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23-12
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pcnsatc for thc imbact of limitcd rcsolution in the
torque commands as wcll as unknown iotcrnal
whcel friction torque. contribution of cross-axk
aogular momcntum components and cxtcrnd disturbaocc
torques undcr eclipse conditions, a rnodel
following loop is incorporated to match the
wheel control torqucs to thc corrrcct valucs. This
tcchnique as used for closed loop AOCS dynamic
knch testing with red hardware at DASA is well
provcn. In vicw of tbc fact that in thc whcel control
conccpt in qucstion hcrc the whccl spccd
variation cxcccds thc usud rmgc considcrably, a
nonimcar friction torqac compensation loop is
additionally superimposed. Iqordcr 16 imprtwc thc
pointing accuracy and stability to the lcvcl rcquired.
disturbancc torquc cstimation and cornpcnsalion
is applied. Thcsc cstimatcs Curt hcrmorc cnsiirc.
that thc necessary yaw attitudc prctliction accuracy
during cclipsc p:issagc is achicvcd.
Stcllar-inertial attitude rcfcrcncc gcncration tvhcn
using r;itc intcgnting g~osc(ipsc in str:ip-down
mode and updatcs from &yo drift Lornputcd by
onho;ird Kalmm liltcr usiny obscncd star transit
times h;is to rcly on upto-d;itc satcllitc cphcmcris
and rclcrcncc star catdog data storcil in thc onhoard
computcr. Thcsc data haw to hc pcriodic;ilIy
uplinkcd togcthcr with corrcctions of the onboard
timc rcfcrcncc. A typical cxamplc of ;I star idcntification
pattcrn ovcr a period of 12 min. ;:s Tor instance
cncountercd during ROSAT mission in sun
modc is shown in fig. 4.4-2. lo wsc nf largc payload-induced
disturbancc torques feed-fonvard control
has to be applied to ensure thc ncccssary
pointing stability for high performancc missions.
JS Prcliminnry AOCS hs.c und I'ower Budget
For th; AOCS conccpt and implcmcntation appro-
ach outlined abovc preliminary mass and powcr
budgcts for thc individual I-LW-itcrns ha\v bccn
summarizcd in tablc 45-1. Assumins th:rt ftir 1
particular mission r.01 all but only the necessary
equipment will simultancouslv be intcgratcd into
thc SIC (31 principly thc locations indicatctl in tig.
4.1-2) the total AOCS budpcts for rcspechc application
C~SCS can be composed.
For typical mass of a propulsion systcm dcpcnding
on thc totd LnpuL~c to be provided rcfcrcnce is
made to figure 3.2-2. The burn-out mass including
12 four Newton bipropcllmt thrusters. tank. piping,
residual Helium in a blow-down sysfcm amounts to
approldmntcly 18.5 kg.
5. CONCLUSION
On thc basis of morc than 29 years of cxperience in
AOCS dcsign and development for communication-
and application SIC in the papcr undcr discussion
here the attempt has been made to identify the
configuration, the cquipmcot and tcchnology of rn
AOCS, which cm provide thc necessary flexibility
for :,crving the large variety of TACSAT mission
objcctives ond the associatcd performance requirc-
mcnts.
6. LIST OF REFERENCES
I.R.Wcrtz: "S/C Attitude Dctcrinination and
Control', Kluwcr Acadcmic Publishcrs, 1378
DASA-Study: "Networking Rcquircmcnts for
Uscr Oricntcd LEO Satcllitc Systcms"
ESTEC Contract No. 973U!VNURE
E.W.Mowle ~1.31.: "The LANDSAT-6 Satclii-
IC: An Ovcrvicw", IEEE AES Systcms Majy.inc.
June IWl
H.Bittncr ct.31.: "Thc Attitude and Orbit
Dctcrmination and Control Subsystcm of thc
INTELSAT V Spacecraft". EFA AOCS -
Conicrcncc, Noorclwijk, i977-ESA SP- 1 W
H.Bittncr c1.d.: "The Attitudc and Orbit
Control Subsystcm of thc TV-SATTTDFI
Spacccraft'. Proc. of thc 9th IFAC Symposium
on Automatic Control in Spacc, Noordwijkcrhout.
July 5-7, 1982
W.Schrcmpp et.al.: "Design and Tcst of the
ROSAT-AMCS'. IFAC 10th Tricnneal World
Conycss. Munich. FRG. 1987. pp 81-NI
P.Bourg etd: Thc Attitude Measurement
and Control Systcm of EURECA". IFAC
10th Tricnncd World Congress. Munich.
FRG. 1987. pp 49-56
H.Bittncr ct.al.: 'The Attiludc and Orbit
Control Subsystcm of the DFS KOPERNI-
KUS'. lOth IFAC World Congress. Munich.
I9R7,
H.Bittncr ct.aI.: 'The Attitudc and Orbit
Control Subsystem of thc EUTELSAT-2
Spacccraft', 11th IFAC Symposium on Auto-
matic Control in Spacc. Tsukuba. Japan. July
1989
MSuraucr c1.d.: 'Advanced Attitudc- i d
Orbit Controi Concepts for 3-Axk-Stabilired
Communication and Application S;itcllitcs".
12th IFAC Symposium on Automatic Control
in Acrospncc, Scpr. 7-11. 1392. Ottobruno.
GcrlDWl;