can configure the cockpit to our needs. Bring up a DPS screen in GNC mode (it should show the ENTRY TRAJ 1) before you, next to it the PFD might be handy, and the APU/HYD and the SPI displays to your right. You may find the information from the FG-native HUD useful, though if you want to be realistic, switch the layer off (before you do so, check that the DAP selection in the upper left reads 'Aerojet' - if not, you'll be in big trouble...) | ||
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To the upper left of the leftmost panel, at the edge of the console, there's four pushbuttons. The upper two change select CSS or AUTO for the pitch channel - change the selection from CSS to AUTO and verify that the button lights up. The Shuttle will respond by automatically pitching up to about 40 degrees. | To the upper left of the leftmost panel, at the edge of the console, there's four pushbuttons. The upper two change select CSS or AUTO for the pitch channel - change the selection from CSS to AUTO and verify that the button lights up. The Shuttle will respond by automatically pitching up to about 40 degrees. | ||
The purpose of this is as follows: During entry, thermal protection requires that we turn the blunt end of the Shuttle into the plasma stream. This translates into a rather strict Mach-dependent AoA requirement - for instance at Mach 23 we <i>must</i> fly 40±3 deg AoA or we'll burn and break up. Setting the pitch channel to AUTO makes the flight computer control AoA very precisely - which gives us the room to worry about trajectory control. | |||
Of course, that means that all we can control is the roll channel, so we need to use that. | |||
* Now wait and see - you can use the native HUD to see range to site decrease and vertical speed increase - we're soon dropping with more than 100 m/s. When range is some 2100 miles and vertical speed above 150 m/s, you should start to see the Shuttle symbol appear on the entry trajectory display: | |||
[[File:Entry tutorial03.jpg|600px|Entry tutorial 3]] | [[File:Entry tutorial03.jpg|600px|Entry tutorial 3]] | ||
This is a display of remaining range (x-axis) versus velocity (y-axis) - be warned, there's no altitude shown on this display! Moving left means you're closing with the site, moving down means you're slowing down. | |||
For the next minutes, one important thing to monitor is whether we're above or below the line - if we're above, we are too fast for the remaining range and need to slow down more, if we're below the line we're too slow and need to brake less. | |||
The second important quantity is ΔAz - the azimuthal offset to target. If it is zero, we're headed right towards the landing site, if it's not zero we're aiming past it. For a perfect guidance solution, we want the Shuttle to move right down the line and keep ΔAz between -10 and 10. | |||
[[File:Entry tutorial03a.jpg|600px|Entry tutorial 4]] | [[File:Entry tutorial03a.jpg|600px|Entry tutorial 4]] | ||
[[File:Entry tutorial04.jpg|600px|Entry tutorial 5]] | [[File:Entry tutorial04.jpg|600px|Entry tutorial 5]] | ||