on Wed Dec 6 03:57:25 GMT 1995
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: VIRGO Switch On and Cover Release
Original Date: Wed, 6 Dec 1995 04:53:53 --100
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Dear all
We just finished to celebrate the first scientific result of SOHO: 1425 Wm-2 (EGSE value with no guarantee) which was measured to prove that the cover mechanism was released properly (not for scientific reasons really). By the way the SOHO is already about 500 000 km from the Earth. All the instruments within VIRGO have been switched on and are in good shape. We will now wait for the daily pulse to synchronize VIRGO which will take place in about 20 hours. Then we will let it out-gas until between Xmas and New Year when we do the final commissioning and start real operations. We will also run sometime later 3 time-tagged command procedures to do electrical calibration of DIARAD and PMOs.
I would like to take this oportunity to thank all the VIRGO team for their efforts in our endavour - we have successully completed the first step.
Best regards, Claus
on Tue Dec 12 19:32:34 GMT 1995
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: VIRGO-Status and Planning
Original Date: Tue, 12 Dec 1995 20:31:19 --100
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Dear All
This is an update of the VIRGO Status and information on the forthcoming actions:
Status: (i) The instrument works fine, the temperatures are reasonably constant. The radiation shield has increased slightly since yesterday. The reason could be a increase in the OSR temperature (we are checking with FOT) which in turn could be due to switch on of other instruments or subsystems. (ii) During the last three days we had some time tagged commands (TTC) in order to switch instrument modes and the reference. These are used to check the electrical calibrations and some instrument performance and are mainly the IcoIs. The following commands have been sent with the relevant times (they are in UTC and the execution in VIRGO should be during the block starting 3 minutes later). Planned activities (most important for the IcoIs): (i) The instruments were intended to be switched to operational on day 23 (radiometers) and day 30 (SPM and LOI), with a test of all covers on day 23.
This was planned to start after MCC2 (second midcourse correction) and related S/C activities. Now the MCC2 by itself is so small that it will not take place as such (only 76 cm/s, Centaur did such a good job, that also MCC1 was quite small 4 m/s and we have a lot hydracine left [possibly for 30 years of operations, some people say]). They will however make a pre-Halo injection maneuver which will then ease the real insertion and make it happen earlier (now planned for 17 March instead of early April). This maneuver will also be used for calibrating some thrusters not yet used in earlier orbit maneuvers. This 'MCC2' is planned for January 4, and the related S/C activities for January 5 and 6.
In view of these changes I have decided to postpone our actions until January, 7 and do the activities of both days (23 and 30) together (PROC20, PROC17 and PROC19). This means that the test of all covers around day 23 is no longer and I would like to propose to open them by TTC for 6-9 minutes each on December 22 or 23. Vicente volunteered to watch the EGSE during that time and signal to us any irregularities. For the instrument we have to put them in a mode where they can see the sun: the PMO's will be set to shutter auto and BU- Mux accordingly, for the SPM we need only to switch the BU-Mux, for the DIARAD we suggest to switch it to 'auto left' before the opening and back to 'long calibration' after and for the LOI we switch off the calibration before and back on after (comments on the proposed actions by the IcoI before Dec. 14). We will test the finally agreed sequence at PMOD/WRC with the VIRGO instrument to make sure that the commands are correct.
Our plans are to send Thomas Frohlich (for the FOT command interface) and have asked SSD to have Udo Telljohann for the EGSE operation during commanding. Thierry Appourchaux will participate also in the January activities as LOI representative mainly for the off-pointing tests. If some other CoI or technical managers would like to participate in the January activities, let me know. (ii) On January 11 and 12 the off-pointing tests are planned. These consists in stepping the pointing of the S/C E-W (1st day) and N-S (2nd day). The steps are 30 arcsec and cover ranges 0 to 10 arcmin E (N), back to 0 and to 10 arcmin W (S) and back to 0. It takes about 10h40 minutes (settling time of the S/C for each step 480 s). Before and after we will lock and unlock the pointing system of LOI in order to have the solar image moving over the detector. This test will be done together with MDI which will also let image move. The objective of this test is flat fielding information for the imagers and offsets for the SPM and may be radiometers (Question to the IcoI: should we open the covers of SPM-B and PMO-B during that test?).
