NASA Propulsion Strategy Reaches Back While Looking Ahead

NASA Propulsion Strategy Reaches Back While Looking Ahead
By Brian Berger
Space News Staff Writer

The initial propulsion work in support of NASA's bid to return to the Moon and go on to Mars will focus primarily on adapting space shuttle systems and developing methane-fueled engines, a technology with which the United States has little experience.

The space shuttle main engine and solid rocket boosters are the basis for two new launchers NASA intends to develop, one for lofting an astronaut-carrying capsule known as the Crew Exploration Vehicle (CEV), and a heavy lifter for Moon-bound cargo loads. As currently envisioned, the CEV and other elements of the Moon and Mars exploration architecture would rely on engines fueled by a mixture of liquid oxygen and methane, NASA officials said.

Relying on a mix of old and new technology will help NASA limit risks in its propulsion development work, said Steve Cook, deputy director for space transportation at NASA's Marshall Space Flight Center in Huntsville, Ala. Marshall is in charge of developing the rockets NASA will need to return to the Moon by 2018 and go on to Mars.

"Historically when we've gone into a program like this, we've had engine developments that start right off the bat," Cook said. "Instead we're saying, 'let's focus our new propulsion development on much smaller-scale efforts. Let's also have back up plans in case it doesn't work out.' It's a balanced risk versus reward that we've laid out here."

NASA's propulsion plan also addresses the need to keep the shuttle propulsion work force intact until the last shuttle orbiter has flown.

NASA's strategy drew praise from the company that stands to benefit the most from NASA's planned propulsion work.

"The whole initiative [NASA Administrator Mike Griffin] has introduced since he took over breathes new life into the propulsion industry," said Byron Wood, president of Pratt & Whitney Rocketdyne of Chatsworth, Calif., the dominant U.S. maker of liquid-fuel rocket engines. "Before we were kind of in a going-out-of-business mode."

Wood added that NASA's emphasis on heritage systems will help Pratt & Whitney Rocketdyne, among others, ensure a safe fly-out of the space shuttle manifest.

"I think [Griffin] came up with a concept that helps preserve the skills by taking advantage of what's available in the shuttle program and adapting it to the new program so you give the existing [work force] a future and utilize their years of experience to make the future a success."

NASA hopes to field the 25-metric-ton CEV and its launcher, known as the Crew Launch Vehicle, by 2012 to support the international space station program. The rocket is based on the space shuttle solid rocket booster built by ATK Thiokol of Brigham City, Utah, and uses a variant of the space shuttle main engine as an upper stage.

That launcher also would be used starting in 2018 for Moon missions, lofting the CEV into low Earth orbit to rendezvous with an Earth Departure Stage and Lunar Lander, both of which would be launched on a heavy-lift cargo vehicle. The heavy-lift rocket, which NASA intends to start developing around 2011, is expected to be powered by two space shuttle solid rocket boosters and a cluster of five space shuttle main engines.

The new methane-fueled engines would be used to power the CEV and the ascent stage of the Lunar Lander. NASA envisions using methane-fueled technology for both the main maneuvering engines and attitude- and reaction-control thrusters on the CEV.

Cook said NASA intends to initiate before year's end an advanced development effort for methane propulsion. The effort, he said, would be run by NASA's Glenn Research Center in Cleveland. Industry sources said Glenn is expected to issue a draft request for proposals for methane research in the coming weeks.

Cook, who was in charge of the launch vehicle portion of NASA's recently unveiled exploration plan, said NASA's decision to develop a pressure-fed methane engine was driven by a look ahead at what would be needed for manned missions to Mars. While methane is a less efficient propellant than liquid hydrogen, it is easier to store for long stretches and is readily available on Mars, making it possible for NASA to meet future propellant needs by taking advantage of martian resources.

Further, NASA sees the Moon as a proving ground for systems needed to explore Mars.

The United States has never flown a methane-fueled engine, Cook said, but has studied methane propellants closely enough over the years to know that it can be done. Some of this work was done by the major U.S. propulsion houses.

Both Pratt & Whitney Rocketdyne and its main rival, GenCorp Aerojet of Sacramento, Calif., are interested in developing methane engines.

Jim Long, Aerojet's director of business development, said the tricky part of methane engines primarily has to do with the storage and handling of the fuel.

"We believe that from an engineering standpoint that a [liquid oxygen]-methane engine is achievable with most of the risk being cost and schedule," Long said. "The greater part of the technical risk is in the tank and feed system."

