NASA, DoD, and the Hidden Secrets of Geodesy

The National Security Archive is one of the great sources online today for Cold War history, and their latest Electronic Briefing Book is a collection of documents on NASA’s relationship with the Department of Defense and CIA, selected by NASA curator James E. David. One of the sections in David’s collection is all about the use of NASA satellites on national security missions, which turns out to be about the tension between openness and secrecy in the esoteric-sounding field of geodesy.

As the NOAA’s handy tutorial defines it, geodesy is the “science of measuring and monitoring the size and shape of the Earth.” This was knowledge of vital importance at the start of the Cold War, since it formed the basis for calculating the trajectories of ballistic missiles. (Something I wrote about, very briefly, here.)

That made geodetic data not just valuable scientific data but also critical for strategic deterrence, which meant the national defense establishment was keen to lock it up. (The same impetus, applied to ocean depth soundings, explains why the Heezen-Tharp sea floor map looks the way it does.) That demand for secrecy and classification was in conflict with NASA’s mission to advance civilian science, leading to the clashes in the documents David has selected.

The problems started with the very first geodetic satellite. Project ANNA, named for its four contributors, the Army, Navy, NASA, and Air Force, was designed around three different measurement systems. The first functioning satellite, ANNA-1B, launched in 1962, was tracked based on the doppler shift of one transmission (Navy), the phase shift of a second, phase modulated, signal (Army), and visual measurements of an onboard flashing light (Air Force). DoD wanted the results to be classified, but as the memo David provides shows, NASA argued international cooperation was necessary to spread around the ground stations and maximize the quality of the data.

ANNA was followed by three NASA Geodetic Earth Orbiting Satellites (GEOS), each fitted with a different range of measurement systems. GEOS-3 was the first to carry a radar altimeter, whose measurements of ocean height would enable better mapping of local gravity. That was valuable information for enhancing the accuracy of submarine-launched ballistic missiles (SLBM), so DoD wanted the satellite’s data link encrypted to keep it out of foreign hands. Once again, NASA pushed back. The compromise, detailed in another of the memos in the briefing book, was that NASA would restrict the release of data from “militarily significant areas.” These were defined as “ocean areas that are between 2,000 n.mi. and 5,000 n.mi. range from U.S. missile sites,” or, in other words, points from which the Soviet Union might launch SLBMs at the United States.

NASA lofted another radar altimeter a few years later aboard SEASAT, raising the same questions once again. NASA proposed shifting the satellites orbit to a different and less militarily valuable orbit, but this time it was DoD who said no, arguing that “the polar orbit would cause a significant degradation in DOD’s ability to use the SEASAT-A altimeter data to improve the accuracy of inertial navigation systems for our operational forces.” (Specifically, the Ship’s Inertial Navigation System [SINS] for ballistic missile submarines.) A presidential directive led to that gravity data being freely disseminated.

The briefing book doesn’t mention anything about it, but I think it makes sense that the next satellite altimeter mission was run by the Navy, not NASA. That was GEOSAT. Launched in 1985, it produced highly accurate data. One US Navy history says it was measuring ocean heights with 3-centimeter precision. No longer beholden to NASA for any part of the project, the US Navy didn’t declassify most of GEOSAT’s data until 1995, well after the end of the Cold War and nine years after its initial geodetic mission ended.


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