# Starshot

I don’t know what this is about, but Stephen Hawking and Yuri Milner are here in New York today, with a press conference downtown scheduled at noon, supposedly to announce a mysterious new space exploration initiative, to be called Starshot. There’s also evidently some sort of Columbia connection, with a reception scheduled up here. More later, when we find out what this is all about. Last year there was a Hawking/Milner announcement of Breakthrough Listen and Breakthrough Message, projects related to communication with alien civilizations.

Update: Livestream will be available here.

Update: According to this source (and Google translate…), this is a project to send a small space probe to Alpha Centauri.

Update: “Breakthrough Starshot” is a $100 million research program, hoping to develop (ultimate cost of order$10 billion) very small probes attached to light-sails, pushed towards Alpha Centauri by ground-based lasers (a “Silicon Valley approach to spaceflight”). The claim is that such things could travel at a significant fraction of the speed of light, get there in 20 years or so. One thing I’m not seeing is how you get a signal back to earth.

Update: They have a website here, there’s a story at the New York Times here, at Scientific American here.

One thought about this is that if you really could accelerate probes this way with lasers, sending them out to solar system planets in days would seem to be a more interesting application.

Update: A more detailed story is here.

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### 37 Responses to Starshot

1. S says:

That is the genius part. The probes will be loaded up with literature about the multiverse. When the Alpha Centaurians find out about the scientific virtuosity of earthlings, they will come up with their own way to send a signal back to earth.

2. Art says:

Light sails accelerate slowly, but they accelerate constantly. A mission to a solar system planet might not be much faster than conventional rockets because it would take so long to get up to that 0.2c speed. Once it gets there though… zoom.

I’m sure communication will be one of the significant engineering challenges. One of the things I’d investigate is if you could have the sail change its shape to modify the reflection of the driving laser and still see the reflection back on Earth.

3. Peter Woit says:

Art,
The plan seems to be to accelerate very quickly (days?) with very high powered earth based lasers, using the fact these things are so light.

Another problem I saw someone pointing out: can you decelerate at Alpha Centauri?

4. Low Math, Meekly Interacting says:

If the thing is small, then I would imagine there’s no way at all to decelerate (short of a collision), unless the Centaurians have some powerful lasers of their own.

5. NoGo says:

On acceleration, for example:
“Propulsion will be outsourced to a facility on Earth. The small spacecraft will be equipped with a light sail, and a phased array of lasers in the 100GW range will provide the sail with enough push to get the craft moving at roughly 20 percent the speed of light in just a matter of minutes.”

6. anon says:

What about all those poor birds and monarch butterflies flying into the 100 GW laser beam? Pretty soon they will need bird traffic controllers…

7. cedric bardot says:

The roadmap for interstellar laser driven spacecrafts has been thoroughly outlined by Philip Lubin in http://arxiv.org/abs/1604.01356

8. Robert says:

This concept is the engineering equivalent of String Theory. You end up with a lot of PR but nothing useful in the long run.

9. NoGo says:
10. Jakob says:

The deceleration part seems like a big problem and I would be very interested in how this could be achieved safely (a very robus parachute maybe?). In the roadmap Cedric linked to the possibility to accelerate larger spaceships with the same method sounds like a really intriguing next step. Although I’m quite sceptical at the moment, I think it’s awesome that such a bold, alternative idea gets funded.

11. AcademicLurker says:

Another problem I saw someone pointing out: can you decelerate at Alpha Centauri?

Important consideration. In case there’s an advanced alien civilization in Alpha Centauri, it would be pretty rude to send even a small space craft slamming into them at 0.2c.

12. Low Math, Meekly Interacting says:

Per cedric’s reference:

“Thus a 1 kg spacecraft going at 0.3 c will have an effective “yield” of 1 MT or roughly that of a large strategic thermonuclear weapon.”

No way in Hell that thing is slowing down, even if it’s a ship-on-a-chip.

Note the word “deceleration” doesn’t even appear in the article.

13. Dale C. says:

There is no need for deceleration. At solar system scale, even at 0.2c there is plenty of time to snap a few pictures when you fly past. I am curious about communication back to earth. The communication appears to be laser-based, but how can that be detected at a huge distance to earth from a device weighing a few grams?

14. Low Math, Meekly Interacting says:

Assuming it’s a wafer craft, what kind of detail could you resolve with optics that tiny (presumably on the order of what my iPhone can boast)? It would traverse the Earth-Moon system in roughly five seconds. How close does it have to get to something to improve on the space telescopes we’ll have when that thing finally arrives? If you needed to be a few million kilometers away for a productive flyby of a planet, is it possible to aim that precisely over those distance and time scales without being able to adjust trajectory? I guess they must be thinking of these sorts of things, but tall order indeed.

