OOT: Proposed Interstellar Mission To Alpha Centauri! (Kinda!)

Submitted by superstringer on
Since prior posts on all things super-sciency and space-related seem to be something of a hit, and given the low level of non-satellite camp activity today, here's something trendy in space news.
 
An uber-rich Russian, with some props from Stephen Hawking and That Facebook Guy and others -- wants to spend some of his wealth on a massive project -- AN INTERSTELLER MISSION TO THE NEAREST STAR SYSTEM.  He proposes launching it in 20 years, for a 20 year trip.
 
 
 
I think it's cool if we break this down.  It's got a lot of, uh, let's call them interesting aspects to it.
 
THE DESTINATION -- Alpha Centauri, which is about 4 lightyears away.  It's actually a binary system, with a third star (Proxima Centauri IIRC) somewhat close.  We have detected more than one planet around one of the two stars, but not remotely habitable.  So, while it's close, I'm not sure what the attraction is to this particular destination.
 
THE "VEHICLES" -- These aren't quite what you see in the movies.  The vehicles he wants to send would be really tiny, like postage-stamp sized, or a few centimeters across at most.  And they'd be FLAT -- little squares or disks -- but unfurl little reflective "sails."  And he'd send THOUSANDS of them, because not all will survive the trip or make it straight to the destination.  All the electronics (and power-production) would need to be nano-sized, way below current technology but not out of the realm of question.
 
THE JOURNEY -- To get to Alpha Centauri in 20 years, and given that it's 4 lightyears away ... hmm ... let me ask Siri ... ok, you need to go 20% the speed of light.  Yikes.  The speed of light is 670 million miles per hour.  So 20% of that is 134 million miles per hour.  Needless to say, humans have never, ever sped up any vehicle anywhere close to that speed.  We've sped up packets of individual atoms in particle accelerators, yes, but... wow.
 
THE PROPULSION -- How do you get a small vehicle (which can carry no engine or fuel) up to that speed?  Here's the idea:  you continually blast it with a super-powered laser (orbiting the Sun, probably far away, like past Jupiter or something).  Light has pressure; if you shine a laser on something, you "push" it.  The effect is very, very little; it's unnoticeable on the surface of the Earth.  (Shining a flashlight on a carefully-balanced object, for instance, won't knock it over.)  But a spaceship with a "sail" (flat surface to reflect the light) would be pushed by, say, sunlight hitting that sail.  If you intensify that "push" with not sunlight but a really really really powerful laser, you can add momentum to the spaceship.  
 
THE LASER -- Ok, so this whole trick really is about building a massive, space-based laser that is so powerful it can accelerate these postage-stamp spacecraft to 20% the speed of light.  It would be a laser far beyond anything humans have ever built.  It would probably orbit far away from the Sun, and remain pointed at the spacecraft, and just keep blasting them to push them away, building up their speed over time.
 
THE PROJECT -- So it turns out, $100M doesn't get you an intersteller space mission.  It gets you some initial design work.  Actually building this project would cost ... well, a lot more.
 
I HAVE QUESTIONS!!! -- Don't we all.  Some of the challenges I see:
 
-- This laser, you know, if you turned that sucker away from space and towards a city of an unfriendly country... yes, this would be the most massive weapon ever, too.  So, you know, I'm not sure about anyone allowing this to actually happen.
 
-- If you accelerate something up to 20% the speed of light... uh, how does it stop at its destination?  You'd need to decelerated it by 20% the speed of light, too, which will require exactly the same amount of push (in the opposite direction) that the craft initially received to speed UP to 20%.  Shining a laser on it to push it up to 20% is only half the challenge; with no laser at Alpha Centauri pointing in the other direction, it'll never slow down.  It's going to zoom past its destination at 134 million mph.  That's not a lot of time to take a photo; assuming you need to be within 25,000 miles for a "close up" picture, you'll be within that distance (assuming you zoom super-close to the surface without hitting it) for only 0.6 seconds!  "Hey ok we're approaching our tarrrrr... rats, we just passed it, see that tiny tiny dot fading away behind us?"
 
