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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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54 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. (...
42
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3answers
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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2answers
612 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. ...
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1answer
376 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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0answers
45 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 ...
4
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1answer
131 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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0answers
63 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 ...
5
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1answer
126 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 ...
13
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2answers
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. ...
2
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1answer
499 views

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 ...
10
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1answer
440 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)...
4
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1answer
177 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, ...
6
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1answer
306 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 ...
7
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1answer
279 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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3answers
18k 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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1answer
334 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 ...
18
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1answer
735 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 ...
15
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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 ...
8
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1answer
750 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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1answer
314 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 ...