Wood said more guidance is needed from NASA on the methane-fueled propulsion system, but that industry is up to the task. "We have been working with methane and talking about methane for 40 years," Wood said. "There has never been an engine produced that runs on methane."

Pratt & Whitney Rocketdyne and Aerojet are likely to face competition from at least two small upstarts that have been working on methane engine technology: XCOR Aerospace of Mojave, Calif., and Orion Propulsion of Madison, Ala.

"We have been looking pretty seriously at it both for auxiliary propulsion and for main propulsion for about two years now," XCOR President Jeff Greason said. "We got interested in it when we were doing a design study for [the U.S. Defense Advanced Research Projects Agency] on a low-cost upper stage."

Greason said XCOR decided late last year to build and test a small methane-fueled thruster "on our own dime to get some experience with the propellant." XCOR expects to be ready to start test firing the small thruster in early 2006, he said.

XCOR also submitted a proposal to NASA last year to develop, build and test a 10,000-pound to 15,000-pound variable thrust liquid oxygen-methane engine. NASA awarded XCOR a contract for a separate proposal to build and test a composite tank for cryogenic fuels, but passed on its methane engine proposal.

Orion Propulsion, meanwhile, has been doing component-level work on small methane thrusters under a Marshall contract, according to a company press release.

Recognizing that the methane engine is fraught with the usual technical and schedule risks, NASA has decided to devote some effort to a hypergolic system as a backup. Hypergolic fuels, such as hydrazine, were used during the Apollo program and are still used by the space shuttle for in-space maneuvering. But hypergolic propellants are not the most efficient propellants and are extremely toxic, requiring cumbersome and costly handling procedures.

Next up on NASA's list of near-term propulsion needs, Cook said, is an upper stage engine for the Crew Launch Vehicle. Rather than design a new engine, NASA's plan calls for using the space shuttle main engine modified to start while aloft rather than on the ground.

Here again, NASA's choice was made with an eye on the future. NASA intends to use a cluster of five space shuttle main engines to power the main stage of its heavy-lift rocket. "Since that won't start until 2011," Cook said, using the shuttle engines for the Crew Launch Vehicle "keeps the [space shuttle main engine] line going" until then.

Cook said he expects the space shuttle main engine air-start program to be in component level testing by the end of the year, with larger-scale testing getting under way at Stennis Space Center in Mississippi "about a year from now."

Wood said adapting the space shuttle main engine to serve as the Crew Launch Vehicle's upper stage is "a very doable thing." He said the company took a close look in early 1990s at what it would take to start the engine in flight.

"The tests we did back then indicated that it would not be a big hurdle for the [space shuttle main engine] to achieve," Wood said. "But it's a matter of getting started and having time to run the verification test program to satisfy everybody that it can meet the mission requirements."

Wood said the space shuttle main engines that NASA flies today could be used for the Crew Launch Vehicle once the shuttle program wraps up.

"When the shuttle is retired I can immediately take the engine assets out of the shuttle program and fly them on these vehicles," Wood said.

NASA has 12 complete engines at Kennedy Space Center in Florida, Wood said. In addition, the agency has several test articles and older variants of the engines, and those plus hardware available at Pratt & Whitney Rocketdyne may bring up to 30 the number of engines that could be assembled relatively quickly in support of the exploration effort, he said.

NASA also needs to make some modifications to the four-segment solid rocket booster that forms the main stage of the Crew Launch Vehicle. ATK Thiokol says the changes needed are minor.

Michael Kahn, ATK Thiokol vice president of space launch systems, said the only foreseen changes have to do with the difference between the way the boosters separate from the shuttle orbiter - they fall off to the side - and the way they will separate from the Crew Launch Vehicle's upper stage. He said there will need to be some changes to the booster's aft skirt.

He also said Thiokol would have to take a careful look at the booster's existing parachute system since the boosters would be falling farther and faster when used for the Crew Launch Vehicle than when used for the shuttle.

The heavy-lift cargo vehicle NASA wants calls for two five-segment solid rocket boosters that will require a significant development effort. Kahn said the sooner NASA gets started on the five-segment booster, the better.

Looking further out into next decade, NASA needs an engine for the Earth Departure Stage it intends to use to send the Crew Exploration Vehicle and Lunar Lander on their way to the Moon. NASA intends to use the J2-S or an equivalent engine. Built by Pratt & Whitney Rocketdyne, the J2-S is a never-flown variant of the engine that powered the second- and third-stages of the Saturn 5 rocket

Tell it yourself. Since you seem to be on a talking basis with them.

