Author Topic: Breakthrough Starshot  (Read 79011 times)

Offline Eric Hedman

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Re: Breakthrough Starshot
« Reply #60 on: 04/13/2016 09:24 pm »
Making a planetary flyby in another star system at 0.2c? What if the 1g probe's course is slightly altered by interstellar dust or similar? Does it have its own propulsion? How is it supposed to navigate?

IMO this is one of those "Moore's law will fix everything" concepts.
If a spacecraft is 4 meters wide and flies 4 light years, how much dust on average is in a column 4 meters by 4 meters by 4 light years?  I can imagine even a gram of dust in that column will pulverize a spacecraft flying at 0.2c.

Offline NovaSilisko

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Re: Breakthrough Starshot
« Reply #61 on: 04/13/2016 09:26 pm »
Making a planetary flyby in another star system at 0.2c? What if the 1g probe's course is slightly altered by interstellar dust or similar? Does it have its own propulsion? How is it supposed to navigate?

IMO this is one of those "Moore's law will fix everything" concepts.
If a spacecraft is 4 meters wide and flies 4 light years, how much dust on average is in a column 4 meters by 4 meters by 4 light years?  I can imagine even a gram of dust in that column will pulverize a spacecraft flying at 0.2c.

I'd be less worried about dust in interstellar space and more about dust in the target system (and our own, for that matter)

Offline Lar

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Re: Breakthrough Starshot
« Reply #62 on: 04/14/2016 12:09 am »
let's stay serious... (burning dollar bills for fuel isn't very serious, is it?)
« Last Edit: 04/14/2016 12:33 am by Lar »
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Offline testguy

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Re: Breakthrough Starshot
« Reply #63 on: 04/14/2016 12:15 am »
Instead of providing propulsion for a micro craft, wouldn't the laser array be a death ray weapon if the energy was reflected off a heavy mirror in orbit around the earth?  If there is a military application then funding the laser array shouldn't be a problem.  I really do like the concept and never thought we would be seriously talking about an interstellar probe or probes in our life times.

Offline TrevorMonty

Re: Breakthrough Starshot
« Reply #64 on: 04/14/2016 01:15 am »
The in stellar mission maybe a long shot and decades away but there are lot of near term missions that would benefit from this technology.

 Smaller laser arrays  (megawatts) should be able to send cubesats to most of solar system. As the laser array grows larger planetary craft can be used.

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Offline the_other_Doug

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Re: Breakthrough Starshot
« Reply #65 on: 04/14/2016 01:20 am »
I think there are a lot of extremely difficult engineering challenges facing the announced concept, and people like us here out on internet fora will no doubt pick it apart.  But I am very, very much in favor of raising money to be spent on solving these problems, and in some instances finding there are better or more feasible means of accomplishing some or all of the mission.

Just getting people thinking about it, and money spent on looking at the engineering challenges, is worthwhile and exciting.
-Doug  (With my shield, not yet upon it)

Offline sanman

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Re: Breakthrough Starshot
« Reply #66 on: 04/14/2016 02:30 am »
Regarding the probe's ability to transmit back to Earth - is it possible that the sail could also act as a radio antenna? The same sail that is catching the laser beam to push it ahead would also be able to use some of that caught laser energy to power any transmissions.

Would the dimensions of the sail be large enough to make that feasible?

Offline ChrisWilson68

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Re: Breakthrough Starshot
« Reply #67 on: 04/14/2016 02:40 am »
Regarding the probe's ability to transmit back to Earth - is it possible that the sail could also act as a radio antenna? The same sail that is catching the laser beam to push it ahead would also be able to use some of that caught laser energy to power any transmissions.

Would the dimensions of the sail be large enough to make that feasible?

I wouldn't think it would be feasible.  Remember, it gets accelerated up to speed while it's close to Earth, and the portion of energy it reflects will be the same 4 light years away, but the amount of energy hitting it will be orders of magnitude lower.  If it could harvest energy from the sail when 4 light years away, it would burn up when close to Earth.

