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China Eyes Extended Mission Beyond Moon
by Morris Jones
Sydney, Australia (SPX) Oct 12, 2010

With plenty of fuel onboard Chang'e 2, one option for an extended mission would be to explore the Lagrange points in the Earth-Moon system, before heading out further into heliocentric orbit.

The mysteries surrounding the mission of China's Chang'e 2 moon probe are gradually being solved. Prior to the launch, China was exceptionally shy about revealing many details of the mission, including the launch vehicle. This led some analysts, including the author, to wonder what was being left out of the public domain.

Thankfully, we now know more about the souped-up launch and the course of the mission. Chang'e 2 does not seem to be a radically different spacecraft from its sister, Chang'e 1, which was launched to the Moon in 2007. In theory, China could still have launched this bird to the Moon with the same Long March 3A launch vehicle used for Chang'e 1.

However, the upgrade to the more powerful Long March 3C rocket does produce its advantages. It leaves Chang'e 2 well stocked with fuel. The mission hadn't reached the final stages of countdown when China's state media began to discuss this, suggesting a great deal of confidence in the fuel surfeit. The confidence was so high that the media was openly speculating that the spacecraft would leave lunar orbit at the end of its primary mission.

What a surprise! Prior to this, it seemed to be a solid assumption that Chang'e 2 would end its mission with a controlled impact into the Moon, just like the first mission. Such is the fate of almost every object placed into lunar orbit.

The notable exceptions to this rule were the Apollo spacecraft sent on manned lunar missions, which came back to Earth, and the Clementine spacecraft, a small US-built lunar orbiter. Clementine flew a similar mission profile to a Chang'e orbiter, mapping the Moon globally. Controllers later steered it out of lunar orbit, hoping to fly past the asteroid Geographos. Sadly, Clementine malfunctioned soon after being dispatched towards its second target, and never made the rendezvous.

Chinese media have spoken of different options for a post-primary mission for Chang'e 2. Evidently, controllers are keeping their options open. Exactly what happens to Chang'e in another six months will probably depend on the exact amount of fuel left, the state of the spacecraft, and the outcome of some conscientious debate that's probably already underway.

The easiest plan would be to remain in lunar orbit for an extended mission. This could be useful if China wants to closely reconnoiter more areas at close range. The orbit could be shifted to dip downwards at several key areas, enabling high-resolution photos to be taken.

A catalogue of potential landing sites for future missions could be built up this way. Closer studies of the polar regions of the Moon, which currently hold such a strong fascination for space scientists, would be welcomed.

One article mentions "landing on the Moon", which does not seem realistic for a spacecraft like this. Chang'e 2 has no landing gear and would not function well even after a gentle descent to the surface.

Another option is to return to Earth and enter Earth orbit. This doesn't sound exciting or useful. It's useful if one wants to observe the Earth from space, or probe the properties of near-Earth space. But China has already done this well with a flotilla of dedicated satellites. There seems to be little novelty or scientific gain in doing this.

The most ambitious option would be to fly the spacecraft well beyond the Moon, into heliocentric orbit, where it would enter the domain of the planets. This has engineering advantages, allowing China to run communications tests at vast distances, as well as checking the performance of the spacecraft and its instruments in deep space.

There would also be some modest scientific gains to be made from particles and fields experiments. Examining the Earth and Moon together from a distant viewpoint could also provide insight into the Earth-Moon system.

It's possible that Chang'e 2 could be targeted for a rendezvous with a near-Earth asteroid, but this would require carful attention to trajectory windows. It's possible that no practical course to such an object will be feasible in the near-term.

Another option for an extended mission for Chang'e 2 could be to explore the Lagrange points in the Earth-Moon system.

Most space and sci-fi fans know the Lagrange points. They are a series of imaginary points in space where the gravitational fields of two large bodies are produce stable regions for spacecraft. There are five points, named L1 to L5, for any two-body system such as the Earth and Moon. Right now, two NASA spacecraft are exploring the L1 and L2 points of the Earth-Moon system.

This is the Artemis mission, which started when two spacecraft from the Themis constellation of particle/field exploration satellites were flown out of ordinary Earth orbits and sent to the Moon. L1 is a point on a line between the Earth and Moon. L2 lies on the same line, but is on the opposite, far side of the Moon.

The two most famous Lagrange points are L4 and L5. These are not exactly in a straight line between the Earth and Moon. One is close to the Moon and slightly to the left. The other is to the right. The off-balance nature of these points is caused by the fact that the Moon is moving in its orbit around the Earth.

L4 and L5 have been celebrated as potential locations for deep space industries, smelting rocks launched from the surface of the Moon into metal, glass and concrete. The result of this industry would be the construction of huge space colonies in the same regions of space.

Despite their attractions, the Lagrange points remain unexplored. Admittedly, there is little there to see, as these are just areas in space. But we should know more. Japan's first lunar mission, Hiten, passed through one of the points on its way to the Moon, hoping to sample dust impacts with a small instrument. As far as this author knows, there has been no other in-situ space experiment performed at these points.

Sending Chang'e 2 to L4 and L5 for an extended period would have some historical importance, as the first proper exploration of this area of space. It would also allow us to see if the region is really as empty as we think. Dust and other debris could lurk there. We could also gain a proper understanding of the gravitational perturbations that would be experienced by anything placed in orbit around these points.

There's always the chance that Chang'e 2 could fly a three-stage mission. It could finish its primary mission in lunar orbit, then move to a Lagrange point, then fly off into heliocentric orbit. Alternatively, it could explore both L4 and L5, comparing any differences between the regions.

Dr Morris Jones is an Australian space analyst and author. Email Replace NOSPAM with @ to send email.


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China's second lunar probe enters moon's orbit: state media
Beijing (AFP) Oct 9, 2010
China's second lunar probe entered the moon's orbit on Saturday, eight days after the Long March 3C rocket carrying the Chang'e-2 blasted off from the launch centre, state media reported. The unmanned probe will start "scientific exploration activities soon," said the official Xinhua news agency, citing the Beijing Aerospace Control Center. The Chang'e-2 will first circle the moon at a d ... read more

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