The primary objective of the group's ongoing HST observations of an outflow
source is directed towards the momentum problem and includes the temporal
evolution of the 3D velocity fields in a supersonic jet at the highest
attainable spatial resolution. The source L1551 IRS5 was selected on
the basis of its favourable aspect in the sky, of its short jet length, and
of the important fact that momentum is transferred to the associated
molecular outflow within the HST field of view at a rate comparable to that
on spatial scales more than a hundred times larger, i.e. 
AU.
IRS5 at 150pc is the most nearby known source of its kind allowing a
smallest spatial resolution of a few AU with the HST (WFPC2) to be compared
with a resolution of >50AU with NOT. The high resolution allows
comparison with modern numerical hydrodynamical calculations required for
determination of the momentum carried by the jet.
The first observing runs with the HST was completed during 1996, resulting in truly perplexing detail and beauty. Combining ground based spectroscopic data, obtained at the NOT, with the HST data we were able to demonstrate that the presently observed jet does not carry sufficient momentum to drive the large scale molecular outflow, as has commonly be assumed. Furthermore, we discovered that there exist two independent jets, each probably fed by either protostar of the close binary (40AU separation).