Saturday, October 27, 2012

A Planet of Alpha Centauri


The nearest stellar system to our own, as Sky and Telescope reports, has a planet. Which is a vindication of sorts for rocketpunk-era science fiction, which made our neighbor a favored location.

The newly discovered world's name, at least for now, is distinctly unromantic: Alpha Centauri Bb. The capital B signifies that it orbits the slightly less luminous of the main Alpha Centauri pair. (Alpha Centauri C, AKA Proxima Centauri, is a very distant companion of the AB pair, and slightly closer to good old Sol.) The lower-case b marks the first planet to be discovered in the system.

Its mass is roughly comparable to Earth's, but Bb is almost certainly not inhabited by tall blue cat people, and even less likely to ever be inhabited by us. It is a 'hot Earth,' or at any rate just plain hot, orbiting Alpha Centauri B at a distance of 0.04 AU. This fact is in no way discouraging. Our search methods heavily favor planets in furnace orbits, and where there is one planet there is a decent chance of more.

In fact, as extrasolar planets go there is nothing special about Alpha Centauri Bb except for its address. But its address - Alpha Centauri - is special indeed.

When interstellar settings first developed back in the Golden Age, the preference was for familiar named stars, as I noted in the Tough Guide entry on Nomenclature. Thus notable SF worlds circled such dubious candidate stars as Sirius or even Betelgeuse.

By around the 1950s, as the theory of stellar evolution made these locations problematic, attention turned to nearby sunlike stars. Alpha Centauri ruled this list - with some hesitancy, ironically, because of doubts whether planets in double-star systems could have stable orbits, or for that matter form in the first place.

These doubts were only laid to rest when we started actually finding planets in double-star systems.

A few things distinguish Alpha Centauri. It is the third brightest star in the night sky, after Sirius and Canopus. But it lies far in the southern sky, thus invisible to observers in most of the northern hemisphere. Hence its lack of a familiar given name. Though in fact it does have a given name, Rigilkent, known mainly to the dwindling ranks of people familiar with celestial navigation.

According to Wikipedia, Alpha Centauri A is about 1.5 times solar luminosity, while B is about half solar luminosity. Component A, with a spectral type of G2, is often described as a near-twin of Sol, though in mass and luminosity, though not spectral type, Sol is more nearly intermediate between the two. (B, the one now known to have a planet, is spectral type K1.) They orbit each other every 80 years, ranging from a little more than Saturn distance to considerably more than Neptune distance.

The third component, Proxima, is dim and distant, nearly a quarter of a light year from the bright pair (and somewhat closer to Sol). Travel between them would thus be more like a short interstellar voyage than a long interplanetary trip. The system is probably somewhat older than the Solar System - what that means for life, if it has a lifebearing planet, is anyone's guess.


Alpha Centauri is an interesting stellar (and planetary!) system, but of course by far the most interesting thing about it - to us - is its distance, 4.37 light years to the AB pair. Which invites speculation about going there, or at least sending a probe. Proxima is closer, 4.21 light years, but a mission would almost certainly be aimed at the main pair, possibly with a secondary probe to be deflected to Proxima.

So ...

Nuclear electric propulsion, of the sort I have often discussed here, should be good for on order of 300 km/s if tuned for maximum specific impulse. Since Alpha Centauri is itself approaching Sol at about 25 km/s, it will be appreciably closer by the time the mission gets there, in about 4000 years. Which is an awfully long duration for mission planning, not to mention getting it funded.

Getting there sooner requires some admixture of handwavium to the spacecraft specifications. But there is handwavium and there is handwavium. And this is probably as good a place as any to link the Engine List page at Atomic Rockets.

The short form is that, for credible mass ratios, high-end fission technologies can potentially reach on order of 0.03 c, about 10,000 km/s, for travel times on order of 100 years. Fusion can, in principle, bump you up to around 0.1 c, and you get there in not too much over 40 years. And there are other propulsion options.

Bear in mind that you will probably want to slow down, not flash through the Alpha Centauri system at an appreciable fraction of the speed of light. So mission delta v must be twice the travel speed, plus a bit of margin for local exploration once you get there.

By the way, I am thinking here mainly of robotic missions. Human missions involve a whole 'nother set of complications, the first two of which are long term life support and a much heavier payload.

