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:
- Transfer of hydrazine monopropellant between ASTRO and NextSat.
- Use of ASTRO’s robotic arm to detach and reattach a flight computer from a bay onboard ASTRO.
- Use of the arm to detach a battery from its bay on ASTRO and transfer it to a similar bay onboard NextSat.
- 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.
- Multiple rendezvous and capture scenarios with a number of different sensors, at ranges up to seven kilometers (4.4 miles).
- “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?
ps would someone who has the reputation please add the DARPA tag to this post? thx :)