Issue Date: February 5, 2007
NASA Gets Ready To Revisit The Moon
It's been nearly 35 years since the National Aeronautics & Space Administration's Apollo missions last sent humans to the moon. Since that time, the agency has focused its human space program on establishing and maintaining a presence in low Earth orbit using the space shuttle and the International Space Station (ISS). But with the shuttle fleet nearing retirement and the space station providing only limited capabilities, the agency's human space program has faced an uncertain future. Amid these realities, a question has been looming: Can NASA be content to continue sending astronauts to ISS or should it redirect its efforts elsewhere?
The answer came in the form of the Vision for Space Exploration, which President George W. Bush rolled out in January 2004. The vision directs NASA to move beyond low Earth orbit and return to the moon by 2020 in preparation for exploring Mars and other solar system bodies. Although NASA embraced the idea of going back to the moon as a stepping stone to deeper space missions, concerns are growing over the cost of such missions and NASA's ability to follow through on long-term programs.
"There is a history in NASA's space program, especially on the human space flight side, of not paying much attention to the cost of a mission as a constraint," says Howard E. McCurdy, chair of the department of public administration and policy at American University in Washington, D.C. "The result is that some technologies may be developed for the short-term objective like getting back to the moon, but they may not be applicable for the long-term objectives like expanding missions into the inner solar system."
This lack of focus on the financial constraints at NASA means that undertakings with a longer term purpose get short-circuited, and the shorter term component becomes an end in itself. For example, McCurdy explains, the space shuttle was always intended to go to a space station, but there was no station for it to go to until the past few years, so the shuttle had to be its own space station. Similarly, he adds, "ISS was supposed to be a means to something else, but now it's become a laboratory in space where you don't get to do experiments."
NASA is hoping to avoid repeating this history. As a first step, the agency unveiled its plan in December to return astronauts to the moon by 2020. The plan outlines a timeline for lunar missions, the location of a lunar outpost, and other mission details. One detail absent from the plan is the cost. NASA officials acknowledge that the agency will have a fixed budget for the foreseeable future, which means the agency will have to allocate resources carefully and tweak the performance capabilities of mission components. In other words, NASA may not be able to afford to do everything to the extent it would like.
McCurdy points out that it's possible to squeeze a lunar mission using Apollo-era technology into NASA's $16 billion-per-year budget, but the story is a bit different for a Mars mission. "If you scale up the moon mission for a Mars mission, it comes out to something like $800 billion, and that's just not within NASA's budget in the foreseeable future," he says.
The question McCurdy has for NASA is whether the agency wants to go to Mars badly enough to be willing to reinvent the space program. "The answer I've heard to date is 'no,' and that NASA would rather stay with old approaches, old technologies, and the easy way of doing things," he says.
One way NASA is hoping to supplement its tight budget is through international and private-sector partnership. Agency officials have already begun talks with several countries interested in being part of the lunar mission, and they also are looking for ways to involve the private sector.
For its part, the private sector doing business in human space travel isn't waiting for NASA to get to the moon. In fact, some observers believe NASA should let the private sector develop the details of how to get to and from the moon and should focus instead on next-generation technologies, such as nuclear propulsion, which will enable deeper space travel.
"NASA should be playing a Lewis and Clark function with respect to space travel," says Rick Tumlinson, president of X-Tremespace and Orbital Outfitters. In other words, he says, "NASA should go over the hill and tell us what's there. Then the private sector can go out there and figure out ways to utilize it and create wealth from it."
Tumlinson points out that companies are developing the capabilities to go to the moon and are likely to have private citizens there before NASA returns its astronauts to the moon. Because these companies are already building rockets and vehicles to carry payloads and people to space, he says, NASA would make better use of its limited dollars by providing incentives to the private sector. "NASA should buy the ride, not the rocket," he says.
