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The small size aaad low mts of the
FGlkUb2 tXUd SCWf S bITI%ideRed hl
this papea win1 resu ? t in sipificm~ cost
savings waking the dcplsymeno cf
constdlmiolms of satellites vcuy much
more attractive. Tbis has the ffurther
sdvaamuqge of redusing revisit atimcs and
conseqancw~Py providing information not
otherwise available from amy I other
source, and of improprimg iystem
sumivmbility. In the next scc~ion some of
the options for a sensor CQDCX~P ape
descrnbed. This is followed by a
considcraaion QP system aspects md cost
and schedule drivers.
2 Ilmpac~ OP a PodsaeQixnO TACSAT' Slhw
Missrim om S~RQMO~~ Desdgm
2.1 A PotermUdaP TACSAT Mhdanop
The TACSAT mission is onc w&b is
associated with a Theatre conflict wheee
the Theatre is defined as being a region
measuriq some 2WOh by 20WEm aund
the duraunon of the conflict is mtid ated
as being relativcly short, typicin8 P y of
months, rather than weeks or years.
Although areas of political and mniimy
risk can Pic at my lati.ude, the emding of
the Cold Wx suggests that if there were
to be ~mch a Theatre conflict, then its
occurrence in the lower latitude regions,
rather than the more Northerly latitudes,
seem more likely.
The mission envisaged for a TACSAT
SIIR is to provide the Theatre
Commander with a dedicated saxvice
yielding surveillance data only mer the
crisis ~PCZB. In this a er, the dedicated
nature of the TA U2.g. A mission Brim beam
taken to mean that the Theatre
Findip, the dedicated nature of the
~trvici propsed for thc TACSAT S M
facilitates some interesting departures
from the system thinking associated with
global space suweillmce concepts: these
departures influence the choice of orbit,
the spacecraft bus design, and the basic
sensor design.
The expectation of a Theatre location
away from tbe NQP~~w~ latitudes invites
consideration of orbits of a smaller
inclination than the golae sunspcbroncpus
orbit which is characteristic
of civil remote sensing missions. In
particular, if the chosen opercting
philosophy for the TACSAT SAR is one
of launch-on-demand in time of crisis,
then the orbit inclination can be chosen to
maximise viewing opportunities over the
crisis area. if9 how eve^, the philosoph is
one of in-orbit storage then an ear I ier
decision must be made about inclination
because of the large fuel overhead
involved in effecting chamEes in orbit
inclination. Wowever, even in this latter
case, it may well be appropriate to set the
inclination oh the storage orbit so that
covera e is optirnised for the smaller
latitu t e repions. The absence of
sun-synshromwn, come
orbit inclination,
particular problem
which is ca able of operating as well by
nightasby B ay.
In addition, the relatively short duration
envisaged for a Theatre conflict allows
serious camideration to be given to orbits
significantly lower than those used for
long duration remote sensing missions:
these lower orbits, perhaps as low as
Z4bk.m. would be suited to a ghiloso hy of
launch-om-demanwd. However, a1 t R ough
miculwly low orbits we less attractive
For the case of in-orbit storage because of
the short life time which results from