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aLRaqy1 rsmnto ,.verviaw
An incrooairvgly important aoqpirawmt
cnnc~rno tho rovimit intorval with which
military rolovant sitae, mat Rxa obaeovdr
typical value14 from few dmyo to ad hourer
apply rsinly to fixed aaoota. Obeorvitq
targeta variable in tino or apcico
requieoo, however, much ohontor raviait
Intorvalo, of the ordm 00 ton houro.
Concariring ground resolutlon, 3 a are
suffictont for detection, In none
cases rocognitIon, of fJeIrQteqliC ally
relevant fixed or low-mobility aoaata.
Tactical applications nead, howewe,
better resolutlons down to 2 tn or leos.
The swath width , or instrntanooub fiold
ol viow, must be commonoureto to tho
thoaton: 20 CO 40 Km , depondlppgl from tho
qround reoolutlon, are likely WQ~UO~. The
swath m0t also be oloctronicnlly
repositioned inside tho acconn anyls,
providiq a high operational Blcnibility
in gaehoring SAR images of aolectodl opots
duriq oatollItee* overpassea. WdQo access
anqlow FAYQ instrumental to :BOCU~B a
covcrsqlo without *holes* and td n1nirsir.e
tho con~utallation*o satellites nunhr.
TIme dalay ninim1ratlon hotwoo; o reqluaet
for dater and its wailability to tho onduser
io of utmoot importance, apclally In
8 taCtaCQl eituetion. Direct aCCOOa to tho
satollitm~, during sites oworpmssca,
followodl by 10~91 dnta fux~ooain9 and
intarprotation by multlple,dmto atatlono
doployed in the theater, pro nom am an
ekfectlve answer to auch nemo.
In a oeacteqic occnario thQK0 in the
additional requirement of tming &$lo to
oboorvo dintant nitan with a ohort
turnaround time. Hclajinq lmegouy data vIa
a Data Walsy Satollite network bn tho most
logical and performant solutlon Ito the
prob lei. 1 .
3LCCNETELUTIONS DESIGN CRITERIA
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WO must diatinquiah bctvcon syntono aimed
at providing a global Earth covaraqe and
thooo Intendod to covar a narrower
latitude bclt around the equator.
AD a mattor of fact, most Countrloo whera
politicel instability is oxpectm! to occur
also in Pueure are includod in tho SO' U
to 50' 6 latltudo belt: which m y justify
tailored constellations.
3.1. Conetellationn for-qlobal cowsraqw-
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A modul~lr solution &onsiete in injocting
oquispacod lhqht6atn in olnqie plan0 munoynchronouo
orbitnr the SAR con bo
provided virh just ono or two antmnnem
looking on both sides of tho flight path.
Multipla raguispaced orbital planma Can
cop. with vory stringent reviait Intorval
rof~uirowntm, i.e. less than 12 hours.
3.1.1. Ljalhtbat C-tolkat Iona u m o x
sneonns
The capability of e 6AR to inago tarpot
oreas inaddo a wide oarth strip is
proportional to the a-xoaa an910, dof1n.d
polv tho alninun and rwximrr ole-nadir
nerglleci. TRQ conetol lat ion daml@n -cr'itorib
ohould peoi*ida for a contigypad, iarth
covorag~, wIthIn the above'~on~trhinis. To
thio and, the fundaQental inteeval is
divided into U oubintarvala whose vidth
corraaponde to the SAR antenn8 access
angle projected mto the evator. If the
ainimum and maximum off-nadir anglos
cstiofy tho conotraints of Fig. 3.1.1..
then tho strips accoroiblo to tho U
astellitom vi11 bo contiguous.
FLg. 3.1.1. SYSTEM GEOYETny
right antenna
accoee angle accoee anglo
I i
In ono orbit period, the N satellites vi11
have covor-ed an Earth slico as vide as the
fundamental interval, and the cycle will
repeat providing a continuous Earth
coverage up to a latitude close to the
munsynchronoue orbit inclination.
with tho constraint of keeping ha
rainimum and maximum off-nadir angles close
to 20' and 50' roapaxtlvely, the number of
setallites N depends frota the orbit
altitude and acceoo angle, as shown in
tIp.3.1.2. and Table 1.1.1.
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'I * U. .ll.I..ll. .*I.
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