15. lzp says:

Can a laser beam be focused to achieve such an incredibly small divergence at such distances? A related question: how large is the best focused laser dot on the Moon–I kind of recall ca. 1 km in diameter?

16. Steve Huntsman says:

Quoting from the Economist story on this: “At its destination it would beam back pictures of the star’s planets with its on-board laser. No current observatory could possibly pick up such a signal—but the kilometre-wide launch array should be able to. The optical systems used to meld the output of the lasers could be used in reverse as a vast and sensitive telescope.”

17. JackLothian says:

One of my favourite low-brain activities is reading science fiction. I will have to read it & see how it compares with Larry Niven novels.

18. M says:

A photo taken at v ≈ c would be an interesting demonstration of relativity, even without going to Alpha Centauri

19. Hans says:

Of coarse anybody is free to think/believe that there are ‘aliens’ out there and fantasy about technology to contact ‘these things’ – but actually doing so is not to decide to the likes as ‘some nutty professors’ and/or ‘some wealthy Santa Clauses’ – this is first and fore all a serious political issue that concerns us all and should be dealt with at the UN or so.

20. Avattoir says:

What’s with all these negative waves?

Sure, maybe there’s no way to decelerate the little wafer ships, or retrieve and relay back here pictures or data of any kind, and maybe all that ends up happening is firing off the equivalent of an armada of thermonuclear devices that’ll vaporize anything any of them strike. But why isn’t anyone posting how beautiful this all is, something righteous and hopeful for a change?

21. Daniele V says:

At 0.2c even a very small dust particle could destroy the probe if they clash, this is also a big problem.

22. bugannoyer says:

I’m sure their engineers have thought of this, but since I didn’t see it addressed in the articles, I’d wondered how they intended to deal with the likelihood of radiation damage from ambient particles impacting the electronics at ~.2C.

23. Low Math, Meekly Interacting says:

This multi-kilometer mirror array…it can theoretically receive a data stream from something like a laser pointer 4.4 light years distant. If you made two of these things half as big each and used it as an interferometer, what could you resolve at the same distance? I’m just not getting why one would spend that kind of money to send a downsized 2MP phone camera to the closest star system under the proposed conditions when much of the required technology would apparently yield an instrument with such sensitivity to light in the (I assume) visible spectrum. It’s a ginormous laser cannon, but it’s also the most amazing light collector anyone has dreamed of building. Avattoir has a very good point: we can strafe Alpha Centauri with a hail of kiloton kinetic energy ordnance, or, you know, maybe just look at it.

24. Ben says:

The likelihood of them getting destroyed is why they launch so many.

As far as the damage the probes themselves could do… even at 0.2c, a few grams is more in the kiloton range, and detonations that large (from meteorites) happen in our upper atmosphere reasonably often, sometimes without anybody on the ground noticing (without specialized instruments).

I think “phoning home” is really the biggest problem. It’s not just a question of increasing sensitivity, because if the signal is that faint than other sources and noise will be present as well.

25. Herr Weh says:

At this point it seems more like a research project for interstellar travel in general rather than an already fixed proposal with predetermined details. What counts – and I think that is very interesting – is that somebody came up with real money to actually get it on. Definitely better use for his money than some of the other projects Milner has funded. For those interested in interstellar travel I recommend following Paul Gilster’s excellent Centauri Dreams blog. Here’s his take on the Starshot project: http://www.centauri-dreams.org/?p=35402

26. Low Math, Meekly Interacting says:

Looks like it’ll be a 1 watt laser sending bursts of telemetry, so relatively much more powerful (during a burst) than a laser pointer at least should be. The array will reportedly receive 10-14 of the photons transmitted, assuming it can be aimed, because the beam would only be about 1000m wide, if the sail can focus it well enough.

This is all obviously way, way beyond me.

27. paddy says:

What makes me think that long before these cell phone probes arrive for their flyby, solar system based technology will have learned all about Alpha Centauri?

28. vmarko says:

I have a feeling that the Starshot project is similar in many aspects to the Mars One project. In short, it’s a nice-sounding idea that attracts a lot of attention and wishful thinking, sounds plausible when looked at naively, but is ultimately burdened with some insurmountable engineering problems which eventually render it fail. The devil is in the details, as usual.

Hopefully they’ll prove me wrong. 🙂

🙂
Marko

29. Ken Wrona says:

The probe can most certainly be decelerated. If aimed squarely at the host star it will decelerate from photon pressure. The question is whether it will be destroyed before it reaches a sufficiently slow speed. The Lubin roadmap isn’t sanguine about this but it is discussed. There are a lot of variables.

Anyway, this is an interesting engineering project that should rightly be undertaken with private money. It’s likely that a lot of interesting things would be learned.

