by Morris Jones
Sydney, Australia (SPX) Sep 28, 2010
As we approach the launch of China's second Moon mission on October 1, some major questions about the spacecraft and its launch vehicle remain unanswered. China's media has been generally low-key about covering the upcoming flight. There has been little recent talk in China's major newspapers, despite the supposed impending launch.
That's a bit strange for a nation that loves to trumpet its spaceflight achievements. Coverage was better for the Chang'e 1 mission, China's first Moon orbiter, in 2007. Admittedly, doing a similar mission again isn't as historically significant, but we should still expect more coverage.
Why is Chang'e 2 so publicity-shy? Perhaps it reflects a general tightening of security around China's spaceflight activities. China recently launched a high-resolution spy satellite. The launch was admitted, but there was little coverage of this sensitive mission. Security concerns for this launch could have prompted a general fall of the curtain on all space activities in recent weeks.
Lately, China has also been preoccupied with the detention of a Chinese sea captain by Japanese authorities. The politics of this dispute won't be explored here, but it's been a major story in China and elsewhere. Perhaps the heavy news coverage of this incident pushed other stories off the pages.
There's another mystery that goes against the previous expectations of this reporter, and others in the aerospace community. For years, we expected that the Chang'e 2 probe would be launched aboard a Long March 3A rocket, just like its predecessor.
These Chinese themselves supported this conclusion for some time. But things have changed. Photographs posted to the Internet of the upcoming launch show that this is not the case, and muddled reporting in China's People's Daily newspaper also suggests a new rocket.
Internet photographs suggest that the Chang'e 2 orbiter will be launched by a Long March 3C rocket, a more powerful launch vehicle. Why has China made this change, when the spacecraft itself is supposedly almost identical?
It could be the case that Chang'e 2 has gained more weight than Chang'e 1. No statement released by the Chinese allows this to be determined, and even if the spacecraft were a little heavier, it could still possibly be lofted by the Long March 3A.
If there have been major weight gains, they could have come in the form of an impactor probe, which is known to be carried on this mission. This is a small module that will detach from Chang'e 2 and de-orbit, hitting the lunar surface and creating an impact. The results of the impact will apparently be observed from Chang'e 2.
If the impactor is to produce a significant event on the surface, there's a good chance that it will need to strike with a lot of force. This could require a heavy object, or a strongly powered flight into the ground, or both. Both the impactor and its de-orbit engine could both be heavy.
Another potential source of weight could be on-board fuel. China is planning to fly the spacecraft in a much lower orbit than its predecessor. More fuel could be needed to counteract orbital perturbations in the Moon's irregular gravitational field.
Let's suppose, on the other hand, that Chang'e 2 isn't really heavier than her sister. Why do we need such a big increase in the lifting capacity?
China has regularly stated that Chang'e 2 will fly to the Moon more quickly than Chang'e 1, a feat that seems easily achieved with more power. By itself, this doesn't seem like enough of a reason to switch rockets. There was nothing wrong with Chang'e 1's time of flight to the Moon, which took less than two weeks.
This is easily managed by controllers and the spacecraft. In a previous article, I suggested that a faster flight could reduce the exposure to Earth's radiation belts, but this seems like a minor issue too.
Let's take a look at the Long March 3C rocket. This is a big step up from the Long March 3A, even though it's in the same family of vehicles. The Long March 3C has the same first stage as the Long March 3A, but it uses a more powerful second stage, and also has two strap-on booster rockets attached to the first stage.
The Long March 3A lofts around 2,600 kilograms to Geostationary Transfer Orbit, while the Long March 3C lofts 3,800 kilograms to GTO. That's a big jump in payload capacity!
Perhaps this extra lifting capacity is genuinely needed. There are no mass figures on Chang'e 2 in the public domain, and no detailed diagrams or photos of the spacecraft. China may be hiding something here.
There could be some foresight for future missions involved. The next generation of Chinese lunar missions will be landers. The first one, expected for launch in 2013, will fly on board a Long March 3B rocket. Despite the lower alphabetical order, this is actually more powerful than the Long March 3C. Here's the family tree.
The Long March 3B was developed first. It's a very powerful rocket, with four strap-on boosters, and carries a whopping 5,100 kilograms to Geostationary Transfer Orbit. The Long March 3C rocket is almost the same as the Long March 3B, but it has two strap-on boosters instead of four.
What's the message here? By flying a Long March 3C on a lunar mission, you're actually demonstrating most of what a Long March 3B will go through on a similar flight to the Moon. Of critical importance here could be the performance of the rocket's second stage, as well as any smaller "kick" motors placed beneath the actual spacecraft.
For the record, a story in People's Daily claims that the launch vehicle for Chang'e 2 will be a Long March 3B. This does not seem to be the case, as the rocket in the Internet photos is unquestionably a 3C. Any extra boosters would have been added long ago.
As usual, I sit and yearn for more solid answers to solve these mysteries. If experience is any guide, I will be waiting a while for conclusive answers.
Dr Morris Jones is an Australian space analyst and writer. Email morrisjonesNOSPAMhotmail.com. Replace NOSPAM with @ to send email. Dr Jones will answer media inquiries about this mission.
- The Chinese Space Program - News, Policy and Technology
China News from SinoDaily.com
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