Unmanned Mission to Alpha Centauri, A study of an unmanned mission to the Alpha Centauri system Options

[YesRushGen]

Hi all, I am a frequent lurker here at UMSF and rarely post. I came across the following link today and I found it a fascinating read. I thought I would share for any interested persons who had not read this before.

http://ntrs.nasa.gov/archive/nasa/casi.ntr..._1989007533.pdf

Cheers!

Kelly

[Juramike]

Project Longshot (from link above) proposed using existing technology to get to the Centauri system and would take about 100 years.
(faster loading summary here: http://en.wikipedia.org/wiki/Project_Longshot )

Project Daedalus, proposed about 10 years earlier, would've used not-yet-invented technology to get to the Centauri system and it would have had a flight time of 50 years. Here's a quick summary link: http://en.wikipedia.org/wiki/Project_Daedalus

(Interesting that existing technology would only double the proposed flight time to the nearest star. The key quote from Wiki was that "although some technological development would still be required" - probably for the inertial confinement fusion thruster.)

I'm guessing the selection and funding process would also take at least 100 years....

[JRehling]

This seems like an exercise in continual obsolescence. Whenever you launch something like that, you're tempting fate that long before it arrives, you would have a faster way to get there.

A triple-star system is also a highly risky target. There may be nothing to see but stars and comets (which you wouldn't really see, because you wouldn't be lucky enough to pass close to one). Epsilon Eridani might be a better investment. We could actually target the known planet for a close flyby.

Imagine a Voyager-type craft coming into our solar system at an oblique angle traveling 10% the speed of light. Let's say it identified the major planets up until the last day before arrival and planned observation sequences for them. It wouldn't come very close to any planets but by luck. It also might get stuck in several cases having a closest approach of a planet that showed only a crescent. Most of the encounters would be on the order of a few to tens of AU away. The screamingly fast trajectory would mean that the planets would display very limited rotation/weather during the encounter. And, for reference, consider the MRO image of Jupiter and the Jupiter image taken by Cassini from Saturn orbit.

http://photojournal.jpl.nasa.gov/jpegMod/PIA08899_modest.jpg

http://www.planetary.org/image/PSP_002162_9030_cut_b.jpg

The MRO one suggests some excellent science could be done from 4 AU away, but it would mainly be one (highly multispectral) snapshot and that's it. And that's a heavy camera to lug along.

A still better investment would probably be better telescopes in our solar system which could show us multiple extrasolar planets before we try to blast past a few of them many decades from now and get just a teacupful of science.

[Juramike]

A still better investment would probably be better telescopes in our solar system which could show us multiple extrasolar planets before we try to blast past a few of them many decades from now and get just a teacupful of science.

I absolutely and totally agree. One really neat concept I like is a 150-km space hypertelescope made from 150 3 m linked space telecopes.

Check out Figure 8 in Luc Arnold's 2008 article which simulates how Earth would look at a 10 light year distance from such a flotilla of linked scopes. (Looks pretty dang good!) And the technical ability to launch this is much, much closer to our grasp and probably attainable within our lifetimes.

Luc Arnold, Space Sci. Rev 135 (2008) 323-333. "Earthshine Observation of Vegetation and Implication for Life Detection on Other Planets: A Review of 2001-2006 Works". doi: 10.1007/s11214-007-9281-4 Freely available here.

-Mike

[JRehling]

For what it's worth, take that Jupiter image and imagine that our interstellar craft got one picture of Mars, at that resolution, and it was in a half phase. The science value of the image would be pretty low. I mean, as a novel data point, it would be astonishing, but as far as beginning to perform comparative planetology on it, forget about it. And spectroscopy, which is actually interesting, seems much more plausible to do from our solar system and putting the money you'd spend on propulsion on light-gathering.

Also, it's interesting to contemplate, if/when we do get images of terrestrial-class bodies with more than ten pixels of diameter, how clear their skies will be. In our solar system, excluding the Earth as a biased data point, of the terrestrial planets with atmospheres, we have:

Mars -- usually >90% clear, but sometimes totally obscured by dust; spectroscopy is not racking up major successes except when the spatial resolution is exceptional
Venus -- the surface is only visible with radar and thermal IR; prospects for spectroscopy are hypothetical
Titan -- IR actually does some good work here, but spectroscopy is still tough

And the prospect of radar-mapping a cloudy terrestrial body while a craft moving at 0.1 c blasts through the system is laughable. That seems impossible even in principle if you wanted to get any geomorphology information. Radar resolution drops off with the fourth power of distance, so forget about it. Cassini can't even use RADAR effectively on Enceladus due to the large relative velocity.

