New Moons Rising - GPS Declassified: From Smart Bombs to Smartphones - page 8

ellite called Orbiter. Although the use of the well-established Redstone rocket
promised an earlier launch date, the satellite as originally proposed lacked any
means to transmit tracking signals and could perform no scientific experi-
ments. 40 The Naval Research Laboratory's proposal, A Scientific Satellite Pro-
gram , dated April 13, 1955, notes that such a satellite would be visible only at
dawn or sunset, in favorable weather, and would be “exceedingly difficult to
acquire in an optical instrument of sufficient power (and hence restricted field
of view)” unless its location were already known. 41 “Indeed, it is readily con-
ceivable that an object could be placed in an orbit and never observed, if only
optical methods are used,” the proposal warns. 42 To address this issue, eight
pages of the proposal are devoted to describing in detail a tracking system
called Minitrack, based on modifications to the guidance system used in the
Viking rocket program. The modified Viking rocket and modified tracking sys-
tem, Minitrack, together with a new, instrumented satellite design, became
Project Vanguard.
Milton Rosen, chief engineer of the nrl's Viking rocket program, conceived
Viking as a research tool to study the upper atmosphere, and at the time of the
proposal, it held the altitude record for single-stage rockets—158 miles. 43 Rosen,
an electrical engineer, had worked on guided missiles at the nrl as World War
II ended. 44 First launched in 1946, Viking incorporated innovative “gimbaled”
motors, which could be angled for steering the rocket, intermittent gas jets for
stabilizing it after the main propellant was exhausted, and radio telemetry. 45
In his bid to win the igy project, Rosen collaborated with Roger Easton, who
had joined the nrl in 1943 and worked on radio beacons and blind aircraft
landing systems, and Easton's boss, John Mengel, who headed the laboratory's
Radio Division. 46 Mengel coined the name Minitrack from a phrase used in
the title of a memo, “Proposal for Minimum Trackable Satellite,” that he and
Easton wrote to describe the system. 47 By switching to a lower radio frequency,
which Rosen had suggested, and using large, ive-by-ifty-foot ground antenna
arrays, the system could pick up the relatively weak signal generated by a trans-
mitter small enough to fit in the satellite. Minitrack used trigonometry to cal-
culate the satellite's position by comparing the different angles of the
incoming radio signal at pairs of ground antennas connected to receivers capa-
ble of detecting tiny differences in the signal wavelengths. As Mengel explained
in a Scientific American article, humans use the same the technique to locate
the direction of a sound that reaches their ears at different times. 48 For a visual
illustration, think of sitting on a long, straight beach. Waves arriving perpen-