http://www.abc.net.au/news/2016-04-13/breakthrough-starshot-aims-to-launch-tiny-spacecraft-deep-space/7321588

Tiny spacecraft could reach another solar system within a generation as part of a groundbreaking, $130 million project.

The capsules, about the size of a mobile phone, would need to travel trillions of kilometres, which under existing technology would take 30,000 years.

But British scientists said the tiny new craft, travelling at a fifth of the speed of light, could in theory reach a nearby star in just 30 years.

Billionaire internet investor Yuri Milner is backing the new project called Breakthrough Starshot, and if successful, scientists could determine if Alpha Centauri — a star system about 40 trillion kilometres away — contained an Earth-like planet capable of sustaining life.
—-
If the nanocraft reached the star system and succeeded in taking photographs, it would take about another four years to transmit them back to Earth.

—-

So … how is something that small supposed to transmit a signal from Alpha centauri that can be detected from Earth?

dv said:

http://www.abc.net.au/news/2016-04-13/breakthrough-starshot-aims-to-launch-tiny-spacecraft-deep-space/7321588

Tiny spacecraft could reach another solar system within a generation as part of a groundbreaking, $130 million project.

The capsules, about the size of a mobile phone, would need to travel trillions of kilometres, which under existing technology would take 30,000 years.

But British scientists said the tiny new craft, travelling at a fifth of the speed of light, could in theory reach a nearby star in just 30 years.

Billionaire internet investor Yuri Milner is backing the new project called Breakthrough Starshot, and if successful, scientists could determine if Alpha Centauri — a star system about 40 trillion kilometres away — contained an Earth-like planet capable of sustaining life.
—-
If the nanocraft reached the star system and succeeded in taking photographs, it would take about another four years to transmit them back to Earth.

—-

So … how is something that small supposed to transmit a signal from Alpha centauri that can be detected from Earth?

telstra should have mobile coverage for alpha centauri

uses an inflatable dish that is covered with solar cells to power the signal

dv said:

http://www.abc.net.au/news/2016-04-13/breakthrough-starshot-aims-to-launch-tiny-spacecraft-deep-space/7321588

Tiny spacecraft could reach another solar system within a generation as part of a groundbreaking, $130 million project.

The capsules, about the size of a mobile phone, would need to travel trillions of kilometres, which under existing technology would take 30,000 years.

But British scientists said the tiny new craft, travelling at a fifth of the speed of light, could in theory reach a nearby star in just 30 years.

Billionaire internet investor Yuri Milner is backing the new project called Breakthrough Starshot, and if successful, scientists could determine if Alpha Centauri — a star system about 40 trillion kilometres away — contained an Earth-like planet capable of sustaining life.
—-
If the nanocraft reached the star system and succeeded in taking photographs, it would take about another four years to transmit them back to Earth.

—-

So … how is something that small supposed to transmit a signal from Alpha centauri that can be detected from Earth?

They hinted at several potential show-stoppers. That may be one.

Michael V said:

dv said:

http://www.abc.net.au/news/2016-04-13/breakthrough-starshot-aims-to-launch-tiny-spacecraft-deep-space/7321588

Tiny spacecraft could reach another solar system within a generation as part of a groundbreaking, $130 million project.

The capsules, about the size of a mobile phone, would need to travel trillions of kilometres, which under existing technology would take 30,000 years.

But British scientists said the tiny new craft, travelling at a fifth of the speed of light, could in theory reach a nearby star in just 30 years.

Billionaire internet investor Yuri Milner is backing the new project called Breakthrough Starshot, and if successful, scientists could determine if Alpha Centauri — a star system about 40 trillion kilometres away — contained an Earth-like planet capable of sustaining life.
—-
If the nanocraft reached the star system and succeeded in taking photographs, it would take about another four years to transmit them back to Earth.

—-

So … how is something that small supposed to transmit a signal from Alpha centauri that can be detected from Earth?

They hinted at several potential show-stoppers. That may be one.

Maybe they send a swarm of them both for redudancy and when/if they arrive they connect together to form a large transmission disc.

Cymek said:

Michael V said:

dv said:

http://www.abc.net.au/news/2016-04-13/breakthrough-starshot-aims-to-launch-tiny-spacecraft-deep-space/7321588

Tiny spacecraft could reach another solar system within a generation as part of a groundbreaking, $130 million project.

The capsules, about the size of a mobile phone, would need to travel trillions of kilometres, which under existing technology would take 30,000 years.

