Tim Furniss/LONDON
British Aerospace Defence wants to sell its Royal Ordnance Rocket Motors division - which supplies about 50% of the world's spacecraft liquid apogee engines and thrusters. Among the potential buyers are Primex, Marquardt and AlliedSignal (Flight International, 5-11 November).
The sale offer comes at a time when RO's profile has been raised by its success in supplying NASA and others with its Leros 1b engine, which on 11 September made the retro burn that placed NASA's Mars Global Surveyor (MGS) into orbit around the Red Planet.
In October, the Leros 1b was used again to raise the orbit, which had been reduced, as planned, by aerobraking manoeuvres which then had to be suspended because of a problem with one of the MGS solar panels (Flight International, 29 October-4 November). Similar engines will be used on future NASA craft and have been flown on several commercial-communications satellites, providing propulsion and geostationary-orbit stationkeeping and attitude control.
The Leros 1b bipropellant rocket engine, using propellants of mixed oxides of nitrogen (MON) oxidiser consisting primarily of nitrogen tetroxide and hydrazine fuel, was supplied to Lockheed Martin for the MGS. It was among nine engines delivered for use on other spacecraft. A further five are in production.
TRAJECTORY CORRECTIONS
The MSG's engine was first used to make cruise-phase trajectory-correction manoeuvres (TCMs) before arrival at Mars. The first TCM took place 14 days after the craft was launched in November 1996 and made a 27m/s velocity adjustment. Later TCMs involved much smaller changes.
The Mars Orbit Insertion burn placed the MGS into an initial elliptical orbit and lasted for 22min 32s, consuming 75% of the propellants originally loaded. The onboard telemetry from the MGS indicated an average specific impulse of 318s.
Specific impulse is a measure of the engine's performance, equal to the ratio of the thrust of the engine to the propellant consumed.
The MGS then began the series of aerobraking manoeuvres, using the Martian atmosphere as a "brake" on the craft, to alter its orbit.
The Leros 1b is a liquid-apogee engine (LAE), more common on communications satellites, where it is often used to transfer a satellite from geostationary-transfer orbit to circular geostationary orbit.
The engine is a derivative of the original 500N-thrust Leros 1, development of which was completed in 1990 and which is on board the NASA Near Earth Asteroid Rendezvous spacecraft, launched in February 1996, and scheduled to enter orbit around the asteroid Eros in 1999.
A total of 26 Leros 1 engines was produced before the introduction of the higher-performance Leros 1b. In addition to the NEAR, the Leros 1 has been the engine choice for Lockheed Martin's 7000-series spacecraft bus, used in the Intelsat 8, Telstar 4 and Echostar satellites.
The Intelsat 803 and Echostar 3 satellites, which were launched by Ariane 4 and Atlas 2AS boosters in September and October respectively, each use two Leros 1 engines for propulsion. The GE 3 communications satellite that was launched on an Atlas 2AS in September uses a Leros 1b.o
ENGINES ARRAYThe Leros 1 and 1b engines - and a new, 460N-thrust, Leros 1c engine being qualified with Lockheed Martin - are among 13 models of liquid space engines being manufactured and supplied or under development at the British Aerospace Defence subsidiary's factory in Wescott, near Aylesbury, Buckinghamshire.
Royal Ordnance Rocket Motors division also manufactures composite solid-rocket propellants, missile motor cases, vertical launch systems, thrust-vector-control motors and pulse-motor technology. It also provides solid motor propellant, insensitive munitions, the Rayo rocket weapons system and the MLRS reduced-range practice rocket.
Smaller LAE engines include the original Leros 2 (production of which has ceased), the 400N-thrust Leros 2b and the smaller 2c, which use MON and mono-methyl hydrazine propellants. The 2b is being qualified at Matra Marconi Space (MMS), while the 2c is under development as a European Space Agency-sponsored programme, using advanced high-temperature materials and a 300:1 expansion cone to enhance thrust.
The LAEs are used as unified bipropellant propulsion systems, which include sets of about 20 smaller thrusters for attitude control and stationkeeping, feeding either off the same propellant source or as dual-mode propulsion systems with the thrusters, using just monopropellant hydrazine. Lockheed Martin prefers the dual-mode systems.
The small, complementary, thrusters include the bipropellant of the Leros 20H, which is under qualification with Lockheed Martin, and the similar Leros 20 and 10 engines.
Another bipropellant attitude-control thruster is the new Low Thrust Thruster (LTT) which has been baselined for use on the Hughes HS-601 High Power communications spacecraft bus. The first LTTs were on board the PanAmSat 5 launched on a Proton in August.
Royal Ordnance also offers monopropellant power-enhanced thrusters, the Augmented Catalytic Thruster (ACT) and the Arc Jet.
The Catalytic Thruster (CT), designated the ROMR103C, is manufactured under licence from Primex, with 24 engines having been already been delivered to MMS for use on the Skynet 4D, E and F satellites. These are marketed as different combinations of thrusters with a Leros 1b.
Source: Flight International
