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Athena landed in a dark crater where the temperature was -280° F / -173° C

arstechnica.com

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Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#111

Post by mncharity »

alwayslikethis wrote: post #90
usrnm wrote: post #86

Earlier quoted context omitted.

It's not like using Kelvin or Celsius helps you grasp these temperatures. -173C is very, very cold, but how cold? What can you compare it to? Not many humans have any experience with something of this scale

Liquid nitrogen (boiling at -196 C) is a semi-common substance that people would have heard of, though not everyone would have seen or interacted with it.

That's the example Copilot used when asked to make a list of temperatures in 50 C steps with an example or two of something around that temperature that people might have heard of. Also cryogenic freezing of biological samples.

Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#112

Post by inetknght »

alwayslikethis wrote: post #90
usrnm wrote: post #86

Earlier quoted context omitted.

It's not like using Kelvin or Celsius helps you grasp these temperatures. -173C is very, very cold, but how cold? What can you compare it to? Not many humans have any experience with something of this scale

Liquid nitrogen (boiling at -196 C) is a semi-common substance that people would have heard of, though not everyone would have seen or interacted with it.

I've seen liquid nitrogen, briefly, as it was sprayed out of a hose. It immediately boiled into a (quite cold) gas, of course. I was told not to play with it too much because they would have to evacuate the building. Oh the joys of "bring your kid to work" days in manufacturing facilities

Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#113

Post by kiicia »

usrnm wrote: post #86
scotty79 wrote: post #73

Earlier quoted context omitted.

I refuse to believe anyone knows how cold -280F is. When you have such extreme temperatures you think in Kelvin or at least Celsius.

It's not like using Kelvin or Celsius helps you grasp these temperatures. -173C is very, very cold, but how cold? What can you compare it to? Not many humans have any experience with something of this scale

-173C is just twice your typical winter in Yakutia

Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#116

Post by abdullahkhalids »

dietr1ch wrote: post #62
layer8 wrote: post #37

Earlier quoted context omitted.

It’s roughly a third of room temperature.

Which is hard to grok since a third of something warm doesn't seem to be extremely cold.

This is an interesting explanatory challenge.

Temperature is roughly how fast molecules are moving, vibrating etc. And the impact of low/higher temperature are really how fast molecules are knocking you. For an ideal gas, temperature is proportional to the square of the velocity.

So at room temperature (300K), the speed of the molecules is roughly 300^0.5 = 17.3 in some arbitrary units. If you drop down to freezing point of water, (273K), speed is 16.5. And that is starting to get cold. -40C (as cold as most humans will experience) is 15.3. So each drop of 1 in speed is pretty drastic.

At 100K, the speed is 10, or 7 drops from 17. That should be a lot colder than room temperature. But not cold enough. Most of the speed is still there, we haven't even cut it by half. It's the next few 1/3rd cuts of the temperature that will start to get us closer to zero speed.

Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#117

Post by nomel »

ceejayoz wrote: post #8
1970-01-01 wrote: post #7

Still unclear what happened. Did they not anticipate a big moon hole or did navigation fail when the rangefinder failed?

I'm not sure what you find unclear. Navigation was fine - "Athena knew where it was relative to the surface of the Moon" - but without a working altimeter it was kinda fucked for actually touching down. Hard landing, skid, tip.

> "Athena knew where it was relative to the surface of the Moon" - but without a working altimeter it was kinda fucked for actually touching down.

Z is an axis that exists in our 3d world, and a required value for any relative position, which means it DID NOT know where it was, relative to the moon.

Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#118

Post by ted_dunning »

layer8 wrote: post #89
dietr1ch wrote: post #62

Earlier quoted context omitted.

Which is hard to grok since a third of something warm doesn't seem to be extremely cold.

It’s sort-of the point to realize that it actually is (a third of something). The lander is receiving a third of the thermal energy that it would receive at room temperature. Warm-blooded mammals of course have a reference point based on their thermal homeostatic capabilities (ability to maintain body temperature). “Warm” and “cold” is in relation to that.

I don't think that black-body radiative transfer is a linear process.

The Stefan-Boltzman relation says power scales with the fourth power of temperature. So 1/3 absolute temperature would be 1/81 the inbound radiative energy. If you are getting 800W inbound at room temp, you would get 10W inbound at 100K (=300K/3).

Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#119

Post by ted_dunning »

JumpCrisscross wrote: post #82
sandworm101 wrote: post #80

Earlier quoted context omitted.

Lol. SpaceX has landed on prepared surfaces, concrete pads on land or on large barges. They literally have a big X to mark the target. Let's see them land on some random beach, an uneven surface that may or may not subside. But that is still peanuts comparted to the moon's surface.

> that is still peanuts comparted to the moon's surface Sure. I'm not trivialising the problem in an absolute sense. Just going from floating barge or chopsticks to Moon is a simpler set of problems than reïnventing the sort of translational velocity and attitude control needed to get to first base.

You say this based on your history of landing rockets on the moon?

And on your history of dealing with the lunar regolith near the poles?

Re: Athena landed in a dark crater where the temperature was -280° F / -173° C

#120

Post by accrual »

> For the second mission in a row, the lander's altimeter failed

That's a bummer. Altimeters are relatively simple and defined hardware as far as I know. Send a ping, receive a ping, calculate. Too bad they didn't incorporate a backup solution.

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