
Oumuamua may be a hydrogen iceberg - elorant
https://news.yale.edu/2020/05/29/ahoy-oumuamua-may-be-hydrogen-iceberg
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fenwick67
This is great sci-fi fodder, imagine if you could land a tiny craft on that
thing and then use the hydrogen as fuel without having to haul all that fuel
into deep space (very unlikely to be practical but the idea is exciting).

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motoboi
Imagine you just land a tiny craft on that thing and let the thing take you to
interestelar space without you having to burn no more fuel.

Unfortunately, if you can't catch it, you don't need it for that, as you'll be
traveling faster that it to be able to intercept it and would just burn fuel
trying to break enough to match its speed.

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TeMPOraL
Rule 1 of orbital mechanics: if you're about to dock with something, you're
already on the same trajectory as that thing.

Might make a good radiation shield, though.

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ragebol
I'm not into orbital mechanics at all, just an interested layman, but how does
a space tug work in relation to your 'Rule 1 of orbital mechanics'?. What is
the point of a space tug then?

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walrus01
One of the purposes of a proposed 'space tug' is to use slow low thrust but
high delta-v, high efficiency engines to do things such as:

Raise the orbit of satellites in LEO which are affected by atmospheric drag.
Or re-boost things like the international space station, proposed future
Chinese space station, etc.

Extend the lifetime of geostationary satellites which are still electrically
functional, but out of station keeping propellant. One such thing docked for
the very first time with a satellite earlier this year.
[https://en.wikipedia.org/wiki/Mission_Extension_Vehicle](https://en.wikipedia.org/wiki/Mission_Extension_Vehicle)

On unmanned missions, slowly move cargo from low earth orbit to destinations
at the Moon or Mars. If you can use ion and hall effect type thrusters for
your missions to move cargo around, you can establish a logistics supply chain
for essential supplies consisting of unmanned craft.

[https://en.wikipedia.org/wiki/Delta-
v_budget](https://en.wikipedia.org/wiki/Delta-v_budget)

[https://en.wikipedia.org/wiki/Specific_impulse](https://en.wikipedia.org/wiki/Specific_impulse)

An interesting example of using ion engines to maintain low earth orbit,
through long continual thrust was this mission:

[https://en.wikipedia.org/wiki/Gravity_Field_and_Steady-
State...](https://en.wikipedia.org/wiki/Gravity_Field_and_Steady-
State_Ocean_Circulation_Explorer)

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TeMPOraL
I try to follow interesting space missions, but I've never heard about either
of the two you linked to here. Thank you!

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jamestimmins
"It has now passed beyond Saturn’s orbit and will travel another 10,000 years
before exiting the system".

How big is our solar system? I always assumed it referred to everything
between the sun and Pluto, but 10,000 years suggests it's far larger.

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saberdancer
I'm not sure of what definition they used here, but one that is common is
heliosphere, or in other words sphere around the Sun where solar wind is
dominant. This is about 120 AU.

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wahern
‘Oumuamua's incoming and outgoing speed is ~5AU/year. In 10,000 years that's
50,000AU, which is approximately the distance to the outer most region of the
Oort Cloud:
[https://en.wikipedia.org/wiki/Oort_cloud](https://en.wikipedia.org/wiki/Oort_cloud)

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lgl
I always thought the Oort cloud was a scientifically proven thing but
apparently it's "a theoretical cloud of predominantly icy planetesimals
proposed to surround the Sun at distances ranging from 2,000 to 200,000 au
(0.03 to 3.2 light-years)"

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divbzero
Thanks for correcting my similar misimpression.

It’s curious to note that the proposed outer limit of the Oort cloud (3.2 ly)
is more than half the distance to the closest star system (4.4 ly) [1] though
I’m unclear whether the cloud would be roughly spherical or have some sort of
directionality.

[1]:
[https://en.wikipedia.org/wiki/Alpha_Centauri](https://en.wikipedia.org/wiki/Alpha_Centauri)

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bovermyer
I like the idea that these things could be potential star-seeds. It would be
an interesting way for new solar systems to form.

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monadic2
Makes me wonder if you could slingshot around the sun towards relativistic
speeds with thermal power. At the very least it could save fuel on the egress,
if not the second half.

Can you aerobrake around a star?

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ddxxdd
Thermal power requires a reservoir of cold temperature; your car's engine
would do nothing if the incoming air was just as hot as the post-ignited air.

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dmurray
I'm sure this is true in practice, but I can't wrap my head round why it's
correct in theory. Let's say I hook up my exhaust to my intake, I can still
squirt some gasoline into the engine, make it explode and expand and thereby
drive a piston, at the cost of having even hotter air the next time round.

If I repeat this long enough, my engine will melt, but that's a minor matter
of materials science. Maybe I can win my drag race before it melts. Is that
the limiting factor or is there some other reason I'm missing that we need a
heat gradient?

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marcosdumay
If you heat it more each time, yeah, the old air can act as a cold reservoir
and make things run.

If you do draw it with enough detail, you'll notice that if you do not heat it
more at each turn, you won't be able to get any pressure difference at your
"explosion".

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crimsonalucard1
Is there an element or compound in the universe that will remain a gas at 0K?
Does everything become solid at that temp?

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caymanjim
To be pedantic, it's impossible to get to 0K due to quantum fluctuations. Even
empty deep space is over 2K. In laboratory settings, we've gotten way below
1K. I don't think anything qualifies as a gas at that temperature. It'd be a
solid or a BEC.

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radioactivist
This is true, but doesn't have anything to do with quantum mechanics -- the
third law of thermodynamics is basically a statement that you can't cool
things to absolute zero.

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crimsonalucard1
Your input caused me to google a video about this:

[https://www.youtube.com/watch?v=kswiDQ2aAKA](https://www.youtube.com/watch?v=kswiDQ2aAKA)

Very intereting!