But British scientists said the tiny new craft, travelling at a fifth of the speed of light, could in theory reach a nearby star in just 30 years.

Billionaire internet investor Yuri Milner is backing the new project called Breakthrough Starshot, and if successful, scientists could determine if Alpha Centauri — a star system about 40 trillion kilometres away — contained an Earth-like planet capable of sustaining life.
—-
If the nanocraft reached the star system and succeeded in taking photographs, it would take about another four years to transmit them back to Earth.

—-

So … how is something that small supposed to transmit a signal from Alpha centauri that can be detected from Earth?

They hinted at several potential show-stoppers. That may be one.

Maybe they send a swarm of them both for redudancy and when/if they arrive they connect together to form a large transmission disc.

G-FORCE

dv said:

http://www.abc.net.au/news/2016-04-13/breakthrough-starshot-aims-to-launch-tiny-spacecraft-deep-space/7321588

Tiny spacecraft could reach another solar system within a generation as part of a groundbreaking, $130 million project.

The capsules, about the size of a mobile phone, would need to travel trillions of kilometres, which under existing technology would take 30,000 years.

But British scientists said the tiny new craft, travelling at a fifth of the speed of light, could in theory reach a nearby star in just 30 years.

Billionaire internet investor Yuri Milner is backing the new project called Breakthrough Starshot, and if successful, scientists could determine if Alpha Centauri — a star system about 40 trillion kilometres away — contained an Earth-like planet capable of sustaining life.
—-
If the nanocraft reached the star system and succeeded in taking photographs, it would take about another four years to transmit them back to Earth.
—-
So … how is something that small supposed to transmit a signal from Alpha centauri that can be detected from Earth?

To answer the last question first, by using large antennas on Earth. The cost of these large antennas would be a lot less than the cost of the space mission.

I find the idea of interstellar nanocraft extremely intriguing. I calculated many moons ago that no spacecraft powered even by hydrogen fusion could travel at even 1% of the speed of light. But my “small” spacecraft for the calculation weighed several kilograms. I also tried a spacecraft powered by a black hole, and one powered by antimatter. Even those weren’t good enough to get to high relativistic speeds.

The only sensible way to get beyond that sort of speed, for an interstellar nanocraft, would be some sort of linear accelerator. Sort of a cross between a railgun and a SLAC. This would have to be built off-Earth because otherwise the atmospheric drag would both slow down the craft and heat it up to unacceptable levels.

mollwollfumble said:

dv said:

http://www.abc.net.au/news/2016-04-13/breakthrough-starshot-aims-to-launch-tiny-spacecraft-deep-space/7321588

Tiny spacecraft could reach another solar system within a generation as part of a groundbreaking, $130 million project.

The capsules, about the size of a mobile phone, would need to travel trillions of kilometres, which under existing technology would take 30,000 years.

But British scientists said the tiny new craft, travelling at a fifth of the speed of light, could in theory reach a nearby star in just 30 years.

Billionaire internet investor Yuri Milner is backing the new project called Breakthrough Starshot, and if successful, scientists could determine if Alpha Centauri — a star system about 40 trillion kilometres away — contained an Earth-like planet capable of sustaining life.
—-
If the nanocraft reached the star system and succeeded in taking photographs, it would take about another four years to transmit them back to Earth.
—-
So … how is something that small supposed to transmit a signal from Alpha centauri that can be detected from Earth?

To answer the last question first, by using large antennas on Earth. The cost of these large antennas would be a lot less than the cost of the space mission.

I find the idea of interstellar nanocraft extremely intriguing. I calculated many moons ago that no spacecraft powered even by hydrogen fusion could travel at even 1% of the speed of light. But my “small” spacecraft for the calculation weighed several kilograms. I also tried a spacecraft powered by a black hole, and one powered by antimatter. Even those weren’t good enough to get to high relativistic speeds.

The only sensible way to get beyond that sort of speed, for an interstellar nanocraft, would be some sort of linear accelerator. Sort of a cross between a railgun and a SLAC. This would have to be built off-Earth because otherwise the atmospheric drag would both slow down the craft and heat it up to unacceptable levels.

Could you start off with a huge craft use nuclear explosions to propel it and gradually jettison parts of it until a tiny payload is left, the problem I suppose is how do you decelerate it

Are there any developments coming in examining spectrum, gravity waves, emmissions etc, that will give us more and finer grained information without needing to build a device to go there?