And even for a robotic mission there will be engineering complications. For fusion, these begin with getting it to work at all, in a form that won't vaporize the spacecraft. (We have already accelerated appreciable masses - in the kilograms - to a few thousand km/s. Unfortunately, these masses were internal components of nuclear weapons.) Probably you should expect realistic technologies to achieve around 1 percent  of theoretical propulsive performance, or at best 10 percent  - thus, a tenth to a third of ideal mission speed.

Those provisos made, no heroic/fanatical effort should be required for a mission to reach Alpha Centauri at some date within the plausible midfuture. The difficulty level is on the same order as a substantial permanent base (and incipient colony) on Mars, outposts in the outer system, and regular travel among them. Which, to be sure, is a far more demanding order than people thought at midcentury. But it is doable.

Discuss.




Note: Just when I was trying to get back into a more frequent posting rhythm here, all the usual excuses raised their ugly heads. But at least the World Series will end this coming week, one way or the other. (No one knows better than SF Giants fans that it really ain't over till it's over. But it will be over soon.)


The image comes from the Sky & Telescope article link at the beginning of the post.

48 comments:

Byron said...

(We have already accelerated appreciable masses - in the kilograms - to a few thousand km/s. Unfortunately, these masses were internal components of nuclear weapons.)
So? We use those same nuclear weapons (or similar ones) to drive the spaceship. Simple.

That said, I'm a lot more dubious about completely unmanned missions over the decades required here. Spacecraft are designed to be reliable without maintainence, but that's really pushing it. The cost would be high enough we'd probably only go if we knew there was life. Or if we got FTL. We need to get Luke back. He needs to finish up his wormhole network so we can go see what's there!

But at least the World Series will end this coming week, one way or the other. (No one knows better than SF Giants fans that it really ain't over till it's over. But it will be over soon.)
There was much anguish over the sportsball both on facebook and at school on the night of the last debate. I still don't understand why everyone cares so much about a bunch of people running around and whacking a white sphere.

Damien Sullivan said...

I've still got a soft spot for Project Longshot, fission-driven fusion pulses, without a need to extract power from the fusion plasma. Get more thrust and delta-vee than pure fission, use a known technology for system power. Seems closer to being doable than anything other than Orion. Of course, I still estimate costs of $400 billion to $4 trillion, mostly from a 10x-100x development factor. Longshot's supposedly got a cruising speed of 4.5% c, and stops to examine the system in detail.

Of course, you still need automation good for a century. And as someone pointed out, what kind of hypertelescope can you buy for $400 billion? Not a perfect substitute for a close orbiter, but faster payoff and usable for many targets.

In reality, NASA canceled the Terrestrial Planet Finder projects (coronagraph and interferometer both) which would have been in the single billions range.

CAPTCHA failures 2

Mangaka2170 said...

Considering the challenges of whipping a spacecraft up to any respectable fraction of c, I would think that even a flyby of another star system would be a monumental accomplishment in and of itself, regardless of what scientific treasures such a mission may or may not deliver. That said, an unmanned charting expedition would probably yield better and more long-term results, even considering the additional cost and engineering challenges.

Brett said...

I'll have to echo the first two and question whether we can actually design a probe that will survive in interstellar space for 120-400 years, never mind the longer periods of time required for an engine that doesn't depend on a form of power that we haven't even got to "sustained ignition and burn" on Earth. What's the life expectancy of computer parts here on Earth?

Especially since it's going to have to be an extremely autonomous and fairly intelligent probe, capable of doing everything in the mission plan by itself due to mission control having a 4+ year communication lag (nearly 9 years for communication and response).

Doesn't Tony work in a computer-related field? I wonder if he knows.

@Damien Sullivan
Of course, you still need automation good for a century. And as someone pointed out, what kind of hypertelescope can you buy for $400 billion? Not a perfect substitute for a close orbiter, but faster payoff and usable for many targets.

You could probably buy a really good array of space telescopes for that kind of money.

@Rick
They orbit each other every 80 years, ranging from a little more than Saturn distance to considerably more than Neptune distance.

Can you imagine what it would be like to be on a habitable planet orbiting one of those stars on a close approach? When you are in the part of your year where the planet is between the two stars, night would effectively disappear for a while. During the other part, when you're getting closer and closer to where the home star is eclipsing the binary partner, you'd have two suns rising and setting in the sky.

