Jahresbericht 08 - PMOD/WRC

16
Instrument Development
SOVIM
A reflight Instrument was built around original components
from the SOVA/EURECA instrument. The start
of the project was in 1998, launch occurred 10 years
later on February 7, 2008. SOVIM contains 4 absolute
Radiometers two Sunphotometers and a Two-Axis-
Sun-sensor.
The launch, originally planned for December 7, 2007, was
unfortunately cancelled and shifted to February 7, 2008.
Hansjörg Roth, Project Manager of SOVIM, and Dany
Pfiffner, Project Engineer, travelled to Kennedy Space Center
to witness the launch.
After a few days in orbit (Figure 3), SOLAR was attached to
the International Space Station (ISS) (Figure 4). First switchon
of SOVIM occurred on the night of February 15 to 16,
2008. The initialization commands were sent from the Belgian
User Operation Center (BUSOC) at Brussels. After
solving a few troubles upon switch-on, SOVIM functioned
and operations were nominal on the next day.
We received the first data from SOVIM on February 15,
2008. The Coarse Pointing Device (CPD) was not working
properly from the beginning. No measurements were possible
during the first sun-window, however, during the second
sun-window the first useful data with a calculated
pointing were obtained. The sun sensor and its software
were not yet functioning. During the third sun-window we
then obtained the first real pointing, which unfortunately
was off by more than 1º, and so the data could not been
used. A Criss-Cross was performed to find out the offsets
and to provide the necessary information for an appropriate
correction of the sun sensor. Finally, a few hours of rea-
Figure 3. SOLAR in orbit within the STS.
sonable data out of the available 250 hours of that window
were collected. The end of that window was on early May
11, 2008, nearly 3 months after switch-on. During the 4th
sun window, only about 70% of observation time was available,
mainly due to some resets and other accidents with
the CPD. The next sun window was completely lost because
of a communication problem between COLUMBUS
and SOLAR, which turned out to be due a failure in
COLUMBUS.
The next sun window began at the end of July and only
slightly more than 60 % of the available observation time
could be used – still due to recurring failures of the CPD.
Similar coverage occurred for the next two solar windows,
namely between 55 and 65 % of the available observation
time.
In preparation of the next observation window on October
25, 2008, SOVIM was suddenly switched-off and
could not be re-activated. This was the unfortunate end
of SOVIM’s observation phase. After a comprehensive investigation
by PMOD, ESA and NASA, the understanding
surfaced that it is no longer possible to switch on SOVIM
instrument. The switch-on circuitry of the old EURECA
power converter had apparently failed. The main reason
for the re-use of this circuitry was the program schedule –
if the delay of nearly 10 years could have been foreseen
then this circuit would have been replaced with a new design
to prevent a single-point-failure. Although we only had
about half the available observations we obtained excellent
data and the corresponding results are reported in the science
section.
Figure 4. Mounting of SOLAR outside of COLUMBUS.