Launch And Assembly

In all the proposals for sending humans to Mars, the crucial first step is launching the spacecraft into a low Earth orbit (200 to 500 kilometers up). The basic problem is that any manned craft using present-day propulsion technologies will need a huge supply of propellant to get to Mars and hence will be extremely heavy: at least 130 metric der 25 tons. Moreover, with launch costs currently as high as $20 million per ton, boosting a Mars spacecraft would be prohibitively expensive.

Aerospace companies are developing more cost-efficient rockets (such as the Delta 4) and reusable launch vehicles (such as VentureStar), but none could lift a 130-ton payload. The Apollo-era Saturn 5 could do the job, and so could the Ener-

tons and possibly twice that much. No launch vehicle now in use can lift that much mass into orbit. The space shuttle and heavy-lift rockets such as the Titan 4B have maximum payloads un-

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