And interplanetary travel in that system would be merely be very difficult. If the timing was right, you could actually launch a manned mission (or several of them) to planets orbiting the binary partner.

Brett said...

To go further, I wonder if the trade-off between reliability and energy spent in acceleration/deceleration is what kills interstellar travel for most civilizations. Either you have to design spacecraft that can survive in interstellar space for centuries and millenia, or you have to spend god knows how much energy accelerating ships that carry enough fuel to slow down at the destination system.

Z said...

Re: Braking delta-v at the far side- various proposals have been made to brake in the solar wind of the destination system with a magnetic sail to obviate the need for braking propellant, and the effect on mission masses is pretty spectacular- the faster you're going, the greater the braking delta-v, just like if you were aerobraking. It also makes tolerable in-system propulsion if you need to drive around when you get there.

As for mission durability, I think the Voyagers are living proof that it's within our capabilites. We made probes with lifetimes on the order of half of the lifespan required, by accident, decades ago. If lifespans of a century were needed, we'll just build them.

Byron said...

Brett:
I'll have to echo the first two and question whether we can actually design a probe that will survive in interstellar space for 120-400 years, never mind the longer periods of time required for an engine that doesn't depend on a form of power that we haven't even got to "sustained ignition and burn" on Earth. What's the life expectancy of computer parts here on Earth?
It's not the computer parts alone I'm worried about. Everything has a failure rate, and most of the spacecraft failures I'm familiar with have been mechanical in origin. Also, space is much harsher on computers than the Earth environment is. I ask for a couple years before I have to give precise numbers.

Z:
The problem with pointing to Voyager is that we've gotten lucky. They were designed so that everything would be working at the end of the Neptune pass, pretty much no matter what. The Alpha Centauri probe has to be fully operational when it gets there, which is orders of magnitude more difficult.

Locki said...

1. At a significant fraction of C (1-10%) aren't potentially microscopic/nanoscopic collisions becoming a serious concern? Not to mention drag (afterall this killed the bussard ramjet idea)

2. I've been watching with very keen interest the sheer number of rocky planets we are discovering. I'm coming to the conclusion the vast majority of stars (even binary systems!) have rocky planets. They are very common. Many of these planets will be in the Goldilocks zone. Even the most cynical of us at rocketpunk believe we could get a probe to Alpha Centauri in the next few centuries.

Given our theoretical and engineering knowledge it can be done.

So I can't help but think. Where are all the probes? I don't want to hijack this thread with a discussion of the fermi paradox but given what we now know of the universe I can't help but think someone else's probe will probably reach us first.

Locki said...
This comment has been removed by the author.
Unknown said...

@Locki So I can't help but think. Where are all the probes?

Chances are we wouldn't have spotted it. For most of human history we've had no means of detecting a probe. Even now we'd probably only spot it if it used a very bright engine to decelerate into orbit. We definitely wouldn't spot a probe that didn't stop.


@Z Braking delta-v at the far side- various proposals have been made to brake in the solar wind of the destination system with a magnetic sail to obviate the need for braking propellant, and the effect on mission masses is pretty spectacular- the faster you're going, the greater the braking delta-v, just like if you were aerobraking. It also makes tolerable in-system propulsion if you need to drive around when you get there.

If the solar wind is sufficient to brake with then surely it would also be possible to use it to accelerate away from Sol?

Geoffrey S H said...

There are an awful lot of sf works that focus on alpha centauri. There are an awful lot of sf works that focus on the year 2150 (presumably because of the way the date sounds catchy when said aloud). There are a large number of works that focus on alpha centauri in the year 2150 (Avatar being the most recent example). I'd be very interested to see what happens in that system around that date.

As regards the name, given the large number of real and fictional astronomical locations with Roman, Greek and Latinish names that end in "I", or "a", I do myself prefer "Rigilkent" to "Centauri". Sounds more unique a name.

Brett said...

@Unknown
If the solar wind is sufficient to brake with then surely it would also be possible to use it to accelerate away from Sol?

Yes.

Of course, we'll need to find a super-conducting material that we can make into a tens-of-kilometers wide space loop for the sail. We'll also need a pretty big power source for it as well.

Rob Lopez said...

If we can get fusion propulsion to work, and if the realistic velocity is about 10% what it says on paper (if lucky), then does that turn a 40 year journey into 400 years? (Yes, my maths is crap)

Nothing since the industrial revolution (less than 200 years ago) has run that long without maintenance.

