I don’t envy the track chairs at any conference, particularly conferences that are all about getting large numbers of scientists into the right place at the right time. Herding cats? But the track model makes inherent sense when you’re dealing with widely disparate disciplines. Earlier in the week I mentioned how widely the tracks at the 100 Year Starship Symposium in Houston ranged, and I think that track chairs within each discipline — already connected to many of the speakers — are the best way to move the discussion forward after each paper.
Still, what a job. My friend Eric Davis, shown at right, somehow stays relaxed each year as he handles the Propulsion & Energy track at this conference, though how he manages it escapes me, given problems like three already accepted presentations being withdrawn as the deadline approached, and one simple no-show at the conference itself. Unfortunately, there were no-shows in other tracks as well, though the wild weather the night before the first day’s meetings may have had something to do with it.
Processes will need to be put in place before future symposia to keep this kind of thing from happening. Fortunately, Eric is quick on his feet and managed to keep Propulsion & Energy on course, and I assume other track chairs had their own workarounds. A high point of the conference was the chance to have dinner and a good bottle of Argentinian Malbec with Eric and Jeff Lee (Baylor University), who joined my son Miles and myself in the hotel restaurant.
The Antimatter Conundrum
I found two papers on antimatter within Eric’s track particularly interesting given the challenge of producing antimatter in sufficient quantity to make it viable in a future propulsion system. We’d love to master antimatter because of the numbers. A fusion reaction uses maybe one percent of the total energy locked up inside matter. But if you can annihilate a kilogram of antimatter, you can produce ten billion times the energy of a kilogram of TNT. In nuclear energy terms, the antimatter yields a thousand times more energy than nuclear fission, and 100 times more energy than fusion, a compelling thought for interstellar mission needs.
Sumontro Lal Sinha described the requirements for a small, modular antimatter harvesting satellite that could be launched into the Van Allen radiation belt about 15,000 kilometers up. I was invariably reminded of James Bickford’s ideas on creating an antimatter trap in an equatorial orbit around the Earth that could harvest naturally occurring antiparticles — Bickford has always maintained that space harvesting of antimatter using his ‘magnetic scoop’ is five orders of magnitude more cost effective than producing antimatter on Earth. In any case, antimatter resources here and elsewhere in the Solar System offer useful options.
Remember that the upper atmosphere of the planets is under bombardment from high-energy galactic cosmic rays (GCR), which results in ‘pair production’ as the kinetic energy of the GCR is converted into mass after collision with another particle. Out of this we get an elementary particle and its antiparticle. Planets with strong magnetic fields become antimatter sources because particles interact with both the magnetic field and the atmosphere. Sinha’s harvester would be an attempt at pair-production that he describes as lightweight and modular. I haven’t seen a paper on this one so I can’t go into useful detail. I’ll hope to do that later.
Storing macroscopic amounts of antimatter for propulsion purposes is the other side of the antimatter conundrum, an issue tackled by Marc Weber (Washington State), who described long antimatter traps in the form of stacks of wafers that essentially form an array of tubes. Storage is an extreme issue because like charges repel, so that large numbers of positrons, for example, generate repulsive forces that magnetic bottles cannot fully contain. Weber’s long traps are in proof-of-principle testing as he tries to push storage times up.
Image: One of Marc Weber’s slides, illustrating principles behind a new kind of magnetic storage trap for antimatter.
Thermonuclear Propulsion and the Gravitational Lens
It’s always a pleasure to see old friends at these events, and I was happy to have the chance to share breakfast with Claudio Maccone, whose long-standing quest to see the FOCAL mission built and flown has come to define his career. But in addition to speaking about the gravitational lens at 550 AU and beyond, Claudio was in Houston to discuss the Karhunen-Loève Transform (KLT), developed in the 1940s to improve sensitivity to artificial signals by a large factor, another idea he has long championed. The idea here is that the KLT has SETI applications, helping researchers in the challenging task of sifting through signals that may be spread through a wide range of frequencies.