I think us apes have done a remarkable job mapping the universe from this little blue arsed planet so far.

Cymek said:

Could you start off with a huge craft use nuclear explosions to propel it and gradually jettison parts of it until a tiny payload is left, the problem I suppose is how do you decelerate it

Plans for such craft have existed for 50 years.

It’s not similar to this nanocraft mission, though. Completely unrelated concept.

dv said:

Cymek said:

Could you start off with a huge craft use nuclear explosions to propel it and gradually jettison parts of it until a tiny payload is left, the problem I suppose is how do you decelerate it

Plans for such craft have existed for 50 years.

It’s not similar to this nanocraft mission, though. Completely unrelated concept.

I was thinking in regards to accelerating this small craft to a decent percentage of the speed of light

Cymek said:

dv said:

Cymek said:

Could you start off with a huge craft use nuclear explosions to propel it and gradually jettison parts of it until a tiny payload is left, the problem I suppose is how do you decelerate it

Plans for such craft have existed for 50 years.

It’s not similar to this nanocraft mission, though. Completely unrelated concept.

I was thinking in regards to accelerating this small craft to a decent percentage of the speed of light

Yeah I know.

Cymek said:

dv said:

Cymek said:

Could you start off with a huge craft use nuclear explosions to propel it and gradually jettison parts of it until a tiny payload is left, the problem I suppose is how do you decelerate it

Plans for such craft have existed for 50 years.

It’s not similar to this nanocraft mission, though. Completely unrelated concept.

I was thinking in regards to accelerating this small craft to a decent percentage of the speed of light

I wonder if when a craft goes through the light barrier it will experience similar shock waves or handling distortions that happens when you go through the sound barrier.

I wonder if when a craft goes through the light barrier it will experience similar shock waves or handling distortions that happens when you go through the sound barrier.

i don’t think we’ll ever know.

Peak Warming Man said:

Cymek said:

dv said:

Plans for such craft have existed for 50 years.

It’s not similar to this nanocraft mission, though. Completely unrelated concept.

I was thinking in regards to accelerating this small craft to a decent percentage of the speed of light

I wonder if when a craft goes through the light barrier it will experience similar shock waves or handling distortions that happens when you go through the sound barrier.

It is not possible for craft with a non-zero mass to go “through the light barrier”, or even to light speed, in this universe.

Having looked further…

The plans appear to be a little sketchy at present but it does involve using tight laser aimed right at earth, in order to bring down the transmission power requirements. The technology to do this doesn’t exist yet so that’s one of the things on his to-do list.

The novel Accelerando has a similar concept

The alien router, orbiting a 3-light-year-distant brown dwarf star named Hyundai +4904/-56, is visited by the spacecraft Field Circus, a Coke-can-sized mass of computronium propelled by a Jupiter-based laser and a lightsail.

The biggest problem I can see is the trade-off between image resolution and speed. Let’s do a calculation of size vs speed. CERN uses 180 megawatts on occasions. Let’s assume that that is all the power available (remember that this is off-Earth) where power is more difficult to obtain. Assume that passive cooling in space means that superconducting magnets use a negligible fraction of that power.

Calculate a G-force. Calculate one that limits uniaxial compression stresses to 250 MPa (The nanocraft is solid state, Some solids can take much higher stresses than that). Give it a density of 3100 kg/m^3. Then acceleration times length = stress divided by density = 80,000 m^2/s^2. For a length of 0.1 metres that’s 80,000 G. Let’s choose 5 cm long and 1,600,000 m/s^2.

The time to reach relativistic speeds is therefore about 120 seconds. So let’s see what mass we could accelerate using 180 megawatts.

(to be continued)

dv said:

Having looked further…

The technology to do this doesn’t exist yet so that’s one of the things on his to-do list.

Get wookie onto it, “you just…”.

Basically if you were going to do this, you’d want the craft to be able to autonomously detect planets and arrange close, fairly slow, flybys of them.

That’s going to be the hard part. Slowing down. You can’t use an earth-based laser blast to slow it down.

And at 20% of c, you can forget about any gravitational maneuvres to decelerate. It will just pass through the system unperturbed.

mollwollfumble said:

The biggest problem I can see is the trade-off between image resolution and speed. Let’s do a calculation of size vs speed. CERN uses 180 megawatts on occasions. Let’s assume that that is all the power available (remember that this is off-Earth, where power is more difficult to obtain). Assume that passive cooling in space means that superconducting magnets use a negligible fraction of that power.