And no civilization has ever stayed wealthy enough to stay at the top in that time either. Mission control will have weeds growing out of its ruins before the return signal makes it back.

Maybe the Transatlantic Hegemony of Lithuania will pick it up. If they know what to listen for.

Jim Baerg said...

"If the solar wind is sufficient to brake with then surely it would also be possible to use it to accelerate away from Sol?"

Yes but the solar wind flows away from the sun at 'only' a few hundred km/s, something additional would be need to get the spacecraft fast enought to reach the next star in a reasonable time. Some sort of particle beam hitting the field of the magnetic sail might do the job.

BTW the discussions I've seen on using a magnetic sail for braking an interstellar spacecraft involve braking against the interstellar medium before reaching the heliosphere of the target star in order to not overshoot.

Tony said...

Okay, Rick, Los Gigantes sealed the deal. No more excuses.

WRT Bussard ramjets, I'm not sure what to think. It could be that they can be made to work, but have a speed limit based on drag. And a pretty low one at that -- something like 10-12% c. Or they may be effectively unworkable in practice. Or maybe they have a speed limit, but given realistic technologies, the speed limit can't be approached. For example, maybe we can only achieve 5% c, meaning voyage times to even nearby stars will be on the order of centuries.

Which means probably crewed. And necessarily large crews, since we're into generation ship timeframes. On the scale of multi-generational communities, humans can be thought of as more reliable than machines, even with multiple redundancy.

That consideration isn't limited to ramjets, BTW. It applies to any method that can't get much above .1 c, which includes, probably, Orion, anti-matter, and much else besides.

Of course, if we find a way to get up to say, .5 c, things get a bit different. Then you're merely talking careers, presuming it's a round trip. And it could be a round trip. If you've got the ability to get up to really relativistic speeds, you probably have a drive beyond any known physical principles -- perhaps some kind of metric manipulation machine. Or power sources based on reactions at the GUT level, with exhaust velocities just this side of the speed of light.

Or something partaking of a little bit of both -- maybe local metric manipulation, allowing the squeezing of ordinary matter (any ordinary matter, from diamonds to pig slop) down to and beyond the level of degeneracy. Open a pinhole at one end -- pointing away from your crew cabin, of course -- and get a stream of realtivistic subatomic particles to push you anywhere you want to go. Just don't point it at any nearby planets, since it would probably also have electromagnetic side effects similar to a gamma ray burst. Woo-hoo! the stars are ours!

Brett said...

I might agree to be part of a one-way colonization trip to Mars, but I wouldn't join a centuries-long, multi-generational trip to Alpha Centauri. I want to actually live to see the destination in question that I depart for.

You may be right about needing them, though. Send a fleet of ships, each with redundant parts and components plus raw materials and some pretty advanced manufacturing, capable of effectively replacing most of the ship during the journey with new parts made from stored and recycled materials. All of it powered by nuclear energy, and a lot of it.

Man, that sounds politically and socially risky. What if the next generation of crew members decides that they don't want to just be the suckers in the middle of the journey who never know anything but the show, and they turn it around and head back for Earth? Or if they get to the destination, but are so bred and used to living in a flying habitat that they don't want to live on the planet? I remember there was a SF story like that, where the crew gets to the destination and decides that they don't want to leave the "heaven" of the spaceship for a planet.

As for the pinhole spaceship, I'm guessing that's probably beyond PMF. :D

Brett said...

EDIT: "Ship", not "show.

Anonymous said...

My personal favorite hope for a relatively realistic relativistic drive (sounds good!) is the singularity engine: using Hawking radiation from an appropriately sized singularity as a drive.
Here a paper from Cornell University speculate on the possibility http://arxiv.org/abs/0908.1803

It's clearly a technological feat well beyond anything we can dream now, and advancement in physics could still reveal it as altogether impossible.

But a positive thing is that apart for its use as propulsion it would be one of the best energy production method possible if you can feed it, and so it's likely that if the technology will be ever available we will try to do it anyway, if only to have access to all that energy.

With such a drive you could go almost anywhere, and with ample payload.

Tony said...

The risks of generation ships are many, but if that is the class of tool at your disposal, those are risks you have to take. Of particular note, second or third generation rebels couldn't return to Earth, simply because there wouldn't be enough fuel to stop and return; there's be just enough to stop at the detination star.

