I’m just back from the Tennessee Valley Interstellar Workshop in Oak Ridge, having made it through the Smokies on a rainy, chilly night that saw fog along the ridges and often down in the valleys. It was a haunting drive in ways, the low ceilings making for slow driving and the sense of being surrounded by unseen peaks and deep gorges that were always just out of view. I had hoped to meet with Les Johnson and Robert Kennedy at the latter’s house for the pre-conference festivities, but arrived too late and worn out to do anything but get to sleep.

The workshop was an intense, one-day affair (a good thing I got that sleep!) that started at 8:00 the next day and concluded about 10:40 that night, and judging from the discussion at the end, it will become a regular event. It was great to see old friends. Les and I last talked at Aosta two years ago. Claudio Maccone had come from Italy and would be lecturing at Oak Ridge National Laboratory on the Karhunen-Loève transform the following day (search this site under ‘KLT’ to get the rundown on the possible uses of the transform in SETI, although SETI was not, presumably, ORNL’s chief interest in the subject). Al Jackson was in from Texas, as was Richard Obousy, and Greg Matloff and C Bangs had come down from Brooklyn.

Image: Les Johnson introducing the workshop.

The Tennessee workshop grew out of conversations last summer at the Aosta conference between Les and Claudio, allowing for a schedule that made an excellent fit for Claudio’s US trip — he leaves Oak Ridge today (Thursday) for Stanford (he’ll be having meetings at the SLAC National Accelerator Laboratory and will later be going to the SETI Institute). At the workshop, he discussed the gravitational lensing precursor mission concept called FOCAL that he has championed as a precursor to a true interstellar mission. 550 AU is one-half of a light week, 3.17 light days out, a useful distance at which to test a variety of interstellar technologies.

Communications Between the Stars

Claudio is pointing out that a model of the ‘naked Sun’ that derives 550 AU as the gravitational lensing distance doesn’t take into account solar corona effects that can distort imaging and communications, and the whole point of the mission is to use gravitational lensing to study what is on the other side of the Sun — to use the lensing phenomenon and a careful choice of departure directions for astronomical and perhaps SETI work. 1000 AU proves to be a better distance than 550 AU because of the coronal problem, and it’s interesting to note that the TAU Mission designed at JPL by the Meinels, a husband and wife team working in the 1980s, aimed at 1000 AU as well, although the Meinels had no knowledge of the gravitational lens.

TAU would have been flown using nuclear electric propulsion, and would have taken approximately 50 years to reach 1000 AU for studies of the heliosphere and the nearby interstellar medium, as well as improved parallax measurements of nearby stars. A true FOCAL mission like Maccone is proposing would be able to exploit the Solar lens for communications, allowing low bit error rates (BER) that conventional communications methods cannot touch. Thus we have the potential for communicating with an interstellar probe through a lensing mission that serves as a relay — in fact, you can get 8 light years out using a FOCAL relay before you show significant BER loss. And if you go into the deep future, the possibility of exploiting a similar lens relay around another star could allow the beginning of an ‘interstellar internet.’

And here’s an interesting point that came up in the discussions: Carl Sagan had hypothesized that gravitational lensing might be responsible for at least some of the thirty or so anomalous SETI signals that have never repeated (the famous WOW signal is the classic case in point). A non-repeating signal like this is conceivably the result of a low-powered transmitter occasionally having its gain boosted enormously by stellar focusing, all of this by sheer chance, so that what we pick up is simply a strong but unrepeated signal that tantalizes us as evidence for extraterrestrial technology. It’s an intriguing thought, but we have to fly a FOCAL mission at some point to find out whether the perceived benefits of the Solar lens are in fact exploitable. A FOCAL mission using tethered antennae inscribing Archimedean spirals to boost receiving capability is a project that might be flown using nuclear electric or solar sail technologies to investigate this.

Solar Sails Missions and Materials

Of course, with solar sails you start thinking about materials and how to deal with extraordinarily thin films. But as Greg Matloff pointed out, we’re coming off a banner year for solar sailing, with the launch of the Japanese IKAROS mission and, later, NASA’s NanoSail-D. IKAROS has been a stunning success, deployed as part of an interplanetary mission and able to demonstrate not just propulsion by sunlight but attitude control. Matloff pointed out that the hyper-thin solar panels deployed on the sail are continuing to work perfectly after a year, and their success may lead, eventually, to the Japanese launch of a solar power satellite that would explore options other than nuclear for meeting the nation’s intense power needs. What happened at Fukushima just underlines the need for space-based research on alternative power technologies. In any case, JAXA is on course for a sail-based mission to Jupiter later in the decade.

As to materials, beryllium has long been studied for sail use in inflatable, hollow-body sail concepts that Greg has explored in books like Deep Space Probes (Springer 2nd edition, 2005). One problem with it is that beryllium is a toxic poison, with all that implies for care in handling, but we do know that in the realm of high temperature metals studies, beryllium is a clear candidate. Graphene, though, gives you the best performance — in fact, Greg noted that graphene coupled with a close Solar pass could reduce trip time to Alpha Centauri to about 1000 years, about as fast a journey as it’s possible to make with a solar sail unaided by laser or microwave beaming.

Image: Greg Matloff runs through the promise, and the problems, of solar sailing.

We’re still talking futuristic concepts, given the fabulous cost of graphene today, and as far as laser or maser beamed sail concepts, we have issues like pointing and aiming. Matloff pointed out that we could not achieve the kind of tightly focused beam of sufficient power needed to fly such missions today. Laser technologies cost more than microwave, but are easier to collimate — the longer wavelength makes keeping the beam tight more of a challenge for the latter. Imagine the pointing and aiming problems involved in a concept like Robert Forward’s mission to Epsilon Eridani, where you have to deliver a beam to a sail that separates in Epsilon Eridani space to provide a deceleration option for the incoming spacecraft.

There’s much more to talk about but I’m running out of time this morning, so I’ll extend the Tennessee Valley Interstellar Workshop into tomorrow. It’s important to discuss C Bangs’ thoughts on interstellar studies and art, as exemplified by her evocative work, and to get into Les Johnson’s presentation on the various concepts proposed for interstellar flight. Robert Kennedy (The Ultimax Group) offered up thoughts on a concept called ‘shell worlds’ that I had missed when they were presented in a JBIS paper not long ago. I’ve got the paper and supporting materials now and want to get these thoughts out there, as they’re fascinating.

So much to do. I want to cover Richard Obousy’s presentation on the state of the Icarus project as well, and touch on ideas that grew out of other papers and the discussion sessions. Astrophysicist Al Jackson gave me a copy of Sentinels: In Honor of Arthur C. Clarke (2010), in which is included a story he wrote with Howard Waldrop called “Sun’s Up” which I read last night after the drive back. I had quite a night, the story entering into my dreams to produce visions of a titanic Orion-class starship that rides a shockwave like no other. We’ll have to talk about all this tomorrow.