Calculate a G-force. Calculate one that limits uniaxial compression stresses to 250 MPa (The nanocraft is solid state, Some solids can take much higher stresses than that). Give it a density of 3100 kg/m^3. Then acceleration times length = stress divided by density = 80,000 m^2/s^2. For a length of 0.1 metres that’s 80,000 G. Let’s choose 5 cm long and 1,600,000 m/s^2.

The time to reach relativistic speeds is therefore about 120 seconds. So let’s see what mass we could accelerate using 180 megawatts.

(to be continued)

Power = mass times velocity times acceleration = m*v*a
First calculate this using peak velocity, say 20% of the speed of light.
m = 180*10^6 (watts) / 1.6*10^6 (m/s^2) / 0.2*300*10^6 (m/s)
m = 1.87 milligrams.

That’s a heck of a small mass for a spacecraft.

With reduced spacecraft length (L<<5 cm) the stress on the craft components drops off, reduced acceleration (a<<1.6*10^6 m/s^2) would drop both the stress level and the power requirements, and variable acceleration (eg. acceleration proportional to 1/velocity at large velocities) would even out the power requirements.

By how much could we reduce the acceleration, if at all? Let’s suppose the linear accelerator is s = 27 km long, the same as the circumference at CERN. Remember that this is off-Earth. IIRC, acceleration is calculated from a = v^2/2s = (0.2*300*10^6)^2 / 27,000 = 133*10^9 m/s^2 >> 1.6*10^6 m/s^2 calculated earlier. That’s an error by a factor of 83,000.

In conclusion, it can’t be done.

No nanocraft with even a mass as small as 1.87 milligrams could be made to fly at a relativistic speed with conceivable future power availability and space limitations.

mollwollfumble said:

Power = mass times velocity times acceleration = m*v*a

blink

…and just checking, that is dimensionally accurate. There ya go, I’ve learnt something today.

sibeen said:

mollwollfumble said:

Power = mass times velocity times acceleration = m*v*a

blink

…and just checking, that is dimensionally accurate. There ya go, I’ve learnt something today.

They’ll teach you this stuff when you get to high school. Patience…

dv said:

sibeen said:

mollwollfumble said:

Power = mass times velocity times acceleration = m*v*a

blink

…and just checking, that is dimensionally accurate. There ya go, I’ve learnt something today.

They’ll teach you this stuff when you get to high school. Patience…

True, true :)

I must admit I doubt I’ve every used an equation like *kg before. I may have, and perhaps it has slipped my memory.

Hmm, square bracket stuffed up the formatting on that. The second thing I’ve learnt today.

I must admit I doubt I’ve every used an equation like {(m^2)/(s^3)}*kg before. I may have, and perhaps it has slipped my memory.

i wonder if you could have a block of plutonium a neutron source which then goes on to heat liquid mercury to a high temp turning it to a gas thats expelled out the back

OR

you have an earth based laser that supplies electrical power to the craft that then uses a mercury fuelled ion engine

the coke can sized ship then unfurls a dish covered in solar cells as it nears the star and beams back info

wookiemeister said:

i wonder if you could have a block of plutonium a neutron source which then goes on to heat liquid mercury to a high temp turning it to a gas thats expelled out the back

OR

you have an earth based laser that supplies electrical power to the craft that then uses a mercury fuelled ion engine

the coke can sized ship then unfurls a dish covered in solar cells as it nears the star and beams back info

Neither of these methods (you are describing ion engines and simple thermal rockets) will get you anywhere near light speed.

dv said:

wookiemeister said:

i wonder if you could have a block of plutonium a neutron source which then goes on to heat liquid mercury to a high temp turning it to a gas thats expelled out the back

OR

you have an earth based laser that supplies electrical power to the craft that then uses a mercury fuelled ion engine

the coke can sized ship then unfurls a dish covered in solar cells as it nears the star and beams back info

Neither of these methods (you are describing ion engines and simple thermal rockets) will get you anywhere near light speed.

http://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions

wookiemeister said:

dv said:

wookiemeister said:

i wonder if you could have a block of plutonium a neutron source which then goes on to heat liquid mercury to a high temp turning it to a gas thats expelled out the back

OR

you have an earth based laser that supplies electrical power to the craft that then uses a mercury fuelled ion engine

the coke can sized ship then unfurls a dish covered in solar cells as it nears the star and beams back info

Neither of these methods (you are describing ion engines and simple thermal rockets) will get you anywhere near light speed.

http://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions

ion thrusters are so interesting — is that they have a fuel efficiency that’s 10 to 12 times greater than chemical thrusters. Obviously, for long trips through space, fuel efficiency is very important.

