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@ MTA Monitoring Report 4/07/00 - 4/13/00 @
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************ CTI trend *************
No changes are observed. Please read some comments below.
************** MTA Problem Tracking. *****************
We have a minor software problem this week. No problem is reported
due to this problem.
******** Trending ***********
No new trend is observed. Same upward trends on some temp and
electric related msids are still strong. Spacecraft Electronics
msid: OHRMAPWR is peaked around day 160 (DOM) to 62 now back
to the starting value of 59.
*********** ACIS Focal Temperature ********
Acis focal temperature peaked twice this week at DOY ~99 (-108 C),
and ~101.5 (-110 C).
************* Telemetry ***********
Nothing special happened; only usual HRMA violations and jumps
due to possible bugs.
*********** Photon Page ************
Only three observations are added. Non of them have a clear
images, and it is hard to judge image quality.
BSID DETECTOR GRATING TARGET ANALYSIS
---------------------------------------------------------
963 NO INFORMATION OK
82 ACIS-S NONE 1E0056.8-7154 OK
90 ACIS-I NONE 4U 1538-52 OK
************ Some Comments from Experts ********
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From Catherine Grant (4/3/00) --- about ACIS CTI
-----------------------------------------------------------
Hi Scott,
I just read your comments on the MTA Weekly Reports page and I just wanted to
add my two cents.
- - Monitoring the mean CTI is a good idea, because the S/N is much better.
You just have to be careful which CCDs you use in the mean. I'm currently
looking at the mean of the I-array CCDs which seem to have cleaner measurements.
The real changes in CTI, from degradation or background changes, should be
highly correlated between CCDs. If you believe your error bars are reasonable,
I'd recommend a weighted mean to throw out the occasional bad or messy fit.
- - Dropping measurements where the CTI seems to improve will not help the
background situation. The background flares reported by Fred and Maxim occur
seldom enough that they are not important for the CTI measurements. The
real killer is the slow trend in the background rates over 10-100s of days.
Go to http://space.mit.edu/~cgrant/cti/index.html to see what I mean. Dropped
exposures are not a good measure of this phenomenon. The eventual fix will
have to incorporate some kind of CTI normalization using the background rates.
For more on this see Bev's original memo:
http://icxc.harvard.edu/cal/ACIS/cntVtime.ps
- - The focal plane temperature is a critical factor which we have been
monitoring for some time now. At this point, most of the CTI measurements going
into the radiation belts are not holding at -119.9C so we already are suffering
some loss of CTI measurement accuracy. Calibrating the CTI versus temperature
relation is a good idea however there are some complications, namely the anti-
correlation with particle background will also depend on temperature. Perhaps
just as important is the fact that once we start to heat up, the temperature
is not being regulated and is constantly changing.
I hope this helps!
----------------------------------------------------
From Dan Schwzrtz (4/4) ----- about HETG/ACIS focus
----------------------------------------------------
As Eli Beckerman's analysis of the recent
ACIS-S plate focus showed, the ACIS-S focus
has remained stable. A similar conclusion is
visible in the FWHM along CHIPX for HETGS
observations - recently updated at:
http://space.mit.edu/HETG/technotes/zo_1d/focus_trends.000404.html
-----------------------------------------------------------------
From Dan Schwzrtz (4/7) ----- about ACIS Focal Plane Temperature
-----------------------------------------------------------------
We are concerned about ACIS focal plane warming up when the
radiator views the earth.
I suggest the SOT-Lead include a note about the focal plane temperature
in the shift report, especially during CTI OBSID periods, and also
if it is ever warmer than -119.7.
The temperature can be found on the ACIS GSE machine emily (the right
of the two machines).
----------------------------------------------------------------
Correspondences among Catherine, Shanil, Steve, and Dan (4/11)
---------CTI measurement during last perigee ingress
----------------------------------------------------------------
Catherine -
In an earlier e-mail (Thu 04/06/2000), you found dCTI/dt = 0.012*10^-6 /d
between Jan. 29 and Apr. 01, or dCTI = 0.77*10^-6 over those 64 days. This
number is comparable to the dCTI = (0.82+/-0.12)*10^-6 difference between
the average of the 32 points before 2000D096 and the 2 points after
2000D100. Thus, in order to establish the magnitude of the step increase
associated with the 2000D097 event, I suggest that you de-trend the data as
follows:
(1) Fit a straight line (not a constant) through the 32 points prior to
D096.
