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update 2020-11-20: OSAM-1 (Formerly Restore-L) Continues to Make Progress, Fuel Tank Installed

note: the recent 2019 news Northrop's satellite refueling spacecraft launches on October 9th which is sourced from Mission Extension Vehicle Headed for Space reminded me that there may be some closure on this 2016 question, so I've un-accepted the old answer for now.


I've just read here that:

Also this week, the agency announced that it is moving ahead with plans to create a robotic spacecraft designed to service satellites. Dubbed Restore-L, the mission has two objectives: refuel a communications satellite, possibly the government-owned Landsat 7, and test autonomous docking and navigation capabilities that could be used in future flights to Mars.

NASA also hopes Restore-L will usher in a new era of robotic servicing for commercial and scientific satellites.

"Restore-L effectively breaks the paradigm of one-and-done spacecraft," Frank Cepollina, who led the five-crewed servicing missions to Hubble, said in a statement. Space robots could be valuable to commercial operators like a joint venture between Airbus and the start-up OneWeb, which wants to send more than 900 mass-produced satellites into orbit starting in 2018.

(I'm not sure if the "communications satellite" is a misnomer, or refers to an additional satellite besides Landsat 7.)

I followed links to the Educational Outreach page of the NASA Satellite Servicing Capabilities Office, which links to the announcement and a description of the Restore-L mission.

On the outreach page there is a YouTube video, and an animation there caught my eye. Here is a GIF reconstructed from frames of the video:

enter image description here

The announcement says:

Restore-L technologies include an autonomous relative navigation system with supporting avionics, and dexterous robotic arms and software. The suite is completed by a tool drive that supports a collection of sophisticated robotic tools for robotic spacecraft refueling, and a propellant transfer system that delivers measured amounts of fuel at the proper temperature, rate, and pressure.

Future candidate applications for individual Restore-L technologies include on-orbit manufacturing and assembly, propellant depots, observatory servicing, and orbital debris management. NASA is also directly applying several Restore-L technologies to the Asteroid Redirect Mission.

To me, the animation suggests that the satellite (is it Landsat-7?) might have a refueling port for easy access, and the robotic maintenance craft would not need to cut open panels, turn valves, bleed and then cut into lines "manually" in order to replenish propellant. (don't forget to reseal and leak-test the lines and close the panel as well!)

But, if the port were for loading the satellite with propellant before launch, I would suspect that it be sealed reliably somehow - I don't think it would be as simple as a quick connect type of fitting.

How accessible are the couplings and valves for replenishing propellants to Landsat-7?

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My reading of the Aviation Week article on this seemed to suggest that while Landsat-7 was not designed to be refueled, when they looked at its design, they found a fuel line, they could patch into that could be used to fill the tanks again.

They need to cut away the insulation to get to the pipe, and then will probably use some variant of a vampire tap to connect to the system.

I have used these in air conditioning repair to refuel Freon in sealed systems and they are really simple. Heck there is even a kind of vampire tap for 10-Base5 coax cable.

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  • $\begingroup$ OK! I'll check the libraries. Is it one of these? NASA Plans Satellite-servicing Spinoff To Industry (Aviation Week, May 9, 2016) or Satellite-Servicing Test Could Replace Asteroid Mission (Aviation Week, February 12, 2016)? So it sounds like Landsat-7 is not exactly "robot-ready". It is not equipped with a refueling port. Instead, it is a good candidate for a real, unscheduled, unplanned, untested type of remote, robotic repair mission. Great! $\endgroup$
    – uhoh
    Jun 26 '16 at 23:46
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    $\begingroup$ I'd hope they don't use a standard OTS HVAC vampire tap, or else the customer's gonna be pretty annoyed in 6 months when the hydrazine or whatever's leaked out :) $\endgroup$
    – 0xDBFB7
    Aug 17 '17 at 2:28
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    $\begingroup$ I've unaccepted without prejudice; it's been three years and there may be more information available now. $\endgroup$
    – uhoh
    Oct 7 '19 at 1:31
  • $\begingroup$ I've added an update to the top of the question $\endgroup$
    – uhoh
    Nov 20 '20 at 0:54
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    $\begingroup$ I would not be surprised if they have some kind of special vampire tap with a metal crush gasket. $\endgroup$
    – ikrase
    Nov 20 '20 at 5:34
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I would expect that if a satellite had no special design for in-orbit propellant transfer then the initial list of options would centre around the normal ground propellant supply interface, normally referred to as a "Fill and Drain Valve", FDV.

Typical characteristics of interest are:

  • often has an internal valve that can be operated by a "ground half coupling" ( i.e. the part at the end of the ground hose) which makes an outer seal during transfer - this prevents external propellant leak when the valve is opened/closed. i.e. no "tap"-like handle on the spacecraft side.
  • external metal cap to provide a second seal.
  • this two-seal approach allows for the external dribble volume of the valve to be evacuated to remove propellant prior to removal of the ground-half coupling
  • the external cap is often wire-locked to provide safety assurance for post propellant loading operations
  • the FDV protrudes through any satellite structure panels and is covered by blankets that can be removed and refitted a pre-launch propellant loading.

Obviously this all looks great from an in-orbit propellant transfer perspective except for the wire locking. By comparison however, solutions that involve cutting into a section of pipe, no matter how creative, will at least be up against the problem of accessibility behind structural panels or blankets that were not designed to be removed and refitted easily.

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