Chang’e 4 (嫦娥四号) Lands on the Far Side of the Moon

Chang'e 4 landing site on the far side of the MoonAt 02:26 UTC on 2019-01-03, the Chinese Chang’e 4 (嫦娥四号) soft lander and rover touched down in the Von Kármán crater on the far side of the Moon.  This is the first soft landing on the far side of the Moon, which is never visible from the Earth.  Here is a video including animation of the landing and actual images captured during the descent and of the surface after landing.

The lander carries a rover and a number of experiments.  It was originally built as a back-up to the Chang’e 3 lander and rover which landed on the near side of the Moon on December 14th, 2013, becoming the first spacecraft to soft land on the Moon since the Soviet Luna 24 in 1976.

The major challenge in exploring the far side of the Moon is communicating with Earth.  You can’t transmit radio signals through the Moon, so the only way to provide a direct communications link is to place a relay satellite in a “halo orbit” around the Earth-Moon Lagrangian point 2 (L2).  On 2018-05-20, the Queqiao (鹊桥) satellite was launched into such an orbit (the first such relay established at the Moon).  It was only after this relay was checked out that Chang’e 4 was launched on 2018-12-07.

The landing site at 177.6° E, 45.5° S on the floor of Von Kármán crater, is a relatively flat and uncratered area, relatively easy to get into compared to the rugged highlands of much of the Moon’s far side.  Here is a synthetic image of the landing site from Earth and Moon Viewer, seen from 500 km above the Moon, with an “x” indicating the reported touchdown point.

Chang'e landing site

Here is an image of the Moon’s far side returned by the lander.

Image of the Moon's far side from Chang'e 4

Colour in this image should be taken cum grano salis.  The Moon is a pretty uniform dark grey colour, although the shade may appear different depending upon the Sun angle.  This picture was taken right after landing, and the camera’s white balance may not have yet been calibrated.

In addition to cameras on the lander and rover (which has not yet been deployed), there are instruments to study the solar wind and its interaction with the lunar surface, the composition of the surface, and a ground penetrating radar to explore the sub-surface.  The lander carries a sealed “biosphere” with seeds of potatoes, Arabidopsis, and silkworm eggs, with a camera to monitor growth.  One hopes that the silkworm experiment will end better than the introduction of the gypsy moth into North America in 1868.

You may hear reports in the legacy media that Chang’e 4 landed “near the Moon’s south pole”—this is nonsense. Von Kármán crater is at latitude 45.5° S, half way between the equator and south pole; it is no closer to the lunar south pole than Portland, Oregon is to Earth’s north pole.  The confusion is due to the landing site being within the South Pole-Aitken basin, an enormous (2500 km diameter) impact crater on the lunar far side.  Because the basin is so huge, it extends from the south pole to half way to the equator.

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Author: John Walker

Founder of Ratburger.org, Autodesk, Inc., and Marinchip Systems. Author of The Hacker's Diet. Creator of www.fourmilab.ch.

18 thoughts on “Chang’e 4 (嫦娥四号) Lands on the Far Side of the Moon”

  1. Interestingly, they chose to land when the Sun is near the zenith at the landing site.  Here is an image of the far side of the Moon at the time of the landing from Earth and Moon Viewer:

    Far side of the Moon at the time of Chang'e 4 landing

    The Apollo Moon landings were timed so the Sun angle was relatively low (usually around 13°) so that small craters and boulders which might interfere with the landing would be more visible.  I haven’t heard anything about Chang’e using any kind of active obstacle avoidance (and it’s targeted for a reasonably flat and unobstructed area, by lunar far side standards), so they probably opted for a time which would provide maximum solar power during the descent and landing.

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  2. It seems so simple task now to land a drone once you get it close enough to a landing spot. The lunar surface doesn’t have any wind or others things to complicate a landing does it?

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  3. The right side of the Chinese character is character for woman 女. The one on the left has the character for “I” 我. I wonder what it means.

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  4. 嫦娥四号

    The first two characters mean “goddess of the moon”. I take it to be a name in a story. The last two mean “four” and “number”. The character for moon is 月.

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  5. 10 Cents:
    It seems so simple task now to land a drone once you get it close enough to a landing spot. The lunar surface doesn’t have any wind or others things to complicate a landing does it?

    Here is a list of unmanned lunar landing missions (hard- and soft-landing) which got within the vicinity of the landing site.

    • Ranger 4 (US, April 1962) Failure: lunar impact
    • Ranger 6 (US, January 1964) Failure: lunar impact
    • Luna-5 (USSR, May 1965) Failure: lunar impact
    • Luna-7 (USSR, October 1965) Failure: lunar impact
    • Luna-8 (USSR, December 1965) Failure: lunar impact
    • Luna-9 (USSR, January 1966) Success
    • Surveyor 1 (US, May 1966) Success
    • Surveyor 2 (US, September 1966) Failure: lunar impact
    • Luna-13 (USSR, December 1966) Success
    • Surveyor 3 (US, April 1967) Success
    • Surveyor 4 (US, July 1967) Failure: lost contact
    • Surveyor 5 (US, September 1967) Success
    • Surveyor 6 (US, November 1967) Success
    • Surveyor 7 (US, January 1968) Success
    • Luna-15 (USSR, July 1969) Failure: lunar impact
    • Luna-16 (USSR, September 1970) Success
    • Luna-17 (USSR, November 1970) Success
    • Luna-18 (USSR, September 1971) Failure: lunar impact
    • Luna-20 (USSR, February 1972) Success
    • Luna-21 (USSR, January 1973) Success
    • Luna-23 (USSR, October 1974) Failure: landed, but sample return failed
    • Luna-24 (USSR, August 1976) Success
    • Chang’e 3 (China, December 2013) Success
    • Chang’e 4 (China, January 2019) Success

    Total: 24 landing attempts, 10 failed, 14 succeeded.  Batting average .417 .583.  This does not include the many attempts which blew up before reaching Earth orbit, failed to reach the Moon, or missed the Moon entirely.