[Del Palmer]

If we ever develop the technology to accelerate a spacecraft to 0.1c, one would hope we would also be able to slow-down from 0.1c at the other end. Seems a waste to take all that time/resources reaching the target star system, to then just flyby at high velocity. You'd want to take fields and particles instruments along, to do science that cannot be done from Earth.

[JRehling]

I wonder if a special sort of ballute system could be used to aerobrake on the other end. Something radically different from anything you'd use at conventional velocities. Something like a strand of spider silk a million km long that dragged through the atmosphere of a giant planet producing very low drag for a very long time. Although I can't think of any particulars that would make sense, but then I've only been thinking about it for a minute.

It would also be valuable simply to get the craft into the plane of the system which could be arbitrarily easy if the system happens to be aligned correctly. Slicing through our solar system at right angles, if you flew right by Saturn, you'd be no closer than 3 to 20 AU from the other planets. You could have a good pass in the inner solar system, but in the ideal case, say you flew right between Earth and Venus or Earth and Mars, you'd only see the night side of one at C/A.

It'd be a nice problem to have, though...

[centsworth_II]

I wonder if a special sort of ballute system could be used to aerobrake on the other end.

I'd say you better start braking quite a distance from the star system you are approaching, not waiting until after you have entered the system. Maybe a solar sail that would be extended to use the radiation from the target star to slow the craft down. Sort of a solar parachute.

[Stephen]

Project Longshot (from link above) proposed using existing technology to get to the Centauri system and would take about 100 years.

<snip>

Project Daedalus, proposed about 10 years earlier, would've used not-yet-invented technology to get to the Centauri system and it would have had a flight time of 50 years.

For the record, Project Daedalus would have targeted Barnard's Star, a red dwarf, not the Alpha Centauri system (G type + K type + a (distant) red dwarf).

That aside it could also be argued that both projects would be relying (in one way or another) on "not-yet-invented technology".

Due to the great distance at which the probe will operate, positive control from earth will be impossible due to the great time delays involved. This fact necessitates that the probe be able to think for itself. In order to accomplish this, advances will be required in two related but separate fields, artificial intelligence and computer hardware. AI research is advancing at a tremendous rate. Progress during the last decade has been phenomenal and there is no reason to expect it to slow any time soon. [Page 4 of Project Longshot proposal]

AI is arguably another one of those "not-yet-invented" technologies. AI research may well have been "advancing at a tremendous rate" when this report was created back in 1988 but the sad reality remains that here we are in 2008 , twenty years on from that report, and artificial intelligence remains "not-yet-invented".

To make matters worse, to the best of my knowledge researchers still have only the vaguest of ideas about how to go about creating one. (In fact it could be argued we know more about the principles of creating a functioning fusion reactor or thermonuclear pulse propulsion than we know about the principles for creating a functional artificial intelligence!)

I don't doubt artificial intelligence will be invented some day, but at the same time until the principles are understood nobody will be creating an AI except through sheerest accident.

======
Stephen

[JRehling]

[...]

[Stephen]

A triple-star system is also a highly risky target. There may be nothing to see but stars and comets (which you wouldn't really see, because you wouldn't be lucky enough to pass close to one). Epsilon Eridani might be a better investment. We could actually target the known planet for a close flyby.

1) Proxima Centauri is so far from its companions that Alpha Centauri is for all practical purposes a binary rather a triple star star system; and a fairly wide binary at that.

2) Epsilon Eridani is 10.5 light years away, over twice the distance of Alpha Centauri, and therefore over twice the mission time (200+ years) for a Project Longshot-type craft. If NASA or anybody else was going to send a mission that far and of that length I suspect many would probably prefer it be sent a smidgin farther, to Tau Ceti, which although 11.9 light years away is, unlike Epsilon Eridani (but like the Sun and Alpha Centauri A), a G-type star.

