Sending a spacecraft to Alpha Centauri | Hacker News Reader

Sending a spacecraft to Alpha Centauri

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72 pointsantoviaque48 comments

"In other words, we could all too easily become lost in the virtual worlds we make for ourselves, and lose interest in the stars. Or, more probably, we could squander our resources and experience profound and irreversible technological regression. Sometimes, I pessimistically hold with some combination of these two extremes."

I believe indifference to exploration and learning is the biggest threat. We've shown a remarkable ability to take useless things (buried dead organisms, uranium) and make them useful resources, so I'm not as concerned about that.

I'm always fascinated by the lack of "space" like exploration projects for the ocean. Seemingly closer access, as if not difficult technical problems, but with greater access to actual resources. Thoughts as to why?

http://oceanexplorer.noaa.gov/

Meh link: http://www.huffingtonpost.com/george-spyros/colbert-report-d... One of the biggest issues facing the oceans is a lack of awareness. You can't see what goes on in the ocean the same way you see what happens in a forest or in an African savanna. So people don't know that we waste 54 billion pounds of fish every year while 8 million people die of starvation. They don't know that every single fishery will have entirely collapse by 2048. Or that 90 percent of all large predators in the oceans are gone. And if people could see that. If people could see the amount of waste and destruction in the oceans they wouldn't stand for it for a second.

It should be noted however that perviously Dr. Ballard has, in the process of drumming up enthusiasm for increased funding and interest in ocean exploration, touched on the rich bounty of resources yet to be tapped beneath the sea floor. As always, the needs of man and nature are not mutually exclusive should we choose. Balance between the amazing scientific and educational benefits often described by Ballard and the interests of commerce can be achieved if we keep our eye on the prize.

http://roastedpinebark.hubpages.com/hub/Ocean-Exploration-Ne... “The ocean is home to the greatest diversity of the planet. It’s still ironic that there are more footprints on the moon than there are on the bottom of the sea, and we’re only 7 miles away,” says biologist Sylvia Earle (Marino). Ocean exploration does not receive the amount of funding that it should, especially compared to the space program.

http://www.thespacereview.com/article/1202/1 Answers me a bit: It is common for books on undersea exploration to include a throwaway comment about how we know far more about the surface of the Moon than the bottom of the ocean, or how more people have been into space, or on the Moon, than have reached the bottom of the sea. These comparisons are often not terribly accurate. Every year thousands of sailors travel under the oceans in military submarines, thousands of commercial divers work on pipelines, cables and oil rigs, thousands of hobbyists engage in recreational diving, and hundreds of researchers travel to great depths in the interests of science. Robots regularly venture where humans do not. What is usually fueling these claims is jealousy, or more politely, professional envy: the United States spends billions of dollars exploring space every year, and far less money exploring beneath the sea.

There are many similarities between deep sea exploration and space exploration, and also some important differences. Deep sea exploration has existed for nearly twice as long as space exploration, and followed a different path. But the differences are diminishing and the two endeavors are starting to look more and more like each other. More importantly, deep ocean exploration is having a major effect upon space exploration.

My opinion is that we have not given anti-matter a serious enough thought. It certainly is expensive to create now, but it seems like the scientists are and were focused on creating antimatter to confirm it's existence and properties. Once they were able to confirm these things, they moved on to trying to use their devices to confirm the existence of other things, like the Higgs Boson (a noble effort). Has there actually been a concerted effort in the physics community to design a more efficient anti-matter creation/storage mechanism?

Do the back-of-the-envelope calculation on antimatter. I did it once, then mislaid the results. First question: make it or farm it?

If you want to create antimatter then, at the very best, energy in = energy out. The energy required to accelerate a small mass of human seeds + associated robot farmers (say 100kg total) to a reasonable speed and to slow it down around the star at the other end is enormous, and a sizable fraction of the annual energy consumption of the entire human planet. It might not be impossible to realise, but it will require as much of a political effort as a scientific/engineering one.

