European Space Agency (ESA) engineers have upgraded the Large Space Simulator (LSS) at the European Space Research and Technology Center (Estec) to prepare for the upcoming BepiColombo mission to Mercury, where the spacecraft will encounter temperatures much hotter than those found at planets further from the Sun.
Mercury’s orbit takes it within 46 million km. (29 million mi.) of the Sun, while Earth averages about 150 million km. (93 million mi.).
That means spacecraft orbiting the innermost planet must endure temperatures on the order of 350C from the Sun itself, and heat reflected from the planet’s surface that is literally hot enough to fry eggs.
To ensure that BepiColombo’s thermal protection system can handle the extreme environment around Mercury, ESA has modified the LSS to simulate 10 solar constants — 10 times the amount of energy passing through a square meter of space at Earth’s orbit every second.
Previously, the LSS could simulate only two solar constants — adequate for ESA probes like Mars Express and Venus Express but not up to the task of qualifying BepiColombo.
To jack up the heat, engineers have been running the heat lamps that provide the “sunlight” in the LSS thermal vacuum changer at full power, and have shifted the mirrors reflecting the infrared light onto the spacecraft being tested so it produces a cone 2.7 meters in diameter at the test article, instead of a parallel beam 6 meters across.
The first tests with the upgraded system involved the mission’s Mercury Magnetospheric Orbiter, supplied by Japan to measure the planet’s magnetosphere for comparison to the one at Earth. The 250-kg. (550-lb.) octagonal spacecraft is protected by an ESA sunshield, which performed as planned in test temperatures above 350C.
“The sunshield test was successful,” says Jan van Casteren, BepiColombo project manager. “Its function to protect the MMO spacecraft during the cruise phase was demonstrated.”
Next up in the LSS at the Estec facility in The Netherlands will be ESA’s Mercury Planetary Orbiter, which will dip to within 400 km. of the planet’s surface on its elliptical mapping orbits, facing severe temperatures at both extremes of its orbital altitude. Based on testing with the Japanese vehicle, some adjustments will be needed before the MPO enters the test chamber next year, according to van Casteren.
BepiColombo is scheduled for launch on an Ariane 5 in summer 2014. NASA’s Messenger spacecraft, which already has made six flybys of Mercury, is on track for an insertion maneuver March 18 that will make it the first probe to enter orbit there.
Like the European spacecraft, Messenger is protected from the harsh environment at Mercury by a sunshade, radiators, one-way heat pipes and multilayered insulation that has kept the temperature behind it at about 70F, eliminating the need for high-temperature electronic components.