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contains thc H/w systcm configuration data
,and dynnaric S/W pcuamctcrs
- Prccisiou Clock Module (PCLK)
. Powcr Converter Modules (PCV)
provides necessary voltages for the OBCU
modulcs
provides central on board reference time
countcr
Sofnvarc
Thc complctc AOCS and related DMC-sofdvarc
(SIW) will bc cxccutcd in thc redundant ICDS-on
board computer and runs fully automatic and
autonomously under normal circumst:inccs.
Bcfore thc mission. the S/W will bc (prc-) stbrcd
in the PROM and copied into the RAIM ;iftcr.itk
first activation in the orbit. This allows modiii+.
tions - ;is fat as thc 3ppticatii)n SAV is concertrcd -"
;it any timc via tclccomrnands ("mcmorv load'). It
is also possiblc to adapt important svstcm t,hlcs
and the S/w configuration from ground.
Telcmctry and tclccomrnand S N parts arc iniplc-
mcntcd according to thc Est\ "standard p;ickct
TMITC'.
A ccntrai rolc within thc on hixird S/W plavs ttic
XtOSES I t operating systcm, an updated vcrsion of
thc MOSES opcrating systcm uscd in thc shuttlc
pallet satcllitc (SPAS)-progsm. It is cspccidlv
dcsigncd for the I
- managcment of piudlcl proccscs and ;is!chro-
nous cvcnts under rcal-timc conditions
but can also meet the requirements of
- strictly synchronous operation modcs. e.g. sen-
sor data acquisition activation of thc UPS.
The maintainability and adaption capability of Ihc
SflV-systcm ncccssitatc J transparent modular
functional structurc. hicrarchichlly oruanixd and
properly dcfincd intcrfaccs not only within thc
opcration system. but also to the application S/W
modulcs.
The application SN-parts (johs arc dividcd into
one or scvcral tasks. Additiimallv, ihcrc arc spc-
cific error tasks. which can be att;ichcd to a
jobltask. Thcy will bc activated automaticailv by
the opcrating system in cast of a failurc (exception
handling),
4.4 Attltudc- and Orbit Control Loops
4.4.1 Acquisition connol
Bemuse of the short visibility periods of low carth
orbiting S/C from individual ground stations onbo-
ard autonomy of fundamental opcrational functions
is cxtremeiy important. Automatic acquisition,
reacquisition and safety procedures ensuring initial
orientation and S/C survival (power & thcrmai
conditioning) ia case of attitudc loss arc such fun-
damental functions. Classical, well proven concepts
consisting in a rcoricntation of a prcfcrrcd S/C axis
(and the active surfaces of thc solar arrays) to the
sun are dso applicable hcrc and will lhcrefore not
be discussed in dctail (see e 5. refs. 4 to 10).
5.52 On-orbit conrml loops
23-1 1
In classical satcllitc attitude and orbit control conccpts
clcar distinction is made bctwcen attitudc
control during orbit correction maneuvers and in
normal rrrodc (NM), thcsc modcs of operation
employing csscntially diffcrcnt control principlcs
(c.s. rcaction jet control and kW1 wheel control).
For the ICDS concept under discussion hcre ;i
common control approach is regardcd supcrior.
The mcst obvious advantagcs arc:
- lnhcrcnt back-up c:ipabilitics uing diffcrent
types of actuators if rcquircd.
- Modular 3wis attitudc mcasurcmcnt cstimation
-
and rcfcrcncc ycncrntion principle throughout.
Smoot h transitions bctwccn diffcrcnt operation31
conditions due to continuous statc propagation
of cstimation and control vafiablcs.
- Activation of combined actuators c.g. for fccd-
forward cornpcnsation in case of hcavy prcdicta-
ble (payload) disturbanccs
A schematic blockdiagram of thc on-station attitudc
control modc is shown in fig. 4.4-1.
Thc raw srnsor data from sun scnsors and earth
scnsors (in casc of low accuracy pcrformancc mis-
sions) or star sensors and ratc intcyntinp: gyros for
high pcrformoncc mission3 arc procc.zscd to'gcncra-
te attitudc information (I$*, 8'. 9'). Based on
systcm modcls orbit paramcler updatcs from
ground and additional mcasurc:ncnts (whccl
spccd), optimal cstimatcs nf systcm statc variables
H, (prop. ~r), E!, (prop. 4). e. w,, U,. (w., prop.
U,), H., H, and 8 are gcncratcd. In application
cascs. whcrc attitudc rcfcrcncc is gcncratcd from
earth and sub scnsors onlv. during cclipsc rcpions
yaw attitudc is propagated by means of the obscrvcr
equations of tbc angular momentum in orbit
coordinates Jupprcssing the nutation by adequate
fdtering.
Under normal modc conditions attitude stabilizaticrn
is pcrformcd by controlling the flywheel and
rcaction whcels in torquc mode. in order to com-