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December 1998

Space shuttle flies HAO's white light coronagraph

Greg Card. (Photo by Carlye Calvin.)

Most folks realize that the space shuttle Discovery carried more than Senator John Glenn on its 29 October to 7 November mission. Among the scientific instruments on board was a white light coronagraph (WLC) developed and built at HAO in collaboration with scientists at NASA (including former NCAR staff member Dick Fisher, now at Goddard Space Flight Center).

The WLC and its companion instrument, an ultraviolet coronal spectrometer (UVCS) developed at Harvard University, were on the Spartan 201-05, a small satellite laboratory launched from Discovery on 1 November and retrieved by its robot arm two days later. Data from the WLC and UVCS collected on 26 observational orbits will be used to investigate the solar corona and the solar wind. In particular, the WLC provides a tool for determining electron densities of the corona. By launching the WLC from the space shuttle, researchers avoided the scattering of light caused by dust in the earth's atmosphere, which interferes with ground-based coronagraphs.

Project engineer Greg Card has been HAO's liaison with NASA. He spent several years commuting between Boulder, Goddard Space Flight Center, and Kennedy Space Center to prepare the coronagraph and integrate it with the Spartan spacecraft. During the mission, Greg managed a new WLC telemetry system from a desk at the Mission Control Center at Johnson Space Center in Houston. The Technology Experiment Augmenting Spartan (TEXAS) system allowed transmission of images in near-real time, while an onboard recording system stored additional data. Traditional analog tapes were complemented by the Mini Gigabyte Backup (MGB) hard-disk recorder, designed and newly upgraded by HAO and Electricon with housing and internal components fabricated by the NCAR machine shop.

When Discovery landed, Greg was enthusiastic: "It was so amazing!" He had high praise for the shuttle crew operating the Spartan. That crew included flight engineer and computer operator Scott Parazynski, mission specialist Steve Robinson on the Remote Manipulator System (the robot arm), and shuttle pilot Steve Lindsey. "They had rehearsed it so well it made it look effortless," says Greg. Within a few hours, "we were getting these spectacular coronal images [transmitted] to our Payloads Operations Control Center at Johnson."

The new telemetry system functioned beyond Greg's best hopes. With the faster data rate of the TEXAS system, the WLC captured a new image every 10 seconds, sending back about 700 images in near-real time. That's a lot more data than would have been possible with the onboard storage system alone: "One third more than we'd normally get," Greg says. There were two configurations for transmission: a "bent pipe" from the Spartan to the shuttle to the Tracking Data and Relay Satellites System, and a direct send from the Spartan to ground stations. The bent-pipe method allows almost 30 minutes of communication time, but it ties up orbiter resources. The ground-station method frees up those resources, but diverts resources from other satellites during a maximum of 10 minutes of transmission.

"On orbit 16, we wanted to take a look and see what the WLC was doing, so we sent about 75 images to our control center via ground stations at Dryden and Mila [in Florida]. Everything was working exceptionally well. We were getting enough engineering information from the coronagraph that we could tell a lot about the spacecraft's health: batteries, pointing, et cetera."

On past missions, the team had no way of knowing until Spartan was back on the ground whether or not systems were functioning and data were being gathered. "This time, we could interact with the instruments and see the data," says Dick Fisher. Because TEXAS transmitted data about ten times faster than the onboard recorder, the mission has opened up a new area of investigation. "It lets us explore a temporal regime we haven't been able to see before. So we're going to look to see if things are happening more rapidly than we've seen [in the past]." Summing up the performance of the new telemetry, Fisher adds, "It worked out great. When it was at the very worst, it was at the wonderful level."

As Staff Notes Monthly goes to press, Greg is at Kennedy Space Center for post-flight operations: taking the data from the MGB recorder. A quick check shows a full-mission-length science and engineering data set, according to NASA's Craig Tooley. Greg will be back in Boulder with a copy of the WLC data in time for Thanksgiving.

When the recorded information gets back to HAO, Andy Stanger will do the preprocessing, extracting images out of the raw data. Since the Large Angle and Spectrometric Coronagraph (LASCO) aboard NASA's Solar and Heliospheric Observatory (SOHO) satellite detected two or three coronal mass ejections during Spartan's deployment, there's hope Andy will find some near-real time images of the ejections in the MGB data.

The processed data will go to Dick Fisher at Goddard and to HAO researchers Tom Holzer, David Elmore, Alice Lecinski, and Joan Burkepile. In addition to matchups with the data from the UVCS, over the next year the team will examine the WLC results in relationship to coronal data from the Mauna Loa Solar Observatory's MK3 and MK4 coronameters, as well as SOHO's LASCO instrument.

According to Greg, this is the last flight for the Spartan solar research craft. NASA is turning its attention to constructing the space station, and "the shuttle [payload schedule] is tight, so it's hard to squeak in another Spartan mission." He adds, "It was a good thing to have Spartan fly at this time in the solar cycle. With SOHO and the new TRACE [Transition Region and Coronal Explorer] satellite launched this year, plus Mauna Loa up and running, we had [multiple] observations running simultaneously." •Zhenya Gallon

On the Web:
WLC images transmitted via the bent- pipe mode and processed for polarized brightness only are available on the Web.

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