Aside from concerns that NASA may repeat history by failing to reach its long-term goals and isn't focusing its limited dollars on next-generation technologies, there is also growing concern that the agency will reallocate funding from other programs, including scientific ones, that are not essential for exploration. This concern is shared by space-minded scientists both inside and outside of NASA.
"The NASA budget is so tight that we must be careful not to squeeze out good science," says David S. McKay, chief scientist for exploration and analysis at NASA's Johnson Space Center. He admits that cuts already have impacted research areas such as astrobiology, but he hopes that the cut funds will be restored eventually. "Those cuts have not been the best thing for the science part of NASA, but hopefully, we'll recover from that," he says.
NASA's Earth-observing satellite missions already are feeling the pinch. A report released by the National Academies last month detailed significant cuts to satellite missions that collect climate data at a time when such data have become ever more essential (C&EN, Jan. 22, page 7).
With evidence like that in the National Academies' report, NASA's funding decisions are being watched closely by Congress. Even though the 109th Congress passed legislation in support of the vision plan, the House of Representatives Committee on Science & Technology as well as the Senate Committee on Commerce, Science & Transportation have been monitoring the agency's allocation of funds within the ambitious new context. The committees' aim is to ensure that important science isn't being squeezed out. This oversight of NASA will likely lead to congressional hearings as the agency moves forward with its exploration agenda.
Observers also are concerned about how the astronauts will occupy themselves once they get to the moon. "Nobody is clear on what science the astronauts are going to do on the moon," says Robert L. Park, physics professor at the University of Maryland. For him, it's another case of NASA designing a mission and then going back to find the science to rationalize it.
"To invent the project and then look for the science to justify it is not the way it should be done," Park says. He explains that this model was used for ISS, which "is why it is such an abysmal failure."
The underlying problem is that there is no apparent demand for a human lunar lab, Park points out. "If the science community is interested in working on the moon, they should be hounding NASA" for the opportunity to set up a research lab on the moon, but that's not what's happening, he says.
The lunar plan spelled out by NASA says only that the lunar base will be used to test exploration techniques and technology, as well as serving as a science outpost, but does not give a list of specific objectives.
It's this use of the base as a science outpost that has some stakeholders baffled, since science objectives have yet to be set. The only science-related objectives expressed as essential are the development of the necessary technologies to take advantage of the moon's natural resources to produce oxygen, hydrogen, and propellant. NASA says it will rely on input from the scientific community to devise a complete list of other scientific objectives.
In light of the questions surrounding mission objectives, and because of the great success of the Mars rover program, Park questions why humans need to be sent into space at all.
"Sending humans to the moon is so old-fashioned," Park says. "To put human beings in dangerous places is bad enough, but to do it at an enormous expense compared with robots" is unacceptable, he tells C&EN.
"For the kinds of things the rovers are doing on Mars, for example, robots are just fine," he says. "If there are other robotic capabilities that need to be developed, let's do it." After all, he adds, "there's a market out there for robotic technology as compared with a limited market for advanced space suits."
Although others agree that robotic technology has come a long way, they are not ready to give up the human space program.
"Robotic technology has advanced far more rapidly than human space flight technologies have," McCurdy acknowledges. But, he adds, the most objective studies he's seen still suggest that a human presence has an advantage over robots, although one that may be short-lived as artificial intelligence continues to improve.
For its part, NASA remains committed to continuing its human space program in tandem with its robotic program. To that end, the agency has nailed down some of the general details for its mission to the moon in its lunar strategy. Perhaps the most important decision is that NASA will not be doing the Apollo-type of sorties that hopscotched around the moon. Instead, the agency will select a single location and develop the capabilities necessary to support a permanent, self-sustaining lunar base there.
The success of NASA's return endeavor on the moon lies with three key factors, according to Lawrence A. Taylor, director of the Planetary Geosciences Institute at the University of Tennessee, Knoxville. Taylor has studied lunar science and resources for decades and is developing techniques using microwave radiation to process lunar soil. The factors he and others cite are power, location, and resources.
