Earth’s far-off ‘cousin’ could support life

[Breadknife]

Even the tiniest of errors are magnified greatly by distance. Even the slightest of orbital eccentricities are magnified by time. Take my word for this: We're not going to score a 4.4 light year bullseye on a moving target.

Early adjustments, as soon as finer details are known, even while the mission is getting up to speed. "Getting to a thing where a thing will be" is already a thing. It may not be as trivial as http://what-if.xkcd.com/82/ but... And it would be arriving at a destination with a significant gravitational well to 'edge in' a very-nearly-but-not-quite trajectory on course. (In fact, you wouldn't want to aim for the star, in case you hit it, so you'd be 'aiming off', deliberately.)


The biggest thing is tying down some sort of receiving combination of "gravitational de-assists", assuming you're not going to accept just a fly-by.

No, scratch that. The biggest thing might well be getting the telemetry back. Those nice pictures the probe takes would be difficult to squeeze back (although, if relativistic travelling speeds are still involved, we should at least have pre-planned taking up the slack in the doppler-shift). Imagine the signal power needed... that provision would probably dominate the package we send (second only to the propulsion/retro-propulsion units, maybe).

[Northwest Slobovia]

Based on current knowledge of physics, that is.

True.
Still, our current knowledge of physics seems to be fairly accurate as long as stuff like a 500 ly travel is involved. I don't see a warp drive coming up any soon.

Miguel Alcubierre would like to have a word with you. It's not known if his math is right, but it is consistent with GR, and a fellow named Sonny White at NASA/Ames(?) is conducting fundmental research to see if the "warp effect" can be physically realized.

You may be correct that "any time soon" might rule out the next couple of decades -- it was something like a century between the development of the theory of powered flight and its realization -- but it might not take changing the laws of physics. Insert ObOldTrek line here.

[Shnercropolis]

Even the tiniest of errors are magnified greatly by distance. Even the slightest of orbital eccentricities are magnified by time. Take my word for this: We're not going to score a 4.4 light year bullseye on a moving target.

Early adjustments, as soon as finer details are known, even while the mission is getting up to speed. "Getting to a thing where a thing will be" is already a thing. It may not be as trivial as http://what-if.xkcd.com/82/ but... And it would be arriving at a destination with a significant gravitational well to 'edge in' a very-nearly-but-not-quite trajectory on course. (In fact, you wouldn't want to aim for the star, in case you hit it, so you'd be 'aiming off', deliberately.)


The biggest thing is tying down some sort of receiving combination of "gravitational de-assists", assuming you're not going to accept just a fly-by.

No, scratch that. The biggest thing might well be getting the telemetry back. Those nice pictures the probe takes would be difficult to squeeze back (although, if relativistic travelling speeds are still involved, we should at least have pre-planned taking up the slack in the doppler-shift). Imagine the signal power needed... that provision would probably dominate the package we send (second only to the propulsion/retro-propulsion units, maybe).

Gamma lasers?

And once we do a few flybys, we could probably make some pretty accurate predictions on exactly how to slow down the probe to a nice orbit. In any case, I think it's more important to explore the planets in our own solar system more.

[The Fascist American Empire]

I don't think it would change very much. Even if it DOES support life, it would take forever for us to get to it, if at all. I think 80% of us would be dead by the time they get efficient enough technology to make a sustained voyage, but I could be wrong.

And we may reach them, then be turds and take over their planet and colonize it for humanity. Standard human nature.

Oh, I wasn't saying we SHOULD colonise it. Unless something Mass-Effecty happens and we end up with technology hundreds of years ahead of ours, we probably won't get there for ages. I was just saying that if any proof came that lifeforms could survive there, those people who hate the idea of life on other planets would hopefully shut up.

I believe in life on other worlds, but the thought of intelligent lifeforms makes me chuckle.