WRT the PMFness of any particular propulsion system, pretty much anything that gives you relativistic velocities in a useful, crewed ship is beyond PMF considerations. Still, they make interesting speculative toys.

Cambias said...

Given the amazing durability and longevity of vehicles like the Voyager probes, a 50-year unmanned mission doesn't seem particularly impossible. The biggest issue I can see is how do you transmit data back? The power to send even very crude binary data over four light-years would be enormous. We may be faced with the problem that any vehicle light enough to launch to Alpha Centauri in a reasonable time would not be able to send back any useful information when it got there.

Spugpow said...

Re communication: The Daedalus study proposed repurposing the engine bell of the ship as a radio dish. Nowadays they're looking at lasers.

Thucydides said...

The other issue is what could sustain the people on Earth while the ship is on its way?

Most people can't sustain interest in a project for a prolonged period of time, and even 5 years seems to be the effective planning limit for anything (given there will be enough unanticipated events during that time to unravel most of the starting conditions and assumptions). Now we are talking about generations of effort to sustain the project.

The only good examples in our history that I can think of would be based on religion; European cathedrals often took 200 years to build, so the planners and financiers would never live to see the completed project. Given the relatively short life span of peoples in Ancient times, similar considerations were probably in effect for the Pyramids, temples to the gods or Ziggurats.

It might be possible to create some sort of religious or quasi religious motivation for interstellar travel, but even that is suspect, just look at how theology changes over the span of time (Christians from 1700 were much different from those of 1500, and if they were to be transported to today, they wold hardly recognize the Christian religion as practiced in most churches).

Horselover Fat said...

Some of you are a wee bit pessimistic about slow missions.

For instance Thucydides wrote:
"Most people can't sustain interest in a project for a prolonged period of time, and even 5 years seems to be the effective planning limit for anything"
New Horizons launch to target: 9+ years
Rosetta launch to target: 10+ years
And those aren't major or very exiting projects. Check out some of the planning horizons for stuff people actually care about like critical infrastructure...

The gap between where humanity is and an interstellar probe is so large, there's no need to make it sound bigger than it is.

Tony said...

The planning horizon for space missions from authorization to launch runs about five years in most cases. Preliminary conceptual sutides you either get for free, from enthusiasts, or on separate study contracts with only two or three year time horizons. by the time the vehicle is launched, the majority of the project money is sunk in hardware development and mission planning anyway. Mission operations can cost a lot of money in movie and popcorn terms, but not much in overall project terms.

Horselover Fat said...

I believe the issue raised by Thucydides was the delay from expense to payoff rather than the operating expense.

It must cost a good bit more to operate a spacecraft working on its target than when it's cruising.
But Cassini was launched 15 years ago and is still working on its target.
That's not surprising: the last mission extension was supposed to cost 60 megabucks a year against well over 3 gigabucks of total cost.

Oh, and that beats Voyager I think: ICE was launched in 1978 is apparently still fully operational even though its orginal mission ended in 1982. It then observed a couple of comets in the mid-eighties.
They're considering reactivating it and burning some of the spare propellant in 2014 to reach a new target a few years later...

Tony said...

The launch is the payoff, from a funding standpoint. After that, you've got as much mission as you're willing to pay for, but the total cost per year is reltively low. For example, $60M, in inflated dollars, is a pretty low annual cost for a continued mission, where most of the billions of the total cost was spent up front just getting the hardware into space. According to Encyclopedia Astronautica, the up-front cost for Cassini, for hardware and launch was $2.3B, in 1997 dollars. Ongoing mission operations is chickenfeed.

In an interstellar mission, where Mission Control type operations are out of the question, all of the money is spent just putting the thing on trajectory. After that, your entire cost back home is manning a listener network, to pick up any data sent back. And if your objective is purely expanding the physical scope of the human race, that's not even necessary.

Brett said...

@Tony

I realized the propellant issue a few minutes after posting, so it's true, they probably couldn't turn around and head back.

Of course, then I wonder what the "mid-flight" crew generations would think of their forefathers. Would they curse them for imprisoning them on the ship, so far from their homeworld, on a journey where they'll never see the destination themselves?

jollyreaper said...

I would still put a probe mission far out in the future, not within our lifetimes. I would think our computer tech would handle the automation tech at that point.

