At 8:51 a.m. on December 25 (Spanish peninsular time), the Japanese space agency JAXA officially announced that the SLIM mission, which had left Earth in September, had successfully entered the orbit of the Moon and that the ship was "in normal conditions".
Over the next few days, the engineers responsible for the mission will adjust the trajectory of the SLIM several times to prepare for the final lift-off maneuver, scheduled for 4:20 p.m. on January 19. The operation will be carried out with unprecedented precision so that the spacecraft manages to touch the lunar soil with a maximum deviation of 100 meters on the intended target, on the edge of the Shioli crater, a place where rocks from the lunar layer would be found and of great scientific interest. If successful, Japan will become the fifth country to land on the moon, after the US, the former Soviet Union, China and India.
According to the data provided by the space agency JAXA, the entry into orbit of the Moon of the SLIM has been made with a very elongated polar elliptical trajectory that, at the lowest point (called perilunium ), reaches up to 600 km high and rises to 1,200 kilometers in the apoluni or farthest point.
From now on, and during the next few days, the route of the ship will be adjusted to reach a circular orbit of 600 km high, which will be corrected again until it enters a new ellipse that will place the SLIM only 15 km above the surface of the Moon in the perilunium and with a speed of 1,700 meters per second. This will be the position from which the final descent maneuver is attempted. The spacecraft will use an autonomous navigation system, which will compare the vision during the descent with the set of maps that a previous Japanese mission, called Selene, captured in 2007. Throughout the maneuver, an onboard radar will constantly monitor the altitude of the SLIM, and the last meters a laser device will allow to obtain high precision readings of the height and carry out the necessary automatic adjustments. The objective is to achieve a distance no more than 100 meters away from the planned site, on the edge of the Shioli crater. This level of precision is unprecedented in lunar operations and, to achieve this, JAXA has developed special algorithms to process with great speed and accuracy the bank of images that will be used as a guide.
If all goes well, the SLIM will move away with the help of devices capable of absorbing most of the impact against the surface. The maneuver faces the challenge of landing in a place that is inclined about 15 degrees.
The place chosen for the descent of the SLIM is an impact crater of about 270 meters in diameter located in mid-latitudes, to the southeast of the visible face of the Moon. The choice of the target has been based on the data collected by the Selene mission, which suggest that at the edges of the Shioli crater there would be exposed minerals that come from the lunar layer. To carry out the planned studies, SLIM is equipped with a camera capable of observing objects up to 30 meters away and which will use various filters to analyze how the exposed rocks reflect sunlight and learn about, thus, the composition. The mission will need to be able to complete the analyzes in the span of one lunar day period (equivalent to about two Earth weeks), since the spacecraft's electronics are not prepared to survive the low temperatures of the long lunar night (which go down to -130ºC).
