NEW TRENDS IN ASTRODYNAMICS ------------------------- John Pazmino NYSkies firstname.lastname@example.org 2006 September 19
Introduction ---------- I attended the conference 'New trends in astrodynamics' at Princeton University on 16-18 August 2006. I was a delegate from both NYSkies Astronomy Inc and the New York City chapter of National Space Society. This is the third annual running of this conference, whence its short name 'Astrocon III'. The inaugural run was in 2004. While there were talks on new trends in astrodynamics at other astronomy and astronautics conventions, 'New trends in astrodynamics' is today the dedicated annual meeting for this subject. All activity was in Peyton Hall of Princeton University or at Triumph, a nearby restaurant. All activities were a level walk from each other, the hotel, and the Princeton train station. The conference ran from Wednesday, the 16th, morning, thru Friday, the 18th, evening. I went to Princeton on Tuesday afternoon and returned to the City on Saturday morning. That way I took in the entire event, even tho it meant two extra nights of lodging. I was honored to present a talk 'Gravity behaves like that?'. This talk was assembled based on discussion with Dr Edward Belbruno, conference host, in May 2006. Belbruno is at Princeton University's Department of Astrophusical Sciences and at Innovative Orbital Design Inc. He also organized the first two astrcons.
Train service ----------- I rode a comet to this meeting! No kidding, I really did. The rail coach I sat in was one of the 'Comet' series of cars operated by New Jersey Transit. From Penn Station, New York, trains leave for Princeton Junction about every half hour from dawn thru midnight or so. Both Amtrak and New Jersey Transit work Princeton Junction. While trains may skip certain stations along the way, just about every train stops at Princeton Junction. A similar situation applies for the trip from Princeton Junction back to Penn Station. Princeton Junction is the station on the Northeast Corridor line of New Jersey Transit, running along the spine of New Jersey. To get to the Princeton University itself, you must transfer to a shuttle train, the 'dinghy', at Princeton Junction. The extra ride is only five or so minutes but it would be a three-kilometer round-about walk without it. Be sure to have a ticket to 'Princeton' and NOT to 'Princeton Junction'. If you goof, the conductor on the dinghy collects the extra fare. Going back to Penn Station, ticket dispensers at the Princeton station collect the combined fare. There is a caution about this transfer. You got FIVE MINUTES, at most!, to get your butt off of the one train and on to the other. Seasoned riders poise at the first train's doors, then gallop to the other train. Follow -- and keep pace with -- them. If you miss the connection, take a seat, soak up the breeze. The next train comes along in no more than half an hour.
Besides train ----------- Princeton is served by NJT buses from all over New Jersey, Coach USA intercity bus, shuttle bus from Newark Airport, and campus minibus. I saw buses with other markings, so there could be services I missed. Air service is at Newark-Liberty airport, which in tu4n is tied to the NJT railine. Service is also at Philadelphia airport, with train or bus links to Princeton University. Princeton is nestled among several major highways, including the New Jersey Turnpike (I95). Parking is included with the hotel room and is free at the conference hall. For other parking, there are metered spaces on and off street.
Princeton ------- Princeton, New Jersey, developed out of the colonial English town and college in the center of the state. The town retains that flavor, mixed with some ersatz architecture on the campus. Streets have typical British-sounding names. Except for its 'southern' latitude, I could have been in the Hamptons of Long Island or in Cambridge, Massachusetts. Like other similar towns in the American northeast, the town and college grew into each other, with a weak stability boundary between the two. Streets and shops were filled with collegiate folk and off- campus residents. I don't know if there is a 'town-&-gown' syndrome here, like in Greenwich Village and New York University or Morningside Heights and Columbia University. The Europe delegates were awed at the overall beauty of Princeton, town and college. Universities in Europe are typicly unadorned by lawns, gardens, trees, paths. They are more like Hunter College or Manhattan Community College. There is no real campus. Luminous graffiti abounds in the sky of Princeton, with a curious mix of sky-friendly and sky-hostile outdoor lighting. On the whole, street and area lighting is pretty miserable, with glare and spray of light into the sky. Stores and other small properties, on the other hand, generally have sound outdoor lighting. Their lamps are shielded or aimed at their target.