[Northwest Slobovia]

Here's the problem: When we look at Alpha Centauri, we are looking at it as it was four and a half years ago. It's position will have moved since then. It will move even further by the time a probe approaches it. So the chances of one or more course corrections being necessary during this probe's trip are extremely high; almost a certainty. But as we are several years away by radio, the probe will have to be capable of making these course corrections automatically based on observations en route. That's a pretty tall order for a computer. Not the calculations, the observations.

We might have the technology to build the rocket and the probe, but the brain needed to fly it is still a few generations away.

Orbit plotting is something that computers can do with ease. And we can predict Alpha Centauri's motion easily, so it's unlikely we'd miss the system entirely. The hard part, I think, would be getting the probe to slow down once it enters the system. Getting down from relatavistic speed isn't easy. Perhaps we could reverse the gravitational slingshot with another one? Or maybe have the probe do a quick fyby? Then we'd have to send multiple probes to get anything of substance back. It's an engineering problem for sure, but if we really wanted to there's no reason we couldn't. It's just that people are more interested in Obamacare and the Crimea crisis.

Even the tiniest of errors are magnified greatly by distance. Even the slightest of orbital eccentricities are magnified by time. Take my word for this: We're not going to score a 4.4 light year bullseye on a moving target.

Early adjustments, as soon as finer details are known, even while the mission is getting up to speed. "Getting to a thing where a thing will be" is already a thing. It may not be as trivial as http://what-if.xkcd.com/82/ but... And it would be arriving at a destination with a significant gravitational well to 'edge in' a very-nearly-but-not-quite trajectory on course. (In fact, you wouldn't want to aim for the star, in case you hit it, so you'd be 'aiming off', deliberately.)


The biggest thing is tying down some sort of receiving combination of "gravitational de-assists", assuming you're not going to accept just a fly-by.

No, scratch that. The biggest thing might well be getting the telemetry back. Those nice pictures the probe takes would be difficult to squeeze back (although, if relativistic travelling speeds are still involved, we should at least have pre-planned taking up the slack in the doppler-shift). Imagine the signal power needed... that provision would probably dominate the package we send (second only to the propulsion/retro-propulsion units, maybe).

Since these both are similar, I might as well answer them in one post.

1) Slowing the probe down

Right, trying to brake into orbit from relativistic speeds sucks. Gravitational assists are basically useless, since the maximum delta-V we can get from any body is its surface escape velocity. Even for main-sequence stars, this isn't close to what we need -- Sun's escape velocity: ~600 km/sec, 1% of c: ~3,000 km/sec -- so even a star-skimming approach is just gonna change the departure trajectory, not get a bound orbit.

If we want a tiny, tiny probe, we could "just" build a two-stage relativistic rocket, and the second stage slows the probe down to orbital speeds at the destination. It's just a matter of engineering. Robert Forward proposed a similar trick with light sails and a big launching laser in our solar system: the probe has a big mainsail and a little braking sail. Once it reaches the destination, the proble and the braking sail detach from the mailsail, which is used to reflect the laser from here to there into the braking sail.

The "best" answer I know of though uses magsails. It turns out Bussard's ramjet doesn't work, because its drag exceeds its thrust for real interstellar media. But that's precisely what we want to slow down when we get somewhere else. 'course, we don't actually know how to build one, but details, details.

2) Fly-bys and telemetry

There's a couple of mission profiles that don't stop at the destination, but simply whip through it at relativistic speeds. This requires impressively fancy instruments to gather data on the destination, and equally fancy computers to deal with the pointing, stability, and data processing problems, but solves the "how do we stop?" problem really well. To the best of my knowledge, it's considered the least difficult of the ways of exploring a nearby star system. (Edit: See Forward and Landis' "starwisp" mission profile.)

