Transit provided continuous navigation satellite service from 1964, initially for Polaris submarines and later for civilian use as well.

[4] Discussing the way forward for their research, their director Frank McClure, the chairman of APL's Research Center, suggested in March 1958 that if the satellite's position were known and predictable, the Doppler shift could be used to locate a receiver on Earth, and proposed a satellite system to implement this principle.

[9] The Chance Vought/LTV Scout rocket was selected as the dedicated launch vehicle for the program because it delivered a payload into orbit for the lowest cost per pound.

The second problem concerned the increased vibration that affected the payload during launching because the Scout used solid rocket motors.

The first prototype operational satellite (Transit 5A-1) was launched into a polar orbit by a Scout rocket on 18 December 1962.

The satellite verified a new technique for deploying the solar panels and for separating from the rocket, but otherwise it was not successful because of trouble with the power system.

A malfunction of the memory occurred during powered flight that kept it from accepting and storing the navigation message, and the oscillator stability was degraded during launch.

[11] In fact, the elevation of Mount Everest was corrected in the late 1980s by using a Transit receiver to re-survey a nearby benchmark.

In the 1970s, the Soviet Union started launching their own satellite navigation system Parus (military) / Tsikada (civilian), which is still in use today besides the next generation GLONASS.

Improvements in electronics allowed GPS receivers to effectively take several fixes at once, greatly reducing the complexity of deducing a position.

The orbits of the Transit satellites were chosen to cover the entire Earth; they crossed over the poles and were spread out at the equator.

[citation needed] The Transit satellites used arrays of magnetic-core memory as mass data storage up to 32 kilobytes.

In the case of the modern GPS system, dozens of such measurements may be taken depending on which satellites are visible at that time, each one helping improve accuracy.

The spacecraft traveled at about 17,000 mph (27,000 km/h), which could increase or decrease the frequency of the received carrier signal by as much as 10 kHz as measured on the ground.

Additionally, the rotation of the Earth provided another Doppler correction which could be used to determine whether the satellite was to the east or west of the ground station.

The orbit ephemeris and clock corrections were uploaded twice each day to each satellite from one of the four Navy tracking and injection stations.

The two frequencies were used to allow the refraction of the satellite radio signals by the ionosphere to be canceled out, thereby improving location accuracy.

The Transit system also provided the first worldwide timekeeping service, allowing clocks everywhere to be synchronised with 50 microsecond accuracy.

The navigation software used the satellite's motion to compute a 'trial' Doppler curve, based on an initial 'trial' location for the receiver.

If the receiver was also moving relative to the earth, such as aboard a ship or airplane, this would cause mismatches with the idealized Doppler curves, and degrade position accuracy.

This was the navigation criterion demanded by the U.S. Navy, since American submarines would normally expose their UHF antenna for only 2 minutes to obtain a usable Transit fix.

ELTs measure the Doppler shift of the transmitter on the boat or aircraft as it passes overhead and forwards that data to the ground where the location of the craft can be determined.

This data was sent to the Satellite Control Center at Applied Physics Laboratory in Laurel, Maryland using commercial and military teleprinter networks.

This receiver, power supply, punched tape unit, and antennas could fit in a number of padded aluminum cases and could be shipped as extra cargo on an airline.

A Geoceiver was permanently located at the South Pole Station and operated by United States Geological Survey personnel.

It was equipped with 8,192 words of 15-bit core memory plus parity bit, threaded by hand at their Canoga Park factory.

[19] The AN/UYK-1 was a microprogrammed machine with a 15-bit word length that lacked hardware commands to subtract, multiply or divide, but could add, shift, form ones' complement, and test the carry bit.