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
Hi Paul,
"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?"
Perhaps I am misunderstanding this part of your comment. The main purpose of L5 is to meet safety of life applications by forming L1/L5 combination as they are both in the protected aeronautical radio navigation bands. So I would be surprised to learn that they are considering choosing between the two.
Is not L5 supposed to be better than L1, I would not expect them to drop L2.
I did not quite understand that proposal, so will have to wait for future information.
Paul in PA
There is absolutely zero possibility that L1 will be "dropped" from GPS.
As a side note, L1 is not in the aero protected band. You can view the FCC spectrum dashboard here
http://reboot.fcc.gov/spectrumdashboard/searchSpectrum.seam
> Hi Paul,
>
> "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?"
>
> Perhaps I am misunderstanding this part of your comment. The main purpose of L5 is to meet safety of life applications by forming L1/L5 combination as they are both in the protected aeronautical radio navigation bands. So I would be surprised to learn that they are considering choosing between the two.
Maybe on a related note;
LightSquared cancels spectrum auction, Centerbridge makes $3.3B bid, Ergen suit still at issue
Apparently this is a separate asset not included in any potential deal to date.
Yes, I get that but if it was in the aero protected band, how could LightSquared have been considered in the first place?
> Although it is tough to see the L1 frequency falls into the protected band 1559 - 1610 MHz shown here allocated for radio navigation.
>
> Also, a little less credible but clearer to understand 🙂 : navipedia
From my understanding, Lightsquared controls a block of spectrum (1525-1559 MHz) adjacent to the protected band which contains the GNSS L1 frequency. This part of the spectrum was intended for Mobile Satellite Services but Lightsquared claimed that they were granted permission to use it for a combined terrestrial service.
Lightsqured then claimed that the only reason that there is any interference for GNSS receivers is that the GNSS manufacturers designed poor receivers that infringed on their part of the spectrum.
My point is that this LightSquared stuff would never happen around the L5 frequency because it's buried in the aero protected band. There's too much stuff going on around L1 for it to have the same level of protection.
> From my understanding, Lightsquared controls a block of spectrum (1525-1559 MHz) adjacent to the protected band which contains the GNSS L1 frequency. This part of the spectrum was intended for Mobile Satellite Services but Lightsquared claimed that they were granted permission to use it for a combined terrestrial service.
>
> Lightsqured then claimed that the only reason that there is any interference for GNSS receivers is that the GNSS manufacturers designed poor receivers that infringed on their part of the spectrum.