Walking ----- You better enjoy walking. Most New Yorkers don't mind long walks, but some of us in car-country may quail. The walk is entirely on level ground with only gentle slopes. Most streets have sidewalks and ADA curb cuts. Traffic control points often have pedestrian-priority buttons. Cars travel at modest speed, allowing for casual jaywalking. However, at many corners cars enjoy, and pedestrians suffer, right- turn-on-red. Keep alert! Street signs are sometimes hidden or missing. Bone up on orienteering with a street map and the Sun. Recall that Princeton is both a town and a campus. You'll come across, in seeking directions, people who know the town but not the campus, and vice versa. From the train station to the hotel or downtown Princeton is about a kilometer. From the hotel to the conference in Peyton Hall is also a kilometer. With the mild, sunny, breezy weather, my walking was refreshing.
Lodging ----- The conference hotel was Nassau Inn, in the center of Princeton and a walk from just about anyplace in town and on campus. This hotel keeps the English coziness with lots of rugs, wood furniture, soft chairs, mellow lighting. Its appointments are thoroly modern and expertly provided. In general for any visit to Princeton this is the place to lodge at. Other hotels are beyond walking distance from campus and downtown. My room was in an annex, of modern motif harmonizing with the old structure, reached by skywalk. The room was entirely comfortable, acclimatized, and furnished with all the usual hotel amenities. A copy of USA Today was delivered each morning; more on this a bit later. For meals at the hotel, the restaurant on the first floor offered good selections at pleasant prices. I took supper there on Tuesday night and breakfast on Saturday morning.
Poster board ---------- One characteristic of mine when on travels is to use the room door as a poster board. Until 2002 I composed a hometown poster with scenes of New York City. These I collected from tourist books and ones I took myself. I pasted them in collage on a flipchart sheet, which I hung to the room door with low-tack masking tape. The hometown poster served two purposes. First it generated interest in the City, sparking conversation among the delegates. Second, it made it easy to find my room in a corridor of similar- looking room doors. Alas, my hometown poster was confiscated at the AAVSO convention in hawaii in July 2002. That's a whole other story involving World Trade Center and National Park police. I didn't yet build a replacement. For meetings since that episode, I use the room door to display my talk. I print out the slides, arrange them in order, tack them up. At these meetings, delegates in my section of the hotel love it! It may induce them to put up their presentations on hotel doors at other conferences. At 'New trends in astrodynamics' one delegate told me he showed the slides on my door to his colleagues! He explained thru them several astrodynamical features, which in fact was the whole pwah of my talk!!
Meals --- The conference fee included a banquet dinner on Thursday night and refreshments for the breaks. The latter consisted of cookies, coffee, rolls, sodas, and bottled water. These were replenished so only at the end of each day did they run out. I did my duty to rescue lonely sweets for a late night snack at the hotel. The banquet was a glatt Italian eat-'em-up at Triumph in downtown Princeton. After entering what looked like a small pizzeria, a gentle down slope brought the delegates to a cavernous consumptorium of a couple hundred seats on three floors! The place was filled with college folk and their chatter. We had a party room upstairs for ourselfs. Drink and food were plentiful, all Italian-style, no schlock-a-roni. Beers included several local blends, which I found quite hearty. Lunch was taken at a college cafeteria a ha'K from Peyton Hall. The food was tasty, filling, cheap. On my first lunch, under mistaken instructions, I missed this cafeteria. I was told to go to a certain corner and look for a huge building I couldn't miss. I did see a huge building, about 15 stories tall. I didn't miss it. And I didn't get in it! This tower was circumvallated by construction barriers. I ended up going back to downtown and getting a bite at one of the many shops there. Corrected directions worked on Thursday and Friday. I had to cross the corner first and then spot the proper, other, huge building.
Peyton Hall --------- Peyton Hall is the home of the Department of Astrophysical Sciences. It is situated next to the football stadium! There was no game during the conference. in fall of 2004 I with other NSSers went to Peyton Hall to hear Dr Richard Gott speak on space and the survival of humankind. Cheering and narration from a game running then filtered into the hall. 'New trends in astrodynamics' convened in the first floor theater. Breaks were taken in the main lobby, with refreshments, handouts, and book display. Restrooms were on this same floor. It was easiest to enter and leave thru the 'back' entrance, fronting Ivy Lane, than thru the front. Construction adjacent to Peyton Hall, for a new science hall, blocked roads on that side. More over, the back entry has a car park across the street. A side room was available for Internet link via terminals. The delegates carried out email and web searches.
