Another alternative is to increase the length of the upper tether to raise its center of mass and lower its orbital velocity and at the same time increase its mass so that it could handle bigger payloads. I'm assuming the upper tether is the "hanging" type that trades altitude for momentum when a payload moving below orbital velocity is attached (because I couldn't open the files - computer issue).
I'm no expert, but I'm skeptical about the tether being stable and not flipping over and spiraling along its length as a ribbon will if it's held across the wind.
Hi,Thanks for the feedback.
Some clarifications below:
Sonic Boom - This should be minimal due to the low wing loading of the inflatable wing. The sonic boom overpressure is proportional to the wing loading and the tether will have a wing loading similar to an airship. The tether should reach Mach 1 at an altitude around 30km.
The velocity of the tow aircraft depends on the radius of flight. This would be optimized for energy efficiency. For an aviation system, the tow radius would be smaller. For space launch, the radius can be extended to increase the tip velocity. The radius could be varied during flight.
The economics would depend on aviation as it's a proven market. A pair of launch systems could deliver freight for prices comparable to rail with lower capital costs. Another startup called Matternet (http://matternet.us) is developing drone based air freight. This could be a scaled up version for moving commodities (e.g. agriculture, minerals etc).
Hypersonic point-to-point travel would be a cool. Flying coast-to-coast in an hour with electric propulsion would be an awesome way to travel. I agree that developing hypersonic space planes will not be cheap.
Tether stability would depend on ballast and the horizontal stabilizer. Inflatable wings are a proven technology. Goodyear developed an inflatable aircraft for the army (http://en.wikipedia.org/wiki/Goodyear_Inflatoplane) as an example. A university group flew an inflatable wing at 100,000 feet also.
It will need funding to have professionals work on the concept. In the meantime, amateurs can build prototypes using model aircraft and prove some of the concepts at low velocities. It might be possible for amateurs to break the sound barrier with electric aircraft which would be a historic milestone.
Lets start off with a rather "simple" one: The "assumed" positioning of the system is a land based flight facility near the equator. I've another "possible" location: How about an "ocean" based system? Using a "Pneumatically Stabilized Platform" System and a variable ballest system as a "hold-down" this would avoid many of the possible "conflict" issues with normal air traffic as well as simplifying some of the deployment issues. (Just a suggestion )http://en.wikipedia.org/wiki/Pneumatic_stabilized_platformhttp://tmp2.wikia.com/wiki/Pneumatically_Stabilized_Platforms_-_PSPhttp://tmp2.wikia.com/wiki/Aquarian_SE_Downstation
30km is a bit over 98,000ft, and from what I understand sonic booms over 100,000ft most times don't reach the ground.While the wing loading per segment is pretty low I'm wondering about the fact it's going to be a rather "two-dimensional" and very long supersonic footprint. That's going to make for some interesting aerodynamics and heating issues along the length
One thing I was struck by when I read up on the concept was that there seem to be some "advantages" to the "variable" supersonic airflow along the upper tether. I recall some work done on supersonic ramjets using something similar to the "Busseman-Biplane" effect (IIRC the Napier in-wing ramjet for a proposed supersonic recon-bomber) as a rather simple but efficient engine. The problem was the "fixed" intake meant it was much LESS efficent at any speed above or below its "nominal" design speed.Which seems to me would be much LESS of an issue for auxilary/momentum make up propulsion for the wing-tether segment of the concept. As an "added" bonus if electricity is supplied to upper tether segments the "heat-added" for the ramjets can be supplied by heating elements instead of having to have "fuel" for the ramjets.Thoughts?
IMHO I'm "iffy" on the idea of the economics being "dependent" on aviation as a market because I don't see this as actually offering enough incentive to the aviation industry to make the changes needed to embrace the concept. We're talking a lot of design changes to the basic aircraft frame along with new power plants and flying methods. I hope I'm wrong here but I suppose we'll have to "see" when something gets "flying" as it were.
While the "time" factor would be a savings I agree I'm not so sure that hypersonic travel is all that "useful" for anything less than INTER-continential distances. Given the costs of designing and building a hypersonic aircraft and then building one capable of using the proposed concept...
