9 Comments

1. Astronist on October 1, 2011 at 9:07

   Thanks, Paul; looking forward to your reports.

2. ljk on October 1, 2011 at 11:59

   So… we’re going to use escalators to get to Alpha Centauri? Novel, at least. :^)

   Have a great time, Paul, and I definitely wish I were there. Looking forward to all the reports.

3. Paul Gilster on October 1, 2011 at 15:13

   Larry, ‘Stairway to the Stars’ has a nice ring, don’t you think? Maybe better than ‘Escalator to the Stars,’ but the escalator is what the Orlando Hilton offers…

4. David OHara on October 1, 2011 at 22:04

   The first thing I think needs to be said about the 100 YSS Symposium is that we really need to thank and praise the organizers for this as it went off very well. I do not know any of these guys but you have my appreciation. We also need to thank the presenters for even discussing something that many would think to be “out there”.
   Next, I do not know anybody in this field and so when I discuss something I am professing my ignorance of who has done what before I make any remarks and I do not intend to slight anybody. Not being much of a Sci Fi reader, I would often see people whose names were familiar and eventually I learned they were authors I had heard of.
   The attendees were an interesting mixture of technical people to people who professed to simply be “space geeks” with very few of them I talked to actually being in the space business. There were three brothers who agreed to meet there, two from Europe and one from Ecuador, a level of interest that is truly inspiring. I met a guy who said his normal job was writing a column about gardening but was there simply out of interest. I halfway expected to see every sort of flying saucer crazy and would be trekkie but instead it was a very sober well grounded group of attendees. Up to Friday morning I was hesitating to attend although it is only 4 hours away but am now so excited I just had to rush home to tell how it went.
   There were several sessions with interesting things that overlapped so I had to make the decision to only attend the propulsion (Time and Distance) sessions. Perhaps there were some whacko things in other sessions but what I attended was grounded in known physics and engineering. In considering the various propulsion options, chemical means were first discarded. Then came a discussion of Isp and thrust of other methods. It seemed agreed that Nuclear Thermal Rockets will normally be used within the solar system but not for interstellar. Most agreed that fusion will be required. I was disappointed at the cursory discussion of the old Orion nuclear pulse technology as it is still the only way we currently know to do this and a modern Orion might be interesting. There was also no discussion of Zubrins Nuclear Salt Water Rocket and no discussion of fission fragment rockets.
   The fusion concepts all seemed to require higher than breakeven fusion which I thought was a problem as breakeven has never been accomplished (it is always 10 yrs away). A guy from U of Mich had an interesting idea of a hybrid fusion/fission rocket with a fusion source surrounded by a Thorium blanket so the D-D fusion neutrons would cause the Thorium to fission as a neutron multiplier. Being non-critical is a major advantage of this. I’d thought I was the only person advocating Thorium fission rockets but I had no idea of where to get the neutrons before hearing his talk. This was interesting because it does not need fusion breakeven. I think the author agreed that much less than breakeven would be ok. He wants to use a fusion source with a magnetic mirror containment but wouldn’t it be easier to use a cylindrical geometry electrostatic confinement? It does not matter if the fusion rate is very low, the gain comes from the Thorium fission.
   I’d never been fond of solar sails until this symposium but I now see some good applications. However, I was puzzled that the solar sail types seemed to not know of material properties and fabrication methods for ultra-thin large area materials. For example, they advocated the use a ultra-thin Beryllium films but Beryllium is an awful material and in free standing films cracks just by thinking about it. When they told me that the recent sail experiments used polymer sails that are about 4 microns thick, I was aghast, that is seriously thick (I work a lot with ultra-thin free standing films as windows for very soft x-rays). I suggested that .3 micron thick polyimide can be made in areas up to 900 cm2 and could easily be scaled up and that the polyimide is then coated with boron hydride (by CVD) to make it reflective. They discussed using graphene and discussed that large area graphene is bizarre expensive, however when I suggested that one need not use graphene that free standing carbon films as thin as 10 nm are common (used as accelerator stripper foils) the response was that graphene was most desirable. I suggested that one does not even need single sheets of graphene because graphene paper can be made ultra-thin by allowing it to settle on filter paper and then dissolving the filter medium. People also need to consider hex Boron Nitride which is often called “white graphite” because it is intended for ultra-high temp applications and it has a graphitic planar structure. Fabrication of free standing ultra-thin materials of large area is ideal in space because it requires high vacuum. This could easily be done robotically in space.
   However, the bottom line seems to be that solar sails seem feasible. I think a solar sail should be used to carry a spectrometer to the 550 AU sun’s gravitational focusing distance so the suns’s disc acts as an ultra-large aperture telescope to get very highly spatially resolved data for a destination planet prior to an actual interstellar mission. By itself this would be a great pre-cursor mission.
   There was a talk on using microwave beamed propulsion to a wispy receiver sail and photos of an experiment in a vacuum chamber using what looked to be 3 Ghz microwaves to lift and accelerate a “sail” (this was a cool looking carbon gauze material). One interesting thing was that the carbon fibers absorbed so much power that they glowed white hot. Such carbon fibers would make a great thermionic emitter of electrons for some use. He made an allusion to a large beam forming optic to direct the diverging beam onto the distant sail with no description of said optic. Why not use a large ionized sphere of low density gas to refract the microwave beam onto the sail. Sure, the refractive index would be very low giving very long focal length but that is what we want. The ultra-large focal length would minimize the effects of aberrations. When the gas ball dissipated (or deionized itself) the spacecraft would emit another one and wait till it was many AU away to receive microwaves going thru it.
   Another author discussed the use of laser beamed power pointing out that x-ray lasers and x-ray focusing optics would be best for this. This got my attention (my area of expertise is x-ray optics) because I can readily imaging making very large aperture (km diameters) x-ray grazing incidence optics. I do not think he was considering Tellers old nuclear pumped x-ray laser but why not? Tellers laser would have used a focusing lens of fully ionized gas produced by absorption of x-rays from the nuke bomb. Imagine a pulsed source consisting of numerous nuclear pumped x-ray lasers . Another note to self is to look into the amount of momentum that could be transferred to a sail by means of soft x-rays from the sun combined with a focusing optic.
   It was a great symposium that will cause me to spend waaaaay too much time thinking of such things instead of work.

   David OHara (aka “Frogwatch”)

5. guest on October 2, 2011 at 15:06

   Would you happen to know if people are going to be publishing their talks/presentations online, or if they were being videoed? I’m looking forward to various peoples’ reports on the event, and it would be very interesting to read any papers or discussions that come out of this. Hopefully those will be made available online.

6. Paul Gilster on October 3, 2011 at 9:24

   Re publishing online, there has been talk that the entire symposium’s talks may be made available online — everything was recorded and this could be done, assuming approval of the speakers. But I don’t have anything official on that. I’ll be sure to let people know when I learn more.

7. ljk on October 3, 2011 at 9:44

   Will a book with all the papers and other details of the Symposium be done as well? Thanks, Paul.

8. Paul Gilster on October 3, 2011 at 10:27

   Larry, yes, all the papers from the Symposium will be published in a special issue of the Journal of the British Interplanetary Society.

9. guest on October 4, 2011 at 16:39

   That’s great news! I’ll keep an eye out for that JBIS issue.