I just detected a strange object in space, and it appears to be of alien origin! Telescope readings seem to indicate it is some sort of deep space probe, with a golden disk of some sort attached to it. It appears to have some engravings on it, and grooves around the edge, but it's a bit fuzzy. As luck would have it, it's headed straight for our system, and will likely collide with our planet!

We have access to about present-day-earth level tech. We are obviously very curious about this object, and would like to land it safely to inspect it, or, barring that, redirect it into a safe orbit around our planet or at least get some close up pics or something. What's the best we can do? How much warning could we get to prepare? If recovery is impossible with our current level of tech, how advanced do we have to be to pull this off?

To clarify, I am an alien in a distant solar system, and Voyager 1 is heading towards me, and my goal is to recover or at least get a close look at it.

  • $\begingroup$ Afaik it is impossible with voyager1. A new space probe has to be built. $\endgroup$ – Gray Sheep Apr 21 '17 at 3:13
  • $\begingroup$ Is this actually Voyager 1 flying along the path that the real Voyager 1 took, or is it just a similar probe that is flying at a fairly high relative velocity into the star system? This would make a big difference. $\endgroup$ – Jarred Allen Apr 21 '17 at 3:20
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    $\begingroup$ With present day tech you would not see it, let alone see details, while it is headed towards the solar system. That's off by at least 4 orders of magnitude. $\endgroup$ – JDługosz Apr 21 '17 at 3:49
  • $\begingroup$ @JDługosz so we would need outposts in other solar systems, plus a lot of luck, to notice it in time to do something about it? $\endgroup$ – dn3s Apr 21 '17 at 4:16
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    $\begingroup$ Outposts in other solar systems? Well, that blows away any present-day tech. And this would mean the probe passed through the other system at close range, which is unlikely. Oh, that would be 10000 years before it got here. $\endgroup$ – JDługosz Apr 21 '17 at 4:21

As other users have mentioned, it's going to be very,very unlikely that earth-level tech would be able to ramp-up in time to catch it - though the rocket is technically feasible, it's a bit of a stretch to assume that the scientists would be able to:

  1. Actually see the probe with their telescopes (the probe is very, very small - it took over 80 years to find Pluto!)
  2. Settle academic debate on what the probe is - remember, at a distance it will just be a speck of light indistinguishable from a perfectly mundane asteroid. The only chance for very early detection is that a very lucky radio signal (let's say the probe's been sent spinning, so the high-gain antenna is no longer pointed directly at earth, and its pings get picked up as a peculiarly regular signal by a radio observatory)
  3. Get funding for this tremendously expensive mission
  4. Build, test and launch the rocket

all within the launch window - including the time taken to match the speed of the probe, which will be a long time if you're using ion propulsion.

My suggestion: Treat it like Pluto

Intercepting a fast object is hard, but it's much, much cheaper to do a flyby - build a New Horizons-style probe, launch it with a number of very high resolution cameras and spectrometers and put it on a course to fly by and record as much information about the probe as possible.

E.g. to actually rendezvous with the probe: Proper match but to simply fly by and take pictures, you only need to match the position: smile and wave boys

With some luck (and some very fast cameras), scientists would plausibly be able to reconstruct the details of the golden plate (probably not enough to read the record grooves, however), but they would be able to determine the chemical composition and mechanical construction of the probe, determine that it was launched with chemical rockets by looking at chemical emission spectra and verify that it bears alien pictures and was not launched from their own planet (though the debate around that point might be an interesting subplot).

Without launching anything at all, they could get a pretty good estimate of where the probe came from (based on telescope trajectory measurements).

Voyager would also bear characteristic marks from deep space - miniscule holes from micrometeorites, possible a large missing chunk from a not-so-micro meteorite and (maybe) some residual charge from its trip through interstellar plasma.

(Note that these measurements can't be taken from the surface of Kerbin - no terrestrial telescope on the ground or in space has enough resolving power without being very close to Voyager.)

  • $\begingroup$ I think that the hard part would be detecting it and understanding that tiny dot is presumably an alien artifact. Building a probe which catches an object traveling 10-20km/s wouldn't be specially hard or sophisticated, it would be matter of spending cash for big enough rocket as such mission would require plenty of delta-V and time. $\endgroup$ – Shadow1024 Apr 21 '17 at 19:26
  • Get everything into orbit. The Apollo missions to the Moon launched the crew and lander on one rocket. It might be possible to launch what follows next in one step, but perhaps it needs to be assembled from multiple launches.
  • Decide: manned or unmanned? Given the nature of the mission, do you want a remotely-controlled craft? Or do you want people?
  • The expedition needs to match course with the incoming probe. That might involve traveling out towards the probe, then turning around and going on a parallel course. You will need lots and lots of delta-V.
  • Capture. It probably involves a quarantine, to avoid damaging evidence. Is there "alien" DNA left on the probe? Fingerprints? Germs?
  • Turn around and go into orbit of the homeworld. More delta-V.
  • Decide if you can bring it down safely, or if it stays in a space station.