Do you happen to have a link to the information on the University group and thier inflatable wing? (Curious)
As I recall Goodyear even had proposals for "inflatable" space craft including a "Shuttle" type vehicle it would be interesting to see what research as done on heating and reentry stress' for such vehicles.
I was actually thinking an electric control-line model would be an excellent "tow-plane" substitute and testing deployment methods for the towed-tether. Of course I'm also "thinking" that finding a place to do the testing might prove a bit of an issue even given a seriously scaled down version of the system
Hi Randy, Thanks for rekindling the discussion.My comments are below:
Agree that an ocean based system would avoid issues with air-space. There's no technical reason the launch hub could not be deployed at sea. We only need a few hundred tons of ballast, so the platforms you suggest would work. To avoid toppling the floating vessel, you could deploy two tethers operating at a 180 degree offset. The tension of the two tethers would balance the lateral forces on the hub.
At sea, you will have higher costs for electric power and it would be more difficult to provide aviation services without a nearby airport. You could build the system on a remote island with an air-strip perhaps. Another possibility is for the navy to operate the launch hub from an aircraft carrier. The navy could offset costs for jet fuel with nuclear electricity generated onboard.
I don't know how to model the sonic boom. An ocean based system would mitigate any noise issues, but I doubt the supersonic tether will be audible from the ground anyhow. The aerodynamics and heating are very difficult to model. Some physical prototypes are needed to prove the design. A computer model would have to consider aero-elasticity effects and flutter also. My personal preference is to build small scale prototypes to prove the concept.
Incidentally, if you want to break the sound barrier with a tether, it's not difficult. Just buy yourself a stockwhip. http://en.wikipedia.org/wiki/Stockwhip
QuoteOne thing I was struck by when I read up on the concept was that there seem to be some "advantages" to the "variable" supersonic airflow along the upper tether. I recall some work done on supersonic ramjets using something similar to the "Busseman-Biplane" effect (IIRC the Napier in-wing ramjet for a proposed supersonic recon-bomber) as a rather simple but efficient engine. The problem was the "fixed" intake meant it was much LESS efficent at any speed above or below its "nominal" design speed.Which seems to me would be much LESS of an issue for auxilary/momentum make up propulsion for the wing-tether segment of the concept. As an "added" bonus if electricity is supplied to upper tether segments the "heat-added" for the ramjets can be supplied by heating elements instead of having to have "fuel" for the ramjets.Thoughts?Are you proposing to extend the propulsion along the length of the wing tether? Transmitting electric power for ramjets would require heavy conductors embedded into the wing tether. I think the additional mass from the conductors would outweigh the benefits of deploying propulsion further along the tether. During deployment of the tether, each segment of the wing would need to operate at a gradually increasing velocity. It may be necessary to change the geometry of the tether as it climbs in altitude and increases velocity.
QuoteIMHO I'm "iffy" on the idea of the economics being "dependent" on aviation as a market because I don't see this as actually offering enough incentive to the aviation industry to make the changes needed to embrace the concept. We're talking a lot of design changes to the basic aircraft frame along with new power plants and flying methods. I hope I'm wrong here but I suppose we'll have to "see" when something gets "flying" as it were.If a government agency is willing to fund the system for space launch only, it would be fantastic. However, the launch rate is limited by the time required to re-boost the orbiting tether. The wing tether would be idle for most of the time. Aviation is one alternative revenue source.
A very small scale system could be funded by aerial advertising. Companies already pay high rates for blimp advertising. If the FAA would allow tethered advertising, you could make money towing advertising banners on the tether at altitudes below 300 feet. Outdoor advertising is a $30 billion business in the USA.
