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China lands Chang'e-4 on far side of Moon (planetary.org)
1040 points by docbrown 76 days ago | hide | past | web | favorite | 226 comments

"...and if the dam breaks open many years too soon..."

Perhaps interesting to note the origin of this name for spacecraft. The legend "Chang'e flies to the moon" (嫦娥奔月) lies behind the Mid-Autumn Festival (featuring mooncakes, as it were). Point is, the names of Chinese space missions are every bit as carefully steeped in tradition as, say, Mercury/Gemini/Apollo.

The story behind Chang'e is also interesting. Essentially, she is the wife of a legendary hero, Hou Yi(后羿), who saved the mankind from dying of drought due to the presence of nine Suns, by shooting all but one of them down.

Chang'e stole the Immortal Pill, and eat it alone without her husband knowing. After she ate it, her body became to float and she flied to the moon, to live there alone forever as her punishment, with only one rabbit being her companion.

Sounds familiar? Yep I believe if you are a Naruto fan, you can make a lot of connections.

In one (more romantic) version of the lore, the Mystic Realm awarded Hou Yi (the husband) the Immortal Pill/Potion after he prevented the earth from being scorched. He and Chang'e were going to both take the potion so they can be together forever. A group of bandits heard about the potion, and broke into their home while Hou Yi was away, Chang'e had no choice but to swallow the potion entirely and that gave her divine powers in addition to immortality, she was able to escape and ascend into Heaven, and because she's no longer human, she and Hou Yi were forever separated...

> with only one rabbit being her companion.

So that's why one of their rovers was called "Jade Rabbit"

The "moon rabbit" [0] is a rather popular interpretation of the Moons surface in Asian folklore.

Japanese/Korean people believe the rabbit is pounding the ingredients for rice cake.

[0] https://en.wikipedia.org/wiki/Moon_rabbit

The trisolarian plot in Cixin Liu's The Three Body Problem also seems to have borrowed from this myth.

Having read (and enjoyed) that trilogy, I'm not making the connection. Which part?

There is a 3-star system that causes periodic droughts on a planet in the system based on which star(s) the planet's semi-stable orbit crosses.

In the novel, the three-body civilization would go extinct if there are two or three suns in the sky.

And to add to that the relay satellite is named Queqiao (鹊桥, Megapie Bridge). It is how the separated lovers Zhinv (织女, Vega) and Niulang (牛郎, Altair) meet once every year. Zhinv is the seventh daughter of the Yuhuangdai (the god of gods, like Zeus), and fell in love with human Niulang. After discovering with anger, Wuangmuniangniang (wife of Yuhuangdadi, like Hera) separated the two with the Milky Way. Touched by the love story of Zhinv and Niulang, the magpies form the Queqiao bridge to help them meet once a year on July 7, which became the Chinese Valentine (七夕).

Most of Chinese think Yuhuangdadi(玉皇大帝) and Wangmuniangniang(王母娘娘) are husband&wife, they work together to control all the gods(gods are not like western gods, they have 仙 and 神), but there are multiple versions of myths(books) and rumors mentioning them, none of them tells the relationship of them for sure, we can only deduce their relationship from the context. From different versions of sources, they can be: 1. husband&wife, 2. colleagues, 3. sister&brother, 4. mother&son.

Smite fans will know all this lore as well :) Chang'e main here.

Nothing more fun than a duo Hou Yi/Chang’e lane with their respective wedding skins :)

And the rover, Yutu(玉兔) is the jade rabbit, who pounds a mortar and pestle in Guanghan Palace on the moon. She later escapes to earth and Chang'e brings her back to the moon in 西遊記 (Journey to the West) right before Sun Wukong (孫悟空; japanese reading: Son Gokū; yes, like in Dragonball, heavily based on 西遊記) defeats her.

Beautiful story, thanks for sharing :)

The legend "Chang'e flies to the moon" (嫦娥奔月) lies behind the Mid-Autumn Festival (featuring mooncakes, as it were). Point is, the names of Chinese space missions are every bit as carefully steeped in tradition as, say, Mercury/Gemini/Apollo.

The People's Republic of China doesn't think of itself as a "Nation State." Instead, it thinks of itself as a "civilization state." A part of PRC's self appointed charge is to prevent the marginalization of Chinese civilization.


When I was working in Houston, it was a regular occurrence for me to meet yet another Chinese born employee of whatever corporation I was in, who would soon after ask me if I could read Chinese characters, then say it was a "shame" I couldn't. I'm not even Chinese, so I find this a bit parochial. I'm aware of the importance of Chinese characters in the culture of East Asia, but still, there's something a bit too self important about it.

Now, many years later, I'm married to a Chinese woman. Even she gives me this guff! It's like they're trying to match the attitude level of the French.

(EDIT: If you know of something wonderful more people should know about, most of the time, you should try to share it as a direct experience. That way, you're more likely to get across the magic and you're less likely to come across as a lecture.)

That's very interesting to hear. I wonder if it is something specific to that corporation, or perhaps your role at the corporation, though? All the Chinese-born people I know would be pretty surprised if any non-Chinese person could read Chinese.

All the Chinese-born people I know would be pretty surprised if any non-Chinese person could read Chinese.

My experience is that attitudes are often quite different if you look like a Chinese person.

I don't think that attitude is unique to Chinese people. My experience is based on my name rather than looks. Whenever people from my father's country ask me my name, they suddenly expect me to speak their language - and then to tell me what a shame it is when I don't. I've seen the same for British Germans, Polish and Vietnamese too!

One of my computer science professors who defected from Cold War Hungary was very anxious to meet me. It turns out that my Korean Catholic name is also a perfectly cromulent Hungarian name!

Well, that makes sense. If they thought you were a Chinese person, I could see why they would have asked you if you could read Chinese.

By that point in the conversation, however, I had already conveyed that my parents were from Korea, and I was born and had grown up here.

As someone who is learning Chinese (and VERY bad at it), (almost) every Chinese person I've met has been super encouraging and helpful. Most of them are surprised I'm learning it at all. But they also express encouragement differently, so I'm wondering if it is a misunderstanding.

