Ernst Stuhlinger

Ernst Stuhlinger’s graduate-level training began in 1932 in physics and mathematics at Hans Geiger’s institute at the University at Tubingen, Germany. There he worked under Geiger’s tutelage on developing charged particle detectors and applying them to cosmic ray research. For his Ph. D. dissertation, Stuhlinger developed a variation of Geiger’s counter that was sensitive enough to operate in the proportional region for incident electrons. Stuhlinger used his counter to determine the specific ionization of electrons in cosmic ray showers produced in the upper atmosphere. His postgraduate work included applying his experience with nuclear detectors to helping to clarify the possibilities for building energy-producing uranium reactors in Werner Heisenberg’s laboratory in Berlin.

Ernst’s work in pre-WWII Germany put him in a position, much later, to assist in getting Van Allen’s cosmic ray instruments aboard the early Explorer satellites. There were never many engaged in nuclear physics and cosmic ray research prior to WWII. Those few indi­viduals formed a closely knit community that often transcended national boundaries and the turmoil of the times. During his work in Geiger’s and Heisenberg’s laboratories, Stuhlinger became aware of the work of many of those coworkers. Among them was a young post­graduate researcher in the United States—James A. Van Allen. Some of Van Allen’s early published papers dealt with deuteron-deuteron reactions and the detection of high-energy protons in the presence of fast neutrons. That, of course, was closely related to the work that Ernst was doing in Berlin. Although Stuhlinger kept track of Van Allen’s work in those early days, there was no direct contact between them until much later, when Stuhlinger began working in the United States after WWII.

The rise of Nazism and WWII interrupted Stuhlinger’s nuclear science research in Berlin. Following the German invasion of Russia and eventual setbacks on that front, the demand for additional military manpower for the German Army became overwhelming. In the fall of 1941, Stuhlinger was drafted and sent to the Russian front as a private first class. By early 1943, it was decided that there was a greater need for his physics background, and he was reassigned from the Stalingrad battlefront to the rocket development endeavor at Peenemunde. He remained with the rocket group until the end of the war, with his primary work being helping in the development of the guidance and control system for the A-4 (V-2) rocket.

Stuhlinger was among the group of German scientists who were brought to the United States in 1945 as a part of Operation Paperclip, the U. S. operation to collect components and technology needed to assemble and test V-2 rockets following the German surrender. The captured hardware was accompanied by extensive documentation and more than 100 of the senior scientists and engineers who had participated in the rocket development. Those individuals were very helpful in assembling and firing the captured V-2 rockets in Texas and otherwise assisting in jump-starting the burgeoning U. S. rocket development efforts.

The German group, led by Wernher von Braun and including Stuhlinger as chief scientist, was taken first to Fort Bliss near El Paso, Texas. Many of them moved in 1950 to the

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Redstone Arsenal near Huntsville, Alabama. That organization was later reorganized to form the ABMA and, after NASA was formed in 1958, the Marshall Space Flight Center.

Stuhlinger figured prominently in the space program at Huntsville, beginning with plan­ning for Orbiter, the Jupiter C program, and for use of the Juno vehicles for launching Explorers I, II, III, IV, V Beacon 1, Pioneers 3 and 4, Payload 16, Explorer 7, and Payload S-46. In succeeding years, he was active with numerous additional space flights, including lunar exploration flights, the Apollo telescope mount flown on Skylab, the High Energy Astronomy Observatory, various Space Telescope missions, and scientific payloads for the Space Shuttle.

Von Braun, as the director of a large military research and development organization, always had some independent flexibility to conduct limited feasibility studies in areas of high technological interest. After the Vanguard decision in August 1955, he drew upon a special fund earmarked for general research related to the advancement of the art of rocketry for further Orbiter-related studies. Thus, by the time Huntsville was directly ordered to stop all further satellite work in June 1957, theoretical work had been conducted on four capabilities needed to advance from the nose cone-testing Jupiter C RTV to the eventual satellite launcher. They were as follows:

• A new attitude control system to turn and orient the upper portion of the Jupiter C rocket cluster after the end of main-stage engine burning and separation of the forward section from the booster. That had to be done in such a way that the forward section would be exactly horizontal when it reached the apex of the upper-stage cluster flight trajectory.

