HAKUTO-R lunar mission: Here's what happened
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HAKUTO-R lunar mission results announced, here’s what happened

HAKUTO-R lunar mission results announced, here’s what happened

The analysis reveals that the cause of the lander’s failure to make a soft landing was due to the software, especially in the phase just prior to landing

Hakuto mission mapped image credit ispace

Japanese lunar exploration company, ispace reviewed and completed the flight data analysis from its HAKUTO-R Mission 1 landing sequence on April 26.

The flight data was obtained by operations specialists at ispace’s Mission Control Center in Nihonbashi, Tokyo.

The analysis revealed that the lander, which was carrying UAE’s Rashid rover, fully completed the entire planned deceleration process, slowing to the target speed of less than 1 m/s in a vertical position at an altitude of approximately 5 kilometres above the lunar surface.

Although the lander did not complete a soft landing, the cause has been identified and improvements are being incorporated into Mission 2 and Mission 3, ispace said in a statement.

HAKUTO-R lander believed to have “free-fallen” to the Moon

On April 26, 2023, at 00:40 Japan Standard Time, the lander began the descent sequence from an altitude of around 100 kilometres above the Moon’s surface. At the end of the planned landing sequence, it approached the lunar surface at a speed of less than 1 m/s. The operation was confirmed to have been in line with expectations until about 1:43am, which was the scheduled landing time.

During the period of descent, an “‘unexpected behaviour” occurred with the lander’s altitude measurement. While the lander estimated its own altitude to be zero, or on the lunar surface, it was later determined to be at an altitude of approximately 5 kilometres above the lunar surface, ispace said.

After reaching the scheduled landing time, the lander continued to descend at a low speed until the propulsion system ran out of fuel. At that time, the controlled descent of the lander ceased, and it is believed to have free-fallen to the Moon’s surface.

The reason for failure

The most likely cause of the lander’s incorrect altitude estimation was that the software did not perform as expected, ispace revealed.

Based on the review of the flight data, it was observed that, as the lander was navigating to the planned landing site, the altitude measured by the onboard sensors rose sharply when it passed over a large cliff approximately 3 kilometres in elevation on the lunar surface, which was determined to be the rim of a crater.

According to the analysis of the flight data ispace provided, a larger-than-expected discrepancy occurred between the measured altitude value and the estimated altitude value set in advance. The onboard software determined in error that the cause of this discrepancy was an abnormal value reported by the sensor, and thereafter the altitude data measured by the sensor was intercepted. This filter function, designed to reject an altitude measurement having a large gap from the lander’s estimation, was included as a robust measure to maintain stable operation of the lander in the event of a hardware issue including an incorrect altitude measurement by the sensor.

“One major contributing factor to this design issue was a decision to modify the landing site after critical design review completed in February 2021. This modification influenced the verification and validation plan despite numerous landing simulations carried out before the landing. ispace as the mission operator maintained overall programme management responsibility and took into account the modifications in its overall analysis related to completing a successful mission. It was determined that prior simulations of the landing sequence did not adequately incorporate the lunar environment on the navigation route resulting in the software misjudging the lander’s altitude on final approach,” ispace said in a statement.

Based on the fact that communications will not be reestablished with the lander, it has been concluded that the completion of the Mission 1 Milestones Success 9 (completion of the lunar landing) and Success 10 (establishment of stable conditions after landing), could not be achieved, and customer payloads could not be operated after the landing. During Mission 1, the HAKUTO-R lunar lander completed Success 1 through Success 8 of the Mission 1 milestones (see below).

Work on Mission 2 and Mission 3 has begun

Takeshi Hakamada, founder and CEO of ispace, said: “Mission 1 demonstrated a great deal of technical reliability, as our lander reached the lunar surface just prior to landing. Now, we have been able to identify the issue during the landing and have a very clear picture of how to improve our future missions. While it is unfortunate that we were not able to fully meet the expectations of all our stakeholders, including our customers, all of us at ispace are proud of what we accomplished in Mission 1 and are very positive about what we can accomplish.”

Hakamada said the company has already begun work on Mission 2 and Mission 3. “We are prepared to face the challenges and make every effort to improve. We will ensure that the valuable knowledge gained from Mission 1 will lead us to the next stage of evolution. We believe that this is our commitment and our duty to all our stakeholders. ‘Never Quit the Lunar Quest’ In this spirit, we will continue to move forward.”

The information gleaned will be considered for software design, as well as upgrades and expansion of the scope of preparatory simulations of the landing sequence for ispace future missions, including Mission 2 and Mission 3, to improve the accuracy of landing sequences.

On May 23, NASA shared images from its Lunar Reconnaissance Orbiter of the supposed impact site of the ispace HAKUTO-R Lander.


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