Editing Silverstein Committee (section)

==Selecting an upper stage==

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-inch diameter, to a new one with a 160-inch diameter that would require considerably more development. The 160-inch diameter stage was the same as the Titan C upper stage, 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 group listed three missions for the initial Saturn vehicle: uncrewed lunar and deep space missions with an escape payload of about {{Convert|10000|lbs|kg|abbr=}}; {{Convert|5000|lbs|kg|abbr=}} payloads to geostationary orbit; and crewed spacecraft missions of about {{Convert|10000|lbs|kg|abbr=}} in low orbits, such as Dyna-Soar.<ref name=":0" />

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 &ndash; 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 (rocket stage)|Centaur]], a hydrogen-burning stage derived from the [[SM-65 Atlas|Atlas]] ICBM.

For the intermediate stages the designers had somewhat more flexibility. The Committee members outlined a number of possible solutions grouped into three different classes: class "A," class "B," and class "C." Common among all three classes, with the exception of the proposed C-3, was the new first stage consisting of a cluster of eight H-1 engines attached to the Jupiter/Redstone tank cluster, which would become the [[S-I]] stage, as well as the two engine [[Centaur (rocket stage)|Centaur upper stage]]. The class "A" designs were the low-risk solutions; von Braun's current design became the [[Saturn A-1|'''A-1''']], consisting of a [[HGM-25A Titan I|Titan I]] second stage between the S-I first stage and Centaur third stage. The [[Saturn A-2|A-2]] replaced the second stage of the A-1 with a cluster of [[PGM-17 Thor|Thor]] IRBMs. Though the class "A" vehicles would have had the earliest flight availability due to the utilization of existing hardware, they failed to meet the first two mission for the Saturn rocket. Additionally, the 120-inch upper stages posed a potential structural weakness, and the proposed 160-inch upgrade would limit growth potential, violating fourth request of the original directive.

The single class "B" design considered by the committee, the [[Saturn B-1|'''B-1''']], consisted of a four-stage design with the aforementioned S-I first stage and Centaur fourth stage. The second stage would be an all-new 220-inch LOX/RP-1 design using four of the H-1 engines used by the first stage, along with a new four-engine third stage derived from Centaur but with a 220-inch diameter. Though the B-1 vehicle met the mission requirements, it would have been too costly and taken too much time to develop the new second stage. 

The class "C" designs used liquid hydrogen in all upper stages. [[Saturn C-1|'''C-1''']] would consist of the existing S-I booster, a new [[Douglas Aircraft]] 220-inch [[S-IV]] stage powered by four upgraded versions of the Centaur engines with {{convert|15000|lbf|kN|abbr=on}} to {{convert|20000|lbf|kN|abbr=on}} thrust per engine, and a modified Centaur using the same engines as a third stage. The C-1 would become the [[Saturn C-2|'''C-2''']] upon insertion of a new [[S-III]] stage with two new {{convert|150000|lbf|kN|abbr=on}} to {{convert|200000|lbf|kN|abbr=on}} thrust engines, keeping the S-IV and Centaur on top. The [[Saturn C-3|'''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. The first stage of the C-3 would also be increased to over {{Convert|2000000|lbf|kN|abbr=on}} by either replacing the four center H-1 engines with one F-1 engine, or uprating all eight H-1 engines.<gallery mode="packed" caption="Saturn C variants">
File:Saturn C-1.png|Saturn C-1
File:Saturn C-2.jpg|Saturn C-2
File:Proposed Saturn C-3 Apollo Configuration.jpg|Saturn C-3
</gallery>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, by developing the rocket in a building-block manner maximum vehicle reliability would be achieved as each new stage is added to already tested and proven stages.

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 stage. 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, NASA Administrator [[T. Keith Glennan]] 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.