Silverstein Committee - Selecting An Upper

Selecting An Upper

Nevertheless, the Air Force continued to agitate the development process. In December, ABMA, still part of the Army at this point, received an order to change the upper stage of the Saturn from the Titan-derived vehicle with a 120" diameter, to a new one with 160" diameter that would require considerably more development. The 160" diameter was the same as the Titan C upper, and by making this change to the Saturn the DoD would have two competing upper-stage designs for the SLV-4 requirement, as well as allowing Saturn to launch Dyna-Soar if the need arose. ABMA was already testing the engines for their Titan-derived upper stage, and was upset with this new request.

A meeting of all involved parties was arranged under the direction of Abe Silverstein, whose earlier efforts were instrumental in Saturn being selected for NASA missions. The committee established two criteria for a successful Saturn program: fast development time of an initial system, and growth potential for future launches. The group listed three missions for the initial Saturn vehicle: unmanned lunar and deep space missions with an escape payload of about 4,500 kg; 2,250 kg payloads to geostationary orbit; and manned spacecraft missions in low orbits, such as Dyna-Soar.

To make such "high altitude" missions practical, the performance of the upper stages would be key. Every pound used in the stage or its fuel would mean that much less cargo, given any particular booster (first stage). Since it was the power-to-weight ratio that they needed, upper stages based on liquid hydrogen seemed to be the only way forward – the light weight of the fuel makes up for any difficulty handling it. The Saturn proposal had always included such a stage for orbital insertion, the Centaur, a hydrogen-burning stage derived from the Atlas ICBM.

For the intermediate stages the designers has somewhat more flexibility. The Committee members outlined a number of possible solutions grouped into different classes. The class "A" designs were the low-risk solutions; von Braun's current design became the A-1, consisting of the Jupiter/Redstone clustered lower stage, the Titan I as the intermediate, and the Centaur upper. The A-2 replaced the intermediate with another cluster made up from Thor missiles. The single B-1 design replaced the intermediate with an all-new 220" LOX/RP-1 design using four of the H-1 engines that the lower stage also used, along with a new four-engine third stage derived from Centaur but in a 220" diameter. The C designs used hydrogen-burning uppers only; C-1 would consist of the existing Saturn booster, a new Douglas Aircraft 220" S-IV stage powered by four upgraded versions of the Centaur engines with 15,000 lbf (67 kN) to 20,000 lbf (89 kN) thrust per engine, and a modified Centaur using the same engines as a third stage. The C-1 would become the C-2 upon insertion of a new S-III stage with two new 150,000 lbf (670 kN) to 200,000 lbf (890 kN) thrust engines, keeping the S-IV and Centaur on top. The C-3 was a similar adaptation, inserting the S-II stage with four of the same 150-200,000 lbf thrust engines, keeping the S-III and S-IV stages of the C-2, but eliminating the Centaur.

Examining the results strongly suggested that the C models were the only ones worth proceeding with, as they offered much higher performance than any other combination and offered great flexibility by allowing the stages to be mixed-and-matched for any particular launch need. Additionally, the Titan-derived intermediate had little growth potential, its weight already being near the maximum the Saturn booster could lift. If more performance was called for in the future, a new middle stage would be needed anyway. The same analysis eliminated the 160" stage; designed for the smaller Titan, the Saturn booster would be wasting much of its potential performance lifting this lighter load.

Thus the decision came down not to performance, which was clearly settled, but development risk. The Saturn had always been designed to be as low-risk as possible, the only really new components being a minor upgrade to the engine for the lower stage and the Centaur as the upper. Developing entirely new hydrogen-burning stages for the entire "stack" would increase the risk that a failure of any one of the components could disrupt the entire program. But as the Committee members noted: "If these propellants are to be accepted for the difficult top-stage applications, there seems to be no valid engineering reasons for not accepting the use of high-energy propellants for the less difficult application to intermediate stages." von Braun was won over; development of the current design would continue as a back-up, but the future of the Saturn was based on hydrogen and was tailored solely to NASA's requirements.

On the last day of 1959, Keith Glennan, Administrator of NASA, approved the Silverstein recommendations. Chances of meeting the schedule improved with two Eisenhower administration decisions in January 1960. The Saturn project received a DX rating, which designated a program of highest national priority, which gave program managers privileged status in securing scarce materials. More important, the administration agreed to NASA's request for additional funds. The Saturn FY 1961 budget was increased from $140 million to $230 million. On 15 March 1960 President Eisenhower officially announced the transfer of the Army's Development Operations Division to NASA.