Of course, antimatter from space colides with our planet every second, so why not just harvest it? Imagine the entire planet covered with a web that captures every particle of antimatter arriving from space. Well, it would take hundreds of millions of years to harvest enough energy though antimatter to send that 100kg mass to a nearby star.

Chemical rockets aren't going to get us there. Antimatter is currently the densest energy source known to man, and it's not enough. Barring the invention of warp drives, we're stuck here. Make the most of it.

I was mostly thinking of your first version, where antimatter is really more of a battery. We would create it from some energy source at the launch site and use it as the most efficient rocket fuel of all time.

Most of my thoughts on anti-matter (though of course I am totally unqualified in every regard) is that the biggest problem with rockets these days is fuel efficiency. We are wasting most of the energy of putting something into space because most of the weight we put into space is actually the weight of the fuel and engine. A minority of the weight of the rocket on the ground is the actual payload intended for space.

There are, to my mind, three competing emerging technologies that could solve the mass-weight ratio problem. They all involve kissing chemical rockets goodbye.

1) Nuclear

2) Anti-matter

3) Energy-beaming technology.

I feel that number 1 gets too much attention.

Obviously, if we ever want to get to other stars, we will have to get to other planets first. But I think once we get a solar-system wide economy our options will be much wider.

I also feel that making predictions about what the human race is capable of in, say, 10,000 years of technological development is silly. Even if you look 200 years back at what people predicted about what we would be capable of now you see wild inaccuracies.

I think that anti-matter could work for an interstellar rocket though. Consider what would happen if we built a factory that could convert 90% of the solar energy hitting the planet mercury into antimatter fuel. I bet that you could create an interstellar rocket from that.

Maybe we'll never be able to do it. But I wouldn't count your chickens just yet.

Unless we can come up with some as-yet-entirely-unknown mechanism to convert matter directly into antimatter, the only known methods of producing antimatter require you to pour energy into subatomic particles, smash them together, and hope to collect antimatter from the wreckage, which means you are bounded by the energy you can put into those subatomic particles. This may be somewhat practical for a Kardeshev[1] type 2 civilization who, hypothetically, have the technology to fully automatically construct the relevant hardware and enough energy that if that was the only way to cross the stars, they might be able to put together enough antimatter to do it. But it's completely hopelessly infeasible within our (non-augmented) lifetimes.

As far as I know, there's no known physics which "forbids" directly converting matter to antimatter with substantially less energy than going via energy (no conservations violated, etc), but to the best of my knowledge there aren't even any far-out fringe ideas on how to do it. That is, nobody even has any ideas on how to do it more efficiently than with rather large particle accelerators and with mind-bogglingly bad efficiencies.

[1]: http://en.wikipedia.org/wiki/Kardashev_scale

> As far as I know, there's no known physics which "forbids" directly converting matter to antimatter with substantially less energy than going via energy (no conservations violated, etc)

I think you'd have to put in at least as much energy as you get back out through annihilation of the antiparticle, which would be half the energy released (the other half coming from the destruction of the normal matter).

And actually, we already have a working energy source that works by annihilation of matter: nuclear energy. Any future antimatter-based power plant would have to compete for full-cycle efficiency against future nuclear (possibly even fusion) designs.

"I think you'd have to put in at least as much energy as you get back out through annihilation of the antiparticle, which would be half the energy released"

Yes, but if you put ten kilograms of matter in, and get back 10 kilograms of antimatter, the energy equations are balanced; 10 kilograms times c^2 on both sides. Some sort of hypothetical device which somehow reaches into matter and flips it to antimatter via some relatively cheap technique, such as perhaps rotating it in a rolled-up dimension in such a way that the result is antimatter (to give one example of plausible sounding English words that have no actual referent in the real world), does not violate conservation. It just doesn't seem to be possible, either.

And if you're going to get technical, nuclear power plants have no special claim on converting mass to energy. All power plants do that. Combustion products are ever so slightly less massive than their original components, corresponding to the energy released in the chemical reaction.

> And actually, we already have a working energy source that works by annihilation of matter: nuclear energy.

