Vision for Asteroids

The best place in the solar system for our near-term future -- the next thousand years or so -- is the big strip between Mars and Jupiter where the asteroids live. It's a long way out there -- the near edge 18 light-minutes out from the Sun, and the far edge 27. For comparison, the Earth is only 8.3 light-minutes out.

And it's mighty thin out there. The Belt has a volume of something like 6000 cubic light-minutes, while the total mass of all the asteroids is about one two-thousandth that of the Earth. I think that probably means that you could fly through that belt one hundred times staring out your front window the whole time and never see a darned thing.

Which brings up the first vision task for the asteroids: finding one.

Our spacecraft will probably know where it's supposed to be going, but it would be just immensely better if it could locate its target visually while it's still distant, and correct it's own course without waiting for the hour round-trip message to Houston. Or maybe it won't know! Maybe we will want it to go prospecting for a rock that no one has ever seen before.

In either case, we will want to be able to detect our asteroid when it still looks like this:

Big sky.

Possible bogey. Zoom 2x.

Maybe...

Zoom 2x.

I see motion. Look near center of image.

Zoom 2x.

Motion detected! Calculating orbit.

Tally-ho! We have a rock.

So this gives us task number 1.

1. Detect and track faint moving objects against a nearly-unchanging stellar background.

 

But of course the stellar background won't always be unmoving. The spacecraft will sometimes have to change attitude, which will make the stellar background change slightly from frame to frame.

Which gives us task number 2.

 

2. Track a gradually moving stellar background.

 

What does that mean? To track the stellar background means you find each star -- or at least each obvious star -- in one frame. Then you find them all again in the next frame, and then for each star in frame n you figure out which one it is in frame n+1. So, for each star, you end up building a little history that says 'Here it entered the field of view in frame n, and then here it is in frame n+1, and here it is again in frame n+2... and here it leaves the field of view in frame n+m.'

And all this talk of stars ... eternal stars. Unmoving...This reminds me of something.

Sometimes in machine vision applications, in cases where the object to be inspected can be manufactured or altered in such a way as to make visual inspection easier -- circuit boards, for example -- the manufacturer is kind enough to print fiducial marks on the object.

Fiducial marks on a circuit board.

Those are marks designed to be easily located by a vision system. In the case of circuit board assembly, they allow a pick-and-place machine to put all the little chips in all the right places. That isn't done by humans, you know. And those machines need to be able, at least a little bit, to see.

Such marks need to be easy to find, and unchanging.

Well, guess what else has such marks.

 

The Fiducial Marks of the Cosmos!

 

 

The Cosmos has its own set -- as long as you don't move very far. And we are not planning to move far. This is not Star Trek, where we zoom around so fast that you can watch the stars drift by out your stateroom window. (Just don't think about that too hard...) We are planning to only go zooming around within our own little 1500-cubic-light-hour solar system. In fact only out to the asteroid belt -- more like half a cubic light hour.

From Manchester, Michigan, in the United States, North America, Earth in the year 2020 -- the great ring of the asteroids looks like the vastness of infinite space. 

To the Cosmos, it looks like nothing at all.

For all of our machines flying around the entire asteroid belt for the next thousand years while we build Solar Civilization, the Cosmos provides us with an ideal set of fiducial marks. They're easy to see, and they never change. They're the same for everyone, everywhere.

It would be easy to memorize ten thousand or so of the brightest ones scattered all over the sky. Our machines will be created already knowing them. Using them, any machine anywhere within Solar Civilization can orient itself to an absolute coordinate system and know exactly where it's pointing.

If it can then also locate the Sun (not hard to do) and a few planets -- and if it has information about how the planets move -- then that machine can also know exactly where it is within the solar system -- a 3D location -- and exactly when it is! The eight planets move like the eight hands of a great clock, never to repeat itself, not in a trillion years. 

If you can see them all, you can use that great clock to determine the correct time down to the hour.

the Big Clock

So finally to use these lovely fiducial marks we will have one more vision task for the stellar background.

3. Given an image which is a subset of a known stellar map, locate the image on the map.

There will be much more later, but with these three visual capabilities we will be able to see our way to get where we're going.