WASHINGTON – Although work has yet to begin in earnest on NASA’s proposed Ares 5 heavy-lift launcher, the U.S. space agency’s rocket designers are preparing to brief top brass on a batch of changes intended to boost the vehicle’s performance.
Adding a sixth RS-68 engine to the Ares 5 main stage, increasing the use of weight-saving composite materials throughout the vehicle, and making major modifications to the pair of solid-rocket boosters (SRBs) strapped to the side of the vehicle are among the changes under consideration, according to senior NASA officials and other experts.
The changes are due to be presented formally to the head of NASA’s Exploration Systems Mission Directorate, Rick Gilbrech, during a Lunar Capability Concept Review slated to take place June 17-20. Constellation Program Manager Jeff Hanley will lead the briefing.
Doug Cooke, NASA deputy associate administrator for exploration systems, said no decisions have yet been made but acknowledged that the changes under consideration are heading toward approval.
“We will probably narrow down the options at the [Lunar Capability Concept Review] in a couple of weeks. Those are possibilities we’re looking at,” Cooke said in a June 3 interview. “What we are looking to do is put Ares 5 in the right ballpark in terms of what kind of mass we think we are going to need to lift.”
Cooke said the weight reductions and performance enhancements eyed for Ares 5 are not intended to relieve any pressure on the Constellation engineers getting the Orion Crew Exploration Vehicle and its Ares 1 launcher ready for their preliminary design reviews this fall. NASA said in May that it was postponing Orion’s review two months to late November to give the spacecraft’s designers more time to work some weight-saving changes adopted last fall.
“It’s not meant to address anything between Orion and Ares 1,” Cooke said of the proposed Ares 5 changes. “We are looking at those masses and margins in their own right … we don’t want to relieve any pressure on Orion’s mass because if it grows then it decreases the mass you can put on the surface of the Moon.”
A source familiar with the proposed changes, who spoke on the condition of anonymity since the changes had not been adopted, formally said adding a sixth RS-68 engine and making more extensive use of composite materials throughout the vehicle could add around 10 metric tons of performance to Ares 5, giving designers more margin to cover future uncertainties and to buy back some performance lost as a result of mass growth on the designs for Orion, the Altair lander and Ares 5 itself.
The source said replacing the solid-rocket boosters’ reusable steel cases with a composite material are among the changes NASA appears likely to adopt. The source said it is unlikely that a composite case would be reusable.
Cooke said the jury is still out on the reusability, or lack of reusability, of a composite SRB case. “I think that’s still a question mark. I’m not sure. That will be part of that discussion. That will be a hard question actually,” he said.
Composites can be a hard sell for spacecraft designers accustomed to working with aluminum and steel. Cooke said NASA has not used composites all that much on its bigger vehicles and systems, but that could change.
“We are looking to use them wherever they benefit us the most,” he said. “We’ve pushed hard on that because it’s sometimes hard to get people to look at them. But they offer a lot of benefit … they are being looked at for the lander as well.”
Cooke said NASA’s Langley Research Center, Hampton, Va., is building a prototype composite crew capsule as “a little side project” that is meant in part to immerse NASA structural engineers in composite spacecraft design.
Cooke also acknowledged that the Constellation Program is evaluating the benefits and drawbacks of designing a 5.5-segment solid-rocket booster for Ares 5. The current Ares 5 concept uses a pair of five-segment solid-rocket boosters identical to the one being designed to serve as the Ares 1’s main stage. NASA’s rationale for going with a five-segment solid-rocket booster for Ares 1 instead of the four-segment booster currently used for the space shuttle was that it needed to design the five-segment booster for Ares 5 anyway. If NASA decides to add an extra half-segment of propellant to Ares 5’s solid boosters, some of the benefits of commonality could be lost.
“That’s one of the trades,” Cooke said. “They are looking at that to understand that question … It’s one that will be in the trades when we see it.”
Lesser commonality aside, Cooke said there are some benefits to going with a 5.5-segment solid-rocket booster for Ares 5. For starters, a 5.5-segment booster would provide more thrust during the early part of the flight.
Cooke said a 5.5-segment design also would allow NASA to put more fuel in the rocket’s liquid main stage by virtue of moving up an attach point that needs to go between the hydrogen and oxygen tanks just like it does on the space shuttle.
“So if you move up another half segment, it moves that cross beam up so you can put more fuel in that first stage,” he said. “It has a dual effect. That’s just another knob they are turning in looking at logical possibilities.”
Scott “Doc” Horowitz, a former NASA associate administrator for exploration systems and a consultant to Ares 1 contractor Alliant Techsystems and others, said he approved of the changes being considered for Ares 5.
“These are very interesting changes and I think a great evolutionary path,” Horowitz said. “Composites are widely used on launch vehicles and allow for reduced cost and improved performance. The option to use up to six RS-68s and an upgraded composite five-segment booster, according to my back-of-the-envelope calculations, has the potential to provide up to 400,000 pounds (181 metric tons) to [low-Earth orbit]. I only wish we could have used more composites on Ares 1 and Orion.”
Meanwhile, NASA is considering awarding its first Ares 5 contracts sooner than 2011 in order to help contractors better prepare for the work force transition that will accompany the retirement of the space shuttle fleet.
“It could possibly be before the 2011 date, perhaps 2010 or slightly earlier, depending how our budget works out this year,” Cooke said.
Comments: bberger@space.com
