Here are the notes I took at the Second Annual Space Elevator conference that took place September 12th to 15th 2003 in Santa Fe, New Mexico. I was only present for two days of the conference, so that is all I will be able to cover. Most of the information here is in the slides that were shown at the conference, and which should be available soon on the ISR website. I expect that these notes are full of errors and misunderstandings, and I of course decline all responsibility if you get into trouble for believing anything that is written here.
That being said, the conference was a very good experience. I feared that there would be some counterproductive freaks preaching strange propulsion concepts that they had dreamed up during the night, and was pleasantly not to find any. The atmosphere was very relaxed, with a lot of dialogue between the speakers and the audience. My only complaint is that a lot of the information was not very recent, though ISR now appears to be getting funded for Space Elevator research, so things should be moving ahead.
Short talk. Talked about the press coverage that the SE is currently getting. Mentioned the problem of space debris. Got assorted questions about his writing, and on his opinion on various technical aspects of the Space Elevator. The answers were rather high level but generally got a lot of laughs out of the audience. When asked, Sir Clarke said that if given the opportunity arose for him to take a ride on the elevator he would be "ready and willing" to go, and his choice of final destination would be Mars without any hesitation.
After a quick break, the core of the conference starts.
Dr. Edwards talked first.
- Usual welcoming remarks. A few words on Santa-Fe and what it has to offer.
- Mentioned Bruce Makenzie who wants to start the Space Elevator Institute to coordinate volunteer effort on the SE.
- History of SE idea: science fiction, and previous SE efforts.
- Overview of SE. 20T, 1 week travel time to GEO, anchored at see.
- Ribbon design. 10-20 micron diameter fibers with tape sandwiches. Initial width 20 cm, final 1m.
- The usual deployment scenario.
- Power beaming.
- List of problems that the elevator has to face (the usual).
Brad's talk was very brief, and essentially said stuff that is in the SE book and the NIAC reports.
Talk followed by an ISR video that presents the SE. Nice flashy video, should be downloadable soon, presumably from the ISR website.
Quick question session while Dr Bryan Laubscher irons out powerpoint issues.
- Is space debris going to be such a problem, given that we already have some tether experience in a debris environment.
Dr Laubscher talked next.
- We should build the elevator as soon as possible. So prepare for it before the materials are ready.
- Comparison with transcontinental railroad. Differences are: cable hasn't been tested at a smaller scale before. Immature technologies. You can build a short profitable railroad. There is no similar stepping stone for the SE.
- When the transcontinental railroad was build, going to the west of the US took 25 times less. SE should have same effect on launch rate, risk and cost in the space industry.
- Goals of the conference: identify challenges, discuss solutions, prepare to write proposals, reinforce the importance of this new technology.
- Asked for opinion on motto: "The Space Elevator, one hundred thousand kilometers of new technology."
Rodney Andrews first:
- Picture of a 5km ribbon of 2% Carbon Nanotube (CNT) material.
- He works mainly with multi-walled CNT. A few pictures. They make 25nm diameter tubs, 50-100 microns long. Depends on the method of making them.
- CNT is the continuation of a trend from graphite to graphite whiskers, to nanofibers, to multi-walled and then single-walled CNT. When you compress these structures, the smaller forms become more stable.
- His group produces high purity CNT arrays. 1.25 kg/day, 95% purity. The 5% that remains is iron catalyst that can be removed easily. So far they are using all their production of CNT internally.
- Predicted properties (SWCNT) : strength 300-1500 GPa, elastic modulus 1000-5000 GPa, strain to failure.
- Good news. Berkeley, Zettle Group. AFM to measure MWCNT. Tensile strength 150 GPa, elastic modulus 1TPa. So MWCNT are strong enough for a 100GPa composite to be plausible.
- The issue in composites is transferring load form polymer matrix to CNT. Different approaches for attaching to nanotubes. Van der Walls forces, wrap polymers around the CNT. Covalent attachment, but might weaken the CNT.
