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Questions tagged [gps]

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

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51 votes
3 answers
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Why would GPS availability be reduced by high demand (or solar eclipse)?

This Newsweek article states that "GPS...will likely be nonexistent near the eclipse zone" because of all the people going to that area. While it makes sense that cell towers might be overloaded and ...
WBT's user avatar
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45 votes
3 answers
9k views

What is GPS' 19 year rollover and does it present a cybersecurity issue?

The NPR new item and audio podcast The Global Positioning System Resets talks about a 19 year cycling of something in the GPS system, but it's not clear what it is. Every 19 years, the Global ...
uhoh's user avatar
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43 votes
3 answers
28k 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 ...
Max Q Lagrange's user avatar
42 votes
6 answers
57k 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 ...
digiogi's user avatar
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40 votes
6 answers
13k views

How can a Mars helicopter be autonomous if there isn't a Martian GPS?

For a drone to be autonomous, it needs something like a GPS to be able to navigate. If it doesn't have GPS, you'd have to manually control it. Do the orbiters provide something like GPS then? I ...
space's user avatar
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32 votes
8 answers
11k views

Why does GPS need the fourth satellite?

I am currently working on a GPS project, so I am doing some research about the subject. I understand that the GPS receiver knows its location by calculating its distances from 3 satellites, and by ...
Yahya Aouled Amer's user avatar
30 votes
1 answer
5k 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 ...
uhoh's user avatar
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22 votes
2 answers
1k 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 ...
gerrit's user avatar
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19 votes
5 answers
1k views

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

Can we use GPS in orbit at the moon? What about on Mars?
Kamic's user avatar
  • 293
19 votes
2 answers
2k 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 ...
gerrit's user avatar
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16 votes
4 answers
6k views

How does GPS work exactly?

For a GPS receiver to estimate its position, it first receives signals from at least 4 satellites. Does the receiver calculate the distance that separates it from each satellite, or does it just ...
Noureddine's user avatar
16 votes
2 answers
5k views

How are GPS satellite clocks synchronized with each other in the earth's frame of reference?

I have been looking at different threads. It seems like the receiver clock on Earth doesn't have to be synchronized with the satellite clocks. But I believe the satellite clocks need to be ...
Ameet Sharma's user avatar
16 votes
4 answers
10k 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 ...
uhoh's user avatar
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15 votes
2 answers
2k views

Can the satellites in Martian orbit be put to use providing a rudimentary GPS system on Mars?

This website conveys the impression a rover on the Martian surface necessarily navigates by dead-reckoning. Stereo images are used to determine how far a rover has travelled; an advancement over older ...
Everyone's user avatar
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15 votes
2 answers
2k views

How can cosmic ray muons be used to replace GPS for positioning information in 3D on Earth and underwater?

Task & Purpose's The Navy is testing a GPS-like device that doesn’t require satellites “The future is extremely bright for this line of research." begins: The Navy is researching a new ...
uhoh's user avatar
  • 149k
14 votes
2 answers
612 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 ...
jinawee's user avatar
  • 243
13 votes
1 answer
862 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 ...
uhoh's user avatar
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12 votes
2 answers
2k views

What is this gap in the GNSS satellite trajectories?

I've recently bought a USB-connected multi-constellation GNSS-receiver with a U-blox 8 chip in it. I've downloaded the U-center software that can display a lot of details about the received signals. ...
Bart Noordervliet's user avatar
12 votes
1 answer
865 views

Why do GPS (but not GLONASS or Beidou) 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)...
costrom's user avatar
  • 1,053
11 votes
5 answers
15k views

What is required to make GPS signals available indoors?

GPS satellites don't transmit strong enough to reach indoors, through the roofs and walls of buildings, like cell phones do. GPS signals that enter buildings through windows are unreliable since they ...
LocalFluff's user avatar
11 votes
2 answers
2k views

Would a GPS receiver with an onboard atomic clock only need 3 satellites to determine position?

GPS receivers need four satellites to determine their position and time. They provide a receiver with data that is fed into four equations. Three equations are solved (simultaneous with the fourth) to ...
chessofnerd's user avatar
11 votes
1 answer
1k 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 ...
uhoh's user avatar
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11 votes
1 answer
898 views

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

This answer to Why are orbital periods different for different GNSS positioning system constellations? suggests that the orbital periods of the four large GNSSS constellations are linked to the ...
uhoh's user avatar
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10 votes
2 answers
2k views

Is the full GPS constellation a Walker Delta constellation?

Through the extremely rigorous method of looking at the animation on Wikipedia's article about GPS, if this does indeed accurately represent GPS satellite orbits, then it looks like not all of the ...
NeutronStar's user avatar
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9 votes
4 answers
2k 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 ...
jnovacho's user avatar
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9 votes
2 answers
3k 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 ...
uhoh's user avatar
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9 votes
2 answers
1k views

How many satellites would be required for Solar System GPS?

