What are the safe structural elements of spacecraft that could be used for on-orbit capture?

Question

I know this depends on the general configuration of a spacecraft, but I am hoping to gain some insights. Assuming you have a servicer spacecraft with an abstracted capture mechanism (i.e., end effector), what might be the general structural features on a (non-cooperative) spacecraft that we could use to capture it? I suspect that not all spacecraft structures are designed to support concentrated loads. For example, solar panels are not suitable for obvious reasons. This review paper https://www.annualreviews.org/doi/pdf/10.1146/annurev-control-042920-011106 mentions the liquid apogee engine (LAE) nozzle and/or launch vehicle adapter interfaces as suitable candidates (note that NASA's OSAM-1 mission apparently plans to use the marman ring of their target spacecraft) but also lists some of their drawback.

I was wondering if there were any other external features that I hadn't thought of.

Answer 1

Just extending the comment by blobbymcblobby. There are some useful concepts to consider:

1 Launch

Everything launched into orbit (that is still in tact) was attached to its launch vehicle somehow.

• For many satellites it is the launch vehicle adaptor ring on the base of the satellite. This applies when the satellite is the primary payload of the launch vehicle. There are standard sizes of adaptor rings from some vendors of separation systems.
• For cubesats I have always assumed it must be the edges of the cube and that these slide along an effective rail in each of the corners of the dispenser.
• For many other satellites these can be quite bespoke, for example there could be three or four short pillars on the launcher, or the satellite, each of which has its own lock/separation mechanism with its counter part on the opposite vehicle.

2 In orbit propulsion

Any thruster on the satellite bears its own force on the satellite. An apogee engine (e.g. for a geostationary satellite) is quite large and axially aligned. Attitude control thrusters can be at all kinds of angles, sometimes arranged symmetrically and sometimes not. The thrust range should indicate the minimum force that can be parted along the thruster's own axis - this can be anything from millinewtons for some electric propulsion, then 0.1 to 20N for attitude control and 500N to 2kN for main translation thrusters.

3 Getting it onto the launcher

Now that we've established the obvious ones...

For any satellite there has to be some way of mounting it onto the launcher without damaging it, noting that obviously one must use something other the separation interface whilst mating it to that separation interface. My own knowledge is pretty sketchy other than for many geostationary satellites there are places high up the +- Y walls (the mirror covered walls) where sling bolts can be attached. Note this doesn't mean that these locations will be accessible in orbit at all, they may likely be covered with thermal insulation once the satellite is on the launcher. The main point is that these are other places designed to bear the full 1g weight of the satellite.

All of these options are going to need some carefully thought out alignment for attaching an external object and whether it includes removing blankets etc.

Hope that helps