• Development of a way to determine the exact moment that the forward section reached its apex. The upper-stage rockets would have to be fired at just that instant.

• Working out the celestial mechanics, orbital parameters, acceptable launch times, and injection conditions for the satellite.

• Development of a satellite payload. Von Braun and Stuhlinger insisted from the beginning that any satellite had to be scientifically useful. The satellite would need to accommodate appropriate detectors, a data transmitter, tracking equipment, antennas, and batteries.

After the unambiguous command to stop further satellite development, von Braun no longer considered it prudent to continue use of that source of discretionary funding for this purpose. Even then, however, a number of the Huntsville technical staff enthusiastically continued the work on their own, often during evenings in their homes. Fred Digesu and Hans H. Hosenthein worked out the theory for the attitude control system. Ernst Stuhlinger developed an “apex predictor” to accomplish the second task. Task 3, orbital considerations, was addressed collectively by individuals in Helmut Hoelzer’s Computation Laboratory, Ernst Stuhlinger’s Research Projects Office, and

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Ernst D. Geissler’s Aeroballistics Laboratory. Charles A. Lundquist developed a method for computing the satellite’s orbit based on a limited number of observations from the ground. Josef Boehm, Helmut Pfaff, and their staffs produced designs for the satellite, as described below, as well as designs for mechanical components of the attitude control system.

Admittedly, the distinction between private and official work during that period sometimes became a little blurred. It should be appreciatively acknowledged that Redstone Arsenal commander general Holger N. Toftoy and, succeeding him, ABMA commander general Medaris, “always turned very generously the other way when they visited a laboratory and spotted on one of the drawing boards a sketch that looked suspiciously like a little satellite.”27

A discussion of Stuhlinger’s apex predictor illustrates the character of one of those behind-the-scenes efforts. It was essential that the firing of the solid fuel stages should be initiated at just the right moment. Basic data to assist in that process were available from a variety of radio, Doppler, and radar measurements. The challenge was to pull all of the information together, and to use it in a systematic way to determine the instant when the cluster of upper stages should be fired.

Some of the basic apex prediction concepts were tested during the first Jupiter C reentry test on 20 September 1956. The written plan for that exercise included the statement, “The three proposed methods to determine the apex of a missile. . . will be tested for the first time in Missile #27 [Missile # 27 was the internal identification nomenclature for the first nose cone reentry test vehicle]. Although that missile does not represent an exact duplication of Missile #29 [the vehicle quietly set aside for the first satellite launch], a number of valuable data regarding feasibility and proper functioning of apex determination methods will be obtained. Also, human operators will have the opportunity to familiarize themselves with their tasks. It is anticipated that more practice runs of this kind will be made before the firing of Missile #29.”28 The three methods referred to above were the Radar Method, the Dovap (Doppler, velocity, and position) Method, and a Back-up Method. The plan went on to describe the backup method.

A third and independent method to estimate the expected apex time has been prepared in the following way: velocity signals from the missile fixed gyro-accelerometer, as received by the telemeter ground station, will be directed through a relay circuit to the operator of the apex computer. The signals are recorded by a Brush recorder, together with a time base. They are entered into a time-velocity diagram, which contains, as a reference, the standard time-velocity diagram. The amount of deviation between the two curves is quickly estimated and entered into another diagram, which gives the apex time variation as a function of the velocity deviation.29

That document stated that no great accuracy should be expected from the backup method; it was being implemented in case the other two methods should fail. The

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backup method used an approach in which the information was assimilated and combined in a manual process employing prepared charts and other graphical aids. Although it did not use any special equipment, it tested the basic approach envisioned for the satellite launches.