3) Epsilon Eridani's "known planet" is almost certainly a gas giant. I suspect any mission sent that far this soon will more likely be looking for (and at) habitable worlds. Whether Epsilon Eridani has any of those, of course, is unknown. That said, I notice that Epsilon Eridani's is apparently in a highly eccentric orbit, approaching the star as close as 2.4 AU and receding as far as 5.8 AU (according to this page at Solstation.com). I'm not an astronomer, but it seems to me that that kind of orbit for a planet 1.5 times the mass of Jupiter at that kind of distance possibly hints that planets closer in (if they exist, or still exist) may be in a similar state, which in turn may not bode well for their habitability.

A still better investment would probably be better telescopes in our solar system which could show us multiple extrasolar planets before we try to blast past a few of them many decades from now and get just a teacupful of science.

That's a fair point, especially for missions of 100 or 200+ years duration.

But that said, it seems to me that an argument of that sort could easily have been levelled at Voyager to keep it on the ground: why bother sending out flyby probes to such farflung places as Jupiter and Saturn to obtain "just a teacupful of science" when building better telescopes back home on Earth or in Earth orbit would have yielded just as useful a result?

Not until Voyager actually went out there and showed what it could do were attitudes like that no longer viable; and of course if Voyager (or Pioneer) had not gone then Galileo, Cassini, and New Horizons would almost certainly have not gone either.

It's a bit like the missions of Columbus and Sputnik. There will always be arguments, often persuasive arguments, against making the effort. Not until somebody shows it's not only possible but worth the effort will attitudes change in the places that matter and the balance of the argument shift.

======
Stephen

[ugordan]

But that said, it seems to me that an argument of that sort could easily have been levelled at Voyager to keep it on the ground: why bother sending out flyby probes to such farflung places as Jupiter and Saturn to obtain "just a teacupful of science" when building better telescopes back home on Earth or in Earth orbit would have yielded just as useful a result?

That argument certainly couldn't stand up for Voyager as they were flown with existing technology and would on paper (and did) provide science well beyond anything possible from the ground, even today. Consider the Uranus and Neptune encounters and the science they produced. Now consider the resolutions we get from the ground.

This is almost diametrically opposite to sending a lone probe on a 100+ year journey for basically only a couple of hours of distant planetary observations as JRehling pointed out. There's a cutoff in resolution depending on flyby distance at which you might as well stay on the ground and just build a larger telescope than send an inferior instrument on site. Voyagers were well inside this cutoff distance so the science paid back big time, an interstellar probe would be well outside of it. This is not even considering the length of time you could usefully observe a target while flying at an appreciable fraction of light speed.

[Stephen]

As a professional AI researcher, I would hazard to opine that the control portion of a mission like this is not even on the long list of the significant challenges, and is probably way below the level that has already been exhibited by the MERs, for example. If a craft whizzed towards an alien solar system and were able to sense its planets in time to steer towards the interesting ones, I see very little challenge on the AI side.

I'm not an AI researcher, but with all due respect I completely disagree with that statement!

1) For a start who would decide which were the "interesting" planets and which weren't? The researchers back home on Earth before it leaves or the spaceprobe itself on the spot on the fly? If the latter, then that merely begs the question: how often do the MERs themselves decide which is an interesting target and which is not?

If the answer to that is "never" (because the researchers make all those kind of decisions themselves), then that leads us to the next question: could the MERs make such decisions if the researchers allowed them to?

If the answer to that is "no" then how is the sort of decision-making that would be required for an interstellar probe "way below the level that has already been exhibited by the MERs"?

It seems to me you have it the wrong way round! Being able to navigate deftly around a rock (which, as I understand it, is about the level of the MERs capabilities) is several orders of magnitude (at least) below a decision like (for example) deciding that that funny-looking soil with all that white stuff my wonky wheel just dug up is ever so much more interesting than that pretty rock with the nice layering I was making for over yonder.

2) Just how do you define "interesting" anyway? For example, if have a target-rich environment what are the criteria and priorities it would use to decide the few targets it would be able to concentrate its attentions on? Would those be rigidly programmed in prior to launch or would they be a thing the probe would be able to work out for itself based on previous observations it had made? For example, suppose the probe had to choose for a close flyby between a planet that looked like a white billiard ball but with spectroscopic signs of water ice, another which had what looked like craters interspersed by icy plains, a third that was smothered completely in craters, and another that looked like a diseased pizza but with a hint of sulphur dioxide. If that was all it had to go on which would it choose and how would it choose it?

3) Being able to decide which are the interesting targets on arrival is only a fraction of what the computing systems (if you want to call them that rather than "AIs") onboard any interstellar probe will require.

