NEWS | Dec. 2, 2020

Celebrating LASCO’s Silver Anniversary of Revealing the Wonders of Our Sun

By Paul Cage, U.S. Naval Research Laboratory, Corporate Communications

Since the early years of the space age, researchers in the Solar Physics Branch of the U.S. Naval Research Laboratory have been involved in observational and theoretical studies of the solar atmosphere.

Experiments developed at NRL have flown on NASA missions such as Skylab/Apollo Telescope Mount, the Orbiting Solar Observatory satellite series, NASA's third space shuttle mission STS-3, Spacelab-2 and Atlas missions; all feats of engineering that have helped humanity understand the wonders of the heavens. But, none have lasted as long as LASCO.

It was Dec. 2, 1995 when the Large Angle and Spectrometric Coronagraph was launched into space as part of the European Space Agency (ESA)–NASA Solar and Heliospheric Observatory (SOHO). Originally planned as a two-year mission, SOHO/LASCO is celebrating its silver anniversary, 25 years of scientific discovery of the sun; from its deep core to the outer corona and the solar winds.

“It is truly amazing,” said Russell Howard, Ph.D., an NRL astrophysicist who has been with LASCO since its inception. “I believe it is the longest mission here at NRL that is still operating at least. It is certainly cost effective to continue operating instruments as long as they are working well.”

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.”

Citizen scientists

The SOHO mission’s open data policy has promoted solar research across the globe, and LASCO in particular has spawned interest in other nations flying such instruments. Karl Battams, Ph.D. is a computational scientist at NRL and in 2020 assumed the role as the principal investigator for LASCO. He also manages the Sungrazer Project, which, since 2000, encourages amateur citizen scientists to discover new comets using SOHO’s images.

“The Sungrazer Project is one of the oldest citizen science projects, “Battams said. “The citizen scientists who participate – whether they realize it or not – they are learning so much more than just how to look for little moving dots of light in an image. They are having to think about the physics of the situation. They are having to understand a coronagraph image. We aren’t feeding them simplified subsets of the science data. We are saying ‘Here are the science products. Go make some new science from it.’”

LASCO’s future

As with any mission, failures do happen with time and a catastrophic failure could occur at any time. Currently the region where SOHO is orbiting, about 1 million miles from Earth, about four times the distance as the moon is from Earth, is much safer than a low-Earth orbit.

Eventually the SOHO/LASCO mission will come to an end. In 2016 LASCO observations were designated essential for space weather forecasting resulting in NASA being requested to maintain observations until a replacement mission could be put in place.

The National Oceanic & Atmospheric Administration commissioned NRL to build two instruments, one to be launched around 2024-2025 in an Earth orbit and one to go to Lagrange point 1, where the SOHO spacecraft currently is bathed in sunlight all the time and can constantly view the sun, which is an advantage over an Earth orbit.

“I would expect LASCO to continue operating for at least one year after the launch of a replacement to perform cross-calibrations,” Howard said. “But the fate of the mission depends on NASA and ESA and then SOHO itself.”

Just like when Thomas Harriot and Galileo Galilei turned their telescopes to the heavens to reveal the moon, planets and stars, LASCOs 25-year mission has revealed the sun’s magnificence amazing scientists and researchers around the world.

“This mission has been half of my professional career,” said Howard. “It has been an absolute joy to participate in creating the concept, building the instrument (with new or emerging technologies), analyzing the amazing data and seeing the result of the dedicated efforts of so many people during the preceding years and becoming such an important capability for the National Space Weather Program.”

In addition to Howard and Battams, there are currently three scientists at NRL who were there at LASCO’s beginning. George Doschek, Ph.D., emeritus, who was the head of the Solar Terrestrial Relationships Branch when LASCO was launched. Astrophysicist Dennis Wang, and research physicist Clarence Korendyke, Ph.D. worked on developing LASCO. Nathan Rich, an aerospace engineer, came a few years after launch and worked on operations.

About the U.S. Naval Research Laboratory

NRL is a scientific and engineering command dedicated to research that drives innovative advances for the U.S. Navy and Marine Corps from the seafloor to space and in the information domain. NRL is located in Washington, D.C. with major field sites in Stennis Space Center, Mississippi; Key West, Florida; Monterey, California, and employs approximately 2,500 civilian scientists, engineers and support personnel.