On this project, most of the time in 1990 was devoted to
preparation of the CPF (Critical Point Facility)-MIM experiment
on the Spacelab mission IML-1. The hardware for the experiment,
which is intended to probe the microgravity behaviour of
near-critical sulfurhexafluoride, was completed in may and an
EPT (Experiment Parameter Table) was built, generating a
timeline for a 58-hours experiment. Two short tests of this
timeline were made on the CPF flight unit at ESTEC (in May) and
KSC (in August). After upgrading the EPT based on these test a
full duration experiment was performed in October at ESTEC with
the CPF engineering unit. This last test proved valuable as a
first g=1 reference experiment to the mission proper.
In November NASA announced that the IML-1 mission duration was
to be reduced from nine to seven days. The proposed time
reduction for the MIM experiment (28 hours) seemed desastrous,
but thanks to excellent cooperation with ESTEC and NASA we
managed to negotiate a reduction of less than six hours.
Nevertheless a completely new EPT has to be built and tested.
This is scheduled to be finalized in March 1991.
Parallel to the MIM preparations we performed (in April) a
second "g-quench" experiment on a parabolic flight, this time
on the Zero-g Caravelle at Bretigny (first: August 1988 on NASA'
s KC-135 at Houston). The improvement of the equipment resulted
in a substantially larger amount of meaningful data on this
mission than on the first, although the difference between the
Caravelle and the KC-135 data posed some new problems. The
results are now being evaluated and will be presented at the
ESA-debriefing on 19 March 1991 in Brussels.
Although the scientific evaluation of both experiments is still
in progress, important conclusions can already be drawn. We
find that in finite samples relaxation rates are indeed
strongly dependent on adiabatic processes, as has been
predicted by Onuki et al.Hence, due to its high compressibility,
a critical system will be extremely sensitive to changes in
g-levels. In a microgravity environment the impact of residual
g-fluctuations could therefore be significant. The results of
the Caravelle experiment clearly point in this direction and
will therefore be considered carefully in the redesigning of
the MIM timeline.
Interferometry image in the CPF
