6 ms·

Missions to and Sample Returns from Nearby Interstellar Objects

96 points by sohkamyung 6y ago

duncan_bayne 6y ago
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 6y ago
  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 6y ago
    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 6y ago
      > 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 6y ago
        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.
        simonh 6y ago
        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.
        cgriswald 6y ago
        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.
    - pcardoso 6y ago
      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.
- simonh 6y ago
  Attaching a probe to a big rock is likely to make it harder to find, as there are so many rocks.
Retr0spectrum 6y ago
Am I parsing the title correctly?: Missions to (and Sample Returns from) Nearby Interstellar Objects
- BjoernKW 6y ago
  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).
  - Gravityloss 6y ago
    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?
    - dcminter 6y ago
      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.
      - Gravityloss 6y ago
        Ah, makes sense!
  - Sharlin 6y ago
    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)".
avian 6y ago
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 6y ago
  > 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 6y ago
    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 6y ago
      We can strap it to a flaming bottle of liquid oxygen and hydrogen :)
  - ceejayoz 6y ago
    Curiosity and Perseverance's RTGs seem to have gone over fine in more recent years, though.
    - avian 6y ago
      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.

96 points by sohkamyung 6y ago

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 6y ago
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 6y ago
  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 6y ago
    > 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 6y ago
      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.
      - simonh 6y ago
        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.
      - cgriswald 6y ago
        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.
  - pcardoso 6y ago
    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.
simonh 6y ago
Attaching a probe to a big rock is likely to make it harder to find, as there are so many rocks.

Retr0spectrum 6y ago

Am I parsing the title correctly?: Missions to (and Sample Returns from) Nearby Interstellar Objects

BjoernKW 6y ago
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).
- Gravityloss 6y ago
  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?
  - dcminter 6y ago
    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.
    - Gravityloss 6y ago
      Ah, makes sense!
- Sharlin 6y ago
  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)".

avian 6y ago

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 6y ago
> 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 6y ago
  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 6y ago
    We can strap it to a flaming bottle of liquid oxygen and hydrogen :)
- ceejayoz 6y ago
  Curiosity and Perseverance's RTGs seem to have gone over fine in more recent years, though.
  - avian 6y ago
    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.