Which leads into getting the data back. Regardless of whether we slow down or not, we have to send rather a lot of data over an interstellar distances. AFAIK, this needs two things. First, a lot of pre-processing in the probe; we really don't want to send back all the raw data of the sort that planetary imaging missions generate, we want to send back only partially-reduced data (ie, rather than thousands of individual, overlapping images of a planet, a finished map). Second, as BK says, it needs a lot of power, big transmitters -- I think the current approaches run to very big lasers because of the diffraction limit for beam-forming (shorter wavelengths spread less than longer ones for the same size aperture, so send light rather than radio) -- fancy error-correcting codes, and really big receivers.

The last is a tradeoff for radio vs light; consider the size of the Square Kilometer Array vs the largest of optical telescopes (Europe's working on a 30m one) -- it's much easier to build huge arrays of radio dishes than telescopes of the same size -- but if more of the signal gets here, we need less receiving area to correctly recieve it. YMMV.

On the plus side, we can work our way up to interstellar problems in logical steps: increasingly autonomous planetary missions, a solar focus telescope (using the sun's gravitational lens to bring distant light into focus, about a 1000 AU out), Oort Cloud/Kupier Belt missions, and so on. It's essentially the Apollo Project of unmanned spacecraft: a step-wise progression of increasingly sophisticated missions to reach a difficult goal.

Ad astra!

[Shnercropolis]

Orbit plotting is something that computers can do with ease. And we can predict Alpha Centauri's motion easily, so it's unlikely we'd miss the system entirely. The hard part, I think, would be getting the probe to slow down once it enters the system. Getting down from relatavistic speed isn't easy. Perhaps we could reverse the gravitational slingshot with another one? Or maybe have the probe do a quick fyby? Then we'd have to send multiple probes to get anything of substance back. It's an engineering problem for sure, but if we really wanted to there's no reason we couldn't. It's just that people are more interested in Obamacare and the Crimea crisis.

Early adjustments, as soon as finer details are known, even while the mission is getting up to speed. "Getting to a thing where a thing will be" is already a thing. It may not be as trivial as http://what-if.xkcd.com/82/ but... And it would be arriving at a destination with a significant gravitational well to 'edge in' a very-nearly-but-not-quite trajectory on course. (In fact, you wouldn't want to aim for the star, in case you hit it, so you'd be 'aiming off', deliberately.)


The biggest thing is tying down some sort of receiving combination of "gravitational de-assists", assuming you're not going to accept just a fly-by.

No, scratch that. The biggest thing might well be getting the telemetry back. Those nice pictures the probe takes would be difficult to squeeze back (although, if relativistic travelling speeds are still involved, we should at least have pre-planned taking up the slack in the doppler-shift). Imagine the signal power needed... that provision would probably dominate the package we send (second only to the propulsion/retro-propulsion units, maybe).

Since these both are similar, I might as well answer them in one post.

1) Slowing the probe down

Right, trying to brake into orbit from relativistic speeds sucks. Gravitational assists are basically useless, since the maximum delta-V we can get from any body is its surface escape velocity. Even for main-sequence stars, this isn't close to what we need -- Sun's escape velocity: ~600 km/sec, 1% of c: ~3,000 km/sec -- so even a star-skimming approach is just gonna change the departure trajectory, not get a bound orbit.

If we want a tiny, tiny probe, we could "just" build a two-stage relativistic rocket, and the second stage slows the probe down to orbital speeds at the destination. It's just a matter of engineering. Robert Forward proposed a similar trick with light sails and a big launching laser in our solar system: the probe has a big mainsail and a little braking sail. Once it reaches the destination, the proble and the braking sail detach from the mailsail, which is used to reflect the laser from here to there into the braking sail.

The "best" answer I know of though uses magsails. It turns out Bussard's ramjet doesn't work, because its drag exceeds its thrust for real interstellar media. But that's precisely what we want to slow down when we get somewhere else. 'course, we don't actually know how to build one, but details, details.

2) Fly-bys and telemetry

There's a couple of mission profiles that don't stop at the destination, but simply whip through it at relativistic speeds. This requires impressively fancy instruments to gather data on the destination, and equally fancy computers to deal with the pointing, stability, and data processing problems, but solves the "how do we stop?" problem really well. To the best of my knowledge, it's considered the least difficult of the ways of exploring a nearby star system.

