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Ispace publishes results of its investigation into Hakuto-R1 lunar landing failure

Hakuto-R1 impact site, before and after
Before and after images of Hakuto-RI, taken by Lunar Reconnaissance
Orbiter (LRO). Click for original blink image.

Ispace today published the results of its investigation into the failure of its Hakuto-R1 lunar landed to touch down on the moon successfully, stating that the cause was a software error which thought the spacecraft was closer to the ground than it was.

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 accordance with expectations until about 1:43 a.m., which was the scheduled landing time.

During the period of descent, an unexpected behavior 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 kms above the lunar surface. 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 company believes the software got confused when the spacecraft crossed over the rim of Atlas Crater.

The resulting crash produced the debris seen by LRO to the right.

Genesis cover

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One comment

  • Edward

    The company believes the software got confused when the spacecraft crossed over the rim of Atlas Crater.

    The darnedest things happen during spaceflight. In this case, the software had not been prepared for the reality of the situation.

    From the linked article:

    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. … 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.

    This is why we learn by doing. It is no wonder that the Apollo astronauts took control of their lunar landers rather than let them land autonomously.

    It is also why care must be taken when deciding to change a plan. What may seem like a trivial change could have large ramifications.

    An example is the loss of Russia’s launch of Galileo 5 and Galileo 6, which used a Fregat upper stage:

    This failure was due to a temporary interruption of the joint hydrazine propellant supply to these thrusters.
    – The interruption in the flow was caused by freezing of the hydrazine.
    – The freezing resulted from the proximity of hydrazine and cold helium feed lines, these lines being connected by the same support structure, which acted as a thermal bridge.
    – Ambiguities in the design documents allowed the installation of this type of thermal “bridge” between the two lines. In fact, such bridges have also been seen on other Fregat stages now under production at NPO Lavochkin.
    – The design ambiguity is the result of not taking into account the relevant thermal transfers during the thermal analyses of the stage system design.

    Fregat had been designed for only one engine burn, in which case it did not matter the routing of the fuel line, and that is why the routing was not more carefully specified. No matter the fuel line configuration, it had always worked for missions with a single burn. However, Fregat started being used for missions with two burns, one to attain a parking orbit and another to raise the orbit. The time delay between burns meant that any Fregat that had its fuel line routed close to the helium feed lines should not be used for such a mission. Because changes in plans do not always come with top-down reviews of the entire system (they rarely do), no one realized the flaw in the system, and the mission was lost.

    It looks like something similar happened with Hakuto-R1. It was designed for one landing zone but assigned to another, for which it was not designed or tested.

    Starship is being designed with a certain amount of flexibility. Think of it as an automobile chassis that different bodies can be mounted upon (e.g. Chrysler’s K-car of the early 1980s). One Starship version is a “Pez” dispenser for Starlink missions, another is a tanker for refueling (retanking) missions, and yet another for regular orbital payloads. Another is for manned missions and another for manned lunar landing missions. Another for crewed Martian landing missions and another for cargo Martian landings. As with Fregat and Hakuto-R1, it would not work well to use a Starship for a mission it was not designed for.

    Scott Manley has a video on the Hakuto-R1 failure: (8 minutes)

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