BI you said you wanted to talk At the bottom of the lead section you have written Its promoter speculated in 1994 that the skyhook concept could be cost competitive with what is realistically thought to be achievable using a space elevator but the skyhook is not competitive with other rotating tether concepts In addition the rotating skyhook is in fact deemed not engineeringly feasible using presently available materials Regarding In addition the rotating skyhook is in fact deemed not engineeringly feasible using presently available materials That statement appears to come from Ref 3 on page 10 The full quote is If the mass of the tether alone started to exceed 200 times the mass of the payload then that was an indication the particular scenario being considered was not engineeringly feasible using presently available materials although the application might become feasible in the near future as better materials become available with higher tensile strengths at higher operational temperatures It then goes on to say As we shall see presently available commercial materials will suffice to make the HASTOL tethers needed The primary message we want to leave with the Reader is We don t need magic materials like Buckminster Fuller carbon nanotubes to make the space tether facility for a HASTOL system Existing materials will do So it would appear that you misread your reference The tether mass of 200 times mass of the payload mass is the upper limit to the problem Systems where the tether mass is less than 200 times the payload mass can be built with presently available commercial materials To further reinforce this the Conclusion to the report states The fundamental conclusion of the Phase I HASTOL study effort is that the concept is technically feasible We have evaluated a number of alternate system configurations that will allow hypersonic air breathing vehicle technologies to be combined with orbiting spinning space tether technologies to provide a method of moving payloads from the surface of the Earth into Earth orbit For more than one HASTOL architecture concept we have developed a design solution using existing or near term technologies We expect that a number of the other HASTOL architecture concepts will prove similarly technically feasible when subjected to detailed design studies The systems are completely reusable and have the potential of drastically reducing the cost of Earth to orbit space access Regarding but the skyhook is not competitive with other rotating tether concepts and A 2000 Boeing report on the possibillity of combining skyhooks with hypersonic planes concluded that In general the non spinning tether HyperSkyhook concept does not look competitive with the spinning tether concepts The full quote is HyperSkyhook In 1995 Zubrin proposed the Hypersonic Skyhook as a solution to the mismatch between the attainable atmospheric speeds of a hypersonic airplane and the orbital speeds of space tethers Since the orbital speed of the space tether decreases with increasing altitu