That could well be. Some aspects of culture are quite subtle. There was this thing where, whenever some driver in traffic made me brake hard, my Chinese born wife would shout, "BE CAREFUL!" Well, here's the thing: I am very careful. I couldn't be blamed for any of those incidents. It's precisely that I'm careful that I was able to avoid a collision. It seemed very unfair that I should be blamed for any of these incidents. (Example, the car ahead of me spots a parking space at the last minute, then slams on his brakes to get the parking spot.)

So after about the 5th time like that, we had the argument. It turns out that she was just being scared and telling me to be careful, not knowing how an English speaker would take that contextually.

Well, it is actually a shame. And by that I mean why wouldn't it benefit anyone to gain access to what is probably as much writing about philosophy, history, etc. as what one is currently exposed to?

You should also keep in mind that the people that are saying this to you have already learned a complete another language and alphabet (since they are presumably communicating with you in English).

Well, it is actually a shame.

Asking someone to be ashamed of not having entirely elective knowledge isn't "live and let live." Nor would that strike me as being likely to be productive. Instead, you should describe how desirable and rewarding that knowledge is.

In my understanding saying "that's a shame" is equivalent to "that's really too bad," and not, "you should be ashamed of your self."

Maybe my interpretation isn't that common? (pause to google)

Apparently it is the common accepted meaning:


that being said, in Chinese culture and education...lecturing is more of a thing. All these new agey experiential education has yet to sink in the mainland yet..

And yet we tolerate the french...

Are there any good sources on the Chinese space program's change in naming convention? It seems like the older programs have names like "Long March" or "The East is Red", but they've now converged to the more common tradition of using mythology/mysticism.

Queqiao(magpies bridge), name of the relay satellite for Chang'e is from another Chinese tale 'The Cowherd and the Weaver Girl '[0], related to Qixi Festival[1]. Queqiao is the bridge built by magpies to help Zhinü and Niulang to reunite.

[0]: https://en.wikipedia.org/wiki/The_Cowherd_and_the_Weaver_Gir...

[1]: https://en.wikipedia.org/wiki/Qixi_Festival


Can you please not post unsubstantive comments to HN, especially nasty ones?

The interesting thing about the comment was the information about that specific name, not the generic point about naming things. Since you could have responded to either, it would be good to remember this guideline: "Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."

It would also be good to review all of https://news.ycombinator.com/newsguidelines.html and not to be a jerk to other users.

They have to be careful then. Apollo now means more about the moon landings than the old traditions to me. I don’t know if that’s something the Chinese would like to have happen to their traditions.

Unless you're an ancient Greek, that isn't particularly surprising; it was not part of current traditions when used as the name of a spacecraft.

Learning about the gods of old greece and their stories is still part of the curriculum in a lot of European countries. I doubt most would think of the Moon Landing first.

I grew up watching Japanese anime which reference ancient Greek mythology.

Pollon[0], for example, focuses on a daughter of Apollo. I didn't even know the "man on the moon" thing was called Apollo until I was in high school.

[0] https://en.m.wikipedia.org/wiki/Little_Pollon

Same here in the states.

Or Battlestar Galactica. XD

better than what Nike is now

The swoosh logo of the Nike company supposedly resembles the wings of the goddess Nike as seen in some ancient sculptures.

The way they used the L2 point to lasso a relay satellite so they could transmit information from the rover on the far side is stunning too. This was really brilliant, China's space program has really become something.

The way they used the L2 point to lasso a relay satellite

So confusing to put it that way. No one has caught anything with a rope or a cable, as far as I know. Basically, they are orbiting a relay satellite around the L2 Lagrange point so that the relay has line of sight with both the landing point and Earth. Obviously, if it just sat at L2, the moon would be in between the relay and the Earth. Orbiting around Lagrange points has been known about for a long time. If you want to cite something more recent and innovative pertaining to Lagrange points, astronomers, rocket scientists, and engineers have been working on fuel saving chaotic trajectories through the Lagrange points.

Arguably, the fact that they are the first to implement the L2 halo does win the Chinese space agency some innovation points.

If you read John Varley's Titan series or Neal Stephenson books like Seveneves they regularly call LaGrange points "L2", "L4", etc. I called it a lasso because, if you look at the diagram, it literally looks like a lasso.

If you read John Varley's Titan series or Neal Stephenson books like Seveneves they regularly call LaGrange points "L2", "L4", etc.

Never got around to Titan. I really liked Seveneves. I think Sonar Taxlaw is the most perfect woman, next to my wife. Nothing wrong with referring to L2, L4, L5...

I called it a lasso because, if you look at the diagram, it literally looks like a lasso.

Arrgh! That would be like when my grade school teacher called the LEM the "moonwalker" because it looked like it could walk around on the moon.

Isn't there a solar telescope around sun-earth L1?

actually things can and have been caught. Space tethers have been succesful https://en.m.wikipedia.org/wiki/Space_tether_missions#TSS-1R...

Yes, but not in this instance.

actually things can and have been caught. Space tethers have been succesful

Indeed, so a choice of words that indicates this was going on in this instance is all the more confusing.


If you continue to post unsubstantive comments and/or break the site guidelines we will ban you.

Poe's law. But at least you afforded the parent commenter the charity to feel good about their smug comment while still making your point.

Also interesting is the 'Dutch NCLE' project, which hitched a ride with the relay orbiter to study how hard it will be to do 'low-frequency' radio astronomy (esp. below 30MHz) from behind the moon.

That may turn out to have more science value than establishing that the far side is old (just joshing ... a bit).

It is known as radio repeating. Radio stations use them to boost their signals into new territories. Cell towers too.

Radio repeating: "[It's]...a combination of a radio receiver and a radio transmitter that receives a signal and retransmits it, so that two-way radio signals can cover longer distances. A repeater sited at a high elevation can allow two mobile stations, otherwise out of line-of-sight propagation range of each other, to communicate. Repeaters are found in professional, commercial, and government mobile radio systems and also in amateur radio. ..."

Although radio receivers on earth don't orbit la grange points.