Delegations --------- Most delegates, of the 100ish in all, came from various astronomy and space institutes in the United States and overseas. Countries represented were Denmark, France, Germany, Israel, Italy, Netherlands, Russia, Scotland[!], Spain, Sweden. Everyone spoke and understood English with good grammar and vocabulary. All the presentations were in English. I had trouble at first with the thick accents of some speakers, but their underlying English did come thru after a while. All delegates were thoroly versed in aerospace or astronomy, but not always in both. Part of the purpose of this convention was to bring the two 'camps' together to learn about the opposite discipline. I was the one home-based delegate! While National Space Society is a national advocate for space exploration with professional staff in its Washington DC headquarters, I represented the New York chapter. This is made of mostly home-based spacefarers. For NYSkies, a newer service in New York, lata mente supports home-based astronomy. My off-campus background was no obstacle in general commingling with the other delegates. They conversed with me as easily as they did with campus delegates.
NYSkies and NSS ------------- Delegates noted my affiliation with National Space Society and NYSkies Astronomy Inc. Unless they were aware of astronomy in New York City, they didn't hear about NYSkies. An other cause is that NYSkies is only a year and half old, quite new among astronomy services. I was floored by the occasional query about Allies in Space! Neither NSS nor NYSkies started to advertise this event. It takes place on November 4th on Manhattan. It seems that word-of-mouth is spreading thru the spacafaring community. Because I did not have in hand a signed rental agreement for the Allies in Space venue, I was careful not to mention it. I sent inquiries to the website 'www.alliesinspace.org' for latest news. As for National Space Society, I caught what could be a disturbing situation. Many of the older delegates know NSS. Many were in NSS chapters at one time or other, A couple were members of the L5 Society that preceded NSS! Because my badge noted only 'National Space Society' I reminded that I represent only the NYC Chapter, not the head office. Among the young folk, almost NO ONE heard of NSS! If they hazarded a guess, to start a convo, it was wildly wrong. NSS is a laboratory?, aerospace firm?, institute?, publisher?, and so on. Even after I gave a quick explanation, they still offered that they never heard of it. I pointed the delegates to the NSS and NYSkies handouts I left on the litterature table in the lobby. By the close of the meeting on Friday there were only scattered copies left. These I discarded.
Pluto --- Pluto would have been a routine topic at this conference, being the target of the New Horizons probe that employs many astrodynamical principles in its trajectory. Recall that USA Today was left at the room door in Nassau Inn? On Wednesday, the first day of the meeting, I picked it up when setting off for Peyton Hall. I tossed it on my bed. to read it when I get back that night. At Peyton Hall I strolled into a gaggle of delegates munching sweets and sipping coffee. One word floated above all: Pluto. One delegate showed me the USA Today. On the front page was an article, with a cartoon chart!, about the IAU treatment of Pluto. The IAU meeting was running in mid August in Prague, Czech Republic. One of its principal topics was the definition of a planet and what to do with Pluto. IAU posted a committee to offer proposals for a full vote. PLUTO IS A PLANET, THANK YOU VERY MUCH. So is Ceres, Charon, and 2003-UB313! IAU has to consider expanding the solar system to TWELVE planets, up from today's nine. Pluto was NEVER deplanetized, altho IAU tried to in 1997. The IAU committee proposed that a planet be a Sun-orbiting body that's large enough to round itself thru self-gravity. Ceres certainly fits this definition. Several other large asteroids are rounded by self-gravity, but they were not mentioned as becoming planets. Charon is now a moon of Pluto. The loophole is that the center of mass of the Pluto-Charon system is between the two bodies. Each does 'orbit the Sun', swerving from one side to the other of the path for this center of mass. Pluto would be the first true binary planet. For decades, Earth and Moon were treated as a double planet, on account of the large fraction of mass in the Moon. However, the center of mass of the two is inside the