Consider the MERs. They may be able to find their way around rocks, but if in doing so they get caught in a sand trap, even a teensy weensy one like that last time Opportunity got stuck at Victoria Crater, and you rapidly reach the limitations of their intelligence. Instead of being able to work out for themselves how to get themselves out they have to rely on human intelligence back on Earth. Now that is not their fault. The MERs were never designed to get themselves out of those kind of problems. However, those are also the very kind of situations an interstellar probe will need to be able to deal with all by itself. The probe will be completely and utterly on its own. Going into safe mode and waiting for mission control back home to get it out of the fix will not be an option if its two or three light years out.

Granted that some of these problems may be standard ones humans back on Earth may be able to anticipate and work out solutions for it in advance. Others, however, will almost certainly not be. In fact given a mission lasting 100 years, or even 50 years, I would say the latter sort are an inevitability. If the probe gets into trouble it has to be able to diagnose and analyze the problem and devise a solution. If one solution does not work, it has to be smart enough an capable enough to try other alternatives, including ones its makers back on Earth may not have planned for, let alone anticipated. It also has to know how to back out a solution if it doesn't work and which ones can't be backed out of (and so which ones you don't try unless you absolutely have to).

That sort of capability goes way beyond anything the MERs have.

And of course heaven help the probe if should ever get into the kind of life-and-death situation Spirit experienced back at the start of its mission. Yet even that an interstellar probe will need to somehow be able to cope with. If it cannot, then the odds of its surviving to complete its mission will probably be not good, for it will be depending more on sheer luck and good engineering to keep itself out of trouble than having the capability available to get itself out of any trouble it might find itself in.

So assuming that a craft had the ability to determine long-range spectroscopy and light curves of a wide range of worlds in a star system, and had the ability to fly more closely by, say, a quarter of them, I think it would be relatively easy to crunch those numbers. Much harder to get them and to act on them. We would have to forgive the craft if it made suboptimal decisions (are Mars, Titan, and Europa easy to prioritize from tens of AU away?), but it should be able to make decent decisions.

Perhaps.

I can't help wondering though how useful those are going to be. For example, how close would a probe have to be before it could detect (say) nitrogen or oxygen or water in a kind of spectrograms the probe would have available to it--bearing in mind:

1) That the instruments it will be carting along will probably have a limited resolution;

2) The results are not likely to be all neatly available all at once but will accumulate over a period of time as the probe approaches the Centauri system, thus it may not necessarily have all the necessary information until quite late, if at all;

Above I gave an equally optimistic example myself that presumed the probe would have the telescopic capability of the Hubble telescope built in. More realistically, the kind of pictures the probe would likely be presented with (and on which it would have to make its decision) would contain a single tiny point of light a few pixels across (at best) with (at best) a few vague smudges on it. Similarly, the spectrograms may well be composed of some indeterminate squiggles that may well be interpretable in several different ways rather than in one single unmistakable fashion.

In other words, the kind of data it may be presented with to make a decision upon may well be sort that even a trained human being of high intelligence and long experience may well have problems making a competent decision on the basis of. It may also be the sort that may require the kind of lengthy study, special enhancement techniques, and access to a library of reference material that the probe may or may not have available.

BTW, note that thus far I'm making the same assumption other people here seem to be making: that the probe would be a flythrough (albeit Longshot would have been at 5% of c rather than the 10% being assumed above). However, in the particular case of the Longshot probe, the proposal was in fact for an orbiter, not a flythrough; and of Alpha Centauri B at that rather than the more Sun-like Alpha Centauri A. In that context note the study's rationale (p28): "Beta was chosen as the target star because it is a dK-Type star, about which we have very little data, while Alpha is a G2 type star like our own, which we have studied extensively." In other words, the star rather than any accompanying planets would have been the mission's primary target. The probe's instrument package would presumably have been tailored accordingly.

Once in orbiter the probe's manoeuvring capabilities, and thus its ability to do flybys of any promising looking planets, would (presumably) have been limited.

If there's a term that heads one down the wrong path, it's to speak of "an AI", which calls to mind some full-blown human mind that can cry and love and so on. Nobody researching AI talks about "an AI". That was sort of an Omni Magazine, 1980ish idea. Since then, artificial intelligence has aced all kinds of tasks, and some of the things I've seen programs do (even ones I've written) leave me pleasantly surprised.

