Paul D. Spudis
The Once & Future Moon
Smithsonian Air & Space
A plan for a human mission to a near Earth object (NEO; an asteroid), designed by engineers from Georgia Tech and the National Institute for Aerospace (GT/NIA), was recently posted online. Keying in on lowering program total costs, this architecture eliminates the need for a new heavy lift launch vehicle (HLV) by advocating the placement and use of space-based propellant depots.
Doug Stanley, one of the co-authors of this study, previously led NASA’s 2005 Exploration Systems Architecture Study (ESAS). ESAS (a.k.a. Project Constellation, NASA’s chosen blueprint to implement the Vision for Space Exploration) was widely reviled by many in the space community as an Apollo Redux-style, unaffordable approach to lunar return. The 2009 Augustine Committee Report concluded that without a significant increase in NASA’s budget, a return to the Moon under the Constellation architecture was not achievable. President Obama’s Administration subsequently announced it was terminating both Constellation and lunar return.
This new study is an interesting approach to the problem of staging a human asteroid mission. It is written partly in response to the recent NASA Human Exploration Framework Team (HEFT) study, which designed and estimated costs for an asteroid mission in 2026 (the date called for in the Administration’s re-design of our strategic direction in space). The HEFT architecture was briefly famous two months ago, when it was pointed out that it had incorrectly concluded that NASA is unable to build a heavy lift launch vehicle under the Congressionally mandated cost and budget envelope of its recent authorization.
The new GT/NIA study proposes that commercial launch services, coupled with Earth orbital propellant depots, can create the infrastructure needed to stage a human mission to a NEO in 20 years (by 2031). While reviewing details of the study, I was specifically drawn to their cost estimates; the GT/NIA study concludes (depending on the specific launch options selected) that a human asteroid mission can be accomplished (by the time specified for a total program cost) for between $73B and $97B (constant FY2010 dollars). This number contrasts with the HEFT study estimate of $143B (an approach that develops and uses a 100 mT heavy lift launch vehicle).
What benefit do we gain with this expenditure? By 2031, we will have conducted a human mission to an asteroid, thereby reaching the first rung of the Augustine challenge for America’s space program to conduct a “series of space ‘firsts’.” We’ll have emplaced a fuel depot system that can support future human missions to other asteroids, or the moons of Mars (also called for in Augustine’s 2009 “Flexible Path” approach). As NASA will have no launch capability in the future, fuel supplied to these space-based depots will be dependent on commercial deliveries of propellant from Earth. This will be the “new way” of space – depots with fuel supplied by commercial vendors for sortie missions to various and as yet unspecified destinations. All of these missions will be dependent on the necessity of everything needed for space operations being launched (currently, deemed prohibitively expensive) from the surface of the Earth.
I have argued elsewhere that the “launch everything from Earth” template we’ve been locked into for the last 50 years has imprisoned us. Because of the “tyranny of the rocket equation,” we’ve been capability limited – hobbled by upfront launch requirements that consume otherwise useful reserves of mass and power – just to get into space. Propellant depots do not address this fundamental conundrum; they simply obviate the need for a very big launch vehicle by allowing us to stage complex, heavy missions from Earth in smaller increments. Propellant depots are a necessary but insufficient element in a long-term space faring strategy. To truly change the rules of spaceflight, we need to learn how to access and use what we find in space to create new capabilities in space. This involves learning how to use extraterrestrial resources of material and energy.
The Moon was picked as the first destination of the original Vision for Space Exploration because it contains resources in an accessible and readily usable form. By skipping past the Moon, it is certain that we will not use space resources for decades because, in order to access and begin using asteroid materials, we will need long-term, if not permanent, presence in the vicinity of the asteroid to characterize, experiment, and learn how to process its resources into usable forms. Initially, robotic missions can begin the characterization of resources, but robots are not sophisticated enough to set up and begin operating a production pipeline, which requires both repetitive and intelligent interaction with the processing. Unlike the Moon, the duration of human presence around a given NEO will be extremely limited by the ironclad laws of celestial mechanics.
It’s interesting to compare the new GT/NIA plan with the lunar return architecture that Tony Lavoie and I recently published. Our architecture also uses propellant depots, initially supplied from Earth but ultimately supplied from the Moon. It creates an expandable, fully functional resource outpost on the Moon, complete, with a reusable, extensible Earth-Moon transportation system capable of exporting rocket propellant to cislunar space within 16 years, at a program cost of $87B.
The affordable lunar return architecture begins the dissolution of space logistics from Earth’s apron strings, leaving in place a legacy infrastructure that can eventually take us beyond cislunar space. Such a system has important scientific, economic and national security value. In contrast, as much as I applaud the GT/NIA effort, their plan spends between $73-97B over 20 years for a single human mission to an as-yet unselected destination, and in the end, has us still launching everything from the Earth.
As painful as this upheaval in the space community has been, it need not be in vain. Both economic and scalable function is required for space operations. A healthy, viable national space program needs purpose and a return on investment. By returning to the Moon and using its resources, we get what we need in order to get what we want.