- Failure modes of CNT. As cracks form in the polymer, the CNT take up the load and hold. But inner tubes might get pulled out of outer tubes if outer tube of WMCNT fails (telescopic failure), can we bond to the inner tubes of a WMCNT? Poor adhesion of the CNT to matrix, it gets pulled out (pull-out).
- Currently we observe pull-out failure, but we would like to see the CNT break.
- Cool pictures, you can see a CNT wrapped in a polymer sheath. But very low adhesion between polymer and CNT.
- Baughman Group - UT Dallas. Gel Spun SWNT bundles, 100m long, 50 micron diameter, 60% by weight of SWNT. Properties 1.8GPa strength.
- Functionalization of CNT by various side groups is being tried. Seems to be improving properties.
- Oxidative opening of MWCNT. Open the end of the CNT, and chemically attach to the the carbon at the end.
- Conclusions. Nanotubes do have strength greater 150 GPa. Challenges exist in stress transfer, controlling the interface and chemical functionalization. Work is progressing in many groups.
- CNT with short composites have low strength and low toughness because when adhesion is low, there isn't enough CNT surface to transfer load from CNT to matrix when the matrix cracks. If adhesion is too good, material becomes brittle because there is stress concentration at the CNT fibers. In short composites, there is a limit of about 20% in volume of CNT, which limits composite strength.
- Fundamentally different approach. Make really long CNT fibers (Continuous-CNT composites). Use weak interface between nanotubes to reduce stress concentrations. This way you get good load balancing and good load transfer between nanotubes. Los Alamos National Labs is trying to produce long CNT fibers. Note typical strength of interface between CNT and matrix is 50 MPa (useful for homegrown calculations of how long you want the fibers to be :-) ), this information is from Rodney Andrews, who was sitting just in front of me.
A flurry of questions occurred here, first Dr Zhu was answering, and then Dr Andrews joined in. I wonder how much of Dr Zhu's talk remains and if he will get to it.
He didn't, we went to the break.
My talk went quite well. I got a lot of good questions which suggested to me that they didn't find me dull or incomprehensible. I hope to get my hands on a video of myself so that I can get a better impression of my performance. The slides for my talk are here.
Francis Canning's talk.
- Coriolis: as the climber goes up, the cable has to lag so that the Earth can accelerate the climber laterally.
- Talked about the oscillations that a climber would cause.
- Talked about David Lang's GTOSS simulations.
A question was asked and I moved to my notepad to try to answer it. I didn't follow Francis's talk too much.
- Cable made of two components: fibers and interconnects. 50 GPa tensile strength used for fibers. Interconnects 1GPa desired, placed every 10-20cm, goal is 1% transfer of load per interconnect.
- Damaged fiber dynamics.
- Recoil analysis (what happens if a thread gets broken).
- You want to optimize the interconnects: spacing, durability in the space environment.
- Alternative designs.
- Finite element analysis is being done on COSMOS. Modeling individual fibers, and modeling the ribbon as a sheet. Comparing with experiments on existing materials to see how valid the modeling results are. Also using tools such as DYNA2D/3D, EPIC, HITF Hydrocode. Need for debris tracking to avoid debris.
- Feasibility studies. High velocity collisions planned at JSC and MSFC. Atomic oxygen effects at MSFC and ITL. Radiation effects at -- oops...
- Additional concerns. Wear of climber on ribbon. Stress of climber.
Covered the usual hazards section from the book/report.
- Overview of Active Vibration control. What sensors to deviate from simulations.
Dr Jorgensen. The magnetospherics.
- Magnetosphere. Magnetospheric storms about 10 times per year. Reconnection events several times per day, which cause various currents.
- Electrostatic field caused by solar wind.
- The space elevator is sweeping magnetic field lines, as there is a small component that is not rotating with the earth. Quoted field strengths that can be expected.
- Estimated to current in elevator from 3 microamps to 3 amps.
- Resistive heating isn't a problem. Only a couple of degrees at most.
- Electromagnetic force between .1 and 300N on whole surface of cable. Would result in displacement from 6m to 20km.
- We have little experience sending humans through the radiation belts.