With such puny thrust, a NEXT-based ion drive would need to run for 10,000 hours — just over a year — to reach a suitable speed for space travel. Dawn, a NASA probe that’s powered by previous-generation NSTAR ion thrusters, accelerated from 0 to 60 mph in four days. As a corollary, ion thrusters only work at all because of the near-vacuum of space; if there was any friction at all, like here on Earth, an ion drive would be useless. The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph).

wookiemeister said:

dv said:

wookiemeister said:

i wonder if you could have a block of plutonium a neutron source which then goes on to heat liquid mercury to a high temp turning it to a gas thats expelled out the back

OR

you have an earth based laser that supplies electrical power to the craft that then uses a mercury fuelled ion engine

the coke can sized ship then unfurls a dish covered in solar cells as it nears the star and beams back info

Neither of these methods (you are describing ion engines and simple thermal rockets) will get you anywhere near light speed.

http://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions

wookie, do you read the articles that you link to?

That link says
“ The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph).”

ROFL. 321000 kph is about 0.0003 of the speed of light…

dv said:

wookiemeister said:

dv said:

Neither of these methods (you are describing ion engines and simple thermal rockets) will get you anywhere near light speed.

http://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions

wookie, do you read the articles that you link to?

That link says
“ The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph).”

ROFL. 321000 kph is about 0.0003 of the speed of light…

as a fraction is 0.0003

as a percentage its 0.03 of light

better than nothing and faster than anything so far

lets say we made the engine more efficient, maybe we added more of them?

we can start boosting the overall speed

wookiemeister said:

dv said:

wookiemeister said:

dv said:

wookiemeister said:

i wonder if you could have a block of plutonium a neutron source which then goes on to heat liquid mercury to a high temp turning it to a gas thats expelled out the back
OR

you have an earth based laser that supplies electrical power to the craft that then uses a mercury fuelled ion engine

the coke can sized ship then unfurls a dish covered in solar cells as it nears the star and beams back info

Neither of these methods (you are describing ion engines and simple thermal rockets) will get you anywhere near light speed.

http://www.extremetech.com/extreme/144296-nasas-next-ion-drive-breaks-world-record-will-eventually-power-interplanetary-missions

wookie, do you read the articles that you link to?

That link says
“ The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph).”

ROFL. 321000 kph is about 0.0003 of the speed of light…

better than nothing and faster than anything so far

But not remotely useful for getting to the stars, and not even a thousandth of the speed of light

dv said:

But not remotely useful for getting to the stars, and not even a thousandth of the speed of light

So getting back to the high speed mobile telephone in the OP, how do the proposers of this device suggest that it can reach such high speeds?

light sail and laser i think.

The Rev Dodgson said:

dv said:

But not remotely useful for getting to the stars, and not even a thousandth of the speed of light

So getting back to the high speed mobile telephone in the OP, how do the proposers of this device suggest that it can reach such high speeds?

By being blasted by lasers on earth.

dv said:

The Rev Dodgson said:

dv said:

But not remotely useful for getting to the stars, and not even a thousandth of the speed of light

So getting back to the high speed mobile telephone in the OP, how do the proposers of this device suggest that it can reach such high speeds?

By being blasted by lasers on earth.

JudgeMental said:

light sail and laser i think.

Is that going to work?

I’m holding up the “nobody knows” card

dv said:

wookiemeister said:

dv said:

wookie, do you read the articles that you link to?

That link says
“ The good news, though, is that the (eventual) max speed of a spacecraft propelled by an ion drive is in the region of 200,000 miles per hour (321,000 kph).”

ROFL. 321000 kph is about 0.0003 of the speed of light…

better than nothing and faster than anything so far

But not remotely useful for getting to the stars, and not even a thousandth of the speed of light

you have more engines

you develop the engines to be more efficient , produce more thrust

the sail could have photovoltaic cells on it, the electrical power is used to run the engine

or

you just have something the size of a Saturn 5 in orbit and then light the fuse, I reckon that should get up some decent speed

wookiemeister said:

I’m holding up the “nobody knows” card

——

I’m holding up the “deceleration card”

20 Percent Light Speed To Alpha Centauri! Nanocraft Concept unveiled

The Breakthrough Starshot project aims to launch a a mission that would be able make it to our nearest star system, Alpha Centauri, in just over 20 years. Science philanthropist Yuri Milner explains the concept that he and cosmologist Stephen Hawking announced on April 12th, 2016.