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  6. John Walker:

    10 Cents:
    It seems so simple task now to land a drone once you get it close enough to a landing spot. The lunar surface doesn’t have any wind or others things to complicate a landing does it?

    Here is a list of unmanned lunar landing missions (hard- and soft-landing) which got within the vicinity of the landing site.

    • Ranger 4 (US, April 1962) Failure: lunar impact
    • Ranger 6 (US, January 1964) Failure: lunar impact
    • Luna-5 (USSR, May 1965) Failure: lunar impact
    • Luna-7 (USSR, October 1965) Failure: lunar impact
    • Luna-8 (USSR, December 1965) Failure: lunar impact
    • Luna-9 (USSR, January 1966) Success
    • Surveyor 1 (US, May 1966) Success
    • Surveyor 2 (US, September 1966) Failure: lunar impact
    • Luna-13 (USSR, December 1966) Success
    • Surveyor 3 (US, April 1967) Success
    • Surveyor 4 (US, July 1967) Failure: lost contact
    • Surveyor 5 (US, September 1967) Success
    • Surveyor 6 (US, November 1967) Success
    • Surveyor 7 (US, January 1968) Success
    • Luna-15 (USSR, July 1969) Failure: lunar impact
    • Luna-16 (USSR, September 1970) Success
    • Luna-17 (USSR, November 1970) Success
    • Luna-18 (USSR, September 1971) Failure: lunar impact
    • Luna-20 (USSR, February 1972) Success
    • Luna-21 (USSR, January 1973) Success
    • Luna-23 (USSR, October 1974) Failure: landed, but sample return failed
    • Luna-24 (USSR, August 1976) Success
    • Chang’e 3 (China, December 2013) Success
    • Chang’e 4 (China, January 2019) Success

    Total: 24 landing attempts, 10 failed, 14 succeeded.  Batting average .417 .583.  This does not include the many attempts which blew up before reaching Earth orbit, failed to reach the Moon, or missed the Moon entirely.

    I didn’t make my point very well. In the old days landing things was hard but recently with modern technology it has become routine. There can be a lot of sensors and computing power put on light weight chips. Just as self-driving cars are not so special, I think landing once you are close enough to the moon is not that special. Getting near there is still special.

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  7. John Walker:

    10 Cents:
    It seems so simple task now to land a drone once you get it close enough to a landing spot. The lunar surface doesn’t have any wind or others things to complicate a landing does it?

    Here is a list of unmanned lunar landing missions (hard- and soft-landing) which got within the vicinity of the landing site.

    • Ranger 4 (US, April 1962) Failure: lunar impact
    • Ranger 6 (US, January 1964) Failure: lunar impact
    • Luna-5 (USSR, May 1965) Failure: lunar impact
    • Luna-7 (USSR, October 1965) Failure: lunar impact
    • Luna-8 (USSR, December 1965) Failure: lunar impact
    • Luna-9 (USSR, January 1966) Success
    • Surveyor 1 (US, May 1966) Success
    • Surveyor 2 (US, September 1966) Failure: lunar impact
    • Luna-13 (USSR, December 1966) Success
    • Surveyor 3 (US, April 1967) Success
    • Surveyor 4 (US, July 1967) Failure: lost contact
    • Surveyor 5 (US, September 1967) Success
    • Surveyor 6 (US, November 1967) Success
    • Surveyor 7 (US, January 1968) Success
    • Luna-15 (USSR, July 1969) Failure: lunar impact
    • Luna-16 (USSR, September 1970) Success
    • Luna-17 (USSR, November 1970) Success
    • Luna-18 (USSR, September 1971) Failure: lunar impact
    • Luna-20 (USSR, February 1972) Success
    • Luna-21 (USSR, January 1973) Success
    • Luna-23 (USSR, October 1974) Failure: landed, but sample return failed
    • Luna-24 (USSR, August 1976) Success
    • Chang’e 3 (China, December 2013) Success
    • Chang’e 4 (China, January 2019) Success

    Total: 24 landing attempts, 10 failed, 14 succeeded.  Batting average .417 .583.  This does not include the many attempts which blew up before reaching Earth orbit, failed to reach the Moon, or missed the Moon entirely.

    My friend Bill Mellberg’s Dad built the Surveyor camera.

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  8. Scott Manley has taken the 10 frames per second video of the landing released by the Chinese National Space Administration and processed it with the butterflow interpolation algorithm to make a smooth motion video, then analysed the view by comparison with Lunar Reconnaissance Orbiter imagery (the same used by Earth and Moon Viewer for the synthetic images in previous comments) to determine precisely where the landing occurred.

    This is the first I’ve heard that Chang’e 4 used an active obstacle avoidance mechanism to choose its landing site.  It killed most of its orbital velocity and then descended to a hover, at which point it scanned the terrain below with a LIDAR instrument to choose a flat region free of obstacles, where it then steered for the final landing.  In the last moments before landing you can see lunar dust flying outward due to impingement of the engine plume.

    There is also video of the deployment of the rover and its first travel on the lunar surface.

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