As always going to the conference was very inspiring. A lot of progress has been made since the last conference, mainly because the money allocated to ISR by congress has arrived. Tuesday's sessions were the most relevant. I have only taken notes for Space Elevator related talks.
The big news since the last conference is that ISR finally has received the money congress had earmarked for it; 2.5 M$ I think. Carbon Designs Inc is also providing funding (2 M$) to a CNT research group at LANL. So things are slowly getting going on the funding side.
The conference website is here. I presented a paper on what happens if the space elevator breaks. You can download a preliminary version here, or get my slides from the conference (ppt) (sxi - OpenOffice) (pdf - no animations). The pictures I took are here.
The following notes are surely incomplete and full of errors, and I naturally decline all responsibility for problems that could result from information herein.
- Introduction to the geological evidence of the end of the Cretaceous.
- Use continuous adaptive mesh for their computations. Goudonov hydro technique.
- Runs at different angles.
In the morning there was a keynote address by Wendell Mendell on the direction of Bush's space program, and what place the moon should play. Then Haym Benaroya talked about engineering of moon bases and William Dempster talked about Biosphere 2. Over lunch a demonstration of a robot that finds a lava tube (a gypsum box in the ground), digs into it and pressurizes it; quite neat!
Bryan Laubscher (LANL) Brad Edwards (Carbon Designs) Others for whom I didn't seem the name written representing ISR, Spacegrant, Space Science and Engineering Institute and one other.
Brad is now working at Carbon Designs which is trying to get the CNT material developed. Little detail on how exactly. Apparently he is also interacting with ESA and some company that would be interested in working on SE engineering in Amsterdam or Spain respectively. ISR has apparently gotten their long awaited funding from Marshall.
Brad also mentioned trying to arrange for an independent evaluation of the current SE proposal to identify key points that need to be worked on. The elevator 2010 climber competition apparently has 15 teems interested in competing, not sure yet when the competition would be. The Arthur C. Clarke foundation is also showing interest.
Brad : At lots of funding meetings people talk about putting a few more billions into rockets to get a few percent improvement. Lack of vision and willingness to take risk and try out a relatively cheap option like the space elevator that much more promise. Not clear that government agencies are going to be able to make the SE happen. Need to talk to other communities (e.g. Paul Allen).
The ISR guy. Held a workshop at university of Kentucky with the leading CNT researchers. Pure CNT appears to have strength of about 200 GPa according to current research. 10 GPa appears to be within grasp within 3 to 5 years. Consensus is that the next step we need for the SE is still completely unclear. Different ways of transferring loads between individual nanotubes will probably be needed. Currently space shuttle replacement seems to be the main funding focus. We need to find a place to get funding for the basic Research.
Brad's response: There is enough funding to get to the 10 to 20 GPa mark within a year or so.
Raytheon guy in audience mentioned that his company is very interested in developing infinite length nanotubes. Brad/Bryan say Bryan are starting to get such things already as well as some guys in Japan. For now growth rates are probably still too slow.
- Inspirational movie showing the SE and its potential.
- Overview of what the SE is.
- Operating costs estimated at 100 kg/lb, ready in 15 years at most optimistic.
- SE would make space economical and opens up lots of new applications. Solar power satellites, large payloads to moon or Mars, tourism, better communications. Tourism (dinner cruises or more).
- Current activities; issues being attacked: dynamics, materials, ribbon design, radiation, applications, public awareness, engineering competitions, technical conferences, overall system design, ... So far these activities are independent and not coordinated.
- Business development. Public promotion, merchandising, investment and revenue generation.
- Future efforts. First priority is the material: basic development and commercial production. We need organized engineering efforts. We need merchandising.
- Ongoing efforts: Carbon designs to develop high strength materials. Organized engineering efforts SEDCO, James Beggs, Barry Thompson on Boards. Centers under development in Barcelona and Amsterdam. Business development. Lots of public promotion: competitions, documentary, sci-fi writing competition, etc.
- Funding: Doesn't think public funding is going to happen, but lots of private interest. May be a possibility of money through merchandising, also.
- People are more aware of highly futuristic methods (warp drive) of access to space than the space elevator. We need to get the message out to them.
- Need to show the public how the elevator can help with their goals. Growth, security, etc...
- Need to analyze the funding situation. Who are we competing with? Need people to work on grant writing.
- Need to develop more conferences, educational partnerships, magazines, etc.
- Everybody invited to contribute to the SE magazine. Has technical and layman content. Authors get magazine for free.
- Conclusion: SE is one of the most important projects of the 21st century. We need to let people know this!
- No they don't have strong enough fiber yet. But they are doing their best to push the envelope. Working with MWNT. Getting the process right is critical to getting strong macro scale materials.
- Need to improve the dispersion of fibers (i.e. they don't clump together when put in water). Critical to getting better materials.
