Transcript (FUSE), but… - Johns Hopkins University

Far Ultraviolet Spectroscopic Explorer
FUSE Operations Overview
Dr. Bill Blair
Research Professor, Johns Hopkins University
FUSE Chief of Observatory Operations
May 29, 2008
FUSE Mission Overview
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Funded by NASA but developed and
operated by JHU.
France and Canada were partners.
FUSE Launched June 24, 1999.
• 765 km (500 mile) circular orbit.
• Inclined 25 degrees to equator.
• P = 100 minutes.
Science Mission began Dec. 1, 1999.
8+ years of operations.
• Approx. 8 Msec/yr of science
observations; ~ 700 objects/yr.
• >1200 publications to date (>475
refereed) and still growing.
Total cost: $225 M (development,
launch and 8-years of operations).
Why FUSE?
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FUSE satellite during integration at
NASA-GSFC, August 1998.
90.5-118.7 nm FUV Spectroscopy at
spectral resolution ~ 20,000.
• Complemented Hubble Space
Telescope capabilities.
• 10,000 x more sensitive than
Copernicus mission from 1970’s.
• Very “interesting” spectral region for
astrophysics.
Example FUSE Spectrum
“A picture may
be worth 1000
words, but a
spectrum is
worth 1000
pictures!”
-Dr. Blair Savage,
Univ. of Wisconsin
FUSE Overview
Light Path Schematic
FUSE at NASA/GSFC (Aug. 1998)
Overall:
3000 pounds
18 feet (5.5m) tall
<--Science Instrument:
Telescopes and
Spectrographs
<--Spacecraft:
Attitude Control,
Communications,
Power.
FUSE Operations
• FUSE was operated by about [20-35] scientists,
engineers, and contractors at JHU.
• NASA selected proposals for FUSE observations on a
yearly cycle.
• All proposal processing, mission planning, timelining,
commanding of the satellite, data processing, and
archiving were done locally at JHU.
• Communications with FUSE were from a Satellite
Control Center at JHU, primarily through a radio dish
located at University of Puerto Rico, Mayaguez (6 or 7
contact periods per day, about 12 minutes each)
FUSE JHU Operations
Satellite Control Center--JHU
FUSE Ground Station
• 5-meter Low Earth Orbit Terminal
(LEO-T) antenna, located at University
of Puerto Rico, Mayaguez.
• Autonomous operations, staged from
Satellite Control Center at JHU.
• 1 Mbps S-band downlink.
• Uses ISDN (128 Kbps) and/or secure
Internet connections for data transfers.
• Real-time: health & safety telemetry
(only); science data transferred after
each pass.
• Radome protected from weather,
permitted environmental control of
electronics.
• H&S contacts through TDRSS.
FUSE End of Mission Status
• FUSE Science Instrument Health Remained Excellent.
• Only ~15-40% sensitivity changes over 8 years.
• Spectral resolution and data quality unchanged.
• Spacecraft eventually lost all 4 Reaction Wheels.
• Most recent loss-July 12, 2007 previous loss Dec. 27, 2004.
• Operated 2.5 years using 1 remaining wheel and magnetic
torquer bars (MTBs) on other two axes. (See next page.)
• Concerns about gyroscope lifetimes.
• 3 [2.5] out of 6 gyros still working at EoM.
• Developed revised control s/w to allow operations with fewer
than 3 gyros; uplinked Apr. 2003.
• July 30, 2003: gyro failed; worked in 1 or 2-gyro mode for
following 1.5 yrs with no significant degradation of operations!
FUSE--A Brief History
FUSE-Dec. 1999
FUSE-Mar. 2004
FUSE-Feb. 2002
FUSE-June 2005
FUSE--A Brief History
FUSE-Dec. 1999
FUSE-Mar. 2004
FUSE-Feb. 2002
FUSE-June 2005
FUSE-Feb. 2006
Spacecraft--Inside Views
Pitch RWA
(failed 12/01)
Yaw RWA
(failed 11/01)
Roll RWA
(failed 12/04)
X torquer bar
(MTB)
Z torquer bar
(MTB)
Skew RWA
(bracket)
Y torquer bar
(MTB)
• MTBs (3) and Skew Reaction Wheel now used for pointing control.
