# 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 such systems been used in real spacecraft? On the one hand, I'd think cubesats might go for such a low-cost solution, on the other hand, the smaller the spacecraft, the larger the error in attitude determination by using GNSS. The technique is not listed on the Wikipedia page on attitude control. Has this been used in practice at all?

• Attitude is kind of a large term, I think specifically you want to know if they have used it to figure out the orientation of the satellite. Jul 21, 2013 at 0:38
• @PearsonArtPhoto Yes, well, orientation and its derivative. What else is the term used for? Jul 21, 2013 at 0:39
• To me, part of the attitude includes the location of the satellite. And I could give you plenty of examples of satellites that use GPS to figure out where they are. But the orientation is a bit trickier, making it a far more interesting question. Jul 21, 2013 at 0:40
• @PearsonArtPhoto "The attitude of a spacecraft is its orientation in space." First sentence in Wertz, J. R. (ed.), 1978. Spacecraft Attitude Determination and Control. It does not include the location. Jul 21, 2013 at 4:43
• @ernestopheles Does it include the time derivative of attitude, i.e. the rotation? Jul 21, 2013 at 13:47

The ISS does it. Source: http://spacestationlive.jsc.nasa.gov/handbooks/adcoHandbook.pdf

Attitude Determination

How am I currently oriented?

The ISS also uses GPS to determine how the ISS is oriented, or facing, as it orbits the Earth. This orientation, or attitude, can be determined by measuring the difference in time that the GPS signals are received by four antennas. These antennas receive the same GPS signal at slightly different times, with the signal traveling at a constant speed (the speed of light).

To calculate attitude, at least four of the nearly 24 GPS satellites in orbit must be in view of these antennas. The GPS receiver calculates the ISS attitude about once a minute, providing information on where the ISS is pointed at that point in time.

Now, in more detail on that:

http://sunnyday.mit.edu/16.355/Gomez-GPS-Lessons.pdf

The ISS GPS antenna array consists of four antennas in a 3 meter by 1.5 meter rectangle on the S0 element of the ISS main truss. The array center is slightly to the port side (4 meters) of the vehicle centerline, as shown in Figure 10.

GPS alone can not meet the attitude accuracy requirements. The multipath environment on ISS is such that the unfiltered GPS attitude solutions can not meet the 0.5 degree requirement. The unfiltered GPS attitude solutions are used as an input in the ISS’s on board software attitude filter.

• You'd have thought that they'd put the antenna's on the corners of the solar array, to get a better baseline and less multipath effects. Jan 17, 2014 at 17:18
• Those arrays were not there all the time, they were added gradually as the station was built. Attitude control was needed all the time. To accomplish your suggestion the antennas would have needed to be relocated multiple times. Oct 19, 2016 at 15:26

The new Soyuz MS does too.

Instead of relying on ground stations for orbital determination and correction, the now included Satellite Navigation System ASN-K (Russian: (АСН-К, Аппаратура Спутниковой Навигации) relying on GLONASS and GPS signals for navigation.[2][11] It uses four fixed antennas to achieve a positioning accuracy of 5 m (16 ft), with the objective to reduce that number to as little as 3 cm (1.2 in) and an attitude accuracy of 0.5°.[12]