But for the most part I feel like, as with mars missions, shorter travel times would make everything more doable.

Rick said...

I didn't pin myself down to a mission time scale in the main post, but I'd guess that with viable tech we could get a probe to Alpha Centauri - and slow it down on arrival - in 100 years, give or take.

Which is not *that* far beyond the time scale of existing interplanetary missions. Yes, it is beyond the normal human life span, a socially important constraint. (And I'm not an optimist about radical life extension.)

It would probably take a period of peak interest in space travel to send the mission on its way, but such periods may recur once or twice per century. (They almost have to, if All That Cool Stuff is really going to happen.)

The keys to mission durability are ruggedness and redundancy. Both cost, but a human mission on generation-ship scale is even more expensive, and asks an awful lot of the crew.

As Tony notes, once the mission is on its way, the ongoing expense is modest. If post-industrial civilization collapses in the meanwhile, there may not be anyone with ability or interest.

But otherwise it doesn't take an unreasonable interest level to set up to receive transmissions from the probe. Especially given that a century-earlier techlevel was able to send the thing off in the first place.

(Thanks, Tony, for your generous comment about the Giants. Hitting a ball with a stick is inherently frivolous, but when done well, damn it can be entertaining.)

Tony said...

Rick:

"Thanks, Tony, for your generous comment about the Giants. Hitting a ball with a stick is inherently frivolous, but when done well, damn it can be entertaining."

My tongue was firmly planted in cheek, even if I didn't indicate it with a smiley. I too watched the series with great interest, though after Game 3 I just wanted the Giants to finish it and put the Tigers out of their misery.

Thucydides said...

A quick look at the reference library suggests the closest "PMF" way to reach Alpha Centauri and look at the planet is to use a solar sail.

The mission profile is rather complex, the sail needs to drop into a hyperbolic path around the sun behind a sunshield, deploy inside the orbit of Mercury and accelerate away from the Sun; reaching the target in @ 1000 years. If you want to slow down in system, the probe would have to "sundive" at the target star to slow down, or deploy a magsail brake or some other means would be needed.

As a positive, assuming the systems could survive a journey lasting 1000 years, the sail would allow the probe to move around the entire system and map out areas of interest.

While the sail is probably PMF, I'm not so sure about automated systems lasting 1000 years.

Byron said...

Thucydides:
I'm positive it won't last even a quarter that long. Stuff breaks, and the stuff to fix the broken stuff breaks. It's an exponential cycle, and at some point, you just can't go any further.

Brett said...

You'd not only need a lot of redundancy, but also probably the ability to make new parts in-flight to replace the old ones (which also means that you're either carrying enough raw material to do that, recycling old parts, or both). I suppose you could do that if you had a Ship O' Robots, but they'd have to be smart robots.

I've read that cosmic rays would have some unpleasant effects on your advanced computers over time, unless you go down for several meters worth of shielding. I'm not sure that's a big problem for a ship that's already planning to take a ton of time in transit.

Tony said...

I was thinking about the cruise population issue for generation ships. It occurred to me that most people just get used to what they know. If you're born on a starship, that's your life. It may be highly constrained, but so was being a serf in Imperial Russia, or a factory worker in Industrial Revolution Brimingham. People got by.

Also, revolution is basedo n the possiblity of there being something better, or at least different. On the starship, what does revolution get you? All it does is decide who gets to be in charge for the moment. But the ship is still going where the ship is going.

Cambias said...

We've been having an on-and-off discussion about Very Long Projects over at the Hieroglyph Project forum.

I pointed out there that some Very Long Projects -- like the Interstate System (50 years and still building) or European cathedrals -- do have short-term payoff. For highways it's obvious, but even for a cathedral, the donor who builds, say, a bell tower or a side chapel gets the spiritual (and social) reward when construction starts, even if he dies before it's finished.

One can certainly imagine an interstellar probe having some short-term scientific payoff -- studying the heliopause and the interstellar medium, proof-of-concept for onboard systems and propulsion, jobs for aerospace workers, geopolitical dick-swinging, etc. If it could be done for about the cost of a Mars mission, it's definitely in the realm of political possibility.

It does require a wealthy enough society to blow that much cash on a project like that. I doubt the United States be able to afford it in my lifetime, at least not unless we can pay down our debt.

Tony said...

Cambias:

"...Hieroglyph Project..."

