A space mission is about to “disappear” by mid-February, as the European Space Agency’s Solar Orbiter (affectionately referred to as “SolO” by the mission leaders) makes a crucial pass behind the sun.
The “occultation” from our earthly point of view is to be expected. ESA mission controllers spent weeks preparing for the blackout phase and uploading commands to SolO so that the spaceship can work autonomously if necessary. The sun creates a lot of noise in the radio spectrum, and SolO’s narrow passage reduces the transmission rate from 255 bits per second to just 7.8 bits per second, slower than the slowest modem in the dial-up era.
SolO’s position relative to Earth in February 2021. Photo credit: ESA
SolO was launched a little over a year ago on February 10 on a United Launch Alliance Atlas V rocket from Cape Canaveral Air Force Station (now Space Force) and plunges into the sun again.
An ecliptic perpendicular view of SolO towards the inner solar system. Image credit: ESA
SolO’s orbit makes multiple passes near Venus, gradually placing it in an inclined orbit around the Sun, thus observing the elusive polar regions of our host star. With a seven-year main mission, SolO reached its first perihelion on June 15, 2020, at 0.46 astronomical units (AU) (48 million miles or 77 million kilometers) from the Sun. Ultimately, that distance will shorten to just 0.28 AU (26 million), 42 million kilometers from the Sun, inside to Mercury’s orbit. The primary scientific operations for SolO are slated to begin in October 2021.
Goals: Courage to touch the sun
From this point of view, SolO will take measurements of the emerging solar wind, which is believed to originate deep in the photosphere, as well as precise measurements of the solar corona and inner heliosphere. To do this, SolO must withstand blazing temperatures of up to 580 degrees Celsius and make useful scientific observations. It does this by looking through baffles that are cut into a 15-inch thick heat shield. The shield is coated with black calcium phosphate to help defeat the heat. The coating is actually an ancient material that was also used to make cave paintings tens of thousands of years ago during the Paleolithic Age. An example of old material that is now finding new use in the space age.
SolO in preparation for takeoff, with visible heat shield and instrument openings. Image credit: ESA
The previous mission completed a first pass of 7,500 km near Venus on December 27, 2020, flew through the ion and gas tails of comet C / 2019 Y4 ATLAS from May to June 2020, and published its first image of the sun last summer in July 2020.
Next, SolO will make a second flyby past Venus this coming August, within a few days after ESA’s BepiColombo mission, which is linked to Mercury, completed it. SolO’s single earth flyby 455 km away will be released later this year on November 27, 2021.
SolO takes a planet portrait of the inner solar system. Photo credit: ESA / SolO
Solar Mission Appeal
SolO joins NASA’s Parker solar probe and the STEREO A spacecraft in heliocentric solar orbit as well as the venerable joint ESA / SOHO mission at the L1 Lagrange point in the sun, which all keeps an eye on our host star. NASA’s Solar Dynamics Orbiter, ESA’s Proba-2 and JAXA’s Hinode continue to follow the sun in Earth orbit.
Tracking solar activity and understanding our host star is vital as the Artemis missions to get people back to the moon get underway. The current solar cycle number 25 also poses an odd puzzle, and the jury is not yet sure whether it is a lackluster phase like the last two previous cycles or an overperformance of historic proportions.
Whatever the future may bring, SolO will be at hand after it has reappeared from behind the sun, a witness to what our stormy host star does.
Main picture: An artistic impression of SolO. ESA / ATG Medialab