CEV: a different approachby Jeff Foust
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| Combine it with an upper stage, proponents argue, and an SRB could carry CEVs into orbit sooner and less expensively than an EELV. |
Despite these problems, and the schedule and cost risk they pose to the Vision, the EELV remains the primary choice for launching the CEV. This is largely because there are few other options for launching a spacecraft the size of the CEV, which will likely weigh in excess of 10,000 kilograms. Once the Titan 4 is retired next year, the only existing American launch vehicles capable of placing that much mass into LEO will be the two EELVs and the shuttle. While entrepreneurial efforts, like SpaceX, might eventually produce large enough vehicles, their focus for the near term is on smaller vehicles.
That’s not to say, though, that there are no alternatives to the EELV. Over the last several months a different concept has emerged that uses one of the components of the shuttle: its solid rocket booster (SRB). Although rarely viewed as a launch vehicle in its own right, the SRB is a capable and reliable vehicle that has been used to help carry humans into space for over two decades. Combine it with an upper stage, proponents of the concept argue, and an SRB could carry CEVs into orbit sooner and less expensively than an EELV.
“It started as an idea of safe, simple, and soon,” NASA astronaut Scott Horowitz said during a plenary session of the Mars Society’s annual conference in Chicago last month. “After the Columbia accident, a few of us in the office were thinking about how we can do this better. How do we get to the point where we can launch lots of people to and from low Earth orbit?”
That philosophy of “safe, simple, and soon” led them to adopt a capsule design for manned spacecraft. Horowitz said they then turned their attention to a launch vehicle for that capsule. “I was thinking, ‘What is one of the most cost-effective, safest pieces of hardware that we have to use as a lower stage?’” Horowitz recalled. “I said, ‘Hey, what about a solid rocket booster?’”
Horowitz said he ran the performance numbers of the SRB on his computer and found that, in his words, it would be “a hell of a ride.” The SRBs burn out after just over two minutes, and although powerful, a single SRB doesn’t have enough performance alone to put a manned spacecraft into orbit. At burnout “you’re going about Mach 18 and pulling about 20 g’s,” he said.
| Although powerful, a single SRB doesn’t have enough performance alone to put a manned spacecraft into orbit. At burnout “you’re going about Mach 18 and pulling about 20 g’s,” Horowitz said. |
Turning the SRB into a launch vehicle requires an upper stage. Horowitz said he and colleagues settled upon the J-2, an engine used on the Saturn 1B and 5. “It turns out that with the J-2 and about 200,000 pounds [90,000 kg] of LOX/hydrogen on this thing, you can launch 40,000 or 50,000 pounds [18,100 or 22,700 kg] to LEO,” he said. While the J-2 hasn’t been used since the last Saturn 1B launch in 1975, he was confident that the engine would be available, based on conversations with executives at Rocketdyne, the Boeing subsidiary that built the J-2. “They actually have 12 J-2s sitting around,” he said, and added that the company felt they could get a production line for new J-2 engines going in a couple years.
The upper stage would be wider than the SRB—about five meters in diameter—enabling the use of a larger capsule. Horowitz said a capsule five meters across could “comfortably” seat six to eight people, compared to four people that the CEV’s predecessor, the OSP, was planned to carry. Horowitz also believed that such a vehicle could launch for about $100 million a flight, although he had yet to run specific cost estimates on the proposed system. That combination of cost and crew size opens up the potential for other markets. “Now you’re almost getting competitive with the rates people are paying to go up on the Soyuz as tourists to the space station,” he said.
Other voices for the SRB
Horowitz and others at NASA are not the only people speaking out in favor of using an SRB-derived vehicle to launch the CEV. As one might expect, ATK Thiokol, the company that builds the SRBs, is a supporter of the idea. “A human rated and flight proven CEV launch system can be available by simply utilizing a single booster combined with a liquid engine second stage,” Mike Kahn, vice president of space operations at ATK Thiokol, said in May during a hearing of the Senate Commerce Committee’s space subcommittee. “Additionally, if there is a 35-40K lb payload/cargo requirement instead of the CEV, the same system could be used, further improving overall cost effectiveness.”
| “So if you polled the astronaut corps,” said Jones, “you’d probably find that people, almost uniformly, would be willing to step onto an SRB on the next flight.” |
In July, the Planetary Society released a report, “Extending Human Presence into the Solar System”. The report was the product of an independent blue-ribbon panel, chaired by Owen Garriott and Michael Griffin, who examined alternatives to implementing the Vision for Space Exploration. “We are recommending that strong consideration be given to a specific design using the Shuttle solid rocket motor (SRM), together with a new liquid propellant upper stage” to launch the CEV, the report concluded. “It allows us to take advantage of the existing Shuttle human space flight assets at the Vehicle Assembly Building (VAB) and Launch Complexes 39A and B that would otherwise become idle upon termination of Shuttle operations.” The report also noted that the reusability of the SRB “could result in significant cost savings relative to fully expendable vehicles.”
Tom Jones, the former astronaut who was one of the members of the Planetary Society’s panel, believes SRBs are the way to go for the CEV. Jones noted that the SRBs have flown 176 times since the 1986 Challenger accident—88 shuttle missions using two SRBs each—without a failure. “That’s the highest reliability of any rocket flying in the world today,” he said during a panel session on space exploration last week at the 2004 International Military and Aerospace Programmable Logic Device (MAPLD) Conference in Washington. “So if you polled the astronaut corps, you’d probably find that people, almost uniformly, would be willing to step onto an SRB on the next flight.”
Is there a future for the SRB?
Despite the discussion within NASA and elsewhere about using the SRB to launch the CEV, it’s not clear whether there’s sufficient momentum behind the idea to at least allow further studies, let alone selection of the concept for development. ATK Thiokol is strongly behind the idea because it gives new life for the SRB—a significant portion of their business—once the shuttle is retired around the end of the decade. For the same reason, the idea may get a lukewarm reception at Boeing and Lockheed, the two companies that would likely be on the inside track to win a CEV procurement contract, because of their vested interest in their own EELV systems.
There are technical issues that a SRB-derived launch system would have to address, notably the development of a new upper stage. However, in the long run the bigger challenges that an SRB-based launcher might have to face are perceptions: that the SRB is an old technology, best left to the past; that solid-propellant motors like the SRB, which can’t be turned off once ignited, are unsuited for manned spaceflight applications; that the EELV will need the anticipated volume of CEV launches to lessen the cost burden of the two vehicle programs on NASA and the Defense Department. Successfully handing those perceptions will depend on the champions the SRB design wins within NASA and industry. In a brief interview after his Mars Society presentation, Horowitz admitted that industry was skeptical about the idea at first but has since started to warm to it. There’s certainly a lot more work that Horowitz and others will have to do, though, to gain converts to an SRB-launched CEV.