have speculated on the profitability of mining metal from asteroids. According to some estimates, a one kilometer-diameter asteroid would contain 30 million tons of nickel, 1.5 million tons of metal cobalt and 7,500tons of platinum; the platinum alone would have a value of more than $150 billion at 2008 terrestrial prices. Space elevators A space elevator system is a possible launch system, currently under investigation by at least one private venture. There are concerns over cost, general feasibility and some political issues. On the plus side the potential to scale the system to accommodate traffic would (in theory) be greater than some other alternatives. Some factions contend that a space elevator — if successful — would not supplant existing launch solutions but complement them. Non-launched efforts Failed spaceflight ventures After earlier first effort of OTRAG, in the 1990s the projection of a significant demand for communications satellite launches attracted the development of a number of commercial space launch providers. The launch demand largely vanished when some of the largest satellite constellations, such as 288 satellite Teledesic network, were never built. In 1996, NASA selected Lockheed Martin Skunk Works to build the X-33 VentureStar prototype for a single stage to orbit (SSTO) reusable launch vehicle. In 1999, the subscale X-33 prototype's composite liquid hydrogen fuel tank failed during testing. At project termination on 31 March 2001, NASA had funded US$912 million of this wedge shaped spacecraft while Lockheed Martin financed US$357 million of it. The VentureStar was to have been a full-scale commercial space transport operated by Lockheed Martin. In 1997, Beal Aerospace proposed the BA-2, a low-cost heavy-lift commercial launch vehicle. On 4 March 2000, the BA-2 project tested the largest liquid rocket engine built since the Saturn V. In October 2000, Beal Aerospace ceased operations citing a decision by NASA and the Department of Defense to commit themselves to the development of the competing government-financed EELV program. In 1998, Rotary Rocket proposed the Roton, a Single Stage to Orbit (SSTO) piloted Vertical Take-off and Landing (VTOL) space transport. A full scale Roton Atmospheric Test Vehicle flew three times in 1999. After spending tens of millions of dollars in development the Roton failed to secure launch contracts and Rotary Rocket ceased operations in 2001. On 28 September 2006, Jim Benson, SpaceDev founder, announced he was founding Benson Space Company with the intention of being first to market with the safest