Lockheed Martin is replacing its controversial Series 7000 bus with the new A2100.
Tim Furniss/LONDON
Most of the proposals for new satellite contracts being made by the Astro Space division of Lockheed Martin in New Windsor, New Jersey, feature the new A2100 spacecraft bus (Flight International, 20-26 April, 1994). The company has two contracts for the A2100, for GE Americom's GE 1 and 2 spacecraft, the first of which is scheduled for an Ariane launch in 1996.
The unheralded introduction and marketing of the A2100 is the opposite of the highly public fall from grace of the Astro Space Series 7000 spacecraft bus. This was involved in controversy concerning its pyrovalve design after an in-orbit explosion of the second Series 7000, carrying the AT&T Telstar 402 satellite, on 8 September. 1994.
The pyrovalves introduce hydrazine into the satellite's propulsion system in preparation for an orbit-changing firing which, in the case of the Telstar 402, would have circularised the GTO orbit to a geostationary one. After several months of denying that the satellite had exploded in geostationary transfer orbit (GTO), despite obvious evidence from tracking data, Astro Space admitted that, "an explosion occurred in the space craft propulsion system and was caused when leaking hot gases from the firing of a pyro-valve, reacted with hydrazine in the valve".
SPACECRAFT LOSSES
The Telstar incident followed the loss of two other Astro Space spacecraft, the Mars Observer and the Landsat 6, in 1993. The loss of the Landsat 6 was the result of a similar pyro-valve incident and had already sparked an industry-wide review of pyrovalves used in other spacecraft, including the recent introduction of new lighter-weight materials, such as titanium piping instead of the traditional stainless steel, and design margins.
The Telstar 402 investigation highlighted a phenomenon called "blow-by", when two pyro-valves were opened in sequence by explosive charges to release the hydrazine propellant into the engine. Hot gas from the first pyro-valve charge escaped and, as the second pyro-valve charge fired, ignited what hydrazine had already been released into the pipe-work.
Astro Space says that it took two immediate steps as a result: to ensure that a vacuum, instead of hydrazine, is present in the downstream side of the valve; and to change the pyro-valve to limit the blow-by in the fraction of a second after the valve is opened. Attention has been focused particularly on the O rings in the system.
There are ten more Series 7000 satellites at various stages of production: six for the Intelsat 8/8A programme, two Echostars, one Telstar 400 and the Asiasat 2, which is scheduled to be launched on a Chinese Long March 2E booster this year. The launch of the Asiasat 2 was delayed while the Telstar investigation was under way, then delayed again when the Long March 2E, carrying the competitive ApStar 2, blew up at T+51s on 26 January. The Asiasat carries 24 C-band and 20 ku-band transponders.
Asiasat says that it is confident that Astro Space is on top of the pyro-valve issue, but AT&T did not take the loss of its $200 million 24 C-band, 24 Ku-band Telstar 402 lying down, despite being compensated by an insurance policy. The company sued Lockheed Martin for at least $250 million, accusing it of delivering the Telstar 402, knowing from the evidence of previous difficulties, that the pyro-valves were faulty.
Lockheed Martin was also accused of being late with the delivery of the Telstar 402R replacement and tardy in ensuring that AT&T gets a priority launch slot. An out-of-court settlement was agreed on 15 May. The 402R will be flown on an Ariane 4.
Astro Space will fulfil its commitments, to existing Series 7000 customers and anticipates possible follow-on contracts for further spacecraft for a same series, such as new Echostars. AT&T plans to launch three Telstar 5s, with four extra Ku-band transponders, after 1997, and is likely to select Space Systems Loral.
Astro Space, meanwhile, is phasing out the Series 7000 and sees its future lying with the versatile A2100 spacecraft bus, which can house a satellite similar to those carried by the Series 7000, but 30% lighter and one which can uniquely be supplied in three sizes, to suit a variety of communications pay load requirements: the A2100 A, B and C, in a 1,000-2,750kg launch weight range. Each is 1.82m wide, with heights of 2.1m, 1.65m and 1.27m, respectively, for the A, B and C.
TYPICAL LOADS
For a typical "A" mission, the spacecraft could carry 24 C-band and 24-Ku band transponders (as for the GE 1 and 2 programme) or 32 Ku-band transponders, while a "C" bus could handle 22 C-band or five Ku-band transponders. Telstar 400s weighs 3,375kg at launch, while a GE satellite, with the same payload mix, weighs 2,585kg. Lower weight could also mean a cheaper launch: for example, the difference between an Ariane 42L launch and one with an Ariane 42P. This, and the A2100's payload flexibility, may be the key to success - pyro-valves permitting.
Source: Flight International
