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' Figure 3. Usa Driven Dwign Future Muria
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Figure 3 shows UIC key uscr necds utisficd by an
clocuuopical T=Sat sysccm. and how lhose n&
map into desired design fcatuns. The Snt syslcm
&sign slcp is lhc dcrinition of kcy mission driven
sRIol ctlaralcristiu. Thcsc cheractuislicr combined
with orbit slechn. define Ihe syrm's 'capability to
rurvcy and collect".
Tdat ryncm pcrfrrmpncc is ~ unklally dcfincd
by the combination of scrim chmcieristics and
mission orbit. As shown in Figurc 4. Ihe pmccss of
slccting lhesc pmacn s m with he delinilion of
mission rcquircmcna: i.e. what. specific mles will UIC
system be dcsigncd IO satisfy dnd what performance
levcls will be required for the.* mlcs. h eanmple.
onc mlc might bc daylight surveillance of a botcle am
IO decst mw. Mocha might bo suneillnncc of n pm
area IO detect shipping activity. Ewh of there
missions rcquircn some spccific qunntifishlc threshold
perfonnnnee and a range of characteristic goals thot
affcct basking. The key IO Sensor and orbit design is
brlnncing ily many lasking thresholds U pnclicpl while
maintaining pufomunce againv UIC varisbk gds. rll
at M affodable cost.
The multiple areas of prlonnanco nquind for TrSu
missions uc achievable in sevcnl ways. Ths
mvaltiooll.pporhisloum Iw0~msat)ps.
me emphasizing wide ficld-of-vicw. be olher iigh
nsoludoo. Tbe key to wc concept b Ihe c*pabllky to
nully lbe key TrS.1 mldocll ritb a s h k -.
31-3
bpmn'blethmgh tholns of two diffmt foal
plmra md che flexibility m e In either 'amingm
or 'running' modor Ths "nuing" mode capons
high n.~lulioo dam d a relatively small geographic
M. In this mode. a sensor continuously wka, 01
%arcs" at a putieular urga and the image site is
limited to Ihe kkl of view 0.
The mm UD scan in eilher Ihe 'push-broom' or
"whisk-bmom" modu When scanning in the "push-
bram' &. I seasor imagrs a nrip determined by its
FOV. A wider area. with reduced dim targct
pcrfonnrre. M be imaged using the "whisk-braom"
lcll mode. This dual-nmdc upbiliy. discuJsed later,
provides a surveillance option 'menu" to the uaer
ranging Ifom small arca. higha nsolution IO large area.
mcdium rcdution. In addition. UIC pointing capability
required foc scanning and staring also allows mget
area sleclim wilhin a field of regard (FOR) of about
MY to crsh rirle of nadir dong Ihe flight pth.
In addition to wr-programmable pointing, che sensor
should feature multi-spccvP1 capability. The scan
modes might be suppaned by a series of multi-element
linor focal-plpne arrays. each covcscd by narrow bend
oplical film. The high resolulioo Waring modc wulJ
uw a rgu~ panchromatic array oprating in the visible
band. This combinnlion makes it possible to suppon
lhe many spccual bnnds Md differing rcsotutions
ncuM IO putam TrSpl missiau.
CClVCrppC
TacSnt system flexibility and timeliness arc. to e luge
cxlcnt. orbit dependent. Of cows?. orbit selection
ofm invdva adcs agairut nsolution. Orbit xlcction
requires consideration of options for altitude.
inclination and. in some cow. ecccnuicily. Figurc S
shows some d che fecws effecting altilude selection.
Environmcntnl facton bound the range of available
optiau. Below aboul4SO KM. wnosphetic dng staris
IO became a factor by increasing propellant for orbit
mainlc- and beginning IO pmduce ntutude conlrol
design issues. At be ocher cxuemc. alitudu abovc
about 1400 KM rcrult in incruccd rcquircmcnU fOr
componcnt hardening against the radiation
envinmmcnt. (Orbiu above he dintion bclu would
rnn rred .ss much hsrdening. but would quire sN0n
dadinirrniclarihmlhosediacmdherc.)