Japan launches moon lander and X-ray observatory

HELSINKI — Japan sent a new X-ray space telescope into low Earth orbit and a first, small lunar lander on its way to the moon with a single launch late Wednesday.

A Mitsubishi Heavy Industries H-2A rocket in a figuration with a pair of SRB-A3 solid boosters lifted off from Japan’s Tanegashima Space Center at 7:42 p.m. Eastern, Sept. 6, heading East over the Pacific Ocean. A previous launch attempt was scrubbed Aug. 27.

The rocket carried within its 4-meter-diameter fairing the Smart Lander for Investigating Moon (SLIM) for the Japan Aerospace Exploration Agency (JAXA), and XRISM, a joint JAXA/NASA X-ray observatory with participation from the European Space Agency.

XRISM separated from the second stage 14 minutes after liftoff, entering a roughly 550 x 500-kilometer orbit inclined by 31 degrees. The second stage performed an apogee-raising burn around 46 minutes after liftoff, with SLIM separating from the stage a minute later.

SLIM won’t be taking a direct route to the moon. After a lunar transfer orbit burn, it will make a lunar flyby, heading into a wide loop away from the Earth-moon system and returning to enter lunar orbit in around four months’ time. This route allows for a smaller burn to enter lunar orbit, saving propellant and mass. 

SLIM will then orbit the moon for around a month before making its 20-minute descent and landing attempt, with the aim of demonstrating a lightweight landing capability with high accuracy.

XRISM is a replacement for Japan’s Hitomi space science observatory, which was lost following an attitude control failure a month after its launch in 2016, resulting in the spacecraft breaking apart

The eight meters long, three-meter-diameter and 2,300-kilogram spacecraft carries a soft X-ray spectrometer and soft X-ray imager. The telescope will spend three years collecting high spectral resolution data of hot plasma clouds enveloping galaxies and extremely energetic cosmic phenomena such as supernovae and accreting supermassive black holes.

XRISM undergoing acoustic tests. Credit: JAXA

Main goals of XRISM are studying how matter and energy move through galaxies and gaining insights into the evolution of the structure of the universe.

XRISM’s “Resolve” X-ray microcalorimeter spectrometer was developed by a team led by NASA’s Goddard Space Flight Center. It will operate at 273.1 degrees Celsius, cooled by liquid helium. This requirement limits the lifetime of the mission, though it may be extended by mechanical cooling.

“We’ve been working to get an X-ray microcalorimeter camera in orbit since the 1990s,” Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics told SpaceNews. “It will give us unprecedented detail on the physical state of the million-degree hot gas in clusters of galaxies and black hole accretion disks, including the composition of the gas and, using the Doppler effect, how fast it is moving.

“Although XRISM won’t have the sharp vision (high spatial resolution) of Chandra or XMM, its high spectral resolution—like hyperspectral imagers on Earth observing satellites—will be a game changer. It’s also an important test of the calorimeter in advance of the next generation of high-spatial-resolution X-ray telescopes.”

Moon sniper

SLIM meanwhile aims to make Japan the fifth country to soft land on the moon. The launch comes just two weeks after India became the fourth nation with the successful Chandrayaan-3 mission landing near the south pole, as well as Russia’s Luna 25 lander which crashed into the moon following a failed orbital maneuver.

The 200 kg dry mass lander aims to demonstrate a small, lightweight landing system and pinpoint landing technology.

SLIM, also referred to as “Moon Sniper,” aims to set down within 100 meters of its target point using vision-based navigation. The lander carries observational data from the SELENE orbiter which will be compared to features detected during the autonomous descent and landing. This will greatly reduce the landing ellipsis, or region within which a probe is expected to land based, which is usually on the order of kilometers.

The spacecraft will use a laser range finder, landing radar and navigation camera for the landing attempt, and carries two main 500N engines and 12 smaller engines.

SLIM will also release two small probes, named Lunar Excursion Vehicles (LEV), immediately before landing to record the landing site and demonstrate autonomous exploration. 

Illustration showing how SLIM intends to land on the moon. Credit: JAXA

The lander has five, crushable aluminum lattice legs which will help absorb the impact of landing. The design will help it land on a slope within Shioli crater at 25.2E, 13.3S on the moon’s near side.

SLIM carries a multi-band camera and a spectroscopic camera to examine surface composition, as well as a passive laser retroreflector array. It will carry out these tasks until the onset of lunar night, bringing an end to the mission.

The performance of SLIM landing technology will have relevance for a future mission. The joint Indian Space Research Organisation (ISRO) and JAXA Lunar Polar Exploration Mission (LUPEX) is expected to launch later this decade.

Japanese company ispace failed with a moon landing attempt with its HAKUTO-R M1 lunar lander earlier this year.

Wednesday’s launch was one of the final missions for the H-2A, which is scheduled to be replaced by the new H3 rocket. That launcher’s first flight failed however earlier this year, bringing a delay of months to the SLIM/XRISM launch.

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