Mobydisc said...

I read in the New Scientist today the satellites required for GPS calculations are getting old. Something like 24 satellites are required to make reasonably accurate calculations.

Indeed, they are getting old, but new birds are sent up too -> the latest has three frequency bands (L1, L2, L5) + other enhancements.

Additionaly, the more birds your receiver can see, the better the positional accuracy. 24 is the minimum number needed in whole constellation around the globe, to be useful (you could have less, but it would be rather useless). If you had all 24 sitting directly above you, it would be quite accurate.

see: en.wikipedia.org/wiki/GPS_modernization

Currently there are around 30 up there but a number are going to fail within two years and bring the numbers down towards 24.

The American Airforce apparently has difficulty building and launching new satellites.

I wonder if this is a bit of scare mongering by the American government in the hope of some other countries contributing towards the cost of the GPS system.

This is a photo of orbital bodies... what do you reckon? Some of it is pure scrap metal from explosions, etc... but I'm confident that we have that surfing-a-controlled-explosion-thing all figured out.

My guess is the comment relates to "need more funding"...



Ref: www.smh.com.au/news/businessinnovations/wireless--the-new-world-order/2008/05/12/1211654227833.html&h=331&w=470&sz=51&tbnid=G9-zaT5QENuHPM:&tbnh=91&tbnw=129&prev=/images%3Fq%3Dsatellites%2Bin%2Borbit&hl=en&usg=__ewOLVwV2dXFWMRuZavrGfnPd1Hs=&ei=4StDSriOIpSNkAX42vmbDw&sa=X&oi=image_result&resnum=5&ct=image

mathew said...

Mobydisc said...

I read in the New Scientist today the satellites required for GPS calculations are getting old. Something like 24 satellites are required to make reasonably accurate calculations.

Indeed, they are getting old, but new birds are sent up too -> the latest has three frequency bands (L1, L2, L5) + other enhancements.

Additionaly, the more birds your receiver can see, the better the positional accuracy. 24 is the minimum number needed in whole constellation around the globe, to be useful (you could have less, but it would be rather useless). If you had all 24 sitting directly above you, it would be quite accurate.

see: en.wikipedia.org/wiki/GPS_modernization

Currently there are around 30 up there but a number are going to fail within two years and bring the numbers down towards 24.

The American Airforce apparently has difficulty building and launching new satellites.

I wonder if this is a bit of scare mongering by the American government in the hope of some other countries contributing towards the cost of the GPS system.

This is a photo of orbital bodies... what do you reckon? Some of it is pure scrap metal from explosions, etc... but I'm confident that we have that surfing-a-controlled-explosion-thing all figured out.

My guess is the comment relates to "need more funding"...



Ref: www.smh.com.au/news/businessinnovations/wireless--the-new-world-order/2008/05/12/1211654227833.html&h=331&w=470&sz=51&tbnid=G9-zaT5QENuHPM:&tbnh=91&tbnw=129&prev=/images%3Fq%3Dsatellites%2Bin%2Borbit&hl=en&usg=__ewOLVwV2dXFWMRuZavrGfnPd1Hs=&ei=4StDSriOIpSNkAX42vmbDw&sa=X&oi=image_result&resnum=5&ct=image

Matt obviously it's not a photo. Actually in terms of the area vs number of objects (12,000 odd) the chances of collision are still virtually zero. Bear in mind that satellites orbit at different altitudes too so their paths nearly cross regularly. Mobydisc fear not, the US Airforce is not the only organisation capable of launching satellites, in fact they're one of many players, including the EU, China, Japan, India and Russia.

GPS Modernisation Schedule
•
Second civil signal L2C
–
Designed to meet commercial / scientific needs
–
Higher accuracy through ionospheric correction
–
1st launch: Sep 2006 (IIR-M); 24 satellites: ~2016
•
Third civil signal L5
–
Designed to meet demanding requirements for safety-of-life
–
1st launch: Mar 2009 (IIR-M / IIF); 24 satellites: ~2018
•
Fourth civil signal “L1C”
–
Designed with partners for GNSS interoperability
–
Begins with Block III
–
1st launch: ~2014; 24 satellites: ~2021

Would it prove a point if the original image came from NASA?



I'm a little dubious of Galileo being finished by 2013... its taken them two years to put 4 birds up - I'm not confident they can do another 2 0 in the remaining 4 years.

nebbian said...
Woooh... Is that big ring made up of satellites in geosynchronous orbit?

Also what about Iridium? Is this a codeword for one of those systems Sailquik mentioned?

yes and no.... they are indeed geosynch, but the shot is a composition of a few hundred images
(geosynch is about 36,000 km from earth), so it looks way more than there actually are.

Iridium is the satellite phone network - orbit of 500 km - they probably are too small + far away to be seen in that shot.

GPS satellites - 20,000km

In theory it would be possible to create a GPS receiver that could use both GPS and Iridium satellites (plus some others, say GOES and NOAA) to create a more accurate receiver... or we could just use the existing L2 GPS frequency...

hey look , iam a fairly basic kind of guy.
very basic on the computer.
Should i go and unfold sum cash for GT31 or not.