Chang’e 3 and China in space

China launched its Chang’e 3 lunar probe atop a Long March 3B rocket on Dec 2, 2013  (Dec 1, US EST).  It is actually two spacecraft — the Chang’e 3 lander and the Yutu rover.


Yutu (Jade Rabbit) (Credit CCTV English).

Rather than try to explain the two spacecraft and their scientific mission, I refer you to Emily Lakadawalla of the Planetary Society, and her blog post on December 2.  She does an amazingly good job of explaining how planetary science missions work, regardless of the country.

I am a flight vehicle and trajectories nut.  I tend to look at how vehicles achieve orbit or other trajectory objectives.  Before I go there, I need to get something out of my system…  <frivolity>What unnerves me the most … is the pronunciation of the name of the rover, Yutu (玉兔), which means “jade rabbit”.  It is NOT “you too”!! Don’t believe me? Then listen to it at!!</frivolity>

So there.

Launch video

Here’s the launch of Chang’e 3 with English commentary:

I was so impressed by the quality of the video received from the flight vehicles that I decided to get the timeline down so I could make better sense of some of the pictures.  The timing below is given in minutes and seconds (mm:ss) from the start of the video.

  • 0:00 – final countdown
  • 0:35 – 1st ignition, launch
  • 2:27 – video from Long March rocket looking downward
  • 2:55 – strap-on boosters discarded from 1st stage
  • 3:12 – 1st stage separation, 2nd stage ignition
  • 6:15 – 2nd stage separation, 3nd stage ignition
  • 10:25 – 3rd stage engine cut-off, enter parking orbit
  • 14:23 – 3rd stage re-ignition
  • 17:57 – 3rd stage cut-off
  • 18:50 – switch to forward camera looking at Chang’e 3 probe; rim of Earth is visible
  • 19:35 – separation of probe from 3rd stage; most of Earth rim, previously obscured, is now visible
  • 20:22 – probe starts a series of attitude correction burns
  • 21:14 – probe engine ignition
  • 29:40 – Earth coming into view of 3rd stage camera
  • 30:00 – By this time, the probe is already on its trans-lunar trajectory.

Shortly after this, the video starts to repeat parts of the launch.

The English commentary is quite nice.  There is one glitch, involving perigee and apogee.  The technical commentator has them reversed; he talks about apogee as the closest point to the Earth in its parking orbit.  In fact, the closest point is perigee; the highest point in the orbit is apogee.

Lander and rover design

Much has been made of the Yutu rover having the same basic shape as the Mars Exploration Rovers (the MERs, Spirit and Opportunity).  The arrangement of the wheels is the same.  Some observers claim this means they stole the MER rover designs.  Actually, Mars Science Laboratory (MSL, Curiosity) has the same 6-wheel arrangement, and so do many other experimental designs.  It turns out to be a good design for navigating irregular terrain.

Mars Exploration Rover. [credit JPL]

Mars Exploration Rover. [credit JPL]

I have not taken a close look at Yutu wheel base articulation, but have to assume it is similar in principle to the MER and MSL chassis designs.

Basically, the instrument chassis hangs on a crossbeam that attaches left and right sets of wheels; the two sets can twist independently of each other.  On one side, a horizontal beam connects the middle and rear wheels.  That beam and the front wheel connect to an inverted V; the vertex of the inverted V connects to the crossbeam going inside the instrument chassis.  Each of these connection points can articulate.

Actually, the beams discussed above do not connect directly to the wheels.  Rather, each connects to a pair of motors. One motor, with a vertical axis of rotation, can turn the wheel assembly left or right, allowing for turns of the rover.  Another motor, with a vertical axis of rotation, makes the wheel itself spin, giving the rover longitudinal or lateral motion.

This is a popular arrangement.  I have seen it in a couple of other independent rover projects.  It’s possible that JPL laid the groundwork, and everyone is stealing that basic design.


The Chang’e 3 lander carries a plutonium-powered radioisotope thermoelectric generator (RTG). Why does it need this?  Isn’t there an alternative?  The reason for it is the lunar night, which is two weeks long.  It is so cold that the electronics would not recover from the deep freeze.  Solar panels are useless since there is no Sun.  Batteries to carry sufficient charge to go all the way to the Moon would be prohibitively heavy and expensive.  (And who knows if the batteries could survive the temperature drop.)  So there currently is no alternative.

