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STRUCTURALLY INTEGRATED
THRUSTER 5 (SIT-5)
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A 5-cm-diameter mercury
ion engine, called SIT-5, was developed
circa 1970 for attitude control and NSSK of
geosynchronous satellites. The thruster
input power was 0.072 kW, and it provided a
thrust of 2.1 mN at a specific impulse of
3000 s. Electrostatic thrust vectoring grids
with a ±10 degree vectoring capability were
baselined. The engine was successfully
random vibration tested at 19.9g rms. The
mass of the thruster and mercury storage and
feed system was 2.2 kg. The propellant
system could store 6.8 kg of mercury which
could provide operation at full-power for
approximately 30,000 hours. The envelope was
about 31 cm long by 12 cm diameter. The
SIT-5 development program focused on the
thruster and feed system development; there
was no PPU technology effort.
Hollow-cathode component tests demonstrated
over 2800 simulated duty cycles. A separate
test of the SIT-5 thruster was conducted for
9715 hours at a beam voltage of 1300 V, a
thrust of 1.8 mN, and a specific impulse of
2500 s. During the initial 2023 hours, the
thruster was operated with a translating
screen grid thrust vector system. For the
remainder of the test the thruster had an
electrostatic thrust vector system. The
electrostatic beam vector grids were
operated at 5 degrees deflection for about
120 hours, at either 2 degrees or 4 degrees
deflection for 1880 hours, and with no
deflection for 5690 hours. There were a
number of grid shorts that were successfully
cleared by the application of 200 V to 400 V
at currents from 6 mA to 70 mA. These tests
were helpful in the later definition of
grid-clear circuits for the IAPS, XIPS, and
NSTAR thrusters.
The SIT-5 mercury propellant system was
successfully tested for a period of 5400
hours in an independent test.
The preceding was an excerpt from:
Sovey, J. S., Rawlin, V. K., and Patterson,
M. J.: "Ion Propulsion Development
Projects in U. S.: Space Electric Rocket
Test 1 to Deep Space 1." Journal of
Propulsion and Power, Vol. 17, No. 3,
May-June 2001, pp. 517-526.
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