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Detection and Stealth in space

  1. Nov 29, 2014 #1
    This is the thread where we discuss some real and some obviously fictional scenarios (hostile spacecraft, missiles, or asteroids in either near-earth, cislunar or interplanetary space) with real world physics only. Specifically, things are detected by optics, radar-system and so on, things that may or may not be designed to be less visible. In the first scenario, it is a perfectly normal rock.

    Scenario #1.
    The trajectory of an asteroid intersects Earth. How likely are we to detect it before it hits? What kind of detection systems can be used? What kind would ideally be built for the task?

    I'm thinking our current satellite systems aren't optimized for "sweeping" the entire sky, in the case where they are turned towards space by design they're viewing far-away objects. A telescope-equivalent designed for looking at an entire hemisphere of space would either be moving or be built like the eye of an insect, with ,multiple telescopes directed against each portion of sky.

    Also, am I right in thinking that an active LIDAR-system in the form of a pulsed laser directed against a portion of the sky would greatly improve our chance of detecting an inert object there?

    Do note that this thread is a bit less specific than this thead, I'm thinking the multi-discipline a third engineering, a third conjecture approach often used when trying to analyze fictional scenarios with real world science might scare knowledgable people off. Here a clearly-defined scenario is given and then it is analyzed. I'll continue the thread with "scenario #2, #3, et cetera if the discussion gets going).
  2. jcsd
  3. Nov 29, 2014 #2


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    There are just a few (like 3-4) objects that got detected before they hit Earth.
    Small objects (<10 m) have to be close to get detected, and then we don't have much time. The larger objects are easier - most 1km-objects that can come close to Earth should be known by now.

    There are all-sky surveys - 2MASS for example. Gaia started taking data a year ago and scans the whole sky as well. Gaia has a good chance to find objects with a diameter of ~500 m or more, below that they have to be closer to earth to be visible.
    There are also concepts like Sentinel that could detect significantly more than existing telescopes.

    Without the retroreflectors from space missions, even detecting the moon that way would not be easy. Radar can be used to track various objects over larger distances, but the emissions have to be directed to hit the target - not very helpful if you want to find unknown objects.
  4. Dec 1, 2014 #3
    How about detecting the heat of the asteroids? I expect them to be heated to lunar average by sunlight, if they come close to Earth.
    Do the distant stars and galaxies produce significant amount of IR background clutter?
  5. Dec 1, 2014 #4
    If it's a very large asteroid, like the Chicxulub asteroid, we'd be able to see that coming years away. Whether we'd be able to do anything about it is another question entirely.

    The smaller ones, under 1 km diameter, would be a bit more troublesome to detect. Simply put, space is huge, asteroids are small. Tracking them isn't the problem, since once you've found it and learned enough about its trajectory you pretty much have all you need. Finding smaller asteroids is the problem. There's just no getting around the fact that an object half a km in diameter millions of kilometers away is going to be difficult to spot.

    Increasing the number of telescopes you're using to scan for asteroids such as in your example would certainly help, though, but it's not a perfect solution.
  6. Dec 1, 2014 #5


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    Visible and infrared observations are the standard methods to find new asteroids.
  7. Dec 1, 2014 #6
    ( I thought, because the atmosphere is warmer than the asteroid, and we dont have that many satellites, giant radio telescopes play a bigger role. )
  8. Dec 2, 2014 #7
    just watched a show on asteroid detection (mistook it for the landing on one mission) the Canadian space agency sent a satellite up to help scan for asteroids in the blind spot created by the sun so we can find those like the one which hit Russia from the blind spot. typical TV show glossed over the kinds of detection being used in favor of repeating how disastrous a big impact would be.
  9. Dec 8, 2014 #8

    The thread title "Detection and Stealth *in* Space" could imply a tactical situation and space-to-space detection. However Scenario #1 implies scientific detection. Obviously all space-located objects are not detected and this is a concern. However this does not mean they're hard to detect, only given current funding and priorities it *seems* hard.

    As already mentioned the proposed Sentinel IR space telescope could detect most NEO asteroids down to 140 meters. That would be one little telescope 1/7th the weight and about 1/20th the cost of Hubble. From this alone it's obvious that detection of objects in space is relatively easy. This makes sense considering the space backdrop is nearly absolute zero and virtually everything else radiates heat.

    Detection of space objects from earth is somewhat harder since the atmosphere blocks the most useful IR wavelengths:

    http://www.mining-technology.com/uploads/feature/feature2049/2-atmospheric-opacity.jpg [Broken]

    This in turn forces reliance on optical detection which is limited by clouds, weather, light pollution, available hours of night, sun/moon, etc, etc.
    Last edited by a moderator: May 7, 2017
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