Releasing energy stored in nuclear bonds between particles is NOT annihilation. Nothing gets annihilated in nuclear reactions.

The resulting products have a lower rest mass than the initial products. The lost mass is converted into energy.

http://en.wikipedia.org/wiki/Nuclear_reaction#Energy_conserv...

EDIT since I can't reply. Particle/antiparticle "annihilation" is the conversion of their mass to energy. This is the same outcome as with the converted mass in a nuclear reaction.

If your argument is that I misused the word "annihilation" because it's a technical term in physics referring strictly to the mass->energy conversion in a matter/antimatter reaction, then I will concede that semantic point to you.

Indeed that happens. But it's still not annihilation[1], it's just a conversion of relativistic mass (which comes from energy of nuclear bonds) into kinetic energy.

[1] - http://en.wikipedia.org/wiki/Annihilation

There was anti-hydrogen that was made and trapped for >1000 seconds in Dec 2010 (http://massen.web.cern.ch/massen/physics/andresen2010d.pdf). Is that what you mean? There are certainly efforts in this direction.

That's storage, which is one possible component of practical anti-matter propulsion. You could generate a lot of it efficiently, store what you made, and send it as lightweight, high yield fuel. The other alternative is to somehow make it as you go: find some way to create pairs and annihilate them in the direction opposite to the direction of thrust you desire.

If there were a cost-efficient, energy-efficient, weight-efficient way of generating even very small annihilating pairs, it would be a major propulsion technology. It would also be a major weapons technology, and the fact that we don't know about research being done on such a cool-sounding thing it means that it probably isn't being done, or is being done with surprising secrecy (kind of unlikely).

Going out on a limb, I think that means we probably have solid theoretical grounding for believing it's infeasible.

(obligatory disclaimer: I am (obviously) not a physicist)

Actually, it may be a feasible driver of mass while not being a feasible weapon. If it takes something the size of 5-6 refrigerators to generate the particles, but they (+fuel) could generate the equivalent of >6ish refrigerators worth of our presently used fuel, it would be feasible for transportation.

For weapons (I was thinking grenades and bombs) you would need to have smaller sizes, and it would have to be efficient to make the particle generators themselves. Spacecraft (at present) can be one-off designs. We could conceivably make a very expensive, reasonably lightweight, reasonably energy-efficient, reasonably large antimatter drive once while being unable to use that technology to make a reproducible superweapon.

How do you give a direction to the annihilation?

The same way you give a direction to the explosions we use to propel ourself now - contain it, and only let it escape in one direction.

Contain it with what? The results of an explosion are gamma rays.

This kind of thing would require large scale industrialization of space (in orbit around various places). If we are doing that, why not create a black hole starship?

Microscopic black holes have been theorized as power sources for starships. The power source is the Hawking radiation that is intense for microscopic black holes, with a mass of around a million tonnes according to calculations in [1].

Apparently, creating a black hole "would require millions of times less energy than a comparable amount of antimatter" [2]. We would need to learn more about quantum gravity first though.

[1] http://arxiv.org/pdf/0908.1803 [2] http://en.wikipedia.org/wiki/Black_hole_starship

The key to a successful interstellar probe is probably miniaturization. You only need about 5kg of Pu-239 (energy density ~8.8e13 J/kg) to accelerate a 1kg payload to 10% of the speed of light (energy requirement ~4.5e14 J). A single large H bomb (2.1e17 J) could accelerate 100kg to 0.2c.

As shrapnel, yeah. Not much can survive those kinds of accelerations. So you'd need to carry a bunch of smaller ones with you, or shoot them at the probe as it accelerates (harder and harder to do), at which point we have the same current problems - large masses, or shooting things at other things to propel them.

After thinking about it for a bit, I don't think miniaturization for very-long-range probes would work very well anyway. You can't focus signals beyond a certain degree, dictated by your reflector size, so you either need a lot of power to send signals long distances or very large reflectors to compensate for lower power.

The reflectors could conceivably be something like a solar sail - huge and light - but you still have to carry it and deploy it and ensure it stays focused as you approach other stars (solar winds). You're stuck with rigid and heavier or flexible and useless, and if it's big enough it'll push you away from the star regardless of its ability to hold a shape.

