Oct 14, 1998

Sunquake telescope appears to be OK

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"Sunquake" telescope
appears to be OK


First look is encouraging

October 14, 1998: A valuable telescope for studying seismic waves and other vibrations on the sun is alive again, although a few more weeks are needed before scientists know for sure if they can resume normal observations with it.

"It does look like the MDI is back," said Dr. David Hathaway of NASA's Marshall Space Flight Center. The MDI is the Michelson Doppler Imager, one of several telescopes on the Solar Heliospheric (SOHO) spacecraft. SOHO accidentally broke contact with Earth on June 24 and was lost until controllers received tentative signals from it on Sept. 16. After bringing the spacecraft under control, they started reactivating the dozen science instruments.

All have worked so far, but MDI - activated on Monday - was a question because a crucial crystal might have cracked during the period when SOHO was not aimed at the sun and thus not maintaining proper thermal control.



Above: An image of the sun as seen through the newly reactivated Michelson Doppler Imager (MDI). The MDI uses subtle changes in the wavelengths of light to reveal how fast features are rising or falling on the surface of the sun. Physicists can then study flows and convections - akin to studying weather and climate in Earth's atmosphere - to understand better what is happening on the sun. Links to 1,204x1,024-pixel, 626KB GIF. Credit: NASA/Goddard Space Flight Center


SOHO instrument status and
planned activation dates
  • CDS (Coronal Diagnostics Spectrometer) Oct. 18
  • CELIAS (Charge, Element, and Isotope Analysis System) Oct. 23
  • COSTEP (Comprehensive Suprathermal and Energetic Particle Analyzer) TBD
  • EIT (Extreme ultraviolet Imaging Telescope) Oct. 13
  • ERNE (Energetic and Relativistic Nuclei and Electron experiment) TBD
  • GOLF (Global Oscillations at Low Frequencies) Oct. 8
  • LASCO (Large Angle and Spectrometric Coronagraph) Oct. 13
  • MDI/SOI (Michelson Doppler Imager/Solar Oscillations Investigation) Oct. 12
  • SUMER (Solar Ultraviolet Measurements of Emitted Radiation) working well
  • SWAN (Solar Wind Anisotropies) Oct. 18
  • UVCS (Ultraviolet Coronagraph Spectrometer) Oct. 10
  • VIRGO (Variability of Solar Irradiance and Gravity Oscillations) working well

The crystal is made of calcite - softer than glass - and is absolutely crucial to extracting from the sun's intense light a narrow set of measurements.

"If it had been been cracked by the mounting contracting too tightly around the crystal, then it will just deliver scattered light and the MDI won't work," said Hathaway, an associate investigator who uses data and images from the MDI to investigate convection in the sun.

"First light" came on Monday.

"They got images through it and it looks good," Hathaway said. "The images are less than perfect."

The Solar Oscillations Investigations web site at Stanford University notes that the images have a "a strange blotchiness" and cautions that they "are made at a non-normal filter oven temperature."

"The instrument hasn't stabilized yet," Hathaway said, "and I wouldn't want to speculate on when we can resume normal science operation. The controllers still have a lot of tweaking to do."

The SOHO recovery web site also reports the Extreme ultraviolet Imaging Telescope (EIT) is functioning well, and all four of its cameras are reporting good status. The first full resolution images from EIT are now posted on the SOHO web site.

Stay tuned to the SOHO recovery operations web site for further developments.



The MDI instrument played a key role in showing that solar flares produce seismic waves, and gigantic seismic quakes, in the Sun's interior.


meteor flash!
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Author: Dave Dooling
Production Editor: Dr. Tony Phillips
Curator: Bryan Walls
Responsible NASA official: John M. Horack