Grrr...Neal Stephenson

Anonymous said...

"The problem with pointing to Voyager is that we've gotten lucky. They were designed so that everything would be working at the end of the Neptune pass, pretty much no matter what. The Alpha Centauri probe has to be fully operational when it gets there, which is orders of magnitude more difficult.:

We seem to "get lucky" quite a lot. 2 out of 2 with Voyager, and we lost contact with Pioneer 10 in 2003 when it lost power. Space probes floating through space seem quite robust, really. Of course, an interstellar one would be moving a lot faster, but I think there's still ground for optimism.

Honestly it seems to me that NASA's expected mission lifetimes have been a joke; things either fail right away or have vastly longer missions than planned for.

Damien Sullivan said...
This comment has been removed by the author.
Damien Sullivan said...

"The problem with pointing to Voyager is that we've gotten lucky. They were designed so that everything would be working at the end of the Neptune pass, pretty much no matter what. The Alpha Centauri probe has to be fully operational when it gets there, which is orders of magnitude more difficult.:

We seem to "get lucky" quite a lot. 2 out of 2 with Voyager, and we lost contact with Pioneer 10 in 2003 when it lost power. Space probes floating through space seem quite robust, really. Of course, an interstellar one would be moving a lot faster, but I think there's still ground for optimism.

Honestly it seems to me that NASA's expected mission lifetimes have been a joke; things either fail right away or have vastly longer missions than planned for.

Tony said...

So far, space probes have been simple machines with relatively few moving parts. (Though the continued performance of the tape memory system on the Voyagers is impressive.) I don't think that experience can be used in anlogy to larger, much more complex interstellar systems. Of particular concern would be power systems, which could not be anywhere near as simple and reliable as RTGs.

Tony said...

And, oh yeah -- the short nominal mission lifetimes have to do with guaranteed science return, in order to get funding. They're not based on fundamental technical constraints.

Thucydides said...

For any practical mission in the PMF, we would probably need to send probes in a "shotgun" pattern.

This approach could make probes and propulsion systems cheaper through mass production, as well as possibly more reliable through having a larger statistical universe of parts and processes to check as probes are assembled.

Each "swarm" of probes is dispatched to the target with the hope that at least a few of them are still functional on arrival. This could also make an interesting check on propulsion systems, packing a bunch of probes on a bus and then having the propulsion system of choice accelerate the probes in the direction of the target.

This would still suck if the best we could do is a 500 year MTBF and the mission takes a thousand years, but constant repetition would refine many systems for uses in the Solar System, where high reliability would still be needed in multi year voyages to the outer planets.

Tony said...

Shotgunning probes is rational only if no failure mode is systemic (e.g. computers becoming unreliable after some predictable time because cosmic rays turn them into silicon sieves at the microscopic level). Also, you only have so much propulsion to accelerate so much mass to interstellar speeds. If you send out a bunch of small probes, you have to see them as being reduntant for each other, but with little, if any, individual redundancy. And even with no systemic failure modes, all of those single point failure modes could add up over time to neutralize each and every probe. It might actually make more sense to build massive redundancy into a single probe, with workflow switching possible at every interface, and even massively reduntant interfaces.

Sean said...

alOn the subject of other solar systems, astronomers believe they've discovered a so-called super-Earth in the habitable zone of HD 40307, 42 light years away.

http://www.sciencedaily.com/releases/2012/11/121108073927.htm

Geoffrey S H said...

Maybe a massive orion engine attached to a large probe is the best way forward. Plenty of room of redundant systems, a little less time spent in transit between the system and a fairly robust method of propulsion. Of course whether the thing would actually work is a whole matter all its own.

Geoffrey S H said...

sp* "room for redundant systems"

"a matter all its own"

Brett said...

@Sean
alOn the subject of other solar systems, astronomers believe they've discovered a so-called super-Earth in the habitable zone of HD 40307, 42 light years away.

It's good news, although there's a pretty significant margin of error - 2.6 Earth masses IIRC. It could be anything from 4.5 Earth masses (either a rocky terrestrial planet or an oceanic planet) to 9.7 Earth masses (meaning a small gas giant).

If you think getting to Alpha Centauri is hard, imagine getting to that planet.

Brett said...

Sorry, that sounded more pessimistic than I meant it to. I'm thrilled that we might have a conceivably habitable planet confirmed within 50 light-years of Earth.