India's and Israel's moon-landing attempts both failed during descent - here's why the '15 minutes of terror' are so difficult
- India's Vikram moon lander, part of its Chandrayaan-2 mission, crashed into the lunar surface last week. It was the country's first attempt at a soft landing on the moon.
- The landing of Israeli nonprofit SpaceIL's Beresheet lander also failed in April.
- Descent and landing are difficult stages of a mission to the moon or any other planetary body - especially the final stages, which India's space-program director referred to as "15 minutes of terror."
- That's because landers must successfully carry out a series of complex commands with little room for failure, while contending with the moon's wonky gravity, uneven terrain, and pesky dust.
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India's attempt at a soft lunar landing appeared to end in a crash on September 6 (September 7 in India), making it the second failed moon landing this year.The mission's main spacecraft, Chandrayaan-2, has since spotted the Vikram lander's hapless hardware from its vantage point orbiting the moon. The lander arrived at the moon's south pole, seemingly in one piece, but India's space agency said it has been unable to restore communications.Advertisement
The crash came just five months after an Israeli nonprofit's lander, called Beresheet, crashed into the moon's surface. In both cases, the fatal errors occurred the final stages of descent.
Robert Braun, dean of the College of Engineering and Applied Science at the University of Colorado, has worked on landing and descent teams for multiple NASA missions to Mars."Among all the things we do in space, landing is one of the more challenging aspects, because time gets greatly compressed," he told Business Insider. "There's very little margin to try something again if it didn't happen as planned."
Here's why the final stages of a moon landing are so challenging.
If India's Vikram lander, part of its $140 million mission to the moon, had touched down successfully, the country would have become the fourth to soft-land on the moon.
But the lander diverged from its intended path 1.3 miles above the lunar surface and lost communication with spacecraft operators shortly after.Advertisement
The Beresheet lander, part of Israeli nonprofit SpaceIL's private moon mission, met a similar fate when it lost communications during its descent in April.
In both cases, the failed landings came down to issues in the final stages of descent. Kailasavadivoo Sivan, India's space-program director, had previously referred to this phase as "15 minutes of terror."Advertisement
"Once you initiate a landing sequence, you're committed. It's kind of like jumping out of a plane," Braun said. "Your parachute has to work."
At the most basic level, a lunar lander begins its descent by propelling itself out of the orbit of the moon and orienting itself in the right direction.Advertisement
As it gets very close to the surface, the spacecraft must slow down. This may be the point at which India's communications loss doomed its lander.
Ultimately, "it doesn't matter too much if the 24th event or the 42nd event is the source of the failure," Braun said. "There's probably a little bit more time to recover from a failure if it occurs early, but you may still not have the capability to actually recover."Advertisement
Just as Sivan talked of "15 minutes of terror," Braun said his Mars mission colleagues often talked about the final six or seven minutes of terror.
As a spacecraft approaches the moon's surface, it suddenly has to contend with wonky gravity and a rocky terrain.Advertisement
Landing teams watch readings that come back from a lander's instruments, checking that each step in the sequence is going as planned.
"When it goes well, I presume it's like winning the Super Bowl," Braun added. "And when it goes poorly, it just is bleak."Advertisement
Even moon dust, or regolith, can cloud a spacecraft's instruments and tip the scales towards failure.
The moon's uneven gravity can make the descent even more complicated.Advertisement
Neil Armstrong encountered the terrain problem firsthand. The Apollo 11 lunar module overshot its intended landing point on a smooth part of the moon's surface by 4 miles, and the new target was covered in large boulders.
The moon is littered with the remains of other crashes, including two unmanned US Surveyor probe missions from the 1960s, one of which lost contact with mission control just 2.5 minutes before its scheduled touchdown.Advertisement
Despite the apparent failure of India's moon landing, Braun said, it's important to remember that the country has now successfully launched two orbiters around the moon.
Next, India could team up with Japan to send a rover to the moon's south pole as early as 2023.Advertisement
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