GPS is a Global Positioning System. it uses satellites in orbit to identify precise location on a globe. Several posts here talk about it being used in Low Earth Orbit (LEO) with success. About 30 ...
James Jenkins's user avatar
9 votes
1 answer
753 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 ...
uhoh's user avatar
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9 votes
1 answer
3k views

Is there any open source software that can compute GPS ground coverage? I need a free alternative to AGI's System Tool Kit (STK)

Does any open source software exist that can compute GPS ground coverage in real time? At work I used STK which would do the job perfectly, but I'm at school now so I only have the free version. For ...
user3069's user avatar
  • 129
8 votes
1 answer
503 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,...
uhoh's user avatar
  • 149k
8 votes
1 answer
309 views

What will the US government start to label its GPS spacecraft after SVN 99

GPS spacecraft are currently identified by their “Space Vehicle Number” (SVN) which now number 01 through 75. What will happen after 99 GPS satellites are launched? Is there any plan currently in ...
johnDanger's user avatar
7 votes
2 answers
1k views

How is the ambiguity in code phase resolved in GNSS code-based positioning?

For positioning using GNSS, a typical introduction text (example PDF) introduces the concept of pseudo ranges as roughly being the time between transmission of a GNSS signal by the satellite $s$ and ...
Ludo's user avatar
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7 votes
0 answers
781 views

Are software defined GNSS (GPS) receivers legal under ITAR and other export regulations?

With the latest update to ITAR rules, it looks like covered GNSS receivers are defined as follows: (2) Global Navigation Satellite System (GNSS) receiving equipment, as follows: (i) GNSS receiving ...
Manuel Menzella's user avatar
7 votes
0 answers
382 views

Interpolating precise ephemerides of GPS satellites

My objective is to obtain at least a sub-meter position accuracy by interpolation of the GPS ephemerides. There is conflicting research outside, where some authors state that a simple Lagrange or ...
Samuel Low's user avatar
6 votes
2 answers
3k views

Why do gps satellites rotate over the Earth

Why do gps satellites rotate over the Earth? Some says because of it there are at least 4 gps satellites at any location of Earth. But I can't understand it. What would happen if gps satellites ...
digiogi's user avatar
  • 593
6 votes
2 answers
2k 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 ...
uhoh's user avatar
  • 149k
6 votes
2 answers
857 views

How are artificial satellites of non-Earth celestial bodies positioned?

A body on Earth's surface can be positioned easily knowing the GPS coordinates, assuming the body is in direct path or 4 GPS satellites. But how is a satellite (say Maven or India's Mangalyaan) which ...
x0x's user avatar
  • 163
6 votes
1 answer
165 views

Inexplicable Offset in Satellite Laser Ranging (SLR) observations

I am struggling with the implementation of a Satellite Laser Ranging (SLR) validation tool. The situation is as follows: I am provided with a framework which gives me the position of a SLR ...
lenxn's user avatar
  • 163
6 votes
1 answer
533 views

What is the magnetic equatorial anomaly and how is GAGAN unique in its ability to compensate?

ISRO's GPS Aided GEO Augmented Navigation system (GAGAN) (see ISRO and Wikipedia) is the first GPS augmentation system designed to deal with ionospheric effects near the geomagnetic equator. From ...
uhoh's user avatar
  • 149k
6 votes
1 answer
260 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 ...
uhoh's user avatar
  • 149k
6 votes
1 answer
71 views

What does "Common frequency offset" plot means in gnss raw measurements?

I'm using Google's MATLAB code to analyze raw gnss measurement made with gnsslogger android app. In plots, there is one in particular that I don't understand the meaning, which is "Common ...
allexj's user avatar
  • 59
5 votes
7 answers
1k 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 ...
uhoh's user avatar
  • 149k
5 votes
2 answers
2k 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 ...
jkavalik's user avatar
  • 5,128
5 votes
2 answers
988 views

TLE and RINEX gps differences

I have TLE and RINEX navigation file for GPS satellite PRN 20, for 01.04.17r. 19:56:56 and 20:00:00 respectively. See also The Receiver Independent Exchange Format Version 3.03. It seems that the ...
kas's user avatar
  • 53
5 votes
1 answer
3k views

How does GPS module gets time even before a fix?

I have a GPS module which outputs NMEA messages at 1Hz. In the data sheet it is mentioned that at cold start, it will get a fix in 29s. I run it cold start and indeed it gets the fix in 29th second. ...
Hassan's user avatar
  • 53
5 votes
1 answer
469 views

Why end-of-life GPS satellites given orbits that seemingly still intersect active satellite orbits but with a different period? Recipe for disaster?

This answer to Where are MEO satellites put at the end of their operational life? says (currently in full): This is an active area of research. As you noted, the main satellites that are in MEO are ...
uhoh's user avatar
  • 149k
5 votes
1 answer
310 views

Why the PRN obtained from Android is different from calculated by TLE

I want to use TLE data to calculate the azimuth and elevation of every GPS satellites at user's location. In order to verify the correctness of TLE calculation, I wrote an Android app that can be ...
AndyShan's user avatar
5 votes
0 answers
235 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 ...
MrYouMath's user avatar
  • 151
4 votes
4 answers
330 views

Alternative to GPS navigation for vertical landing, especially on other planets

Is the GPS data reliable or meaningful only on Earth or below the geo-stationary Earth orbit? For GPS navigation, does a rocket has to fly below the geo-stationary orbit? If GEO is a physical ...
seccpur's user avatar
  • 1,175
4 votes
1 answer
304 views

Can the James Webb Space Telescope's position be determined using GNSS? And if not, how is this done?

As far as I know, the recently launched James Webb Space Telescope will be positioned at 1,500,000 km of the Earth, orbiting Sun-Earth L2 Lagrange point at roughly 4x the distance between the Earth ...
swiss_knight's user avatar