13 min video

dv said:

sibeen said:

mollwollfumble said:

Power = mass times velocity times acceleration = m*v*a

blink
…and just checking, that is dimensionally accurate. There ya go, I’ve learnt something today.

They’ll teach you this stuff when you get to high school. Patience…

They DON’T teach you that stuff in high school. It isn’t on the web either. I derived it myself using:
Power = d Energy / d time
with
Energy = 1/2 m v^2
so
Power = 1/2 m d(v^2)/dv dv/dt
Power = m v a :-)

CrazyNeutrino said:

20 Percent Light Speed To Alpha Centauri! Nanocraft Concept unveiled

The Breakthrough Starshot project aims to launch a a mission that would be able make it to our nearest star system, Alpha Centauri, in just over 20 years. Science philanthropist Yuri Milner explains the concept that he and cosmologist Stephen Hawking announced on April 12th, 2016.

13 min video

I don’t trust anything Hawking says any more.

At last! Now we know who Hawking got his computer-synthesised voice from.

> Voyager 40,000 miles an hour.
That’s an exaggeration, 35,700 mph.

> Freeman Dyson. Project Orion.
Good.

> Some versions of Orion would reach Alpha Centauri in half a century.
Is that true? First I’ve heard of it.
Web says “an Orion spaceship theoretically could have reached 1/10th the speed of light”, “fantastic speeds (8% to 10% of the speed of light”, “Nuclear explosion propulsion (5% speed of light) “.
Hmm, I’ll have to think about that some more. In my calculations many years ago even fusion power couldn’t get me up to 1% of the speed of light.

> Chemical fuel. Speed of light. All the stars in the Milky Way.
Hmm.

> Leave the fuel behind.
Yes, we all know about that.

> A gram scale wafer containing cameras, photon thrusters, navigation and communications equipment. It’s about the size of a large postage stamp. Light sails a few metres wide weighing just a few grams. Phased light beams, many small lasers giving one beam.

Good. But laser-based acceleration is incredibly slow.

> The beam could eventually be scaled to 100 Gigawatt level.

Hmm. In my calculations above I assumed only 100 Megawatts, the entire power supply for CERN, and then for my calculation I assumed a short acceleration time of 120 seconds or so, whereas they assume a much longer acceleration time. Could that 100 Gigawatts be ridiculously excessive?

The presently most powerful laser is actually 20,000 times that 100 Gigawatts, two petawatts, but lasts for only a tiny fraction of time, 1 picosecond. The energy in 2 petawatts in one picosecond is that same as the energy in 2,000 watts in one second.

(To be continued)

mollwollfumble said:

CrazyNeutrino said:

20 Percent Light Speed To Alpha Centauri! Nanocraft Concept unveiled

The Breakthrough Starshot project aims to launch a a mission that would be able make it to our nearest star system, Alpha Centauri, in just over 20 years. Science philanthropist Yuri Milner explains the concept that he and cosmologist Stephen Hawking announced on April 12th, 2016.

13 min video

> The beam could eventually be scaled to 100 Gigawatt level.

Hmm. In my calculations above I assumed only 100 Megawatts, the entire power supply for CERN, and then for my calculation I assumed a short acceleration time of 120 seconds or so, whereas they assume a much longer acceleration time. Could that 100 Gigawatts be ridiculously excessive?

The presently most powerful laser is actually 20,000 times that 100 Gigawatts, two petawatts, but lasts for only a tiny fraction of time, 1 picosecond. The energy in 2 petawatts in one picosecond is that same as the energy in 2,000 watts in one second.

(To be continued)

> This is the beamer on the ground.
LOL. Those are radio antennas, not lasers. Also, being Earth-based it would pump a heck of a lot of heat into the atmosphere: enough to create a tornado, or a hurricane?

> Hundreds and maybe thousands of them to one target.
Yes.

> 20 minutes. To 20% of light speed.
That calculation may not be too far out. Be aware that multiple pulses over a longer time interval is better than a single sustained pulse because it aids cooling between pulses. On the other hand, focussing (eg. beam distortion by atmospheric turbulence) is better if there is a single sustained pulse.

> send information back home in a beam of light.
Hmm.

That looks reasonable.