- Radiation shouldn't be a problem for the CNT [Edwards]. But the radiation belts are nasty for satellites. Shielding the electronics is a concern.
- Radiation on passengers on SE would be prohibitively high, especially at low space elevator velocities. How much shielding would be needed to protect humans? Some proposals of "radiation belt vacuum cleaners", a satellite that would sweep particles out of the radiation belts into the atmosphere, reducing the radiation to acceptable levels.
Steven E Patamia on oscillations with brief boundary conditions.
- Counterweight is mobile. How does this change the modes?
No notes here because I was busy checking his calculations which didn't agree with mine.
- Various power methods have been considered. Nuclear RTG, too heavy and politically unacceptable. Solar panels don't have enough power and get eclipsed at night when the climber is low. Conducting electricity through the cable isn't possible due to excessive resistance. RF power beaming tends to be too large to get good focusing. Optical power beaming seems best so far.
- Beam system by Bennet Optical. Free Electron Laser designed for other. 13m segmented mirror and adaptive optics.
- GaAs photo-cells, 92% efficient at 840 nm. Less than 100kg for the receivers (missed the exact number).
- Cloud cover at the beaming site is low, but need multiple beaming stations to get continuous coverage, and also to run multiple climbers.
- Safety: the beam is eye safe when you are far from the focus point. Quote from Bennet: the laser is designed and ready to be built. Laser imposes large (150m) platform to support it. High stability is required.
Roy Goeller (LANL) on Solar Cell performance.
- What is the temperature rise of the solar panel due the power beaming? Finds an equilibrium temperature of about 100C above ambient. But that causes degradation of performance of solar cell around 37%.
- Goal of systems engineering: enable space elevator through engineering insight. Very pragmatic principles.
- Systems engineers need to see the big picture, and think out of the box. A system is more than the sum of its parts.
- Will require planning, tools and good communication to make the SE system possible.
- System architecture is critical to making a large system like this possible. Need to define the problem and solve it. For now there are tons of unknowns in the SE that need to be understood. How can you understand a problem when there are so many unknowns? In a project this huge you need everybody working in phase, so you need a common vision guiding all the available efforts.
- The system architect is pulled between performance and cost, and has to make those ends meet.
- Customer's needs for SE: How long to GEO? Where do we want platforms along the cable? How many elevators would be needed? etc...
- Some tradeoffs: Existing vehicle to launch cable, or new? Electric or chemical propulsion? etc...
- Example of tradeoff: electric vs chemical propulsion. Electric slower and less mature, but lighter thus lower launch cost. Consequences on cost and speed of deployment.
Dr Swan, the example of making the space elevator survivable.
- Remediation strategies for debris. Ribbon Design, Multiple base legs for the elevator. Ribbon redundancy (extra strings that are not always used).
- Other aspects. Introduce "Zero Debris Creation" policy. Attempt debris reduction and elimination. Improve tracking. Impose that satellites only cross equator at certain latitudes.
- Various aspects can be prioritized to give a good description of how to solve the debris problem.
- So far, nobody is thinking about this.
- Climber has: tread traction drive system to climb the ribbon without damage; electric motor to drive traction system; powered by solar power; splices ribbon to build it up during deployment phase; limited ground control.
- Climber is slow, so it operates a long time in the troposphere. They have to deal with weather and temperature variation. They also operate in the stratosphere, pretty benign. The thermosphere (includes ionosphere), -100 to 1200C for 2 to 4 days, spacecraft will get charged. Magnosphere during 495 hours, with lots of problems to deal with, but some experience from satellites.
- Climber has to run 100000km reliably (think about your car) in various environments. Will need redundancy. Must not damage ribbon. Weighs 7T on ground. Will get energy from ground. Can be used for launching payloads or for repairing/building cable. Need control from ground. Need mass producability and flexibility for various payloads. Must be powered efficiently. Beyond GEO, must do everything in reverse.
- Different missions imply different designs. Cable layer. Payload carrier. Diagnostic/Repair. Construction. Tug. New Elevator carrier. Round-trip Climber that would go up one cable and down another. Science climber bearing active experiments.
