Destinations for exploration: more than just rocks?
by Dan Lester and Giulio Varsi
|Certainly our national goals for space exploration involve more than just science. However, a large amount of the science we want to do in space has little need for surface locations and, in fact, would benefit by not relying on them at all.|
A thoughtful overview of proposed destinations is important at this time. NASA is designing its approach to the President’s Vision for Space Exploration (VSE) by focusing entirely on the development of a human-tended lunar outpost. While many space science pursuits have been suggested for the lunar surface, it is by no means clear that many are uniquely or even conveniently enabled by it. With the important exception of science that explicitly involves geological and perhaps atmospheric research, much of what space scientists want to do can actually be done better in free space. We’d like to share an increasingly common view within some science communities about how major, publicly-appealing goals can be achieved by using NASA’s evolving space exploration technology and the vehicles (what is often called the “architecture”) of the President’s exploration initiative. Such achievement is possible if we think more broadly about human and robotic destinations as “vantage points” on the Universe, including the Earth.
Yes, we’re going back to the Moon as human explorers but, as the architecture is developed to do that, is it going to provide capabilities to build, maintain, and oversee facilities in free space as well? Might this architecture also allow us to construct the large craft that will eventually take people to Mars? While such free-space capabilities were repeatedly demonstrated with the development of the International Space Station (ISS) and the regular servicing of Hubble Space Telescope (HST), our nation has no future plans to use these capabilities in the context of the new architecture. Without some serious reconsideration, a modern counterpart to the failure in the Apollo legacy appears to be looming: a huge investment in capabilities that were largely shelved. On the one hand, NASA plans to have us travel vast distances to Mars while, on the other hand, it seems willing to abandon the very in-space construction and maintenance capabilities that may be necessary precursors to such long voyages.
It is a common theme in the evolving exploration initiative that destinations for our nation in space include only sites that people can walk or drive around on. The Moon-to-Mars (and maybe Near Earth Objects) premise of the initiative would seem to explicitly define priority destinations as those endowed with rocks, volatiles (ices), and dust. Perhaps it’s just backlash from the "round-and-round" frustration with ISS in low Earth orbit. But this definition has to be rooted in much more than a simple call for flags and footprints, as the architecture now being developed is wholly focused on getting to a place where our flags and footprints can already be found. So it must be more than that.
Our historical picture of exploration is truly well “grounded”, in that “going where no one has gone before” has almost always involved a solid surface. From Magellan to Roald Admunsen, from Meriwether Lewis and William Clark to Edmund Hillary, we admire explorers through the grit they bring back on their boots, if not the footprints that they leave. Perhaps the only historical counter-examples were the early ballooning and aircraft pioneers, the barnstormers for whom exploration was the adventure of leaving the Earth’s surface. While exploration often explicitly involves the search for riches that would improve someone’s quality of life—and such material riches are not as likely to be mined in the vacuum of free space—exploration can just as well be used to proudly assert endurance, planning, fortitude, and the pursuit of strategic knowledge. Those qualities are independent of dust and rocks. With respect to identifying riches, exploration has a strong subtext of fence-building and property rights. That’s hard to do without a solid surface. The Montgolfier brothers never had a chance to drive stakes into the upper troposphere nor did Chuck Yeager in the stratosphere nor astronauts in low earth orbit. Merely flying through air or space thus seems to be a lesser form of adventure and exploration. That’s a pity, because a picture of exploration defined by standing on rocks does not reflect the new Information Age in which we live, where high bandwidth enabled immersion allows more people to come along for the adventure.
