0 - FTP Directory Listing - Nato

e
communications, point to point, point to
hultipoint and netted arrangements tray
be all required. The End Usen may wsh
to call upon any or all of these sewices at
,my time. In the tactical situation the
un p r e d i c t a b i li t y of the operation a 1
environment dictates that
communications must be instantly
available, reliable and trustworthy (in
terms of a low probability of detection),
have a high robability of timely
connection,l and i! ave an appropriate level
of information security.
It is evident that the introduction of
complex procedures for terminal
operation, access constraints and rul :s
requiring a high degree of user skill to
understand and implement will detract
from the usefulness of the system as
perceived by the tactical user comnunity.
TACSAT systems can be classified as
providing either image data derived from
spaceborne sensors or relay
communications channels between sites
on the ground, or both. Classically these
requirements are met by standardised
systems architecture as follows: I
Image Data - High resolution,
Sun-synchronous,
polar, circular
- Geostationary
Communications - Geosptionary .
As has already been stated, it is not
particularly useful here to analyse the
@ ground/space interface within such
architectures, beyond stating that
TACSAT applications in similar
architectures are possible, principally
because of excess capacity becoming
available for tactical purposes within
strate@ systems. For example, "sparc:"
capacity sometimes becomes available
when a spacecraft suffers a partial failure
and can no longer meet the full strategk
-equirement. When it is replaced by a
cw spacecraft of the standard design, the
degraded s acccraft cm then be operated
as a TA 8 SAT. In another case, a
standardised design of geosynchronous
satellite has been deployed to three (or
more) stations in the geosynchronous arc
to provide a global system but strate ic
conimunications requirements on one or
more) of the stations do not call for such a
f
large s acecraft. "Spark" trmponder(s)
on suc B under-utilised strategic comsats
can hen be o erated as a virtual
TACSAT. Final P y, it is sometimes the
case that "spare" launcher payload
into polar orbit becomes
availab e because spacecraft desi n
constraints were too conservative for t % e
actual lamchet performance achieved in
a parallel development, and small
TACSAPS can be launched into similar
polar orbits with this spare capacity. Ln all
these cases the ground/space interface is
similar to, if not identical to, the parent
system. In some further cases, very
similar mission concepts are chosen for
purely tactical reasons. However, ic
general, different mission concepts tend
to be favoured because of the tactical
military requirements for TACSAT
systems, for example: .
Flexibility under unsophisticated,
local control
Low cost
Minimum revisit times
Localized area of interest
Surprise
Seciecy
but, most of all,
Ease of use.
Other papers in this series illustrate
instances of this tendency. Here, a typical
"novel TACSAT" mission may be
sunimarised as:
Intermediate orbit inclination,
optlmised for target area coverage.
Low altitude, for maximum resolution
and/or link margins.
Elliptical orbit, minimising
geodymnic drag.
1 iCHigRly manoeuvrable spacecraft to
mbntam orbit alignment with respect
+
to the target area.
Pre-programmed payload operation.