Earth. The Moon 'orbits the earth', not the Sun. This is in spite of the concave path the Moon pursues around the Sun. 2003-UB313 poses a problem. We know too little about it to say it is round. The thing could be a jagged lump, too weak to smooth out into a ball. It could be a loosely-bound aggregate of city-size boulders. Its size is still only estimated based on photometry and colorimetry. We all debated the pros and cons of the proposal. One thing was forte mente stated by every one. No one will accept an IAU-declared deplanetization of Pluto. Several balked at taking in the far outer new icy blobs as planets. Let us first learn more about them first before assuming they fit the new definition. We can later enroll them as planets if they qualify. We bantered about a corollary question: What's a satellite? This sounds trivial. A satellite is a body that orbits a planet. End of story. The wrinkle is that the body has to be individually identified and tracked. The stones making up Saturn's rings are not satellites as such. Now for the killer. This whole convention concerns such issues as temporary satellite capture by, typicly, Jupiter! Jupiter snares up comets, makes them orbit him for some years, then releases them into new solar orbits. Shoemaker-Levy-9 was discovered as a comet while in Jupiter orbit. If we found it several years earlier and it was dormant at the time, we would likely have listed and named it as a satellite. A chaotic one, like the other outer moons of Jupiter, but a moon it would be. Then, bingo!, it breaks open from the tides of its deep swingby of Jupiter. Suppose we found comet Helin-Roman-Crockett while it was orbiting Jupiter. We book, name, and follow it as a new moon of Jupiter. It, too, would be a chaotic outer moon. Then it leaves Jupiter and migrates into its own heliocentric orbit! We lost a satellite and gained a comet?
Presentations ----------- The speakers delivered their papers by digital projection or overhead, or viewgraph, transparencies. I at first planned to cut a CD, like I do for AAVSO, but then learned that each speaker must bring his own computer with the show loaded into it. With no desire to scrounge up and lug along a laptop, I stamped out the transparencies from my digital images. It was lucky that I went with overheads. I reviewed my talk on Thursday night and found I had too many slides for my 25-minute time slot. I pulled out a few extras. At the conference on Friday, before I was called to the podium, I yanked out more extra slides. With a digital show I would have frittered time in the talk to manually skip over these slides, they being embedded on the CD. This actually works out best for my repeat presentations for NSS and NYSkies. I would need a computer for them, also, to use their digital projectors. I can now use their overhead projectors. The digital presentations caused substantial deadtime between speakers. Because each had his own computer, the previous computer had to be unhooked from the projector and the new one attached. This chore ate up a couple minutes. Then there were niggling glitches in the computers. A conference technician jumped in to get things working.
Sessions ------ The presentations were grouped by broad topic for each morning and afternoon session. There were two phyla: spaceflight and celestial dynamics. I do not try to summarize many papers here, due to their complexity and number. I picked out just two, one in spaceflight and one is astrodynamics. Others I comment on as a group. Abstracts and roster of speakers are on the convention website 'www.math.princeton.edu/astrocon'. You may also visit the website of each speaker at his institution. The conference procedings will be issued around yearend 2006. There was a keynote speaker on Wednesday night, Dr Richard Gott, Princeton University. He gave a shorter version of his 2004 space and human survival talk. This may be his theme at 'Allies in space'. Wednesday night also featured the cinema 'Day the Earth stood still'. As corny as it is, it is a wonderful harmless sci-fi film. The younger American delegates recall it from reruns or remakes; us olders saw it in the flesh in the 1950s. Some of the overseas delegates were a bit wowed at the theme. In their home countries, there are very few 'flying saucer' cinemas for public entertainment. When I explained that in an other cinema 'War of the worlds' the Martians landed in Grover's Mill, a town only ten or so kilometers from the convention, they were thoroly amused.
