Cruise Activity Request (CAR) Form
Observation Name: UVIS Scattered Light Characterization at Earth’s Moon
(deferred activity in Calibration & Maintenance Handbook)
Requesting Instrument: UVIS
Objective: (both measurement and scientific objectives)
1. Characterize telescope’s scattering of light by observing a well-known extended bright
source. Earth’s moon is the only source bright enough to see a sharp 10^6 drop in signal at
edge.
2. Observe a source which has the potential to serve as a calibration target across missions and
time.
3. Measure HDAC’s sensitivity and red tail using a known target
Description of Activity:
With the spacecraft z axis pointing at the sun, the spacecraft is rolled about z to position the -y
axis (UVIS boresight) in the direction of the moon. The spacecraft motion will then carry the
UVIS slit across the moon. The observation is centered on the geometry at which the phase
angle of the moon is 90 degrees.
The UVIS FUV, EUV and HDAC channels will be on. As the UVIS EUV and FUV slits cross
the moon the signature of the moon will be detected in one pixel after another as illustrated in
Figure 1. This allows us to characterize the scattered light which would be detected in pixels
adjacent to the pixels filled by the moon. The HDAC will be operated in its photometry mode to
characterize its sensitivity using a known source. e. Use of the HDAC requires no additional
resources.
Activity Time Period: (window when the activity can take place)
This window for this activity is centered on the moon having a phase angle of 90 degrees as seen
from the spacecraft, beginning 15 minutes before this geometry is achieved. The total duration
of 30 min allows the observation to start with the 64 milliradian slit completely off the moon,
then to drift across the moon and off the other side, lengthwise, as illustrated in Figure 1. (The
slit drifts across the limb of the moon perpendicular, not tangent, to the limb.)
This window opens at earth closest approach minus 1 hr 15 min and closes at earth c/a minus 45
min.
Activity Duration:
The activity itself takes 30 min. Depending on results from ICO, it may be recommended to
condition the HDAC channel before it is used at closest approach. This conditioning activity can
take from few hours to 48 hours. UVIS has to be powered on during the conditioning activity
and the turn on can be done anytime prior to the start the conditionning activity.
System Requirements:
Pointing
One roll about the z axis is required to point the UVIS boresight (-y axis) in the direction of the
moon.
Power
8.5 Watts
Data volume
45 Mbits. Data from HDAC conditioning (if the activity is conducted) does not to be returned. If
returned this data adds around 12 Mbits to the data volume.
Data rate
25.2 kbps
Data mode
SAF248c or S&ER3
Real-time commanding
Not necessary during the activity. No IEB load will be necessary. UVIS commands can either
be in the background sequence or in a mini-sequence.
Dependence on other instrument activities: (eg. Support imaging required)
No dependencies. Coordinated with VIMS.
Ridealong Activities:
VIMS
Criticality: (how important is this activity to your instrument and why)
Needed to characterize telescope scattered light. Moon only source because must be bright
enough to see sharp 10^6 drop in signal at edge. Facilities not available to do calibration on
Earth. Only way to correlate to Galileo observations. Will help determine if a feature observed
during a satellite limb scan is real or an instrument artifact. Lack of these calibrating data adds
uncertainty to detections of satellite atmospheres.
use hand book words
Special Requirements:
S/c roll, SAF248c or S&ER3
Notes on Instrument Configuration:
(details about the instrument configuration that you thought about when you designed the activity
and you want to document)
Geometry:
Earth c/a at 3:10 UTC on August 18, 1999
Time
(UTC)
1:40
1:55
2:10
Range
Phase angle
375,318
377,142
379,477
88.2
90.3
92.4
Count rate Calculations
Start
Center
End
EUV
FUV
HDAC
30,000 counts/sec
Instrument configuration
EUV
2 mrad x 61 mrad (low resolution slit)
2x spectral binning
1 x spatial binning
no windowing
square root compression
24 sec integration time
FUV
1.5 mrad x 61 mrad (low resolution slit)
2x spectral binning
1 x spatial binning
no windowing
square root compression
24 sec integration time
HDAC
photometry mode
HSP
off
Instrument Setup
Turn off supplemental heater, turn on UVIS, load RAM code from SSR, execute RAM code, set
active flag, execute HDAC conditioning, execute experiment, halt experiment, turn off UVIS,
turn on supplemental heater (109 commands in background sequence).
ECR or Flight Rule Reference: