You may have already heard that the Galileo EU satellite navigation constellation is out of service since last Thursday July 11th. Currently the Galileo constellation status page shows that the status of most Galileo satellites is not usable because of a service outage. The satellites not affected by this outage are E20, which was made unavailable on 2014-05-27, and E14 and E18, the Galileo eccentric satellites, which failed to achieve the circular nominal orbit and are only used for testing purposes.
The European GNSS Agency has given very little information regarding the causes of the problem. The available information boils down to NAGU 2019026, posted on 2019-07-13 20:15, which states that starting from 2019-07-12 01:50 the Galileo signals should not be used.
This has originated many rumours and confusion about the problem. It seems that the major cause was a failure in the Precise Timing Facility, which is in charge of the generation of a realization of the GST, the timescale used by Galileo. This has affected the OSPF, which is the service that generates the orbit and clock products (ephemeris) for the satellites. Thus, since Thursday, no new ephemeris are being computed and uploaded to the satellites.
Taking rumours aside, in this post I will look at some facts about the outage which can be learned by analizing the Galileo signal. Other people have published similar studies, such as the NAVSAS group from University of Torino.
During this week, the Amateur payload of DSLWP-B has been active on the following slots:
2019-07-09 12:30 to 14:30 UTC
2019-07-10 13:50 to 15:50 UTC
2019-07-12 02:00 to 04:00 UTC
2019-07-12 16:30 to 18:30 UTC
In these activations, the last remaining image of the eclipse was downloaded. Also, images of the lunar surface as well as stars have been taken and downloaded. This post is a summary of the activities made with DSLWP-B over the week.
Now that the DSLWP-B eclipse images have become widespread, appearing even in some newspapers, I have taken the time to identify the features of the lunar surface that can be seen in two of the images. As with any Earth and Moon pictures of DSLWP-B, the part of the Moon that can be seen in these images belongs to the far side, with longitudes of approximately 100º E and 100º W (the division between the near side and the far side happens at 90º E and 90º W, and 0º is the middle of the near side).
I have compared the images with a simulation of the camera view done in GMAT. Using this simulation as a reference and these lunar surface maps as well as Google Moon, I have labelled the features that are visible in the images. The 4K lunar surface map from Celestia Motherlode has been used in GMAT, instead of the default, lower resolution map.
The figure below shows the GMAT camera view simulation for one of the images taken as DSLWP-B was hiding behind the Moon. The field of view in this figure is much larger than the field of view of the DSLWP-B Inory eye camera. The up direction is the normal to DSLWP-B’s orbit around the Sun (defined as the plane containing the position and velocity vectors with DLSWP-B with respect to the Sun). Therefore, it points approximately towards the north pole. DSWLP-B is moving towards the upper right corner of this image.
The figure belows shows the ground track view. The satellite has crossed the near side and is now starting to orbit over the far side, soon becoming hidden behind the Moon.
Image 0xE2, taken on 2019-07-02 18:57:20 is shown below. The image has been rotated to match the orientation of the GMAT camera view simulation.
The craters that are visible in this image are labeled in the figure below. These belong to the Mare Australe region, and several well known craters such as Jenner and Lamb can be seen.
Tammo Jan Dijkema has done a similar exercise with image 0xE3, which was taken a minute after the image shown above. DSLWP-B has moved towards the upper right corner of the image, so that a larger portion of the lunar surface is visible.
The figure below shows the GMAT camera view simulation corresponding to image 0xE5, which was taken shortly after DSLWP-B exited the occultation, so that the Earth was visible again.
Below we see the ground track corresponding to this image. The satellite has crossed the far side of the Moon in a south to north direction and soon will cross over to the near side.
The figure below is image 0xE5, which was taken on 2019-07-02 19:33:05. It has been rotated to match the orientation of the GMAT simulation.
The craters are labelled in the figure below. Important craters in the Coulomb-Sarton basin such as Stefan and Bragg are visible. An image of this region with the craters labelled can be seen here.
I have devoted the lastfewpoststo the planning of the imaging times for the eclipse test run and the validation of the test run done on June 30. This post is a detailed account of the results of the eclipse imaging. Between July 3 and 5, five of the six eclipse images taken on July 2 were downloaded, as well as some other images taken later. Here I give a summary of the downloads during these days and compare the images to the predictions I made.
Yesterday I did an analysis of the image taken and downloaded during the test run for the imaging of the solar eclipse shadow on the Earth with DSLWP-B on July 2. Only one of the six images taken to validate the camera exposure and pointing and orbit errors was downloaded yesterday. The window to download the remaining images was during today’s activation of the Amateur payload between 05:30 and 07:30 UTC.
Three images were downloaded today, with a few missing chunks. Moreover, Wei Mingchuan BG2BHC has sent me better ephemeris, which give a more accurate prediction of the orbit both on the June 30 test run and on the eclipse imaging run on July 2. This post is an analysis of the images downloaded today.