Reply to post: Re: Yet Another Satellite Navigation System

Blighty stuffs itself in Galileo airlock and dares Europe to pull the lever

Flocke Kroes Silver badge

Re: Yet Another Satellite Navigation System

The reason for Galileo is so the EU can have precision GPS even if the US says no you can't. I am sure there is plenty of room for argument about whether that reason is worth the money for the EU. For the UK, £350 million per week for most of a year should pay for it, and thanks to Brexit, we will have an extra £350 million per week for anything and everything by delaying the money promised for the NHS.

Civilian GPS is subject to spoofing. Military GPS is supposed to be able to deal with it, but at a cost. A huge cost. Such a huge enormous cost that even with their gigantic budget, parts of the US military use civilian GPS. So many civilian GPS units that the US decided turning on selective availability hurt them more than their enemies.

One satellite tells you the time. A second gives you a pair of big egg shaped lines for where you could be. With three, the GPS gives you a position but has to assume you are at sea level to do it. This may have consequences for aircraft and missiles. You need four to get altitude, and if any three are on the same great circle (like geostationary) one of the three gives you no useful information. To avoid the great circle problem you effectively need at least two rocket launches. A cube sat cannot direct its power limited signal accurately enough to get enough signal from geostationary orbit to a hand held GPS antenna.

If you are not launching till you need the satellites you then have to buy a bunch of kit that cannot be tested and has no civilian use to bring the price down to something sane.

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