The effects of winds, sideslip angle feedback, and the data reference (air or inertial) on the Reaction Control System (RCS) propellant requirements during entry were investigated. It was determined that in the presence of a 3 sigma crosswind an addition 188 pounds of RCS propellant was required for entry control which is within the present 200 pound allotment for winds. The absence of air data information does result in slightly higher RCS propellant demands

Devall, O. R.

English

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https://ntrs.nasa.gov/search.jsp?R=19760020269 2020-03-22T14:49:07+00:00Z
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C3 u	 E';Tf;Y REACTION CO'ITROL SYSTC'! PPGPELLA'lT ANALYSIS
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This desi gn note r'oeurents an analysis which investinated the effects
of rinds, sidesli p an g le feedback, and the data reference (air or inertial)
on the Reaction Control System (RCS) propellant requirerents durinq
Entry. It was deterrined that in the pr.isenee of a 3 a crosswind an
additional 1' 11 Pounds of RCS propellant vas reni;ired for Entry control
which is within the present 2111 0 pound allot-ent for winds. The ahsence
of air data inforration does res^,lt in slightly higher RCS propellant
derands.
This analysis ti-as conducted under contract ';unber ';AS 0 -13070, Task
(Irder "urber ('0211.
2.f) MTROMICTIO'c
The present haseline control syster utilizes anrile of attack (a ),
sideslip an g le (" ), and hank anr7le (7) feedback data in controlling
i	 the Orbiter during Entry. There has been sere concern; in using u
feedhacl: in the prisence of a crosswind without the benefit of air
data infcrration.	 A. 3 measurement derived from the inertial system
will not have any knowled;e of the wind. Under this condition a ? feedback
controller normally requir-2s additional p ropellant to maintain an
angle relative to the wind. This analysis triefly investigates this
phenomenon and the resulting propellant requirements in a wind environment
durin g
 the Entry flight regime.
3.0 DISCUSSIO'i
The data presented in this discussion were obtained from the SpacA
Shuttle Functional Sir^ulator (SSFS), Reference (1) and Referrnce (?).
The Guidance and Control (G°,C) for this analysis were the ?0.5° constant
an gle of attach: guidance, Reference (3), and the RockVrell International
(P.I) Syster X Entry FCS, Reference (4). Finure (1) is a blocs: dianrar.
of the RI S.-ster X Entry FCS. The sideslip angle feedback, depicted
in Figure (i) as 3 , is utilized in the lateral-directional channel
fror the initiation of the Fntry fli qj ht phase to a dynaric p.essure
((a) of 2 q . Lb/Ft?
 to aid in hank angle naneuver coordination.
ORIGINAL PAGE 15
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This analysis consisted of four runs fc, • the sar •e entry initial
conditions. The Orbiter was initialized with a vehicle latitude
and longitude of ).?° and 17.2 4 , an airnurt iatiVide and longitude of
0.0° and -121.567°, and a heading of ISM*. These initial coni!itions were
selected h^_, cause the '.rind p rofile used for this anal ysis would basically
produce a cross-And ef fect. A X-axis and Z-axis center of
gravity offset of M inches and a 'r-axis center of gravity
offset of 2.2.P inches were used throu ghout the analysis.
AVEH5, GPAV3, RCS1r, , "1ASS?-). A.ER021, and ACS12 are the SSFS
math rodels which are cor7on to each rirn. '.'?!:rF is the grind
profile rath yodel; and it is shown in Fi g ure (2). Details of
all the math models can be found in feference (2).
4.0 PE511LTS
The RCS on-time and propellant required were r!onitored for each
run and tabulated in Table (1) and Kahle (2), respectively. In
Table (1) cn-tire is the surrration of the US firing durations
about the roll, pitc;r and yaw axis. Propellant required in Table
(2) was cc — uted assumin g that each thruster produced 375.1
pounds of thrust and that the specific impulse was 2f9.0 seconds.
P-in (1) is th Q no wind case with the baseline FCS and resulted in
a total PCS propellant requiter-ent of 51M pounds. Run (2)
is ieentic3l to the first run except a crosswind ,.as applied. In
the second run perfect .air data kncwledge is assumed. This run
required a total of 720.3 pounds of RCS pro pellant. The disturtance
created by the ~rind required an additional 1"".3 pounds of propellant.
This is loner than the 200.0 pound allotment for ~rinds (!urine the
Entry flicht reg ire hilt not significintl-v l3wer. This 210.6 pound