(iii) The IcoI shall prepare a first report on the instrument performance by assessment of the level0 data of day 6 to 12 (7-13 Dec, day 5 is not very relevant because of synchronization only at the end and because of OBT phase corrections around 23h00 which messed-up some blocks). This evaluation will also be used to check the VDC algorithms for level1 calculations. The report should contain a comparison of the values from the last ground tests with the ones now in order to assess: (i) general performance (e.g. internal temperature distributions) (ii) electrical performance (e.g. resistors, electrical calibrations) (iii) noise performance (e.g. power spectral of the dark signals). If you have any questions concerning this report please let me know before Friday.
Best regards, Claus Frohlich
on Fri Dec 22 17:51:18 GMT 1995
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: Pi-Message
Original Date: Tue, 19 Dec 1995 10:33:51 +0100
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Dear all
I had to write a VIRGO Status report, which is copied to the end of this message for your information. I hope you agree with my statements.
As to the plans over X-Mas: We will have a series of cover tests by time tagged commands on 24 December - a real X-Mas present for the European (timewise). Vicente will watch the tests from the EGSE at EOF. The data will be evaluated to level0 files by the VDC and will be available after about 14h00 (CET) on 25 December for further evaluation by the ICoIs.
The next action will be after the manoeuvres which are now planned for the first half of January. We are preparing the corresponding TSTOL procedures which are slightly different from the ones originally planned for execution on mission days 23 and 30. Both actions are now combined in one which is planned to be executed on 16 January.
**************************************************************
VIRGO Status Report
VIRGO was switched on during day 5 and the cover released the success of which was tested by opening the cover of one radiometer which delivered the first 'science data' of SOHO. Some electrical tests have been run on mission days 8, 9 and 10 with time tagged commands. The data of each instrument have been analyzed as far as this is possible with no sun. The performance of the data acquisition system is nominal. The temperatures of the sensor unit and the power supply are well within the range expected. There is an oscillation in the heat sink temperature of the sensor unit and the bottom of the power supply with a 195 minutes period and an amplitude of about 0.1 K. Also other temperatures show a similar oscillation but smaller amplitudes which could indicate that it comes from the outside. We have not yet been able to test whether this oscillation is in the VIRGO reference temperatures measured by the S/C.
Each ICoI has evaluated the data of his instrument:
***************************************************************
on Tue Jan 16 18:03:25 GMT 1996
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: VIRGO Science start
Original Date: Tue, 16 Jan 1996 18:52:37 --100
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PI-Message 17 January 1996
Dear all
Tomorrow will start the real measurements. Thomas Frohlich and Udo Telljohann will command VIRGO to start the measurements of PMOA, SPMA and LOI (after some tests of the guiding which can only be done with the sun). This is foreseen for 17 January 18h00-21h30 UT. DIARAD asked for another day of calibration tests with the cover open and will start in its mode left a day later (18 January 20h00 UT by time tagged commands).
So the first level1 data will be available some time during Friday for PMOA, SPMA and LOI. The DIARAD data have to wait still some time because the evaluation of the electrical calibration needed for the irradiance calculation is not yet available from IRMB. For the time being the daily values for the SOHO archive will be the irradiances of PMOA (until DIARAD is available, then the average of both), SPMA and LOI.
I think it is a good moment to thank the VDC for all their work done in the last few weeks and also the IcoIs who have helped them to get everything ready for the production of level1 data. Congratulations, and we all look forward to gather good and interesting data.
After 8 February some test of the S/C pointing will start and essentially continue until February 26. Within this time around the 20 we will have the two days of off-pointing tests together with MDI. The first few days of this period will not disturb us too much, so we will probably get a month of data to play with and to test our evaluation procedures. Between 27 Feb and the Halo Orbit insertion which starts at 13 March we will have another 2 weeks of data. Then the covers will be closed for protection of the instruments until 23 March when the first month and the real mission of SOHO Science starts.