Which leads into getting the data back. Regardless of whether we slow down or not, we have to send rather a lot of data over an interstellar distances. AFAIK, this needs two things. First, a lot of pre-processing in the probe; we really don't want to send back all the raw data of the sort that planetary imaging missions generate, we want to send back only partially-reduced data (ie, rather than thousands of individual, overlapping images of a planet, a finished map). Second, as BK says, it needs a lot of power, big transmitters -- I think the current approaches run to very big lasers because of the diffraction limit for beam-forming (shorter wavelengths spread less than longer ones for the same size aperture, so send light rather than radio) -- fancy error-correcting codes, and really big receivers.

The last is a tradeoff for radio vs light; consider the size of the Square Kilometer Array vs the largest of optical telescopes (Europe's working on a 30m one) -- it's much easier to build huge arrays of radio dishes than telescopes of the same size -- but if more of the signal gets here, we need less receiving area to correctly recieve it. YMMV.

On the plus side, we can work our way up to interstellar problems in logical steps: increasingly autonomous planetary missions, a solar focus telescope (using the sun's gravitational lens to bring distant light into focus, about a 1000 AU out), Oort Cloud/Kupier Belt missions, and so on. It's essentially the Apollo Project of unmanned spacecraft: a step-wise progression of increasingly sophisticated missions to reach a difficult goal.

Ad astra!

Hrmm.... I think I need to read more hard-sf books.
To the local used book store!

[Northwest Slobovia]

Hrmm.... I think I need to read more hard-sf books.
To the local used book store!

Damn right!

A lot of this stuff is in serious non-fiction proposals.* I edited in a reference to the "starwisp" mission profile after you replied; it's a "simple" microwave-beam-powered fly-by mission. It's probably something we could build today. NASA pays for a fair amount of blue-sky research on the off chance something will come of it, and some of that ends up online.

*: for example, there's a few variations on the solar-focus telescope (eg, TAU: thousand astronomical unit mission) that are "serious" sketches, even though they're more fiction than fact.

[Breadknife]

Gamma lasers?

Gamma lasers or space-capable carrier pigeons, there'd still be problems sending information back home... (Albeit different ones.)

And once we do a few flybys, we could probably make some pretty accurate predictions on exactly how to slow down the probe to a nice orbit.

I think we could probably send one package off with the capability to narrow down the fine details, with which the next probe (already on its way) could be appraised. Either directly, being equipped to work out the best adjustments itself, or as a rebroadcast from Earth (via Earth's experts, and any new thinking) at the expense of a longer delay.

But that's with no guarantee that there's actually a sufficiently convenient (mis-)alignment of planets to use. Given the velocities involved, at least on entry to the system, you'd find it difficult to aim to 'skim' one planet. And you really don't want to try aerobraking, at this first stage, lest you accidentally create a Tunguska event (increased by at least several orders of magnitude, and possibly seriously 'annoying' any actual residents of the planet, even as you lose your probe), so don't skim too close! And yet at 'safe' fly-by distances you probably wouldn't get that much of a significant purturbation, so to encounter another planet for another go (each time velocity-bleeding) would require a conveniently-placed secondary/tertiary target.

If you're using (amongst others) a Jupiter-assist and then a massive propulsion package (e.g. Orion-esque) to head away from Sol, you need (albeit marginally less, if you've dumped your outward-only propulsion stage(s), now that you only have to push the remainder) a similar retropropulsive effort before a Jupiter-like encounter, to bring yourself back down to 'sensible' speeds within the other star's orbit.


For the Alpha Centauri 'system', perhaps you can start with the assumption of using one or other of the stars in the AB-C configuration as a gravitational focus to lead onto one of the others, then improvise with any significant planets then discovered (if any). With A and B being slightly-more-than and slightly-less than a solar mass, respectively, that's a lot of gravity. C (a.k.a. Proxima) is much smaller (but hundreds of Jupiters in size) and some way off from the other pair (as much as 1/20th of the distance from Sol, IIRC, but I'd have to look that up) so would be produce a significant journey time between them (especially after the probe velocity has been reduced.