The energy needs of the lunar base will initially be supplied by solar cells. To maximize its ability to generate solar power, NASA says it will target a location on the south pole of the moon that is nearly continually exposed to the sun.
The current plan is for a solar tower to be carried to the moon and assembled there by the astronauts. This approach would require NASA to send all of the materials for the tower from Earth, which at a cost of $200,000 per kg by some estimates, would add noticeably to the mission's price tag.
One way to avoid the material transport cost would be to use the moon's resources to build the solar panels on-site. That's exactly what a research group led by Alex Ignatiev, director of the Center for Advanced Materials at the University of Houston, is working on.
Ignatiev's approach takes advantage of two key lunar resources: the ultra-high-vacuum environment and the lunar rocks and soil. It turns out that the vacuum on the moon is comparable with the best vacuum chambers found on Earth; that is, the vacuum is at about 10-15 atm. Also, the lunar rocks are composed of oxides that include silicon dioxide from which silicon can be extracted.
The process Ignatiev has designed couples the vacuum environment with on-site silicon extraction to produce thin-film solar cells that can be deposited directly on the lunar surface. To do this, lunar rocks on the surface are melted to form a glass, which serves as the solar-cell substrate. From there, "we process additional lunar rocks, extract out the silicon, and use it to make thin-film silicon solar cells in this great vacuum chamber that is the moon," Ignatiev says.
These cells are not very efficient—less than 10%, according to Ignatiev. But, he says, the low efficiency is not necessarily a detriment. He notes that his team has shown that a large number of solar cells can be made and deposited directly on the lunar surface. This production and deposition can be done using a small autonomous crawler, which is in the early design phase and is expected to be about 1 meter wide by 2 meters long and weigh about 300 kg, he says.
The crawler will move across the lunar surface at about 1 meter per hour and deposit interconnecting solar cells that, over time, could generate as much as 100 MW to a gigawatt of energy capacity, Ignatiev says. Because a lunar base may require only hundreds of kilowatts to a couple of megawatts, he explains, "you can then think about taking that extra energy and beaming it to Earth or elsewhere in space."
Another key factor in deciding where to establish a lunar base, according to Taylor, is the diurnal temperature cycles. These swing wildly for regions near the moon's equator, going from an average daytime temperature of 125 °C to a nighttime one of -150 °C, he points out. The temperature at the poles is more stable, he says, with the temperatures in the dark areas ranging from -220 to -250 °C and in the sunlit areas holding at about -50 °C, with an up or down swing of only 20 °C. These conditions reinforce the sunlit areas of the pole as an optimal outpost location.
The final factor, Taylor explains, will be NASA's ability to effectively use the moon's natural resources. The initial focus of the astronauts will be on finding oxygen and hydrogen sources from which key materials can be derived, including oxygen for breathing, water for drinking and other uses, and propellant for space travel.
The key elements—oxygen and hydrogen—are widely available in the lunar soil as oxides and as particles delivered by the solar wind. There may also be water at the poles in the form of ice, which could be used to yield the key elements directly.
Probes now set for launch in 2008 will be looking closely at the polar regions, where ice caps may be hidden in the dark areas. But if they fail to find ice or if ice there turns out to be unusable, then the materials will have to be mined from the soil through a variety of techniques depending on the exact soil composition.
One technique involves heating the lunar soil to extract the hydrogen, McKay explains. At a high temperature, the hydrogen can then be used to reduce the iron oxide in the soil to yield oxygen. Early missions will set up test plants to determine the most efficient extraction methods.
As NASA works through the details of the lunar mission, the agency will continue to be asked to justify itself-both for how it's allocating its resources and why the mission is worth pursuing. After all, McCurdy tells C&EN, "there are useful things one could do on the moon, but they, in and of themselves, would not justify the establishment of a lunar infrastructure."
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