Monday, May 17, 2010

Flexible Path to the Moon: Cislunar Space

This post continues yesterday's discussion on NASA's cislunar space plans on the Flexible Path to Mars by comparing those plans with those of the Flexible Path to the Moon at the same destinations.

The Flexible Path to the Moon includes three phases:
  • establishing a solid foothold in LEO with commercial and international participation as well as technology development while robotic precursors blaze an exploration trail
  • moving beyond LEO to cislunar space destinations like GEO, lunar orbit, and Earth-Moon Lagrange points
  • returning to the surface of the Moon

Each phase is intended to be self-sustaining, to produce useful economic, science, and security benefits, to develop reusable space infrastructure, and to enable more ambitious steps.

It's natural to concentrate either on the first or the last of the three steps on the Flexible Path to the Moon. The first step, establishing a foothold in LEO while robotic scouts move ahead, is our most immediate concern. In the context of the 2011 NASA budget, the NASA human spaceflight exploration work for the next several years will be entirely devoted to this step, although with a view towards the Augustine Flexible Path to Mars. Most of our near-term decisions center around this first step, so it's no surprise it's of great interest.

It's also natural to emphasize the activity that will take place on the lunar surface. The Moon is an entire world waiting to be explored and developed. Although the activities to be done on the Moon's surface would be quite different from the ones performed during the Apollo missions, Apollo gives us a conceptual framework that allows us to easily imagine what might be done there. Fiction and our experience on Earth fill in the gaps that Apollo leaves out. Not only that, but reaching the Moon is the central destination and ultimate goal of the Flexible Path to the Moon. Right?


In the Augustine Flexible Path to Mars, it is probably fair to say that Mars is the ultimate, central destination. The Flexible Path to Mars is about exploring new places to learn about them while getting closer to exploring and learning about Mars.

In the Flexible Path to the Moon, the Moon is actually not the ultimate, central destination, in spite of the name. The Flexible Path to the Moon is intensely focused on the Earth. It is about exploring and developing LEO, cislunar space, and the Moon for the benefit of people on Earth. This can be illustrated by considering the second step on the path, developing cislunar space.

Apollo 8's lunar flyby wasn't our goal in the 1960's. The Ares rockets weren't intended to allow astronauts to linger at cislunar space destinations or to develop infrastructure there. Even in the Augustine Flexible Path to Mars, the cislunar space destinations are treated as mere stepping stones on the way to adventuresome excursions to more distant destinations like asteroids and Mars moons.

In contrast to the Apollo, Constellation, and Flexible Path to Mars approaches that minimize beyond-LEO cislunar space destinations, the Flexible Path to the Moon treats the work that can be done and the benefits that can be gained at GEO, Earth-Moon Lagrange points, and lunar orbit as the heart of the Flexible Path to the Moon. All of the steps on this path can produce benefits for the taxpayers on Earth, but it is the intense focus on deriving economic, security, science, and other benefits from the cislunar space destinations where the Flexible Path to the Moon contrasts the most with Apollo, Constellation, and the Flexible Path to Mars.

In the Flexible Path to the Moon, cislunar space destinations "between" LEO and the lunar surface are not like the empty airspace between your departure and arrival locations on a plane trip, even though there are no rocky bodies there. These destinations are like unpopulated versions of the American West that the new nation on the Eastern seaboard (LEO in our analogy) looked forward to exploring and developing on the way towards the future great cities on the Pacific ocean (the Moon in our analogy).

In other words, cislunar space is not just a "middle-man" between LEO and the lunar surface. We don't want to skip past this step as quickly as possible on the way to the Moon, because this step not only makes the lunar surface more accessible in the long run, but it also serves the same sort of purpose that the Moon itself serves.

