by David Warmflash

Created on: July 30, 2009   Last Updated: July 31, 2009

Currently, the focus of the NASA cost-benefit debate is Project Constellation. Consisting of the Orion spacecraft, Ares I and V booster rockets, and Altair lunar landing craft, Constellation is slated to replace the space shuttle program, known as the space transportation system (STS), as NASA's means of carrying astronauts into space. The transition will take place during the next decade.

There will be a gap of a few years, during which NASA will depend solely on the Russian Space Agency for delivering astronauts to and returning them from the International Space Station (ISS). Looking at the new system, anyone older than 50 will be reminded of the Saturn-Apollo program of the 1960s and 1970s.

Orion, also called the crew exploration vehicles (a name which has been criticized, since the crew is not an object of exploration) resembles the Apollo command-service modules that carried astronauts to the Moon and to the Skylab space station and that linked with a Soviet Soyuz spacecraft during the final Apollo mission.

Orion is bigger than Apollo, to be sure, conceived to carry up to six people, though NASA announced recently that it will be scaled down to four, whereas Apollo could carry only three. And, there are several other improvements: As you might guess, computers aboard Orion will be much more advanced compared to those used on Apollo, or on current space shuttles.

The air breathed by Orion astronauts also is improved from the Apollo days. The fire that killed three Apollo astronauts during a ground test on Apollo 1 was a result of several design issues, many of which were improved for later Apollo missions, with one major exception; the Apollo atmosphere was 100% oxygen.

The reason for this was two fold: First, 100% O2 in the cabin allows for a lower overall pressure. Second, because air pressure in space suits 'must' be kept low so that astronauts can move their arms and fingers, moving from a nitrogen/oxygen, higher pressure atmosphere prior to extravehicular activity (EVA), puts astronauts at risk of decompression sickness resulting from the formation of nitrogen bubbles in the blood.

Nevertheless, because of the Apollo 1 fire, the space shuttle and ISS have been designed with a mixed nitrogen/oxygen (N2/O2) atmosphere. On the shuttles this can be set at sea level pressure (101.3 kPa/14.69 psi) or slightly reduced (55.2 to 70.3 kPa/8.01 to 10.20 psi). While this requires astronauts to pre-breath oxygen prior to a spacewalk, it constitutes major

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