|Thirty years ago, astronomical telescopes on the lunar surface looked profoundly enabling because we simply didn’t know how to point telescopes in free space. We do now, and we do it better—using, for example, the twenty-five-year-old technology of the Hubble Space Telescope—than with any telescope on the surface of the Earth.|
While the promise of in situ resource utilization (ISRU) in a low-gravity potential well is an oft-cited justification for a human-based lunar return, its marketability and feasibility are problematical. This promise has yet to excite any substantial private interest, and the engineering is hardly as simple as some have suggested. Moreover, using those resources off the Moon involves in-space capabilities that NASA appears ready to abandon. NASA’s Decadal Planning Team (DPT) and the NASA Exploration Team (NExT), quietly constituted in the early part of the decade (see “Forging a vision: NASA’s Decadal Planning Team and the origins of the Vision for Space Exploration”, The Space Review, December 19, 2005), attempted to break the lock that the lunar surface had on the imagination of human spaceflight advocates by identifying destinations in free space as more suitable stepping-stones to other scientifically-fertile destinations such as Mars. Nevertheless, the US space agency appears once again to be focused solely on the old rocky landscape of the Moon, important as it may be for understanding our Solar System, but also limiting in terms of the vantage point it provides.
That’s not to say that free-space is being ignored. Such free-space science is already substantially funded through the NASA Science Mission Directorate. However, a broad commitment by the science community to the human exploration initiative and the architecture it develops will strongly depend on what else, besides the lunar surface, it can be used for. From the perspective of many science investigations, the value of the lunar surface is limited, even without accounting for the enormous cost of landing and surface operations. An exception may be studies of the Moon itself, for which we are seeing a renaissance of profound questions. See, for example, the newly released final report from the National Research Council’s Space Studies Board “The Scientific Context for Exploration of the Moon”. This seminal view of the Moon as a vantage point on the history of the silicate planets in the Solar System is compelling, but many of the important goals may well be achieved cost-effectively using robotic methods with a sustainable program of robotic lunar science missions, as is already being accomplished very effectively on Mars.
As mentioned earlier, the diminishing value of the lunar surface is due to advances in supporting technology. Thirty years ago, astronomical telescopes on the lunar surface looked profoundly enabling because we simply didn’t know how to point telescopes in free space. We do now, and we do it better—using, for example, the twenty-five-year-old technology of the Hubble Space Telescope (HST)—than with any telescope on the surface of the Earth. A “debate” on the relative merits of the Moon for astronomy is found in a recent issue of Physics Today. The situation is the same for the Earth sciences and observations of our Sun: costs and operational simplicity seem to favor by a large margin locations in free space such as the Earth-Sun Lagrange points over the lunar surface. While lunar soil may offer a record of solar activity that is valuable to heliophysicists, realtime monitoring of the Sun and the solar wind does not need to be anchored on regolith. Overall, the lunar surface presents a challenging environment, with dust and power generation problems as well as the difficulty of precision soft landing.
It is useful to point out that a focus on the value of in-space locations should not be misinterpreted as diminishing nor threatening the role of human spaceflight. While many science communities are unexcited about the costs and complexity of lunar surface operations conducted by humans, many of the same communities have nevertheless gained substantially from human spaceflight. In addition to the exciting HST servicing, astronauts were able to free a recalcitrant antenna on the Compton Gamma Ray Observatory and regenerated the Solar Max mission. On the other hand, it is equally true that the human spaceflight effort promised, or at least led scientists to believe, that it would lead to huge science returns. That hasn’t happened. So while it is with some trepidation that we reach for human exploration-enabled science that has a broad scope, that shouldn’t stop us from trying. However, it seems wrong-headed to accept casually the additional costs of operating on the dusty and thermally-variable lunar surface where any offsetting gains seem implausible.
Considering only the architectural elements, there are some extraordinary capabilities being developed by our new space exploration program. The Orion Crew Exploration Vehicle (CEV) will be the new human transport craft and will, in principle, be capable of operating through cislunar space, perhaps even at the Sun-Earth Lagrange points, where many of our future science missions will be located. Whether this would permit astronaut EVAs giving hands-on access to science facilities (à la HST), or just zero-latency telerobotic maintenance and servicing, will need to be determined. The present Orion CEV has no airlock, for example, and those EVAs might depend on developing such a capability. Accessibility by humans to the Earth-Moon Lagrange points is more plausible, and these points are connected with the more distant Sun-Earth Lagrange points by very low-energy pathways. The Earth-Moon Lagrange points could thus be enabling jobsites for facilities usually stationed much farther away. The advantage of free-space operation from a logistics perspective was recently summarized in Logistics Spectrum, vol 41, p. 4.
