Satellites mating via robotic arm
The launch of the Orbital Express mission, with its two satellites ASTRO and NextSat, the first one servicing the other, was widely covered a month ago. But what is happening in space now? In "Robotic satellite servicer rehearsal underway in orbit," Spaceflight Now reports about the progress done. A week ago, the two satellites were able to link to each other to operate the first transfer of hydrazine fuel from ASTRO's propellant tanks into NextSat. This weekend, ASTRO's ten-foot-long robotic arm is going to be used to move objects to NextSat. But what does it mean for international satellite operators when they need help with their space birds? Will they use a system designed for U.S.'s DARPA? We'll see.
Before going further, below is an image showing how the robotic arm on ASTRO can transfer objects called Orbital Replacement Units, or ORUs, to another satellite -- NextSat in this case (Credit: Boeing).
And here is another image of this robotic arm (Credit: Boeing). You can fond larger versions of these images on this page at MDA Corporation which built the robotic arm.
Here is how Spaceflight Now describes the first experiment to be done with this robotic arm.
[According to Jan Walker, a DARPA spokesperson,] the first experimental use of the arm will come Friday [April 6, 2007], when it will snatch the spare battery from ASTRO and plug it into NextSat. The arm will transfer the battery to and from NextSat several times during the mission, but the battery will remain onboard NextSat to provide extra power during unmated operations.
According to MDA Corporation, this robotic arm will perform several key functions, such as an autonomous capture of a client satellite (more details here).
As the servicer satellite (ASTRO) approaches the client satellite (NEXTSat), the Robotic Arm on ASTRO will drive autonomously, using highly-reliable vision feedback from a camera at its tip, to capture NEXTSat. The arm is capable of safely capturing the client satellite even under large relative drift rates and initial offsets.
This 3-meter and 71-kilogram robotic arm will also allow to transfer ORUs from the servicing satellite to the client.
The actual servicing begins when fuel is transferred to the client, and when damaged or upgraded components are replaced on the client spacecraft. The standard ORU container may contain batteries, a new flight computer, science instruments, or any other replaceable component. During the OE mission, the OE Robotic System will demonstrate transfer of a battery and a replacement flight computer to and from the client satellite.
For more information, please visit the Orbital Express home page at Boeing. In particular, you can read the mission updates and access the mission books. You may also want to look at the Orbital Express website at MDA Corporation.
Sources: Stephen Clark, Spaceflight Now, April 3, 2007; and various websites
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