Defending Constellationby Jeff Foust
|
| Clearly one of the biggest impacts Griffin had on NASA, and the future of American human spaceflight, was his implementation of the Vision for Space Exploration. |
That architecture has, since its release in the fall of 2005, been widely discussed, debated, and, in some corners, dismissed on technical and/or financial bases. Those concerns have grown, even as NASA has issued contracts for the development of the Ares 1 rocket and the Orion spacecraft, and a panoply of alternative architectures have emerged from various quarters, such as DIRECT (see “Another voice in the wilderness”, The Space Review, February 19, 2007). Enough concerns have been raised, and enough questions have been asked, the Griffin himself recently felt compelled to defend the ESAS architecture in a major speech.
Speaking at a Space Transportation Association (STA) breakfast on Capitol Hill on January 22, Griffin explained why he was taking the time to explain the rationale behind a decision made more than two years ago. “Today’s topic is motivated by the inquiries I’ve had lately, in one forum or another, concerning various aspects of NASA’s post-shuttle spaceflight architecture,” he said. While those inquiries, he felt, did not raise issues not already addressed by ESAS, “people come and go, new questioners lacking subject matter background appear, and the old questions must be answered again if there is to be general accord that NASA managers are allocating public funds in a responsible fashion.”
Much of the speech, then, featured Griffin describing the choices NASA faced and the constraints it was under from technical, policy, and other directions, and how that shaped the decisions the agency ultimately made on ESAS. The policy side is shaped by both President Bush’s original goals for the Vision for Space Exploration when he announced it in 2004, as well as the NASA Authorization Act that Congress passed in 2005 that added to those goals specific language about the ISS and the use of shuttle-derived hardware for the next-generation vehicles. “Not that anyone asked,” Griffin said, “but I personally consider this to be the best civil space policy to have been enunciated by a president in four decades or more, and the best authorization act to be approved by the Congress since the 1960s.”
That policy introduced some practical constraints as well. Although it would be “highly desirable” from an engineering perspective to have one transportation system optimized to serve the ISS and another specifically for lunar missions, NASA’s budget is not large enough to support multiple architectures. “We get one system,” he said. “It must be capable of serving in multiple roles, and it must be designed for the more difficult of those roles from the outset.” Similarly, he noted that successful aerospace systems, including both aircraft and rockets, often remain in service for decades; the same will be true for Constellation. “We are designing today the systems that our grandchildren will use as building blocks, not just for lunar return, but for missions to Mars, to the near-Earth asteroids, to service great observatories at Sun-Earth L1, and for other purposes we have not yet even considered.”
Another constraint that went beyond the strict wording of the policy was the desire to have a system more capable than that developed for Apollo. “To return after fifty years with nothing more than the capability we once threw away, seems to me to fail whatever test of common sense might be applied to ourselves and our successors,” Griffin said. So in developing ESAS, NASA planned for lunar missions that would initially feature sortie missions for one week and a four-person crew, capable of landing anywhere on the lunar surface, with the later development of a lunar outpost.
Those enhanced requirements require additional mass: a translunar injection (TLI) mass of 70-75 metric tons, compared to the 47 metric tons on Apollo 17. “If we need more capability to TLI than can be provided by a single launch of a Saturn-class vehicle, we can reduce our objectives, we can build a bigger rocket, or we can attain the desired capability by launching more than one rocket,” Griffin said. The first option is undesirable and the second, while desirable from an engineering standpoint, is infeasible given the existing launch and manufacturing infrastructure, and would be overkill for missions to the ISS. Thus, NASA settled on a mission architecture that involved the launch of two rockets whose payloads rendezvous in Earth orbit before heading to the Moon.
| “Not that anyone asked,” Griffin said, “but I personally consider this to be the best civil space policy to have been enunciated by a president in four decades or more, and the best authorization act to be approved by the Congress since the 1960s.” |
The simplest dual-launch system, Griffin said, would be to simply launch two identical rockets. It would require the development of only one vehicle, saving money; further cost savings would some from the higher flight rate of the single vehicle. However, such a vehicle would end up being “vastly overdesigned” for ISS missions. It would also be, in Griffin’s view, undersized for eventual human missions to Mars. He estimates that a human Mars mission would have a mass on the order of the ISS, and it would be preferable to place such a mass in orbit using a few launches of a larger vehicle than many launches of a smaller vehicle. “I hope we’re smart enough that we never again try to place such a large system in orbit by doing it in twenty-ton chunks,” he said.
