Comments on Next Big Future: Photonic Laser Propulsion

So IF beam quality can be maintained and IF focusi...

2007-02-26T09:11:00.000-08:00

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:
http://pdf.aiaa.org/jaPreview/JSR/1984/PVJAPRE8632.pdf
http://www.ugcs.caltech.edu/~diedrich/cgi/search.cgi?forward%2C+r

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.
http://www.niac.usra.edu/files/library/meetings/fellows/mar06/1133Powell.pdf

All the pieces of the system would then be difficult but not insane.

http://www.rametzger.com/whatif32.htm
has some more on 2000 reflections being doable for the Mars launch for a 96 day trip.

What do you think is a conservative expectation of...

2007-02-25T21:19:00.000-08:00

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.

Depends on how technologically optimistic you want...

2007-02-25T16:21:00.000-08:00

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:
http://www.sciencedaily.com/releases/2007/02/070213101025.htm

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

But it might be a reasonable approach.

btw: I am happy to see that you read my site, I re...

2007-02-25T13:03:00.000-08:00

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

So do you think this 20,000 to 100,000 bounce syst...

2007-02-25T13:01:00.000-08:00

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.

http://www.rametzger.com/nonfic-mblbs.htm

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.

Cool.Robert Metzger and I did an analysis of using...

2007-02-25T10:57:00.000-08:00

Cool.

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)