Using lasers to travel to the stars
The competition really heats up! A research team at the University of California, Santa Barbara (UCSB) has proposed that an array of space-based lasers can be used to accelerate a solar sail to speeds as much as 26% the speed of light, thus making interstellar travel possible.
[The] key breakthrough was the development of modular arrays of synchronized high-power lasers, fed by a common “seed laser.” The modularity removes the need for building powerful lasers as a single device, splitting them instead into manageable parts and powering the seed laser with relatively little energy. Lockheed Martin has recently exploited this advance to manufacture powerful new weapons for the US Army. In March last year, the aerospace and defense giant demonstrated a 30 kW laser weapon (and its devastating effect on a truck). By October, the laser’s power had already doubled to 60 kW and offered the option to reach 120 kW by linking two modules using off-the-shelf components.
The UCSB researchers refer to their own planned arrays as DE-STAR (Directed Energy System for Targeting of Asteroids and ExploRation), with a trailing number to denote their size. A DE-STAR-1 would be a square array 10 meters (33 ft) per side and about as powerful as Lockheed’s latest; at the other end of the spectrum, a DE-STAR-4 would be a 70 GW array covering a massive area of 100 square kilometers (39 square miles).
…Lubin stresses that even a relatively modest orbital array could offer interesting propulsion capabilities to CubeSats and nanosatellites headed beyond Earth orbit, and that useful initial tests would still be conducted on the ground first on one-meter (3-ft) arrays, gradually ramping up toward assembling small arrays in orbit. While even a small laser array could accelerate probes of all sizes, the larger 70-GW system would of course be the most powerful, capable of generating enough thrust to send a CubeSat probe to Mars in eight hours – or a much larger 10,000-kg (22,000-lb) craft to the same destination in a single month, down from a typical six to eight.
Further upgrades would make it possible to send a cubesate and its lightsail to Alpha Centuri in about fifteen years.
The important point here is that it appears that all the technology for building this already exists, or is relatively straightforward to develop.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
The competition really heats up! A research team at the University of California, Santa Barbara (UCSB) has proposed that an array of space-based lasers can be used to accelerate a solar sail to speeds as much as 26% the speed of light, thus making interstellar travel possible.
[The] key breakthrough was the development of modular arrays of synchronized high-power lasers, fed by a common “seed laser.” The modularity removes the need for building powerful lasers as a single device, splitting them instead into manageable parts and powering the seed laser with relatively little energy. Lockheed Martin has recently exploited this advance to manufacture powerful new weapons for the US Army. In March last year, the aerospace and defense giant demonstrated a 30 kW laser weapon (and its devastating effect on a truck). By October, the laser’s power had already doubled to 60 kW and offered the option to reach 120 kW by linking two modules using off-the-shelf components.
The UCSB researchers refer to their own planned arrays as DE-STAR (Directed Energy System for Targeting of Asteroids and ExploRation), with a trailing number to denote their size. A DE-STAR-1 would be a square array 10 meters (33 ft) per side and about as powerful as Lockheed’s latest; at the other end of the spectrum, a DE-STAR-4 would be a 70 GW array covering a massive area of 100 square kilometers (39 square miles).
…Lubin stresses that even a relatively modest orbital array could offer interesting propulsion capabilities to CubeSats and nanosatellites headed beyond Earth orbit, and that useful initial tests would still be conducted on the ground first on one-meter (3-ft) arrays, gradually ramping up toward assembling small arrays in orbit. While even a small laser array could accelerate probes of all sizes, the larger 70-GW system would of course be the most powerful, capable of generating enough thrust to send a CubeSat probe to Mars in eight hours – or a much larger 10,000-kg (22,000-lb) craft to the same destination in a single month, down from a typical six to eight.
Further upgrades would make it possible to send a cubesate and its lightsail to Alpha Centuri in about fifteen years.
The important point here is that it appears that all the technology for building this already exists, or is relatively straightforward to develop.
On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.
The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.
The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.
"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News
Beamed power is certainly the way forward for interstellar travel. Not having to launch the “engine” or “fuel”. Nature’s young stars, neutron stars and black holes spontaneously generate tremendous jets. Some of them throw huge (by earthly measures) amounts of materia at relativistic speeds over intergalactic distances. It is physically possible, it is happening. The question is how and when humans will engineer this potential.
It’s interesting that Lockheed Martin is also developing a compact fusion device that could power these laser arrays in space. They hope to eventually have a device that could fit on a flatbed trailer and produce enough energy to power a small city. The article on their web cite makes for interesting reading. If it were anyone other than the Skunk Works I would be skeptical, but they have quite a track record. We live in interesting times indeed!
Wonder how to power that 70GW laser array?
Huge solar array I suppose.
I wonder how far into the atmosphere such a beam can penetrate (if someone wanted to)
Really, a cube sat could reach Mars in eight hours? How is it going to slow down enough to do anything useful?
Really, a cube sat could reach Mars in eight hours? How is it going to slow down enough to do anything useful?
2nd try.
> Wonder how to power that 70GW laser array?
