What's up June 14

What's up June 14

The last couple of days have been more interesting than planned.   After a successful launch, the NuSTAR satellite reoriented to position its deployed solar arrays toward the sun and entered a stable sun pointing mode as planned using its coarse sun sensors and reaction wheels.    The spacecraft changes orientation by changing the speed at which the reaction wheels spin.    The spacecraft power systems indicated excellent performance with over 23 Amps of current from the arrays and the batteries were fully charged. Thermal, radio communications and Command and Data Handling subsystems were nominal and the spacecraft bus commissioning process, expected to take one week, began as planned.  

 Shortly after NuSTAR started to use its attitude control system, which employs a combination of reaction wheels and magnetic torque bars to maintain spacecraft pointing, the engineering team noticed that the reaction wheels started to spin faster than needed to maintain its proper orientation.   This was not expected, because the magnetic torquer bars are controlled by the spacecraft software to create a magnetic field that torques against Earth’s field.   This enables a low reaction wheel speed to be maintained. The NuSTAR team temporarily disabled the torque bars, and the spacecraft continued to point using the reaction wheels alone.  The cause of this issue was traced to a bad calibration on the magnetometer and a phasing error with the torque bars.   These were corrected, and attitude control was reenabled.    Momentum management is back in control and the attitude control is funcitoning as expected.  With this behind us we will continue as planned bringing up the spacecraft to a state good for mast deployment next week.

uews© Caltech 2012