

The search for Apollo 10's "Snoopy" (lunar module) - geuis
http://news.discovery.com/space/apollo-10-search-snoopy-astronomy-110919.html

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kmm
While this may seem impossible, it has been done before. A supposed asteroid
has been identified as the fourth stage of the Saturn V [1]. This is so
fascinating. What I would give to get a look in there. I presume it's still in
pristine condition, because what could have done damage safe for the constant
heating and cooling?

[1]: <http://en.wikipedia.org/wiki/J002E3>

~~~
celoyd
Isn’t identifying an unknown body as debris going to be way easier, generally,
than going the other way? Especially when the body is in solar orbit, and
therefore somewhere in a bigger volume and presumably dimmer?

I don’t know much about orbital mechanics, but this line really got me:

 _The key problem which we are taking on is a lack of solid orbital data since
1969_

If it hasn’t been observed at all for 42 years, don’t minuscule errors in the
initial observations give a huge uncertainty to its current position? Not just
where it is on its orbit, but what its orbit is? Especially if it’s been in
solar orbit at roughly 1 AU, and thus presumably interacting with the Earth-
moon gravity well periodically? And perhaps accidentally venting from
overheated tanks etc.?

I have heaps of respect for the numerical methods that the astrophysics people
have. I’ve seen little bits of them and they’re uncannily accurate and
efficient. But how much can they help you if you don’t know where Snoopy was
to the millimeter in 1969?

Maybe this makes more sense to people with a stronger grasp of physics than
mine. I just don’t see how you can go from the ephemeris data they presumably
have to a realistic set of angles at which to point telescopes.

Anyway, even if they don’t find it, it’s a really neat project – and, as Howes
says, they’re sure to find _something_ interesting.

~~~
kmm
Of course it's easier, I was just trying to show that we do have the
technology to identify objects of a scale of some tens of meters from a
distance of hundreds of thousands of kilometres. It's a pretty amazing feat of
technology, which also allows us to do geological research of the planet Venus
without a probe[1].

I haven't researched the three-body problem personally, but I have had some
concepts explained and as far as I know it is chaotic (like almost every
dynamic system in nature). We won't be able to predict the exact position. But
there are still laws similar to those of conservation of energy and momentum.
In this problem they take the form of the constancy of the Jacobi integral[2].
Thus, while we don't know exactly where Snoopy is, we can exclude huge volumes
where it certainly never went. It's probably still very close to the Earth-
Moon system.

[1] <http://en.wikipedia.org/wiki/Venus#Ground-based_research> [2]
<http://en.wikipedia.org/wiki/Jacobi_integral>

~~~
celoyd
Yeah, real-world _n_ -body is very hard. But astronomers can do it with said
amazing integration methods. The thing is that they tend to do it for known
start states.

With Snoopy, our major masses are Sol, Terra, and Luna. Their dynamics are not
trivial, but we have precise and accurate models. And we can drop a massless
particle into the model and make really strong predictions, usually, about its
position in 42 years. (Only usually because it might do complicated things
like skip off our or the sun’s atmosphere, but we can overlook that.)

What I’m trying to grapple with is that I don’t see how they’ll know where,
and along what vector, to insert Snoopy. Say we know its start state to within
±100 m (x, y, z) and ±0.01 m/s (dx, dy, dz). I don’t think it really matters
how well your methods conserve energy at that point – they’re working on too
rapidly widening a volume of possible configuration space. Or is there some
kind of attractor/anti-chaos effect that I don’t understand here? I’m honestly
asking; I only have little bits and pieces of the knowledge here, and I’d be
very interested to know the details of why my incredulity is unfounded.

 _we can exclude huge volumes where it certainly never went. It's probably
still very close to the Earth-Moon system._

Granted we can exclude huge volumes – the vast, vast majority of the space in
the solar system. But say we know it’s within 0.1 AU of Earth’s orbit (not
Earth itself), in a solar orbit as the article suggests. Wolfram Alpha says
that’s still a volume of about 3e24 km^3.

And here’s what’s worse (as far as I can see). Say we’re lucky and, by ruling
out slingshot effects and so forth, we know it’s in a medium earth orbit
instead of random solar orbit. That’s a volume of about 2e14 km^3. Say we’re
even luckier and also know it’s at lowish inclination. So in terms of the
volume in the solar system, we have it basically pinned down. The thing is,
that still leaves us something like half the solid angle of the sky to examine
with telescopes.

In other words, as long as we’re using optics that can identify it at all, its
distance doesn’t really matter as much as the projected area, the area of
_observed sky_ as opposed to real volume, that it could be in. And I have
trouble believing intuitively that that can be narrowed down very much when we
don’t know the starting state well in any dimension other than time – but I
really would like to be convinced otherwise.

I think the parsimonious explanation here is probably that they had much
better starting observations in 1969 than I’m imagining.

~~~
kmm
Again I don't know for sure but I fear that predicting the position of Snoopy
over a period of more than some months is impossible. There's not only the
gravitational interaction, but also the orientation dependent radiation
pressure, tidal effects and gravity gradient torque. I would say the
configuration space isn't just huge, it's probably all of the dynamically
allowed space.

I think the distance does matter. You have to observe an object ten times more
distant a hundred times longer to receive the same amount of photons. If
conservation laws dictate that it's still in the Earth-Moon system, that could
mean significantly shorter observation times.