Offline aep

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Re: Breakthrough Starshot
« Reply #68 on: 04/14/2016 04:14 am »
Did some BOTE calc for the fun. Assuming 4m diameter disc weighing one gram the required beam intensity to accelerate the craft at 60000g is 7GW/m2. Further assuming 99,9999% reflectivity on the mirror side the craft absorbs 7kW/m2. If the other side is perfect black body it can reradiate the heat at required rate if the craft can survive about 600K. Not horribly hot, but is hextuple-9 reflectivity within realm of possible idk.
A search shows 'optical supermirrors' which are dielectric mirrors which can do six 9s but at limited wavelengths (e.g https://goo.gl/Xjff60). One issue - as the mirror accelerates to .2c, a blue laser at 450nm will end up shifted to green at 550nm (z = 0.225). Either the lasers would have to be tuned as it accelerated or they could stack multiple layers with the shorter wavelengths getting vaporized as the mirror accelerates.

Offline vapour_nudge

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Re: Breakthrough Starshot
« Reply #69 on: 04/14/2016 08:24 am »
let's stay serious... (burning dollar bills for fuel isn't very serious, is it?)
Sorry Lar.  It was silly.
It concerns me when $100m is spent on such things. If it is about technology spin offs then yes that would be a good reason to use this seed money else IMHO it's burning money that could be used for other more worthy causes. The fact they wheel out well known people also worries me.

I'd like to hear how they are proposing to target the communications back to Earth, who'd be listening and how faint that signal would be and the spread of the beam. Pioneer 10 went silent using RF and its transmission power levels were far higher than what they would be for this project. It also had trouble locking on to a signal & having bore sight focussed at Earth. That was far closer. However you could argue that money spent on investigating distant Comms like this would be worth the money for other missions too
« Last Edit: 04/14/2016 10:57 am by vapour_nudge »

Offline Ben the Space Brit

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Re: Breakthrough Starshot
« Reply #70 on: 04/14/2016 10:04 am »
Just a couple of thoughts. Remember that I'm an enthusiastic amateur so I don't know how practical this is:

1) The light sail would work just as well with sunlight (although with reduced thrust); so the laser burns, a hour or so per Earth day, IIRC, would be boost periods rather than the only propulsive system;

2) The light sail would also serve as a brake as the vehicles approach the A-Centauri system. The two larger stars in the system equal to around 2x Sol so that would be a lot of braking power over such a long-duration mission;

3) A good starting point would be the EML-1 halo, as this would reduce the amount of energy required for Earth escape; however, I'm wondering if this would be more than offset by the loss of thrust from being further from the boost laser array;

4) Finally, could these probes be tasked with a flyby of the hypothetical Sol-IX? A long distance but in-system target might make for a good technology test of things like the sail steering, sensors, control system and communications laser.
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Offline R7

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Re: Breakthrough Starshot
« Reply #71 on: 04/14/2016 10:44 am »
1. Instead of providing propulsion for a micro craft, wouldn't the laser array be a death ray weapon if the energy was reflected off a heavy mirror in orbit around the earth?
2.  If there is a military application then funding the laser array shouldn't be a problem.

1. Most certainly, SDI Star Wars redux. Btw most of the "death ray" would get reflected anyway, from the SC. Wondering what the plan is to make sure launch won't lase people and property on the ground. Shoot the SC at such inclination that the reflection misses Earth?

2. The unavoidable military application may very well be a big geopolitical problem. White House occupant would have tough negotiations with Russia and China.
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Offline Oli

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Re: Breakthrough Starshot
« Reply #72 on: 04/14/2016 10:52 am »
Making a planetary flyby in another star system at 0.2c? What if the 1g probe's course is slightly altered by interstellar dust or similar? Does it have its own propulsion? How is it supposed to navigate?

IMO this is one of those "Moore's law will fix everything" concepts.
If a spacecraft is 4 meters wide and flies 4 light years, how much dust on average is in a column 4 meters by 4 meters by 4 light years?  I can imagine even a gram of dust in that column will pulverize a spacecraft flying at 0.2c.

The dust is only another issue. I was reading about how New Horizons targeted Pluto. It's not exactly trivial. I don't see how a 1g probe could do that for an exoplanet in another star system at 0.2c. Anyway, only one of many issues.


Offline R7

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Re: Breakthrough Starshot
« Reply #73 on: 04/14/2016 11:09 am »
If a spacecraft is 4 meters wide and flies 4 light years, how much dust on average is in a column 4 meters by 4 meters by 4 light years?  I can imagine even a gram of dust in that column will pulverize a spacecraft flying at 0.2c.