Thus, ESAS settled on a two-launch architecture with two different vehicles: a smaller vehicle for putting a crewed spacecraft in orbit, regardless of destination, and a larger vehicle carrying the payload needed for missions to the Moon and, eventually, Mars. This leads to one of the biggest questions about ESAS: the use of a shuttle-derived vehicle for the smaller rocket than something derived from the existing EELV families, the Atlas 5 and Delta 4. “Now that’s been a really charged question,” Griffin admitted. It’s a logical approach, he said, and something he himself had supported in the past. “To cut to the chase, it will work, as long as—key point—you are willing to define Orion as that vehicle which can fit on top of an EELV. Unfortunately, we can’t do that.”
One obstacle is performance. The exploration architecture requires placing 20.3 metric tons in orbit for ISS missions and 23.3 metric tons for lunar missions, requiring the development of a new upper stage for the EELVs. A second issue is risk: the EELVs were not designed for manned missions and thus would have to be human rated. While that term can mean different things to different people, Griffin specifically mentioned the need for “significant upgrades” to the Atlas 5 core stage, and than an abort from a Delta 4 would exceed allowable g-loads on the crew. A probabilistic risk assessment developed during ESAS concluded that the Ares 1 would be nearly twice as safe as an EELV-derived launcher.
Then there is the issue of cost. While Griffin did not go into details, citing proprietary data used in NASA’s analysis (which, he made a point of stating, had been shared with various offices ranging from the White House to the Pentagon to Congressional committees), an EELV-derived architecture for both the crew and cargo launches would be 25 percent more expensive to develop than a shuttle-derived system and would have recurring costs for the crew vehicle “at best” similar to the Ares 1, with the Ares 5 much less expensive than an EELV-derived counterpart.
“So, while we might wish that off-the-shelf EELVs could be easily and cheaply modified to meet NASA’s human spaceflight requirements, the data say otherwise,” Griffin concluded. “Careful analysis showed EELV-derived solutions meeting our performance requirements to be less safe, less reliable, and more costly than the shuttle-derived Ares 1 and Ares 5.”
The shuttle-derived approach that ESAS settled on, Griffin concluded, “is the architecture which I think best meets all of the requirements of law, policy, budget, and common sense that constrain us the post-shuttle era. It certainly does not satisfy everyone, not that I believe that goal to be achievable.”
Griffin gave that speech, though, because some people have been unsatisfied with the ESAS architecture, and have pointed to a number of technical issues with the vehicles. Griffin’s speech came just days after NASA officials admitted that they were studying a “thrust oscillation” issue with the first stage of the Ares 1 that, in some of the more dramatic media reports, threatened the future of the entire program.
Not surprisingly, this came up almost immediately during the question-and-answer session that followed Griffin’s STA speech, and he went to great pains to try and minimize the problem. “I think I have rarely seen more of a mountain made out of less of a molehill than this particular technical issue,” he said, then spent the next several minutes endeavoring to “pound this one flat”.
| The assembly of the ISS has provided a lesson on the need for heavy lift for planning future missions to the Moon and Mars, according to Griffin: “I hope we’re smart enough that we never again try to place such a large system in orbit by doing it in twenty-ton chunks.” |
Thrust oscillation, he explained, is caused when vortex shedding off fuel grains, as the motor approaches burnout, strikes a resonant frequency of the casing. It’s a problem that most solid motors have had at some point in their development process; it was particularly severe during the early development of the Minuteman missile, Griffin said. There are several technical solutions to the problem, ranging from reshaping the fuel grains to detuning the motor case to isolating the stage or the payload from any vibrations caused by the oscillation.
