Aura Science Team Meeting Mission Operations Working Group HIRDLS – Jim Craft, Chris Hepplewhite Oct 1 - 5, 2007 JPL, Pasadena, Ca.

2 Purpose and Scope Summary of HIRDLS performance since last meeting With emphasis on science capability and sub-system performance Summary of Mission activities supporting HIRDLS since last meeting Emphasis on pitch maneuvers. An illustration of HIRDLS short-period rotation Data obtained from the HIRDLS gyroscopes give disturbances at the optical bench. Outline of changes to Ops and the Ground Segment. Future planning.

3 Summary of HIRDLS Performance Summary of HIRDLS performance since last meeting Highlights include: Only about 5 science data packets were lost due to instrument problems over past year. Three days of 4 orbits of pitched data leaves % possible data for processing geophysical data. All pitched data successfully captured and utilized for radiometric correction. The instrument has been nominal for the duration with exceptions: The Cooler has continued to control the focal plane detectors to within a milli- Kelvin of specified temperature which is within specification by order of magnitude. Furthermore, the cooler duty cycle has increased only by about 1% since launch and has 15% headroom – suggesting de-icing is unlikely during mission life. The mean power consumption has not changed since launch (except in respect of the contribution of the decreased cooler efficiency). The thermal balance has not changed – we have noted that the sun-shield door peak temperature (which occurs at sunset when the sun illuminates the door directly) has increased a few Kelvin. The scan mirror has continued to operate faultlessly.

4 Summary of HIRDLS Performance The exceptions: The Chopper had several intermittent “episodes” of duration two hours, separated by a few days or weeks, when the speed would fluctuate out of specification with associated spikes in the current drawn by the motor. Some of these led to out of synchronization conditions in which a science packet was lost. The last event occurred on day and led to the packet timing generator switching from the chopper to internal clock. For several days until the timing was restored, the phase of the detector sampling would be less certain than otherwise and may result in larger radiometric errors. Since there have be no similar events. The gyroscope subsystem lost one of the four units, thereby loosing the redundancy – any three of the four units are required for complete determination of rotation in the inertial frame. Gyro no. 0 signal diverged up to full scale over the period to -063 whilst all other functions of the channel remained unchanged. Experiments were conducted in flight to help gather evidence about the nature of the failure and in an attempt to recover the channel. Recovery was not possible and the investigation is awaiting further analysis of the capture loop controller in the unit. It is expected that this work will be completed by December 2007 when a final report can be made to FoT.

5 Summary of Mission Activities Summary of Mission activities supporting HIRDLS since last meeting The major items in which HIRDLS has been supported by mission control center are: Recovery of the chopper synchronization timing source. Experiments on gyroscope no. 0. Three Aura pitch maneuvers: (#8) 3 rd Nov ’06; (#9) 1 st Mar ’07; (#10) 13 th July ‘07. The pitch maneuvers are timed to coincide with the maximum, minimum and an intermediate point in the annual cycle of the solar beta angle on the spacecraft. The radiometric correction due to the obstruction in the telescope is sensitive to the mean thermal loading, of which solar heating is a significant factor during ascending node of the orbit. The pitch angle is the smallest necessary in order that the atmosphere is NOT visible for any channel over the full vertical scan range. During the pitch several scans are performed including the standard science scan, and scans to measure the emission pattern from the obstruction.

6 Summary of Mission Activities What we’re doing different: The raster scan across the obstruction is performed more slowly than on previous occasions so that the mirror motion does not excite the obstruction. What we’re learning: That the obstruction has remained remarkably invariant since first being measured early in the mission (good thing). That the area fraction of obstructed view has yet to be determined more accurately as suggested by the measurements. That the emission from the obstruction can be better determined given the pitched data and applied to normal orientation data. This is particularly relevant to the intra-orbit and inter-orbit variability. The pitch maneuvers have been used to check the long term stability of the HIRDLS gyroscope scale factor.

7 Example of HIRDLS Motions An illustration of HIRDLS short-period rotation and alignment The Aura spacecraft is a remarkably stable platform from which to perform limb scanning. Data provided in the Aura attitude and ephemeris files are processed so as to meet the pointing requirements of HIRDLS. The HIRDLS gyroscopes provide a direct measurement of the short period rotation of the optical bench and could be used to provide a “correction” of the Aura attitude data within HIRDLS vertical scans if desired. The HIRDLS gyroscopes detect periodic motions not reported in the Aura attitude files that are due to instrument mechanisms. The following charts illustrate these observations:

8 Example of HIRDLS Motions Derived roll, pitch & yaw body rates from HIRDLS gyros for 2.75 hours Derived roll body rates from HIRDLS gyros for 30 min period of previous graph.

9 Example of HIRDLS Motions Integrated rate (accumulated angle) of rotation about the HIRDLS line of sight scan axis for 250 secs (left) and 30 secs (right) around mid point of previous graph. (1 arcsec = 14.5 m at the limb).

10 Operations and Ground Segment Outline of changes to Ops and the Ground Segment. HIRDLS lost 2 Science Packets due to FMU anomaly ( /13:06:51 (July 4, 2007) /05:56:22 (August 5, 2007) ) Oxford University and UCB successfully swapped out the old MMS Boxes (old Sun boxes) with the Windows based 2-Factor Authorization DMZ System (we would like to dispose of the Sun Boxes). The Online IST’s will be implemented with a similar 2-Factor Authorization in the very near future (HIRDLS is ready for this change-over). HIRDLS would like to have access from “home” networks during “After-Hours”. Summary of products regularly used by HIRDLS Lunar predictions (8 week – actually done manually in advance.) Orbit events file (8 week & 3 days)

11 Future Planning. HIRDLS currently expects to need further Aura Pitch maneuvers to support radiometric calibration and correction analysis. The timing, frequency, duration and magnitude of the maneuvers are expected to be very similar if not the same as the past few. HIRDLS would like to extend its gratitude for support for these maneuvers from the Operations team and the other Aura instrument teams. Thank you for all your support

12 HIRDLS Focal Plane Array

HIRDLS CSS Stroke Amplitude (Actual) 13

HIRDLS Chopper Motor Temperature 14

HIRDLS Chopper Housing Temperature 15