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Space Shuttle Navigation: Difference between revisions
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== Area navigation == | == Area navigation == | ||
The point of area navigation is to guide the Shuttle accurately through the final entry phase and terminal area energy management (TAEM) onto the runway. | |||
During the high thermal load phase of atmospheric entry, the Shuttle is enclosed by a plasma sheath which blocks all communications, i.e. neither state vector uplinks, nor GPS information nor any radio beacon is available, and it is impossible to deploy air sensors into the hot plasma. During this phase, only altitude can be sensed as <b>drag altitude</b> by using a model to relate deceleration forces sensed by the IMU to atmosphere density given the propagated state vector. | |||
Area navigation starts after the high load phase, with first GPS information becoming available after the communications blackout. At Mach 5, the air data probes can be deployed which supply measured Mach number, AoA and pressure altitude. About 400 miles to landing site, the TACAN receivers start to pick up the radio beacon signal, and during the final approach phase, the Microwave Landing System (MLS) provides glideslope information. | |||
=== Using area navigation in FG === | |||
Unlike Most of the area navigation information is summarized on SPEC 50: | |||
[[File:Shuttle avionics spec50.jpg|600px|HORIZ SIT display of the Space Shuttle]] | |||
The landing site is selected as part of the de-orbit preparation via item 41. Since the Shuttle has rather special navigation requirements, it does not use the normal FG-wide net of radio beacons but special definitions, i.e. like in the real Shuttle, area navigation is only available for a number of selected sites. Currently valid landing sites (including transatlantic abort landing (TAL) sites) with their index are | |||
{| | |||
| index || site || status | |||
|- | |||
| 1 || Kennedy Space Center || regular | |||
|- | |||
| 2 || Vandenberg Air Force Base || regular | |||
|- | |||
| 3 || Edwards Air Force Base || regular | |||
|- | |||
| 4 || White Sands Space Harbor || regular | |||
|- | |||
| 5 || Zaragoza Airport || TAL, currently no TAEM guidance | |||
|- | |||
| 6 || RAF Fairford || TAL, currently no TAEM guidance | |||
|- | |||
| 7 || Banjul International Airport || TAL | |||
|} | |||
Once the site is selected, items 2 and 3 show the available primary and secondary runway choice (and executing the item allows to change the choice). Item 5 shows the associated TACAN channel (which can currently not be changed). | |||
Items 6 and 7 allow to select the intended TAEM pattern from OVHD (overhead) to STRT (straight-in) and to change the aim point from nominal (NEP) to minimal (MEP). Both options should only be used if the Shuttle is low on energy at TAEM interface, for a detailed explanation refer to the crew manual. | |||
The lower portion of the display summarizes the area navigation data sources and their fit into the current Kalman filter, i.e. TACAN azimuth and range, drag altitude and air data altitude and GPS information. The right lower part shows the direct output of the TACAN receivers as azimuth and range where items 34 and 35 can be used to switch from relative to absolute azimuth. TACAN azimuth can be flown after entry guidance ΔAZ is no longer displayed after passing the TAEM interface and before the graphical portion of the display shows the heading alignment cone (HAC). | |||
For the air data altitude, QNH at landing site can be adjusted with item 9. Faulty TACAN receivers can be deselected with items 31-33. | |||
Once some 30-40 miles to range, the graphical center portion of the display shows touchdown point, final approach line and HAC <i> as determined by the current state vector</i>. A corresponding picture of the desired altitude dependent on remaining range is supplied by OPS 305 (VERT SIT) which should be used together with SPEC 50 during TAEM. | |||
[[File:Shuttle avionics ops305.jpg|600px|VERT SIT 1 display of the Space Shuttle]] | |||
Staying on the central trajectory vertically and aiming the trajectory predictors around the HAC horizontally leads the Shuttle right into a good final approach. | |||
Note that the vertical display always assumes that the Shuttle flies the nominal horizontal groundtrack. Once you deviate from the HAC, vertical information is no longer reliable. | |||
In addition, if so desired, the raw data coming from the air data probes (once deployed) is available on SPEC 51 as ADTA roughly in the center of the right column. | |||
[[File:Shuttle avionics spec51.jpg|600px|OVERRIDE display of the Space Shuttle]] | |||