At which point we're pretty much stuck with using, thus carrying, more power beyond the inflection point. No clue where that would be, but I doubt it would bring us past all but the closest stars, if any.

Yes, of course you wouldn't directly use an H bomb, the idea was that the quantities of fissile materials needed to propel a 100kg interstellar probe to 0.2c are easily within reach of several nations. Controlled fusion can be achieved in very confined spaces:

http://en.wikipedia.org/wiki/Hohlraum

I agree that communication equipment is a major problem. The best way to solve it is probably to oversize the local equipment: a dedicated space telescope and a powerful orbital laser. This may let you get away with a very lightweight emitter/receiver pair on the probe itself.

I haven't seen the Hohlraum article before - interesting stuff. And for the earth-side receiver, I was generally assuming hugely-sensitive equipment. But I may be underestimating the sensitivity of what we can build - clearly we can detect individual photons, so the probe emitter would just need to ensure it sends enough that the receiver can capture enough to reconstruct the message...

In any case, interesting stuff :) I'm sure there's a calculation that we could do to figure out the actual power requirements given background radiation and receiver sizes, but I don't know the associated math.

A thought just occurred to me - given a big reflector, you could emulate a transmitter by varying its reflectiveness / target, beaming a massively-powerful, regular pulse from Earth, and watching what comes back. That could eliminate transmitters (and their power requirements) entirely from the probe, though you still have the solar wind problem if it's really big.

Your second idea has already been done, to a certain degree. http://www.hindawi.com/journals/wcn/2005/930810/abs/ is one example of a (highly miniaturised) sensor network that communicates with a corner-cube retroreflector returning modulated laser light back to the base-station. It has no active comms emission.

"Yes, of course you wouldn't directly use an H bomb"

Well, hydrogen bombs, no. Nuclear bombs in general, sure!

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propul...

If we had an emergency of some sort and Absolutely Had to lift several hundred thousand tons of material into orbit or beyond in the next couple of decades or face annihilation, and we have to work with real engineering and real physics as we know them, Project Orion is the only thing that stands a chance of really, truly working. However, the negative side effects are considered too much for people to bear. (Incorrectly, in my opinion. People badly overestimate the negative effects of a couple nuclear explosions in the atmosphere and really really really really really badly overestimate the negative effects of nuclear explosions in the solar system (hint: it's like it's being constantly nuked all the time by that big bright thing in the sky, the solar system isn't going to notice your wet squib of a firecracker), and against the value of what this would let us lift, I think it could be worth doing. But I concede the odds of this are basically identical to the aforementioned exisitential risk, since it would take nothing less to shift opinions that far within my lifetime.)

Assuming there's no microscopic debris in space and it's pretty empty, wouldn't it be possible to accelerate faster than c relative to Earth and get there sooner in terms of body age? I mean gradual increase of acceleration, of course.

I understand that Earth will just see the ship time flow more slowly.

You can't go faster than c from anyone's reference frame (that's why space and time contract, to prevent that).

"I understand that Earth will just see the ship time flow more slowly."

You have that reversed: Earth will see time same as usual, but time for you will slow down.

Lorentz factor only makes a large enough difference when you're very close to the speed of light.

Edit: changed from 'c' to 'the speed of light'

c, as in Earth's view of ship's speed?

Probably the most interesting question from the comments: "How important is the time gap of interstellar travel?"

The information we gather today about the state of the universe is terribly "out of date" considering we are looking into the past. If we found a pale blue dot, it could be gone by the time we could manage to get there. Alternatively, there may be one in the making that we don't recognize but would be habitable by the time we made it there. We should solve the FTL travel problem first. :)

Planets don't disappear in a matter of years. Even in the 100,000 to few million years it would take to traverse the entire galaxy they wouldn't disappear (although any life would evolve significantly).

Time travel from whose perspective? To you what seems like ten-thousands of years will seem to a traveler going at relativistic speeds like hundreds of years.