- Nobody has designed crafts like these climbers. There are plenty of challenges and plenty of constraints.
- Need to coordinate all the people doing research on the Space Elevator and improve communication. Need to help students find funding for projects related to space elevators.
- Need to give more power to volunteers who are willing to spend a few hours per week.
- Need to help research find each other and form virtual research teams. Perhaps we could get some useful software on the web. We might need some funding for these teams.
- Public outreach. Inform the public and stir up excitement.
Mention of the International Astronomical Conference that will have space elevator sessions.
- Contacts with universities worldwide. A number of projects.
- NIAC charter. Independent of NASA. Focus on revolutionary concepts. Operate over the Internet. To get funded, need succinct technical proposal and peer review.
- "Don't let your preoccupation with reality stifle your imagination". What is revolutionary? How do you distinguish between a revolutionary idea and one that isn't plausible.
- Time frame is 10 to 40 years into the future.
- Phase 1 award: $50000 to $75000, phase 2 award: $400000.
- So far 107 concepts have been funded by NIAC. Examples: Mini-Magnetospheric plasma propulsion system, Used for propulsion and provides radiation protection. Electromagnetic formation flight. Antimatter driven sail for deep space. Inherently adaptive structural systems. Enemopter vehicle design, a vehicle for use on the Mars surface. Solid State Aircraft. Global Environmental MEMS sensors, to take measurements over the Earth. Chameleon suit to liberate human exploration of space environments. Astronaut bio suit system for exploration class missions. Cave subsurface constructs for Mars Habitation and scientific exploration. Very large optics for the study of extra-solar terrestrial planets. X-ray interferometry. Laser trapped mirrors in space.
- Short video of a robotic Mars exploration mission with little flying surveying robots.
- NIAC has more than 80 publications. The Space Elevator is one of NIAC's stars.
- The future: NIAC contract renewed in July 2003 for another 5 years.
Michael Laine commented on a video on a ribbon climbing competition (http://gotrobots.com).
Joe Gardner (ISR):
- His goal is to determine where the anchor should be located on Earth.
- Want to make database (GIL -- Global Information System??) of Earth features and then pick best location from database.
- Issues include: Temperature, cloudiness, precipitation, winds, cyclonic storms, lightning.
- Atmospheric dynamics, wave-mean flow interactions. Lots of things going on the atmosphere. All must be taken into account to pick a good location.
- Structure of Earth's atmosphere. Troposphere, stratosphere, mesosphere, thermosphere. The structure of these layers isn't as simple as the terminology suggests. Very dynamic processes present. Must be taken into account.
- Temperature in Earth's atmosphere. T goes down in troposphere, up in stratosphere, back down in mesosphere, and then back up in thermosphere.
- Surface temperature and temperature at altitude is going to help determine location for anchor.
- Cloudiness must be as small as possible. Interesting locations: Sahara, Australia. Generally southern hemisphere has simpler climate.
- Winds are tamer near equator.
- Jet streams need to be considered.
- Clear air turbulence needs to be considered (seems to be a winter phenomenon).
- Cyclonic activity to be considered.
- Lightning. Nice locations in Indian ocean, West of South America.
- So far they have just begun to scratch the surface. So far there are a few types of areas that have been excluded, and some candidate locations have been suggested.
Lots of discussion on anchor location ensued, with questions from the audience.
Dr Allyn Smith:
- Major deployment phases: boosting to LEO, orbital transfer to GEO, deployment of ribbon. Will cover nominal approaches and alternatives.
- Mass to LEO: 80 to 186 tons. Ribbon, spacecraft, MPD,... 4 to 9 Delta IV heavy launches, a shuttle launch to assemble at LEO.
Lots of questions.
- Orbital Transfer from LEO to GEO. Three options: Fast and expensive with boosters. Slow and cheap with MPD and beamed power, would need 3 beaming stations and 137 days. Compromise with MPD and MMH/NTO combination, still needs 3 beaming stations and 91 days.
