Tim Furniss/LONDON
Boeing is claiming the third flight of its Delta III booster carrying a dummy satellite on 23 August was a success, despite the satellite not reaching its intended apogee of orbit. According to previous classifications of commercial launcher performance, however, the flight should be classed as a partial failure. The launch followed two failed Delta III flights in 1998 and 1999.
The dummy satellite payload ended up 4,737km (2,942 miles) short of the intended apogee of the hybrid, non-geostationary transfer orbit (GTO), announced before the launch.
A London-based space insurance company source says that the launch was "not very good", and if the booster had been carrying a commercial satellite, the Delta III undershoot on a flight to GTO could have resulted in a loss claim for the reduced lifetime of the satellite. The satellite would have had to use on-board propellant to reach the intended GTO before firing its engine to circularise the orbit to reach geostationary orbit. The loss of propellant from a system which also supplies the spacecraft's stationkeeping thrusters could result in the supply running low and the satellite's lifetime being reduced.
A Delta II launch of a Koreasat satellite in 1995 was classed as a partial failure when the spacecraft was placed into a GTO 6,000km short of its apogee and the satellite lost operational stationkeeping thruster propellant making up the shortfall. A successful insurance claim was made and Boeing classified the launch as a partial failure.
The $85 million Delta III demonstration flight, funded by Boeing, deployed a 4,310kg (9,500lb) spool-shaped dummy satellite payload at a lower altitude than planned, concedes Boeing, but the manufacturer says the launch met "the commitment performance that would have been given to a commercial customer". The deployment was "2.6 on a scale of 3", Boeing says, adding that the lower deployment does not explain the reduced final orbit.
The nominal maximum orbital parameters for "launch day vehicle drag and atmospheric conditions" were 23,378km by 181km, with a minimum of 20,026km by 178km, which was described by the insurance company source as parameters "that would be regarded as a very wide target range for a commercial mission".
These figures, produced after the flight, differed from Boeing's initial target figures of an intended orbit of 25,408km by 185km in its pre-launch handbook. "Boeing changed the goalposts after the launch," says one space analyst. Due to launch-day conditions, the actual orbit achieved was 20,671km by 153km, says Boeing, adding: "We missed the bullseye, but were close." Attributing the difference totally to launch-day conditions "just doesn't make sense", says one analyst.
The mission was flown to depletion of the upper stage propellants, unlike the Delta II which features a commanded shutdown. Depletion missions, which will be flown commercially by the Delta III, normally have a greater expected orbital range than those with commanded shutdowns.
Source: Flight International