Overall. May be possible. I’d want to know more about the laser array before saying yay or nay.

mollwollfumble said:

I don’t trust anything Hawking says any more.

To be fair to Hawking, this is engineering, and many good theoretical physicists are not very good engineers (including Freeman Dyson).

mollwollfumble said:

> The beam could eventually be scaled to 100 Gigawatt level.

Hmm. In my calculations above I assumed only 100 Megawatts, the entire power supply for CERN, and then for my calculation I assumed a short acceleration time of 120 seconds or so, whereas they assume a much longer acceleration time. Could that 100 Gigawatts be ridiculously excessive?

The presently most powerful laser is actually 20,000 times that 100 Gigawatts, two petawatts, but lasts for only a tiny fraction of time, 1 picosecond. The energy in 2 petawatts in one picosecond is that same as the energy in 2,000 watts in one second.

I guess they must be talking in terms of 100 GW in very short bursts, rather than an average, but even if the average was 100 Megawatts, how do you apply that much power to something the size of a postage stamp without instantly vaporising it? Surely the average power levels need to be very much lower, with acceleration occurring over a much longer time (probably years)?

>> This is the beamer on the ground.
> Earth-based it would pump a heck of a lot of heat into the atmosphere: enough to create a tornado, or a hurricane?

Not a hurricane. 100 Gigawatts is too small a power by a factor of 3,000 to create a hurricane. Good. Also, 100 Gigawatts is not beyond the generating capacity of Earth-based power stations, it’s of the order of 7% of world power capacity. Good.

The Rev Dodgson said:

mollwollfumble said:

I don’t trust anything Hawking says any more.

To be fair to Hawking, this is engineering, and many good theoretical physicists are not very good engineers (including Freeman Dyson).

mollwollfumble said:

> The beam could eventually be scaled to 100 Gigawatt level.

Hmm. In my calculations above I assumed only 100 Megawatts, the entire power supply for CERN, and then for my calculation I assumed a short acceleration time of 120 seconds or so, whereas they assume a much longer acceleration time. Could that 100 Gigawatts be ridiculously excessive?

The presently most powerful laser is actually 20,000 times that 100 Gigawatts, two petawatts, but lasts for only a tiny fraction of time, 1 picosecond. The energy in 2 petawatts in one picosecond is that same as the energy in 2,000 watts in one second.

I guess they must be talking in terms of 100 GW in very short bursts, rather than an average, but even if the average was 100 Megawatts, how do you apply that much power to something the size of a postage stamp without instantly vaporising it? Surely the average power levels need to be very much lower, with acceleration occurring over a much longer time (probably years)?

> how do you apply that much power to something the size of a postage stamp without instantly vapourising it?

Excellent point.

I guess they must be talking in terms of 100 GW in very short bursts, rather than an average, but even if the average was 100 Megawatts, how do you apply that much power to something the size of a postage stamp without instantly vaporising it?

well, the propulsion would come from photons hitting a lightsail and not the probe. plus you have the spread of the beam. plus you have the distance v intensity drop off.

The Rev Dodgson said:

mollwollfumble said:

I don’t trust anything Hawking says any more.

To be fair to Hawking, this is engineering, and many good theoretical physicists are not very good engineers (including Freeman Dyson).

mollwollfumble said:

> The beam could eventually be scaled to 100 Gigawatt level.

Hmm. In my calculations above I assumed only 100 Megawatts, the entire power supply for CERN, and then for my calculation I assumed a short acceleration time of 120 seconds or so, whereas they assume a much longer acceleration time. Could that 100 Gigawatts be ridiculously excessive?

The presently most powerful laser is actually 20,000 times that 100 Gigawatts, two petawatts, but lasts for only a tiny fraction of time, 1 picosecond. The energy in 2 petawatts in one picosecond is that same as the energy in 2,000 watts in one second.

I guess they must be talking in terms of 100 GW in very short bursts, rather than an average, but even if the average was 100 Megawatts, how do you apply that much power to something the size of a postage stamp without instantly vaporising it? Surely the average power levels need to be very much lower, with acceleration occurring over a much longer time (probably years)?

> how do you apply that much power to something the size of a postage stamp without instantly vapourising it?

I just calculated the theoretical minimum mass for a solar sail that could reflect without melting the specified 100 GW for 20 minutes. I checked reflection from six metals (aluminium, lithium, gold, osmium, palladium, silver) at the wavelength of maximum reflectivity (which happens to be in the microwave), heating up from a temperature of zero Kelvin.