- Major questions in orbital transfer: Chemical or electric propulsion? Beamed power or fuel? Automated controls or directed? Technology needs? What are the available cost, schedule, and design trade-offs?
- Ribbon deployment from GEO. It is feasible, the major question is how to optimize. Move spacecraft to 100000km as you deploy the cable to remain synchronous with Earth's motion. Need to impart downward force on ribbon until gravity gradient takes over. Impart momentum to spacecraft. Maintain constant angular rotation. Anchor the ribbon quickly. Capturing the ribbon at the base station is an interesting question as well. Lots of problems here. 45 to 71 days.
- Nanotube fibers might cause problems similar to Asbestos. Refractory, extremely high aspect ratio. The human body has never been subjected to this.
- Mechanisms of injury: Surface contact (skin), ingestion, inhalation (fibers and dust can be toxic to the respiratory system; the effects of extremely small fibers in the tissues of the body are unknown).
- Environmental health. Large quantities are and will be manufactured, the manufacturing processes must take this into account. How do we dispose of nanotubes? Transport to landfill, possibility of leaking into water stream, etc. If elevator fails possibility of dust, nanotubes and matrix material in the environment.
- Human health. Not much information. Animal studies are just starting, there is NO human data (this is a GOOD!). It is likely that if the fibers are similar to asbestos, we will have similar problems to asbestos. We don't really know what effect extremely high aspect ratio, small, refractory fibers might have on human tissues.
- If you work on nanotubes, be careful! Use a hood, don't be a Guinea pig! Don't abrade surfaces without precautions.
Dr Yancey, M.D.:
- There are concerns for people who work with nanotubes (production and use). In the 30s Asbestos was used in construction. 20 years later it was discovered to be a carcinogen. Whole list of problems that asbestos causes, and that nanotubes might cause. So we need to find out more.
- Fiber health science. Recent literature search on CNT did not reveal a single study on toxicological considerations and mitigation. Another literature search found a few animal studies and one study on the effect of nanotubes on human skin.
- Description of where fiber deposition can occur based on length and diameter (lots of information but not much on the slides, so hard to take notes). Macrophages are responsible for removing any debris that ends up in the alveolae. If debris is too large, the macrophages are ineffective.
- In toxicology, you consider a number of things. Dose: how much before it is a problem? Dimensions: can they get in? Must be long and thin to be inhaled (less than 3 microns in diameter) and not be removed. Durability: how long do they stay? If fibers are dissolved/broken down in the lung then they are not a problem. So in the case of CNT, durability is going to be a very important factor.
- If fibers are not respirable or non durable, then there is no problem. If they are respirable and durable then they must be evaluated for biological activity. Described in detail the mechanism by which asbestos is toxic.
- Many government agencies are calling for studies on nanotube toxicity, notably EPA.
- Slides of normal lungs (X-ray, picture, cross-section, ...).
- So far $570k has been spent or R&D efforts. Need at least 2 years of engineering development before construction can be considered.
- Next phase of the program. Need about $60M over the next few years to work out details and decide whether the project should go ahead.
- Current total cost estimate is $6.2B. Launch to GEO $1.02B, cable production $390M, Spacecraft $507M, Climbers $367M, power beaming stations $1.5B, anchor station $120M, tracking facility $500M, other $430M, contingency (30%) $1.44B. This is only technical cost. Legal costs are not here, regulatory costs are not here.
- Initial cost analysis based on available component and operational costs. Detailed cost analysis needs to be completed. So far only technical costs have been considered. The final cost will depend on the method of construction.
- Budget for second elevator. Launch cost drops significantly, the spacecraft is no longer necessary, the tracking facility is no longer necessary. Estimated total $2.17B.
- What is our goal? Profit or glory? Most of us want the glory, but profit will be needed to make it happen. Currently space is too expensive. $500B has been spent on space, but all we have is a transportation hobby, not a transportation system. The transportation system must become an incidental part of the cost of space projects for space to really become accessible. The space elevator has the potential to achieve this goal. Better use of workforce, only lift what we need to lift, energy coming cheaply from the ground. Cost of getting to GEO is only 55 cents in energy terms, how close can we get to that in a real launch system?
