Operational Orbit

The original INTEGRAL orbit is a highly excentric one, inclined by 51.6 and with a perigee height of 9000km and an apogee height of 152600km. The period of the INTEGRAL orbit is 3 sidereal days, so that the perigee occurs always above the same geographical point on Earth. Since one sidereal day lasts 23h 56m 4s, the local time of the perigee changes by 12 minutes on every revolution. While the perigee height and the inclination have changed a lot over the years, the period remained constant until 2015.

In early 2015, ESA performed a series of manoeuvres towards a safe disposal of INTEGRAL in February 2029, via natural re-entry in the atmosphere. These operations took place from 13 January (end of rev. 1495) to 12 February 2015 (end of rev. 1506). The resulting orbit is no longer of 3 sidereal days, but has a repeating pattern of 3 revolutions in 8 sidereal days. The orbit period is thus of roughly 2 days and 16 hours. The loss of science time due to a higher fraction of perigee passages does not exceed 5%, and the seasonal visibilities do not change significantly either.