By analyzing the closed data from the last 6 weeks we have found that the long calibration of DIARAD gives a 'nice' 192 minute oscillation of the temperature of VIRGO which is also seen in the signals - the first g-mode! We will never have this mode continuously so this effect should not influence our science. We are preparing a strategy for the DIARAD calibration with a minimum of influence on the other signals. Moreover, we find some more noise in the SPM and LOI data than we had during the TV tests here in Davos. It seems that this phenomenon was always there when mounted on the S/C as evaluation of some recent GSCTs have shown. We do not yet understand, but the noise level is still acceptable (well below the solar noise).
Lets hope for a good start and good data.
Best regards, Claus Frohlich
VIRGO message # 98 on Mon Jan 22 16:24:34 GMT 1996
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: LOI Cover Problems
Original Date: Mon, 22 Jan 1996 17:17:28 --100
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Dear all,
Last Wednesday when we started measuring we get very good data from the SPM and the radiometers. But we have a problem with the opening the LOI cover. It did open on the 24 December, but from all we know now only half way, and seems to open still now, but it bounces back and remains closed. This is known because LOI sees the sun shortly, but long enough for locking its pointing to the sun. So the instrument works fine; but .....
In the following I send you a description of what we know or think to know or what we simply assume. This is a report which is the basis for a planning meeting today after the daily meeting at 10h00. On Wednesday morning we will have another oportunity to execute commands during 4 hours. At the moment it is not clear whether we can do what we propose to do for a definitive opening of the cover.
Any further ideas are obviously welcome. Let me know.
Best regards, Claus Frohlich
VIRGO message # 100 on Mon Feb 12 19:38:12 GMT 1996
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: VIRGO Status
Original Date: Mon, 12 Feb 1996 20:36:49 --100
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Dear all
Before I leave the EOF for Switzerland I would like to give you a short status of what was done and seen in last few days.
During the thermoeleastic tests the temperature of the radiation shield cooled by about 2 degrees. We tried the LOI cover several times during the cooling down and at low temperatures (hoping to get thermal stress in the actuator and thus friction). As expected these small temperature changes were not able to increase the friction and all tests showed a essentially constant exposure time as usual (about 565 ms). The plans are as follows:
That is the story of the LOI cover. We have another problem with PMO-B
you may remember since 17 January when we did the opening. We do not understand
it in detail, but the effect is the following: when the shutter is actuated
to open the electronic fuse is triggered and any further shutter movements
are inhibited. Yesterday the same happened to PMO-A and that is really
bad. We will be able to use both of them as back-ups for occasional
measurement but no longer as operational instruments. May-be we can find
a way around the problem and can run the shutter again continuously; but
this is uncertain - first we have to understand what is going on. We will
have to review the startegy and in the next few days when I am back to
Davos I will
discuss this with the radiometrists.
Best regards, Claus Frohlich
VIRGO message # 101 on Tue Feb 27 18:29:59 GMT 1996
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: Status report by PI
Original Date: Tue, 27 Feb 1996 19:12:00 --100
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to: virgo@solar.stanford.edu
thomas@pmodwrc.ch
utelljoh@vmprofs.estec.esa.nl
ml@radio.oma.be
wolfgang@pmodwrc.ch
sanchez@esa.nascom.nasa.gov
Dear All
After reactions from some of you and from outside I see a strong need to inform about the status of VIRGO. It is not at all as bad it may sound when I am informing about problems; we have also very nice data.
The SPM work just fine and the data profit from the nice and stable
environment of SOHO and the continuity of the observations. The degradation
is much smaller than in former experiments: about 0.07% per day for the
green and the blue compared to the EURECA green channel with 0.5% per day
during the first 50 days. The red VIRGO channel at the beginning was at
about the same rate, but when we reduced the temperature of the SPM-A head
by about 7 degrees the rate decreased by about a factor 2.5 being now at
0.03% per day. The solar noise is behaving as the model of
Bo (he said; a plot is on OBSUN.PMODWRC.CH anonymous ftp in /user/pub/virgo/
as nois_1st.ps): above the five minute region the power decreases in all
colors as about 1/nue^4.5, above them it varies as 1/nue^1.5 in the red
and green and flattens out in blue to a nearly constant power around 0.6
mHz. A similar behavior is
observed in the PMO data: the 5 minutes are readily seen but influenced
by the bad sampling and a reliable power spectrum can be assumed below
about
1.5 mHz (12 minutes period) which varies first as 1/nue^0.5 and flattens
out also as the blue does at frequencies below about 0.6 mHz. The p modes
from a time series of about 15 days show just a marvelous spectrum (probably
the best ever see for irradiance observations, and that is just the beginning.
