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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

#121

Post by Rooster61 »

ptero wrote: post #114
sizzzzlerz wrote: post #111

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…

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.

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

#122

Post by ngcc_hk »

brainwipe wrote: post #54
A2017U1 wrote: post #4

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 Ear…

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.

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

#123

Post by Rooster61 »

vermontdevil wrote: post #104

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.

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.

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

#124

Post by eps »

computerex wrote: post #88
eps wrote: post #79

Earlier quoted context omitted.

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.

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

#125

Post by balabaster »

Retra wrote: post #118
vermontdevil wrote: post #104

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.

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

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

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

#126

Post by SCAQTony »

jackconnor wrote: post #3

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.

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. ..."

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

#127

Post by ptero »

Rooster61 wrote: post #121
ptero wrote: post #114

Earlier quoted context omitted.

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…

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 r…

> 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.

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

#128

Post by bluGill »

vermontdevil wrote: post #104

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.

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".

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

#129

Post by scrumbledober »

jsjohnst wrote: post #85
A2017U1 wrote: post #26

Earlier quoted context omitted.

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.

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

#130

Post by Rooster61 »

ptero wrote: post #127
Rooster61 wrote: post #121

Earlier quoted context omitted.

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 r…

> 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 i…

> 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?

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