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Genuine moon landing - a bit rough?

axeman3d

By axeman3d
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axeman3d

axeman3d

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Just watched the raw footage of the Chinese lander coming down...

Discovery Website news footage

It all goes swimmingly, it comes down nice and smoothly and then they stop all forward motion and hover over the landing site for a few seconds. When the actual descent starts and they land it looks like one of my landings where I leave the braking a little too late!

The one thing that always gets me is how the moon (and the Mun) look almost exactly the same from 5m as from 5000m. Trying to judge distances without some context such as the lander shadow or a radar altimeter is practically impossible.

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AlternNocturn

AlternNocturn

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The Chang'e 3 lander is designed to cut the engine at about 4 meters above the surface and drop straight down. This is to avoid kicking up dust, which would get everywhere. (most of the lander's components are designed to be dustproof, but better safe than sorry!)

EDIT: Huh, looks like the engine didn't cut out completely. I doubt the casters during the live launch would have lied about the engine cutting out though, perhaps that was fuel venting.

Edited by AlternNocturn
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Rastaman

Rastaman

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It looks fast...... but I think that's okay due to the extremely low gravity there. It's only going to suffer 20% of the shock something landing at the same speed on earth.

I think......don't quote me as I'm not a scientist. :wink:

That doesn't sound right... :) Momentum and kinetic energy is the same no matter the gravity. We don't have a time stamp, so it's hard to say if it is real time.

Fascinating video.

Edited by Rastaman
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NeoMorph

NeoMorph

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It looks fast...... but I think that's okay due to the extremely low gravity there. It's only going to suffer 20% of the shock something landing at the same speed on earth.

I think......don't quote me as I'm not a scientist. :wink:

There is something called "Ground Rush" where the speed at landing seems to get faster than it actually is. I used to get it when I went skydiving... nice... slow... glide... in... to... landing... and... then.... OMGHERECOMESTHEGROUNDREALLYFAST. Got me every time lol.

BTW, I don't think they landed on the moon at all. They just took KSP, did a bit of a retexture and made it out to be real. :wink:

Seriously though, the image where it hovered for a bit made me think it was still miles up. Was a shock when it started kicking up dust...

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Sirrobert

Sirrobert

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It looks fast...... but I think that's okay due to the extremely low gravity there. It's only going to suffer 20% of the shock something landing at the same speed on earth.

I think......don't quote me as I'm not a scientist. :wink:

Gravity is irrelivant in this respect. If you go 10m/s and you suddenly hit the surface, you will get the same crash on earth, the moon, or on Eve. The difference is how fast you accelerate. Thus how fast you GAIN speed when your engines cut out.

An example is a car crash. There is no gravity actiong on the car that pulls it toward the wall, but the hit is still a crash

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SlyReaper

SlyReaper

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What a great video! Congratulations to China for this amazing achievement! I wish there would be a manned mission though :( I wasn't even born when they (USA of course) pulled that one off... Man, I would be glued to the screen the entire mission. Please, someone... make it happen.

If there's one thing guaranteed to cajole the US into sending another manned mission to the moon, it'll be China announcing their intention to send a manned mission to the moon. :D

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peadar1987

peadar1987

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It looks fast...... but I think that's okay due to the extremely low gravity there. It's only going to suffer 20% of the shock something landing at the same speed on earth.

I think......don't quote me as I'm not a scientist. :wink:

Not quite, it will suffer far less of a shock when dropped from the same height because of the lower gravity, but momentum (which is what really causes the damage) is related to your mass and the speed you're going, no matter what the gravity is where you are.

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maccollo

maccollo

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EDIT: Huh, looks like the engine didn't cut out completely. I doubt the casters during the live launch would have lied about the engine cutting out though, perhaps that was fuel venting.

Maybe they just set the engine to minimal thrust to minimize the chance of failure? They probably did some testing to see just how much thrust they could apply at the surface without kicking up significant amounts of dust.

I believe Curiosity was rated to land at 4 m/s so its really not that unusual for a bit of a bump.

4 m/s is actually quite fast. It's just jogging into a wall.

http://youtu.be/cPgsGkPtiVw

In this drop test they lowered the rover quite slowly, I'd guess no more than 1 m/s, and even tho was capable of dealing with these forces it sounds like it's gonna fall apart.

I saw a different video where you could also see the reactions of the team after the test, and it can basically be sumerised as "oh dear, that's a lot rougher than I thought".

