Ever since I misread the report about SpaceX’s Dragon capsule, it’s had me thinking about the utility of manipulator arms. When I first read the report linked to in my previous post, I thought that they were saying that SpaceX’s capsule would include an arm, and that its arm would grab the station and allow it to dock. Unfortunately, as a commenter pointed out, it looks like I was wrong. They are planning on getting close to the station using some sort of LIDAR system, then having the space station’s arm grab them and berth them at a CBM port.
I still think though that having a spacecraft with a manipulator arm on it (or at least modularly attachable as an optional feature for any given flight) would be a very useful thing to have. I did a little reading about the ISS’s “Canadarm 2”, and realized that this is way bigger than what would be needed for an on-board manipulator arm. The stat’s I’ve been able to see so far indicate that the Canadarm on the shuttle weighed in at about 450kg total, and the Canadarm 2 tops the scales at a hefty 1800kg. The important thing to realize though, is that both of these are capable of handling really big payloads (over 100,000kg for the station’s Canadarm 2), like oh, mating the shuttle to the space station or vica-versa. A small capsule drying to mate itself to a station or trying to move a satellite is likely only going to need something a fraction as heavy. Say something in the 50-150kg range. Since this would be mated on the ground to the vehicle preflight, and could be brought back for maintenance on the ground between flights, it wouldn’t need a lot of the bells and whistles that were added to the Canadarm 2.
Since there are many companies out there developing CEV’s, capsules, or other sorts of manned or unmanned spacecraft, there could be some serious potential business if MDA Space Missions were to develop a generic manipulator arm. Right now they’ve been building expensive one-offs for the shuttle and the station, but imagine if they could sell a dozen or so of these smaller, simpler, generic systems? I don’t know if they could really make the busines case close at a reasonable price, but if they could, here’s my guess at what some ideal stats would be:
- Total Arm Mass: 100-150kg
- Maximum Handling Capacity: 15000kg
- Maximum speed: ~12cm/s unloaded, ~2-3cm/s fully loaded
- Power Consumption: Less than 250W
- Length: 8-12m extended
- Stowed Envelope: Less than 2m x .5m x .5m
Those are just a guess. Don’t actually know if that’s feasible or not, or if any of those suggested requirements are mutually exclusive.
The applications of such a system would be numerous:
- Recovery of damaged satellites
- On-orbit check-out and deployment of satellites
- Simpler “docking” with space stations and propellant depots
- On-orbit assembly of satellites, transfer stages, stations, etc
- Simplified rendezvous and docking proceedures
The list could go on much longer.