This nicely explains the relay's orbit and the trajectory they took to get there: http://www.planetary.org/blogs/guest-blogs/2018/20180615-que...

This comment threw me for a loop - "L2" and "lasso" triggered the pattern recognition in my head for "regression regularization" and it took a moment to realize the topic was still orbital dynamics.

Come to think of it, saying "Lagrangian" wouldn't have prevented my confusion - not that there's anything wrong with the terminology in OP. I'm reminded of a passage in Cryptonomicon, which I've been rereading:

    "Newton wrote a *different* book, *also* called *Principia Mathematica*, which isn't *really* about mathematics at all; it's about what we would todaycall physics."
    "Then why did he call it Principia Mathematica?"
    "Because the distinction between mathematics and physics wasn't especially clear in Newton's day--"
    "Or maybe even in zis day," Rudy said.

Off topic: That quotation is a bit strange because the full title is "Philosophiæ Naturalis Principia Mathematica", or "Mathematical Principles of Natural Philosophy", which describes exactly what it is ("Natural Philosphy" basically being "science").


(Can you edit the fixed width formatting? It's impossible to read without horizontal scrolling)

This comment threw me for a loop - "L2" and "lasso" triggered the pattern recognition in my head for "regression regularization" and it took a moment to realize the topic was still orbital dynamics.

Yeah. It's not the most apt choice of words.

It's a fine choice of words. It's just a coincidence.

No one is capturing anything with a rope or cable. It's a rotten choice of words.

For what it's worth, I'm from Texas where I see actual lassos somewhat regularly, and I perfectly understood the phrasing here. Maybe it's just a regional difference in how the word "lasso" is understood.


"Please respond to the strongest plausible interpretation of what someone says, not a weaker one that's easier to criticize. Assume good faith."


The use of a relay is something less than "stunning" and "brilliant". The use of relay satellites when ground stations do not have line-of-sight to the primary spacecraft (or, when you have reduced bandwidth or other restrictive conditions) is standard practice. This concept is used to relay telemetry from Mars landers, for instance.

You realize the words "stunning" and "brilliant" are subjective, right? Your "standard practice" here is both incredible AND the first time ever done in this scenario to achieve something brand new in space travel. Not sure why you need to tell people not to like things, but it's a really bad habit you should break.

I do like the notion of using a relay.

In 1999, JPL lost Mars Polar Lander, and didn't have telemetry to know why. One of the major lessons learned from this loss was to always have telemetry of Entry, Descent, and Landing (EDL). This telemetry is usually provided by a relay. So despite the fact that we both like it, using relays is not new.

(See sec. 5.1 of [1]: "The omission of EDL telemetry was justifiable from a project perspective. However, the loss of MPL without yielding any clues as to the cause of the loss jeopardized the potential for success of future Mars landers. Therefore, the decision was not justifiable in the context of MPL as one element of the ongoing Mars exploration program.")

I like that they put it in an orbit about the Earth-Moon L2 point. I think it's the first such satellite there.

[1] https://spaceflight.nasa.gov/spacenews/releases/2000/mpl/mpl...

Copying earlier comment:

Wikipedia seems to say the rover mission duration is 3 months, yet the previous rover traveled for a year and transmitted a bit longer. The Chinese seemed quite coy about it failing last time (as with many things) so perhaps underpromising in this case?

This all preparation for China's planned permanent radio telescope on the far side which would be a huge boon for astronomers by escaping Earth's EM interference.

Also out left field is the 3kg "self sustaining" biosphere of silkworms and plants with a camera inside. Interested to see how long it survives.

Regarding underpromising - there might be a little management of expectations but to paraphrase a friend in "the biz": facing away from the Earth means that the stuff you need to be reliable jumps up in complexity and with that complexity comes a foreshortening of life. She then babbled incoherently in a way I enjoyed but didn't understand.

Love the idea of a dark side telescope!

Dark side is not really not dark side as the moon is shined by the sun all rounded and hence we have eclipse (by the moon).

But I guess the other side would as someone posted no em wave from earth and that help.

So it's "radio dark", not "sun dark". (At least per human radios.)

Silent side of the Moon?

I'd interpret the stated duration as a criterion for whatever budget they came up with. Building something that'll last 90 days in a harsh environment is a lot less expensive than one that needs to last at least a year. And assuming the folks monitoring the rover aren't working for free, the budget needs to include their cost of employment for a fixed amount of time.

I'll note that the mars exploration rovers Spirit and Opportunity were meant to last 90 sols (Martian days). Spirit lasted 2,210, and (assuming it doesn't reply) Opportunity lasted 5,111.

When you have everyone working on the mission trying to make sure their part isn't the one that causes the mission to end before the 90 days are up, you get a long-lived rover.

The flip side to over-engineering is ever-ballooning budgets, fewer missions and more chance of random events curtailing the few missions that are flown.

If the requirements state 90 days, design for 90 days - even if 180 days is achievable 'for free'. Otherwise there is no feedback loop to inform future requirements and 90 becomes an implicit 2000.b

If JWST was designed for two years and a hard shutdown it would have flown years ago and we'd be on JWST Gen 3 by now, doing actual science.

You're making the false assumption that designing something that last at least 90 days, but ends up lasting 2000 days is more expensive than something intended to last at least 90, and at most 180.

Planned obsolescence of hardware operating on another planet can be hard, much harder than over-engineering it.

Consider the wheels on the rover as a simple example (Curiosity has had structural issues with those). Next time they can either just say spend an extra 10 kg of payload to make the metal thicker, and be assured that it's "definitely 90, or way more" and move on to the next task.

Or, they can consider them lasting beyond 180 a failure. Then they'll need tens of thousands or hundreds of thousands of hours of design and testing to ensure that various types of Martian terrain wear them out at just the right rate, and no more or no less.

Easier to just say "this isn't worth micro-optimizing", eat the fixed cost of the extra payload, and move on. There's going to be tens of thousands of components on the rover that are like that, e.g. try finding a camera sturdy enough to operate on Mars but just fragile enough to reliably fall apart in 180 days.