At the same place you can find a plot as pmod_1st.ps): very low noise (for
the short period of time already a signal-to-noise ratio (amplitude) for
the highest peaks of about 6) and one may see even l=3 at 3.1 mHz. The
ratio of (l=0)/(l=2) and also (l=1)/l=3) varies with wavelength as expected
due to the weighing by the limb darkening.
With the PMO radiometers we have a problem with their shutters, the
one of PMO-A failed on the 11 February (electronic fuse problem) and PMO-B
was not working when we started the observations on January 17. Both worked
at Xmas. Before its failure PMO-A worked fine as the power
spectrum shows. We started last week to operate them in a different way
with the covers: PMO- A is open for about 8h and then closed for 21 minutes.
9 minutes before it closes PMO-B is opened for 39 minutes. In this way
we have really continuous observations with a sampling every minute (instead
of every 2 minutes during the shuttered operation). From the time series
point of view this is much better, but we obviously reduce the absolute
accuracy due to the much fewer reference values. We are presently developing
a new algorithm to evaluate data with the operational scheme (major problem
is to improve the thermal model to enable accurate calculation of the 'closed'
power during the long open phases. The absolute accuracy is now fully under
the responsibility of the DIARAD which works fine, I was told, but the
evaluation is not completed, so I have not seen any results yet. We have
a period of about 2 weeks with real comparisons between the two types of
radiometers which will be used to determine the way the VIRGO irradiance
will be calculated. Very
preliminary comparison show a rather large difference between
DIARAD and PMO-A. As the evaluation of DIARAD is not yet finalized and
the PMO thermal model is still under investigation this difference will
hopefully be resolved soon.
As to the operation of the VDC: It works fine and struggles mostly with data transmission problems over the net. You probably wonder why no level 1 data of the SPM are available. The reason is simple: the orbit data had some problem some time ago and have still some for the velocity. In order to overcome this problem we will calculate the velocity data from the distance differences (velocity correction are now in any case in the sub- ppm range) and Antonio will make the level1 data of SPM available soon. The PMO algorithm for the 'old' data needs some refinement (thermal model, see above) and the new one is under development. DIARAD is still under development. It is hoped that all these data will be available before end of March.
The present planning for the LOI cover opening looks as follows: at
the moment the mechanics people at ESTEC are looking into the model Thierry
has
developed which is constrained by a lot of measurements on the Spare
Model here in Davos (e.g. position recordings with TV camera under different
conditions, motor performance, cover properties). The model seems to work
quite well to explain the behavior on ground. For the moment being there
is
no real explanation for the behavior in space (several hypothesis exist
but could not be proven on ground). Nevertheless, we are confident that
shortening of the pulse will open the eventually. All technical problems
which could lead to a blocking which would never allow to open it fully
could be excluded (hopefully not too much by our hopes and fears). The
project in co-operation with MMS and SAAB has developed a method which
will allow to shorten the pulse in a well defined manner. This needs a
patch of the on-board S/W, which is being developed and will then be loaded
in an existing patch area reserved for tests. Tests of the S/W patch are
planned at SAAB with our Spare Model and support in the week of 19 March
and the upload of the S/W and the LOI cover opening on the 26 and 27 March.
This is the planning and I am confident that we will open the cover.
When asked about the VIRGO status, you should now know what is going on and what is planned and distribute this knowledge to who ever would like to know.
Best regards, Claus Frohlich
VIRGO message # 103 on Mon Mar 25 16:49:26 GMT 1996
Mail from: cfrohlich@obsun.pmodwrc.ch
Subject: PI Message
Original Date: Mon, 25 Mar 1996 17:47:45 --100
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PI-Message 25-March-1996
Dear all
First point I want to inform you is that we will open the LOI cover
tomorrow. The project has provided a S/W patch for the on-board computer
which enable us to switch off VIRGO at a given time accurately. In this
way we can change the pulse length to what ever value below the maximum
length we wish. This S/W patch was tested last week successfully with the
VIRGO spare instrument at SAAB in Goteborg. The test with the
real LOI cover starts tomorrow around 15h30 UTC. First we will send the
normal open command and see whether it behaves as usual. I do not expect
do see any difference, but who knows it may even open. If not we will start
with a pulse length of 450ms which is the most probable value for opening
if we can assume that it behaves as on ground. This is somewhat hypothetical
as from all tests we made and from the models of the cover we have no explanation
of the behavior other than that the pulse length is not 720ms but 520ms.
