So, how is a tiny smartphone-sized probe supposed to transmit data back to Earth from 4.37ly away?
Does having them spread out over a few AU make beamforming possible? They do have their light sails to do double duty for comms.
A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
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Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#22This is a pretty cool initiative — I looked into beamed propulsion a bit while teaching a course this past fall, and it seems to me that if we (or human technologies) are going to reach a star in our lifetimes, this is by far the most likely way. Still very challenging though.
For a quite detailed recent treatment of optical/IR propulsion see this paper by Philip Lubim:(http://www.deepspace.ucsb.edu/wp-content/uploads/2015/04/A-R...)
For a thorough, if somewhat outdated, treatment of the “starwisp” idea using microwaves rather than optical/IR lasers, see this paper: http://path-2.narod.ru/design/base_e/starwisp.pdf by Robert Forward.
To poll the success of this overall endeavor, as well as start to make predictions about which components will/won’t work, Metaculus is launching a series of questions —check it out if you have expertise or opinion: http://www.metaculus.com/questions/#/?order_by=-publish_time
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#23So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will instantly vaporize) while maintaining structural integrity under the acceleration of 60,000g for two minutes?
And whatever laser sources we're using must track this smartphone-sized object during these two minutes across several million kilometers. Perfectly. (It also means that whatever course deviation the object experiences must be anticipated seconds before it happens, because at the end of the two minutes the object will be ~10 light-seconds away.)
If they could pull this off it will be the next Apollo, but I'm skeptical.
Edit: Just realized we have even more problems, about the reflective coatings. If the laser is green, by the time it's flying away at 0.2c, the laser won't be green any more thanks to the Doppler effect! I'm too lazy to calculate, but it will definitely shift toward the red. So whatever reflective coating we use must be able to work near-perfectly over a wide range of spectrum.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#24Oddly the most practical use for this is as an interstellar weapon. You don't need to solve the problem of communicating back to Earth, you just need a little terminal guidance.
If an iPhone weighs 100 g and we use a non-relativistic formula for energy at 1/4c, that is 2.8 x 10^14 joules, a ton of TNT equivalent is about 4.1 x 10^9 joules, so that is a cool 70kT -- The impact velocity would be high enough to break the Columb barrier as well, so you might get a nuclear boost to the yield as well.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#25Let's build a mass driver around the circumference of the Moon. Like a cannon in a particle accelerator shape.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#26Sending a swarm of unguided relativistic projectiles across the universe seems profoundly rude.
It would be nice if they could use solar wind to decelerate as they approached. I know there's not enough energy there to insert them into an orbit, but they might get time for a few more pictures?
Just flip the battery in the laser around and it will pull instead of pushing.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#27So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will instantly vaporize) while maintaining structural integrity under the acceleration of 60,000g for two minutes? And whatever laser sources we're using must track this smartphone-sized object during these two minutes across several million kilometers. Perfectly. (I…
The plan calls for ultra-reflective coatings that are tuned to the wavelength of the laser. Apparently these exist, though I have not checked the numbers. In my class I abandoned laser propulsion quickly for just this reason (incinerated the target), but with these coatings it might work.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#28I thought very strange things start to happen at even 10% the speed of light (mass increase, etc.) so 20% sounds impossibly ambitious? Also the fastest physical object we've ever observed is only 1000 miles per second. A far cry from even 10% of c Then there is that pesky problem of deceleration.
At 20% the speed of light, time would dilate by around 2%, but that's about the extent of the effects, afaik. Also: why bother decelerating at all? Take a picture as you fly by.
Wouldn't want to program that particular timer. Talk about hard real time requirements!
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#29Moreover, to keep the beam tightly focused on one probe at a time would require an adaptive optics system that compensated for atmospheric turbulence — something astronomers know how to do over a span of 10 meters, the size of a big telescope mirror now, but not over a mile. Would it be easier just to put the lasers on the moon?
It might be easier to fire the lasers from the moon, but getting the lasers to the moon would be a huge pain.
Not to mention supplying these hypothetical moon lasers with enough power to blast these mini-probes into another star system.
Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away
#30So the whole thing should weigh in the order of several grams, yet it should be able to deflect 100GW of incoming radiation near perfectly (otherwise it will instantly vaporize) while maintaining structural integrity under the acceleration of 60,000g for two minutes? And whatever laser sources we're using must track this smartphone-sized object during these two minutes across several million kilometers. Perfectly. (I…
Setting incredibly ambitious goals has definitely lead to impressive achievements in the past. I think it's definitely worth studying. Worst case, we'll learn something.