The result. The mass of the solar sail would have to be at least 148 tons, and made of lithium.

So the specification of “a few grams” for the solar sail is totally impossible.

The plan is a long acceleration, which means keeping a laser columnated for a longer distance than current technology allows.

The man who launched this idea, Yuri Milner, is a physicist so I assume he has sat down and done the BOTE calculations to find out that this project requires breakthroughs in half a dozen fields.

He is also an entrepreneur so it might be that he is just trying to fleece investors.

columnated

pffft you say that like it’s a real word!

and yes, i know it is a real word.

:-)

mollwollfumble said:

The Rev Dodgson said:

mollwollfumble said:

I don’t trust anything Hawking says any more.

To be fair to Hawking, this is engineering, and many good theoretical physicists are not very good engineers (including Freeman Dyson).

mollwollfumble said:

> The beam could eventually be scaled to 100 Gigawatt level.

Hmm. In my calculations above I assumed only 100 Megawatts, the entire power supply for CERN, and then for my calculation I assumed a short acceleration time of 120 seconds or so, whereas they assume a much longer acceleration time. Could that 100 Gigawatts be ridiculously excessive?

The presently most powerful laser is actually 20,000 times that 100 Gigawatts, two petawatts, but lasts for only a tiny fraction of time, 1 picosecond. The energy in 2 petawatts in one picosecond is that same as the energy in 2,000 watts in one second.

I guess they must be talking in terms of 100 GW in very short bursts, rather than an average, but even if the average was 100 Megawatts, how do you apply that much power to something the size of a postage stamp without instantly vaporising it? Surely the average power levels need to be very much lower, with acceleration occurring over a much longer time (probably years)?

> how do you apply that much power to something the size of a postage stamp without instantly vapourising it?

I just calculated the theoretical minimum mass for a solar sail that could reflect without melting the specified 100 GW for 20 minutes. I checked reflection from six metals (aluminium, lithium, gold, osmium, palladium, silver) at the wavelength of maximum reflectivity (which happens to be in the microwave), heating up from a temperature of zero Kelvin.

The result. The mass of the solar sail would have to be at least 148 tons, and made of lithium.

So the specification of “a few grams” for the solar sail is totally impossible.

The calculation of that mass was based on the assumption that the solar sail was made of a normal material. The best material reflectivity I’ve found is 99.8%, and that’s for Lithium in the microwave energy range. The next best was 99.4 to 99.5% reflectivity from Gold, Silver, Osmium and Palladium, also in the microwave range. Photons that aren’t reflected are absorbed, which heats up the solar sail enormously.

Again in the microwave range, some superconducting mirrors have been made with much better reflectance than that. When cooled to 0.8 Kelvin in https://arxiv.org/ftp/quant-ph/papers/0612/0612031.pdf which reports that “Microwave photons are stored in a superconducting cavity for decay times of 0.129 seconds.” That’s equivalent to a reflectivity of the order of 99.99999993%

Could the solar sail of a nanocraft be kept at that low a temperature under such a bombardment of energy without the temperature rising enough to destroy the superconductivity?

Perhaps, but it wouldn’t be easy, in part because superconductivity is destroyed in the presence of a strong electromagnetic field. The destruction of this superconductivity by single photons of sufficient energy (eg. 1 micrometre wavelengths = near IR) is even used as the guiding principle behind superconducting photon detectors.

I mentioned superconducting solar sails above, thinking it to be impossible.

There was also a recent thread asking about the use of an electromagnetic shield for radiation protection of spacecraft personnel, and I said that it wasn’t what you want.

I could have been wrong on both. What I didn’t realise is that CERN is already working on placing superconducting magnets onboard spacecraft for radiation protection. News article https://www.rt.com/news/311896-space-radiation-cern-shield/

“The superconducting material was utilized for the Large Hadron Collider, to create ultra-bright particle beams at a low temperature. For the spaceship, the MgB2 coils at 25 Kelvin could create an envelope that would not be penetrated by high energy cosmic-particles. If the prototype coil we will be testing produces successful results, we will have contributed important information to the feasibility of the superconducting magnetic shield.

“Space radiation particles, which come from our sun, and other objects beyond the solar system, inflict damage on the human DNA and organs, which accumulates over time, causing conditions ranging from cancer to dementia. Because of this, exploration missions to Mars or other distant destinations may only become realistically possible if an effective solution is found.”