|While many science communities are unexcited about the costs and complexity of lunar surface operations conducted by humans, many of the same communities have nevertheless gained substantially from human spaceflight.|
Whether done by humans on site, or by teleoperated robots, the value of servicing, maintenance, and upgrade to high-dollar science investments in free space seems compelling, but should be carefully evaluated. Actual construction of large science facilities in space is a more clearly enabling capability. From an astronomical perspective, the six-meter diameter aperture James Webb Space Telescope (JWST) is pretty much the largest filled aperture telescope that can fit into a currently-available launch vehicle. If we ever want a significantly larger telescope with these launch vehicles, it will have to be assembled in free space. So it is particularly important that these potential Orion and robotic capabilities be assessed sooner, rather than later, so that provisions may be made for their subsequent addition rather than having to resort later to a complete and vastly more expensive redesign. So far, NASA has expressed some interest in these potential capabilities of Orion that might broaden its value and public appeal, but it has not taken proactive programmatic steps to look at them carefully.
A second capability that is starting to generate interest in the science community is the Cargo Launch Vehicle (CaLV), or Ares 5. This mammoth vehicle is being designed to loft both the lunar lander module as well as the Earth Departure Stage that will carry the module, after docking with the independently-launched Orion CEV, to the Moon. The Ares 5 is potentially enabling to science not just because of its huge lift capability—60 metric tons to Earth-Sun Lagrange points—but also because of the enormous payload shroud diameter, now baselined at 8.4 meters, and perhaps expandable well beyond that. Compare this with the 4.4-meter shroud diameter for the Ariane 5 (to be used as a launcher for JWST), or the five-meter diameter of the 500-series Atlas 5 (both being able to lift roughly 10 metric tons to the Earth-Sun Lagrange points). Why is shroud diameter so important? Ares 5 could easily launch a six-meter monolithic telescope with the primary mirror fully deployed, and perhaps even the ten-meter Single Aperture Far Infrared (SAFIR) mission, the concept for which has been examined carefully by NASA. Launching the primary mirror of a telescope fully deployed dramatically reduces mission complexity and risk. It is mind boggling to realize that Ares 5, roughly comparable in capacity to the now discontinued Saturn 5 and Energia, could launch a state-of-art six- to eight-meter-class ground-based telescope like Gemini or Subaru! As for the CEV above, early understanding of the potential of Ares 5 for other uses could assure a design that offers maximal value.
Although we have highlighted some remarkable free-space science opportunities that could derive from the exploration architecture, it should be understood that Moon- and Mars-centric efforts for human exploration could benefit as well. Support for sustained operations on the lunar surface could benefit from depoting in free space, as could sample-return from operations there. Eventual ISRU propellant and life-support products could be accessible more widely if stored in free space, rather than on the lunar surface. As stated above, development of the transportation system that will carry humans to Mars could benefit from refined skills of in-space construction, ideally using straightforward augmentations of the exploration architecture. While perhaps a return to the Moon, as currently planned, is the best stepping-stone for a trip to Mars, perhaps it isn’t the only pathway worthy of consideration, just as the Decade Planning Team discovered five years ago.
Non-lunar science opportunities for the exploration architecture appear attractive. As a result, it is probably naïve to reflexively dissociate the broader priorities for space science from the efforts of an initiative that is conventionally perceived as creating just a human-attended lunar outpost. It is essential that human spaceflight advocates recognize that desirable destinations for this architecture extend well beyond those characterized by regolith and gravity. Free space remains a scientifically compelling venue. The VSE calls for destinations driven by multiple goals, one of which is science, and the science that can be done from free-space vantage points as well as on the surface of Mars are both ultimate goals. Let’s not craft a vision for space exploration that just finds itself up on the rocks.