February 23, 2007

Photonic Laser Propulsion

Photonic Laser Propulsion has had a proof of concept demo it generated 35 micronewtons of thrust using mirrors that generated 3000 times amplification. The low power version would be great for position control of multiple satellites to nanometer precision.

UPDATE: It has been proposed that extremely small payloads (10 kg) could be delivered to Mars in only 10 days of travel time using laser-based lightsail caft (Meyer, 1984), but in order to do so, would require a 47 GW laser system. With 47,000 reflections then only a 1MW laser system would be needed. (fifty 20KW lasers). Scaling up 100 times would be able to deliver 1 ton payloads to Mars in ten days.
"Multi-Bounce Laser-Based Sails", written by Robert A. Metzger and Geoffrey Landis

Molecular nanotechnology could help put this technology over the top, with far better mirrors, lighter systems, better lasers, mass production of lasers and other benefits.

The 10 watt laser was based on 100 watts for the total satellite power budget. Thus the best mirrors (20,000 times amplification) would deliver 1.3 milliNewtons.

If they can use the MIT dielectric mirrors those are supposed to reflect 99.999% of the light which would have 100,000 times amplification.

Scaling it up for more power.
130 millinewtons per kilowatt (0.13 N/kw)
But 10 MW lasers would give 1300 newtons.

Continuous beam electric lasers have about 27 kilowatts of power. Although stay on all day lasers seem to be at about 10-13 kilowatts.

more on lasers at wikipedia In some applications you could use more powerful chemically pumped or other types of lasers.

The website for the research group talks about using the system for ground launch and for accelerating to light speed. I could see ground launch.
This PDF looks at another study for using many lasers to ground launch. The mirror system could make such a ground launch system more efficient.

Get a big power source and a very powerful laser(s). As a major propulsion system it would still seem to have issues maintaining targeting between the two mirrors.

Robert forward originally proposed the laser sail concept Robert Forward first proposed the idea of the laser sail, though his ideas used 1000 km lenses, a laser producing 10-million-gigawatts and 1000 km sails.
Geoffrey Landis has done work to advance laser and microwave pushed lightsails
Other laser sail concepts

It would seem that the mirror amplification could be helpful in reducing certain system requirements.

I presume the architecture is to stick the launching system in space where there would not be atmospheric distortion and losses. The mirror on a large asteroid or body without atmosphere and far heavier than the thing being launched. Then firing up the nuclear generator on the asteroid and firing the lasers that bounce between the mirrors. One mirror on the ship and one on the asteroid.

If the problems of making the more powerful lasers, targeting and better mirrors can be overcome. The ISP in the tables for the photonic laser propulsion is 40 million. (between 10**7 and 10**8). This is the highest ISP system that I have seen.
ISP Hours ISP seconds
Photonic drive 11,236 40 million
AM-Beam MAX 2,834 10 million
H->Fe Fusion MAX 1,417 5.1 million
H->He Fusion MAX 850 3.1 million
IC-Fusion MAX 2831 million
ORION MAX 278 1 million
NSWR 90% UTB MAX133 479,000
AIM 17 61200
mag Orion 8.230000
VASIMR (high gear) 8 28800
Mini-Mag Orion 6 21600
ORION Low Altitude414400
Space Shuttle0455


Geoffrey said...


Robert Metzger and I did an analysis of using reflections to amplify the thrust from a laser-pushed lightsail a while back, it's presented here:

R. A. Metzger and G. Landis, "Multi-Bounce Laser-Based Sails," presented at the STAIF Conference on Space Exploration Technology, Albuquerque NM, Feb. 11-15, 2001. AIP Conference Proceedings Volume 552, 397.

(The article was sort of a compromise between Metzger's technology optimism and my technological pessimism about the concept)

bw said...

So do you think this 20,000 to 100,000 bounce system would work?
And could we use the modular array of 10Kw lasers in place of the more powerful lasers which we do not have yet.

Do you think the more powerful lasers would work? I was not sure since I did not think they were continuously emitting. I guess it depends on the mission profile and how long the laser needs to be firing.

bw said...

btw: I am happy to see that you read my site, I really liked the work that you have done to determine ways to make laser based sails practical

Geoffrey said...

Depends on how technologically optimistic you want to be-- I'm a little dubious about keeping beam quality up, and of course for a large number of reflections even a small deviation from perfect reflectivity destroys the concept. Robert Metzger, on the other hand, is a bit more of a technological optimist, and thinks it's reasonable, and he's a really smart guy.

I don't know if you've seen this one:

Source: University of California - Berkeley
Date: February 25, 2007
Researchers Create New Super-thin Laser Mirror

But it might be a reasonable approach.

bw said...

What do you think is a conservative expectation of performance with maintained beam quality ?

Is it a lower number of bounces with the highly reflexive materials.
1000 reflections instead of 20,000-100,000 from the best dielectrics ?
A high number of reflections but more leakage?
Unfocused beams in the later reflections, that then start missing the mirrors.

Boosting 1000 times would still be big as it could still bring massive performance boost.

If it could be used for ground launch systems, then we would just need to use wavelengths that were not absorbed by the atmosphere. Then the array of laser modules could start launching at least small payloads cheaply. There is the issue of designing the mirrors and the launch vehicle.

bw said...

So IF beam quality can be maintained and IF focusing and targeting issues can be handled plus all the other engineering(perhaps molecular nanotechnology or metamaterials could be useful in maintaining the beam in each reflection.)

NOTE: the deceleration using lasers would not be helped by the multi-bounce. So deceleration would need to be using magnetic sails.

then the big missions that Robert Forward had proposed were:

Major components of the systems include circular thin-Al- film sails (optimum thickness about 16 nm for 650-nm radiation),
powerful solar-driven CW-laser arrays with a 1000-km diameter in
earth or solar orbit, and 1000-km-diameter Fresnel zone lenses to focus the laser beam.

A fly-by mission to Alpha Centauri (with a 65-GW laser system, a 3.6-km-diameter sail, a maximum speed of 0.11 c, and a travel time of about 40 yr)

a one-way rendezvous mission to Alpha Cen (7.2 TW, 100 km, 0.21 c, 36 yr; deceleration phase 26 TW, 30 km, 5 yr* not helped with multi-bounce), and

-a manned return mission to Epsilon Eridani (43 PW, 1000 km, 0.5 c, 51 yr earth time or 46 yr crew-aging time, including 5 yr for exploration)

1,000 Reflections drops the laser power requirements to
65MW instead of 65GW (0.11c)
7.2GW instead of 7.2 TW (0.21c)
43TW instead of 43PW (0.5c)

10,000 reflections laser requirements
6.5MW instead of 65GW (0.11c)
720MW instead of 7.2 TW (0.21c)
4.3 TW instead of 43PW (0.5c)

100,000 reflections laser requirements
650KW instead of 65GW (0.11c)
72MW instead of 7.2TW (0.21c)
430GW instead of 43PW (0.5c)

The systems are still beyond us but the issues seem less daunting than matter/anti-matter drives or the other approaches.

Plus the near term fast trips to Mars and the 0.11c probes look doable (with say 10 years of hard work and a few billion) even with only 1000 effective reflections.

Use magnetically inflated cables to deploy the 1 kilometer diameter (or larger) sail to go to Mars. The sail could be folded to fit into a large current rocket.

All the pieces of the system would then be difficult but not insane.
has some more on 2000 reflections being doable for the Mars launch for a 96 day trip.