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The Future For GPS ?
Some choices made in 2013 will affect us til GPS is no more.
In 2013 the 2014 and future GPS budgets were cut.
Then the Air Force began looking at future GPS satellites. A type III satellite costs about $450 million including launch. With continuing improvement in GPS life a full constellation of type IIIs was off the budget scale, so a new concept was proposed. Only 3 new type IIIs would be in the second build contract and a new “NavSat” concept would be used to fill in.
Prior and type III satellites include a nuclear detector, adding weight and about $100 million to cost. With 30+ satellites up there all do not need the detectors, so it was dropped from the NavSat concept. Less weight and less electronics meant less power required and less cooling capacity required. That plus moving from low efficiency to higher efficiency solar cells further decreased the weight. Going one step further the Air Force said they could line with only 4 signals instead of 5, 2 civilian and 2 military. That could be a problem, will they drop L1 to expand the L5 constellation?
In the end they proposed a NavSat at $110 million, 4 for the price of 1 and even proposed launching 4 at one time.
Multiple launches sound nice but present other problems. GLONASS can launch 2 or 3 depending on the vehicle and there are only 3 orbital planes. We have seen planes get seriously depleted between multiple launches and recently satellites have been launched to be inactive spares until needed. Galileo can do 2 or 4 satellite launches which is no problem until all orbital planes are filled. GLONASS and Galileo satellites are both lighter than current GPS. With 6 orbital planes I would not like to wait while a plane became so depleted to make a 4 satellite launch worthwhile. In any case a 2 satellite launch could be done on the rockets in current use with the addition of a few strap on boosters.
Will 2014 see the NavSat concept move beyond the concept phase?
Paul in PA
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