PARIS — Satellite fleet operator SES, which was the inaugural customer for the Space Exploration Technologies Corp. Falcon 9 rocket’s commercial launch to geostationary transfer orbit, is using the Falcon 9 rocket to debut a novel use of chemical and electric propulsion to carry a telecommunications satellite into final orbital position.
Because the Falcon 9 v1.1 is optimized to launch satellites weighing well under 5,000 kilograms, industry officials have been speculating for weeks on the mission profile of the next two satellites that Luxembourg-based SES plans to launch aboard Falcon rockets.
The two satellites, SES-9 and SES-10, both weigh about 5,300 kilograms and carry a mix of electric and chemical propulsion systems. The question is, what tradeoffs is SES making to be able to fit their launches on the Falcon 9?
Using electrical propellant affords substantial weight savings compared with chemical propellant, allowing a satellite normally too big for Falcon 9 to ride aboard the vehicle. The first two all-electric commercial satellites are scheduled to ride together on a Falcon 9 in 2015.
SES-9 and SES-10 are too big to ride together on a Falcon 9, and at first look would appear too large to ride even singly on the SpaceX vehicle.
Speaking in Paris April 10 during the Space Access conference organized by Astech Paris Region, Olivier Lebrethon, SES manager for new launch risks, said SES-9, built by Boeing Space and Intelligence Systems of El Segundo, Calif., will use both electric and chemical propellant to make its way from its rocket drop-off point to final geostationary position.
Conventional satellites take no more than two weeks to make the journey to final geostationary position 36,000 kilometers over the equator. For comparison, the two all-electric Boeing-built satellites take six months or longer to reach their final operating positions.
Lebrethon said that for SES-9, the company will use both the electric propulsion and chemical propulsion systems to reach final geostationary position about three months after launch — much longer than using chemical only, but shorter than an all-electric solution. The satellite is scheduled for launch in 2015.
For SES-10, built by Airbus Defence and Space, only the chemical propulsion system will be used for orbit-raising following its Falcon 9 launch set for 2016. To compensate for the Falcon 9’s limits, the satellite will carry larger-than-usual chemical propellant tanks and make an extra couple of orbit-raising burns, meaning the time to final position will not be that much longer than with chemical propellant only.
“The use of electrical propulsion is really only a matter of fleet management,” Lebrethon said. “You design in to your program the extra time needed to reach final position, so in the case of SES-9 we started three months earlier.”
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