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SLIM leaves Earth orbit and is on its way to the Moon

SLIM's planned route to the Moon

The Japanese lunar lander SLIM fired its engines on September 30, 2023 to begin its journey to the Moon. The map to the right indicates the planned route after this trans-lunar injection burn, first flying past the Moon to put it on a trajectory that will bring it back to the Moon at the proper speed and direction for its landing several months hence.

The main goal of this mission is engineering, to test the ability of an autonomous unmanned spacecraft to land precisely within a small target zone about 300 feet across. If proven, this ability will make it possible to send unmanned landers to many places that are presently impossible due to their rough topography.

The route that SLIM is taking to the Moon is also unusual, and is probably also an engineering test of its own. Flybys of planets to change a spacecraft’s path is not a new technique, but in the past it has been used to slingshot the probe to another object, not send it back to that planet.

Genesis cover

On Christmas Eve 1968 three Americans became the first humans to visit another world. What they did to celebrate was unexpected and profound, and will be remembered throughout all human history. Genesis: the Story of Apollo 8, Robert Zimmerman's classic history of humanity's first journey to another world, tells that story, and it is now available as both an ebook and an audiobook, both with a foreword by Valerie Anders and a new introduction by Robert Zimmerman.

The ebook is available everywhere for $5.99 (before discount) at amazon, or direct from my ebook publisher, ebookit. If you buy it from ebookit you don't support the big tech companies and the author gets a bigger cut much sooner.

The audiobook is also available at all these vendors, and is also free with a 30-day trial membership to Audible.

"Not simply about one mission, [Genesis] is also the history of America's quest for the moon... Zimmerman has done a masterful job of tying disparate events together into a solid account of one of America's greatest human triumphs."--San Antonio Express-News


  • Edward

    Robert wrote: “The route that SLIM is taking to the Moon is also unusual, and is probably also an engineering test of its own. Flybys of planets to change a spacecraft’s path is not a new technique, but in the past it has been used to slingshot the probe to another object, not send it back to that planet.

    Scott Manley explains the use of these strange or unexpected routes to the Moon. (14 minutes)

    It seems that with computing power at the level we have these days, we don’t necessarily have to solve the three body problem (or, in this case, a four body problem: Earth, Moon, Sun, and spacecraft*) to find new and unusual — but useful — orbits. Manley does not have an example of using the Moon in the way Robert described: slingshot the probe with the Moon to send it back to the Moon. This may be a first.

    Notice that these strange orbits take weeks and months to reach the Moon, rather than the three days that Apollo missions took. The advantage is that less propellant is required; the disadvantage is that more time is required.
    * The two-body problem is easily solved. It is a simple inverse-square law solution that results in elliptical orbits. The Lagrange Points are a specific solution to the three-body problem, and as Manley shows, it is not a simple solution, but has some locations and concepts that are fairly easily understood.

  • Jeff Wright

    I wonder if ISS could be sent out of Earth’s orbit gradually…a Starship giving a constant but gentle push.

  • Cloudy

    If you want a “gentle but constant push” you don’t need chemical rockets such as those used on the starship. You need some high-ISP, low thrust system like an ion drive. The ISS can provide plenty of energy to power it.

    On the other hand, ISS was designed for low earth orbit. Period. Adapting it for someplace else would cost so much you might as well build a new station. The radiation environment is different. The thermal environment is different. The ISS’s resupply needs are also a problem. The first long term habitat for humans in deep space will have to be purpose built, since moving the ISS carries too much additional risk. Its hard enough to do new things in newly built hardware By the time human occupied deep space stations are proven, the ISS will likely be at least a decade older and still in its present location. Or it will be taken apart and used on other LEO stations.

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