• The forum software that supports hummy.tv has been upgraded to XenForo 2.3!

    Please bear with us as we continue to tweak things, and feel free to post any questions, issues or suggestions in the upgrade thread.

Space junk

Trev

Trev

The Dumb One
Just seen this bit about using a satellite to 'sweep up' space junk.
They said that bits of junk can hit other satellites at velocities of up to 27,000 MPH.
As the junk is likely to be in substantially the same low earth orbit (LEO) as the 'wanted' sat, how can the closing velocity be that high when the velocity for LEO is around 17,500 MPH. I suppose that this relative velocity could be achieved by the approach of a polar(ish) orbiting object to and equatorial(ish) orbiting object? Otherwise it would require that one object is orbiting 'the other way round'.
Presumably, as there is likely to be more junk in equatorial(ish) (as opposed to polar(ish) orbits, this is what they will 'go for' first.
The animation showed the 'collector' orbiting a short distance from the 'debris' at a similar velocity so unless the 'collector' satellite itself presents a 27,000 MPH closing velocity hazard to collect the 27,000 MPH junk, how does it all work?
 
For the closing speed of debris to be of any real danger to an asset at all, the debris has to be in an orbit at considerable angle to the orbit of the asset (including retrograde). The junk collector will be hunting things at a very low difference in orbital trajectory (to the junk collector, not the asset) and therefore with a very low difference in velocity.

What amazes me is that something like a fleck of paint, with a very low mass-to-surface-area ratio, can remain in orbit for so long.
 
Yes, I've often wondered about some of this. I have assumed that my doubts are in part down to the typical "we're all gonna die" reporting style of the press and TBH I've never bothered to do any deeper research into it.
Better put that on my bucket list :)
 
Black Hole said:
the debris has to be in an orbit at considerable angle to the orbit of the asset (including retrograde).
Click to expand...
Pretty much what I assumed. Are there any retrograde orbiting sats? They would have to be polar(ish) orbiting? Seems a shame to miss out on the 1,000 MPH(ish) of the earth's equatorial rotational velocity:eek:
Black Hole said:
The junk collector will be hunting things at a very low difference in orbital trajectory (to the junk collector, not the asset)
Click to expand...
Thet could prove pretty expensive, as it seems likely that the various bits of junk would be in considerably different orbits (to themselves, rather than the asset), so the junk collector would be a 'once only' or have the ability to change orbit considerably to 'collect' the next bit of junk.
Whilst I appreciate that, at the moment, they are just trying to prove the concept, but as it seems that it will 'pick up' the larger bits of junk and the tiny bits of junk are a real hazard, they are on a hiding to nothing anyway unless there is a big bit of junk presenting a real and present hazard to a very expensive asset and perhaps even life such as the ISS.
 
As the article infers, having every Tom, Dick and Harry sending his personal cube-sat up is not going to help.
It's a bit like flying cars - can you imagine what will happen when thousands of people get fed up with the traffic jam they are in and take off?
But maybe Skynet will have sorted us out before then :eek:
 
Trev said:
Whilst I appreciate that, at the moment, they are just trying to prove the concept, but as it seems that it will 'pick up' the larger bits of junk and the tiny bits of junk are a real hazard, they are on a hiding to nothing anyway unless there is a big bit of junk presenting a real and present hazard to a very expensive asset and perhaps even life such as the ISS.
Click to expand...
The thing is that the little bits of debris come from big bits that collide. Get the big bits out of the way and it will reduce the rate of increase in little bits.
 
Black Hole said:
What amazes me is that something like a fleck of paint, with a very low mass-to-surface-area ratio, can remain in orbit for so long.
Click to expand...
Why? What force would you expect to be exerted on it to change its orbit? And what's mass-to-surface-area got to do with anything?
 
prpr said:
Why? What force would you expect to be exerted on it to change its orbit?
Click to expand...
Drag caused by solar wind and the rarefied earth's atmosphere?
prpr said:
And what's mass-to-surface-area got to do with anything?
Click to expand...
I think a large surface area/mass ratio will make its orbit decay quicker. That's what they said on breakfast this morning when talking about fitting 'sails' to spacecraft to make their orbits decay quicker when at end of life.
 
prpr said:
Why? What force would you expect to be exerted on it to change its orbit? And what's mass-to-surface-area got to do with anything?
Click to expand...
Mass provides momentum, surface area provides (as stated above) drag and solar radiation pressure etc etc. I guess you're not a physics student.
 
Black Hole said:
It's the same reason big floaters are more difficult to flush away than small floaters.
Click to expand...
Strange, it always seems to me to be the small ones that hang around.


Black Hole said:
What amazes me is that something like a fleck of paint, with a very low mass-to-surface-area ratio, can remain in orbit for so long.
Click to expand...
... and while I'm picking at things; how long does it have to be in orbit before it's allowed to hit the ISS?
 
It matters not . You may use 'may' as a substitute for 'might' as on OED
may1
MODAL VERB
  • 1Expressing possibility.

    ‘that may be true’

    ‘he may well win’
 
AvP! In that case, the "may" clause is generally followed by a "but" clause (or an implied "but" clause).
 
Black Hole said:
I said "can" (is able), not "may" (has permission). :p
Click to expand...
Yeah, I was attempting a bit of humour while asking what length of time you believe the flake had been in orbit. It could have been flicked off another low orbit satellite (eg. by a micro-meteorite) hours, even minutes, before.
 
You must log in or register to reply here.
Back
Top