1958 · Satellite Instrument Package · Work 834 of 1,871
A satellite instrument package on an oak workbench in a university physics laboratory in the American Midwest, a cylinder thirty-six centimetres long and fifteen centimetres across built of plain cream potting blocks fitted together in slices and wedges, along it an open channel with a bundle of fine red, green, blue and yellow wires and tiny parts, at one end a round tarnished brass end plate with a toothed rim and a bright steel shaft, beside it a soldering iron, a slender glass counter tube, the hands of a young man in rolled checked shirt sleeves testing a solder joint with two probes, snow outside the window, cold daylight from the left.
What it was used for
At launch on 31 January 1958 Explorer 1 carried an 8.32 kg instrument package in a satellite weighing 13.90 kg; 40 per cent of the total payload weight was batteries for the two transmitters. It measured cosmic radiation with a Geiger-Mueller counter, temperatures inside, outside and in the nose cone, micrometeorite impacts with a microphone and erosion with a ring of gauges. James Van Allen's group at the University of Iowa designed the science instruments; the Jet Propulsion Laboratory built the instrument package and the satellite. The batteries ran out on 23 May 1958. The object in the Smithsonian was long held to be a fully instrumented flight spare; opened in late 2005 it was empty but for a micrometeoroid sensor, with "Payload II" marked inside the frame.
What was new
George Ludwig, who developed the counter instrument in Iowa, reports that the complete instrument used over 100 transistors; by October 1956 the design had changed from germanium to silicon transistors. Explorer 1 carried an abbreviated version that JPL engineers derived from the full package. The gain was not computing power but power consumption: by Ludwig's account the transistors drew less current than the filament of a single vacuum tube - decisive when 40 per cent of the payload is battery and the battery sets the lifetime. The package had been built from the start to fit both the Vanguard and the Juno I configurations, which is why after Sputnik it was the obvious choice for the Army's rocket.
What the sources leave open: Masses and operating life from the NASA mission page, the transistor figures from George Ludwig's own account (University of Iowa, 2004). What "Payload II" denotes is unsettled: the Smithsonian record links the marking to the flight backup sent to Iowa, while Ludwig calls Payload II a flight payload of the second Deal launch series. Ludwig was not certain his detector, donated in 2006, had been inside this satellite.
Connections
Every connection names its kind. “Forerunner” on its own would be a claim.