- To recover the costs in 20 years, need to get 1M per day. If one launch every 15 days, then $1150/kg. If one every 70 hours then $224/kg, but actually $400/kg if we recover climbers, and $300/kg if we throw out climbers. Second cable can improve that by allowing you to send climbers back down, which leads to $233/kg if you recover climbers or $183/kg if you throw out climbers, or $150/kg if you charge to bring payloads down. If you build a pair of $200kg cables, then you get down to $51/kg.
- Fractional Load Packing (maximum number of climbers on cable at a time): 6*C/M (C is cable maximum mass, M is mass of climber). This formula holds if mass of climber is less than C/3. With this in mind, we space climbers 10 hours apart and get down to $13.5/kg. With improved processing efficiency, we can get down to $6/kg. Compare all this with the power costs of $2.77/kg.
Lots of skeptical questions in the audience pointing out many missing costs in the analysis. The values are probably off, but the trends are probably valid.
- This would be a transportation where cost is incidental.
- The National Remote Sensing and Space Law Center at U of Mississippi has issued a report that deals with international air, space and maritime law issues. Assumes that SE anchored on ocean platform, passengers transported by ship, communication by radio.
- Outer Space Treaty. The treaty on principles governing the activities of states in the exploration and use of outer space including the moon and other celestial bodies. Issues addressed by report. Is the cable or the counterweight a "space object"? Are payloads "launched" into space? If the SE deorbits, will extraterrestrial matter be introduced into the Earth's environment? Will the elevator have a "potentially harmful interference with activities of other state parties"? Might make it hard for the SE to get insurance, and consequently a license to operate. So lawyers will have to be brought in early to address these issues.
- The liability convention (the convention on international liability for damage caused by space objects, sept 1972, 80 nations). Can SE developer be held liable for damage due to the cable? Due to payloads that have been released?
- Delimitation. None of the treaties defines "outer space". The elevator will probably be covered simultaneously by many different sets of laws.
- The Chicago Convention. Can the state of registry prohibit air traffic from flying near the SE? Answer seems to be yes.
- The Law of the Sea Treaty. Can the SE developer establish a safety zone around the ocean anchor platform? Answer is yes.
- US Licensing and Regulatory issues. Three agencies: Dept of Transportation, Dept of Commerce, FCC. Other relevant agencies. Dept of state, EPA, USAF, US Coast Guard, FAA, AST.
- SE developers would need licenses. Is each payload a separate launch? Range safety issues? What if developer cannot get insurance? Might the US government change the risk sharing liability regime in the future?
- Might the US deny licenses if foreign entities involved in launches? Would the DOE have to review the project (because of power beaming)? Would the FCC have to review the project? Yes because of comm with satellites. Will there have to be an EPA assessment? Are there other issues related to maritime transport of payloads to the anchor platform?
- What happens if there is a formal relation between NASA? In that case the Space Act becomes applicable.
Dr. Brad Edwards:
- Who will build the first SE? Military: how would it be used, would that be perceived as a military threat? Private: who would be serviced, what limits would be placed on what can be launched? Unregulated access to space makes many people nervous. National: if one nation builds will other nations be concerned, will this be a project for international cooperation? Cooperation between US and Australia might be an interesting possibility. Would competition be a good driver for SE construction (cf. space race in the 60s)?
- The SE project needs a champion to take up the legal and regulatory issues to work out the details. Perhaps universities and law schools can be involved.
Questions about satellite slots and such.
- Large scientific and engineering project. Lots of data will be generated. Need to organize an maintain contributions. Proposed answer is a database that would integrate all that data. Would contain: components, analyses, current design (baseline), interdependency of systems, cost and schedule.
- Components: commercial off-the-shelf, customized off-the-shelf, brand new components (along with IP/patent info, data-sheets, ...). All available information on components would be integrated.
An analysis of the other stuff that would be in the database followed.
- Organization of the data.