Re-entry could have posed a problem from another standpoint— aerodynamic stability—but fortunately no difficulties appeared. Configuration was  responsible for this successful development. As to the vital details, the nose cone had a 12.5-inch radius spherical tip joined to a cone frustum of 65-inch base diameter, with an over-all length of nine feet. The nose cone also had a rear cover shaped in the form of a shallow-dished (convex outward) bulkhead, and this was the key part to providing aerodynamic stability for any attitude to re-entry. Tests of this configuration were first made in wind tunnels; then, on the scale re- entry models; and, finally, on the full-scale JUPITER. Thus, from re-entry to impact, the nose cone was a stable component 68 . Guidance and Control At the outset of the JUPITER development program, two G&C schemes were under consideration: the all- inertial guidance system and the radio-inertial guidance system, with the latter being considered as the alternate or back-up means. Subsequently, In 1958, the radio-inertial part of the program was canceled, for  development efforts in the all-inertial area had progressed systematically and successfully. Thus, although ABMA and JPL did laboratory work on the radio-inertial system from September 1957 until its cancellation, principal attention will be devoted to all- inertial development 69 . The JUPITER all-inertial guidance system development program was based heavily on the success of the tried and proven REDSTONE G&C system. From the beginning, this move appeared to be logical as the best     _____________________________

68. Ibid.; JUP Prog Rpt for Aug 56, 5 Sep 56; Present, Aeroballistic Aspects of the Re-Entry Phase, Present for Scientific Advisory Committee for DOD, 14 Jan 57, Hist Off files. 69. DF, RIG Off, G&C Lab to IO, et. al., 24 Mar 58, subj: Cancellation of RIG Program, Hist Off files.