Glad to hear it. But that is arguably not what most of us non-AI researchers would term "artificial intelligence" (even granted that my own use of "AI" was a mere shorthand because I did not want to keep typing out "artificial intelligence").

That said, it is true my intended interpretation was indeed that of a thinking machine, and thus by implication one with a human-like intelligence. Or so at least I interpreted the Project Longshot proposal's own words: "This fact necessitates that the probe be able to think for itself." (pg 4)

The authors presumably did not use that word "think" lightly.

How many of the systems do you work with or know of could be said to "think for [themselves]"?

I don't doubt that many if not all those systems are extremely capable. They may even have some degree of learning capability. However, I will also hazard a guess that many if not most of those specialise in particular areas; and probably (in general) narrowly defined ones at that. Outside their particular speciality, however, would I be correct in assuming they would (probably) be at sea?

Why such an approach may have its uses on such a probe, especially among its various subsystems, the primary computing system will almost certainly need to have something approaching human intelligence, learning capability, and problem-solving capability. In other words something approximating a human mind, albeit I draw the line at the definition you imply with your reference to "mind[s] that can cry and love and so on". I think you're confusing the human mind with human emotions, many if not most of which arguably have physical causes that little to do with intelligence. You don't need to cry, for example, to exhibit intelligent.

To send out such a probe with a capability less than that would to hobble the mission even before it left the ground, as the Project Longshot team clearly recognised.

Remember, this will not be any MER-style mission with a team of human problem solvers only a few light minutes away. For all practical purposes it will be cut off from human assistance for most of its journey. If it gets into trouble it will have to get out of that trouble all by itself.

Are present-day artificial intelligence systems up to that level?

======
Stephen

[ugordan]

I can understand where JRehling's idea of prioritization and automatic selection comes from. If the probe had a very limited delta-V budget and was going at 0.1c, it would have to make a decision a long, long way out. It would basically have to work with unresolved spectroscopic data only - maybe looking for spectral signatures of interest or temperature data deduced from thermal IR spectra. It would then be a matter of automatic targeting of the craft in a manner similar to what Deep Impact did. Not entirely unreasonable and seems doable even with today's technology. The problem is in getting data to select from.

Take into consideration a flyby mission that has a 10 km/s delta-V correction capability and let's say it's initially targeted right at the star and the star system presented itself head-on, as a bullseye pattern. For the probe travelling at 0.1c to be able to target a planet at 1 AU from the star with the onboard delta-V capability, the probe would have to burn all the available propellant while still being 3000 AU from the star. How much can you figure out from spectra at that distance?
10 km/s is a hefty delta-V for today's standards, having a 1000 km/s budget really helps, but how do you get that sort of performance with any reasonably light probe? It would have to be reasonably light if you wanted to accelerate it to 30 000 km/s in the first place.

I say let's build huge space telescope arrays here instead. At least we wouldn't have to worry about them ablating away while hurtling through space at record speeds.

[Stephen]

That argument certainly couldn't stand up for Voyager as they were flown with existing technology and would on paper (and did) provide science well beyond anything possible from the ground, even today. Consider the Uranus and Neptune encounters and the science they produced. Now consider the resolutions we get from the ground.

With all due respect I think you've missed my entire point!

BTW, while the Voyagers that were flown used existing technology, they were cut down missions from a much more ambitious Grand Tour project that never got off the ground. Also the missions that were flown were originally funded only to go to Jupiter and Saturn. Uranus and Neptune were a bonus. What we would now call an extended mission; and even then only Voyager 2 got to go on it (so to speak). In the original Grand Tour the other probe would have gone to Pluto.

This is almost diametrically opposite to sending a lone probe on a 100+ year journey for basically only a couple of hours of distant planetary observations as JRehling pointed out. There's a cutoff in resolution depending on flyby distance at which you might as well stay on the ground and just build a larger telescope than send an inferior instrument on site. Voyagers were well inside this cutoff distance so the science paid back big time, an interstellar probe would be well outside of it. This is not even considering the length of time you could usefully observe a target while flying at an appreciable fraction of light speed.

Project Longshot was to be an orbiter, not a flythrough. It would have orbited Alpha Centauri B.

In addition a primary purpose of the Longshot mission would have been long-baseline astrometry. You can't do that from the ground on Earth or even from a telescope in solar orbit, no matter how powerful it may be. The telescope needs to go out as far from the Earth as it can; and the farther out it goes the better the resolution.

======
Stephen