Initial Defense Communications Satellite Program

Background

The IDCSP was the first stage of the Defense Communications Satellite Program (DCSP), commissioned by Secretary of Defense Robert McNamara in 1962. The DCSP aimed to develop satellite series for long-range communications between fixed, transportable, or shipboard terminals, managed by the Defense Communications Agency. This program followed the cancellation of Project ADVENT, the initial attempt at a military geosynchronous communications satellite, which had begun in February 1960.

ADVENT's original cost estimate of $140 million had risen to $170 million spent by 1962, with a projected total of $325 million. The cheaper IDCSP was chosen as an interim replacement, originally planned as a constellation of 24–30 satellites launched via ten Atlas Agena rockets at a total cost of $165 million. Philco's Western Development Division was initially selected by the U.S. Air Force to build the satellites. However, by 1964, the development of the more powerful Titan IIIC booster allowed fewer satellites to fulfill the same mission at higher altitude, with four to eight launched per rocket.

The satellites would be deployed one at a time over three minutes from the Transtage, drifting randomly at an average rate of 28.5° per day to form an evenly spaced equatorial belt. At least 12 satellites provided full coverage. The Titan IIIC replaced the Atlas Agena as the launch vehicle, a change denounced by the House Committee on Government Operations as a high-risk plan for short-range economies. With this selection, the Pentagon dropped negotiations with Philco and developed the satellites in-house.

Through early 1965, the satellites were still designed for possible Atlas Agena launch if the Titan IIIC was unavailable.

Design

Developed primarily by TRW, the IDCSP spacecraft were identical, spin-stabilized, 26-sided polygons 86 cm in diameter, covered with solar panels, and had a mass of 45 kg. They were designed simply to avoid problems of earlier programs like Courier and Advent, lacking in-orbit control mechanisms and batteries. An automatic radiation shut-off device was included to deactivate them after six years. Each satellite carried a single 3.5 Watt X-band transponder receiving at 8.025 GHz and transmitting at 7.25–7.3 GHz, capable of supporting 600 voice or 6000 teletype conversations concurrently.

Ground terminals used various modulation techniques including FDM/FM, DPSK, MFSK, and SSMA. The Eimac Division of Varian Associates and Watkins-Johnson Company each supplied one of the two traveling wave amplifiers. Due to the low transponder power and low-gain antenna, receiving installations had to be very large.

Operational history

The first launch of seven IDCSP satellites occurred on 16 June 1966 from Cape Canaveral Space Launch Complex 41 aboard the fourth Titan IIIC. After a successful Transtage burn, the satellites were dispersed into orbit, each drifting 27.8° per day. Communications were conducted between Fort Dix, New Jersey, and sites in California, England, and Germany. A second set of eight satellites was lost on 26 August 1966 due to a faulty payload fairing, the last unsuccessful Titan IIIC launch.

On 18 January 1967, the seventh Titan IIIC placed eight satellites into orbit, and on 1 July 1967, four more were launched, including IDCSP 19 (DATS). Ground terminals had been installed at Saigon and Nha Trang by that time. Under Project Compass Link, the satellites enabled high-resolution photography transfer between South Vietnam and Washington, D.C., for near-real-time battlefield analysis. With the launch of the fourth system of eight satellites on 13 June 1968, the Defense Communications Agency deemed the system operational, renaming it the Initial Defense Satellite Communications System (IDSCS).

It provided secure command-and-control communications, while routine messages used commercial satellites. The constellation was also used by NATO states as NATO-1. Of 35 satellites launched in five groups, 27 succeeded. The automatic shut-off device often failed, and as of 1975, six satellites were still functioning.

Technical assistance was provided by The Aerospace Corporation. The IDCSP series was succeeded by NATO-2 and DSCS-2 geosynchronous satellites.