-- How do you change the path of the spacecraft?  What if, when it leaves the solar system, its path is 0.000001% off-target?  It would miss its target by millions of miles.  Or, what if interstellar winds blow it off course.  (Not making that up -- this is a real problem -- intersteller space has lots of tiny dust and debris and charged particles whizzing around.)  Clearly these little vehicles might need to "turn" a bit in space, to re-orient themselves.  How's that happen?  The article linked above says they'd have "photon thrusters," but the amount of thrust from those (basically shining a small light in one direction, to push away into the other direction) is going to be tinnnnnnnnnnny.  At the speeds they'll be moving, it won't allow for much ability to change course.
 
-- How do you ensure the laser is pointed at the spacecraft?  This is the ultimate problem with this plan.  If the direction of the laser is off-target, it won't shine directly the spacecraft (and the laser, being in orbit, is continuously moving; so is the Sun, too, around the center of the galaxy); and if the laser stops blasting the craft, the craft doesn't accelerate (and probably loses its power too).  As the spacecraft get farther and farther away, the accuracy has to get better and better because the target (spacecraft) gets smaller and smaller.  Imagine how accurate the laser has to be, when a postage-stamp spacecraft is trillions of miles away.  But here's the rub:  you won't know exactly where that spacecraft is at any moment.  Since light takes time to travel, when you "see" the spacecraft, you only know where it WAS when the light left it.  For instance, if the spacecraft is 1 light-month from Earth, it takes 1 month for the light to get to us.  So when you "see" it, you see where it WAS a month ago.  How do you keep the laser aimed at it?  Not where you see it now; it's not there anymore.  It's moved somewhere else, and it's going to be somewhere else by the time the laser's re-oriented light gets to it.  For a craft 1 lightmonth away, the laser light will take a month to get back to it; you have to aim at a spot where it'll be a month FROM NOW.  (Like leading the receiver.)  This problem gets worse and worse the farther the craft moves away, because you NEVER have real-time information as to exactly where the craft is, or whether your laser is currently pointed at it.  If you change the laser's direction, it'll be 2 months (for a craft 1 month away) to find out if the laser is back on target.  If you guessed wrong, you try again, but now the craft is 2 months away, etc. etc.   Even with a wide-area laser beam, so your accuracy doesn't need to be pinpoint, this seems like a show-stopper to me.
 
So this is a fun mind-game, but, this joins the space elevator as a mind-numbingly unworkable idea that people are actually going to waste money on.  If he really wants to spend $100M on something useful, design a space-based solar shade to cool the Earth and reverse global warming.  Or, Hugh Freeze needs a sunroom on his house for those summer siestas he seems to enjoy, and the leftover cash can sent Paul Feinbaum to some world where he doesn't have to hear about Jim Harbaugh (hey, that superhot planet orbiting Alpha Centauri might be one!)
 
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MichiganTeacher

April 13th, 2016 at 12:54 PM ^

Yuri Milner, the Russian, has been boosting physics and fundamental research for a long time. I hope he can make this happen.

As for the weaponization of the laser, without comment on that, I'd point out that one real hope for interplanetary travel (not necessarily interstellar, but maybe so as an Ark ship or something) was the Orion-type nuclear-propulsion vehicles. We stopped testing (and ultimately researching) those because of fears of the nuclear bombs involved. Seems to me that at some point, we have to get over it. Space is worth the risk, in my opinion.

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UM Fan from Sydney

April 13th, 2016 at 2:21 PM ^

Well, you'll never see it because it's literally impossible. Changing events in the past is simply fiction and even if time travel were possible, you still could not change past events, otherwise the event you're trying to chance never would have happened in the first place.

