NICMOS
Defocus Mode Status
Ilana Dashevsky
(Commanding)
TIPS (09/20/07)
Ilana Dashevsky
1
Team
•
Developers & Testers:
Colin Cox
Ilana Dashevsky
Tom Donaldson
Rob Douglas
Mark Giuliano
Tony Krueger
Matt Lallo
Jinger Mo
Karla Peterson
Christine Ritchie
Alan Welty
TIPS (09/20/07)
•
Engineering:
Morgan Van Arsdall (GSFC)
John Bacinski (GSFC)
Tom Wheeler
•
Planning & Scheduling:
George Chapman
Beth Perriello
Tony Roman
•
Science & Data Analysis:
Tommy Wiklind
Helene McLaughlin
Nor Pirzkal
Ron Gilliland
Eddie Bergeron
Anton Koekemoer
Ilana Dashevsky
2
Goal
• Improve & simplify process to defocus the
NICMOS detectors
– Use Astronomer’s Proposal Tool (APT) and
standard proposal processing to request a
non-nominal focus for a detector
• Support planetary system investigations of
very bright stars (up to S/N ~10,000)
– Detect spectral features in planetary
atmosphere using grism
TIPS (09/20/07)
Ilana Dashevsky
3
STScI PR 2001-38:
“Astronomers
using NASA's
Hubble Space
Telescope have
made the first
direct detection of
the atmosphere of
a planet orbiting a
star outside our
solar system and
have obtained the
first information
about its chemical
composition.”
- Team led by D.
Charbonneau used
STIS
TIPS (09/20/07)
Ron Gilliland pioneered technique
using NICMOS to observe stars like
HD 209458
Ilana Dashevsky
4
Rationale for Change
• Old implementation required significant manual
intervention and checking
– “Restricted” mode not intended for GOs
– Specify defocus as a delta offset from nominal
requires expert knowledge
– Mistakes may result in mechanism hitting hard stop
• Number of GO requests to defocus detector 3
increased from one in 2003 to six in 2007
• More requests expected
– Defocus detector 1 (narrow band photometry)
TIPS (09/20/07)
Ilana Dashevsky
5
Background
• Pupil Adjust Mechanism (PAM) is used to provide optical
alignment for NICMOS science observations.
– Maximum PAM Motion is +/- 10mm
– Maximum Tip/Tilt +/- 1373 a-s
• All 3 detectors were originally designed to share a
common focus
• Deformation due to the dewar thermal short has resulted
in separate PAM focus positions:
– PAM 1, 2 and 3 are the home locations corresponding to
detectors 1, 2 and 3 respectively
– PAM I is an intermediate position that results in acceptable focus
for detectors 1 and 2
– PAM C is used for coronographic observations
TIPS (09/20/07)
Ilana Dashevsky
6
Life Time Concerns Addressed
• Tom Wheeler recently re-examined PAM usage & failure
modes
– 12,533 PAM moves & 5,431,471 focus motor revolutions on
orbit, as of April 2007
– Motor & gear-head assembly tested to ~3 billion motor
revolutions; never failed
– Bellows assembly tested to 100,000 compression/expansion
cycles; never failed
– Lubricant & other mechanical components have proven track
record in spacecraft
• Component fatigue due to motor overheating
– Engineers at Ball concluded that “fatigue is not a problem”
– Mitigate in schedule by enforcing PAM cool-down periods
– Monitor schedule for possible PAM motor overheating events
TIPS (09/20/07)
Ilana Dashevsky
7
Implementation
• New PAM out-of-focus positions
– Detector 1: -3.0 mm (best focus at 1.8 mm)
– Detector 2: -5.0 mm (best focus at 0.2 mm)
– Detector 3: -0.5 mm (best focus at -9.5 mm)
• More robust defocus commanding implemented
– Command PAM to an absolute position
• Flight Software verifies position and checks against soft stop
• All front-end systems changes installed
– APT, VTT, TRANS, Commanding, SIAF, Science
Operations Database, SMS Review Tool
– APT Version 16.4
– Phase II Proposal Instructions Eng. Version 16.1
TIPS (09/20/07)
Ilana Dashevsky
8
APT Changes
• New apertures for each detector to adjust
the FOV center for the out-of-focus motion
– NIC1-FIXD, NIC2-FIXD, NIC3-FIXD
• New exposure value for existing NICMOS
Optional Parameter
– CAMERA-FOCUS = DEFOCUS
• PI should consult with Instrument or
Contact Scientist
– Available but Unsupported mode
TIPS (09/20/07)
Ilana Dashevsky
9
APT Example
TIPS (09/20/07)
Ilana Dashevsky
10
On Orbit Test
• Verify that the new PAM locations produce
desired science data
• Proposal 11335 consists of two orbits:
– 1st orbit repeats observations for HD 209458
(7.6 mag) using detector 3 and grism G141
– 2nd orbit repeats observations from the routine
focus monitor of an open cluster NGC-3603 to
verify defocus for all detectors using phase
retrieval
TIPS (09/20/07)
Ilana Dashevsky
11
Status
• 1st orbit executed on
September 13th
– Brief analysis by Ron
Gilliland confirmed detector
3 defocus & aperture were
successfully implemented
•
2nd
orbit will execute
September 21st
2007
new defocus
parameter
2006
old method
– Defocus tested for all
NICMOS detectors
TIPS (09/20/07)
Ilana Dashevsky
12
Results
Coming soon to a
TIPS near you ….
TIPS (09/20/07)
Ilana Dashevsky
13