Questions tagged [gnss]

Questions about Global Navigation Satellite Systems (GNSS), such as existing Global Positioning System (GPS) and GLObal NAvigation Satellite System (GLONASS), but also future such systems in development, like European Galileo, China's Compass or India's IRNSS (Indian Regional Navigational Satellite System).

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Time parameters in RINEX navigation file

Currently, I am trying to determine the position of a GPS satellite from a RINEX navigation file. I am using RINEX 2.11. Tables A3 and A4 describe how navigation files are structured. In order to ...
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3 votes
0 answers
62 views

Understanding "classical" algorithms behind RINEX files post-processing

I'm new to this site so I want to apologize beforehand for all the mistakes I could make while writing this. So just to put my situation into context : I am currently an intern in an AI company tasked ...
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2 votes
2 answers
48 views

Which is more accurate, the ellipsoidal height from SLR or GNSS?

Satellite Laser Ranging (SLR) and Global Navigation Satellite System (GNSS) both measure the ellipsoidal heights. Which measurement of ellipsoidal height is more accurate?
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2 votes
0 answers
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What is the difference between SBAS and PPP used in GNSS accuracy corrections?

I've found that Satellite Based Augmentation System uses reference stations to compute a model for correction and send them via a master station to a geosynchronous satellite, then to GPS receiver. I ...
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1 vote
1 answer
94 views

What is "Time To First Fix" in GNSS?

I used an app to test GPS, that shows me TTFF is equal to a few seconds. I want to understand : What is Time To First Fix? Is having internet access useful to improve it?
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1 vote
1 answer
47 views

Is Satellite Based Augmentation System ,used in GPS, a Differential Technique?

I've read that to get a higher accuracies in GPS, we use differential positioning techniques which compute for satellites errors, using well-known position base station. I want to know if the ...
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2 votes
2 answers
63 views

Does using multifrequencies totally eliminate the ionosphere delay on GPS measurements?

I've read that the GPS receiver computes the difference in measurement for two GPS satellite signals (in two frequencies L1 and L2), in order to compute the actual delay that the ionosphere causes. ...
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31 votes
8 answers
10k 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 ...
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3 votes
1 answer
80 views

Precise Orbit Determination (POD) vs GNSS accuracy; seeking references

Precise orbit determination provides performances that are not currently achievable with GNSS systems. I cannot find information of the reason for this. I imagine different possibilities: Use of ...
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4 votes
1 answer
204 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 ...
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3 votes
0 answers
65 views

Are LHCP L-Band antennas for Cubesats available?

I am designing a cubesat to carry out GNSS reflectometry or GNSS-R. To collect the earth reflected signals, I need a nadir pointing array of patch antennas, with Left Hand Circular Polarisation (LHCP) ...
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7 votes
2 answers
345 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 ...
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4 votes
2 answers
775 views

Ephemeris time and clock corrections in RINEX navigation files

RINEX (Receiver INdependent EXchange format) is a set of file formats to distribute satellite navigation systems data, including GNSS. One of these standards, navigation files, provide positional ...
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3 votes
1 answer
296 views

Obtaining position of GPS and GLONASS satellites from RINEX navigation files

I am currently trying to understand the best way to use the available information in RINEX navigation files for GPS and GLONASS satellites. My main goal currently is to calculate the position at epoch ...
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3 votes
1 answer
44 views

generated error terms for positioning based on a pre defined target accuracy level

I would like to ask a question about accuracy level and precise point positioning or PPP. I'd like to design a system such that when the desired accuracy level is provided as an input, the ...
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3 votes
1 answer
120 views

Lunar satellite navigation system

Inspired by some questions: Are People Actually Serious About Mining The Moon? How to estimate that receiving GNSS signals Earth while orbiting the Moon will still provide locations to about 200 ...
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7 votes
0 answers
421 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 ...
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4 votes
1 answer
195 views

How to estimate that receiving GNSS signals Earth while orbiting the Moon will still provide locations to about 200 meters of uncertainty?

IEEE Spectrum's Can Astronauts Use GPS to Navigate on the Moon? NASA Scientists Say Yes says: Kar-Ming Cheung and Charles Lee of NASA’s Jet Propulsion Laboratory in California did the math, and ...
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7 votes
0 answers
175 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 ...
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3 votes
2 answers
1k views

Delay-Doppler maps in space science

Maybe this question might be more physics related, but I've read about mostly in context of space science: What is a delay-doppler map (DDM)? I can find it in exploration of asteroids (e.g. (...
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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 ...
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2 votes
3 answers
860 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. The ...
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1 vote
0 answers
71 views

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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4 votes
1 answer
335 views

Celestrak GLONASS TLE's showing satellite numbers not listed in the GLONASS constellation, others missing

For a project, I'm retrieving TLE information live from http://celestrak.com/ and using them to simulate satellite orbits. The TLE's for the GLONASS constellation (http://celestrak.com/NORAD/elements/...
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5 votes
1 answer
271 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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13 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. ...
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3 votes
1 answer
182 views

Current status of the use of GPS multi-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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4 votes
1 answer
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Is two-way communication really required to use BeiDou GNSS?

The BBC's How China's GPS 'rival' Beidou is plotting to go global mentions a scenario where end-users can send signals to other Earth locations using BeiDou and later says: But despite its ...
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12 votes
1 answer
755 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)...
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4 votes
1 answer
273 views

What function do the GEO satellites have in the BeiDou system?

As the title asks: the Compass/BeiDou-2 system constellation includes five satellites in GEO, while most of their satellites are in MEO at about half the altitude. Do these provide a ranging signal, ...
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10 votes
1 answer
727 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 ...
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7 votes
1 answer
320 views

How might excluding the UK from Galileo set the European programme back years and cost the EU billions?

edit 1: More here: Brexit 'will force Airbus work on Galileo out of UK' and now here: Brexit: UK wants £1bn back from EU if it is excluded from Galileo edit 2: And now more here: UK rebuffed over ...
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6 votes
1 answer
499 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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2 votes
2 answers
525 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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9 votes
1 answer
1k views

Radiation pattern and signal strength of navigation satellite antennas

Where can I find the actual radiation pattern and signal strength of transmitting antennas used by GNSS navigation satellites/constellations (GPS, GLONASS, IRNSS, etc)?
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42 votes
3 answers
25k 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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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 ...
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21 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 ...
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11 votes
1 answer
371 views

In LEO, what is the precision of GNSS-based position compared to traditional methods?

GNSS satellites (at least the GPS ones) are in MEO, so LEO spacecraft can use GNSS for their positioning. I've read that it's quite low-cost compared to the alternatives. How does the precision of ...
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