In aggregate that's why these rovers are exceeding their life span. If it's truly important that missions are extended for whatever reason that can just be decided as a matter of policy. Stop talking to the rover after 90 days, or hand it over to hobbyists.

> You're making the false assumption that designing something that last at least 90 days, but ends up lasting 2000 days is more expensive than something intended to last at least 90, and at most 180.

I think this demonstrates the risk op was getting at. Designed for 90 and lasting more is not an implicit assurance it will last up to 180. It changes expectations and that always Cascades.

I wouldn't say it's overengineering. If you design something to have a 99.9% chance of lasting 90 days, the odds are really good that it's still going to be working at 180 days. I don't know what the bathtub curve for a Mars rover looks like, but I imagine a disproportionate amount of failures occur in the first week. If you can make it through that, you're going to make it until major systems fail or your solar panels die. You could get rid of hardware redundancies like 2 of the wheels, but that'll just increase the odds of you getting stuck on a rock while the rover is still functional.

If JWST was designed for two years and a hard shutdown it would have flown years ago and we'd be on JWST Gen 3 by now, doing actual science.

JWST's design lifespan is not significantly driving its cost. Its cost derives from its complexity, and (crudely) its complexity follows from the aperture diameter and temperature it requires to achieve the scientific objectives chosen for it.

Fair point, guess when you have specs and failure rates to meet the effort/cost goes up dramatically.

Fair chance this rover can last a while though. Good luck to them.

Not so unusual ... look at the spec'd mission times for many US planetary missions ... they are usually -much- shorter than the expectation values. (Opportunity Rover, e.g.)

These sorts of missions are almost always underpromised (or, at least, based on very conservative estimates). See the various Mars rovers.

> Also out left field is the 3kg "self sustaining" biosphere of silkworms and plants with a camera inside. Interested to see how long it survives.

Aw man, that's how you get giant mutant moonworms.

Where's that? I couldn't fimd it in the linked article.

Sounds like Elon Musk's original idea for a greenhouse on Mars, to inspire via realtime cam. Is there any indication they'll have a public cam for it?

It wasn't in TFA, but here's a source: https://www.bbc.com/news/science-environment-46724727

> The lander carries a 3kg (6.6lb) container with potato and arabidopsis plant seeds - as well as silkworm eggs - to perform biological studies. The "lunar mini biosphere" experiment was designed by 28 Chinese universities.

(Source for the silkworms, at least. I must confess that giant mutant moonworms are only conjecture... for now...)

Not entirely sure about all the ISS tests but most space biology experiments seem to be zero-g. We know a lot about how life survives at 1g and 0g but very little about in between, so hopefully it goes ok, quite a unique experiment.

ISS isn’t 0g, it’s actually about 0.89g. Even the moon is 0.166g. And that’s without getting super pedantic by saying there’s always some gravity anywhere you are in the universe.

ISS is in freefall though, which simulates 0G. Yes technically gravity is almost as strong as on the surface where ISS orbits, but there is no normal force opposing gravity.

Actually, the ISS isn’t in “freefall” either. Further, there definitely is a normal force (inertia) opposing gravity too, otherwise without that (and the occasional thruster burns needed due to drag from the atmosphere), it wouldn’t “continually fall and then miss the ground” as it’s normally described in layman terms.

There’s plenty of sources to back up what I said previously and here, but this provides a great description of why it’s wrong to say the ISS is in freefall:


Any bio nerds know why silkworms?

There's an obvious reference to Chinese culture in that one, curious what are the biological reasons to choose that creature over any other.

Hm, doesn't this violate the prime directive (or planetary protection guidelines)?

It absolutely does. You should file a complaint with the PDIPTF (Prime Directive Interplanetary Police Task Force) currently HQ in Ark 9, "My hole is bigger than yours", Holm 42, Level 686 on Makemake. In person. Be sure to ask for a complaints receipt.

The biggest reason for planetary protection guidelines is the risk of life escaping from the spacecraft and being mistaken for native life. The moon is so ridiculously inhospitable that it isn't much of a concern because no known life can survive without air or water, even before taking into account the extreme temperature swings. Somewhere like Mars or Europa has much more strict guidelines. Also, we sent people to the Moon, which are a lot messier than silkworm eggs.

I think they'd have to dump something on the surface, but even if they did, who's going to enforce it? The moon's not Antarctica.

They should've added those to Iron Sky

Awesome. Too bad US freezes China out in working with NASA on space exploration. I think we all should partner up despite our political differences.

China doesn't exactly play nice with others. Even other tech companies have almost given up on working with China. When you deal with them, it is a one way street. What would the US get from any partnership with China besides China stealing any technology they could get their hands on?

If everyone were working together, it wouldn't be stealing. I don't steal someone's software when I fork a project on github, and they don't steal mine when they accept my pull request.

That's like asking what the value of sharing is. China would provide funds, equipment, astronauts, etc that could be partially shared - like with the ISS. Note that the U.S. doesn't have to turn over source code or detailed designs to share stuff. Also, soon, China will develop original technology that others do not yet have (or already has?).

I'm not sure I agree. While there are obvious benefits to cooperation, competition has benefits too.

I think the best cooperation is in terms of emergency rescue, backup communications, and sharing scientific results.

Emergency rescues mean compatible docking systems to that if an opportunity arises technical problems don't stop the rescue. Of course actually catching something in space in time to pull off a rescue is nearly impossible, but just in case the orbits line up...

Emergency rescue also means that moon/mars missions should plan to land ~10km from each other - while the area of exploration is greatly limited it means in the worst case you can walk to the other for safety. It also means a party in the middle one day - moral is itself an emergency.

Backup communication means that radio frequencies are compatible. That way "our relay can't reach our rover" can turn to "but we can - let us control it".

The USSR and USA started cooperating in the 1970s and this has had very good results. For example being able to get to the ISS after the Space Shuttle accident, and arguably in easing political & military tensions. They continued to compete as well.

Competition between the USA and the USSR produced the first orbiting satellite in Oct, 1957 and a man on the moon, twelve years later, in July, 1969. The USSR gave up on Space tech and so did the USA so that we couldn't land a man on the moon if we wanted to 50 years later. If the USSR had continued on to try and go to Mars we would have been there decades ago. Only with Elon Musk's vision for a Mars colony and his company SpaceX, is space technology advancing again. He also has stated that he hopes for some competition as he knows it can really push people to excel.

