Japan has become the fifth country to land a craft on the moon, but problems with its solar panels mean the mission hangs in the balance.
Dubbed the “moon sniper”, the Smart Lander for Investigating Moon (SLIM) probe was attempting a risky landing on a slope at the rim of a crater using “precision” technology.
While the craft landed at about 3.20pm UK time and can communicate with the team on Earth, it cannot generate its own energy – potentially because its solar panels are angled incorrectly.
It means SLIM is relying on its own battery – with 74% charge at the time of landing – and could only have a few hours left.
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Why does Japan want to land on the moon?
The Japan Aerospace Exploration Agency (JAXA) hopes a shift in the sunlight’s angle will hit the panels in a way that can restore its functions.
“It takes 30 days for the solar angle to change on the moon,” Hitoshi Kuninaka, the head of JAXA’s research centre, told reporters after the landing.
“So, when the solar direction changes, and the light shines from a different direction, the light could end up hitting the solar cell.”
Most moon landings – which had only been achieved by the United States, Russia, China and India – aim for a spot within an accuracy of several kilometres.
But SLIM tried to land within 100m of its target, which Mr Kuninaka said was “most certainly achieved”, according to trace data, though its specific location won’t be known for a month.
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SLIM’s heater has been turned off as the team tries to conserve power and Mr Kuninaka said they want to keep the “status quo” for the moment while they wait for more accurate information.
It’s impossible to know what might have gone wrong – at least for now
Until we get another update from JAXA it’s impossible to know what might have gone wrong with the SLIM lander.
However, there was an indication in the news conference that power problems could be because the solar cells aren’t orientated correctly.
One potential cause of that is that SLIM landed the wrong way up.
One of the design choices was for the probe to touch down on two shock absorbing feet and then flop down like a domino onto its other feet.
A problem at the moment of landing, or with the slope of terrain on which it landed could have led to the lander toppling the wrong way leaving the solar cells pointing at the ground rather than the sky.
More data, and hopefully an image of the landing would tell the mission engineers more, but given their need to ration power it’s likely to be a week before we know more.
How did it land?
As the probe descended onto the surface, it was designed to recognise where it was flying by matching its camera’s images with existing satellite photos of the moon.
This “vision-based navigation” is what gives it the ability for a precise touchdown, JAXA has said.
Shock absorbers make contact with the lunar surface in a “two-step landing” method, with the rear parts touching the ground first, followed by the entire body gently collapsing forward and stabilising.
On landing, JAXA said SLIM deployed two mini-probes – a hopping vehicle as big as a microwave oven and a tennis ball-sized wheeled rover – that would have taken pictures of the spacecraft.
SLIM was launched in September and has taken a fuel-efficient four-month journey to the moon.
