The Planetary Society strongly resonates with your desire for an earlier and stronger commitment to the heavy-lift launch vehicle, what we call the Deep Space Rocket [editorial, “Latest NASA Plan Still Falls Short,” April 26, page 18]. Our Roadmap to Space last year made the same call, and our Mars paper submitted to the Planetary Decadal Study suggested that a robotic Mars Sample Return be flown on the Deep Space Rocket — both for easing its design and as a precursor to human flight.

But saying 2015 is not soon enough to start development without referencing where and when such a vehicle will be used doesn’t make sense. You need to consider the requirements. The Deep Space Rocket will take humans into interplanetary space. We recommend its use on robotic precursors, like the Mars Sample Return, and on other robotic science missions of the future, like large telescopes. But these are not missions of the next decade. An engineering program should have a long preliminary design and technology development phase and a short build and test implementation phase. Starting the Deep Space Rocket before 2015 would result in having it ready years before its required use (and hence with old technology) or stretching out its development to make it very expensive.

Citing Constellation’s heavy-lift plan is disingenuous. Work could not be started on Ares 5 before 2017 to 2020 because of the constraints on the program and the way it had evolved. The new NASA plan is an attempt to make it more realistic, and the technology phase now to be introduced (if the Congress will allow it) should make it happen sooner and less expensively.

Louis Friedman
Executive director, the Planetary Society
, Calif.

Louis Friedman is the co-founder and Executive Director Emeritus of The Planetary Society. Prior to that he was Manager of Advanced Programs and the post-Viking Mars Program at JPL.