Greg Olsen -------- Greg Olsen recounted his experience as a space tourist on International Space Station in 2005. He was a rider, not a crew member. There was little he did in running the station during his 8- day visit. Never the less, he gained a deeper appreciation for the dangers of outer space and bravery of the people who travel thru it. Olsen's tour is well known to spacefaring fans. I offer here just a few extra tidbits. The Soyuz capsule was originally built as the housing for 50-megaton H-bombs on Soviet ICBMs! It was cobbled into a human capsule in the 1960s and since has changed very little. Olsen's vessel, while newly minted, is a copy of a 40-year-old design. like riding a newly built 1965 Ford. The launch, rendezvous, docking were totally automated with no action by the capsule crew. Olsen rode up with two Russian cosmonauts. There wasn't much for the crew to do because they were crammed into a 2-meter ball with no room to move around. One feature of a Russian launch freaked Olsen out. People were allowed to wander around the rocket while it's on the pad and preparing for liftoff. Only during the countdown is the area cleared. He was treated, for example, to a bon-voyage party with civilian VIPs and family at the base of the rocket. Because the ride to ISS can take much of a full day, and the crew is sitting tightly together with no way to answer a nature call, everyone wears diapers. On ISS men use a suction tube for urine; women wear a sponge that's discarded when wetted. Both genders use a chemical toilet for bowel movements. Olsen noted that the food diet and changes in metabolism kept him from bowel movement for SIX DAYS. He was in space for too short a time to develop any space effects of health. The worse to happen is that a tourist may aggravate a existing health problem that wasn't caught in the training and testing before the flight. Two common situations, still bedevilling Russia and America, are sea-sickness and claustrophobia. Phobiacs wash out in training because they have to simulate the Soyuz and ISS ride several times. Sea sickness is handled by lots of bark bags. They must be cupped tightly around the mouth to catch every thing, then quickly sealed shut. Neither country yet found a way to tell before flight if a crew member may get sea-sick. He had to stay within the Russian part of ISS, never venturing into the US section. He wore only Russian spacesuits and spoke Russian during his stay. When tourist spacewalks start in 2008, the tourist must leave and enter only thru the Russian hatch and be accompanied only by Russian cosmonauts. The US so far wants nothing to do with space tourism. The spacesuit was custom made for his contours. Since no one else can wear it, it was given to him after the flight as a souvenir. Other cosmonauts keep their suits, too. If a cosmonaut goes back up in a later flight, a new suit is cut for him. He wanted to take pictures of the descent, there being very few good ones of this phase of a Soyuz flight. He lost his camera on ISS, a disgustingly easy occurrence in zero-G. Unless an item is positively restrained, it will eventually drift away into some out-of-reach cranny of ISS. With no camera, he contented himself with the view out of the window on the way down to Earth. The camera was found later and its pictures were sent back to Olsen via downlink. The descent capsule is the middle of the Soyuz ensemble. The retrorocket is jettisoned to burn up in the air. The round ball is filled with rubbish and other discards. Then it's jettisoned to decay. The middle section holds the crew to touch down on land. This middle module is steered by spinning and tumbling it! The air stream presses against its shifting surfaces to manoeuver the craft. As a result, the ride felt like being in a barrel rolling down a bumpy hill. This technique was the topic of one aeronautics talk in the conference. The Soyuz is packed with survival supplies and equipment for both the up and down trip. Overwhelmingly Olsen's training was on survival tactics in space, on the ride up and down, and on the ground. It can take days for a retrieval team to reach the craft after touch down in a far away desert spot. There's no restriction on repeat flights, specially now with the extra-cost spacewalk on ISS. Olsen isn't planning an other trip, but if he does, it's a new $20 million fare ($35 million with a spacewalk and extended stay). There are only two seats per year for tourists.