allotrent may be rlarrinal or ever, inadequate since preliminary
results indicat,2 that the latest baseline Entry autopilot, Reference
(5), requires r'ore	 propellant for ccntrrl than the autopilot
used in th<s analysis.
Run (3) is the care as Run (2) except the SSFS was codified to delete
air data kno.rledge in obtaininn sideslip, Lank a:.(-1e and annle of
attack irforration. The propellant consumed at ';:i)0.1 seconl1s, flicht
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Lire prior to the ouidance han!. cerranc!s (!urin^ the Entr y transition
phase, indicates that thore is onl y a sr-,ill difference between the
propellant reeuired with or trithout air data inforration. Phis
alrost identical pro pellant usage results because a washout filter
processes the f. fee, ;)aci; signal (see FietirP (1)) . 'lithout air data
knowleOne the ; derived from the inertial syster does not allow the
vehicle to weatherrncl', into the wind and thus causes the vehicle
to -aintain an anolr relative to the wind. without the washout
filter Vie Orbiter would require propellant to raintain this angle
relative to the rind. However, this anole essentially has a
steady state val ue and thus its effnets are cancelled by the was!'out
fit t^r.
^uri nn the tra p : i ti r+n phase of the F,.,.ry fl inht regire the rrbi ter
is acquirin g a tan gency point on the TAE'! alignrent circle. :lithout
air data knotil(c!re the vehicle is tr y inn to fly a direct heading
to t'e T .	 ali-nt-mt circle but is continually ! einn pert-ir'Led ;'y
the wi rd. Thi s requires rorr_ tsar!: ccrrand than the run wi t) air
data knowledge where the vehicle weathercocks into the mind. These
additional hank corT'ands requi reJ aporoxiria tely 10.0" 	 RCS
propellant.
Run (") is identical to tun '3) except the sideslin feedback is deleted
initially rather than at tite norinal dyn^ir- • ie pressure switch point
of 20.0 pounds/square foot. .,ith tic sicir^slip angle uncontrolled
any cnar---^ in sic'eslip is reflected in the rnll axis and is darped
cut by the roll jets. This additional disturbance is reflected in
ar increase in roll axis propellant remiirer.ent tip to a dvnaric
pressure of 10. g pounds/square foot where the roll jet cor-r-ands are
zeroed. There is no additional increase in propellant r,^quirer•.ents
until the latter part of the Entr y flirht. This can be seen by
corparing the IFM .O second tine point for Run (3) and Run (4).
Again as in %n(3) the absence of air data knowledr;e re,mired
rore bank corrands than Run (2) during the transition phase and
resulted in higher RCS propellant utilization.
ORIGINAL PAGE IN
OF PUUk QUAL!'I'`;
I ' -:	 _
Page £; of
5 .0 CONC L USI')"
Several conclusions can be derived from this brief anal ysis. The
orininal assurption, that the deletion of the an gle of W.eslip
feedback would res :,lt in a PCS propellant S;vin r;s, was sho, .n to he
invalid because the washout filter in the .0, control loop tends to
cancel the effects of any steady state sid-kislip angle.
Winds can sirnificantly increase the RCS propellant requirerlents
during the Fritry flight rp--ire. Although this analysis indicates
that the 2111.11 pound propellant allotr-cnt for winds is sufficient,
there is sere question that this allotrent will be sufficient ,with
the latest baseline Entry autopilot.
The ahsence of air rata inforration for sideslip, bank: annle
and annle of attack resulted in an additional propellant cost
of approxirately l n .^' due to the increase in renuired hank
naneuvers during the final Entry phase prior to THEM interface.
6.0 PEFE' DICE S
1) S pace Shuttle Functional Sirulator Ennin per/Prorramrer i'ser's
Guide (EXEC b) Revision 1, Lockheed Electronics Cor,:pany, Inc.,
Report %riber LEC-0172, dated fu nust 1914.
2) Space Shuttle Functional Sirulatcr, Environrents Revision
C, JSC Internal "ote JSC-^6- 726, Volume III, dated October 1974.
3) Space Shuttle Functional Sirulator Entry Guidance Update,
Lockheed Electronics Ccrr,any, Inc., Report Number LEC-4161,
dated July 1174.
G) Pockwell International System X Control Systen, Lockheed
E1 , ctroni cs Cor-pany, Inc. , Report Nurber LEC-1731 , dated
anuary 1974.
5) Breckenridge, P. A. ;i'FS Irpler:entatir- of the "unust 12, 1^]^
Version of RI Sys'er X Entry 0AP, Lockheed Electronics Corpany,
1 011C., Report 'lumber LEC-4"6-2, dated October 1974.


Entry reaction control system propellant analysis. Flight control integration

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