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Questions tagged [gps]

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

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GPS PPS stable signal [on hold]

My question concerns the GPS NMEA reading data about PPS signal. Is there any way to know via software using NMEA that the GPS PPS signal provided by its outport is already synchronized with the one ...
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1answer
100 views

Do GPS satellites use the earth's magnetic field in any way?

There's a lot of speculation about how changes or flips in the Earth's magnetic field would affect us, our machines, and sea turtles. I'm curious about the GPS satellites themselves. In one way they ...
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Examples of both hardware and software GNSS recievers

I am writing an essay titled: Critically evaluate the positional fixing capabilities of current smartphone technologies for real world GIS data collection I am wanting examples of both hardware and ...
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1answer
106 views

Displaying NMEA data in text console [closed]

I'm using an ublox EVK M8T and I'm trying to make a script that displays in text console in real time the data from NMEA and also the time marker from when an event happens. Is there a possibility to ...
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0answers
28 views

What is the Cheapest way to track my balloon (only altitude or gps coordinates)? [closed]

I want to build extreme cheap high altitude stuff - balloon, paper plane :) anything. Its cold outside now, and i dont want to track, and collect the my landed "spacecraft". So, i need a very cheap ...
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46 views

Could Galileo GNSS satellites 5 and 6 join the constellation if their orbit was raised, or is even more delta-v needed?

The Gallileo GNSS satellites numbers 5 and 6 have been used to make a record-breaking precision measurement of gravitational time dilation as a bi-product of them being in the wrong orbit. See (just ...
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1answer
114 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 ...
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2answers
1k 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. ...
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6answers
12k 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 ...
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1answer
130 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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60 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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1answer
270 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 ...
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1answer
380 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)...
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21 views

What are RAIM Service Outage, RNP and EnRoute on GPS DOP maps? What does the red line mean?

Reading @Antzi's question about GLONASS and GALILEO led me to the NTSB's Current GPS SPS Navigation Service Display or SPS PDOP (dilution of precision) map for GPS. Each time the map updates (every ...
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1answer
231 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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0answers
317 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 ...
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1answer
129 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 ...
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2answers
529 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 ...
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1answer
126 views

Initial condition for SGP4 in satellites without GPS, before the uplink of TLE data

I believe that the SGP4 model for orbit estimation for LEO satellites uses TLE data as initial condition. Some CubeSats chose to use up-link TLE data than installing GPS. My question is for the case ...
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1answer
106 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 ...
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1answer
210 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 ...
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3answers
9k views

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 ...
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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 ...
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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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2answers
708 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 ...
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1answer
278 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 ...
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1answer
302 views

3D modelling of satellites around the earth

I want to find and see "GPS satellites in view" for different orbits missions. For example I want to see the observable GPS satellites for a specific satellite in GEO, for this purpose I need a ...
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1answer
466 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 ...
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1answer
501 views

Why not use a rotorcraft drone or quadcopter using GPS navigation to live stream SpaceX booster landings on the droneship?

In droneship landings of SpaceX boosters, many times in live streaming, the video has stopped because of vibration in the droneship caused by the 1st stage landing of a Falcon 9 rocket. Would it be ...
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0answers
363 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 ##" ...
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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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3answers
531 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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2answers
972 views

How does a cell phone GPS receiver work without an onboard atomic clock [duplicate]

This question and its answers explain the basic theory behind GPS. I particularly like the second answer by @jah138. Using jah138's notation, GPS satellites provide extremely accurate $x_i$, $y_i$, ...
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1answer
2k views

Ground longitude/latitude under a satellite (cartesian coordinates) at a specfic epoch

The script I'm wanting to develop uses the cartesian coordinates (XYZ) from a satellite, and in conjunction with the range, elevation and azimuth from a location, I then take a satellite’s orbital ...
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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 ...
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1answer
497 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 ...
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0answers
84 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 ...
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4answers
3k 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 ...
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1answer
229 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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2answers
3k 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 ...
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1answer
435 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 ...
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1answer
960 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. ...
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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 ...
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4answers
457 views

Do GPS receivers use trilateration or distances between satellites?

My main question is whether GPS receivers use trilateration or the distances between satellites. On GPS.gov and their videos, it says you receivers use trilateration. But, I have seen people say that ...
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3answers
17k 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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0answers
658 views

Would GPS work above the GPS satellites? [duplicate]

If a rocket carrying a GPS device ascended above the height of the orbit of the GPS satellites (about 20,000km), what height would the GPS device report? Would it keep reporting the correct height as ...
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2answers
3k 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 ...
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2answers
859 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?
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2answers
1k 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 ...
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1answer
2k 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 ...