Edward Belbruno ------------- Belbruno presented an innovative idea about pansermia, the dispersion of life-carrying material from star to star. In his idea, a particle is diverted from an interior orbit to an exterior orbit. This occurs when the particle passes thru the weak stability boundary of the planet. The new orbit sends the particle out of the star's planet system. To reach an other star, the stars should be close and have low velocity relative to each other. Latent life would perish is the trip between stars is too long, mainly from destruction by biocidal radiation. He studied open clusters for having many close stars with low relative velocities. Altho open clusters evaporate after several tens to hundreds of millions of years. In his modeling of star clusters, the ejection speed of the material from one star is fast enough to reach a neighbor star within a few million years. This is well within the life of the cluster and the safe transit thru radiation. At the other star, the particle, in an approach path, is diverted by an outer planets via a pass thru its Belbruno region. The particle is shifted to an interior orbit where other planets may intercept it and let it deposit its life cargo. The chances of a one particle to precisely leave one star and be captured at the next is minuscule. However, the transferred material will likely be a mist, cloud, spray of particles in uncountable numbers. The chances rise into the realm of plausibility. Outside of his talk, during breaks, Belbruno noted a fascinating phaenomenon he's working on. It seems that it's easy for a comet to shift from one resonant orbit to an other via interaction with Jupiter's weak stability boundary. The transition from a 3/2 orbit exterior to Jupiter to a 2/3 interior orbit, or the reverse, seems the most common among comets. The resonance ratio of an orbit is cited in the litterature as that of the periods of the two bodies or the number or laps. Thus 2/3 could mean the comet has a period 2/3 that of Jupiter (about 8 years) or it runs 2 laps around the Sun to Jupiter's 3. In the latter case, the period is 18 years. The author must specify what the ratio means for his article. Is there some rigorous demonstration that such transfers are a general property of chaotic astrodynamics? Is there some deeper feature of gravity that favors 2/3 -> 3/2 or 2/3 -> 3/2 orbit shifts near Jupiter? Belbruno discussed such a mechanism and offered an outline for proving it in 1997. I hazarded that if such a proof can be found, it could have enormous significance in earthly applications. Start with a stable, well-behaved, predictable state of a system. It then is put thru a chaotic, random-like process. Yet it emerges into a new stable quiet state. More over, information from the initial state, in this case the resonant ratio, is carried thru the transition and modified in a simple manner into other information. The original information can be recovered by simply reversing the modification, in this case by taking the reciprocal. Hence, there could exist certain types of randomizing processes that really don't destroy information! An other extension of Belbruno's work, in a broader sense, is in electric and magnetic interference. If we treat these fields as produced by 'bodies, poles and charges, we have the mother of N-body problems! In all my own years in the electric power industry and relating to colleagues in radio-based communications, the intermingling of fields is among the most devastating problems of all. Drop ours, fadings, hum, static, crosstalk, whistle, echo, and other annoying and disruptive effects come from the mixing of these fields. I just never heard of any strong attempt to solve the electromagnetic 'N-body problem' or to find a work around for the troubles it causes. Perhaps some exchange is called for between the astrodynamists and the electromagnetic engineers?
John Pazmino ---------- My own talk related the use of home computers, like the laptops brought by the delegates, can effectively demonstrate and illustrate many of the new trends in astrodynamics. Such computers have the math and speed to do the calculations and display the graphical results as well as the large-scale computers of only a decade or so ago. The new machines are so cheap, a couple hundred dollars for the system box, that litterally any home astronomer and spacefarer can acquire one. Paralleing the hardware availability is that offering of reliable realistic software for dynamic simulations. I used dance in my talk but SolSysIm and ORSA are also good choices. Dance, short for Dance of the Planets, is a commercial product, still at sale despite its vintage from the early 1990s. ORSA and SolSyIm are free downloads. I did not attempt to compare, rank, evaluate the softwares. To simplify the talk, I used events with comets and Jupiter. These were Lexell, Brooks-2, Helin-Roman-Crockett, Gehrels-3, Oterma, and Shoemaker-Levy-9. I finished with Earth meets of asteroid 2004-MN4, or Apophis, because of their newsiness in spring 2006. I showed the concept of chaotic behavior with Lexell and Apophis, temporary capture with HRC, Geherls-3, and SL9, resonant transfer orbits with Oterma and Apophis. Brooks-2 showed a simple gravity resist via a deep hairpin spin around Jupiter. In the Q&A I learned that the term 'capture' means any interaction within the Belbruno region of Jupiter. I used the word to mean a phase of motion around Jupiter during the interaction, like a satellite. In my preparation for the talk I found only three 'satellite' events among comets: HRC, Gehrels-3, SL9. All the others were passbys with greater or lesser deflection of trajectory within the weak stability boundary. The views, all generated by Dance, were either a bird's eye view of the solar system out to Jupiter or a closeup of Jupiter within the realm of his satellites. The perspective was inertial relative to the stars, not the more usual corotating frame. The details I'll give at my repeat talk at the NYC chapter meeting on September 9th and at NYSkies on September 21st. At these meetings I'll elaborate on the dynamical concepts, showing how they are within reach of the home spacefarere and astronomer.
