Satellite Life Extension: The Technology and the Economics

By | March 1, 2012 | Telecom, Via Satellite

The useful lifetime of geosynchronous orbit satellites averages about 15 years, a limit primarily imposed by the exhaustion of propellant aboard. The propellant is needed for “station-keeping” — maintaining the satellite in its orbital slot and in-orbit orientation, or attitude, so that its antennae and solar panels are properly pointed. When the propellant is nearly exhausted, then, notwithstanding that the satellite’s other systems and payload are often in working order, the satellite reaches the end of its active life and must be moved to a “graveyard” orbital slot, failing which it would commence an uncontrolled drift in orbit. The 15-year replacement cycle drives the satellite industry from the capital expenditure cycles of satellite operators, the financing they seek for those expenditures and the resulting order books of satellite manufacturers and launch service providers. Low Earth Orbit satellites may have even shorter life spans, due to the increased atmospheric drag and friction to which they are subjected.

Because propellant exhaustion usually occurs when other satellite bus and payload subsystems have significant useful life remaining, consigning otherwise useful and expensively built and launched equipment to junk, satellite life extension has long been a grail of the industry, although, given the considerations just stated, it would also obviously have a disruptive effect on all industry verticals. In addition to refueling, the ability to conduct robotic repair and modular component replacement missions to in-orbit satellites might extend many satellites’ life spans and thereby change not only their economics, but those of their replacements. For example, according to common industry metrics, the refueling of about 250 kg of propellant might extend a typical geosynchronous spacecraft’s life by five years, a third more than expected at launch. Satellite life extension would not be the only potential effect of an in-orbit refueling capacity. Other choices, such as bigger payloads, smaller satellites or smaller launch vehicles, less expensive to build, insure and launch, carrying less propellant for the same lifespan, could also be built if the economic case existed. In short, the ability to refuel and repair in-orbit satellites would be disruptively transformative for the industry.

Several satellite lifespan extending technologies are in study or development. Among them are ion thrusters, which generate electrons from charged carbon nanotubes. One type, “Hall Effect” thrusters, is already in flight on several U.S. and Russian spacecraft. A grant by the U.S. Defense Advanced Research Projects Agency (DARPA) is funding development of more reliable ion thrusters based on nanotube arrays for reliability and to improve efficiency.

Somewhat more conventionally, also under discussion are robotic service vehicles that could rendezvous with orbiting spacecraft and refuel them, either by direct fuel transfer or by attaching to a docking port a new fuel tank and thruster array. In the former case, the refueling craft might carry enough fuel to service several satellites, rendezvousing with one after the other, and amortizing the costs of its own purchase and launch. Satellite life extension generated a lot of buzz at the SATELLITE 2011 conference, when Intelsat agreed to be the first private customer for a life extension system planned by MDA Corp. of Canada, called the Space Infrastructure System, or SIS. The deal was called off in January, probably owing to uncertainty about securing U.S. government customers for the service, but MDA is continuing to explore the technological and economic feasibility of SIS. Another company, ViviSat, a joint venture of U.S. Space and ATK, is developing plans for a “Mission Extension Vehicle,” or MEV, capable of docking with an in-orbit satellite and serving as a supplemental propulsion system. ViviSat is also exploring possible other component repair or replacement.

These efforts are developmental, but, like ion thrusters, are by no means “pie in the sky.” Robotic rendezvous and docking, featuring systems coupling upon rendezvous, dates back to the mid-1960’s Gemini program’s Agena docking and tandem flight experiments, and has been made as routine as any space mission can be by International Space Station servicing flights. Several satellite life extension players will address the state of this interesting new sector of the industry, including its promise and its technological and economic hurdles, at the Satellite Life Extension panel at SATELLITE 2012.


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