The world consumes 19TW of electricity. If the nighttime part of that capacity were to be beamed to the Moon, collected and then revealed for interstellar propulsion then much greater than CubeSats could be sent.
BSJ wrote: “Really, a cube sat could reach Mars in eight hours? How is it going to slow down enough to do anything useful?”
I got interested in solar sails in the late 1970s. Even back then, this kind of idea had been proposed. One method for slowing down at the destination was to have the sail built in two parts: in inside disk and an outer ring. The ring would break away as the sail neared the destination, and the laser would shine on it, the light would bounce back to the disk and the payload would slow to an orbital speed. One downside to this idea was that the outer ring would accelerate away at a higher rate than the payload would slow down, reducing the effectiveness of the reflected light as time went on.
Another suggested way of slowing down was to use the star’s light as a breaking force. Speeds approaching relativistic speeds would likely overwhelm the breaking force of the destination star, so the travel speed would be limited to the breaking power of that star. This probably would require an even slower approach speed, as the gravitational attraction of the star would also have to be accounted for.
I like the article’s suggestion, however, of having a second laser source at the destination, such as Mars. This may require that we have a serious presence at Mars, though.
So, the article and the video suggested that they were moving from science fiction to science reality, but there is a bit of a problem, so if you want to continue believing that this is possible with current technology, take this as a *** SPOILER ALERT! *** and read no further.
Let’s talk heat dissipation. First, the laser array needs to dissipate a lot of waste heat. For every gigawatt of power sent by the laser, 3 gigawatts will have to be dissipated if the power source is 25% efficient (current solar arrays can be made this efficient). That requires a big radiator for every one of the 70 proposed gigawatts. Fortunately, current solar arrays can dissipate that much on their back sides. But it takes a big array of solar panels. Big. Really big.
For other power source types, imagine a standard Earth-bound power plant with all that steam being emitted from the cooling towers. A standard power plant like that is about 1 gigawatt, so we have to do around the equivalent of 70 of those cooling towers using only radiative cooling. This is a bit tricky.
Second, the worse problem is cooling the poor solar sail. Not all of the light is going to be reflected off the reflective sail. To save weight and maximize the acceleration per gigawatt of laser power, the reflective material, such as aluminum or silver, would be so thin that some of the energy will pass right through. But not all of the energy will reflect or pass through, some will be absorbed into the thin material and heat it up. At 70 GW, it won’t take too much absorption for the sail to (!) melt away.
One proposal that I read, lo those many years ago, was to grow radiative “hairs” on the back side of the sail, and these fibers would increase the surface area that radiates away the heat. The paper that proposed that idea seemed to conclude that the increased light that can shine on the sail more than makes up for the additional weight of the radiative hairs. But … 70 GW is still a lot of power, and it still would heat up that sail quite a bit.
My conclusion is that 70 GW is overpowered, especially considering that it takes them 10 minutes to get to 30% of the speed of light, according to the embedded video. A possible solution is to use a lower power laser, one that does not overwhelm the solar sail material, and station multiple lasers along the longer acceleration route to make up for the lost power of the spreading beam, due to distance. Lasers are not exactly perfectly parallel light, they spread out over distance. Using multiple power sources over the track of the acceleration is how they get subatomic particles up to relativistic speeds in the laboratory — they do it all the time. It is also how a mass driver works/will work (mass drivers have been built in the laboratory, too).
Do not abandon all hope, ye who read this far. Just because the system needs a little work does not mean it is impossible in the long run. It just may not work quite as advertised.
If such a powerful laser can transfer a LOT of momentum to a sail via photons, couldn’t you just put the same laser on the rear of a space craft and impart the same momentum directly to the spacecraft by shooting photons in the opposite direction of travel? Of course, you would have to carry the mass of the power source for the laser as well as the mass of the laser itself which would almost certainly defeat achieving a useful acceleration.
Would need some way to clear a path ahead of the vehicle. At 30%c, a tiny rock would destroy a spacecraft.
“At 30%c, a tiny rock would destroy a spacecraft.”
At 0.3C, it would take much less than a ‘tiny rock’. I have a video where engineers put a small satellite into a chamber and fire a mass equivalent to a small pebble at Earth orbital velocity at the craft. There are a few small pieces left, but everything else is dust.
“If we could generate an inverse tachyon pulse using the ships main deflector array, that might in theory initiate a graviton cascade on the same harmonic resisant frequency as the pebble. It’s never been done before & we only have 7 minutes left in this episode, but,….. it just might work…”
Yo, Blair– anxiously awaiting your blog-post on served & targeted adverts in the blogosphere!
Edward: well said… “It just may not work quite as advertised.”
How about orbiting some sort of magnetic lens/reflector at ~100,000 miles from the surface of the Sun? Then somehow remove beam divergence (using adaptive optics!). Assuming no losses (and you really want to avoid ALL losses when you have 70 GW hitting you), a 70 m^2 “reflector” (5 m radius) could reflect the 70 GW. That was easy.
Yes, Edward raises very good points. Another problem I saw when reading the technical proposal was the acceleration of the 2 gram size spacecraft. It was stated to be 10000 g’s. Another challenge and a bit more than someone dropping a cell phone.