Exploration Shifts Seen Adding Six Months to Development
Aviation Week & Space Technology, 01/30/2006, page 36
Frank Morring, Jr., Washington
Exploration launch plan modifications stretch development, but save money
NASA is trading an estimated six-month hit to its shuttle-replacement schedule by dropping plans to modify the shuttle main engine for the job, in exchange for long-term cost savings on the way to Mars.
A decision to use a modern version of the Apollo-era J-2 upper stage engine to launch the planned Crew Exploration Vehicle (CEV) will eliminate the need to develop a Space Shuttle Main Engine (SSME) that can be started at altitude. And the lower power of the J-2--230,000 lb. vs. 512,300 lb. in vacuum for the SSME--will mean the "single-stick" Crew Launch Vehicle (CLV) will require five solid-fuel segments in its first stage instead of four.
That matches the solid-fuel requirement for the shuttle-derived heavy lifter to be used on lunar missions and has already been tested on the ground, so NASA won't have to maintain two different solid-fuel boosters as it works its way to the Moon. A throwaway version of the SSME still will be developed as a first-stage engine for the heavy lifter, but under the new plan the J-2 will be used on both the CLV and the big lunar rocket's upper stages.
"WE'RE TRYING TO do as much commonality in the initial design and in the overall flow to try to make the long-term recurring costs as low as possible," says Scott Horowitz, associate administrator for exploration systems.
Additional design work has also reduced the baseline diameter of the CEV to 5 meters from 5.5 meters, a change forced by weight, drag and other considerations. The end result will alter the internal layout of the four- to six-seat vehicle, but not its overall capability. Using the new baseline, NASA is just starting to work on the cabin and service module layout designs.
"We wanted to build the biggest CEV [possible]," Horowitz says. "For lots of reasons it looked like that's just too hard to do, so we backed off to 5 meters."
A new version of the J-2--Horowitz calls it the J-2X--with updated electronics, materials and manufacturing techniques, was already baselined to power the Earth Departure Stage that NASA hopes will take a four-seat CEV and a lunar lander to the Moon with a human crew by 2018 (AW&ST Sept. 26, 2005, p. 22). But because the overall J-2 propulsion system will require more development than an air-started version of today's SSME, Horowitz estimates it will take about six months longer to get underway.
That translates into late 2012 for a first flight of the CLV with the new stage, under the latest requirements sent to the teams headed by Lockheed Martin and Northrop Grumman that are bidding to build the CEV. NASA plans to test the crew vehicle with a dummy second stage in October 2011 and had intended to move on to an integrated orbital test with a working upper stage by February 2012, according to a schedule included in the new CEV requirements.
Horowitz stressed that NASA engineers at Marshall Space Flight Center, Johnson Space Center and other field centers are continuing to refine the original concepts drafted by the Exploration Systems Architecture Study (ESAS) last year. Although the engine changes, first reported on the space.com web site, were released on Jan. 20, the new CEV requirements that came out earlier in the month also contained changes from the initial ESAS lunar exploration architecture released last fall.
Those included a decision to drop the liquid oxygen/methane rocket engine originally baselined for the CEV service module and the lunar ascent module as a precursor to extracting methane at Mars to fuel a human return from the red planet (AW&ST Jan. 16, p. 413). Also dropped was a Low Impact Docking System (LIDS) that was originally intended to keep the U.S. in charge of the critical path to the Moon (AW&ST Jan. 23, p. 19).
CEV bidders still will be able to propose a LIDS system, although for near-term missions to the International Space Station (ISS) they may choose to go with the Russian system already in use there. Either way, the CEV will have a separation plate that will be jettisoned before landing, taking the docking mechanism with it. "You don't want all of that weight on top of your capsule during reentry," Horowitz says.
As for the methane engine, Horowitz says research and development will continue, but at a lower level than originally planned. Glenn Research Center, originally slated as the test site for methane-fueled engines, was scheduled to release final details on the revised program this week.
One possibility that could change the ultimate decision to use methane could be discovery of water ice at the lunar poles, which would make a liquid oxygen/liquid hydrogen engine more attractive for lunar ascent, Horowitz says. Meanwhile NASA probably will pick some sort of hypergolic propellant engine to power the CEV service module and the lunar ascent.