Based on the results from the September 1956 flight, Ernst Stuhlinger developed a form of analog computer to simplify the human operator’s task and to make it more precise. The development of that computer, the apex predictor, was described by Ernst Stuhlinger in the following way:

An electro-mechanical analog computer, called “Apex Predictor,” was developed at Stuh – linger’s Research Projects Office, and built largely at home in his garage, with some help from Wilhelm Angele’s Precision Shop in the Science and Engineering Directorate (because the satellite project did not have an official standing at the Army Ballistic Missile Agency at that time, such work could not be carried out as a normal ABMA activity).30

The apex predictor was built well before the first satellite launch and was tested extensively so that it would be ready if needed for that purpose. It was operated in parallel with other methods during the test of a Chrysler Corporation production Redstone rocket in July 1957 (Missile 37), for the fully successful Jupiter C nose cone reentry test in August (Missile 40), and for another Chrysler Redstone on 2 October (Missile 39).31

Ernst informed me recently that two identical apex predictors were assembled in 1957. Both were used for the Jupiter C launches, one as primary and the other as a backup. Those instruments were lost following the launches, but Ernst built a full-size working replica in his garage during the 1990s.32

The fourth task at Huntsville was to design a satellite that could be launched atop the Jupiter C rocket. The general form of such a payload had been under consideration for some time. Ernst Stuhlinger has recounted that, as early as 1952, as he and von Braun were discussing the prospects for eventually using their Redstone rocket to launch a satellite, Von Braun expressed his belief that they should have a “real, honest-to – goodness scientist” involved in their little unofficial satellite project. “I’m sure you know a scientist somewhere who would fill the bill, possibly in the Nobel Prize class, willing to work with us and to put some instruments on our satellite.” Being fully aware of Van Allen’s work as related earlier, Stuhlinger was ready with his reply: “Yes, of course, I will talk to Dr. Van Allen.”33

As the behind-the-scenes Jupiter C satellite effort progressed during 1956 and 1957, ABMA engineers continued to design the satellite under Ernst Stuhlinger’s general oversight. Josef Boehm and his group of design engineers carried that effort forward at the working level.

The JPL engineers participated actively in that work, with their primary focus being the inclusion of their Microlock system. A key meeting of the ABMA and JPL engineers to plan details of the satellite was held in December 1956. After early 1957,

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FIGURE 7.1 A product of the behind-the-scenes collaborative ABMA, JPL, and SUI satellite design effort. Dated 11 July 1957, this satellite drawing was developed during a meeting of the Huntsville and JPL engineers and the author on 10 and 11 July. The instrument package is shown attached to the fourth-stage rocket. It included the Iowa GM counter package, along with a single JPL Microlock transmitter. The caption on the drawing reads, "Proposal. Payload Instrumentation for Purpose of Radiation Measurements. July 11-57. Signed ‘Wag.’” Those initials were by Herman A. Wagner, a senior engineer in Josef Boehm’s group at Huntsville. Note the strong resemblance between this drawing and the one in Figure 8.4 that shows the satellite that was built later at JPL and that flew as Explorer I in January 1958. (Courtesy of the NASA Marshall Space Flight Center.)

we at the University of Iowa also worked closely with the ABMA and JPL groups to add our cosmic ray instrument to the evolving satellite design, as detailed later.

The culmination of that ABMA-centered, three-party collaboration was a rather complete top-level paper satellite design by the end of July 1957, shown here as Figure 7.1.34

At the Jet Propulsion Laboratory The basis for the ABMA-JPL collaboration had a long-standing background. Through their work on the guidance and control systems for Corporal and other rocket programs, JPL developed an early capability in elec­tronics design. Their interest in electronics was additionally stimulated in late 1954, when the Redstone Arsenal and NRL groups sent their Orbiter proposal to them for comment. JPL immediately became an enthusiastic supporter and participant in the Orbiter work. That involvement made them a bona fide partner in early satellite planning and whetted their appetite for further satellite work.