That was not a thrust failure, that was an integrity failure which has been cured. Furthermore, its improbable repetition could not impair or threaten the CEV design.

That is not to say there aren't other issues. Take note of these:

NASA's Lunar Vision: The Devil's in the Details
By Leonard David
Article here
Senior Space Writer
05 October 2005

NASA's grand plan to revive human exploration beyond Earth orbit relies greatly on utilizing a heritage of hardware from the soon-to-be-scrapped space shuttle program.

The centerpiece of this system is a larger Apollo-like capsule. It would haul four astronauts to and from the Moon, six crewmembers on future missions to Mars, and deliver crew and supplies to the International Space Station.

But to get things off the ground, factually, NASA is eying astronaut-carrying and cargo-lofting launch systems that build upon space shuttle components.

In some quarters, NASA's vision of exploration is an anti-doldrums undertaking for the agency. Yet the plan is rife with technical issues that need resolution. Others suggest that the strategy is dead on arrival, or is sketchy at best.

Sporty slap

For the most part, editorial pundits have not been easy on NASA's newly announced strategy.

Gregg Easterbrook is a senior editor of The New Republic, a contributing editor of The Atlantic Monthly and a visiting fellow at the Brookings Institution. He took a sporty slap at NASA in a column he writes for, of all places, NFL.com - the official site of the National Football League.

"NASA says it will take $104 billion and 13 years to build the amazingly 1960s-like hardware. Let's see, that's a target of 2018 -- 49 years after the first Moon landing," Easterbrook wrote.

"So half a century after America was able to land people on the Moon, we'll be able to do it again. Imagine if you had declared in 1952, 49 years after Kitty Hawk, that for a mere $104 billion, you could build a wooden flyer that would remain in the air for 12 seconds," Easterbrook proclaimed. "Isn't this Moon announcement awfully similar?"

Workable solution

Putting those barbs aside, the NASA vision as unveiled last month by NASA chief, Michael Griffin, is starting to undergo technical critique.

"I think Griffin's team has come up with a truly workable solution that really does make sense," said Jerry Grey, Director, Science and Technology Policy for the American Institute of Aeronautics and Astronautics (AIAA). Grey is also Visiting Professor of Aerospace Engineering at Princeton University.

"Certainly there will be technical issues," Grey told SPACE.com, "but in view of the current concerns over shuttle and station, the ever-present budget constraints, the political issues, and the lofty long-term goals -- which are indeed the right ones -- it would be hard to find a better approach."

Given that, Grey continued, there are a host of technical issues that must be dealt with.

Unproven features

For one, the use of a shuttle solid-rocket booster (SRB) as a main stage will require extensive engineering, modeling, and flight-testing, Grey said. "The structural, aerodynamic, vibration, and other environmental conditions for an SRB having an upper stage and a large, heavy, top-mounted payload are very different from those involved in the current usage of these motors," he said.

Furthermore, an SRB has never flown in this configuration but has always had the structural support of the external tank, Grey pointed out. Also, integration of the upper stage and the top-mounted payload, and providing the necessary electric power, guidance and control, communications, and other "housekeeping" functions to the upper stage and the Crew Exploration Vehicle (CEV), raise a whole host of technical requirements -- especially in validation and verification -- that have never been addressed for the SRB, he said.

"So although by itself the SRB is a well-proven piece of hardware, the new flight article will have many new and as yet unproven features that have yet to be human-rated," Grey added.

Vacuum restart

Another hardware hurdle to be overcome is use of the Space Shuttle Main Engine (SSME). Built for re-use, the SSMEs are in the NASA strategy as an upper stage motor, as well as clustering five of them for the heavy-lift booster.

Although well proven in its current usage, Grey said, both projected applications of the SSME involve new technical matters that must be addressed.

The SSME has never been used in an upper stage, which itself will require a whole new design, and as yet not human-rated, Grey said. "This will involve a new propellant feed system to the engine, validation of a totally different set of environmental conditions than the engine has experienced in the past, and almost certainly a re-start capability -- in vacuum -- which involves a whole new set of technical requirements."

"Remember, too, that although the engine has operated in vacuum during part of the shuttle launch trajectory, it will now require not only vacuum re-start, but also an initial chill-down and start under vacuum conditions, Grey noted, utilization that will demand human-rating, he said.

