Introducing innovative techniques for extending mission lifetime

EUMETSAT has commissioned the presentation of the paper ‘Flight Dynamics Analysis of extended Lifetime for the Metop-A GOME-2 Instrument’. This was presented at the International Symposium on Space Flight Dynamics 2019 (ISSFD) in Melbourne, Australia this week.

The ISSFD is a series of conferences providing an international forum for specialists in the field of space flight dynamics. The International Symposium on Space Flight Dynamics takes place every second year and is hosted in turn by NASA, ESA, JAXA, ASA and other leading space agencies.

For this edition, EUMETSAT has commissioned the presentation of the paper ‘Flight Dynamics Analysis of extended Lifetime for the Metop-A GOME-2 Instrument.’

Authored by RHEA Group expert Antimo Damiano and EUMETSAT specialists Pier Luigi Righetti, and Ruediger Lang, this paper presents innovative techniques to extend the mission lifetime.

It showcases the success of multi-approach methods (as described by Damiano, Righetti, Lang, and Sancho, 2017 and Sancho, Fischer, and Tarquini, 2017 and used by EUMETSAT to keep exploiting the GOME instrument), the characterization of discrepancies between the expected and obtained results and the upcoming operational activities in this area, including yaw-bias manoeuvres.

The abstract of the paper

EUMETSATs Metop-A, launched on 19 Oct 2006, is the first flight model of the EUMETSAT Polar System (EPS). The Metop satellites share a sun-synchronous LEO orbit with a 29 days 412 revolution cycle and Local Time of Descending Node (LTDN) of 09:30 UTC. Together with Metop-B, launched in 2012 and Metop-C slated for launch in late 2018, they constitute the EPS space segment in Low Earth Orbit.

All Metop host the Global Ozone Monitoring Experiment–2 (GOME-2), a hyper-spectral Ultra Violet-Visible to Near Infrared Spectrometer. Daily Sun observations are mandatory for signal calibration. As Metop-A is approaching its end of life, Out of Plane (OOP) maneuver have been discontinued. The resulting loss of orbit inclination control leads to LTDN drift. The related orbital plane precession causes Sun visibility gaps lasting several days.

The multi-approach methods used by EUMETSAT to keep exploiting the GOME instrument under these circumstances were described in Damiano, Righetti, Lang, and Sancho (2017) and Sancho, Fischer, and Tarquini (2017). The present paper shows the success of those methods, the characterization of discrepancies between the expected and obtained results and the upcoming operational activities in this area, including yaw-bias maneuvers.

The first part of the paper deals with the link between the last OOP imparted the LTDN evolution, and the comparison between expected and observed GOME Sun visibility in early 2018.

As the gap characteristics depend on possible instrument mounting bias, the second part shows the analyses done to estimate these biases using actual Sun and Moon observations. The platform bias in pitch indeed improves the Sun/Moon observation residuals and the signal timing w.r.t. predictions, although it introduces other geolocation problems.

The third part describes the Sun visibility gap predictions for December 2018-January 2019, the planned platform yaw-bias manoeuvres and their effects on the observations.