Transistor Museum Oral History George Ludwig Explorer I Transistors Page 15

A Transistor Museum Interview

with Dr. George Ludwig

The First Transistors in Space - Personal Reflections by the Designer of the Cosmic Ray Instrumentation Package for the Explorer I Satellite

Oral History – George Ludwig

(Continued)

The data were recorded at the receiving stations on 7-track Ampex tape recorders. For Explorer I, those were all shipped to JPL, who did a quick look at them by playing them out on Sanborn strip chart recorders. Those were used primarily to read out the temperatures that they (JPL) were responsible for. The cosmic ray experiment was entirely Iowa’s, and we did the data reduction at Iowa to do the complete analysis of the cosmic ray data.

You mentioned that there was a meteorite detector.

A micro-meteorite detector. There was both a microphone that listened for "pings" on the shell, and some grids wound with very fine wire. If one was hit by a micro-meteorite, it severed the wire. Of course this was not our experiment – it was the Air Force Cambridge Research Laboratory, by Edward Manring and Morris Dubin.

How was the data on Explorer III recorded?

The tape dumps on Explorer III were quite a different thing. The storage device was a purely digital tape recorder. The tape was stationary, except that once a second, I advanced it 0.005 of an inch. And as it sat there for that second, then it either recorded an output from the scaler or it did not.

Oral History – George Ludwig

(Continued)

It was set up so that with normal cosmic ray counting rates, about every 7^th second the pulse would be blanked, indicating 128 counts during that 7 second period. That was all well and good for the normal cosmic ray rates, but then we ran into the high intensity radiation which saturated the Geiger counter and circuitry. The reason that the counting rate appeared to go to zero on Explorer I, and also on Explorer III, was that the radiation intensity was so high that it saturated the system.

What data analysis techniques of the Explorer III tapes lead to the discovery of the Van Allen radiation belts?

He (Van Allen) got a copy of a tape in the late afteraoon, went to the drug store for a ruler and some graph paper, went to his hotel room, and sat there till 2 o’clock in the morning reading off that record. McIlwain at Iowa City also received a copy of that recording and several of them immediately examined it. When Van Allen, McIlwain, and Ernie Ray got together to compare notes upon Van Allen's return to Iowa City, it was almost completely obvious what was going on. That record showed that, during the orbit, the rate was normal in certain regions. It then started increasing to a high value (all pulses blanked), which would be a rate of 128 counts per second or more.

Go To Ludwig Oral History, Page 16

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