Yet another issue of tasking the SSME to upper stage duty, now optimized for the shuttle launch trajectory, also means that the engine's specific impulse will be lower. Specific impulse is a performance measure for rocket propellants that is equal to units of thrust per unit weight of propellant consumed per unit time.

Engineering attention

Then there's the business end of the shuttle-derived heavy-lift booster.

A shuttle orbiter is outfitted with a trio of SSMEs - a well-proven engine configuration.

"The new five-engine SSME cluster, mounted on a stage that will certainly be very different from the orbiter in its propellant feed and thrust-vector control characteristics and its structural, aerodynamic, and environmental behavior, will require considerable engineering attention," Grey explained.

Grey said that the upper, or side-mounted, stage use of the SSME -- or whatever other alternative engine may be selected -- will also require a new design approach.

"The payload characteristics are certain to be much different than those of the CEV," Grey said. Lastly, the SSME is expensive and was not intended to be expendable. "Keeping budget control on the expenditure of six units on each flight might turn out to be an issue."

Show me the money

Taking a step back from technical aspects of NASA's vision quest, there's the subject of money.

Grey said that while he is supportive of the stated doctrine of allowing the schedule of the whole program to be the "dependent variable", there is an obvious budgetary impact.

"The only valid corollary to this doctrine is not to fix the total budget, or even the budget for each element of the program," Grey said, "but to fix the annual budget cap for the program as a whole. That allows each mission date to move to the right as much as needed to stay within that annual cap."

Grey offered a scorecard account for implementing the new NASA vision.

"I believe that all these technical issues, although perhaps more extensive than NASA has as yet acknowledged, are all solvable," Grey concluded. NASA's approach to focus vision into reality "is probably the best that can be devised under the given set of conditions," he said.

A missing piece

At a fundamental level, the NASA plan is "Apollo II: The Sequel", observed Roger Launius, Chair of the Division of Space History at the Smithsonian Institution's National Air and Space Museum in Washington, D.C

"This architecture for reaching the Moon is certainly one that makes possible a return, but it is also one among several approaches that could have been successful," Launius told SPACE.com. "There is no one right answer and I suspect that before the hardware is solidified NASA will have to make modifications to the approach in response to technical, schedule, political, or economic challenges," he said.

Launius said he sees a missing piece of the NASA blueprint. That is, what is the rationale for taking on the challenge in the first place?

What are we going to do once we reach the Moon?

"If science is the driver, what scientific activities are going to dominate? Decisions on this will affect the structure of the science effort as a whole, the landing site selection, the nature of robotic predecessors, the types of experiments developed, and a host of other issues that require sustained thought and planning," Launius suggested.

Political will or won't

The space historian said he hoped these activities would not be an afterthought, as was too often the case during Apollo.

"The Apollo program was about flags and footprints, and it was effective in helping to win the Cold War with the Soviet Union. The Apollo leadership also managed to tack on some science activities, but they were definitely afterthoughts," Launius recalled. "But those times have passed, and we must move beyond the Apollo concept to embrace a more engaging and sustained approach. I hope this program is successful in doing this. I will be properly ecstatic if program officials are successful in doing so," he said.

Leaping back to the Moon in 2018 will demand sustained political will, Launius said. That will be a major challenge for NASA's current chief, Michael Griffin, and perhaps especially for his successors, he said.

"At a fundamental level, political will is the most critical challenge facing those who wish to venture into space in this century. It is even more significant than the technological issues that also present serious challenges to returning to the Moon," Launius advised.

Governmental decision-makers, supported by the taxpaying public that elects them, have to agree over the long haul that the expenditure of funds for this exploration agenda is in the best interest of the nation, Launius said. "Without that political will, discovery and exploration cannot take place at an aggressive rate."

Historical trends

How real is the $104 billion price tag for NASA's Moon, Mars and beyond manifesto?

While the funding profile for the initiative is modest, "historical trends for earlier projects suggest that despite efforts to contain costs, they will escalate in response to technical challenges encountered in the project," Launius added.

Now toss in the Iraq war and Hurricane Katrina rebuilding.

The NASA vision must compete for federal dollars with both those priorities, and a host of other Congressional agenda items.

"As a person excited by the prospect of returning to the Moon, I am thrilled that the United States is finally intent on moving beyond Earth orbit," Launius concluded. "Like everyone, I am curious to see how this plays out over the next few months as project definition becomes more solid. The devil will be in the details."

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