Debris Field around space wreckage

Question

I am writing a story in which a crew is investigating a wreckage of two space vessels that collided at enough speed to disable the vessels without completely annihilating the two structures. The wreckage is orbiting a system far enough from any planet to be negligibly affected by their gravity. The ships are very large (~10km in length, ~1 trillion liters in volume) and the wreckage is hundreds of years old.

My question is this: Would there be a debris field around the two ships if they came to rest relative to each other after the collision (essentially the momentum relative to each other is cancelled)? How long would the field remain, and would it be moving?

Answer 1

The escape velocity for such a system is very low, of the order of less than m/s. For a reference, when Philae landed on 67P Churyumov–Gerasimenko, it had to keep a very low velocity to stay gravitationally bound it

The acceleration due to gravity on the surface of Churyumov–Gerasimenko has been estimated for simulation purposes at $10^{−3} m/s^2$,

For perspective, had the lander exceeded about 44 cm/s (17 in/s), it would have escaped the comet's gravity.

The comet is, as a first approximation, comparable to your spaceship in terms of gravitational field, so it is very unlikely that any debris resulting from the impact will stay orbiting the wreck, unless the impact happens at a very slow relative velocity.

To make a comparison with a car accident, if the impact looks anything like an impact happening after crossing with the red light, most debris will have velocities large enough to escape the gravitational field of the wreck. If instead the impact looks like a light bump given when parking in reverse, it's likely that the resulting debris will be orbiting around the wreck.

Answer 2

It really depends on the speed of your ships

If the ship is designed to travel between planets, and is inhabited and would need thus to reach its destination within it reasonable time, it would need to travel extremely fast. Keep in mind our current space probes travel at up to 330,000 mph, and yet we still wait months or years for them to reach a planet.

For interstellar speeds, this is several orders of magnitude worse, requiring relativistic speeds (ie. speeds close to the speed of light) to get to a nearby star system within a standard human lifetime.

Unfortunately at velocities capable of travelling between stars, let alone planets, all material bonds are incapable of resisting any impact or the energy of any collision, such that solids more accurately behave like liquids when impact occurs.

The ships would collide as if they were made of liquid, so imagine your ship made of water (just temporarily held in shape) upon impact and use this to guide the predicted behaviour of your debris field. Basically it would disperse almost like a gas in many directions almost like water droplets. I doubt there would be any useful components remaining, unless the collision was not fully centred between matching ships, in which case part of an original section of ship would remain largely on-course and potentially unaltered, with the other part removed.

However, it may be possible in your world to have a 'debris field' like in films, for instance:

• If the velocities are so low that they collide more like ships in a sea.
• For the velocities to be low, perhaps your ships are sleeper ships, generation ships, or even not inhabited at all, such that they reach their destinations in millions, or tens of millions, of years instead.
• There is a collision avoidance system, that slows them down but perhaps only marginally successful so they still collided at a slow speed
• The collision was actually in the same direction with enough force to generate a salvageable debris field, perhaps intended to be so such that parts could be salvaged (ie, a military action)

In which case the debris field would indeed be more like ocean collisions - however if nothing stops their dispersal (like gravity) then eventually the parts would continue to travel outwards for almost eternity, and may indeed congeal eventually under the attraction of their own gravity.

Answer 3

Collision causes damage and fragmentation

When two large bodies collide, there is damage and fragmentation as explained here. The damaged parts remain together, but the fragments move away at angles to the line of collision conserving the momentum.

Figure taken from here.

Low speed fragments

Fragments with low speed may get back to the damaged bodies because of gravity and remain there.

High speed fragments

Fragments with high speed will escape from the gravitational pull of the large bodies.