Moreover, he said, “We’re not even certain that we have a problem.” The thrust oscillation concern comes from old test data, and there are plans to collect test data on some of the remaining shuttle flights, as well to also see if the loads on the Ares 1 caused by the oscillation are “enveloped” within those experienced by the vehicle during max-Q, the period of maximum dynamic pressure during launch.
After spending more than five minutes discussing the potential problem and solutions, Griffin sighed, sounding a little exasperated. “I don’t know what to say, guys. It’s a neat and interesting engineering problem. We didn’t think we were going to develop this system without such problems. We certainly think we can solve it—I think I ran out of fingers on both hands before I got through with all the different ways we can look at to deal with it if, in fact, it’s a problem.”
That exasperation also stemmed from the impression in some quarters that NASA was not being as forthcoming about the thrust oscillation issue as it should. “We’re kind of in a no-win position,” Griffin said. “If we encounter issues and take them seriously, people think it’s a big deal and it’s a showstopper. If we encounter issues and say, ‘this is stuff everybody’s seen before, we’ll get to it’, then people think we’re not taking it seriously and we get beaten up for that. So it’s hard to know how to win.”
When asked later what other technical concerns he had about Constellation, Griffin deferred to Jeff Hanley, manager of the Constellation program, who identified three: post-landing contingency to support a “deconditioned” crew in a remote area after an emergency landing, the ability to land on either land or water, and developing a new thermal protection system for the spacecraft. However, Griffin cautioned, “we don’t really have problems with the things we think of ahead of time. It’s the ones that we don’t think of that bite us.”
Griffin made a few waves last September when he suggested that China would land humans on the Moon before the United States returned. “I personally believe that China will be back on the Moon before we are,” he said in response to a question during a September 17 speech. “I think when that happens, Americans will not like it, but they will just have to not like it.”
| “We’re kind of in a no-win position,” Griffin said. “If we encounter issues and take them seriously, people think it’s a big deal and it’s a showstopper. If we encounter issues and say, ‘this is stuff everybody’s seen before, we’ll get to it’, then people think we’re not taking it seriously and we get beaten up for that.” |
He returned to that point in response to a question after the STA speech, arguing that a return to the Moon is essential before the US can plan to go on to Mars. “I will be surprised if the United States is back on the Moon before China is on the Moon,” he said. “It will be no good in the affairs of the world if we find one day that a nation or a coalition of nations has gotten to the Moon and the United States is talking about going to Mars. Talking and doing are vastly different things.”
Griffin said that, with two pairs of launches of the Long March 5 rocket under development, separated by weeks or a few months, it would be possible for China to place an Apollo-class lander on the Moon. “I can’t be the only person to have figured out how to do that.”
China is not the only country that Griffin is thinking, if not worrying, about. Russia, he noted, has all the building blocks needed for a human lunar mission except for the lander, and after more than a decade of economic duress is now benefiting from an influx of petrodollars. “Russia has held on to its human spaceflight program against odds that would have made us quit,” he said. “When they have had a little more time to consolidate their gains from energy money coming in, to consolidate their economy, to figure out who they are and what their place is going to be in the world, I will be very surprised if they don’t venture out beyond Earth orbit.” He added that Russia “can pretty much do it” within about a half-dozen years of starting a human lunar effort.
Griffin also singled out India, a country that as yet does not have a human spaceflight program but has expressed an interest in developing one, funding permitting. “India is not going to allow on the Asian continent for a Chinese capability that they don’t have,” he said.
Griffin warned that, in his opinion, having a human spaceflight program was essential to being considered a leading world power. “I consider it to be impossible that other nations will be leading in space and the US still regarded has having primacy in the world. If other nations are leading in space, then the United States will be like Spain or Holland: once great, but no longer important in the affairs of humankind. I think that ought to matter to us… I don’t think we want to become Spain.”
Perhaps, then, that is the real legacy that Mike Griffin will leave NASA and the nation: a fear that the United States will become irrelevant, or at least no longer a world leader, if it does not maintain a leading role in human spaceflight by implementing ESAS. Like all legacies, though, it will take the judgment of time to determine if that concern, and its solution, are correct.