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aratman

April 13th, 2016 at 5:06 PM ^

If you went on a 5 year trip at 99.5% of the speed of light when you get back, you would have aged 5 years while those on earth have aged 40+ years.  The realationship between mass gravity and time have been proven.  Right now we can not time travel into the past, but there is no reason we can not with our current understanding of relativity,

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PopeLando

April 13th, 2016 at 3:02 PM ^

Time travel already exists. We can move into the future one second per second. But really if it ever were going to be discovered, we'd already know about it. That's the thing about time travel: once it's available to somebody sometime, it's available to everybody every time. Either that, or time travel works like in Langoliers. Isn't that a nice thought?

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sadeto

April 13th, 2016 at 1:00 PM ^

I can see the horror movie script, the giant laser is bumped either deliberately or accidentally and points towards Earth and starts zapping us. 

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Brhino

April 13th, 2016 at 1:56 PM ^

1. tracking a target the size of a postage stamp as you accelerate it away to relativistic speeds would be impossible even with Star Trek level technology.

2. creating a laser with the precision, power, and limited beam divergence (how much the spot size expands the further from the laser you get) to hit a target hundreds of thousands of miles away would be impossible.

3. Creating an electronic device that could handle the proposed acceleration would be impossible with anything near current technology.

4. Creating an electronic device that could withstand the proposed laser energy and be pushed by it rather than obliterated would be impossible with anything near current technology.

5. Creating a device with a powerful enough set of sensors and communication devices to tell us anything by the time it's any appreciable distance away, yet remains the size of a postage stamp, would be impossible with anything near current technology and probably just plain violates the laws of thermodynamics.

And that's just off the top of my head.

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Balrog_of_Morgoth

April 13th, 2016 at 3:12 PM ^

Milner addressed some of those concerns (at least number 4) in his interview with the Atlantic. He mentions that we do not currently have even close to the technology needed to do this today. As he says, “[The $100 million is] to do extensive research into all of these challenges, and try to convince ourselves that this is possible in the lifetime of a single generation.”

Will the research pay off? Who knows. My bet is that we will figure out fusion before developing the necessary technology to use this laser method.

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Brhino

April 13th, 2016 at 3:56 PM ^

That's fair enough, but eventually you run into certain hard limits of physics.  I haven't crunched the numbers but I think the super laser would require atomic-scale precision.  Which... good luck with that.

Unless you find a way to "cheat" (ie if we figure out a way to make warp drive feasible) there are certain things that can't be avoided just by hand-waving "technology will have to get better".

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Space Coyote

April 13th, 2016 at 1:13 PM ^

Which is why I don't believe this will happen. Space lasers, as cool as that sounds with it's Star Wars-iness, basically sounds far fetched. Now it's a mini Death Star, yeah, that'll be difficult to push forward. All the other issues you note are very real as well, especially the "slowing down" problem that has no obvious solution even with any technology we may develop in the next 20 years. That said, we could still get a ton of data throughout the mission, so it wouldn't be a total waste if it was even feasible.

The bigger issue is that this proposal uses a lot of technology that will not be proven 20 years from now. It will be in its infincy. Spending $100M with so much uncertainty seems like a bad plan. How do you get this laser tested and functional on the ground, much less tested and functional for a deep space environment millions of miles away from earth with no option of correcting issues, and then actually launched, placed, and oriented correctly in that orbit, in 20 years? And the laser itself, there are just so many questions I have with that one.

I love space. I work in the space exploration field. I'm all about wild ideas, because ideas need to be wild before they can be feasible. But this doesn't seem feasible in the next 20 years. I think there are other, just as cool things that could be developed in the next 20 years that could advance our understanding of space and our willingness to discover throughout the universe that would one day make something like this practical. That seems to be the better path forward for now.

All that said, I'm all for this board topic and ones like it.

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Number 7

April 13th, 2016 at 1:14 PM ^

Sounds like the Russians want to build a giant sun-orbiting laser that can blast things out of the solar system with pinpoint accuracy. No, I do not think this is a good idea. Not even for a Bond flick.



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blueinIN

April 13th, 2016 at 1:18 PM ^

There is a novel called "The Three-Body Problem" that is based on the hypothesis that there are intelligent life on Alpha Centuria and they would like to colonize Earth and eradicate human kind. Very interesting, great read.



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