_                   
                                                         |_|                  
      V   V   SSSS   OOO   PPPP                 \__      |_|      __/         
      V   V  S      O   O  P   P                   --____/ \____--            
      V   V   SSS   O   O  PPPP                    _ _ _ --- _ _ _            
       V V       S  O   O  P                      |_|_|_|  @|_|_|_|           
        V    SSSS    OOO   P                             o-o                  
                                                          /                   
      ***  N    E    W    S  ***                        <)                    
                                                                              

OPERATIONS MEETING

From November 11-13, thirty or so members from the various VSOP mission elements gathered in Vancouver to discuss the status of the mission. A wide range of issues was discussed and below is a brief summary of some of the issues of more relevance to readers of the VSOP News.

In-Orbit Checkout at 1.6 and 5 GHz is effectively over. Engineering tests will continue to be made but, for example, the current schedule for December (available from the VSOP WWW site) contains 15 General Observing Time observ- ations, 7 VSOP Survey Program observations and one test observation. In-Orbit Checkout at 22 GHz is likely to continue for the rest of the mission lifetime. The VSOP observing efficiency has been limited thus far by sun-angle limitations, HALCA maneuvering overheads, tracking station anomalies and correlator throughput. Taking these in turn:

• The sun-angle is the angle between the sun and the target source. HALCA cannot observe sources within 70 degrees of the sun as the main antenna shadows the solar paddles at these angles. The allowed sun-angle range has also been limited to date to regions around 90 degrees and 180 degrees by excessive angular momentum build-up experienced at intermediate angles. On-board software upgrades have improved this situation, and the allowed sun angle range is slowly being extended.
• After maneuvering between sources, both of HALCA's star trackers need an hour or so to calibrate and fine-tune the pointing. Until recently, observing has had to wait until the next tracking pass over the Kagoshima Space Center to confirm that the maneuvering and calibration has proceeded correctly. It is now believed the on-board software is sufficiently robust that maneuvers can be carried out `automatically', and so the limitation of six maneuvers per week (as there are only six KSC passes per week) has now been lifted.
• Two distinct 15 GHz tracking station problems currently exist. The tracking stations generate Time Correction Files (TCFs) which are needed at the correlators to correct the delay and Doppler errors in the predicted satellite orbit. Problems with the TCF generation at the Usuda tracking station have limited its usefulness to 1.6 GHz observations thus far. The DSN tracking stations have a different, intermittent problem with discontinuities in the delay term occurring. Both problems are being actively investigated.
• Finally, all three correlators have now gained experience in handling space VLBI data, and have been fine-tuning their software and procedures. Efforts are underway to tighten the delay and delay-rate windows used in correlation to reduce the output data files to more manageable sizes.

One final decision endorsed by the meeting: by the end of December an observing schedule through to the end of the first AO period will be available. All PIs will be contacted individually regarding the observations they had proposed.

 
                Editors: Phil Edwards and Hirax Hirabayashi