Why are GLONASS satellites launched on Christmas Day?

Why are GLONASS satellites launched on Christmas Day? Question posted on CANSPACE on December 10, 2006, by Kerry Matthews

The latest triple-satellite GLONASS launch occurred on December 25th at 23:18 Moscow Time. This launch is the sixth GLONASS December launch in a row. In fact, all 9 launches since December 1995 have occurred in the last month of the year with the exception of the launch on October 13th, 2000 (see a list of GLONASS launches going back to 1990).

Including this month’s launch, three of the recent launches have occurred on December 25th and one originally scheduled for the 25th, occurred on the 26th. Why the preponderance of December launches and launches on Christmas Day in particular?

First of all, we should realize that for most people in the Russian Federation, there is nothing special about December 25th. Most Christians in Russia belong to the Russian Orthodox Church which celebrates Christmas according to the Julian calendar — on January 7th. And in modern Russia, January 7th is a state-wide holiday. So, GLONASS launches don’t occur around December 25th because it’s a special day on the Russian calendar. So why do they occur then?

I posed this question to Col. (ret.) Nikolai Shienok, the former chief of the Information Department of the Coordination and Scientific Information Center of the Russian Ministry of Defense. After conferring with officials from Roscosmos (the Russian space agency) responsible for the GLONASS program, Col. Shienok confirmed that it is only for financial or organizational reasons that there is a preponderance of launches in December. “It is the last month of the year and it is impossible to postpone a planned launch further” Col. Shienok said.

Nevertheless, there may be some operational calendar constraints on GLONASS satellite launches as there are for launches of other satellites. Satellite operators typically try to avoid launching satellites when the Sun-orbit-plane or beta angle for the intended orbit is unfavorable. The beta angle is the angle between the geocentric position vector to the Sun and the satellite’s orbital plane. This angle determines if and for how long a satellite will be in the Earth’s shadow during its orbit. For a given orbit (altitude, inclination, and initial right ascension of the ascending node), the beta angle will vary over the year. Operators try to avoid a launch date when the satellite would be in eclipse for a significant fraction of its orbit so that during the crucial satellite deployment and commissioning phase, the satellite’s solar panels receive as much sunlight as possible to keep the satellite’s batteries fully charged. The recent GLONASS launch put the satellites into Plane 2 which is actually in one of its eclipse seasons right now. However, the satellites will be out of eclipse by early January.

Prof. Richard B. Langley

Dept. Geodesy and Geomatics Engineering

University of New Brunswick