“Isn’t the Moon’s gravity just 1.63 m/s2? Why would one fall into the sinkhole at 18m/s?”

1.63 m/s2 = 1.63 m/s/s = acceleration of 1.63 m per second per second. After 11 seconds of fall from the lip of the pit, the speed at which one would hit the bottom is (1.63 m/s /s) * 11 s = 18 m/s.

How to derive 11 seconds:

Distance fallen = 0.815 m * t^2, where t is time of fall in seconds.

Solving for t: t = sqrt(distance/0.815).

So a 100 m fall would take sqrt ( 100 / .815 ) seconds = sqrt(123) seconds = 11 seconds.

I have a question. You wrote “The lava can carve a groove in the surface, and eventually the top of the lava flow solidifies even before the flow stops. When the lava flows away, you’re left with a tube under the surface, like a subway tunnel. At that point, the roof of the tube can collapse in spots; on Earth this is common in Hawaii and other volcanic spots. ”

I understand how this works on Earth, because heat is conducted away from the lava by the atmosphere. But of course on the moon there is no atmosphere. Wouldn’t the underlying lava conduct heat to the surface lava faster than the surface could lose heat in a vacuum?

Christian

I’m baffled by the “roundness” of the pit. If it is a result of a collapsed “roof” over a lava-flow-formed tunnel, then why wouldn’t the pit be more elongated–along the length of the tunnel? Or am I missing something? Did the pit form maybe as a result of a meteor hit? That would, I suppose, form a circular hole.

Can anyone help me out with this?

Thank you.

…In some of the pre apollo books about the moon talk about a raging debate about the formation of the craters called the hot moon cold moon theory. Hot moon said the craters are volocanos, cold moon said the craters are meteor impacts both made sense .The Apollo missions settled the issue both were correct some craters were volcanos others were meteor impacts.

Correct me if I’m wrong please, but my understanding is that the Apollo missions confirmed the meteorite impact theory rather conclusively over the volcanic one & that by far the vast majority of lunar craters are caused by bolide impacts rather than vulcanism.

Sure you have lava flows in the lunar maria and the odd volcanic cinder cone and lava floding crater floors .. but not too many craters are volcanic calderas are they?

@53. George Martin :

Aha! That’s the one. Great novel too. Best aliens Asimov ever came up with. I don’t recall the Moon being in that but .. hmmm .. I’ve got an excuse to re-read it again now!

@59. Rincewind Says:

Well, a different Heinlein story, “The Moon is a Harsh Mistress”, had a solution for that. They built a huge linear-induction catapult, powered by solar panels and built with local materials. They could fling loads to Earth (or near Earth) or other locations as needed. If your aim is good, you could probably use it in reverse, to catch incoming ships or cargo and slow them down, and pump the energy back into the system (like regenerative braking).

Formula One racing cars have been used the KERS (Kinetic Energy Recovery) system last year & this. I guess that’s be the same sorta thing, yeah?

@51. vince charles Says:

No, launches involving the Moon cost _MORE_ propellant, not less. As the Moon has no atmosphere, landing equipment there requires landing on engine thrust. This thrust is necessary to brake you, as you’ll fall into the Moon’s gravity well with enough force to break anything useful for propellant processing. Then, once you’ve created spacecraft and supplies, you mush launch _OUT_OF_ the Moon’s gravity well. Here, again, the Moon has enough gravity to make things difficult, but not enough to be useful (i.e., attracting an atmosphere and keeping a fluid, iron core, giving you radiation shielding).

Er .. so lesse then, can you explain again how the colossal Saturn V is required to escape Earth’s gravity well but the Lunar Module’s ascent stage will suffice for escaping the Lunar gravity well & the Lunar Module as tiny and fragile as it is is able to safely land on the Moon?

I think that indicates the situation there isn’t as pessimistic as you seem to believe it is.

It does rather astound and appall me that we could land on the Moon just fine back in the 1970′s but then its somehow become all too hard to do now in the twenty-teens.

We went so far .. only to have fallen backwards so far. What the..?!?

Still if the engine of a Lunar module ascent stage is enough to get us off the Moon I don’t think we have any cause to worry on that particular score.

@ 50. John Paradox Says:

What? You’ve never heard of Jethro Tull’s “For Michael Collins, Jeffrey, and Me”?

Can’t say that I have .. real song or joke there?

,,,plus the moon doesn’t have a pesky atmosphere to get in the way.

Gary 7

Well, a different Heinlein story, “The Moon is a Harsh Mistress”, had a solution for that. They built a huge linear-induction catapult, powered by solar panels and built with local materials. They could fling loads to Earth (or near Earth) or other locations as needed. If your aim is good, you could probably use it in reverse, to catch incoming ships or cargo and slow them down, and pump the energy back into the system (like regenerative braking). Of course, in the story the Lunar colonists, mostly criminals of various kinds dumped on the Moon to get them out of the governments hair, did an America/Australia and started a war of independence. They started dropping BIG rock on Earth, to get their point across.

@23 Dr Flimmer @27 MTU,

It was indeed Apollo 11 that encountered a troublesome boulder field at Tranquility Base, causing Armstrong to take manual control of the LM to avoid possible disaster.

A shape that can accommodate a sunken framework for an underground structure.

The hole is already excavated, saving lots of time that would otherwise be taken up with underground construction in low gravity.

Protection from radiation and micro-meteorites for eventual visitors.

It would be a lot of work and a major effort requiring innovations in technology for lunar structures and construction, but after a livable base is built, the walls of the hole and side channels can be studied, as Phil pointed out, as preserved time capsules of the moon, billions of years ago. Lots of other science and observations could be done from this base but that’s another story.

I bet the warranty on that thing expired a couple billion years ago!

I could’ve sworn it was in an Asimov story but you may well be right. I read a lot of old SF incl. Heinlein too although the name’s not ringing any bells with me.

Actually Asimov also used the concept of people living on the moon flying for recreation. It was in his novel The Gods Themselves (in the third part), published in 1972. I did know that Asimov was not the first to use this. I was raking my brain trying to remember while scrolling through the comments when someone the Heinlein short. “AH YES!”

George

P.S.

The title of the Asimov novel comes from the phrase “Against stupidity, the gods themselves contend in vain.” The novel won the 1973 Hugo award for best novel.

There’s a song about Mike Collins? I’ll have to look it up. I think his book “Carrying the Fire” is the best of the astronaut memoirs.

No, launches involving the Moon cost _MORE_ propellant, not less. As the Moon has no atmosphere, landing equipment there requires landing on engine thrust. This thrust is necessary to brake you, as you’ll fall into the Moon’s gravity well with enough force to break anything useful for propellant processing. Then, once you’ve created spacecraft and supplies, you mush launch _OUT_OF_ the Moon’s gravity well. Here, again, the Moon has enough gravity to make things difficult, but not enough to be useful (i.e., attracting an atmosphere and keeping a fluid, iron core, giving you radiation shielding).

A little knowledge is a dangerous thing… a lot of knowledge is depressing.

What? You’ve never heard of Jethro Tull’s “For Michael Collins, Jeffrey, and Me”?

J/P=?

Couple of things…deficits are a problem that’s for sure. And what do you need to get out of them? The best way to do it is to grow your way out. Putting people to work has an effect. Those people spend their wages on things that other people make and sell. The research has been done, money spent on things like research and scientific endevours………….make money. For the government in taxes and for the econony at large. The space program has a very clear record of paying for itself in spades.

The other argument is of course a little silly, no one has ever loaded a spaceship up with cash and fired it off.