Competition between the USA and the USSR also produced thousands of nuclear ICBMs... but I get your point that space tech development was faster. It's slowed but hasn't stopped and everyone has far from given up. I think we have to use our money & brainpower rationally - especially given the many threats we have on Earth - whereas competition and egos often go against this. For example, I think a manned colony on Mars in the next decade is definitely possible but would be an epic waste (what would it achieve?) - IMHO we should first develop far more advanced robotics, self-replicating machines, etc - to build a proper base before sending humans over.

> very good results

with diminishing returns. Post-Apollo funding was/is but a shadow of NASA's glory days. As soon as the military interest is gone, it's inevitable that a program will lose financial support.

> with diminishing returns

Let's see. From the start of Space Age, October 4th, 1957, to the peak of NASA funding in 1966 - almost 9 years. To the last Apollo flight to the Moon in 1972 - a bit over 15 years. Advancements: unmanned space flight, manned LEO flight, manned flight to the Moon and back (overall manned flights ~43, https://en.wikipedia.org/wiki/List_of_human_spaceflights ).

From the Apollo Soyuz Test Project in 1975 to today in 2019 - 44 years. 3 times as much. Advancements: expanded unmanned space flight, permanent manned LEO outpost, reuseable vehicles (Gemini, STS, TKS, EB, X-37), commercial space flight, international space cooperation (overall manned flights ~270).

Per dollar modern space flights are quite competitive with 1970-s. Manned spaceflight is also safer than it used to be. Per unit of time... Mars flights are quite more robust, but Venus is kinda forgotten. Outer Solar system objects are visited more frequently... Russia retracted from unmanned spaceflight... India, China, Europe are growing...

I don't think funding is the only criteria here. In some aspects Apollo project catapulted humanity to the higher frontiers which are hard to keep, but some other indicators point to steady progress everywhere with way more sustainable longer term approach.

Please keep in mind that space exploration has always been rooted in and primarily (for better or worse) funded as a result of military applications. It's simply not possible to fully dispel that conflict of interest, at least not for the foreseeable future of world politics.

I have long said that the real reason for the international space station is to give Russia cover to keep their space engineers working. That is unemployed ex-soviet space engineers are are vulnerable to evil dictators offering them a job designing ICBMs (when you have no money/food moral considerations are less important)

That was part of it though I think space engineers would never have been unemployed or out of food - just reassigned to much more boring projects. Russia also has ways of ahem "discouraging" unauthorised trade of military secrets.

With China's ICBMs, aren't they already advanced enough that collaborating on space exploration with NASA won't teach them much ICBM technology that they don't already know?

I think the ICBM utility has been played out. The new concern seems to be defense of space in and of itself. Exhibit A: Fearless Leader pushing through the Space Force creation. New field, new theater of war, new way to line defense contractor's pockets.

I disagree. I don't think we should partner up. I think we should compete. The US, China, EU, India and possibly even Japan are wealthy enough and the first 4 is populous enough to explore on our own.

I think we should share our discoveries and knowledge, but we shouldn't be partnering. If we really want space exploration, competition is what is going to drive it.

Do you know why NASA doesn't partner up with China? Because it sounds like you think those political differences are insignificant.

It's currently illegal for NASA to work with China. There's been a line in the NASA appropriations bills for the last 5 years or so saying none of the money they're receiving can be used bilaterally or in cooperation with China

How about working with Taiwan? I think they too have a space program, although I have no idea how big it is.

"The 'One China' policy is not a card on the bargaining table," said Paul Haenle, a former China director at the U.S. National Security Council. "It is the table itself."

That describes the mechanism, not the rational.

Speaking of significant political differences, NASA has been partnering with Russia and nobody seems to have a problem with that.

It's not necessarily the case that nobody has a problem with it, it's just the status quo, and the front lines of most political issues are on one side of the status quo or the other. The "don't work with China" side would push across to "stop working with Russia" if they had the strength to.

They should be... sadly, the political reality often gets in the way of idealism.

On the other hand, this has resulted in something very good. Our (U.S.) space program has been err, lacking, for the last 45 years so it's not like there would have been much benefit to partnering with us. If China, or any other country, wants to take the leadership role we've abdicated and show the world how to do a space program, more power to them. And who knows, it might even give us the push we need to get back out there in a serious way.

Can someone explain how are these types of devices safe from hackers? I mean, it talks back to the space agency, right? Just curious is all. Haven't seen anything related to this question.

A lot of satellites and probes "back in the day" more or less depended on security through obscurity. You would need to know what frequency (or frequencies) to use, and how to encode the commands. Your ground station also needs a bigass antenna, and a good idea of where to point it.

Now most if not all satellites use encryption and/or authentication for command and control, but I wouldn't be surprised if some space programs don't bother. With something like the New Horizons, why waste precious CPU cycles with encryption/decryption when it takes such a tremendous effort to communicate with it. The Deep Space Network costs something upwards of $1,000/hour, and requires huge dishes and lots of land.

Awesome, great to know. Didn't know about the DSN so going to read upon that.

For others that might not have seen it, there's a cool live dashboard of the DSN so you can see which spacecraft are currently transmitting: https://eyes.nasa.gov/dsn/dsn.html

Thanks for this link, never heard of this and it’s been fun for my son and I.

Probably passwords in clear text in the source code. Like you can find it in most other places too...

Feels like a state actor risk in the main. I can't think of a state actor without significant volumes of more attackable assets in earth orbit, and that's without considering their options for eg A one time cipher stream or other serious protection of the uplink signal.

I doubt it's using open comms and a diginotarencrypt certificate.

Wouldn’t the spread spectrum help in preventing any kind of interception?

Apologies in advance for the (hopefully not) stupid questions from a layperson...

How constant is the L2 point for the relay satellite's orbit? If I understand correctly, this is the "balance" point between the earth and sun's gravity. Does the moon's gravity affect this? If so the L2 point will shift as the moon moves towards and away from this point?

