Far Ultraviolet Spectroscopic Explorer

1. Far Ultraviolet Spectroscopic Explorer FUSE Operations Overview Dr. Bill Blair Research Professor, Johns Hopkins University FUSE Chief of Observatory Operations May 29, 2008

2. FUSE Mission Overview • 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).

3. Why FUSE? • 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. FUSE satellite during integration at NASA-GSFC, August 1998.

4. Example FUSE Spectrum • “A picture may • be worth 1000 • words, but a • spectrum is • worth 1000 • pictures!” • Dr. Blair Savage, • Univ. of Wisconsin

5. 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.

6. 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)

7. FUSE JHU Operations

8. Satellite Control Center--JHU

9. 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.

10. 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!

11. FUSE--A Brief History FUSE-Feb. 2002 FUSE-Dec. 1999 FUSE-June 2005 FUSE-Mar. 2004

12. FUSE--A Brief History FUSE-Feb. 2002 FUSE-Dec. 1999 FUSE-June 2005 FUSE-Mar. 2004 FUSE-Feb. 2006

13. Spacecraft--Inside Views Yaw RWA (failed 11/01) Pitch RWA (failed 12/01) Skew RWA (bracket) Roll RWA (failed 12/04) • MTBs (3) and Skew Reaction Wheel now used for pointing control. Y torquer bar (MTB) X torquer bar (MTB) Z torquer bar (MTB)

14. 1-wheel Operations:Pointing Performance RMS ~1” during useful part of orbit (Well within LWRS aperture.)

15. 1-wheel Operations:Sensitivity check IC2448 PN Central Star Before: March 2002 After: March 2005

16. TACO* Plot Examples Shows regions where MTB torque is greater than expected gravity gradient disturbance. Stable region for 24 hours (time selectable) Solid line: 90% of time is stable Dashed line: 85% + is orbit pole (south) Antisun Sun *Torque Authority Contour

17. Momentum Management Not-so-happy days… Sharp gradients, irregular and variable TACO region Happy days… Mild gradient, large TACO region

18. Momentum Management Select alternate targets that help control the momentum of the single wheel. (Top panel)

19. Cy8 Sky Coverage w/Targets

20. 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.

21. FUSE Discovers Hot Corona of Milky Way • FUSE research indicates that the Milky Way sits in the middle of a huge corona of very low density, million-degree gas. • 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. • Galactic corona is a new phenomenon and must be a relic of the formation of the Milky Way or Local Group of galaxies.

22. FUSE Finds Hot Gas Spewing from Another Galaxy • FUSE has detected O VI emission for the first time in the halo of another galaxy. • This emission comes from very hot gas (~106K) as it cools and falls back onto the galaxy: a galactic fountain. • Provides best evidence to date that this hot gas comes from supernova explosions. • Emission may account for the energy input by supernovae to eject the fountain. NGC 4631 NOAO photo

23. First Detection of N2 in the ISM HD 124314 AV ~1.5: Knauth et al. 2004 • 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.

24. FUSE Sees Solar Systems Under Construction • Beta Pictoris, the prototype young stellar system with a dusty accretion disk, contains millions of evaporating comets. • FUSE measurements of H2 are important signatures of the evolution of these disks. • Lack of H2 FUV absorption (FUSE), but… • H2 IR emission from beta Pic disk seen by ISO. • Implies H2 has very clumpy distribution. • Points to possible planet formation!

25. Hot Helium Traces Structure of Early Universe • FUSE gives best view yet of hot gas left over from Big Bang. • Hydrogen observed by ground-based telescopes, Helium observed by FUSE. • Confirms models of how matter in early universe condensed into web-like structure. • FUSE data implies early universe was re-energized by radiation from starbursts and black holes in active galaxies and quasars.

26. 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! • 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. NGC 604 in M33 From HST/WFPC2

27. Mission Totals by Program Type 83.6 Msec executed science; 65 Msec in MAST (post-CalFUSE)

28. 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/

29. FUSE On-orbit Questions?