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Sid

Sid

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I asked my Kerbals and they said it's better than any landing I have ever put them through. Further comments were :-

" At least they remembered to put the descent engine on it, unlike you "

" They landed the right way up ? I didn't know that was possible, why don't you try it next time ? "

" We are all moving to China "

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kiwi1960

kiwi1960

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4 meters is nothing.... its the speed the lander lands at which is the important factor, there is a big difference between dropping at 1 meter a second and 100 meters a second... THAT is the important thing. The moon has only 1/6th the gravity of Earth, meaning, a fall here for anything is only going to be 60% as dangerous on the moon...

The engine doesn't cut out at any height till its safely down, they leave it running in case they have to find a safe landing spot, the engine is cut once its confirmed its down safely. It would be stupid to cut the engine if its still above the surface because who knows what will happen...

And the dust is also not a factor, the rocket(s) would blow that out and away from the lander.... and as there is no wind, its going to settle down rather quickly and nor will it blow back onto the lander...

Before the first manned landing, there were many heated debates about whether the 'dust" would support the lander or it it would sink completely .... just some trivia for you...

EDIT: Engine set to minimum thrust, but not shut down, as I said...

I was half expecting Jeb to show himself in that video... but then, the landing was too perfect... :)

Edited by kiwi1960
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rdfox

rdfox

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For the record, the contact probes on the Apollo Lunar Module were six feet (slightly less than two meters) long, and the engine was *manually* shut off once they lit the "contact light" in the cabin. However, it was close to a two-meter drop.

And just about all spacecraft landings are fairly rough. As an anonymous Grumman engineer said in defending the proposal to switch to a standing flying position for the LM, "legs are GREAT shock absorbers." Even the "gentle" splashdowns of the capsule-type American spacecraft under their parachutes were at a descent rate of about 10 m/s (20 mph) at impact, which is why NASA took great pains to target water landings, while the Soviets had Vostok pilots eject from their capsule and parachute down separately and developed the braking rockets for Voshkod and Soyuz. Even the Space Shuttle tended to thump you in--apparently, the main gear touchdown was rather gentle and tended to be unnoticed, but due to the design of the vehicle, the nosewheel would come down hard enough to loosen your fillings.

Unrelated, but awesome: When Ranger VII was the first success of the Ranger "hard-landing" lunar probe project (i.e., "just crash the damn thing into the Moon, we'll get photos and bragging rights and can save a soft landing for the next program!"), the thousands of photos it sent back during the terminal descent were put together into a movie for release to the press. However, this movie was first shown to the astronauts in a private screening. Of course, for an audience of test pilots, a "pilot's-eye view" movie of an impending crash isn't exactly the most entertaining thing... until, just when impact seemed imminent, Wally Schirra piped up in the back of the room, shouting, "BAIL OUT, YOU FOOL!" And the whole room dissolved into howls of laughter...

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pizzaoverhead

pizzaoverhead

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And the dust is also not a factor, the rocket(s) would blow that out and away from the lander.... and as there is no wind, its going to settle down rather quickly and nor will it blow back onto the lander...

The Mars Curiosity rover had one of its wind sensors damaged by what is believed to be stones kicked up by the landing rockets. It would be possible for this to occur on the Moon also: At low altitudes, some of the thrust reflected from the surface, along with any debris it has brought with it, will be angled at the bottom of the craft.

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  • 3 weeks later...
John FX

John FX

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And 4m/s is a soft landing compared to the impact the KSP landing legs are designed to absorb!

I lithobraked by accident the other day and hit at over 21m/s testing landing near KSC and was fine. I initially thought nothing had broken as I just stopped dead like I had landed normally. I had a rover underneath and four landing legs on the lander, I EVA`d out (yes the kerbal was still alive!) and then noticed four broken legs and four burst tyres on the rover which had absorbed the impact it seems. I repaired them and all was good.

I like the new repairing stuff system. Might need extending to solar panels and other parts, if you can find them you can stick them back on sort of thing.

I`m not even sure how fast 20m/s is. Isn`t it something like 60mph?

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John FX

John FX

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Just worked it out at 2.25mph so I hit the ground at roughly 50mph and was ok...

I think parachuting down to Duna got a lot easier recently...

Right, I`m off to design a Duna drop pod. Made an awesome Kerbin one. You are doing 130m/s at 200m when your main chutes aren`t even open yet, 50m/s at 45m and about 8m/s by the time you get to the ground. Naturally I had to have it operated by KOS or explodey death happens.

Uses a one kerbal pod, 6 separatrons (3 to deorbit, 3 to land) a KOS unit, 3 legs, and a chute

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