QuoteAs I recall Goodyear even had proposals for "inflatable" space craft including a "Shuttle" type vehicle it would be interesting to see what research as done on heating and reentry stress' for such vehicles.Inflatable re-entry shields have been demonstrated by ESA and NASA. For example, see the links below:http://www.spaceflight.esa.int/irdt/factsheet.pdfhttp://www.nasa.gov/home/hqnews/2012/jul/HQ_12-250_IRVE-3_Launch.html
QuoteI was actually thinking an electric control-line model would be an excellent "tow-plane" substitute and testing deployment methods for the towed-tether. Of course I'm also "thinking" that finding a place to do the testing might prove a bit of an issue even given a seriously scaled down version of the system Agree that control-line models would be a small-scale method to demonstrate the system. However, you are limited by the strength of the human operator at the center of the control line. I don't like standing in the middle of my experiments as it makes me nervous! My prototype has an anchor winch mounted on a wooden turntable. It's very crude, but allows some basic testing and I can operate via remote control from a safe distance.
I am going to give a ten minute talk on the Space Show this Tuesday (Oct 16th) at 1930 PST. Call-in if you'd like to join the discussion.
The FAA does not allow commercial use of UAVs at this time. They do allow experimental UAVs with a permit. http://www.faa.gov/about/initiatives/uas/uas_faq/
I don't know the FAA rules for tethered aircraft. There are tethered aerostats deployed in the southern USA (http://en.wikipedia.org/wiki/Tethered_Aerostat_Radar_System).
Makani Power has demonstrated tethered flight with their 8m 58kg prototype flying wing. Their drone flies in a vertical circle to capture wind power, whereas our design needs a horizontal circle.
There are a few potential applications that might attract some early R&D funding to develop electric air freight:1) Military air freight using UAVs launched by tethers. Air transport would avoid the risks of ground convoys, and lower fuel costs with cheap electric propulsion. Jet fuel is a huge cost for the military.
2) Mining companies could use the system to transport ores from remote locations. Electric air transport could be cheaper than building roads or rail connections to the mine site.
Space launch is a more speculative proposition. We have to prove the concept at lower speeds before trying to build a hypersonic tether.
Note the dynamic pressure is relatively low for the higher segments of the wing tether. The maximum dynamic pressure would occur between 30,000-40,000 feet in altitude at subsonic velocity. The tow aircraft would be flying at these altitudes. The aerodynamic stress on the high altitude tether should be quite low.
Randy,Electric aviation is going to be more beneficial to humanity than space-launch in the coming decades. We have to deal with climate change and developing transport without oil. Space tourism is a nice-to-have industry. Not essential for life on Earth. To get really cheap space flights (e.g. $10 per kg), you have to amortize capital costs with aviation anyhow.Here's a link to a spreadsheet with some basic economics for the electric air freight concept. You can adjust parameters like the glide ratio and the electric power cost to see the impact on the overall fuel cost per tonne-mile.https://docs.google.com/spreadsheet/pub?key=0ArN3BBRS37YcdHVkTGN0dl81NWFFSDdWcDBaTDd0MlE&output=xlsThere are a few different business models that might work. I personally like the concept of point-to-point air freight using drones. Matternet have a nice video of this vision.http://matternet.us/our-vision/Here are some other hypothetical revenue sources to get started.- Tourist joy rides to the edge of space. We could tow tourists up to 100,000+ feet so they can enjoy the "overlook" effect with a dark sky above them. - Pilot training. To reduce the fuel costs of pilot training, aircraft could be towed to altitude. This would be helpful for aircraft with high fuel consumption.- NASA / ESA / JAXA. The Japanese space industry seems particularly interested in space elevators, so perhaps they could see this as a viable alternative.- Parachuting / parasailing. A small scale system could tow parachutists to jumping altitude. Tourists are already towed by boats for parasailing rides. This could be a variant for tourists in scenic areas away from the sea (e.g. the Grand Canyon, Las Vegas etc.)- Mining/Fishing/Timber/Agriculture. Bulk air transport for resources in remote locations using tether launched drones.- Media. A reality TV series documenting the development of the system. Towed advertising banners could bring revenue.It should not require billions of dollars to get most of these concepts to cash-flow positive operation.John
What if you had the winged hypersonic component of this system carry a chemical rocket powered upper stage? Less payload and adds cost of an upper stage, but no need to have the orbital tether component.