From 2006-2008 DARPA ran a program called Orbital Express(wikipedia link) which was "a safe and cost-effective approach to autonomously service satellites in orbit." The program had several goals:

  1. Transfer of hydrazine monopropellant between ASTRO and NextSat.
  2. Use of ASTRO’s robotic arm to detach and reattach a flight computer from a bay onboard ASTRO.
  3. Use of the arm to detach a battery from its bay on ASTRO and transfer it to a similar bay onboard NextSat.
  4. Use of ASTRO’s arm to couple to a NextSat grappling fixture and “berth” the spacecraft, allowing a separate capture mechanism to perform final docking.
  5. Multiple rendezvous and capture scenarios with a number of different sensors, at ranges up to seven kilometers (4.4 miles).
  6. “Soft” (low momentum transfer) docking with a special, three-fingered capture mechanism.

This whole program looks like it was quite successful and other elements have appeared in DARPAs other satellite servicing programs. Why wasn't the project expanded and why aren't other organizations working on satellite refueling?

Astro Express parts

ps would someone who has the reputation please add the DARPA tag to this post? thx :)

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    $\begingroup$ We only have four questions which mention DARPA. Usually the military tag is used for that type of question. Would that be fine? $\endgroup$
    – called2voyage
    Sep 16 '16 at 15:27
  • $\begingroup$ DARPA does a lot of cutting edge space work. Maybe people would ask more DARPA questions if there was a tag? $\endgroup$ Sep 16 '16 at 18:31
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    $\begingroup$ I'm not sure. The military tag only has 11 questions even though it already exists. I'm more inclined to add more questions to an existing more general tag that has few questions, than to create a more specific tag and hope that people will use it. You could ask folks on meta what they think if you want. $\endgroup$
    – called2voyage
    Sep 16 '16 at 18:33
  • $\begingroup$ hmmm. You have a point. The eternal question: does information architecture direct or reflect the knowledge that people seek? I tend to favor more permissive structures over restrictive ones because there is little harm in a rarely used tag but great benefit in a tag that grows in usage over time. $\endgroup$ Sep 16 '16 at 19:24
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    $\begingroup$ Yes, and we do tend to lean that way, but in this case it may be contributing to the lack of development of the military tag. In any case, I think any further discussion on this needs to go on meta. $\endgroup$
    – called2voyage
    Sep 16 '16 at 19:26

It's mostly due to nature of how DARPA operates in general. They have few 'programs', they are project and result focused. DARPA tends to form a temporary project team, formulate desired outcomes, see it either fail or come through and move on. The results, if any, will end up in literature and in forms of IP in hands of contracted partners etc.

Their projects are time- and resource-bounded, not open ended. Teams and members come and go. There is a good overview article of of how DARPA operates here

There also are other organizations working on satellite fuelling, including DLR in Germany with DEOS mission, NASA on ISS with Robotic Refueling Missions and upcoming RESTORE-L project. MDA/Space Systems Loral have kept around a low-key commercial project for this for a decade or so as well.

DARPA itself has another upcoming project called RSGS - Robotic Servicing of Geosynchronous Satellites


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