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China lands Chang'e-4 on far side of Moon

planetary.org

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Re: China lands Chang'e-4 on far side of Moon

#71

Post by akfish »

jetison_out_to_ wrote: post #33

Noticed this is the same day as NASA got the Ultima-Thule photos. Was this announced today to overshadow it, like how Uber announced their IPO basically a day after Lyft's? Want to avoid going off about conspiracy theories or who's more patriotic, just curious how the announcements actually lined up. This (wikipedia-sourced) AP wire from Oct 22, 2015 when the Pluto flyby happened said they had re-pointed the probe fo…

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.

Re: China lands Chang'e-4 on far side of Moon

#72

Post by avar »

dingaling wrote: post #50
trothamel wrote: post #23

Earlier quoted context omitted.

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 hav…

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.

Re: China lands Chang'e-4 on far side of Moon

#73

Post by scotty79 »

tanilama wrote: post #41
arduanika wrote: post #5

"...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.

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

Re: China lands Chang'e-4 on far side of Moon

#74

Post by jaimex2 »

golfer wrote: post #15

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...

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

Re: China lands Chang'e-4 on far side of Moon

#76

Post by skilled »

Rebelgecko wrote: post #37
skilled wrote: post #25

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 p…

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

Re: China lands Chang'e-4 on far side of Moon

#78

Post by mattio »

tanilama wrote: post #41
arduanika wrote: post #5

"...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,…

What did the rabbit do, to be punished with her :-P

Re: China lands Chang'e-4 on far side of Moon

#79

Post by eps »

dandare wrote: post #77

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.
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