[单项选择] Space Travel in the Future Space flight may be about to undergo a transformation far more radical than anything planned by national or international space agencies. In the next fifteen years or so , there could be a fleet of fifty space-planes carrying a million people into orbit about the Earth each year, at $ 10,000 per head. A prototype of spaceplane could be up and flying within five or six years. Perhaps surprisingly the main obstacles to realizing this dream are neither technical nor commercial. Space transportation is expensive and risky at present because all launchers so far have used large throw-away components that are based on ballistic missile technology. But the technology already exists for a prototype of a fully reusable, aeroplane-like launcher, and its development costs need only be equivalent to about two space shuttle flights (about $ 1,000 million). The cost per prototype space-plane flight would be about 1 percent of the cost in t
A. Y
B. N
C. NG