1-wheel Operations:
Pointing Performance
RMS ~1”
during
useful part
of orbit
(Well within
LWRS
aperture.)
1-wheel Operations:
Sensitivity check
IC2448
PN Central Star
Before:
March 2002
After:
March 2005
TACO* Plot Examples
Shows regions where
MTB torque is greater
than expected gravity
gradient disturbance.
Antisun
Stable region for
24 hours
(time selectable)
Solid line: 90% of
time is stable
Dashed line: 85%
+ is orbit pole (south)
*Torque Authority Contour
Sun
Momentum Management
Happy days…
Mild gradient, large TACO region
Not-so-happy days…
Sharp gradients, irregular and variable
TACO region
Momentum Management
Select alternate targets that help control the momentum of the single wheel.
(Top panel)
Cy8 Sky Coverage w/Targets
Deuterium in the Galaxy
• Deuterium (or “heavy hydrogen”) formed in the Big
Bang and has been destroyed in stars ever since.
• FUSE observations are demonstrating significant
local variations in gas-phase D abundances and the
complexity of ISM chemistry.
FUSE Discovers
Hot Corona of Milky Way
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FUSE research indicates that the
Milky Way sits in the middle of a
huge corona of very low density,
million-degree gas.
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Corona revealed via O VI absorption
at surface of clouds of cool gas
falling into the Milky Way, like
meteors penetrating the Earth’s
atmosphere.
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Galactic corona is a new
phenomenon and must be a relic of
the formation of the Milky Way or
Local Group of galaxies.
FUSE Finds Hot Gas
Spewing from Another Galaxy
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FUSE has detected O VI emission for the
first time in the halo of another galaxy.
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This emission comes from very hot gas
(~106K) as it cools and falls back onto the
galaxy: a galactic fountain.
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Provides best evidence to date that this
hot gas comes from supernova explosions.
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Emission may account for the energy input
by supernovae to eject the fountain.
NGC 4631
NOAO photo
First Detection of N2 in the ISM
HD 124314 AV ~1.5: Knauth et al. 2004
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N2 should be an important
constituent of the ISM, due to the
relatively high abundance, but
had never been seen.
FUSE measures a column density
larger than expected from models
of diffuse clouds and
significantly smaller than
expected for dense molecular
clouds.
N2 abundance does not explain
the observed N I abundance
variations toward high column
density sight lines, implying that
the nitrogen chemistry models
need significant revision.
FUSE Sees Solar Systems
Under Construction
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Beta Pictoris, the prototype
young stellar system with a
dusty accretion disk, contains
millions of evaporating
comets.
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FUSE measurements of H2
are important signatures of
the evolution of these disks.
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Lack of H2 FUV absorption
(FUSE), but…
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H2 IR emission from beta Pic
disk seen by ISO.
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Implies H2 has very clumpy
distribution.
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Points to possible planet
formation!
Hot Helium Traces
Structure of Early Universe
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FUSE gives best view yet of hot gas left over from Big Bang.
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Hydrogen observed by ground-based telescopes, Helium
observed by FUSE.
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Confirms models of how matter in early universe condensed
into web-like structure.
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FUSE data implies early universe was re-energized by
radiation from starbursts and black holes in active galaxies
and quasars.
Revising the Temperature Scale
of Bright Stars
 Stellar Luminosities are calculated from Stellar
temperatures:
Luminosity  (Temperature)4
 FUSE has found the temperature scale of the hottest,
brightest stars to be in error by up to 20% (too high).
 This translates into a factor of ~2 error in the expected
flux output from these hot stars!
NGC 604 in M33
From HST/WFPC2
 Important implications for the
stars themselves (lower masses)
and to the stars evolve over time.
 Extremely important for
understanding star forming
regions and their interaction
with surrounding gas.
Mission Totals by Program Type
83.6 Msec executed science; 65 Msec in MAST (post-CalFUSE)
Epilogue
Thanks to the ~600 people who worked on the
development of FUSE, to NASA and our
International partners for their continued support,
and to our dedicated operations team!
For more information on FUSE, pictures, and status
reports, visit our Web site:
http://fuse.pha.jhu.edu
Or our Public Outreach site:
http://fuse.pha.jhu.edu/outreach/
FUSE On-orbit
Questions?