John Logsdon’s Commentary supporting U.S. President Barack Obama’s proposal for future human space exploration [“The Obama Plan: Risks Worth Taking,” March 15, page 27] is right on the mark. It is indeed time to set a new course that looks to the future, not the past — one that capitalizes on the progress we have made since Americans first walked on the Moon.

There is no disagreement with the hard fact that the space shuttle, despite the truly great technical advancement it represented and the excellent work that NASA and the contractors have done in recent years to enhance its safety, is simply too costly and, moreover, is limited in reach to low Earth orbit. The president’s decision to support operation of the international space station to at least 2020 (and possibly to 2028, as has been suggested by the European Space Agency and other partners) does indeed recognize the value of the large investments made in it to date, as well as its great potential for research as a National Laboratory. True, the long period without any U.S. capability to carry crew members there is a valid concern, but represents only a short chapter in the context of Obama’s multidecadal view of human space exploration beyond low Earth orbit.

Ending the shuttle era and canceling the Constellation project are even more of a concern to the economy and loss of jobs in several key states, and the efforts of the relevant members of Congress to alleviate this concern are understandable. There is no doubt that there will be serious effects on the economy of those areas that will slow their recovery from the recession. But this is an issue that will eventually give way to the positive effects of the proposed NASA budget increase and the development of new capabilities that can generate far more wealth than the obsolescent ones they will replace.

This brings me to what is by far the most important and significant element of the new strategy: substantial funding for the conception, design and development of advanced-technology systems for both human and robotic space exploration. These are not just “blue sky” visions of wishful thinking, as some critics contend. Several potential game-changing prospects already have been identified that lean more to the practical evolution of existing, proven technologies than to the visionary.

For example, the need for a new heavy-lift launch vehicle, and especially its propulsion systems, has been recognized by supporters and critics of the new strategy. There are several realistic prospects for such systems that can be derived from well-proven engines. For the boost phase, there are two clear options, as cited by Elaine Camhi’s editorial in the April issue of Aerospace America: the current operational Evolved Expendable Launch Vehicles (EELVs). The Pratt & Whitney Rocketdyne RS-68 engine that powers the Boeing Delta 4, planned for use in the Ares 5 heavy-lifter that is now slated for cancellation as part of Constellation, is certainly still a valid consideration for any new large vehicle, which could benefit both technically and fiscally from the work NASA has done on the Ares 5 design. The boost engine for the other EELV, the Lockheed Martin Atlas 5, represents what might turn out to be an even better choice. The RD-180 engine, currently being manufactured by Russia’s Energomash, is itself a half-scale derivative of the operational Zenit launcher’s RD-171 engine and the RD-170 engine of Russia’s heavy-lift Energia booster that orbited Russia’s space shuttle Buran on its sole (unmanned) mission. Energomash says the RD-170 is reusable and, because it was to launch a human-carrying vehicle, readily susceptible to being human-rated. For those who might be concerned about too much reliance on Russia, it should be pointed out that RD Amross, a U.S. joint venture by Pratt & Whitney Rocketdyne and Energomash, is very close to producing a U.S.-built version of the RD-180, and with some infusion of NASA funding could be manufacturing that engine (and perhaps even a 1.7 million-pound thrust equivalent of the RD-170) in a few years.

Because it is almost certain that any heavy-lift vehicle will require some thrust augmentation, the use of the shuttle’s proven, human-rated, four-segment Alliant Techsystems solid-propellant rocket motors for that purpose could be a wise choice, and also would help relieve some of the economic hardship resulting from the Constellation project’s cancellation.

Another long-recognized requirement for human exploration beyond low Earth 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, a derivative of the J-2 used for Apollo, placed unrealistic (and very costly) demands on the required launch mass for such missions, as was pointed out by Stanley V. Gunn and Ernest Y. Robinson on this page a few weeks ago [“Recovering the Vision for Space,” March 8, page 19]. They argue that the basic cost driver for Mars and equivalent high-energy human missions is the inadequate performance of upper-stage chemical rockets, which also impose lengthy trip durations that exacerbate concerns about crew exposure to galactic cosmic radiation. Gunn and Robinson make an excellent case for addressing these issues by using nuclear-thermal propulsion, which was brought to the brink of operational use in the 1960s by the $1.5 billion NASA/U.S. Atomic Energy Commission Rover/NERVA (Nuclear Engine for Rocket Vehicle Application) program. Building on the existing bank of that technology to develop, test and deliver an operational nuclear-thermal upper stage, thereby enabling practical pursuit of human missions to Mars and beyond, would be a truly judicious use of the new NASA technology development budget.

Another area for NASA technology investment that would facilitate human space exploration is orbital refueling and assembly of spacecraft for extended solar-system exploration missions. Successful initial demonstrations of refueling and repair capability were conducted during the Defense Advanced Research Projects Agency/NASA Orbital Express project in 2007, and subsequent efforts have shown much promise. Incidentally, China has given strong indications that it plans to use orbital assembly for its upcoming lunar missions.

These are but a few of the opportunities that could be opened by the infusion of technology funding that is a centerpiece of the new NASA strategy. As Logsdon pointed out, Obama’s proposal is certainly not a step back for human space exploration by the United States. Indeed, it enables the implementation of the long-term, multidecadal approach that is essential to the success of human space exploration beyond low Earth orbit.


Jerry Grey is a consultant to the American Institute of Aeronautics and Astronautics and Universities Space Research Association, and a former professor of aerospace engineering at Princeton University.