NavList:

R William McAllister, you wrote:

"A primary reference for the technical data regarding "gravity parties"—the precision gravity and geodetic surveys at Kennedy Space Center (KSC)—is NASA Technical Report 19830043154, "Navigation of the Space Shuttle." This document describes how the Inertial Measurement Unit (IMU) was initialized at the moment of launch using data from high-precision surveys conducted at the launch pads."

That's fascinating. Thanks. Were you familiar with the Space Shuttle inertial navigation in your NASA days?Do you know the degree of detail (maybe the spherical harmonics degree?) used by the inertial system in orbit?

Of course the small variations in the Earth's gravitational field fade away with altitude quite quickly. At sea level, it's quite complex. By an altitude of, say, 25,000 miles, the detail has averaged out, and the Earth's gravity is extremely well modeled by a point source plus a small ring (for oblateness). But in Low Earth Orbit, there are still significant undulations and wobbles in the gravitational field that have to be accounted for in a pure inertial navigation solution. They must have updated the model regularly, as better data became available, over the decades of the Shuttle's operational life, right?

Speaking of inertial navigation and the history of navigation... Here's one with a maritime context. We all know that USS Nautilus famously sailed under the ice to the North Pole on 3 August 1958. There is a "relic" from that voyage, the navigation "ticket", showing the position as 90° 00.0' N (see it on wikipedia). This was an important Cold War "stunt". The truth of the latitude was guaranteed by decree, and the relic is the symbol. But really? Did they?? Any estimates on the actual uncertainty of the latitude by the time they reached the pole using this very early inertial system?? The inertial system aboard USS Nautilus was a "phoenix" —reborn from the "Never-go Navaho" supersonic cruise missile, which was cancelled just a year earlier. And —looping back to the original post— the Navaho was, in a general way. a conceptual predecessor to the STS Space Shuttle. See this essay and the image below...

Frank Reed
Clockwork Mapping / ReedNavigation.com
Conanicut Island USA

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