The final report from NASA‘s Exploration Systems Architecture Study threw its support behind using a shuttle-derived solid rocket booster (SRB)-based launch vehicle for the agency’s mission to return humans to the moon and eventually to Mars.

Originally, this vehicle was to be based on the same four-segment booster made by ATK Thiokol for the space shuttle; topped by a liquid-fueled second stage. This configuration was chosen "due to its lower cost, higher safety/reliability, its ability to utilize existing human-rated systems and infrastructure and the fact that it gave the most straightforward path" to building the launcher, the report said.

The move found support among industry observers.

"I think the shuttle-derived model is the way to go," John Logsdon, director of the Space Policy Institute at George Washington University, told Satellite News. "The shuttle solid rocket booster is the safest launch vehicle in the world, having been launched 228 times with only one failure. That works out to a 99.5-plus percent reliability rate."

A study performed by the Planetary Society, a nonprofit organization that promotes exploration of the solar system, also recommended using shuttle-derived technology. One of the co-authors of the June 2004 Planetary Society study, "Extending Human Presence into the Solar System," was Mike Griffin, now the NASA administrator. "He came to the conclusion that using shuttle-derived technology was the best course, long before he had any inkling that he would be taking over NASA," Logsdon said.

"The five-segment SRB is the evolution of a flight-proven design," said John Pike, director of Globalsecurity.org. "It would not be a clean sheet of paper, and it certainly is the case in the space business that you to avoid clean sheets of paper."

But NASA will have to do some development after it was determined that the four-segment booster does not have enough lift to do the job. In January, NASA modified its plans, announcing it would develop a five-stage SRB.

This support is good news for ATK, which downplays the issue that developing a five-stage SRB will be radically different than the four-stage version used for the space shuttle. "They’re made of identical segments," ATK spokesman George Torres said. "So adding another one is not a major issue. … We are absolutely not designing a new vehicle in making the five-segment SRB. In fact, they are so close, that we have already been able to successfully test-fire a five-segment SRB in static tests. Granted, the nozzle may need some changes, but that’s something that’s being analyzed over the summer."

While the SRB-based booster continues to have strong support from officials inside and outside of NASA, there are many that still favor using technology based on the Evolved Expendable Launch Vehicles (EELV) developed by Lockheed Martin and Boeing.

"An initial [Crew Exploration Vehicle] configuration could and should be delivered to [low-Earth orbit] by highly reliable, human-rated launch systems," according to the June 2004 report. Human-rated launchers "can be derived from present and soon-to-be operational vehicles. This would include Delta 4 and Atlas 5 in the domestic market, with the Proton and Ariane 5 being readily available international alternatives. … There are many reasons to make the [Crew Exploration Vehicle] compatible with as many launch systems as possible."

The Planetary Society also downplays the idea that man-rating the EELVs for human spaceflight operations would be to difficult. "Technically, evolving the EELV fleet to carry a capsule-like [Crew Exploration Vehicle] would appear to be a relatively straightforward engineering task."

While providing NASA with multiple options for launch astronauts seems to make sense, the space shuttle-derived technology remains the frontrunner for the job, help in large part by its incumbency status.

"If [NASA] came up with the obvious solution, namely, ‘Let’s just put a capsule on top of an EELV.’ Then what would you do with all the shuttle infrastructure that’s already in place?" Pike said. "You would put thousands of people out of work, which just wouldn’t fly politically.

"I think the shuttle contractors put it to NASA Administrator Mike Griffin that, ‘You don’t have enough votes in Congress to kill the existing shuttle infrastructure,;" Pike said. "That’s why the [Crew Exploration Vehicle] is going to fly on top of a shuttle-derived SRB."

— James Careless