30. Jesper says:

I think that the best solution to the “phone home” problem would be to kindly ask the Alpha Centaurians to make the call for us. I mean, if you live in the Alpha Centauri system you must have some super-cool powerful equipment and surely you won’t mind making a collect call for a crazy flyby probe that hurtles through your system at near light speed

31. SunJammer says:

From Wikipedia article, “Sunjammer”:
“Sunjammer” is a science fiction short story by Arthur C. Clarke, originally published in 1963,[1] and included in the March 1964 issue of Boys’ Life. The story has also been published under the title “The Wind from the Sun” in Clarke’s 1972 collection of short stories with this title. It depicts a yacht race between solar sail spacecraft.

Plot Summary:
John Merton, a spaceship designer, develops and promotes a lightweight spacecraft with a large area of solar sail, to be powered entirely by radiation pressure—the so-called wind from the sun. The sun-yachts start their journey in Earth’s orbit, and, pushed simply by sunlight, can achieve a speed of two thousand miles an hour within a day.

The concept leads to the development of the sport of sun-yacht racing, and after several years of refining his ideas, Merton competes in what will be his final race. His hopes for victory rest on the low mass of his craft which he has made possible through advances in automation enabling him to fly it solo.

Soon, all but two of the competitors have dropped out, mainly due to damaged craft, and it is a straight race between Merton’s craft and Lebedev, entered by a Russian crew from the University of Astrograd. Although the Lebedev is lagging Merton’s yacht, its senior pilot delivers a surprise blow by announcing that he plans to jettison his co-pilot in an escape capsule now that the earlier, navigationally intensive part of the race has finished.

Merton responds by recalculating his expected margin of victory and realises that the race is now going to be neck-and-neck at the finish line. At this point news arrives of a massive, and potentially deadly, solar flare. The race has to be abandoned, and there is no winner, though Merton abandons his craft with its sail still fully extended in order to ensure that it will be blown into interstellar space.

Planned 2014 solar sail mission

NASA planned to launch a solar sail technology demonstration mission titled ‘Sunjammer’. The title is a reference to the story.[3] The mission was cancelled in October 2014.[4]
…………
Comment: of course the nano-idea and use of lasers is a new twist on this idea.
Don’t know if Clarke was the first to think of it, but my memory was jogged by this
item and I remembered some great story by him, so thanks to Google, in one second I had found it!

32. Ralph says:

Re comms back to earth, another problem: receiving a very weak signal requires very fine tuning. But the tuning will have large uncertainties…

The signal from the probe will have a large doppler shift. In principal you just change the tuning of your receive to compensate but…. Any residual drag from radiation pressure etc will cause a drift in the doppler shift, destroying the tuning.
The latter tune drift is proportional to frequency, so using lasers not radios for communications makes this orders of magnitude worse.

Multi kilometer phased array operating at very-precise-but-constantly-changing optical frequencies coping with both 100GW and sub attowatt power levels?

Also, what will be the heat load from interplanetary / interstellar gas at 0.2c? Changing temperatures will cause further frequency drift on the source making the comms even more challenging.

33. In Hell's Kitchen (NYC) says:

Let’s hope the Centaurians don’t mistake Yuri’s armada for a relativistic weapon and retaliate: https://en.wikipedia.org/wiki/The_Killing_Star

34. ZZZ says:

A related idea is to use ground based lasers to heat propellants in a spaceship to achieve much higher specific thrust than possible with on-board chemical energy. Some national governments have been pursuing this for a while.

35. MikeS says:

Whatever the engineering merits of this project, it is clearly intended in the realm of space exploration rather than SETI.

If we really though there was intelligent life at Alpha Centauri then it would make more sense to just send the laser beams – with some suitably encoded data – and wait for the Centaurans to fire back.

36. anon says:

In principle you can actively decelerate a craft like this the same way you accelerated it – incorporate a detachable mirror that reflects the laser beam backwards onto the main craft, whose light sail is turned around once it has detached from the mirror – the mirror would of course be rapidly accelerated away from the main craft. In practice, this would need the ability to maintain a near-earth-based laser focused over interstellar distances. I have no idea if that is practicable.

37. Paul D. says:

This idea requires multiple engineering “miracles”, many of which would be very useful for other applications by themselves, even at lower levels of performance. So I’m not sure why he’s funding this instead of going after the pieces individually.

Example: he imagines reduces the cost of the continuous lasers from $10/W to$0.10/W. At that cost it becomes feasible to power aircraft via lasers in orbit (no CO2 emission, unlimited range, no fuel weight.)

As for sending spacecraft elsewhere in our solar system: the likely application there would be beamed power for plasma engines, like Hall thrusters or VASIMR, with an exhaust speed of perhaps 100 km/s. The power and energy requirements would be orders of magnitude lower than if one used light pressure for thrust.

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