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tional and storzge capacity aad TM-lwiority
during ground station contact.
4. AOCS BASELINE CONCEPT
In the past SIC design has oftcn been pcrformed
with thc emphasis placed primarily on mecltankid
and structural configurdtion aspccts wit bout taking
into account thc impact on othcr subsystems to the
ncccssary cxtcnt. As far as the AOCS is concer-
ncd. it is of course understood that its SIC intcrnal
and cncrnd communication- and ~CCCSS capahili-
tics can providc the ncccsary flcx&ilitv for adapta-
tions to a givcn environment hut disrccarding
ccrtain demands from thc AOCS on thc S.'C hus
and cquipmrnt configuration would entrain thc
nc+cssiiy to establish a dedicated A( ICS-concept
;ind mnkc ;I special dcsign hir cnch misTicm Ihicc-
live and associatcd payload undcr cliscussion hcrc.
Thc approach outlincd suhscqucntiv .time ,I! rna-
king hcct possiblc usc I)! the inhcrcnt Ilcubilitv
fcaturc\ of thc AOCS for Ihc bcnctit id thc ovcrall
systcm and is c.rpcctcd to rncct thc different mis-
sion rcquircrncnts without rn;ijnr modifications.
tkncral Ccaturcs of the concept in cluestion arc:
a The AOCS shall hc dcsiuncd to incorporatc
scnsor and actuator equipmrn! altcrnalivclv o r
in cornhination as rcquircd to mccr the pointinp
and LOS sthilitv pcrform;incc of labl:: 3 - 1 .
The Data ,Managcmcnt and Ccintrol (DMC)
functions of section 2.3 shall he intcarntcd with
thc AOCS (Intcgratcd Control and Data llrrna-
-
-
pcmcnt System - ICDSI.
Data transmission within :hc SIC shall 1% pcr-
formcd hv mcans of a tiiy.itai scriai iI:ita hus.
HAV and S/W implementation shall bc b:iscd.
Thc capability of pcrforminu ortiit c!orrcctions
shall be prcwidcd.
Payload Ja~a managcrncnt (and prcproccwnc).
which rnav nccesitatc cxtr-mclv high cornputd.
tional and storage efforts is rcpardcd ;IS ;I lark
complctcly scpruatcd from the ICDS.
4.1 Srnsnr Conngumlon
It is undcrstood that the wholc scale id ni. *ssions
under discussioo hcrc cur bc best scmcd. if the
highest pcrformancc attitude mcasurcrncni quipmcnt
is xlcctcd. i.e. prccision star scmors a1.d ratc
inlegratin8 gyros in strapdinvn mdc of opcration.
This will. however. bc thc most cxpcnsive
solution and rcprcuni M ovcrdcsip Cor less omhitious,
e.g. communication applications. Subscqucnt-
i
ly the attempt is made to dcfme a sensor configu-
ration. which could cover dl situations, but incvita-
bly imposes restrictions on the system layout.
It is assumed that TACSATS on request of strate-
gic demands shall operated in bctwcen near polar
(sun synchronous) down to near equatorial low
earth orbits. the sun incidence mgk with rcspect to
thc orbit normal also possibly varying between zero
and M". If it is furthermore iusumcd that thc array
dcsign provides thc double axis orientation capabili-
ty discusscd earlier, an orientation of the solar
array axis of rotation approximately parallcl to the
dircction of motion is favourable (see fig. 4.1-la)
for vcry low altitude orbits (e Soc) km) due to
-
air drag (sce fig. 2.1-3)
if the sun is in 3 region around the normal fo
Ihc orbit planc (say 2 45 dcg)
- hi low inclinations of thc orbit planc w.r.1. thc
cqu;l(Or
An owntation ol thc SA. xis of rotation pcrpcn-
ilicular to thc dircction of S/C motion (parallcl to
the earth surface) is more favourablc (sec fig. 4.1-
Ibl
- for high altitude. high inclination (near polar)
orbits
- lor low sun incidcncc angles w.r.1. the orbit
planc
Thc highest flcxibilitv would bc cnsurcd. if - for
rcspcctivc application orbits - the SIC orientation
w.r.1. flight dircction could be sclcctcd cithcr way
.id thc payload (pointins in nabr dircction) alter-
nativclv rotatcd by 'XI dcgrccs around its line of
si*t in the S/C.
A icasiblc uranpcmcnt of all (optical) ;il!itudc
rnc3surcrncnt cquipmcnt. is schematically indicatcd
in fig. 4.1-2. The S/C axes arc dcnotcd bv x. y, z
(roll. pitch. yaw). whcrc the yaw-axis is always
nadir-pointing. Thc schematic of optical scnsor
;irranpcrncnt on thc S/C body surfacc of fig. 4.1-2
shall not postulate that all scnsors indicatcd hmc to
hc available simultancouslv in thc s;imc S!C. For
ccimmur.ication missions e.g. thc cxpcnsivc sensor is
not rcquircd. in hi@ performance missions with
stcllar-incrtial rcfcrcncc on the other hand thc IRS
is obsolctc.
Thc conical scan IRS points 'into S/C y-direction
(or opposite to it. depending on thc sun incidence
angle w.r.1. the orbit). which is tbc dircction of
motion in fhc CSC of fig. 4.1-la and scans thc earth
undcrneath wdcr 0 JS dcg cone angJe. Thc star
sensor is mounted on the -z face (nwoy from the
earth) inched into the pducction (or opposite IO
it) scanning the sky as the S/C rotates around its X-