Orion vs. Apollo: NASA's new moonshot

By Jim Banke

updated 5:51 p.m. ET Sept. 29, 2008

CAPE CANAVERAL, Fla. - When astronauts return to the moon by 2020, they will do so following a familiar path and flying in a cone-shaped capsule that echoes the "good old days" of Project Apollo.

But the skin-deep similarities between Apollo's Command Module and Constellation's Orion spacecraft are far outnumbered by differences — more like improvements — that NASA's 50 years of spaceflight experience make possible.

"We've learned a lot, but we still have a lot of questions," said Bret Drake, Chief Architect in the System Engineering and Integration Office for Constellation at the Johnson Space Center in Houston.

For example, the best Apollo could offer by 1972's final lunar excursion was a two-man crew lingering for about three days at a landing site that was generally near the moon's equator.

Constellation is shooting for a means to land anywhere on the moon and eventually grow the capability to build up a permanent presence at one site, likely near one of the poles, Drake said.

"We're trying to evolve a capability, right out of the box, where we're going to have four-member crews staying on the surface for seven days," Drake said. "But eventually we'll get to the point where we have four crewmembers on the surface for 180 days."

That potential still is more than a decade away, and though the fine details of what all the hardware is going to look like continue to evolve, the picture of how the United States will go back to the moon is coming into focus.

"Functionally, physics drives you in a lot of the same directions we went through in Apollo," Drake said. "We're doing a lot more with the systems than we were with Apollo."

Skin deep beauty
To start, that means the Orion spacecraft will be shaped like a cone, Drake said.

When determining the best shape to deal with the speeds and heat of reentry encountered by a spacecraft returning from the moon, the laws of physics are the same in the 21st Century as they were in the 20th Century.

So from a distance the Orion spacecraft looks almost identical to the Apollo Command Module. Up close the differences become more apparent, especially the size.

Orion is now set to be 16.5 feet (5 meters) in diameter and 10.8 feet (3.3 meters). It will weigh about 31,000 pounds (14,000 kg) empty and have a habitable volume of 692 cubic feet (11 cubic meters).

Apollo's Command Module by comparison: A diameter of 12.8 feet (3.9 meters) and a height of 11.4 feet (3.47 meters). Total dry weight was 12,787 pounds (5,800 kg) and its crew cabin volume was 218 cubic feet (6.17 cubic meters).

Both spacecraft had or will have an attached Service Module that will have a single large engine fed by storable propellants and contain storage and bays to support the main cabin systems.

Both Apollo and Orion's Service Module will have batteries and electricity generating fuel cells, but the Orion also has a pair of solar arrays to help keep the vehicle powered during its intended long stay in lunar orbit.

And that brings to light some of the key difference between the Apollo and Orion mission scenarios, or more simply, the paths they will follow from the Earth to the Moon.

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