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&ring the full novel TACSAT mission
there will be the following, distinctly
different, phases of operation.
hunch Preparation Phase
It is possible that there will be a choice of
Launch Vehicle configuration. For each,
there will be a complex trade-off betweed
orbit parameters (especially orbit
inclination), payload mass (oat
functionalit and tar et area revisit
periodicity. t ere iwill s so be a compled
trade-off for the phasing of any particular
orbit beweeh spacecraft constraints (e
sun angle at injection), operationa
coverage requirements and spacecraft fuel
launches, ;is to the nature of the intended
tactical support, especially phasing over
t k target area. Finally, there may be a
requirement to defend the TACSAT
system against jamming.
The trade-offs must be resolved and the
1 au n c h e rl sp a ce cr aft c o n f ig u r a t i o n
finalised (including programming of
on-board computers) early In the Tactical
Deployment when the Tactical Staff will
have many other pressures to finalise
deployment plans and logistic sup ort.
However, since it cannot be assume B that
these staff will be familiar with spacecraft
operational constraints and speedy
decision making may be of the essence,
0 previous in-depth training in system
operation will be a pre-requisite of
successful TACSAT operations.
Launch and Early Operations (LEOPS)
Phrase
Launch services would be provided by a
specialist supplier requiring minimum
interaction wth the Tactical IJsers. The
boosted ascent and spacecraft separation
will be pre-pro rammed. However,
determination o B the initial orbit by
ranging during first apogee will be
necessary frord appropriately located and
equipped ground stations. Note that the
spacecraft ranging transponders may well
need to be rotected by encxypters from
ranging, an B /or from jamming, by enemy
ground stations; hence digital ranging,
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staff and cypher distribution
channe s Will be preferred. For accurate
early 'orbit determination, these ran
stauons would be on a long (> 10o0
baseline and must pass ranging data sets
by communications links to a Central
Control facility equi ped to compute the
initial orbit. It wi P 1 be convenient to
arrange €or this Centre to also compute
necessary manoeuvres, predict the
subse uent orbit evolution and, most
proba 8 ly, execute the manoeuvre
sequence in a manner consistent with any
requirements for payload deployment/
activatiodcalibration. To effect the
manoeuvre/activation sequence, Trackin ,
Telemetry and Command (TT and 8 )
access would have to be provided via
several, well-distributed Ground Stations
if this phase is to be completed with
minimum delay. In short, this entire
hase could be under the control of the
Lunch site, rovided with support from a
network of appropriately equipped
Ground Stations.
However, in view of the military
sensitivity of TACSAT missions, it is
more likely that all Ranging, Telemetry,
Manoeuvre Computation and
Telecommand functions would be
exercised by a suitably equipped and
military-staffed Facility. For reasons of
compatibility with Launch Site and
back-up orbital support, TT and C
functions could be conducted at S-Band
usin the Space Ground Link System
(SGh standard, but with encryption
enabled shortly after successful injection
into initial orbit. Ranging, Telerne
Telecommand functions coul
exercised by a 19 m S-Band Telemetry &
Command Station (TCS , supplemented
by relative1 small (3 m) b -Band terminals
co-locate dy with selected permanent
Ground Stations. Alternatively, the entire
TT and C support could be exercised
within the X-Band channel allocations for
Milsatcorn and Earth Resource Downlink
channels. In either case, TT and C
baseband connectivity durin the periods
of TACSAT visibility must %e provided,
:. for example via orderwire channels
'.* within permanent communications
. accesses.
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