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posted by martyb on Friday June 22 2018, @01:28PM   Printer-friendly
from the gonna-need-a-bigger-net dept.

Astronauts eject UK-led space junk demo mission

A UK-led project to showcase methods to tackle space junk has just been pushed out of the International Space Station.

The RemoveDebris satellite was ejected a short while ago with the help of a robotic arm.

The 100kg craft, built in Guildford, has a net and a harpoon.

These are just two of the multiple ideas currently being considered to snare rogue hardware, some 7,500 tonnes of which is now said to be circling the planet.

Previously: SpaceX Launches CRS-14 Resupply Mission to the ISS


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  • (Score: 4, Interesting) by Immerman on Friday June 22 2018, @04:38PM (3 children)

    by Immerman (3985) on Friday June 22 2018, @04:38PM (#696815)

    Umm, what parts of space junk" and "deorbit" do you not understand? There's countless tons of orbitting junk left over from old collisions, to say nothing of the retired satellites boosted to graveyard orbits where things will slowly collide and build a cloud of smaller debris over time.

    And deorbitting means just that - remove from orbit. Let's take the ISS as an example - the biggest target in orbit. As soon as you decelerate something enough to hit the atmosphere its days in orbit are extremely numbered - to hours or minutes if you're actively decelerating it via rocket or drag-chute. Even if you're only grazing it at ISS altitude. Meanwhile space is big - even the ISS's extremely low, tight orbit is about 43,000 km around - it physically occupies less than 0.00025% of its orbit. And any intersecting orbital path will either share a very similar orbit, and thus be relatively stationary compared to the ISS, or only intersect it at a couple points a few hundred meters across, and it's thus extremely unlikely that either body will be in the intersection point at the same time as the other. That would still still be a problem for long-term satellites, since unless intersecting orbits are perfectly synchronized the satellites *will* eventually collide, but if you're deorbitting one of them even remotely effectively you're unlikely to be in an intersecting orbit long enough for the risks of collision to be worth mentioning - even assuming you're not taking any precautions to avoid it, which you almost certainly would. Moreover, for something like the ISS that's already skimming the atmosphere, anything on an intersecting orbit will be plunging significantly deeper into the atmosphere at significantly higher speeds - even without active deceleration the atmospheric impact will deorbit it rapidly.

    Meanwhile, matching orbits is comparatively easy - every supply run to the ISS does it with extreme grace and precision. The hard part is identifying your target in the first place, since orbitting junk generally doesn't reliably sport an active transponder or obvious visual profile - especially smaller debris like old cube-sats and escaped crescent wrenches. The other potentially hard part is capturing it - but a net fired at a relatively stationary object seems quite likely to succeed. Micro-gravity may make it a bit more complex though, we don't really have a lot of experience net-fishing in a free-fall vacuum, which is one of the reasons why they're actually testing such systems instead of immediately deploying "production ready" models.

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  • (Score: 2) by ledow on Friday June 22 2018, @05:48PM (2 children)

    by ledow (5567) on Friday June 22 2018, @05:48PM (#696860) Homepage

    Gosh, what would I call a spy sat that I didn't want people looking at? If only I could call it, say, a failed launch that remained in orbit but ended up "unpowered" (very common).

    Your sweeper sat comes along, trashes the Russian sat thinking it's junk, bang you've just started a war.

    Either:

    - Someone owns that debris, and will give you permission, if you can trace that person
    - Nobody knows who owns it (because if we know who owned every piece of space junk, we wouldn't have to track it, would we?)

    An orbit is a hard thing to achieve in perfection (proven by the REAL failed missions). While things stay in their orbits, you're fine. They're not space junk. They're orbiting in the right bands. But space junk will collide with anything, and move, and then end up in an elliptical orbit and now you're buggered - it could end up anywhere, crossing every "safe" orbit out of control and possibly quite unpredictably - it'll also accelerate in angles you didn't intend and become lethal and wide-spread. We've not seen a 10km asteroid in the past, what makes you think we'll see a sat out of line on a non-circular orbit?

    Decelerating the orbit wrong also does exactly what I just said - it doesn't deorbit, or it skims the atmosphere, or it goes eliptical which means it comes back to bite you (faster than ever intended on it's longest path) on a different timescale to that which ANYONE intended. Do you not remember how slim the Apollo 13 margins were to enter the correct orbit-exit trajectory? It's a damn miracle they could do it at all.

    It's not that it's not possible - it's that it's not as easy as you make out. And needs power, control and time to get it right. Luxuries you don't have in a sat that you're using to deorbit things. Either it's a one-time deal at HUGE expense, or that device has to be able to suck up a TON of propulsion power to do such maneouvures.

    Things that are circling nicely in prescribed orbits occupying regulated bands of space, that kind of space junk is never a problem because it's easy to avoid, and there's literally no point clearing it. It's the stuff that's in your way, unpowered, failed orbits, unusual orbits, random, unregulated, uncontrolled, unpredictable and untrackable that's the problem

    • (Score: 2) by frojack on Friday June 22 2018, @07:47PM

      by frojack (1554) on Friday June 22 2018, @07:47PM (#696915) Journal

      Your sweeper sat comes along, trashes the Russian sat thinking it's junk, bang you've just started a war.

      You realize that this has actually happened already and there was no war, right?

      https://www.space.com/20138-russian-satellite-chinese-space-junk.html [space.com]
      https://www.huffingtonpost.com/entry/the-worst-collision-of-orbiting-satellites-and-space_us_59406ffee4b04c03fa26166e [huffingtonpost.com]

      --
      No, you are mistaken. I've always had this sig.
    • (Score: 2) by Immerman on Friday June 22 2018, @07:48PM

      by Immerman (3985) on Friday June 22 2018, @07:48PM (#696916)

      First off, "space junk" is generally used to refer to the debris created by previous collisions (and dropped wrenches, etc.), small enough to be difficult to track - intact satellites are easily tracked navigation hazards.

      Destroying something you publicly called trash has got to be one of the least-compelling reasons to go to war I've ever heard. It's not going to be a *reason* to go to war - at best it will be a really bad excuse. And of course we have to track space junk even if we know who "owns" it since, as you pointed out, there's no such thing as a stable orbit.

      Any de-orbit attempt that skims the atmosphere is successful, though it may take several more passes to complete than planned, since every subsequent orbit will also skim the atmosphere.

      As for Apollo 13 - the orbit-exit in question was NOT to de-orbit, but rather to boost out of lunar orbit on a trajectory that would carry it across the it 239,000 miles to just skim the 8,000-mile diameter target of the Earth on a path that would allow for orbital braking and reentry without killing the crew. A *far* more difficult thing to do than simply de-orbit junk that you want to have burn up in the atmosphere. De-orbitting is easy - just fire your rocket directly against your line of motion, to impart enough delta-v to lower the opposite side of the orbit into the Earth's atmosphere. For safety you can impart too much delta-v so that you take a more direct route to collision with Earth - only a problem if deorbitting something large and durable enough to have a fair chance of reaching the ground if it comes in at a steep angle.