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capability bought, the higher the cost. OEIior factors
that will tend to reduce cost are limited coverage
(theater rathQr than workhide) reduced lifotima, and
a minimum of extras, such as heroic survivability.
A number 01 potential TACSAT missions were
studied. These in c I u d e d sur ve i I I a 'ice,
communicalions, environmental sensing, nuclear
detomtbn detection, space surveillame and space
experiments. The first two missions were chosen lo
be discussed in furlher detail in this paper because
they illustrate two levels of commonality than can bg
achieved. Tho use of a single satellite desip to
perform two diflerent surveillance missions, thtiater
surveillance and tactical missile tracking, was
explored. Although these missions have different
requirements, it will be shown that by selecting the
@ proper orbits, both missions can be met with a
conimon payload dasign. Theater surveillance
involves looking at relatively small target areas in
order to do target location and then bomb damage
assessment. These rarameters are also required to
allow the user to monitor the battlefield in order to
determine deployment and strategies. To do this
with reasonable size optics requires that tho satellite
be flown at relatively low altitude. A 500 hm circular
orbii was chosen lor this applicalion. Tactical missile
tracking, on the other hand, requires cove# age over
a larger area and the ability to ,detect and track
missile launches from the infrared signature given
off by the rocket plumes. For this application,
satellites in geostationary orbits were postulated.
The theater surveillance system uses an electro
optical payload in the visible region lor imaging of
the selected target areas. At 500km altitude, the
payload would be able to acquire targets within an
area of 2900 km in track and 1000 km cross track.
Within this acquisition basket, the payload would be
directly commanded by the user to image target
areas up to 9 X 9 km. The data taken by the satellite
would be trarlsmitted directly back to the user who
would have the capability to do data exploitation in
near real time. It is envisioned that the entire
process from tasking of the satellite, acquisition of
the data and downlinking to the user would take a
minimum of 15 minutes. The maximum timeline is
governed by the revisit time and is a function of the
number of satellites in the constellation and tho orbit
inclination. The theater missile tracking, system,
deployed in a geostationary orbit, uses a scanning
infrared sensor 00 dePm tadical missiles and after-
burning aircraW in a 2000 x 2000 km area. Within that
target area, iRe system is capable of processing up
to TOO0 potential targets and, after processing,
tracking up to 100 real targets simultaneously. For
ballistic missiles, b lh launch and impact points can
be predicted. These predictions could then be
used to initiate a counterlorce strike or cue
defensive systems.
A single sensor that could do both the theater
surveillance and tactical missile tracking missions
was conceived and is shown in Figure 1. The
sensor has common opiics far both missions and a
*ai focal plane array to accommodate both the wide
field of view and the high resoiution requirements.
The payload was compact in design and weighed
approximately 100 kg. It was now possible to satisfy
one of our aftordability criteria; a single satellite that
could do more than one mission depending upon
the orbit into which the satellite was deployed.
Once the spacecraft and its payload had been sized,
a study was conducted lo determine whether the
spacecraft could do missions other than those for
which it was designed. Figure 2 shows that the
missions of multi-spectral imaging and space object
surveillance could also be done from a satellite in a
500 km orbit and that the mission of cloud and
ocean imaging could be done from geo. The
imaging missions would ulilize both the IE and
visible spectrum at the discretion of the use!'
depending upon the operational and environmental
conditions at the iime. The surveillance of space
objects from spacc would be done solely in the
visible band. To summarize the potential for
commonality in the surveillance area, preliminary
analysis has shown a minimum of five missions that
corJld be accomplished hy a single satellite design.
It is expected that a mwe ddtailed analysis could
sudace even more potential missions.
As noted earlier in lhis paper, a second level of
commonality would be to have a common bus
capable of accepting interchangeable payloads. To
explore lhis possibility, a second mission area,
communications, was selected for study. The study
developed conceptual d3signs of satellites sized to
provide direct communications support to tactical
commanders. Design concepts at both SHF and
EHF were formulated. The tactical users have
idenlilied the need for small portable ground
terminals that are lightweight, relatively inexpensive,
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