
Missions to and Sample Returns from Nearby Interstellar Objects - sohkamyung
https://arxiv.org/abs/2008.07647
======
avian
Lot's of unproven technologies in the proposed missions: thermal nuclear
propulsion (a big can of worms by itself), zero-boil-off hydrogen tanks,
microsat swarms, ...

One point that I haven't seen discussed in similar papers was the need to deal
with uncertainty in the object's trajectory. You have to be able to do
targeting (i.e. carry a big enough telescope) and do course correction on-
route (i.e. carry enough fuel).

~~~
f00zz
> a big can of worms

I'm all for nuclear rockets, but it's a bit hard to believe that people will
accept a flying nuclear reactor when you remember the controversy over
Cassini's comparatively puny RTG.

~~~
sp332
I don't mind having a nuclear rocket _in space_ , but I am worried about the
part of the trip where it's still in the atmosphere and strapped to a flaming
bottle of kerosene.

~~~
spaetzleesser
We can strap it to a flaming bottle of liquid oxygen and hydrogen :)

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duncan_bayne
It might also be worth leaving artifacts on them, in case of discovery by
future spacefaring species - assuming the objects still possessed system
escape velocity.

Actually, wouldn't it be a blast if we found signs that someone had done just
that already?

~~~
misanthropian00
Would be even better if Oumuamua turned out to be an artifact itself. Its
acceleration without any visible off gassing is still unexplained.

~~~
duncan_bayne
If it was an artifact - especially a discarded solar sail, explaining the
acceleration - there might be a follow-up.

Imagine you were making a sail-propelled probe, with the intent of slowing the
probe so it was captured by the target system. So the probe would have two
sails. The first would be deployed after launch, to catch the initial laser
beam, then later solar winds, to accelerate to system escape velocity.

You'd then _detach_ that sail, and cruise. Later, you'd deploy a second sail
to start braking on your way into the target system, to slow to capture
velocity.

The first thing the inhabitants of the target system would see would be the
first, discarded, sail as it tumbled through their system and accelerated back
out ...

~~~
JumpCrisscross
> _You 'd then detach that sail, and cruise_

Why? Just accelerate towards the target as long as possible and then flip
around. Assuming a columnar source ( _e.g._ from a laser) and non-columnar
target ( _e.g._ from our sun), this could be done with minimal (if any) cost
in time to arrival.

Carrying two solar sails is expensive. If it’s not, I’m not sure one would be
using solar sails at all.

~~~
duncan_bayne
I'm guessing here, as I've never built a sail-propelled interstellar probe :)
But I'm assuming that:

1) The characteristics of a good laser-propelled acceleration sail would be
different to those of a good solar-powered braking sail.

2) Flipping around while attached to a deployed solar sail would be _hard_. In
my head I'm imagining something like looping a paraglider
([https://www.youtube.com/watch?v=-oEeTtQIEjs](https://www.youtube.com/watch?v=-oEeTtQIEjs))
but much harder. It'd have to be autonomous (no fly-by-wire at those ranges),
and for recovery purposes I'd want to have a spare sail _anyway_ that it could
deploy in the case the primary got tangled.

~~~
cgriswald
I’m not sure how you’d detach the sail at speed. It’s in front of you with the
same velocity. You’ve got to go around it or it around you. And you’ve got to
do it at speed without modifying your trajectory.

That’s got to be more difficult than spinning around because any mistakes will
be amplified over the vast distances, whereas a slight trajectory problem once
you’ve arrived is much less of an issue and is correctable with onboard
guidance. If you screw up the detach procedure.... you can’t steer to correct.

Assuming two different methods of acceleration (laser on departure, solar on
arrival), why not construct the sail in such a way that the probe goes
_through_ the sail? It could pull the sail in, and mechanically route it’s
connections to the rear of the craft. If there are material or structural
difference needed, it could be incorporated into the design and two opposing
surfaces.

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Retr0spectrum
Am I parsing the title correctly?:

Missions to (and Sample Returns from) Nearby Interstellar Objects

~~~
BjoernKW
That's one strangely phrased title. Intuitively, I'd agree.

However, the 'correct' parse would be: "(Missions to and Sample Returns from)
Nearby Interstellar Objects", i.e. the two nouns 'missions' and 'returns'
(with 'sample' as its specifier) are linked by conjunction because only words
of the the same type (noun, verb etc.) can by linked by conjunctions (or
disjunctions, for that matter).

~~~
Sosh101
What is "Missions to and Sample" supposed to mean?

~~~
Aardwolf
No, it's "Missions to and Sample Returns from"

So in expanded form:

"Missions to Nearby Interstellar Objects and Sample Returns from Nearby
Interstellar Objects"

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TheOtherHobbes
"Missions" is redundant, because you're not going to get a sample return
without a mission.

So "Collecting Samples from Nearby Interstellar Objects" would have been
enough to do the job.

~~~
Keysh
Not really, because "missions without sample returns" (aka "flyby/impactor")
is one of the options considered.

