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Flying the Shuttle - Entry: Difference between revisions
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== How it feels in FG == | == How it feels in FG == | ||
Since the Shuttle is pitched up most of the time, you don't see much except the HUD during the entry phase. | Since the Shuttle is pitched up most of the time, you don't see much except the HUD during the entry phase. Make sure the entry DAP is engaged when reaching entry interface - as the Shuttle is not aerodynamically stable in the yaw axis during entry, this needs to be agressively managed by the yaw jets. | ||
Important HUD readings to monitor are pitch and roll angle, nose temperature, vertical speed, Mach number and acceleration. | The next thing is to activate the guidance computer. If you adjusted your starting position / deorbit burn such that the groundtrack intersects with a landing site, you can select the site and activate the computer - guidance information will then be displayed in the lower right part of the HUD. At the same time, you can monitor the predicted trajectory on the map. If the computed ballistic impact point is close to the landing site, the entry is flyable (note that due to the cross range capability of the Shuttle, there's a significant margin for deviation, so the ballistic end point does not need to be perfectly aimed). | ||
This is how a guidance solution for an entry to Vandenberg looks like: | |||
[[File:Shuttle-landing01.jpg|600px|Groundtrack map and entry guidance computer for the Space Shuttle]] | |||
Important HUD readings to monitor are pitch and roll angle, nose temperature, vertical speed, Mach number and acceleration and pf course the guidance information in the lower left. The guidance information includes range to target, current deceleration, deceleration needed to reach the landing site, azimuthal deviation to target and deviation from ideal AoA. | |||
Pitch up and wait for the atmosphere to grab the shuttle. This will be felt initially by a very slow drift of the attitude, trying to reduce pitch. Apply thrusters to keep the nose up. The thrust level needed to hold the 40 degrees will increase with increasing qbar, and eventually the controls will revert to aerodynamical surfaces for roll (qbar = 10 psf) and pitch (qbar = 20 psf). The steering characteristics changes quite drastically - initially it is probably easier to make minute thruster adjustments with the keyboard, in the later phase a stick or mouse is a much better option. | Pitch up and wait for the atmosphere to grab the shuttle. This will be felt initially by a very slow drift of the attitude, trying to reduce pitch. Apply thrusters to keep the nose up. The thrust level needed to hold the 40 degrees will increase with increasing qbar, and eventually the controls will revert to aerodynamical surfaces for roll (qbar = 10 psf) and pitch (qbar = 20 psf). The steering characteristics changes quite drastically - initially it is probably easier to make minute thruster adjustments with the keyboard, in the later phase a stick or mouse is a much better option. | ||
Once the Shuttle is under aerodynamical control, watch descent rate slow and reverse. Once the rate comes back up to about -50 m/s, you can initiate the first careful high-bank roll. Do it gently in order not to lose the AoA! Watch the response of nose cone temperature and acceleration and the slow drift in course. The descent rate will fall again, don't let it fall too fast, or you'll get too hot. Allow for some lag, get a feeling for how the trajectory responds to what you're doing. This is actually piloting, and you can influence a lot of what is happening here. | Once the Shuttle is under aerodynamical control, watch descent rate slow and reverse. Once the rate comes back up to about -50 m/s, you can initiate the first careful high-bank roll. Do it gently in order not to lose the AoA! Watch the response of nose cone temperature and acceleration and the slow drift in course. The descent rate will fall again, don't let it fall too fast, or you'll get too hot. Allow for some lag, get a feeling for how the trajectory responds to what you're doing. This is actually piloting, and you can influence a lot of what is happening here. Once deviation to target azimuth exceeds 10 degrees, do a roll reversal. | ||
Monitor Mach number and altitude decrease, | Monitor Mach number and altitude decrease, reduce pitch angle later in the flight as commanded by the guidance computer. Around Mach 3.5, you should finally get the rudder back with RCS jets switched completely off, at which point the Shuttle definitely feels like an aircraft. It can now actually change course and turn, although still sluggishly. Steer the course towards the landing site if you're close. Aim for TAEM interface of 85.000 ft, Mach 2.5, around 60 miles before the runway. Don't try to brake too fast, as the manual has it: | ||
<i>It is better to arrive at TAEM interface with too much energy than without wings.</i> | <i>It is better to arrive at TAEM interface with too much energy than without wings.</i> | ||
(NASA has a sense of humor...) | (NASA has a sense of humor...) | ||
== Further reading == | == Further reading == | ||