- Functionalizing. With KOH (adds OH groups sticking out) or other methods. Methacrylation then replaces OH groups with larger functional units. This way you get very good dispersion water.
- Next you polymerize around the CNTs (Acrylonitrile). Even better dispersion, can now be used for spinning.
- Make the fiber by extruding out of a die and drawing it down to thinner diameters. Drawing very important to get better strength. Currently drawing by factor of 40 about. Smaller fibers are stronger. Down to 5 to 10 microns.
- Carbonization process used to replace the PAN (Polyacrylonitrile) by carbon. Drives out all the non carbon material by heating.
- Tensile properties. Looked at variations in E and sigma with percentage of CNT and draw ratio.
- Low draw ratio is good (fewer voids, and something else).
- X-ray study of MWNT alignment. Higher draw ratios have better alignment of the nanotubes.
- Voids are the worst defects as far as causing failure. Increasing the draw ratio reduces the number of voids.
- Interface failure. MWNT can pull out of the matrix, or inner tubes can slide out of outer tubes (telescoping). As they improve the process telescoping is become more common (this is good, it means the other problems are getting solved).
- During carbonization, the carbon tends to template itself on the nanotubes increasing the organization of the sample.
- Reduce diameter!! Fewer defects and better alignment. Need to control tension during carbonization to reduce shrinkage. MWNT may seed the growth of oriented carbon. As alignment is improved, the effect of increasing MWNT concentration will have a much bigger effect on strength.
- Trying to figure out baseline design for the tether, and test it.
- First order model based on Edwards and Pearson. Trades were run for tension, tether taper and total mass as a function of bulk density.
- Looked at various amounts of prepreg keeping the ribbon together.
- Main criteria for tether: large strength to mass ratio, needs to survive impact from orbital debris. Considered cables or ropes, but less good. Considered hoytether and ribbon with interconnects (Edwards style).
- Ansys modeling, 11 strands with 14 tape sections. Simulating breaks.
- Did testing with exist CNT materials. Difficult to get nice uniform ribbon.
- They have been making a ribbon winding machine to make the ribbon. They manage to make nice uniform ribbons with CNT or with stainless.
- They use painter's tape to interconnect the threads. Need this kind of tape so that there is actually some slippage. Then they break threads and see how things evolve.
- Goal: determine material property requirements of a SE between 0 and 1000 km.
- Considering 10 micron carbon nanotube reinforced composite.
- The question is what is the coefficient of thermal expansion? What are the temperature changes you are considering?
- Temperature profile: little annual variation near earth, more at higher altitude. I got somewhat lost in the numbers.
Larry Bartoszek, Bartoszek Engineering, Space Elevator Ribbon and Climber from a Machine Design Perspective.
- This is a sequel to his June talk, more detail has been fleshed out.
- His goal: work out the details of the 230 construction climbers. First climber is limited to 900 kg.
- He favors a design with two ribbons squeezed against the ribbon. Has made a detailed CAD model. Uses spring loading to maintain the tension on the ribbon. Uses a Schmitt coupling so that one of the wheels can move relative to the frame and still have drive.
- Guesses coefficient of friction, gets the amount of force you need to apply to the ribbon. Pretty large so you need to worry about fatigue.
- 20" roller has to rotate 63 million times to get to the top! Worried about cracking a wheel axle, or cracking the periphery of the wheel, leading to sharp pieces. 3 wheel pairs seems to be optimal.
- Not much data available on existing axial gap motors. He can't find a torque-speed curve.
- He is 3x too high on the mass of the drive system compared with Brad's mass budget. He doesn't know how he can do that.
Brad Edwards, Carbon Design Inc Allyn Smith, Ronald Morgan, LANL George Whitesides, National Space Society 1 other guy from NASA
Brad : Little incentive for existing rocket companies to reduce launch cost. If you halve the cost, you double the consumption and their revenue stays about the same.
Whitesides : Current new commercial launch prospects are very exciting.
NASA guy: we have reached the limits of ISP for rockets, we need something new to really get access to space.
Brad : His pet access to space is the SE. He wants money to do the engineering, no building yet. He isn't expecting much from NASA.
NSS guy: 2 other exciting new access to space concepts. Inflatables. Mass driver on the slopes of the Kilimanjaro.
Brad : hopefully China's interest in space will help spurn US government to continue funding space. He has even been invited to speak there.
- Elevator 2010 wants to do what air-shows did for airplanes. There will be a climber competition each year. This year it is at the end of September in mountainview, CA. They will build a "vertical solar car on steroids" that will climb using power from a xenon lamp. Will need to climb at 1 m/s, up 200 ft. Later (2006) teams will also provide the beaming system. So far 20 credible teams are signed up.
David Lang, Approximating Aerodynamic Response to the Space Elevator to Lower Atmospheric Wind Parameters.
- Introduction to GTOS and showed us the size of the finite elements he is considering.
- Aerodynamic model. Uses a model that works well for kites.
- Reminds how the elevator is a very loose spring.