NASA is looking for an alternative through its Centennial Challenge program.  The Night Rover competition is aimed at finding the best energy storage system for a lunar rover that could help the rover survive the lunar night.  This challenge is offering $1.5 million in prize money.

(And there is so little plutonium-238 in the world that it would be best to keep it for outer planets missions.)

Policy Issues

I typically stay out of discussions of the future of China in space and its implications for the United States.  But with the launch of Chang’e-3 to the Moon with its rover Yutu, I sensed a lot of misinformation, tending toward public apprehension, which will lead to public policy positions based on shaky reasoning.

Military fears

The Chinese space program is administered by the People’s Liberation Army (PLA), a military institution.  As a result, many people see Chinese space as a military program.  In the same line of thought, people incorporate espionage, spying on peoples’ Gmail accounts, the Chinese anti-satellite missile test of 2007, possible military attack on US space assets, etc. And then human rights gets added.

Of course, the anti-satellite test created a lot of space debris, fomenting a lot of international criticism.  In my opinion, the right hand did not know what the left hand was doing (scientific vs military leadership). I suspect there was a lot of internal bickering and in-fighting in the leadership while this was sorted out.

Some people fear that China will take over the Moon and launch missiles from there toward targets on Earth.  This is highly impractical, and the missiles would take several days to reach Earth.  (One does not just drop a missile straight down; the Moon is rotating around the Earth.  Any object leaving the Moon would start with its orbital angular momentum.  To drop straight down, one would have to kill that momentum, that is fly the opposite direction from the Moon.  The descent needs to be timed so that the missile ends up on your adversary’s head and not your head or your friend’s head.  There’s more, but I’ll stop there.)

For some groups, all the possible justifications for not cooperating with China are brought to bear.  It goes to the extent of any business that has contracts with businesses or the government in China cannot take part of US federal contracts.  (I don’t know how large semiconductor and telecom companies get around this, if they do.)  And the NASA administrator is not allowed to have direct talks with his counterpart in China, in spite of what his predecessor in the previous administration did.

And then there is the problem of presumably respectable media jumping to conclusions.  A few days after the launch of Chang’e 3 and Yutu, I saw a post in LinkedIn titled, “Why does China want to militarize space?” The post cited an article in the Christian Science Monitor from October 2010. [article] In my opinion, the content of the article did not support that title.  There was Pentagon analysis of the possibilities.  But most of the article dealt with the just-launched Chang’e 2, and the other matters related to the emerging Asian space competition.  In my view, someone wanted the article headline to sell papers.

In response to the poster’s question of “Why does China want to militarize space?”, I asked “What makes you think China is militarizing space any more than the US?” (We have recon satellites and the like, which I consider a valid use of space military assets. Now, why would a LinkedIn reader cite an article from over three years ago?  I didn’t ask.

(In recent months, I’ve run into a lot of cases either in LinkedIn or Facebook where readers are citing articles which are years old, or do not really support their argument, or the headline doesn’t really represent the article. I fear we are being overrun by sound-bite culture.)

Lunar Base

Does China want to establish a permanent human presence on the Moon?  This idea has more credibility.  Various groups see value in the Moon as the first step of human settlement for a space faring society. It does not matter what country you are from.  Some claim that it doesn’t adequately represent Mars, that Mars has an easier environment to adjust to.  In many respects, that may be true.  But there is still basic development which can be done before pushing ahead to Mars.  The fear some Mars advocates have is that focusing on the Moon will suck resources away from going to Mars; that is a valid fear.

There is political value in a society sending humans to the Moon to stay on a long-term basis.  It is something the US has not done.  Doing so would likely be considered a show of superior technology and intellectual capability.  If you are a small nation and you are evaluating who you should have alliances with, this capability forms part of a convincing argument.

The grand prize may be how to mine and manufacture materials in space so that they don’t need to be brought from Earth.  There is a potential for materials processed in space to have value on Earth. However, until manufacturing in space is actually proven, the value of this idea is unclear.

In establishing a settlement on the Moon, you can take members of your society and your value system, and establish them there along with representatives of your allies.  But in large measure, if you are building the base, you establish the ground rules.  When it comes time to spread humans throughout solar system, your values and trade system are the ones that spread with them.

Some number of world leaders probably understand this.  I suspect the Chinese are among them.

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