Consider our own civilization’s use of code division multiplexing. Mason Peck was also talking about this at the conference — the reason you can use your cellphone in a conversation is that multiple access methods (code division multiple access, or CDMA) allows several transmitters to send information simultaneously though using the same communications channel. Spread-spectrum methods are at work — the signal is sent over not one but a range of frequencies — and you’re actually dealing with a combination of many bits that acts like a code. If we’re using these methods, perhaps a signal we receive from an extraterrestrial civilization may be as well, and perhaps the best way to unlock it is to use the KLT.
I missed Claudio’s session on the KLT but was able to be there for his talk on using the gravitational lens as a communications tool. Beyond the propulsion question, one of the biggest problems with putting a probe around another star is data return. How do we get a workable signal back to Earth? Fortunately, the gravitational lens can offer huge gains by employing the focusing power of the Sun on electromagnetic radiation from an object on the other side of it. Using conventional radio communications would require huge antennae and substantial (and massive) resources aboard the probe itself. These would not be necessary if we fly the needed precursor mission to the distances needed to use the gravitational lens.
Thus we send a relay spacecraft not toward Alpha Centauri but in exactly the opposite direction. Ordinary radio links can be easily maintained. If we tried conventional methods using a typical Deep Space Network antenna and a 12-meter antenna aboard the spacecraft (assuming a link frequency in the Ka band, or 32 GHz, a bit rate of 32 kbps, and 40 watts of transmitting power), we still get a 50 percent probability of errors. A relay probe at the gravitational lens, however, shows no bit error rate increase out to fully nine light years.
I’m moving quickly here and I can’t go through each presentation, but I do want to mention as well Friedwardt Winterberg’s talk on thermonuclear propulsion options. Dr. Winterberg has a long history in researching nuclear rocketry, dating back to the days of Ted Taylor, Freeman Dyson, and the era of Project Orion (which he could not join because he was not yet a US citizen). The Atmospheric Test Ban Treaty of 1963 was one of the factors that put Orion to rest, but Fred has been championing nuclear micro-bombs with non-fission triggers, an idea he first broached at a fusion workshop all the way back in 1956. His most recent paper reminds us of von Braun’s ideas about assembling a huge fleet in orbit for the exploration of Mars:
A thermonuclear space lift can follow the same line as it was suggested for Orion-type operation space lift, but without the radioactive fallout in the earth atmosphere. With a hydrogen plasma jet velocity of 30 km/s, it is possible to reach the orbital speed of 8 km/s in just one fusion rocket stage, instead of several hundred multi-stage chemical rockets, to assemble in space one Mars rocket, for example. .. The launching of very large payloads in one piece into a low earth orbit has the distinct advantage that a large part of the work can be done on the earth, rather than in space.
Exactly how to ignite a thermonuclear micro-explosion by a convergent shockwave produced without a fission trigger is the subject of the new paper, and I’m looking for someone more conversant with fusion than I am to give it a critical reading to be reported here. The basic Orion concept remains in Winterberg’s work with fission bombs replaced by deuterium-tritium fusion bombs being set off behind a large magnetic mirror rather than Orion’s pusher plate.
All Too Little Time
So many papers occurred in different tracks at conflicting times, exacerbated by the need to attend advisory board meetings, so I missed out on a number of good things. I wish I could have attended Kathleen Toerpe’s entire Interstellar Education track, and there were sessions in Becoming an Interstellar Civilization and Life Sciences in Interstellar that looked very promising. I hope in the future the conference organizers will set up video recording capabilities in each track, so that attendees and others can catch up on what they missed.
Several upcoming articles will deal with subjects touched on at 100YSS. Al Jackson is writing up his SETI ideas using extreme astronomical objects, and I’ll be talking about Ken Wisian’s paper on military planning for interstellar flight — Ken and his lovely wife joined Heath Rezabek, Al Jackson, Miles and myself for dinner. The conversation was far-ranging but unfortunately the Friday night restaurant scene was noisy enough that I missed some of it. Miles and I stopped down the street the next night at the Guadalajara, a good Mexican place with a quiet upstairs bar. Great margaritas, and a fine way to close out the conference. Expect an upcoming article from Miles, shown below, on his recent interstellar presentation in a seriously unconventional venue. I’m giving nothing away, but I think you’ll find it an encouraging story.