A.I. 1 Assess the risk to STIS during the NCS cool down. Evaluate if the schedule
should be adjusted to help mitigate the risk. Response provided by Teri Gregory,
Colleen Townsley, and Jeff Valenti.
It is recommended not to turn on the STIS MAMAs until after 100 hours after the NCS
initial turn-on, assuming that the valve heaters are shown to be cycling properly and
controlling the value temperatures above their leak level. This recommendation may
change depending on the final assessment from the CHAMPS Thermal group of the
following risk periods. This final assessment is dependent upon the NCC portion of the
model finalized. The Thermal group expects this work to be completed by the end of
May01. [Emphasis added by C. Biagetti]
There are three times of high risk times for turning on the high voltage on the MAMAs
due to potential leaks from the NCS during initial turn-on and cool down:
Risk #1: There is a risk of a potential leak during the initial fill of the NCC. The
initial fill will be done prior to the first maximum cool-down.
a. The initial fill will be done via the command plan, and the instruments will
be safed during this time. Since STIS will be safed during this time period
this is a non-issue for managing the MAMA high voltage.
Risk #2: Preliminary thermal assessment shows the first 10 hours of NCC operation
as the greatest rate of temperature change for the cool down of the values and
bayonets.
a. Recommendation is to wait until approximately 48 hours after the inlet
valve and bayonet have stabilized (~10 hours after initial cool down).
During the first 48 hours, the system is reaching equilibrium and a
possible leak could occur.
Risk #3: Another risk period for a potential leak could occur as the NCC begins its
cool down before the valve heaters are shown to be cycling properly and controlling
the valve temperature above their leak level. Preliminary thermal assessment show
that the valves settle into their cycling in approximately 100 hours.
[Note: The 100 hours in question occurs between the start of SMOV day 7 and
SMOV day 11 thereby forcing the final STIS End-of-BEA Test, which uses a MAMA,
to occur no earlier than ~ day 11.5, a couple of days later than originally planned.
Therefore, adding some analysis time for the decision to end the BEA and allowing
some time for scheduling of uplink opportunities means that the BEA period may need
to extend by a day or two. We will have a better estimate as detailed proprosal
processing proceeds. Note also that, according to the italicized statements in the first
paragraph, the constraint period may increase to something greater than 100 hours,
thereby further extending the BEA period. Depending on the magnitude of this
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extension, we may wish to revisit the plan for starting NICMOS cooldown on SMOV
day 7.-- C. Biagetti].
A.I. 2 Determine the first opportunity to take ERO pictures for ACS and NICMOS.
A.I. 2a ACS EROs – Response provided by Guido De Marchi.
Early release observations not requiring accurate pointing (thus
excluding, for instance, all coronographic observations) could be
scheduled right after the end of the coarse and fine alignment
programmes (ACS13 and ACS14, respectively). Observations carried out as
part of the fine alignment proposal will allow the IDT to verify the
quality of the PSF over various regions of the FOV of the cameras. As
suggested by A. Fruchter, a series of three exposures of a moderately
crowded stellar field of about 15 min duration each will be scheduled
at the end of the fine alignment tests. These data will be used to
verify that the PSF is indeed stable over time spans typical of ERO
images and over a wide spectral range. Assuming a launch date on
Jan. 17, 2002, the first ERO frames could be collected on approximately Feb. 25, 2002,
i.e. during the fifth week of SMOV. We estimate that about
three weeks will be necessary to the ACS team to process the ERO data,
in light of the complexity of the latter and of the novelty of the
instrumentation. OPO have estimated that they will need an additional
10 days to prepare the ERO data for final release (including all the
printed products).
Because no flight calibration data will be available prior to the
execution of the first ERO programmes, calibration data collected on
the ground will be used to process the ERO frames. We do expect,
however, the geometric distortion programme (ACS28) to begin execution
in parallel to ERO. Depending on the complexity of the data analysis,
it might be, thus, possible to use the new geometric distortion
calibration obtained in this way to process the ERO data.
We should like to note here in passing that the short PSF stability
test run at the end of fine alignment cannot replace programme ACS17
(pointing stability). The latter will still have to be executed to
prove that the PSF is stable over time also for longer exposures and,
more importantly, in different thermal environments.
Some of the ERO programmes require accurate pointing, which in turn
need the ACS to be properly aligned with the reference frame of the
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FGS. These observations can only take place after the ACS to FGS
alignment proposal (ACS11) has been executed and after having updated
the appropriate calibration tables (apertures location) in the flight
software. We expect all keywords to be in place by the end of week 8 of SMOV (Mar.
21, 2002).
A.I. 2b. NICMOS EROs – Response provided by Carl Biagetti with STScI NICMOS
Team concurrence.
NICMOS EROs were originally scheduled for execution at launch plus 9 weeks (~ Jan.
30 based on a 29Nov01 launch) following instrument recooling (week 2) during the BEA
period, a 2-week monitoring and analysis period for temperature set-point determination,
and a 2-week PAM alignment operation for all 3 cameras. The remaining 3 weeks were
a conservative allotment for NICMOS for parameter updates occasioned by the PAM
alignment.
In response this action item, the team believes that, since PAM focussing is relatively
insensitive to temperature changes, it will be possible to commence the PAM alignment
process very soon after SI cooldown rather than waiting the additional 2 weeks for
temperature set-point determination. In addition, the resulting parameter updates can
probably be accomplished in two weeks instead of three, as long as we assume the
NICMOS-to-FGS frame alignment is not required for at least the initial EROs.
In this case, the initial NICMOS EROs can be accomplished at approximately 6 weeks
following launch (~ Mar. 3 for a 17Jan02 launch). Note that, in the event of observations
requiring optimized pointing accuracies, e.g., a coronographic observation, such EROs
would not be achievable before early May02.
