As with all missions, LASCO started as a concept to answer three questions related to the quiet sun: What is the structure and dynamics of the solar interior? Why does the solar corona exist and how is it heated to the extremely high temperature of about 1-million-degrees Celsius? And, where is the solar wind produced and how is it accelerated? Those questions started to define the LASCO instrument concept in the early 1980s.
“At the time, the ESA was planning a solar mission as one of it four cornerstone missions,” Howard said. “We thought we should collaborate with them on this new mission in some way. We discussed the goals we wanted for the instrument, and in 1987 we submitted the proposal in response to an opportunity announcement issued jointly by NASA and ESA.”
The NRL team also became co-investigators on a European Principal Investigator instrument called the Extreme-ultraviolet Imaging Telescope that flew on SOHO.
With the mission greenlighted, the NRL team got to work. The original principal investigator was Donald Michels, Ph.D. As the mission continued to be built, Guenter Brueckner, Ph.D. was made principal investigator since his branch was supplying a lot of technical personnel and laboratory space. Howard was a project scientist for LASCO until after launch when Brueckner became ill and asked him to take over.
“The original concept of the mission, to study the quiet sun during the 2 1/2 year lifetime of the mission, evolved because of the increase in activity of the sun to study the active sun, keeping its original objectives,” Howard said. “Now, because it has been observing for 25 years, it has evolved adding solar cycle studies - it is now into its third solar cycle (of eleven years each), an unprecedented opportunity.”
LASCO had three telescopes on SOHO at launch, two were traditional coronagraphs, a special type of telescope that uses an occulting disk to completely block direct sunlight, allowing scientists to see the atmosphere around the outside of the sun’s corona, much like the moon blocks the sunlight during an eclipse. But LASCO’s third telescope, C1, was very unconventional in its design and purpose.
“C1 allowed us to create an image of the corona at specific spectral wavelengths, and particularly the increased telemetry allowed us to operate LASCO much more completely,” Howard said.
Like the Martian rovers, SOHO/LASCO has had its share of going dark. For the first two-and-a-half years, all three instruments worked perfectly. However in June 1998, SOHO would have its first mishap, forcing scientists and mission specialists to scramble to save the operation. A bad command was sent and the whole spacecraft lost power becoming “lost in space”, frozen for several weeks.
“We estimated that the temperature inside the box surrounding our telescopes was about minus 90 degrees Celsius,” said Howard. “This was about 60 degrees Celsius colder than the test temperatures and several components failed.”
A month after the loss, the Arecibo Observatory radio telescope in Puerto Rico transmitted a radio signal that bounced off the SOHO spacecraft and was received by the 70-meter antenna at NASA’s Deep Space Network. This was a very important step in the recovery process, because the SOHO team located the spacecraft in space and learned that the spacecraft was rotating about an odd axis. Two months later, the team regained control and slowly powered-up and thawed out the fuel lines to be able to execute a maneuver to point back at the sun. The recovery of the mission took five months; however, one system that failed was critical to the operation of the C1 instrument.
Like Lazarus though, the little spacecraft beamed back to Earth, “I’m not dead! What do you want me to do now?” Since then, LASCO continues to work, sending images and data back on a daily basis.
“My top success is the demonstration of the importance of Coronal Mass Ejections (CME) in forecasting geomagnetic effects,” Howard said. “Because CMEs had not been observed regularly, the primary sources of geomagnetic storms were thought to be flares and the recurrent co-rotating interaction regions. But the observation of the "halo" CME (a CME that is directed at Earth) was now a regular event, which was probably the key to convincing people of its significance.”