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GRACE operational issue: Switch-on of MWA / ICU and orbit manoeuvre

01 July 2015

The GRACE-A and -B Microwave Assemblies (MWA) and Accelerometer Instrument Control Units (ICU) have been switched-on again on:

  • 22 June 2015, 07:22 UTC: GRACE-A and GRACE-B ICU
  • 26 June 2015, 12:02 UTC: GRACE-A MWA
  • 28 June 2015, 12:00 UTC: GRACE-B MWA

The GRACE-B MWA has been ON in sunlight and OFF for 29 minutes during eclipse. GRACE-B MWA time OFF will progressively decrease over the next ~10 days.

Since 29 June 2015 08:27 UTC, after a commanded reboot of the GRACE-A Instrument Processor Unit (IPU), the Ka-band microwave link is in lock again.

Additionally on 11 May 2015 an orbit manoeuvre has been executed on GRACE-B in order to accelerate the drift towards GRACE-A as initiation of a satellite switch. The satellite swap intends to save fuel on GRACE-B by staying on the better performing GRACE-B star camera for the second half of 2015. During the manoeuvre the two satellites had a minimum distance of 260 m on 24 May. A drift stop manoeuvre followed by a 180 degree yaw turn of both satellites on 11 June finished the swap. GRACE-A became the leading satellite.