NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
August 11, 1972
OFFICE OF THE ADMINISTRATOR
Dr. John A. Simpson
The Enrico Fermi Institute
University of Chicago
933 East 56th Street Chicago, IL 60637
Dear Dr. Simpson:
Your letter of 11 July 1972 to Dr. Fletcher has been referred to me. Your arguments for committing Pioneer H to an out-of-the-ecliptic mission are well taken and very persuasive. The relatively low-cost of such a mission, since the Pioneer H spacecraft is a spare for Pioneers 10 and G, and the considerable scientific value to be derived, argue very strongly in favor of the mission. In fact, this kind of mission was described to the Space Science Board 1971 Woods Hole Summer Study by our Science Advisory Group. Moreover, on 15 June 1972 our Outer Planets Science Advisory Group presented to NASA management their recommended strategy for exploring the outer planets, in which the Pioneer H out-of-the-ecliptic mission was an important item.
On the other hand, there are other considerations that argue against committing to this mission at the present time. Quoting from the Woods Hole Summer Study referred to earlier:
"The radiation belt of Jupiter constitutes a hazard of undetermined magnitude for close-in Jupiter flybys, orbiters, and entry probes. We recommend that Pioneers F and G be utilized to evaluate the radiation environment of Jupiter as fully as possible, even at the risk of possible disablement of the spacecraft, and that Pioneer H be held in readiness for use as a Jupiter magnetosphere mission for further evaluation of the radiation hazard if it has not been clarified by Pioneers F and G. This will permit the choice of safe trajectories for both Grand Tour missions and those for the more intensive study of Jupiter. Studies of instrument design for Pioneer H to operate in a high-intensity radiation environment should also be started soon in case such hardened instrumentation should turn out to be the only solution for Jupiter exploration conducted within its radiation belt."
NASA agrees that we must determine the radiation environment of Jupiter in order to support the overall outer planets exploration strategy that has been proposed to us by a majority of the planetary scientists working with us. Although Pioneer 10, presently on its way to Jupiter, is still working well, we cannot assume that it will give us all the definitive information on the radiation environment of Jupiter that is required. Nor, can we be certain that the combination of Pioneers 10 and G will complete the task. Thus, to determine Jupiter's radiation environment adequately to plan and design orbiter and probe missions to Jupiter, it seems prudent to hold Pioneer H as a backup for this very vital objective.
Later, if Pioneers 10 and G have given us sufficient information for planning and designing the further investigation of Jupiter, we can then reconsider the use of Pioneer H for other attractive missions that various scientists have urged NASA to undertake. Since there are many such missions, we will again have to make a choice, and your arguments for the out-of-the-ecliptic mission will be of considerable assistance in deciding, and we greatly appreciate having your recommendations. Because of your interest, we will keep you informed. In the meantime, my very best regards and sincere thanks for your thoughts.
Homer E. Newell