The required delta-V budget could be very high -- the speed of Voyager relative to the sun isn't the same as the speed of Voyager relative to the alien homeworld.

As mentioned by JDługosz, you will need lots and lots of delta-V. That means the spacecraft will be optimized for long-range travel, not an atmosphere-capable launch/landing system. Think of some of the Mars proposals, or similar designs.

Timing might throw a spanner into the works, however. If they waste a decade building the perfect craft for the mission, the alien probe will have passed. Perhaps the best bet is to re-purpose an Asteroid mission that happened to be almost ready to launch. Dump most of the science payload, take extra fuel, and there you go. Worry about quarantine when the mission comes back.

  • $\begingroup$ Large delta-v budget doesn't necessarily follow directly from long-range-travel optimized spacecraft. Take New Horizons; designed to go out to Pluto, initial delta-v of more than 16 km/s (IIRC it was 16.26 km/s relative to Earth) for direct transfer orbit injection on an Earth escape trajectory, but minuscule delta-v capability in flight. By the time you no longer have to contend with an atmosphere, aerodynamics are of little concern. $\endgroup$ – a CVn Apr 21 '17 at 6:29
  • $\begingroup$ @MichaelKjörling, I think a large delta-V will be required, and that will preclude wasting any mass aerodynamics. $\endgroup$ – o.m. Apr 21 '17 at 15:06
  • $\begingroup$ "the speed of Voyager relative to the sun isn't the same as the speed of Voyager relative to the alien homeworld" could make things better; the craft's velocit could be very slow relative to the homeworld. of course, such a vector would make any attmpets to investigate the source planet that much more impossible... $\endgroup$ – dn3s Apr 21 '17 at 16:02

The xkcd What if? article on an unmanned mission to retrieve Voyager I? covers this — a rendezvous would amount to the same thing.


So, using conventional rocket technology to go to a body moving at high speed relative to us, and return with it, would be very expensive and impractical, though technically possible (assuming nations could still afford it).

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    $\begingroup$ I have read this, however in this case though Voyageur is headed towards us, not away from us. $\endgroup$ – dn3s Apr 21 '17 at 4:14
  • $\begingroup$ It doesn’t make that much of a difference. You still have to go there and match speeds with it, bringing enough fuel to cancel its speed. $\endgroup$ – JDługosz Apr 21 '17 at 4:19
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    $\begingroup$ I don't think a rendezvous "would amount to the same thing" as rendezvous and course reversal for retrieval. To rendezvous, you need to do little more than match velocity (course and speed; remember that velocity is a vector quantity, whereas speed is its absolute value thus a scalar quantity). XKCD discusses rendezvous and retrieval on the assumption that the probe is moving away from us. For a probe moving toward us, you could make do with far less if you are willing to let the retrieval take longer, for example by using gravity slingshots to bleed off speed relative to your target planet. $\endgroup$ – a CVn Apr 21 '17 at 6:34
  • $\begingroup$ Your probe needs to go out there, turn around (matching speed with the arriving craft) and return. That's “there and back”. $\endgroup$ – JDługosz Apr 21 '17 at 6:59
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    $\begingroup$ @Philipp In all fairness, gravity assists don't change your Δv requirements or budget, only how much of that you need to apply under power (which can be important enough, mind you!). JDługosz, you don't need to meet the probe head-on; it's plausible to do something like move toward it on a trajectory which will approach it from behind, thus likely greatly reducing the Δv requirements for rendezvous and ensuring that you are on a trajectory similar to that of the probe when you do. Tricks like that is why the probe moving toward you makes the OP's stated scenario very different from XKCD's. $\endgroup$ – a CVn Apr 21 '17 at 21:40

Recovery of the probe would be extremely difficult, but you can slow it down so that it just misses your planet and hopefully slingshots into an orbit that allows you additional opportunities to slow it down until you can capture it.

  1. Hit it with a laser. This will not only push it (slowing it) via radiation pressure, but it will also ablate the surface of the probe, causing it to slow down as it ejects mass. Hopefully the etchings on the surface are not just a molecule thick :)

  2. Put a thin cloud of hydrogen in its path, so it slows down via friction. You have to be careful not to heat the probe up too much.

