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Index of CfA Almanac stories.

The CfA Almanac

February 1998

SMA TAKES "FIRST LIGHT" The prototype antenna for SAO's Submillimeter Array (SMA) was rolled out of the assembly building at Westford, MA, in early December for a series of field tests. Its first celestial observation was made of the waning Moon on January 23, just six days before New phase, when a scan of thermal radio emission clearly showed the "hot," bright, Sun-lit edge. Then, on February 1, three days after New, the first "photographic" image was obtained by reconstructing data taken in raster-scan mode. The image shows the bright Sun-lit edge standing in sharp contrast to the cooler, dark side of the Moon. (Images by Nimesh Patel and Masao Saito.)


The TRW Space and Electronics Group has notified NASA that it will be unable to deliver the Advanced X-ray Astrophysics Facility (AXAF) to NASA's Kennedy Space Center on June 1, 1998, as had been expected, because of delays in assembly and testing of the facility. TRW is NASA's prime contractor for the spacecraft, which will carry instruments designed and fabricated by the Smithsonian Astrophysical Observatory (SAO).

The delay of delivery is expected to delay, in turn, the launch of AXAF, originally scheduled for August 1998. The earliest date a new launch might be expected is now sometime in December. Once launched, SAO will direct and monitor orbital maneuvers and observations through the Operations Control Center (OCC) located in Cambridge. Observational data will be received, analyzed and archived by the AXAF Science Center (ASC), also operated by SAO in Cambridge. "The delay in delivery of the observatory is unfortunate," said Fred Wojtalik of NASA Marshall Space Flight Center. "However, our first priority is to launch a world-class observatory which has been thoroughly tested and meets all requirements. We will work closely with TRW to ensure that happens."

The delay is primarily due to TRW's difficulty in configuring and programming its Integrated Spacecraft Automated Test System to test the observatory before it is delivered to NASA.

AXAF is expected to play a vital role in answering fundamental questions about the universe, including its age and size, and will probe the nature and amounts of so-called "dark matter." The observatory also will allow scientists to see and measure the details of hot gas clouds in clusters of galaxies; observe X rays generated when stars are torn apart by the incredibly strong gravity around massive black holes in the centers of galaxies; and, provide images that will help understand how exploding stars create and disperse many of the elements necessary for new stars, planets, and life.

The Marshall Space Flight Center manages development of the observatory for the Office of Space Science at NASA Headquarters. Made of glass purchased from Schott Glaswerke, Mainz, Germany, the telescope's mirrors were built by Hughes Danbury Optical Systems, Danbury, CT, and assembled by Eastman-Kodak Company, Rochester, NY. SAO's Leon van Spreybroeck served as Telescope Scientist.

The science instruments, including a High Resolution Camera (HRC) produced by SAO under the direction of Principal Investigator Steve Murray, were integrated into the science instrument module at Ball Aerospace and Technologies Corporation, Boulder, CO, before testing and shipment to TRW.


Watching the Super Bowl from the Goodyear Blimp offers a great overview of football. However, to get a full picture of the sport, one needs close-ups on the field, showing the actions--and reactions --of individual players. Only then, when combined with the wide-angle shots, does one get a true feeling for the game.

While there are not yet plans to send sportscasters into space, scientists hope that the Transition Region and Coronal Explorer (TRACE) satellite will gather the crucial details that, when combined with its own "mosaic" ability plus another spacecraft's "big picture" overview, will help unlock mysteries of the Sun.

Scheduled for launch aboard a Pegasus XL on March 5, TRACE will gather data on solar flares and magnetic storms, heating in the solar corona, and the role that magnetic fields play in the Sun's behavior.

Although to observers on Earth the Sun looks like a smooth, perfectly circular, bright ball, in fact, it has an atmosphere that extends millions of miles into space. This diffuse atmosphere, or "corona," has long puzzled astronomers, because it is many times hotter--millions of degrees--than the cooler, visible disk, or "photosphere," immediately below it. TRACE is intended to study the high temperature corona and the so-called "transition region," the largely unexplored space where corona meets photosphere.

"TRACE will be the highest resolution telescope ever flown to image the corona and transition region," says Leon Golub, SAO scientist and TRACE co-investigator. "Our goal is to trace the connection between surface convective motions and coronal heating."

SAO scientists and engineers have had a leading role in the development of this NASA project. "SAO built the telescope, provided the multilayer coatings of its mirrors, and built the entrance aperture filter assembly," according to Golub.

TRACE will complement the joint NASA-ESA Solar and Heliospheric Observatory (SOHO). Launched in 1995, SOHO makes continuous wide-angle images--the Goodyear Blimp shots, so to speak--of the Sun's corona. By contrast, TRACE will provide scientists with images of small-scale features near the solar disk, including three-dimensional magnetic structures that protrude through the visible edge of the Sun.

The timing of TRACE's launch is also significant. The Sun is not a steady beacon of light and energy, rather it is a variable star with cyclic periods of activity, including sunspots and solar storms that increase and decrease over 11-year periods. The most active portion of the current cycle is about to begin--and scientists hope to have both TRACE and SOHO on line to watch the buildup of magnetic activity directly for the first time.

As part of NASA's Small Explorer (SMEX) program, TRACE was designed and built under the new "cheaper, faster, better" mantra. All SMEX projects are required to cost under $35 million, and to be launched within less than three years after their initial approval. TRACE is on track to meet all those strict requirements. TRACE's mission is scheduled to last one year, but scientists are hopeful it will operate through the next solar maximum.

						--Megan Watzke


The CfA's Shadia Habbal will lead a research expedition to the island of Guadeloupe in the Caribbean to observe the total solar eclipse of February 26. This is Habbal's third eclipse expedition in almost as many years, with previous trips to India and Mongolia.

Habbal's team, which includes scientists from the CfA, Goddard Space Flight Center, and Jet Propulsion Laboratory, and which has gained some national attention for its high percentage of women members (nearly 100 percent on previous expeditions, and 60 percent on this one), will attempt to measure the amount of visible light emitted by iron molecules in the Sun's gaseous outer atmosphere, or corona, a phenomenon detectable only when the Moon blocks the Sun's disk.

The observations from Guadeloupe will be coordinated with the SOHO satellite, the Very Large Array in New Mexico, and the Galileo spacecraft, with the latter transmitting--from its orbit around Jupiter--a radio beam back to Earth that will pass through the corona, thus providing a unique probe of the Sun's atmosphere. By combining results from experiments conducted on other islands of the Caribbean lying in the eclipse path, as well as in space, Habbal and her colleagues hope to produce an unprecedented model of the Sun's corona.

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