This would explain the behavior with only a few adjustments of the parameters
(within reasonable limits). It is,
however, very unlikely because a failure in the Logic Cell Array which
controls the sequences, is needed. The pulse length is made by counting
the 10Hz signal from 8 down to 0 and 100ms after the start of the count
down power is enabled to the cover motor yielding the 700ms nominal and
720ms with the delays. A change in the pulse length would be common to
all covers. The small covers have no problem with such a pulse length,
so they work without problem as shown (the PMO covers work 6 times each
every day since mid of February as replacement of the shutters) and the
DIARAD cover is
heavier than the LOI cover and is most likely just on the other side
of the range (we will not try again in any case). Other scenarios with
some obstacles in the way have to be rejected, Hansjurg checked the proper
opening when he did late October last year the alignement check during
which the LOI cover is opened manually.
The second point I would like to touch is more general and relates to
the presentation of early results. For the moment being we have only preliminary
results and nothing which can or has to be published yet. Probably, this
will be true still for some time. But the VIRGO team is asked to show results
during meetings of any kind as e.g. scientific discussions, presentations
to our funding agencies, more formal ones as AGU Spring meeting and COSPAR
where
abstracts had to be submitted already some time ago. There is also
the IRIS meeting next week where Thierry A will present some p mode results.
In order to handle these things in a concerted way I propose the following
common policy for all future activities:
(i) inform the VIRGO team
of such intentions by e-mail to virgo@solar.stanford.edu in advance;
(ii) put the viewgraphs
you intend to show as postscript files in the VDC /virgo/doc/ directory
(see NB1 for instructions);
(iii) if you have an abstract
put it as ascii or ps file in the VDC /virgo/doc/ directory (indicate format
by extension .asc or
.ps); as an example I have put the COSPAR and AGU abstract allready submitted
to /virgo/doc/;
(iv) label the material
as "VIRGO preliminary Results" and put the ICoI name concerned, your name
if you want and "the VIRGO
team" as reference.
(v) tell the organizer that
this material is not for publication yet; this may change after a first
VIRGO team publication with the results (one is planned
for Solar Physics, organized by SOHO, see NB2 below).
The third point is the next VIRGO team meeting: We discussed this point
last September and agreed in principle to have a meeting in Tenerife in
March 96. Due to the situation with the LOI cover I have implicitely postponed
the meeting. Now, we should start thinking about it again. It will probably
not be possible to have it before the big PR event on May 2nd which is
at the same time in Paris and at GSFC about the first month of SOHO (I
will be at ESA-HQ
during this event). Would like to get your feelings about that.
For the moment that is it. Lets cross fingers for tomorrow.
Best regards, Claus Frohlich
VIRGO message # 104 on Fri Mar 29 13:46:19 GMT 1996
Mail from: thierrya@so.estec.esa.nl
Subject: LOI status report
Original Date: Fri, 29 Mar 1996 14:42:00 +0100
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Dear colleagues,
Now the LOI has been working fine for more than 2 days. It now almost fully commissioned, I just have to get the off pointing data next week and something with it.
The instrument is slowly setting in temperature and we can see in the
high voltage guiding signal: we had a drift of 1 arcsec over one day!
The short term
guiding stability is very good about 0.03 arcsec at 1 sigma; it is
even better as we make a short integration for the guiding pixels.
The temperature stability on the detector is about 0.002 deg C peak-to-peak!
Overall Udo and I are very pleased with the performance of the instrument.
Oh! By the way we did see the 5-min oscillations in the integrated signal over the 12 pixels.
We should start to get level_1 data in about 1 month from now after cross checking everything with the Spanish tribe.
See some of you in Nice.
ThierryA (and Udo of course)
Last updated by Thierry Appourchaux on Wenesday, January 21, 1998 at 13:28