Questions tagged [gps]

Questions regarding the Global Positioning System's satellites and uses.

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5
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2answers
1k views

Did the NASA PhoneSat actually try to use the GPS from the phone itself?

I was reading this article about NASA's PhoneSat Flight Demonstrations and came across this sentence. "To achieve this, NASA's PhoneSat design makes extensive use of commercial-off-the-shelf ...
18
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1answer
791 views

How far up have satellites used a GNSS for positioning, and how does the precision degrade with altitude?

GNSS satellites (at least GPS ones) are in Medium Earth Orbit (MEO). LEO satellites can use GNSS for positioning. Is this still possible for satellites in elliptical, such as Molniya, orbits? For ...
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5answers
45k views

How does GPS receiver synchronize time with GPS satellites?

GPS satellites transmit time values regularly, but if we put in consideration the time delay between the satellite and the receiver, the time value received wouldn't be accurate insofar as I know GPS ...
13
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1answer
627 views

Will Glonass, Galileo, or BeiDou-2 satellites provide better cis-lunar navigation than GPS?

My question is: Has there been any effort to improve or optimize the radiation patterns on the subsequent satellite navigation constellations (e.g. Glonass, Galileo, BeiDou-2) to facilitate trans-GEO ...
10
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4answers
5k views

Current situation with CoCom regulations and GPS receivers for balloons and cubesats

I wanted to ask this at aviation SE because they are quite rules-and-regulations oriented there, but this question is not (really) about aviation. I'm trying to understand the current situation for ...
9
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1answer
474 views

Does the “17” really mean anything with respect to GNSS orbits being rational factions of a sidereal day?

This answer suggests that the orbital periods of the four large GNSSS contstellations are linked to the sidereal rotation period of the earth by rational numbers with 17 or 34 as the denominator in ...
39
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3answers
22k views

Why are the GPS constellation satellites in such a high orbit?

Most satellites are in Low Earth Orbit. Some other satellites are in Geostationary Orbit because their function requires it. The GPS (and other GNSS, e.g. GLONASS) satellites are in a much higher ...
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5answers
1k views

What is the deepest position in space we can get a GPS signal?

Can we use GPS in orbit at the moon? What about on Mars?
6
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1answer
177 views

Does the Soyuz spacecraft really try to achieve attitude accuracy of 0.5° from GLONASS and GPS signals?

This answer mentions that the Wikipedia article Soyuz MS (Союз МС, the latest revision of the Soyuz spacecraft, evolution of the Soyuz TMA-M) says: Instead of relying on ground stations for orbital ...
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2answers
1k views

Do any spacecraft use GNSS for attitude determination?

In principle, by placing a GNSS-receiver on all extremities of a spacecraft (or aircraft, for that matter), one can determine the orientation of the satellite. Google lists some studies, but have ...
3
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2answers
1k views

GPS constellation for Mars

How would a constellation of GPS satellites differ for Mars? For Earth the system is supposed to work with at least 24 satellites orbiting at ~20.000 km. Would Martian equivalent need less of them? At ...
2
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3answers
635 views

How can the CYGNSS spacecrafts (actually) measure ocean roughness?

The Cyclone Global Navigation Satellite System is a group of 8 smallsats which will orbit near the equator (inc=30°) and work as a constellation to take data on typhoons and hurricanes. While they are ...
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0answers
93 views

Has GPS been used beyond GEO? [duplicate]

When researching this question I came upon a presentation entitled Enabling a Fully Interoperable GNSS Space Service Volume; slides 12, 24, 25, 26 are also shown below. The idea is that while GPS ...
7
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1answer
353 views

How far from earth have atomic clocks (or ultra-stable oscillators) been placed and monitored?

The various flavors of GPS satellite constellations use atomic clocks on each satellite. As far as I know, all of the constellations are "shells" of circular MEO orbits in 3 to 6 planes, 20,000 to 25,...
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1answer
320 views

What do these GPS-related emblems represent? Does one of them show “Marvin the Martian”?

The Wikipedia page linked in @OrganicMarble's answer about the Air Force Space and Missile Museum contains the image below, of a (now retired) GPS monitoring station. To the right of the station ...
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2answers
1k views

How to get velocity vector from GPS NMEA data?

I am writing a program to receive and interpret NMEA data from a GPS receiver. I am working with an Adafruit Ultimate GPS Receiver integrated with an Arduino. The $GPRMC NMEA Sentence contains the ...
6
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1answer
480 views

Would a GPS type system on Mars really need a ground station?

This question and answer has got me thinking. Would one or more ground stations be necessary (or even just very beneficial) for a GPS-like system to operate around Mars? The atmospheric issues are ...
2
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3answers
730 views

Does GPS spoofing ever come from space? How are spoofings usually detected?

The BBC News article Study maps 'extensive Russian GPS spoofing' says: (GPS spoofing) involves the state using strong radio signals to drown out reliable navigation data, says non-profit C4ADS. ...
2
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1answer
110 views

Current status of the use of GPS mutli-antenna time differentials for satellite attitude determination?

I am certain that I read a year or three ago about an unmanned satellite that was going to be testing a method of attitude determination that relied upon two (or more) separate antennas on one ...
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0answers
487 views

PRN number in TLE files are the same in RINEX files? (in GPS constellation)

I want to compare the position calculated with Pyephem and TLE files, with RINEX files and GPSTK library in a specific date and time, but I have not the certainly if the name of the satellite "PRN ##" ...
10
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1answer
573 views

Do operating GPS satellites ever make orbital maneuvers for station-keeping?

Since GPS satellites need to face the Earth, they might execute momentum-unloading from time to time using pairs thrusters so as to produce torque but minimal change in the orbit, but I am guessing ...
30
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1answer
4k views

Could a Falcon Heavy really put six GPS Block III satellites in orbit at the same time?

This answer says: GPS Block III satellites are being launched to replace failed or aging Block II satellites, which doesn't require launching more than one at a time. A Falcon Heavy could fill up ...
9
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1answer
555 views

Why do GPS satellites have increasing eccentricity over time?

When comparing GPS, Beidou, Galileo, GLONASS, and potentially other GNSS, we can see that the eccentricities of GPS spacecraft are increasing with time (i.e. apogees increasing and perigees decreasing)...
8
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4answers
421 views

Does GPS work at ISS?

I've recently seen movie Gravity. The protagonist detaches from the shuttle and is hurled into space. The mission commander then asks her for GPS coordinates. This happenned while they were fixing ...
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2answers
2k views

Height of navigation satellites above Earth

What is the distance between the Earth's surface and the motorists' satnav satellites?
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2answers
472 views

Why multiple GPS satellites are never launched on the same rocket?

From what I've read, GPS satellites have been always put in orbit one at a time. In contrast, Galileo (aboard Ariane or Soyuz) and GLONASS (aboard Proton) sometimes are launched at the same time. Is ...
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2answers
1k views

Is GPS time at least “really close” to TAI (International Atomic Time)?

@DavidHammen's answer got me thinking. GPS time "comes from" (US Naval Observatory) a whole bunch of atomic clocks, in space and on Earth. TAI or International Atomic Time also comes from a whole ...
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0answers
179 views

GPS Receiver Autonomous Integrity Monitoring (RAIM) - parity space method

I am trying to understand RAIM. My teacher explained three RAIM methods, I will just quote all of them because I think that the jargon might not be consistent. Maximum separation / Position ...
3
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1answer
266 views

Why are orbital periods different for different GNSS positioning system constellations?

My question is restricted to global positioning systems (Regional ones have geosynchronous constraints, which limits drastically the orbit choice) The diagram in this question highlights different ...