As the moon orbits the earth, presumably the relay satellite would stay put and not follow the moon in its orbit. This would mean that communication from the lander and rover to the satellite is only possible when the moon is in a particular position (between the earth and the sun), correct?

The balance is between Moon and Earth gravity. However it is more subtle than that at L2 as both gravitational forces are in the same direction so they don't apparently cancel. The way to see it is to realize that L2 is relatively stationary to the Moon but not the Earth. As the L2 point is farther away than the Moon but has the same angular velocity as the Moon, Earth gravity alone is not able to keep any object at the L2 in synchrony with the Moon. One may want to recall that Earth gravity is just right for the Moon in its orbit so any satellite further away will have a longer orbital period than the Moon. The Moon gravity therefore supplies the additional force needed to keep an object at L2 orbiting the Earth in synchrony with the Moon. This balance (Earth gravity + Moon gravity = centrifugal force) determines the location of L2.

Thank you for the good explanation!! Cheers!

Lagrange points are found near any couple of large bodies. They are points where a smaller object will maintain its position relative to the large orbiting bodies.

The Chinese relay satellite is orbiting the L2 point of the Earth-Moon system. That is beyond the Moon on a line which goes from Earth to Moon. Hence, this L2 point orbits the Earth like the Moon does, and the whole system orbits the Sun as well.

Now if the spacecraft would be exactly at that point, the Moon would be blocking communications between the probe and Earth antennas. So instead, it follows a halo orbit which is quite stable around that point, but goes over the Moon horizon so that there is always a direct line of sight between Earth and the spacecraft.

Not a stupid question at all !

I just wanted to add that L2 (and L1 and L3) are unstable in that if a satellite is a bit further than the exact point it will tend to get ever further with time and a satellite that's closer will tend to get even closer. But the closer you are to the exact L2 point the smaller these tendencies are and the amount of fuel needed to remain on station is minimal, a satellite will just eventually run out some day and fall out.

The L4 and L5 Lagrange points are the stable ones. Something that finds its way there is going to stick around indefinitely. That's why many planets have asteroids in the L4 and L5 they make with the Sun. These are called Trojan asteroids and the names of the Jupiter-Sun Trojans are taken from the Trojan war.

So how can this craft orbit a point that is not a gravity well but a gravity hill, so to speak?

It's a gravity saddle! From Earth's perspective it's a hill in the r direction but a well in the phi/theta directions. To orbit at a location always visible from Earth it needs to move in the phi/theta directions but moving the the r direction doesn't help, so it doesn't.

And you clearly know this but i had to refresh my own knowledge of spherical coordinates - https://en.wikipedia.org/wiki/Spherical_coordinate_system

Thank you for taking the time to explain. Very helpful :)

The L2 point that the satellite is orbiting is a Lagrange point [1], a place where the gravity (edit: and centrifugal forces) of the Earth and the moon balance. L2 follows the moon as the moon orbits, because the moon is what makes it exist.

[1] https://en.wikipedia.org/wiki/Lagrangian_point

It's the L2 point in the earth-moon system, it is different from the earth-sun L2 point. And yes, the satellite follow the moon in its orbit, the point in the L2 point.

Israel and India may be sending landers to the Moon too. India has sent orbiters to the Moon and Mars. https://en.m.wikipedia.org/wiki/Mars_Orbiter_Mission_2 https://en.m.wikipedia.org/wiki/Chandrayaan-2

An Israeli group got pretty far with an entry in the lunar lander XPrize. But the prize reached its deadline dates and expired. I hear they may be shopping for a deep space launch vehicle.

I think the Israeli group is SpaceIL, currently scheduled to launch (alongside a satellite) on a Falcon 9 in February. https://spaceflightnow.com/launch-schedule/

China releases photos from first-ever mission to land on the dark side of the moon


Is there a way around the paywall for business insider?

The photos were originally published here: http://www.cnsa.gov.cn/n6758823/n6758838/c6805034/content.ht...

It's the original source. I chose to post the BI article because the original source is in Chinese.

I believe they have an English version of the page: http://www.cnsa.gov.cn/english/n6465652/n6465653/c6805049/co...

I don't blame you, but next time you go to a foreign website, you can look out for icons that resemble national flags or EN.

There is usually an English version of the website available for important government websites (as with this case, the button is on the top right corner).

Thanks. I'll keep that in mind. I have lousy eyesight. It's easy for me to miss details like that.

Just open the link in an incognito tab.

Their logo has similarities to a certain sci-fi TV show..


I mean http://memory-alpha.wikia.com/wiki/Starfleet, "Seal of Starfleet in the alternate reality"

FTA: "In addition to its value as a scientific exploration target, the Moon’s quiet, airless far side makes it one of the best places in the inner solar system for science applications like radio astronomy."

It what way is any part of the moon not "quiet and airless" ?

The near side is bathed in radio (and other) waves from the Earth. It's not "radio quiet". Also, the Earth "leaks" a surprisingly large amount of air, especially when it's a full Moon and the solar wind is carrying outer reaches of the atmosphere with it.

The amounts are small, but scientific instruments are - by design - quite sensitive.

The sun is really loud. [0]

But in all seriousness, it produces a lot of radio signals. So it is completely accurate to call it loud. The moon doesn't have a magnetic core so it doesn't produce its own noise like Earth does.

[0] https://youtu.be/Rvvsw21PgIk?t=17

The sun shines on the "dark side" just as much as it shines on the near side.

Well there's 28 days that it isn't shining (yes, sidreal days exist on the moon). But you also don't have Earth in view (ever). The Earth is also loud. Combine these two and you got a great place for radio astronomy.

The far side also has a lot more craters. There are also places in the poles that are always in darkness, but those aren't the best places for observatories.

Think about what you just said, in context of why one side is light and one is dark. Where does the light come from?

The "dark side" of the moon refers to the side that is always pointed away from Earth. It has day/night cycles just like the rest of the moon does.

Also try not to take this condescending tone with people. Especially when you're wrong.

re "airless", the moon does have some semblance of atmosphere, but i think it's neither constrained to the near side nor in general particularly notable.