A.I. 3. Supply the Project plan for implementing dual SSR capability. SM/Pilkington
Response TBS
A.I. 4. Present to Project management the assessment for using the second transmitter
during SMOV. Response provided by Carl Biagetti.
Prior the SPR, Alan Patterson, STScI Planning & Scheduling, issued a white paper on
projected SMOV data volumes. While the paper's principle recommendation was to use
both Solid State Recorders (SSR) in SMOV3b, it also assessed the effect of using both
high-rate transmitters for the same time period. This assessment appears in section 3.1.2
(2-SSR/1-transmitter operations) and 3.1.4.(2-SSR/2-transmitter operations).
The recommendations (Sec. 4.0) are reproduced below.
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===============================================================
High Data Volume SMOV Requirements and TDRS downlink capability
Alan Patterson, 17Jan01
Excerpt:
"4.0 Recommendations
It is recommended that both SSRs be in use at the same time during SMOV. This will
avoid a forced extension in SMOV activities.
If there are very few SMOV activities that require rapid access and these do not include
any high data volume ACS programs then the careful placement of the known visits can
be handled with single transmitter operation. If there are more than a handful of high
data rate and volume ACS visits requiring rapid access it is recommended that both
transmitters be in operation during the first few, critical weeks of SMOV.
If part 2 of ACS program 9005 must be executed contiguously then 2 transmitter
operation is necessary.
It is recommended high data rate high data volume SMOV visits that do not require rapid
access be split into pieces and scheduled separately."
Note: Except for Part 2 (CTE measurement), the ACS CCD functional (9005) will be
scheduled during the first week of SMOV. Part 2 will go later in SMOV at a time
convenient for handling the data volume. The other high-volume ACS activities will not
require scheduling in contiguous orbits. Therefore, two-transmitter operation is not
required by ACS.
The only SMOV3b activities that require rapid downlink (rapid enough to require a
second transmitter) are the initial WFPC2 Cooldown & UV monitors (WFPC2-03) which
occur shortly after the Bright Earth Avoidance (BEA) period. These are relatively lowvolume (compared to ACS) but they occur during the high-volume NICMOS internals,
requiring some judicious scheduling but not a second transmitter.
Conclusion: While two-transmitter operation during SMOV3b would be handy in 2 or 3
specific instances, it is not required for planned SMOV execution.
A.I. 5 EPS personnel should add to their analysis plan, tracking of the SADM
Performance. Data should be compared to SA2 SADM performance. Response
provided by S. Krol and N. Seftas.
Data extraction of SA-2 Command Profile Error has started. Following SM-3B,
Command Profile Error data for SA-3 will be compared to that of SA-2.
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A.I. 6 Investigate solar array position optimization during -V1 pointing during
the VDT. Response provided by S. Krol, N. Seftas.
HST will need to be at the Anti-Sun Attitude (sun vector is within +/- 10
degrees of the -V1, SA incidence angle less than 5 degrees) to support power
measurement calculations.
For SMOV3B, it would be good to more formalize the normal scheduling procedure as
follows (per activity summary EPS-2):
From the end of BEA through the end of SMOV, when the vehicle pointing is within 10
degrees of the antisun for longer than one orbit, ensure that the solar arrays are set to
within 5 degrees of normal.
There are two obvious opportunities currently during SMOV3B that may provide good
data for solar array power determination. 1) Soon after the end of BEA, there will be a 5
orbit Vehicle Disturbance Test that required an antisun pointing (PN format
engineering data). 2) About 6-7 weeks after the end of BEA, there is a ~8 orbit ACS test
that requires an antisun pointing. 3) Any other serendipitous opportunities that occur in
the schedule will be set up to allow them to be utilized.
A.I. 7. Add spacecraft tests to the SMOV timeline chart. Response provided by Carl
Biagetti.
The tests will be added to the network chart as they become known.
A.I. 8 Assess the impact of OTA focus changes on the ACS Pointing Stability Test.
Response provided by Chris O’Dea and George Hartig.
As currently planned, the pointing stability test (ACS16) is intended
to measure the combined OTA plus internal ACS image position drift, as
it is this cumulative effect that will, in practice, reflect onto the
science observations. Although the response of the OTA to thermal
variations may change both image focus and position, we expect that
focus changes will not significantly affect our ability to measure
positional changes. Furthermore, the observational approach has been
devised in such a way that we can separate the two components: OTA
changes will be manifest as image movements in the same direction and
magnitude (projected on sky) for both HRC and WFC detectors, whereas
various instability mechanisms internal to the ACS will likely result
in different behavior for the two channels.
During the review, M. Reinhart suggested that the order of the
observations could be reversed and that the spacecraft should drift
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from a cold to a warm attitude during the test (instead of moving from
warm to cold). The advantage of this approach would be to leave the
spacecraft, at the end of the test, in a more nominal condition for the
observations to follow. Since the order of the temperature changes will
have no significant effect on the pointing stability test, we fully
agree with M. Reinhart's suggestion.
A.I. 9 Assess requirement J.10.4.4.5.3. In particular, determine if one month is the
proper length of time for the +/- 0.5 deg K stability requirement. Response provided by
Carl Biagetti and Bahram Mobasher.
The requirement stands as is. The one month timeframe is proper for a SMOV
requirement, though it is understood the CEI spec requirement spanning a year-long
interval is the more scientifically meaningful one.
A.I. 10 Add to the SMOV timeline chart a Project technical review date to determine
the NCC set point. Response provided by Carl Biagetti.
A NICMOS temperature set point FRR has been added to the network chart at a point
two weeks after completion of the NICMOS cooldown. Thus, the FRR would be
expected to occur at about Release + 26 days (~20Feb02 for 17Jan02 launch).
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