Encyclopedia Astronautica
Program 661


EOS electric/cesium rocket engine. 8.9 mN. Flew 1962-1964. Isp=7400s. Cesium contact ion propulsion system used on three sub-orbital flight tests aboard Blue Scout Junior launch vehicles.

In November of 1961, Electro-Optical Systems was awarded a contract from Air Force Space Systems Command to develop an 8.9 mN, cesium contact ion propulsion system for three sub-orbital flight tests. The Program 661A cesium contact engine incorporated an ionizer array of 84 porous tungsten buttons. The power level, thrust, and specific impulse were 0.77 kW, 8.9 mN, and 7400 s, respectively. The beam extraction diameter was about 7 cm. The neutralizer was a wire filament which was not immersed in the ion beam. Power to the primary propulsion unit was supplied by 56 V batteries. The longest ground test was 1230 hours. For the space test 2 g of propellant were loaded. The Code A test engine did not operate at all due to a high voltabe power supply failure. The Code B engine operated in space stably for 19 minutes. However at the end of the period the spacecraft potential had risen to 1000 V. The Code C thruster differed from Code A and B in having the wire filament neutralizer in the ion beam in an attempt to prevent spacecraft charging. The Code C engine ran in space for only about four minutes due to a third stage booster malfunction, and achieved only 20% of its rated thrust.

Electrical Input Power: 0.77 kW.

Status: In Development, 1962-1964..
Thrust: 0.0089 N (0.0020 lbf).
Specific impulse: 7,400 s.
First Launch: 1962-1964.

More... - Chronology...


Associated Countries
See also
Associated Launch Vehicles
  • Blue Scout Junior American suborbital launch vehicle. Smaller Air Force version of Scout used for suborbital military tests. More...

Associated Manufacturers and Agencies
  • EOS Electro-Optical Systems, Queanbeyan, NSW, Australia. More...

Associated Propellants
  • Electric/Cesium The many versions of electric engines use electric or magnetic fields to accelerate ionized elements to high velocity, creating thrust. The power source can be a nuclear reactor or thermal-electric generator, or solar panels. More...

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