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Tb lSB in &a "heat" of ha TacSet spacecdk. It is a
hat ~ ~ U tIs rcnvcntiol. n oparlh of Imfmd smcam ~ln~la e k m h pbgo with a mudular dm bus. A
quires cooling of detecton and 0th Docn! hemal safis of mhbn d applica i .i specific cards attach to
phom mise sawces (optics and SoIPctU"~). ~E~tOOs. the data bus These cads connect the bus systems, and
if MgCdl%e, opwa~c with 3uPficicndy bw CaarBr turrcnt pmylmd if desired, @ the data bus. A high speed CPU
whcn ai 8O0K To cchicve such Rna~mKums ailhout is also on the data bus, ai shown in Figure 16. Locally
Ixgc dintors, mcchnnical coolcrs ~ rn saccdcd. Two generated +tar and ground commands move to the
small radbrors m usdd. one fm the mtlxhaniccpl COoEer pmcessor. Once in mcmory, this data is used to
and on-Bimbn9 electronics, and the mhcr to kccp the generate spacecraft or lrsrnsmission commands.
optics and slructurrs cool. A 9i@~lwei8hl, rapidreadincss,
cooler with long slomgo life codld bc I
--
01IYju%3 manu DItl WO
q u i d for TxSe6 missions. In U!! &ired size range,
-U-
a mmbnicid Stcrling cyclc coolcr is 8 pod choke. It
opcratcs at (I coefficieot of operating paver of
approximatcly 1W Wax consumed per Watt of
cryocaoling dissipath.
Sincc the scnsor is dcsigncd to opernte in the "push
broom" or "whisk broom" mode. it is urllikely that a
radiator would bc continuously shradcd. Some
altcrniivcs are: periodically movin8 'the primary
spacccdt nadir-pointing axis off diu, fitting a sun
shicld, or using a sun-synchronous abit and "whisk
broom" mode cxclusivcly. It might also be possible to
change qrmtional modcs so that mdintm sun capsure
is less than 35 minutcs per orbit. However, the
combination of a sun shicld and nlternating modes
could allow shad4 oprntions with minimal made use
interference and allowing inclination choice frccdom.
I
Figure 14 shows U possible TacSat configuration. The
TacSat bus houscs 8111 cquipmcnt to support thc scnsor
payload and communications cquipmcnt. 'fhc kcy to
TncSat flcxibility and utility is a bus that uscs a singlc
Intcgmtcd Spacccraft Elccmnics !ISE). Figurc IS, the
spacecraft block diagram, shbws major vehicle
components and intcrfaccs and hJw ahr ISE conmls
and cmdinatcs functions. Thr ISE pmccsws attitude
scnsor data and controls or5it and ataituffe through the
rcaction whecls and the propulsion spuem. Thc ISE
also collccls and formats spacmaft ksdiccping data
for storage and/or transmission. i
I =lr
I
Figure 16. ISE Block Diagram
The electricrsl power system (EPS) design should be
simplc and flexiblc. Thc system uses cithcr gallium-
arsenide-on-gmanium or silicon solar cells and nickcl-
hydrogen battcrics. Gallium-arscnide solar pancls,
while more expnsivc. offcr improved packaging, loww
wcighl and rcduce orbital disturbance torqucs and
momcnls of inda comparcd to silicoQ ccll pancls. A
singlc prcssurc vcsxl (SPV) nickcl-hydrogen battery
can lowcr both wcighl and cost comparcd to an
cquivrllcnt individual pressure vcsscl (IPV) system.
Tolcse factors combine to rcducc propcllant mass.
TRrcc-axis stabilized TacSat attitude contro! and
propusion subsystcm functions providc a swblc Sensor
platform and include: dclermination of attitude and
'