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A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

nytimes.com

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Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#41

Post by Jtsummers »

guelo wrote: post #18
RIMR wrote: post #2

So, how is a tiny smartphone-sized probe supposed to transmit data back to Earth from 4.37ly away?

Thinking out loud: You need an ingenious design that allows the laser sail to double as a directional antenna. And you pick a frequency which is not radiated by many other objects in space so it's easier to pick up the dim signal. And then you build a ginormous radio telescope bigger than any ever built before. Luckily you have a decade or two to build the telescope after the probes are launched.

And/or establish a chain of these spanning the distance between here and Alpha Centauri. They don't need to actually stop, but if enough are traveling at lower speeds or depart sufficiently late in the program then they'll be in position to act as repeaters. Possibly larger probes (which would travel slower) that have more power available for reception and retransmission.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#42

Post by avian »

I wonder what plans they have for communicating with a probe light-years away. Consider New Horizons. It has a power budget and antenna gain way beyond something that can be crammed into a few grams. Yet, the bit rate is so low it's still sending back data it gathered in 2015 from an encounter mere light-hours away.

Even if the laser propulsion aspect of this works out, I think communicating with something that far away is fantastically beyond state-of-the-art in wireless communications.

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#44

Post by turbohedgehog »

RIMR wrote: post #2

So, how is a tiny smartphone-sized probe supposed to transmit data back to Earth from 4.37ly away?

Use the same tech you used to send the first probe to send relay satellites to Alpha Centauri to create an Alpha Centauri-Sol bridge.

http://link.springer.com/content/pdf/10.1007%2F978-3-642-274...

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#46

Post by fsloth »

onesun wrote: post #35
mabbo wrote: post #8

Earlier quoted context omitted.

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.

Have you ever tried to take a picture from a moving car? They never turn out.

The sun is 8 light minutes away from earth. These babies would span that distance in 40 minutes. If the plan is to take planetary images I would call that basically crawling speed in terms of angular velocity (unless they are on actual collision course).

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#47

Post by noir_lord »

nkrisc wrote: post #14
ck2 wrote: post #6

I 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.

They're not going to put them into orbit, just a fly-by. Then they'll continue until they hit something some time in the future. In a million years some unlucky alien might get hit by an iPhone.

Travelling at 20% of the speed of light, I think it'll probably bend..

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#48

Post by jessriedel »

yongjik wrote: post #23

So 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…

Agreed on the extreme skepticism warranted.

I am imagining these "solar sails" to be essentially spherical, both for structural reasons and so that their response to applied laser power does not depend on orientation. The electronics in precision guided mortars in the US army survive 50,000g.

http://proceedings.ndia.org/C347/Davis.pdf

(This is only for the fraction of a second when they are fired, and I don't know how it generalizes for longer durations.)

I conjecture that the laser profile will be "shaped", if at all possible, so the trajectory of the projectile is somewhat self-correcting: if the projectile starts to get ahead of the planned trajectory, the acceleration will decrease, while if it lags the acceleration will increase. This wouldn't require any realtime feedback by the laser emitter.

With many projectiles and a massive investment in a laser array, there will be some ability to repeatedly attempt this and iterate.

Still, this is extremely aggressive even many decades in the future.

EDIT: Their proposal confirms that the beam will need to be shaped for feedback. ("By modulating the beam modes, get greater uniformity could be attained, and feedback between the nanocrafts and the beamer array would allow real-time adjustments.") No details though.

http://breakthroughinitiatives.org/index.php?controller=Foru...

Rather than the spherical shape a supposed above, they propose a thin sail with some undefined graphene skeleton. No idea how that is supposed to survive 2-minute long explosive accelerations.

http://breakthroughinitiatives.org/index.php?controller=Foru...

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#49

Post by [deleted] »

mabbo wrote: post #8
ck2 wrote: post #6

I 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.

[deleted]

Re: A Visionary Project Aims for Alpha Centauri, a Star 4.37 Light-Years Away

#50

Post by Eyght »

guelo wrote: post #31

It seems to me that the accuracy required to aim an unguided projectile anywhere near the target stars will be impossible. They'll fly by pretty far. At what distance to Alpha Centauri does an iPhone quality camera outmatch the Hubble's photos?

"It's not impossible. I used to bullseye womp rats from my T-16 back home."

It's a serious point though. Perhaps the gravity of the star will be enough to help them right?

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