Solar sails --------- In the sessions on spacecraft propulsion, many papers related to solar sails. At first, in the mindset of orthodox rocketry, solar sails seem like a silly way to travel about the solar system. In fact, they could, if perfected, be a useful cheap, low mass/fuel means of getting from planet to planet. The problem to hand is that for the foreseeable future, a spacecraft's ENTIRE provision to survive its flight must be taken on board the craft at launch from Earth. This burden includes rockets for manoeuvering in space, entering orbit at other planets, and transferring from one target to an other. Such rockets are large, heavy, complex. They are prone to failure or detonation. Their fuel must be compounded, stored, handled, with substantial safety risk. In the initial applications of the Belbruno technique to spaceflight in the 1990s, the rocket failed in some way. The craft was left with only a minimum of manoeuvering. That was all the umph needed to ride the weak stability boundary and complete the original mission. Inverting the situation, endowing the craft with a tiny thrust system, the mission must exploit the Belbruno trajectory. Solar sails receive unlimited energy from the Sun, but deliver only the barest minute power output as thrust. In this way, space missions can be vastly cheaper, smaller, lower mass/fuel, less complex, safer. In turn this means a cheaper, simpler, smaller launch vehicle from Earth. The downside is that the trip takes forever. An example is the SMART-1 craft, which took some 15 months to reach the Moon. (It used tiny jets, not solar sails.) The mission, once arrived at its target, procedes just like a conventional rocket-driven one. SMART-1 is now doing superb mapping of the Moon. The talks were a mix of trajectory planning and engineering of the sails. Some cunning mechanisms were shown for packing the sail into the launch vehicle and then unfurling it in space into a sheet the size of an airport. One design was a vessel -- including the payload - - that weighs 14 grams per square mater of sail. Ordinary photocopy paper weighs 75g/m2; thin typing paper, 40. A similar theme was expressed in papers promoting assorted ion and radiation propulsions. The scenario is the same, fitting a ship with a low fuel, low thrust device and riding a Belbruno path..
Awards ---- At the Thursday night banquet, Belbruno presented awards for two speakers, Dr David Dunham and Dr Pini Gurfil. Dunham, Applied Physics Lab at Johns Hopkins University, provided substantial logistics and support for the conference. He also spoke at the convention about the Belbruno trajectory employed by the upcoming STEREO mission to monitor the Sun. Home astronomers know Dunham for his decades-long study of grazing occultations of stars by the Moon. One of the purposes of this work is to improve te orbit theory of te Moon, which eventually incorporated elements of chaotic dynamics. Gurfil, Department of Aerospace Engineering at Israel Institute of Technology, presented an intriguing perspective on chaotic astrodynamics thru gauge theory. This is a new and major advance of quantum gravity theory, which so far is applied to 'regular' gravity situations. There is as yet no complete integration of gravity into a quantum system, but any successful melding must explain the features of capture and chaos. Deeper down, the application of a tool from quantum mechanics successfully in gravity mechanics could lead to a unification of the two disciplines. This was a hope of many scientists, including Einstein, for quite a full century.
Conclusion -------- This was a scholarly meeting, yet many talks were well within reach of the home spacefareer or astronomer. Other papers were, well, as high as the Moon, Mars, and beyond. Many papers worked thru various aspects of the Belbruno theory, for trajectories near the Moon and Jupiter. Some used real natural examples, like I did in my paper; others, hypothetical particles. The weak stability scheme is a stunning example of chaos in nature. The interaction of the gravity fields and the exquisite sensitivity of a trajectory thru them to its starting conditions, can generate wildly different paths. Which of the possible results actually occurs can not be predicted because it is impossible to know in advance or later replicate the exact starting state of the trajectory. Spacefarers and astronomers since the 1990s had to expand their litteracy, if not expertise, into chaos theory. This applies to home astronomers and spacefarers, not just those on campus. My talk explained how home computers are quite capable ot demonstrating chaos in the interaction of comets with Jupiter and an asteroid with Earth. Hence, there is now in hand, or in a nearby bush, the tools for building this litteracy. Unless you acquire some awareness of the new trends in astrodynamics, you'll be mired in the low Earth orbit of brute force space travel. Was 'New trends in astrodynamics' worth it for me as a home astronomer? Yes!, for the cultural enrichment from the other delegates, new ideas to explore -- Ed and I chatted about them during the breaks -- and the overall holiday value of visiting Princeton.