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Relatedly, I find it deeply troubling at some level to know that the exact shape of the Earth (specifically, mass and magnetic distribution) is highly classifie
by rdl 11y ago
Relatedly, I find it deeply troubling at some level to know that the exact shape of the Earth (specifically, mass and magnetic distribution) is highly classified, since it's important to ICBM guidance.
- marklyon 11y agoDoesn't ITRF2008 and (to a lesser extent) WGS-84 give you what you want?
- wyager 11y agoSource? I'd like to read about this.
- teh_klev 11y agoCould be something to do with this: http://nsarchive.gwu.edu/NSAEBB/NSAEBB509/ http://nsarchive.gwu.edu/NSAEBB/NSAEBB509/ "NASA's Applications Satellites and National Security Requirements: NASA planned on launching the Geodynamics Experimental Ocean Satellite-3 (GEOS-3) with a radar altimeter whose data would generate more accurate gravity models than any measuring devices previously flown. The data would be used to meet civilian requirements and by the U.S. Navy to improve the accuracy of its submarine-launched ballistic missiles (SLBMs). Because it also had the potential to be used by the Soviets for the same purpose, the DoD requested NASA to encrypt the data, limit the acquisition of data over the ocean areas where Soviet ballistic missile submarines operated, or delay the planned April 1975 launch until the issue could be resolved. It also requested encryption of the data from the even more capable radar altimeter planned for SEASAT-A. NASA rejected these requests but quickly agreed to restrict the dissemination of the GEOS-3 data collected over the regions where Soviet ballistic missile submarines operated (Document 38)." However is it still the case that NASA continue to withhold this data, or is it data collected by the NSA/NRO/et al's satellites that's considered classified?
- 8note 11y agothey should be keeping that secret; good gravity models are a major part of the difference in accuracy of American missiles vs Russian ones.
- dogma1138 11y agoYes because the last thing you want is for the "soviets" to be able to hit their target. Surely them hitting instead a city near by or just using bigger nukes to compensate for lesser accuracy is a much better approach.
- hga 11y agoNo, the more inaccurate their targeting, the harder it was for them pull off a counter-force first strike. No need to lead them into temptation.... Once they're launched, you've already lost catastrophicly, no matter exactly where they come down. And why the scare quotes for our adversaries who build 40,000 nuclear warheads, most of them aimed directly at us?
- 8note 11y agoFor important things like ICBMs, you don't want to trust easily spoofable navigation like GPS. Instead, you double integrate over the acceleration data obtained from very accurate accelerometers and gyros. since these sensors measure acceleration, and gravity is acceleration, any change in gravity over the missile's path will cause it to think it had moved differently than it did. Knowing the precise earth gravity then you can account for these changes. Changes in the magnetic field will affect compass readings, which help you decide what direction the missile is facing. Knowing the (fixed over time) change will help account for measurement error in the compass. I'm not sure how much that helps though, since the compass' earth field is constantly changing anyways due to the sun and magnetisation of the missile itself. The actual surface shape has an effect on the gravity experienced above the ground, but is also important to make sure you know what height you're aiming for, and that there's nothing in the way.
- rdl 11y agoMagnetic info is sensitive more for detecting hidden equipment, like submarines.