There's no guarantee that the "FTL travel problem" is in any way solvable. If we wait to solve and unsolvable problem then we will never go.

I'd just be happy with a sequel to Sid Meier's Alpha Centauri, one of those franchises that has languished and whose reappearance, alas, seems as far away as an actual mission to Alpha Centauri.

There are ways to get from planet to planet with almost no energy: http://en.wikipedia.org/wiki/Interplanetary_Transport_Networ...

There must also be ways to get from star to star. If there are Sun-Earth Lagrange points, there must be Galaxy-star Lagrange points, and a way to transfer from the Sun's to Alpha Centauri's. This would probably take a while though.

I always liked the concept I read about in an Asimov short story years ago; the (rough) idea being that you somehow "pin" a ship/probe to the CBR/fabric of the universe and let the solar system / galaxy accelerate away at 2.1 million km/hr.

Note: I am obviously not a physicist, so feel free to demolish my fantasy :)

There are no preferred inertial frames, etc etc. It is a cool idea though; something to keep in mind in case relativity is ever subverted.

Sounds like a one-way trip

Much like time travel if it was possible.

We need a new method of transportation through space. Could the higgs boson be removed from a neutron so that it would not interact with the higgs field? We could create a tin can sized ship with it and accellerate the near zero mass object close to light speed and decelerate just as easily if zero mass fuel could also be made.

This does assume that the higgs boson is real and we can come up with a way of manipulating it at relatively low power levels. Not much good in the short term if it takes the power output of a star to achieve :)

Alastair Reynolds' Revelation Space series of hard sci-fi has quite a bit about ships called Lighthuggers that basically travel at about 0.95c and exploit relativity to achieve short journeys for crew members when hundreds of years pass in the real world. A more advanced technology in the books is one which reduces the inertia of an object to achieve even higher speeds, the higgs isn't mentioned explicitly IIRC but I think it's what the books are getting at.

.95c only gives a time dilation factor of ~3x, that's not very much.

Yeah, they still used sleeper technologies, but were only sleeping for 30 years rather than 100. But the universe takes the view that sleeper technology is dangerous and shouldn't be used heavily, it also only slowed down metabolism rather than freezing it ala stasis.

If we have zero mass fuel... what do we use to accelerate?

Add the higgs as you go. ;)

Which means detaching them and keeping them around. Wouldn't that mean dragging your mass around as you go, letting it decrease as you expend fuel, similar to the current setup? And if you let yourself get too light, you'd be blown along by solar winds, never able to approach a star system.

More separately, I've been wondering: once we remove them, what happens at the destination, and we're largely massless? Do we cannibalize some of the planet's? Otherwise we'd float in the atmosphere, probably pretty high up, or get blown away by breezes...

In any case, we'd probably be far too distracted by unhigging things and floating around to actually achieve speedy space-flight for quite a while.

It won't work either way, my comment was not intented to be serious. According to the theory, the larger part of mass is originated in sea quarks which form and annihilate from the binding energy of the "real" valence quarks in very short time spans - how to approach those?

There will be other problems too.. gravity is the weakest force, but it still plays a role. If it is taken away, the chemistry of our ship (and us) could change critically.

Additionally, if there is no mass, electron and nucleons will all have the same mass (none), and all elements will have the same mass - uhoh. If you're lucky you might get an entire new set of particles, or maybe try hydrogen plasma..

I agree, we'd be far to busy figuring this out. But imagine, maybe overhigging would be possible as well and we'd have gravity generators! (Low g is one of the big health problems in space.)

I'm enjoying the mental pictures :) And know little about the details, so I'm finding this fascinating.

Now I've got a mental picture of lifting something light, cranking up its higgs-bosonity, and dropping something far heavier. As long as it uses more energy to raise the effective-mass than it can produce, we don't create a perpetual-motion device, but there could be tons of fun to be had :) Winning those hammer-and-bell challenge things at fairs, for instance - crank up the mass, thus inertia, as you swing down. Handy for destruction in general, too.

If we can make zero-mass fuel, why bother shrinking the ship?

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