Does it have to fly head-on like that the whole trip? It would be almost 2D object, turn it to fly sideways after launch.
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Offline su27k

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Re: Breakthrough Starshot
« Reply #74 on: 04/14/2016 11:40 am »
Some of the challenges and possible solutions are listed here: http://www.breakthroughinitiatives.org/Challenges/3

I think it would be helpful if everyone read them first since they covered most of the things discussed above.

Offline MATTBLAK

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Re: Breakthrough Starshot
« Reply #75 on: 04/14/2016 11:42 am »
When I expressed skepticism for this project and it's technological feasibility on a Space.com announcement feed on Facebook - jeez; you should have seen the feral responses and attacks I got! I was called all sorts of names, most of which have been deleted now. The mildest response I received was folk wondering how the great Professor Hawking could be so wrong and me - the wise and all-knowing 'Matthew Black' could be so right?! I responded "It's not about that; this kind of project and conceptual kite flight is part of how Prof. Hawking makes a living these days".

I conceded that the whole concept is vaguely plausible, but that there would be considerable technical, financial and scheduling challenges to overcome. Not unlike 'Mars One' in that regard!!
« Last Edit: 04/14/2016 11:43 am by MATTBLAK »
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Offline john smith 19

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Re: Breakthrough Starshot
« Reply #76 on: 04/14/2016 12:11 pm »
Leik Myrabo knows a lot about using ground based lasers for launch systems, especially the launch laser market.

If the launch and trajectory correction phases per vehicle are quite short, and the vehicles quite cheap the logical approach is a) Multiple launches to a star b)Multiple stars

TBH the number of options for a star ship with minimal development of existing technology are quite limited.

The fission fragments of a fission fragment rocket are expected to exhaust at 0.03-0.05c but that would be a lot heavier.

If people want a shot at seeing another solar system up close in their lifetime this is pretty much it.  :(
MCT ITS BFR SS. The worlds first Methane fueled FFSC engined CFRP SS structure A380 sized aerospaceplane tail sitter capable of Earth & Mars atmospheric flight.First flight to Mars by end of 2022 TBC. T&C apply. Trust nothing. Run your own #s "Extraordinary claims require extraordinary proof" R. Simberg."Competitve" means cheaper ¬cheap SCramjet proposed 1956. First +ve thrust 2004. US R&D spend to date > $10Bn. #deployed designs. Zero.

Offline Star One

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Breakthrough Starshot
« Reply #77 on: 04/14/2016 01:22 pm »
When I expressed skepticism for this project and it's technological feasibility on a Space.com announcement feed on Facebook - jeez; you should have seen the feral responses and attacks I got! I was called all sorts of names, most of which have been deleted now. The mildest response I received was folk wondering how the great Professor Hawking could be so wrong and me - the wise and all-knowing 'Matthew Black' could be so right?! I responded "It's not about that; this kind of project and conceptual kite flight is part of how Prof. Hawking makes a living these days".

I conceded that the whole concept is vaguely plausible, but that there would be considerable technical, financial and scheduling challenges to overcome. Not unlike 'Mars One' in that regard!!

This is nothing like Mars One. At the moment it's one rich individual deciding to spend his money on a variety of research projects. TBH how he chooses to spend his personal wealth isn't anyone else's business, he's not taking the money out of your or mine's pockets. No doubt plenty of billionaires spend such money on art or property without the associated online debate about how they chose to spend their wealth.
« Last Edit: 04/14/2016 01:24 pm by Star One »

Offline MarkZero

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Re: Breakthrough Starshot
« Reply #78 on: 04/14/2016 01:23 pm »
On the problem of getting a signal from the small probe over the light years:

Since they are planning to make lots of those probes anyways, couldn't they just send them one by one, making a trail of them from here to Centauri. That way each probe would only need to be able to get the signal to the one behind it. Enough of the probes and the distance between two of them would become short enough.

Plus, you would get more observations from the multiple flybys that would follow, for as long as you would keep sending the probes so that the distance between the Earth and the last probe sent wouldn't become too long.


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Offline Robotbeat

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Re: Breakthrough Starshot
« Reply #79 on: 04/14/2016 02:14 pm »
Dielectric mirrors can definitely exceed five nines reflectivity. So 99.9999% isn't absurd. Maybe improve reflectivity a bit to reduce the temperature.

EDIT: Yes, better than 99.9999% reflectivity has been done for dielectric mirrors: https://www.rp-photonics.com/supermirrors.html
« Last Edit: 04/14/2016 02:22 pm by Robotbeat »
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