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Laying a Foundation for Human

Space ExplorationBy Jerry Grey

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John Logsdons Commentary supporting U.S. President Barack Obamasproposal for future human space exploration [The Obama Plan: RisksWorth Taking, March 15, page 27] is right on the mark. It is indeed timeto set a new course that looks to the future, not the past one thatcapitalizes on the progress we have made since Americans first walkedon the Moon.

There is no disagreement with the hard fact that the space shuttle,despite the truly great technical advancement it represented and theexcellent work that NASA and the contractors have done in recent yearsto enhance its safety, is simply too costly and, moreover, is limited inreach to low Earth orbit. The presidents decision to support operation ofthe international space station to at least 2020 (and possibly to 2028,as has been suggested by the European Space Agency and otherpartners) does indeed recognize the value of the large investmentsmade in it to date, as well as its great potential for research as aNational Laboratory. True, the long period without any U.S. capability tocarry crew members there is a valid concern, but represents only a shortchapter in the context of Obamas multidecadal view of human spaceexploration beyond low Earth orbit.

Ending the shuttle era and canceling the Constellation project are evenmore of a concern to the economy and loss of jobs in several keystates, and the efforts of the relevant members of Congress to alleviatethis concern are understandable. There is no doubt that there will beserious effects on the economy of those areas that will slow theirrecovery from the recession. But this is an issue that will eventually giveway to the positive effects of the proposed NASA budget increase andthe development of new capabilities that can generate far more wealththan the obsolescent ones they will replace.

This brings me to what is by far the most important and significantelement of the new strategy: substantial funding for the conception,design and development of advanced-technology systems for bothhuman and robotic space exploration. These are not just blue skyvisions of wishful thinking, as some critics contend. Several potentialgame-changing prospects already have been identified that lean more tothe practical evolution of existing, proven technologies than to thevisionary.

For example, the need for a new heavy-lift launch vehicle, and especiallyits propulsion systems, has been recognized by supporters and critics ofthe new strategy. There are several realistic prospects for such systems

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that can be derived from well-proven engines. For the boost phase,there are two clear options, as cited by Elaine Camhis editorial in theApril issue of Aerospace America: the current operational EvolvedExpendable Launch Vehicles (EELVs). The Pratt & Whitney RocketdyneRS-68 engine that powers the Boeing Delta 4, planned for use in theAres 5 heavy-lifter that is now slated for cancellation as part ofConstellation, is certainly still a valid consideration for any new largevehicle, which could benefit both technically and fiscally from the workNASA has done on the Ares 5 design. The boost engine for the otherEELV, the Lockheed Martin Atlas 5, represents what might turn out to bean even better choice. The RD-180 engine, currently beingmanufactured by Russias Energomash, is itself a half-scale derivativeof the operational Zenit launchers RD-171 engine and the RD-170engine of Russias heavy-lift Energia booster that orbited Russiasspace shuttle Buran on its sole (unmanned) mission. Energomash saysthe RD-170 is reusable and, because it was to launch a human-carryingvehicle, readily susceptible to being human-rated. For those who mightbe concerned about too much reliance on Russia, it should be pointedout that RD Amross, a U.S. joint venture by Pratt & Whitney Rocketdyneand Energomash, is very close to producing a U.S.-built version of theRD-180, and with some infusion of NASA funding could be manufacturingthat engine (and perhaps even a 1.7 million-pound thrust equivalent ofthe RD-170) in a few years.

Because it is almost certain that any heavy-lift vehicle will require somethrust augmentation, the use of the shuttles proven, human-rated,four-segment Alliant Techsystems solid-propellant rocket motors for thatpurpose could be a wise choice, and also would help relieve some of theeconomic hardship resulting from the Constellation projectscancellation.

Another long-recognized requirement for human exploration beyond lowEarth orbit (and especially for long trips such as

those to Mars) is a high-performance upper-stage propulsion system.The performance of the J-2X engine planned for Constellation, aderivative of the J-2 used for Apollo, placed unrealistic (and very costly)demands on the required launch mass for such missions, as was pointedout by Stanley V. Gunn and Ernest Y. Robinson on this page a fewweeks ago [Recovering the Vision for Space, March 8, page 19]. Theyargue that the basic cost driver for Mars and equivalent high-energyhuman missions is the inadequate performance of upper-stage chemicalrockets, which also impose lengthy trip durations that exacerbateconcerns about crew exposure to galactic cosmic radiation. Gunn andRobinson make an excellent case for addressing these issues by usingnuclear-thermal propulsion, which was brought to the brink of operationaluse in the 1960s by the $1.5 billion NASA/U.S. Atomic EnergyCommission Rover/NERVA (Nuclear Engine for Rocket VehicleApplication) program. Building on the existing bank of that technology todevelop, test and deliver an operational nuclear-thermal upper stage,thereby enabling practical pursuit of human missions to Mars andbeyond, would be a truly judicious use of the new NASA technologydevelopment budget.

Another area for NASA technology investment that would facilitatehuman space exploration is orbital refueling and assembly of spacecraftfor extended solar-system exploration missions. Successful initialdemonstrations of refueling and repair capability were conducted duringthe Defense Advanced Research Projects Agency/NASA Orbital Expressproject in 2007, and subsequent efforts have shown much promise.Incidentally, China has given strong indications that it plans to use orbitalassembly for its upcoming lunar missions.

These are but a few of the opportunities that could be opened by the


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infusion of technology funding that is a centerpiece of the new NASAstrategy. As Logsdon pointed out, Obamas proposal is certainly not astep back for human space exploration by the United States. Indeed, itenables the implementation of the long-term, multidecadal approach thatis essential to the success of human space exploration beyond lowEarth orbit.

Jerry Grey is a consultant to the American Institute of Aeronautics and

Astronautics and Universities Space Research Association, and aformer professor of aerospace engineering at Princeton University.

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