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sensors, gyros) intorporated in the AOCS. the
3-axis stabilization tcchnology fo: transfer orbit
operations aod during (repeated) apogec boost
maneuvers has been established using for the
fist time a died Liquid bipropellant propul-
sion systcm for attitude control, orbit control
and Apogee Boost Maneuver (ABM). Furthcr-
more these SIC arc equipped with a coarse
bodv control and M additional antenna fine
pointing system based on RF-sensing and con-
trol of the TX-antenna beam orientation \k.r.t.
it ground beacon to an accuracy bcttcr thatl 2
0.025 dcg cach axis. Spccial reacquisition don-
ccpts in case of attitudc loss or battcry fa!!urc
(recovcry after ilipsej havc bccn incorpor3tcd.
All attitude mcasurcmcnt. data updatinp. for-
matting, monitorinv, mock scqucncing and
control futctions, cxccpt antenna (struclbral
flcxibilitv) stabilization havc bccn implcmcntcd
in ;I ccnlral. diytd. intcrnallv rcdundant onbo-
ardcornputcr. TV-SAT FM1 had to bc dcor-
bited bccausc onc solar array wing failcd to
deplov in GSO and simultancously hlockcd dc-
ploymcnt of an antcnna rcflcctor. Thc rotut-
ness of the AOCS dcsign upcrating then utndcr
most ahtiorma1 conditions,. was. howcvcr, tin-
intcntioually dcmonstratcd. as wcll as its flc:5bi-
lity offcrcd by in-orbit rcprogamming of thc
onboard computer, whcn for dirfcrcnt attempts
of rescuc maneuvers. additional control modcs
and scqucnccs have been implemcntcd.
DFS-KOPERNIKUS a smaller class S/C family
of different geomctricd conligurat.icn ("rabbitear.
antcnna arrangement. liquid bipropcllant
tanks in ABM dicction) is 3-axk stabililcd in
TO and GSO. the solar arrays being fdlv deployed
drcadv in transfcr orbit and during
(repeatcd) liquid bipropellant Apogce Boost
Maoeuvcrs. For this operational motlc the
AOCS dcsign has to cope with panel oscillations
and proFcUant sloshing phcnorncna in
ovcrlappin): frcqucncy bands. the sloshing dynamics
cxpcriencing pole-zcro inqersion during
thc mancuver. Concepts and provisions for in
orbit gyro calibration have becn.incorporated to
also ensure compatibility with midnight launch
conditions.
As compared to the previous communication
satellite in the EUTELSAT I1 AOCS the follo-
Wiag innovations have been incorporated:
The capability to acquire thc earth MY time
of the day
A S/W safe mode for minimitation of outage
duration in GSO
An optimum Nutation and Angular Momen-
tum Control concept to ensure higher yaw ac-
curacy (as compared to WHECON) io pre-
sence df high disturbace torques (NM row-
yaw control)
The capability to perform orbit corrcctions
with yaw refercnce from gyro, i.c. my time
per day (also io colinearity regions)
High pointing accuracy during station kee-
ping maneuver (SKM) trmsients
In-flight recording of the thruster firing .
history for propellant budget monitoring
3.12 Eodt obseniarion und scientific application
satellites
World wide a lrtrgc variety of IOW carth orbit satel-
lites for all typcs of tcrrcstrial and environmental
obscrvation as wcll as scicntific and research pur-
poses havc hccn dcsigncd. dcvclopcd and lawched
within thc national progams of the rcspcctivc
countries or by intcrnational agencics (c g. LAND-
SAT. SWSAT. SPOT, ERS ctc.). Thcy arc cquip-
pcd with dcdicatcd, optical. infrarcd. multispectral
or microwave payloads, their AOC being tailored
for thc individual requirements. Subsequently a
short rcvicw of thc typical AOCS characteristics of
this type of SIC will be given on thc basis of satelli-
tc examples. the attitudc and orbit control subsy-
stems of which have been developed undcr DASA
rcsponsibility.
Table 3.1-3 gives a rcvicw of these satellites, their
dcvcloprncnt pcriocl and launch schedule. Tablc
3.1-4 summarizes their attitude control conccpts
and performances characteristics
- The AOCS for MOS-1, the fist Japanese Mari-
ne Obscrvation Satellite was designed and dcve-
loped up to and including the levcl of dcvelop-
mcnt model hardware implemcntation and clo-
sed loop subsystcm functional- and performancc
testing in a joint GcrrnidJapancsc development
and training progm. Engineering- and flight
modcl manufacturing and acceptance testing has
then been performed under responsibility of
Mitsubishi Electric Cooporation. The SIC wcre
launched into about 900 km circular sun syn-
chronous orbits. Orbit correction capability (and
back-up wheel unloading) is provided by B set of
hydrazine thrusters. Normal mode control is
performed by two momentum wbecls in V-codi-
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