A project likely to evolve in the near or intermediate future is space

tourism. Today space tourism has become a pure commercial activity 【M1】________

that would not have to rely unpredictable government decisions. It would 【M2】________

therefore put space operations on a much more solid, dependable footing

and would enormously expand man’s space activity. If some people see 【M3】________

space tourism as a potential multibillion-dollar business, difficult

technical problems remain to be solved.

First, in order to fulfill the dream of space tourism, a manned

reusable rocket like the Venture Star must be built. Then, the second 【M4】________

serious problem must be addressed: Even today’s most-advanced space

rockets are able to lift only about 2. 5% of their launch weight into

orbit—a ratio that has hardly changed in the last 40 years. But it is 【M5】_________

simply impossible to find other alternations other than a rocket. This 【M6】_________

unsatisfying fact is a result of the limits of material characteristics and

chemical power sources, and there is no indication which any 【M7】_________

fundamental breakthrough can be expected in these areas in the

foreseeable future. Then these who have long-cherished dreams of space 【M8】_________

tourism have to wait forever.

Operational costs may be somewhat reduced by the use of air-

breathing engines to help a reusable rocket penetrate into the earth’s

atmosphere. Today the highest cost attainable to lift a payload into orbit 【M9】_________

is more than $ 4,000 per pound; the price of a ticket to space would

have to be at least $ 50,000. It is questionable whether a sufficient

number of customers could be tempted to pay so a high price for a short 【M10】________

trip around the world.

【M1】