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  V   V   SSSS   OOO   PPPP                         ||            
  V   V  S      O   O  P   P              X\#\/#X#\/||\X/X##X#/X  
  V   V   SSS   O   O  PPPP             \X\#/#X#\/X#||/X#\X#X/    
   V V       S  O   O  P              \X#\/#X#\/X#\X||#\X#/X      
    V    SSSS    OOO   P            \X#\/#X\#/X#\X/X\#X#X/        
                                  \X#\#/X#\/X#\X/X##X#/X          
  ***  N    E    W    S  ***    /X#\/#X#\/X#\X/#X#X/X#            
 

FRINGES!!

Another milestone has been reached in the VSOP mission, with fringes having been found at the Penticton and Socorro correlators over the last two weeks. The fringe detections at the Mitaka correlator were made from VSOP format recordings at the Usuda tracking station and the Usuda 64m and Kashima 34m telescopes. Fringes at Penticton came from S2 format recordings at the Goldstone and Green Bank tracking stations and Tidbinbilla 64m, Hobart 26m and phased Australia Telescope Compact Array during observations of 1055+018. At Socorro, fringes were first found from VLBA recording at the Green Bank tracking station and the phased VLA and VLBA for observations of 1519-273. The last hurdle in finding fringes had been a single 5 millisecond (corre- sponding to a single satellite down-link data `frame') off-set in the time stamps at Green Bank. Once fringes were found in the first experiment from Green Bank at Socorro, they were quickly found in three other experiments, and the knowledge of this off-set allowed fringes to be found from the Green Bank tracking station at Penticton also. The entire tracking passes on which fringes were detected have been correlated, with all indications being that the orbit determination teams and tracking teams are doing a great job.

Congratulations to the Navigation groups, Goldstone and Green Bank tracking station personnel, and Penticton and Socorro correlator staff!

Observations to date have been concentrated at a wavelength of 18cm, the longest of the three wavelength bands the satellite is able to receive, and for which the satellite pointing and orbit tracking requirements were easiest to meet. Observations at 6cm are scheduled to begin in earnest in July.

Data from the HALCA satellite have now been successfully recorded in three different formats at three different ground tracking stations and fringes found at three different correlators! This reflects the truly international undertaking that VLBI in general, and space VLBI in particular, is. Four of the nine tracking-station/correlator links have now been established, and with the tape translators coming on line at Mitaka more links will be able to be tested shortly. ORBIT UPDATES

As described in the VSOP Proposer's Guide, there are three software packages that enable space VLBI observations to be simulated. These were released with the nominal orbit parameters, but are now able to be updated with the actual HALCA orbit. A new page on the VSOP WWW site, /astro/halca/vsop/obs/AO/simulation_soft.html gives the orbital elements, and provides links to the WWW pages describing the three software packages and giving details on how to incorporate the new orbit into the software packages.

 
       Editors: Phil Edwards and Hirax Hirabayashi