Damn..it is an impressive accomplishment by China.

Does China have an equivalent to NASA's Deep Space Network tracking stations? By deploying large antennae in the US, Spain, and Australia, the US was able to maintain 24/7 contact with the space missions. Granted, this isn't a manned mission but I'd still think that they'd want to have continuous comms to their lander.

There is little value in the continuous comms to the unmanned missions. You generally want good tracking during maneuvers (which is where things go wrong), but outside of those motion is highly predictable.

And the comms to the unmanned missions are mostly for forensics (outside of active science or other active payload functions) -- if a problem arises that the automation on board cannot solve it is highly unlikely that a difference between real-time and an hour later warning would matter.

I'd agree with you for anything outside the Earth's SoI, but the Moon is somewhat unique in that we DO have the ability to try to correct things in near-real time.

It's one thing to have to wait 16 minutes to grab telemetry and issue commands to something on Mars, but having only a few seconds lag seems like something mission designers/operators would take full advantage of. The idea of actively controlling a rover rather than having it perform pre-programmed routines seems highly desirable.

> The idea of actively controlling a rover rather than having it perform pre-programmed routines seems highly desirable.

Rover, probably (which I considered payload functions). For delivery vehicle during passive parts of the trajectory the value is doubtful.

Plus, the standard way of getting a ground station outside a country's land footprint is to put one on a ship. That's what Soviet Union did and I suspect this is what China is doing now.

> Plus, the standard way of getting a ground station outside a country's land footprint is to put one on a ship.

Never heard of a ship based ground station, and that's saying something as I'm in the industry. How does that work? I'd imagine the antenna would need to be on a massive gimbal, yeah?

From the top of my head there is Soviet https://en.wikipedia.org/wiki/Kosmonavt_Yuriy_Gagarin

In principle this isn't that different from ships designed to track ICBMs, and I've seen designs both with spinning parabolic radar antennas in radomes and regular antennas on gimbals. In fact many of those tracking ships were used in space programmes, but I'm not certain, whether just for one way telemetry or two-way comms

There was a television story about Chinas DSN station in Argentina. I think it was 60 Minutes, but could not find the link. The story alleged China could be spyingof world satellites with these radio dishes. The locals are of mixed opinion. They like the economic infusion from China but fearful they could get more pushy. The Chinese workers mostly keep to themselves, but there is a grocery store and new restaurants for them.

My guess is that they would need a third location for unbroken 360 degree coverage. I would gues somewhere in Africa would do it. They have lots of development projects ther.

How much lighter is the lander compared to Apollo moon lander? I mean, how far are the Chinese from sending people to the moon? The Russians landed a Lunokhod too but were very far from sending people to the moon.

Russians were on a verge of manned mission, but the program stalled with Korolev's death and then scrapped altogether for non-technical reasons, primarily because of the regime change.

No they weren't. What's your source? Their solution (N1) had inherent flaws that would have taken a long time to work out.

Documentary on the subject that interviewed people from the project. What's your source for the "would have taken a long time" bit?

Edit - ok, read up on it and N1 was not indeed flightworthy. There is however little information on the nature of technical issues and how long they would've taken to resolve. The program collapsed first and foremost because of the politics and personnel/finance issues.

The N1 used closed loop cycles, which was something new at the time and was a lot harder to get right. Also the n1 had some 30 engines that all had to operate perfectly so the inherent risk of failure was higher. The rocket was never even man rated.

USA rocketry school tradition of counting engines by chambers makes R-7 a rocket which uses 32 engines at liftoff 4 main chambers for each of 4 RD-107 and 1 RD-108 (20 chambers) and 12 steering chambers (each with about 3 tons of thrust, about as much as a chamber of British Gamma-8 engine) - more than N-1. Yet R-7 is a pretty reliable rocket overall. Also Falcon Heavy has 27 engines, which not too many complain about.

No, engines didn't need to operate perfectly. N-1 has less gross liftoff mass (GLOM) than Saturn-5, yet N-1 had higher liftoff trust. That's partially because it was supposed to complete the mission with up to 4 engines out during flight.

No it hadn't. There were problems with engines, which were being rectified, moving from NK-15 to NK-33. Fifth flight of N-1 would likely use NK-33 and had a high chance to succeed, given reliability of multiple-use NK-33s and almost-successful first stage flight in 4th attempt.

Only recently did I come to learn, the Soviets had landed a Lunokhod, which actually returned sample of lunar soil back to earth.

USSR landed Lunokhod-1 and Lunokhod-2, and also returned lunar soil samples in programs Luna-16, Luna-20 and Luna-24. Those are all separate flights.

The dark side of the moon, perhaps the perfect place for a big telescope?

The far side of the moon isn't dark. It has the same day/night cycle that causes the phases of the moon visible from Earth.

On the other hand, it is shielded from radio emissions from Earth and might be a good place for a radio-telescope.

Surely it's darker than the earth facing side. I'm no rocket scientist, but I reckon at least some of the light the sun sends our way gets reflected. From experience, a moonless night sure feels darker than when the full moon is up.

The amount of reflected Earthlight would depend on your location on the Moon's nearside and the phase of the Earth.

The corollary of one side of the Moon always facing the Earth is that the Earth hangs in about the same place in the sky for any given point on the Moon's surface. Over a period of (earth) days the Earth's position would slightly but visibly oscillate due to libration [0]. This might slightly vary the incoming Earthlight (analogous to the Moon's illumination at the horizon vs. at the Zenith).

A much bigger effect, however, would be due to the phase of the Earth. As the Moon orbits it will sometimes be between the Earth and the Sun, sometimes further away. On the sun-side, the Earth would be more 'full' and thus there would be more light to reflect. This would significantly vary the incoming light.

[0] https://en.wikipedia.org/wiki/Libration

A "full Earth" would coincide with the sun fully illuminating the far side of the Moon, and a "new Earth" would coincide with the sun fully illuminating the near side of the Moon, so wouldn't you only get maximum darkness anywhere on the Moon during a lunar eclipse?

