GRAHAM WARWICK / WASHINGTON DC
Boeing servicing aimed at improving capabilities of spacecraft after launch, but tasks must be carefully selected
The initial benefit of robotic on-orbit servicing will come from the ability to upgrade satellites after they are launched, says the US Defense Advanced Research Projects Agency (DARPA). Boeing Phantom Works is to demonstrate autonomous on-orbit servicing in 2006 under DARPA's Orbital Express programme (Flight International, 19-25 March).
"We are focusing on what new capabilities servicing can provide, rather than the potential for cost reductions over the lifetime of a satellite constellation," says DARPA Orbital Express programme manager Maj Jim Shoemaker. "The initial applications are for capability improvement. Once on-orbit servicing is up and running, it can be used for cost reduction."
On-orbit refuelling will allow spy satellites to be manoeuvred to change arrival times and improve coverage of regions of interest. On-orbit upgrading will allow new electronics technology to be inserted into in-service satellites. Boeing's demonstration will involve fuel transfer and electronic module exchange on orbit.
While manned on-orbit servicing has been successful, it is expensive and limited in duration and accessible orbits, Shoemaker says. A robotic servicer will stay on orbit longer, operate at any altitude, and be cheaper. "But we have to be careful selecting what to do autonomously," he says. "Some things are too difficult to engineer to be replaceable, so we have to find components that can be packaged into orbital replaceable modules - standard boxes the robot arm can grab on to, pull out and insert."
Orbital Express studies showed an analogy with deep-sea servicing, which is performed using manned and unmanned submersibles. "The human works best on short-duration missions where there are a lot of unknowns. Robots work well when they know what to do, it's not very complicated, and they have to stay down longer."
Two reference missions have been selected for the Orbital Express demonstration: refuelling of a manoeuvrable intelligence, surveillance and reconnaissance satellite; and upgrading the electronics in an orbiting spacecraft. Both missions require the satellites to be designed from the outset for on-orbit refuelling and upgrading, and the Boeing-led team will develop industry-standard interfaces for docking, fuel transfer and module exchange that will be made available to all satellite designers, says Shoemaker.
Boeing will conduct a subscale on-orbit demonstration, using the Astro robotic servicer to refuel and upgrade the Nextsat satellite auto-nomously. The satellites, weighing a combined 1,000kg (2,200lb), will be launched together. Plans call for the six-month demonstration to reach a point where the Astro can accept then autonomously execute a mission plan involving a rendezvous with the Nextsat, manoeuvring in close proximity, and docking to transfer fuel or remove and replace electronics modules.
Source: Flight International