  3. Get a ship to rendezvous with the probe (as it orbits your system) and build an aerobraking shell around it, or attach a laser sail to it. Then you can be more aggressive in slowing down the probe. This has the advantage that your ship only has to meet the probe, not slow it down, and you can slow it down without having to impact the probe itself (via laser or friction slowing). A solar sail, especially if it can be deployed and retracted, would allow for radiation pressure from the sun to slow/accelerate the probe as needed when it is too far from your base laser, so you can constantly be modifying the probes trajectory into more favorable ones for you.

If you start while the probe is far enough away, even a tiny change in velocity will make it miss your planet, then it can slingshot behind the planet and start to slow down. The goal is to put it in an orbit that brings it close to your planet again, so you can keep slowing it and letting it be slowed via your planets gravity. Eventually it will be slow enough you can try to aerobrake it in your atmosphere and retrieve it before it hits the ground or it will have a delta v low enough you can get a ship on a matching course (probably via some long orbit with lots of velocity building slingshots of its own) with enough remass left to slow it to a lagrange point or stable orbit where you can study it at your leisure. This will take a LONG time, probably decades.

Obviously you can take all the pictures you want as it passes, though you well have to get clever with positioning to capture all sides, unless the probe is spinning (or you make it spin with your laser).

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    $\begingroup$ Oh, please don't try to aerobrake an unprotected, unknown probe. It probably wasn't designed for it; you don't know its mass distribution, and if you get that wrong, at best it's likely to start tumbling through your atmosphere; and even if you get it perfectly right, it will cause some non-negligible amount of surface ablation, which could remove important clues or markings. Ruling out aerobraking (and lithobraking) makes capture harder, but far more likely to yield useful scientific results once your people are able to study the probe. $\endgroup$ – a CVn Apr 21 '17 at 21:50
  • $\begingroup$ @MichaelKjörling True, probably your best bet is to get a ship out to the probe, then construct an areobraking shield AROUND it, and set it on a course to start a series of aerobraking runs. That way you don't have to carry all the remass to slow down the ship and the probe. $\endgroup$ – Jason K Apr 24 '17 at 14:02

Possible without any really new technology, but no existing or 'off the shelf' spacecraft could do this. You'd need lots of warning to design, build, and launch one.

You'd need to send a second probe to rendezvous with it, grab it and push it out of an interstellar trajectory to an orbit around the planet.

This would require a lot of delta-v capacity (at least several tens of kilometers per second; as of January 2015 Voyager 1's speed relative to Earth was 27.2 km/s - if it passed through another solar system, this would vary based on the velocity of that star relative to the Sun and the orbital velocity of the planet around the star) - far, far too much for a practical chemical rocket. So you'd want ion engines. NASA's current NSTAR ion engine has a specific impulse over 3000 seconds, and the currently-in-development NEXT (supposed to be ready in 2019 according to Wikipedia will be over 4000. So you could do this with a mass ratio probably in the ballpark of 2.5 - 4.

The problem is that ion engines are power hungry and have low thrust, so you'll need to run the engines for a long time. The probe will probably fly by the sun and leave the high-solar-power area too quickly (though solar panels are getting pretty advanced, so maybe...) Your best bet would be a nuclear reactor - this is possible within current technology, but would require a long lead time and political will to overcome the concerns about launching nuclear materials. I don't know enough but it ought to be achievable in well under a decade given sufficient funding and political will (it was only ~8 years from Alan Shepard's suborbital flight to Neil Armstrong's moon landing, and that required genuinely new developments).

If you already had nuclear-powered ion-engine space tugs in space, the lead time could be much less.


As luck would have it, it's headed straight for our system, and will likely collide with our planet!

This should simplify things. First a quick stat. Voyager 1 is traveling at ~3.5AU per year (roughly the distance from jupiter to mars). That should help establish a timeline for all this. I know the other answers say that it would be almost impossible to see the probe at any real distance, but your question didn't ask if it could be found, but what to do after it is found. So I'll leave it up to you to have it get found with enough time to do something about it.

To recover the probe, you'll need a space-pusher. Since Voyager 1 is coming straight at you, the trick will be to nudge it into an orbital pattern instead of a crash landing.

So build a space-pusher, launch it, get it going around the same speed at Voyager (~1.5 time the speed of a space shuttle), and slowly push it to the side. There is the chance you'll end up slingshotting it instead, in which case you get to nuge it again. Maybe it'll take a few years and several orbits around various planetary and stellar bodies to get to to finally settle into a stable orbit, but once that happens, you'll be able to examine it at your leisure.


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