(2) Extrapolate the fitted line to predict the 2 data points and error after
D100.
(3) Compare these 2 extrapolated values to the measured values and errors.
I expect this would at approximately half the inferred CTI increase due to
the D097 event. Thanks.
- - Steve
P.S. We all appreciate your work in tracking the CTI changes.
> -----Original Message-----
> From: Shanil N. Virani [SMTP:svirani@head-cfa.harvard.edu]
> Sent: Tuesday, April 11, 2000 7:15 PM
> To: O'Dell, Steve
> Cc: Dan Schwartz; 'Rob Cameron'; Paul P. Plucinsky
> Subject: Re: CTI measurement during last perigee ingress (fwd)
>
> Hi Steve,
>
> I just saw your email and the agenda for this Friday's RadEnv
> telecon. Below I forward Catherine's email from today that is _very_
> preliminary. The reason why I am forwarding it to you is that if the
> reported increase stands after further scrutiny, and given the ACE
> fluence associated with last Friday's event, we may have an empirical
> fluence threshold (albeit complicated by the fact that the gratings
> were in for a significant proportion of the time). I have CC'ed Dan
> Schwartz on this email since he may wish to join us on Friday to
> discuss this result. I hope this is ok with the both of you! (Dan, I
> will forward you Steve's email which precipitated this email.)
>
> Shanil
>
> ---------- Forwarded message ----------
> Date: Tue, 11 Apr 2000 16:25:35 -0400 (EDT)
> From: Catherine Grant <cgrant@space.mit.edu>
> To: mwb@space.mit.edu, das@head-cfa.harvard.edu
> Cc: swolk@head-cfa.harvard.edu, plucinsk@head-cfa.harvard.edu,
> ybutt@head-cfa.harvard.edu, svirani@head-cfa.harvard.edu,
> cgrant@space.mit.edu
> Subject: Re: CTI measurement during last perigee ingress
>
> Here's a first try at measuring any degradation from last week's
> proton event. I'm using Bev's extremely strict definition of
> when the temperature is stable, so I don't have a whole lot of
> data since last Friday (ObsID 62091 was not stable by her standards).
> I'm using the mean of the I-array CTI for each ObsID.
>
> To remove the background correlation, I'm using the slope from
> the alternating exposure test we took a few weeks ago. This
> guarantees that the correlation is independent of any actual
> CCD damage since the two exposure times were concurrent.
>
> That slope is -1.47 +/- 0.32 x 10^-7 CTI change / (S3 HE Rej. / frame)
>
> After 'fixing' the CTI, I split the data into two groups; before
> day 96 (32 pts) and after day 100 (2 pts).
>
> Before: Mean = 12.041 x 10-5
> Err = 0.003 x 10-5
>
> After: Mean = 12.124 x 10-5
> Err = 0.011 x 10-5
>
> Difference: 8.2 +/- 1.2 x 10-7 <= possible CTI increase
>
> I would consider these numbers *extremely* tenative, since they
> are based on only two post-proton event CTI measurements, so please
> don't quote me on this. The error in each I-array mean CTI is around
> 2e-7. As more CTI measurements are made, the estimate should get better.
>
> Comments?
>
> Catherine
>
>
>
> > From: Dan Schwartz <das@head-cfa.harvard.edu>
> >
> > The last CTI measurement, on the ACIS-I configuration, occurred
> > after taking our largest single orbit 130-214 keV proton dose,
> > according to ACE data. This was OBSID =62091.
> >
> > This was a fluence of 4,564,446,000 protons/cm^2 /ster /MeV,
> > albeit mostly with the HETG in place giving significant attenuation.
> >
> > What is the limit on CTI degradation (or, perish the thought, the
> > measured degradation) for that passage? This number is important
> > to plan our future operational response to high ACE rates.
> >
> > Thank you,
> > Dan