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''--prop:/mission/filename=sts1.xml'' | ''--prop:/mission/filename=sts1.xml'' | ||
=== Entry guidance algorithm === | |||
A topic speaking about the entry guidance algorithm. | |||
'''Documentations''' | |||
I didnt use hyperlinks to avoid NASA ntrs server spam from forum robots | |||
*A quick overview of the Descent guidance from the Space Shuttle Technical Conference: ''ntrs.nasa.gov/citations/19850008593'' | |||
*A deeper look into the Entry equations formalism with that paper that you might find under: ''Shuttle Entry Guidance JSC-14694 '' | |||
*Entry guidance formulation requirements (code): ''ntrs.nasa.gov/citations/19800016873'' | |||
All the documentations linked in the Entry/TAEM rework are even more useful now, as almost all the parts of Entry guidance are simulated and displayed parameters fed with consistent datas. | |||
https://forum.flightgear.org/viewtopic.php?f=87&t=38777 | |||
'''Overview''' | |||
A short sum up of the main guidance points explained in the former links | |||
First thing is to convert some Geodetic coordinates into Runway frame coordinates to have an accurate distance to runway threshold through the Heading Alignment Cone; and correct Delta Azimuth to the HAC tangency point. | |||
[[File:Entry frame.webp|600px|thumbnail|none]] | |||
It is done through a targeting routine that will update at every guidance computation frame (1.92s) some parameters. | |||
Main outputs will be Range to Treshold Aimpoint and HAC entry point Azimuth Error. | |||
[[File:Entry functions.webp|600px|thumbnail|none]] | |||
Then will come the entry guidance sequence. A bunch of functions that will output a Commanded Angle of Attack and a Commanded Bank that will then go to the autoPilot loop. | |||
[[File:Entry guidance sequence.webp|600px|thumbnail|none]] | |||
*'''EGSCALEHT''' function generates a constant that will be used to calculate the Reference attitude rate term. It corresponds to the H dot ref term that can be seen in the Entry display | |||
[[File:Entry hdot ref display.webp|600px|thumbnail|none]] | |||
[[File:Entry scale height.webp|600px|thumbnail|none]] | |||
*'''EGINIT''' function resets runway dependant parameters to their nominal values in case of Runway Redesignation. | |||
*'''EGCOMN''' function calculates parameters that will be used during the whole entry (targeted Drag, Total Energy, Hdot reference for Entry display, etc) | |||
*'''ISELECT''' and subsequent functions (EGPEP to EGTRAN) calculate specific parameters depending of the Entry phase. | |||
There are 5 different phases with different transfer logic between them depending of Shuttle Energy (High Energy / Nominal / Low Energy Entries) | |||
IPHASE 1: Preentry opened loop until a drag of 3ft/s² is reached. | |||
IPHASE2: Temperature control (aim there is to avoid to burn the Tiles) | |||
IPHASE3: Equilibrium glide | |||
IPHASE4: Constant Drag (Nominal drag targeted there is 33ft/s² for a smooth deceleration) | |||
IPHASE5: Transition (Below 10000 ft/s, transition from high AOA to lower AOA with flight path increasing). | |||
[[File:Entry guidance sequence logic.webp|600px|thumbnail|none]] | |||
Entry profile is shaped to target an i-loaded constant drag around 16000 ft/s (33ft/s² for a nominal Entry) | |||
[[File:Entry profile.webp|600px|thumbnail|none]] | |||
Those different phases might also be identified through the Entry display layout: | |||
[[File:Entry dps display.webp|800px|thumbnail|none]] | |||
*'''EGALPCMD''' function computes the Angle of Attack to be flown. | |||
Profile that was flown is a 40° AOA until 12000 ft/s ish where the AOA starts to ramp down to reach 15° (Max L/D AOA) at TAEM transition. | |||
[[File:Entry_alpha_commanded.webp|600px|thumbnail|none]] | |||
*'''EGLODVCMD''' calculates the Lift over Drag (L/D) ratio to be flown. | |||
L/D ratio to be flown is based on a reference ratio (L/D zero) which would represent our L/D ratio if we were perfectly on the targeted drag profile. | |||
Corrections for drag and vertical speed errors are added to bring us back on the path in case of deviations. | |||
*'''EGGNSLCT''' calculates f1 and f2 factors (error gains) | |||
[[File:Entry_error_gain.webp|600px|thumbnail|none]] | |||
*'''EGROLCMD''' function converts the commanded L/D ratio into a commanded bank angle to have the correct deceleration. It takes into account the Angle of Attack modulation in case of small drag correction initated by a slight change in AOA. | |||
Reference Bank ( no Drag and Hdot errors) and Commanded Bank are visible in Entry display page. | |||
[[File:Entry_bank_commanded.webp|600px|thumbnail|none]] | |||
'''Some specific point concerning TAL entry''' | |||
To avoid too high temperature during first dive into the atmopshere, Alpha will be increased to 43° | |||
[[File:Entry_tal_alpha.webp|600px|thumbnail|none]] | |||
It decreases the temperature from 3100° to 2800°F during the first part of TAL entry | |||
Once the first pullout is gone ( vertical speed above -400 ft/s), normal alpha schedule and alpha modulation are brought back | |||
[[File:Entry_tal_alpha_mod.webp|600px|thumbnail|none]] | |||
After that huge dive into the atmopshere with a peak in Drag, entry guidance converges towards a more nominal entry trajectory | |||
[[File:Entry_tal_drag_spike.webp|600px|thumbnail|none]] | |||
== Avionics and DPS == | == Avionics and DPS == | ||