- Considers a wind profile that ramps up then back up and stays at zero. Different widths were considered, and different climber positions.
- Animations with various winds. The elevator goes very near to horizontal. A climber in LEO can get pulled down. Very thought provoking! Very little extra stress in the ribbon, but huge displacements.
- Considers the effect of solar wind on the elevator.
- Forces he is considering (not all today): currents induced by E-Field, Photon Stream from the Sun, repositioning for debris avoidance, and climber activity.
- Talked about modal analysis and the transverse modes of the elevator.
- Talked about the modes and what happens after a solar event.
- Studying different cases of climbers taking off, starting and stopping in different ways. Lots of graphs, hard to take everything down. Generally, the elevator is a very weak spring, and this appears everywhere in the results.
- Coriolis effects induce east-west libration.
- Higher transit speeds induce greater libration.
- Transit timing may affect libration control.
- Climbing acceleration and arrest are manageable.
- All longitudinal dynamic modes can be excited.
D. C. Dzierski (ISR), A Case Study and Simulation Depicting Orbital Debris Encountered by the Space Elevator
- Goal: access amount of debris, and simulate an avoidance maneuver.
- What he did: Loaded the USSTRATCOM database into STK. Modeled SE with sensors at LEO, MEO and GEO. Counted hits in a 24 hour period June 1 to June 2 2005. Found one "access" during that day. Then ran GTOSS for movement of elevator base. Figure out at what time you need to move the base for the wave to be up there at the right time.
- Says the result is that the problem is manageable, but many of us in the room find there is a big discrepancy here that needs to be resolved.
- Going to talk about the origin and nature of the belts, as well as past experience. Then will talk about ways of shielding.
- Cosmic rays, solar events, radiation belts are the different sources of radiation.
- Dangerous dose 10^2-10^4 Rad.
- Inner belt: protons up to 500 MeV, created by cosmic rays. Stay around for years.
- Outer belts are much less stable, lots of fluctuations.
- Apollo 1 Rad or less.
- Low altitude is not very dangerous, problems occur when you go higher than 1000 km.
- Shielding is unacceptable, 15 T of Al to get dose of 1 Rad for 2mx2mx2m box.
- Shielding with a magnetic field. 5 MA to shield protons, 30 kA to shield electrons.
- Moving off equator would reduce shielding 3x, but reduces payload.
- Speeding up would help, but very difficult.
- Use detachable shields. Didn't understand the scheme here.
- Combination methods? Use cargo as a shield? Only practical when the elevator gets bigger (100 T or more).
Talk went well...
Talking about Space Carousels. I arrived late, and unfortunately didn't get what the scheme is, only a bunch of implementation details.
Work done with his son Jason Laubscher.
- Do simple scaling relationships exist for SE? Planet mass and radius highly correlated because of roughly common density. However the rotation rate is completely variable. Used Brad's Excel spreadsheet to study elevator for various planets and with various counterweight to ribbon mass ratios.
- Plotted SE Length vs. rotation rate. Seems to give a scaling relationship (however does not exist for length vs. rotation rate).
Talk is hard to follow, but he has a nifty design.
Essentially there is a regular space elevator that is used as a support structure for a "double serpentine loop". I.e., a second ribbon, attached to the first that loops down to the ground, up beyond GEO and then back to an anchor on the ground. Mass is distributed along the ribbon so that there is an upward tension at the bottom of the first loop. By placing a payload there, you can get the payload to be lifted. Once again the appropriate mass distribution causes the payload to be decelerated as it approaches GEO. At GEO it ends up stopping, and a down-payload can replace the up-payload. The downwards trip is the inverse of the upwards trip.
Nice features are: no energy input as long as up and down mass transfer is the same, payload can be moving a lot faster.
It is a lot more acrobatic than the standard SE, though.
- We don't know nearly enough. A lot of work still needs to be done. Looks fairly benign to humans, except upon inhalation. Experiments with large doses inhaled by mice show that nanotubes can get into bloodstream. Also mice die of asphyxiation with too large doses, but this is a different mechanism in which disease is caused by the nanotubes.
- Last year there was no real study available. This year there are tons of studies around; not all directly relevant, but many are. So far there doesn't seem to be a consensus. So far Ron recommends caution. Lots of interest, as long as funding is provided. This was not the case last year.
- Dozens of studies ongoing involving organisms from cell cultures to mice and fish. There is also a federally funded panel of experts who will try to establish baseline risk factors for nanomaterials. There was a conference in Houston in February to exchange information about the current state of nanotoxicology.
- Federal report indicates that toxicity to consumers is modest, but factory workers may be at risk. Need to spend more money on toxicology studies.
- Need to study effect on whole organisms and on ecosystems.
Panelists : Eric Westling, Bradley Edwards, David Smitherman, David Livingston, Blaise Gassend
I was on it so I only have written notes. I may scan and post them later (ask if you are interested).