However, counterintuitively, I think you'd be better off with a full Earth and no direct sunlight than a new Earth and full direct sunlight, making the near side a slightly better place for an optical telescope. The near side of the moon even has the opportunity to experience eclipses.

You're probably correct, but I also have know idea how much of a difference it would make.

One other advantage would also be the lack of atmospheric scattering, but they have made huge strides with adaptive optics so it might not be worth the extra cost of getting all the components to the Moon and assembling them.

You would also be limited by how close you could point the telescope to the Sun when it's in the sky. I think Hubble isn't allowed to point closer than 50 degrees for fear of damaging its optics/sensors.

I suppose the light side of the moon is also a very good place. Good enough to start with. Somewhere to the side to avoid having earth in full view.

It is kind of surprising that the Chinese choose mystical names for their space probes, rather than names of revolutionary origin (I guess Long March, is an exception).

After the Cultural Revolution, the PRC seemingly decided that turning their backs on centuries of culture might not have been the best move. And by culture I mean the subset of "Chinese" culture they deem compatible with their planned future society; cultural and religious "fringe" groups are still brutally repressed.

Hopefully they find some carbon in the crust. Only traces have been found so far on the moon.

Unfortunately the likelihood of life on Moon is next to nothing (if that's what you are implying by carbon). Remember, we have some ~900 lbs of moon rock we brought back with Apollo that we have studied. By all accounts the moon is just a dead ball of dust. There isn't even tectonic activity. The little water is trapped as frozen ice in rocks. No atmosphere means constant bombardment by radiation and temperature differentials are in hundreds of degrees. It's as inhospitable as it gets.

Sorry for my ignorance, but what's the significance of carbon in the crust?

Most important building block of life

amazing communication system.


Ironically, at the time of landing, there was no live coverage on the state media CCTV's news channel. Instead, it was covering the story of Utlima Thule.

Also you should know that the launch/landing window of a lunar mission does not occur everyday. And it's predetermined by orbital mechanics.

> Is this what a space race feels like?


New Horizons capturing Ultima Thule is not a large enough event to warrant the Chinese feeling like they need to compete with it. Spectator wise, it's a nice event for anyone that likes astronomy. It will be ignored by most of the people on the planet, just as the Chinese landing on the far side of the moon will be. These are not seminal moments in space history.

> These are not seminal moments in space history.

Intercepting a 20 km object in the Kuiper Belt, the farthest body ever explored by mankind, isn't seminal? This also happens to be the first encounter with a planetesimal. It gives us a unique window into planetary formation. This is a very huge accomplishment.

Correct, but the average person doesn't care. They might have read about it and gone "neat", but they have already forgotten about it.

So what? The hell with the average person. You think the average person cares about any physics breakthroughs like gravity waves detection or breakthroughs in any other field? We don't define seminal moments by what the average person thinks about the science.

New Horizons was the most read story on bbc yesterday morning. China’s landing is today.

It’s no Sputnik or Gagarin or Apollo, but experts at Nasa as "a first for humanity and an impressive accomplishment".

From the NYT article [0] on the topic: "We Chinese people have done something that the Americans have not dared try.” -- someone associated with the Chinese space agency

Why so insecure? Not a good look.

[0] https://www.nytimes.com/2019/01/02/world/asia/china-change-4...

I'm pretty happy if China wants to throw shade at the US over space program accomplishments. I'd prefer a measuring contest over space accomplishments then building more earth-bound weapons systems.

No need to choose, you'll get both!

What's the point of a measuring contest followed by building more weapons?

And how long before the space program accomplishments start looking just a little like space-based weapons systems. I’m sure Chinese military leadership can extrapolate as well as the Pentagon can.

Military interest in the moon goes back quite a ways. See https://en.wikipedia.org/wiki/Lunex_Project for example, and https://en.wikipedia.org/wiki/Project_Horizon

As soon as possible. Man being man, we only seem to be able to accomplish things under threat of violence.

this stupid comment is from a professor from Macau who is not even a part of the team. if NYT cares to spend more time, surely it can find even more extreme views from 1.4 billion average Chinese. the question is how that is newsworthy.

sad for those people who read such NYT junk on daily basis.

It sounds like a flamebait from NYT. I would not bite.

Agreed. This professor didn't even work on the mission.

"have not dared try"

This mission wasn't difficult from an astro perspective, and was only moderately challenging from a satellite comms perspective.

It just wasn't that high on the priority list.

Welcome to any discussion about China.

Weird comment given Space X is about to start moon orbit tourism trips.

Now. 3 years ago the launch date was 2018

It’s easy to promise. I hope spacex deliver, and I hope it does by 2030. That would be great.

But for now “about to start” is as meaningful as Branson’s statements back in 2003.



I was really surprised to see an article on HN about China that wasn't full of ignorant hate and racism in both the article and in the comments, but then down and the very bottom is your sole lonely comment. Stay true, freedom fighter.

Good point :)

Or not :(

But did they find a Nazi moon base?


A great day for listening to Pink Floyd!


And until now nobody is complaining how this moon landing was fake because Jim Bridenstine used a 3D simulation instead of a photo. I'm impressed.

The headline should be "China claims to successfully land..." Given the government and business tendency in China to make claims that later turn out to be fabricated nothing they announce should be taken as true without independent verification.

How clever of them to have faked a rover failure with Chang'e 3 then, so that we'd believe them now if they report that the rover works. But seriously, we haven't seen any indications of the CNSA faking anything. China isn't a person, it's a whole big country. The fact that Bernie Madoff defrauded a huge number of people doesn't mean that you can't trust NASA.

I don't want to sing the praises of CNSA's openness here. They have a history of keeping things secret until they work out, like the Soviets did. And probably there are failures we'll never hear about. But if they say they landed a probe on the far side of the Moon then there isn't reason to doubt them.

This isn't really impressive enough to be worth the risk of lying about, and anything that was impressive enough would be worth verifying so you couldn't lie about it anyway. If they're going to lie about something, it would be something they would have total information control over in the first place, like, "no, of course we didn't try to launch a rocket on this date".

Seconded. That is the proper contextualization for news out of CH.


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