Here are a few observations about the activities that can be done at the cislunar space destinations:

  • Reaching these destinations is easier than reaching more distant destinations like NEOs or Mars moons. We can get there affordably and safely with considerably less capability (low-cost commercial operations, new technology, propellant depots, heavy lift, etc) than these more difficult destinations. We can also be more confident that a development effort to reach these destinations will succeed.
  • Reaching these destinations helps enable later exploration at the lunar surface.
  • Reaching these destinations and spending the considerable time and effort to make the most of these destinations before venturing beyond them helps make later exploration and development at the lunar surface more affordable, achievable, and sustainable, even though it may delay the beginning of these missions.
  • Reaching these destinations helps enable later exploration at more distant Flexible Path to Mars destinations (for example, NEOs and Mars orbit), as implied by the Augustine Committee report.
  • Reaching these destinations and spending the considerable time and effort to make the most of these destinations before venturing beyond them helps make later exploration at more distant Flexible Path to Mars destinations more affordable, achievable, and sustainable, even though it may delay the beginning of these missions.
  • Making the most of these destinations enables a wide variety of commercial space activity. This activity in turn should strengthen the space industrial base, add jobs, and enable more useful services that can be enjoyed by the taxpayer.
  • These destinations offer benefits across the spectrum of space science fields: Earth science (assembly/servicing, full-Earth data collection), Heliophysics (observatory assembly/servicing), Astrophysics (observatory assembly/servicing), Planetary Science (lunar telerobotics, lunar sample return, lunar remote sensing from astronaut spacecraft, lunar orbiting satellite assembly/servicing, preparation for astronauts at the lunar surface, test and setup for later planetary science at more distant destinations), and various ISS sciences (similar activities outside LEO).
  • The capabilities enabled and encouraged by these destinations (satellite assembly/servicing/inspection, fuel depots, reusable space infrastructure, reusable in-space transportation, etc) are highly useful for national security purposes.
  • Many of the activities at these destinations require some sort of space infrastructure like satellite servicing or exploration spacecraft assembly nodes. This may bring visions of multi-decade development efforts to build facilities like the ISS, followed by difficult logistics requirements. This need not be the case. These nodes can be considerably smaller than the ISS, and could be focused on specific tasks. Also, these nodes do not need to be permanently occupied (and given radiation considerations may very well not be), so the logistics requirements could be much easier than those of the ISS.
  • These destinations provide an interesting variation on space stations. They are harder to reach than LEO, but they have advantages, too. These destinations don't present a requirement for reboost because of atmospheric drag as the ISS orbit does. They don't have the same sort of space debris problem. Microgravity work would not have to suffer from perturbations due to Earth's imperfectly symmetrical gravity field. Instruments and materials would not suffer the same sort of weathering.

These benefits the cislunar space step are important, but what about the Moon? Even if our reach falls short and we don't get to the lunar surface sustainably during this effort, we will have accomplished much if we develop cislunar space. If we do establish ourselves on the Moon in a long-term sense, our initial efforts will still be centered on the cislunar space destinations, and thus on benefits to the people on Earth. Our mission at the lunar surface is not to do lunar surface science, although we may do some of that. It is not to set up a permanent lunar colony, although our work in this phase may bring us closer to such a colony. Our purpose on the lunar surface is to use the Moon as a force multiplier to increase our productivity at the cislunar space destinations.

This will be done in part through the demands that the lunar surface will place on the cislunar space destinations. Our capabilities and infrastructure at these destinations will need to grow to satisfy the demands of the lunar surface work.

It will also be done through the use of lunar resources. Lunar resources can help make lunar surface work affordable, but they will eventually be needed in cislunar space destinations, too. The initial cislunar assembly, servicing, and depot capabilities will be greatly enhanced through the use of these lunar resources.

The work on the lunar surface benefits the taxpayer on Earth mainly through the improvements this work enables in cislunar space. The lunar surface and cislunar space destinations become mutually supporting in a virtuous circle of sustainable and even expanding commercial, industrial, and science capabilities and infrastructure.

In the long run we may ultimately use lunar resources to make closer (i.e. LEO) or more distant (i.e. NEO, Mars moon, etc.) activities more affordable. The development of these resources may even result in a strong permanent presence on the Moon that ultimately develops its own reasons for being. However, with the Flexible Path to the Moon, this process will start by using lunar resources to address needs in cislunar space, which in turn address needs on Earth.

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