Perhaps (barring the fine details, maybe to be calculated "in probe", as the view from the approaching probe gives increasingly better resolutions) a slow-down based upon using the stars (noting the added problems of getting too close to them) to "gravitationally de-assist" would be the best bet, the over-riding problem ending up being what to do if you actually spot a Jupiter-like planet along your trajectory. (Not actually on a direct course, which would be highly unlucky and unlikely, but close enough to perturb your finely-tuned trajectory onto the next star-rendezvous.)

In any case, I think it's more important to explore the planets in our own solar system more.

We really need to work out how to build a Rama, though.

[Breadknife]

I believe in life on other worlds, but the thought of intelligent lifeforms makes me chuckle.

I'm sure they think the same of you...

[Benuty]

I believe in life on other worlds, but the thought of intelligent lifeforms makes me chuckle.

I'm sure they think the same of you...

Here on the planet Yuggoth.

Professor Nyarlathotep " I believe this universe has the potential to house life on other planets".

Professor Azathoth " Nonsense this universe and this world were created by the all loving lord of all Cthulhu and his graceful servants from the watery seas of R'lyeh.".

[Nirya]

Very interesting, actually.

[Shnercropolis]

I'm sure they think the same of you...

Here on the planet Yuggoth.

Professor Nyarlathotep " I believe this universe has the potential to house life on other planets".

Professor Azathoth " Nonsense this universe and this world were created by the all loving lord of all Cthulhu and his graceful servants from the watery seas of R'lyeh.".

Nyarlethotep and Azathoth are both superior dieties to Cthulu.

[Benuty]

Here on the planet Yuggoth.

Professor Nyarlathotep " I believe this universe has the potential to house life on other planets".

Professor Azathoth " Nonsense this universe and this world were created by the all loving lord of all Cthulhu and his graceful servants from the watery seas of R'lyeh.".

Nyarlethotep and Azathoth are both superior dieties to Cthulu.

doesn't count for anything. with it is mortals adorning names for deities of the pantheon in a practice as old as time itself.

[United Regions of Verona]

Where's Earths mom? And dad?

[Risottia]

True.
Still, our current knowledge of physics seems to be fairly accurate as long as stuff like a 500 ly travel is involved. I don't see a warp drive coming up any soon.

Miguel Alcubierre would like to have a word with you.

Sure. The day someone builds a working Alcubierre drive.
The Alcubierre thingy is totally theoretical and requires to postulate totally hypothetical stuff, like negative energy density or tachyonic matter. And I'm not even talking the projected energy requirements, of course.

As for Alcubierre on the subject, he has my same opinion: "from my understanding there is no way it can be done, probably not for centuries if at all".
As for the NASA experiment: results have been reported as "inconclusive".

http://en.wikipedia.org/wiki/Alcubierre ... xperiments

[Northwest Slobovia]

Miguel Alcubierre would like to have a word with you.

Sure. The day someone builds a working Alcubierre drive.
The Alcubierre thingy is totally theoretical and requires to postulate totally hypothetical stuff, like negative energy density

AFAIK, the Casimir effect demonstrates that negative energy density relative to vacuum exists, but the CE is laughably too small for space travel purposes (by factors of 10¹⁰-10³⁰, depending on the energy density required).

And I'm not even talking the projected energy requirements, of course.

Oh, those are also entertainingly high also. If Dr. White's estimates are correct, building an itty-bitty field would take (from memory) a good hunk of the sun's energy output for a year, but I can't find my calculations now. I remember the requirements being physically possible but completely impractical.

As for the NASA experiment: results have been reported as "inconclusive".

Aha! I didn't know that... that there's no better source -- I can't find one at least -- suggests that hasn't changed.