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Missions to and Sample Returns from Nearby Interstellar Objects (arxiv.org)
96 points by sohkamyung 34 days ago | hide | past | favorite | 32 comments

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).

> 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.

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.

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

Curiosity and Perseverance's RTGs seem to have gone over fine in more recent years, though.

Would be interesting to see some analysis from a public relations point of view why that was the case.

From a technical standpoint, both Cassini and Galileo did Earth gravity assists. The argument was that an error in navigation could cause them to hit Earth on such a flyby. While RTGs were designed to remain contained on launch failure they wouldn't survive such a high-speed reentry. Another (much less realistic) fear I heard was that the plutonium in their RTGs could ignite fusion in the cores of Jupiter or Saturn when the probes were dumped into their atmospheres.

Neither of these two concerns apply to Mars rovers.

There's no plutonium in the core of Jupiter/Saturn already?

I don't know how much there is in a gas giant - natural concentrations on earth are vanishingly small - but the idea that Cassini's 32.7 kg of it would ignite Saturn was always insanely dumb.

Fast flyby seems fine -- "A combination of Falcon Heavy or Space Launch System, chemical propulsion, and Parker Solar Probe-derived heatshield technology would be sufficient for fast flybys"

> thermal nuclear propulsion

No way we will see something like this without military involvement. Thinking about the huge amount of money to be invested.

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?

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

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 ...

> 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.

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) 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.

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.

Most of the mass is likely to be in the solar sail, so carrying two of them therefore is a major problem. If you need two different surface characteristics in two different directions, which I'm not sure is an issue, just coat the one sail differently on each side.

Sounds a lot like Encounter with Tiber by Buzz Aldrin, only it used a long drogue wire to brake electrostatically. It was only a book, but these details felt realistic enough.

Attaching a probe to a big rock is likely to make it harder to find, as there are so many rocks.

Am I parsing the title correctly?:

Missions to (and Sample Returns from) Nearby Interstellar Objects

If one was a writer of English one would write "Missions To, and Sample Returns From, Nearby Interstellar Objects."

A mathematician or experienced computer programmer would, of course, reach for parentheses instead of commas.

A headline writer uses nothing. Brevity and attention capture are their goals, not clarity of content.

You could also consider the possibility that English is not a native language for the author.

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).

The indirect object "Nearby Interstellar Objects" distributes over the conjunctive clause "Missions to and Sample Returns from". Expanded, we get "(Missions to Nearby Interstellar Objects) and (Sample Returns from Nearby Interstellar Objects)".

What's the difference in the parsing it this or that way? It talks about visiting interstellar objects, with sample return. What's the alternative interpretation?

I think others are getting a sort of garden-path mis-parsing of 'sample' as a verb here:

Missions (Plural Noun) To (Preposition) And (Conjunction) Sample (Verb)

Where they should have

Sample Returns (Compound Plural Noun)

My grammatical terms are probably all wrong, but you get the gist. It reads fine to me, but it can be hard to see these hiccups once you've read it the "correct" way. Edit: Also I think the unusually-placed preposition is pushing them that way.

Ah, makes sense!

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

[Missions (to)] and [Sample Returns (from)] Nearby Interstellar Objects.

"Missions and Sample Returns to and from Nearby Interstellar Objects" is probably what I would have made from that, but no idea if that is allowed or comprehensible.

English is not my native tongue and I noticed that I don't understand capitalization as well as I thought. Why do you do that now? Just because it is a title? And why not for to/and/from? Are prepositions exempt?

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"

"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.

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

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