Author Topic: Lm hovering  (Read 1162 times)

Offline Bryanpoprobson

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Re: Lm hovering
« Reply #15 on: January 30, 2018, 07:03:54 AM »
But this whole topic has more to with two objects moving at the same orbital speeds prior to the LM burn, so the LM will look like it is hovering as would an object travelling at the same velocity in Earth orbit.

Part of the un-docking procedure involved the CM giving the LM a visual once over.
"Wise men speak because they have something to say!" "Fools speak, because they have to say something!" (Plato)

Offline benparry

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Re: Lm hovering
« Reply #16 on: January 30, 2018, 08:24:26 AM »
But this whole topic has more to with two objects moving at the same orbital speeds prior to the LM burn, so the LM will look like it is hovering as would an object travelling at the same velocity in Earth orbit.

Part of the un-docking procedure involved the CM giving the LM a visual once over.


Sorry bryanpoprobson i misunderstand. what 2 objects are moving at the same speeds. is the LM not connected the CM so 1 object moving at 1 speed

Offline Bryanpoprobson

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Re: Lm hovering
« Reply #17 on: January 30, 2018, 08:29:16 AM »
That was me not looking at the video :). I was making assumptions.
"Wise men speak because they have something to say!" "Fools speak, because they have to say something!" (Plato)

Offline benparry

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Re: Lm hovering
« Reply #18 on: January 30, 2018, 08:30:49 AM »
That was me not looking at the video :). I was making assumptions.


oh sorry lol would you take a quick look and see what you think. its about 22 minutes in. it seems ok to me but ... lol

Offline jfb

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Re: Lm hovering
« Reply #19 on: January 30, 2018, 12:43:42 PM »
Hey guys hope everybodies well. I decided to join a FB group on the moon landings. Mostly believers. However a gent has shared with me a video which about 22 minutes in seems to show him that the LM is hovering and not orbiting. Any thoughts https://m.youtube.com/watch?v=3VFQ2eZKXBU&feature=youtu.be

That's footage shot from orbit, using a camera (looks like it's hand held) pointing out a window. 

"Hovering" implies they'd be a couple of hundred feet above the surface, which is definitely not the case here (not enough surface detail). 

Orbital velocity is a function of both mass and altitude.  For a given planetary mass, higher orbits have lower velocity.  For a given orbital altitude, lower planetary masses require a lower orbital velocity.

The orbital speed for a circular orbit can be approximated by sqrt((GM)/r)1, where G is the gravitational constant (6.67408 × 10-11 m3 kg-1 s-2), M is the mass being orbited (for the Moon, 7.342 x 1022 kg), and r is the distance from the center of the mass being orbited (Lunar radius is approx 1740 km, so add that to your altitude above the surface).  Assuming a 200 km orbit, that gives us (very) roughly 1590 m/s.

A 200km orbit above the Earth requires a velocity of ~7800 m/s. 


  • This formula only works for objects that are much less massive than the thing they are orbiting, and when the orbit is roughly circular.  It won't work for orbits of large natural satellites like the Moon, or orbits that are highly eccentric.

Offline benparry

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Re: Lm hovering
« Reply #20 on: January 30, 2018, 02:49:29 PM »
Hey guys hope everybodies well. I decided to join a FB group on the moon landings. Mostly believers. However a gent has shared with me a video which about 22 minutes in seems to show him that the LM is hovering and not orbiting. Any thoughts https://m.youtube.com/watch?v=3VFQ2eZKXBU&feature=youtu.be

That's footage shot from orbit, using a camera (looks like it's hand held) pointing out a window. 

"Hovering" implies they'd be a couple of hundred feet above the surface, which is definitely not the case here (not enough surface detail). 

Orbital velocity is a function of both mass and altitude.  For a given planetary mass, higher orbits have lower velocity.  For a given orbital altitude, lower planetary masses require a lower orbital velocity.

The orbital speed for a circular orbit can be approximated by sqrt((GM)/r)1, where G is the gravitational constant (6.67408 × 10-11 m3 kg-1 s-2), M is the mass being orbited (for the Moon, 7.342 x 1022 kg), and r is the distance from the center of the mass being orbited (Lunar radius is approx 1740 km, so add that to your altitude above the surface).  Assuming a 200 km orbit, that gives us (very) roughly 1590 m/s.

A 200km orbit above the Earth requires a velocity of ~7800 m/s. 


  • This formula only works for objects that are much less massive than the thing they are orbiting, and when the orbit is roughly circular.  It won't work for orbits of large natural satellites like the Moon, or orbits that are highly eccentric.


so in a nut shell because the moon has 1 6th gravity of the earth the object would need to travel a lot faster around earth than it would the moon

Offline jfb

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Re: Lm hovering
« Reply #21 on: January 30, 2018, 04:14:09 PM »
Hey guys hope everybodies well. I decided to join a FB group on the moon landings. Mostly believers. However a gent has shared with me a video which about 22 minutes in seems to show him that the LM is hovering and not orbiting. Any thoughts https://m.youtube.com/watch?v=3VFQ2eZKXBU&feature=youtu.be

That's footage shot from orbit, using a camera (looks like it's hand held) pointing out a window. 

"Hovering" implies they'd be a couple of hundred feet above the surface, which is definitely not the case here (not enough surface detail). 

Orbital velocity is a function of both mass and altitude.  For a given planetary mass, higher orbits have lower velocity.  For a given orbital altitude, lower planetary masses require a lower orbital velocity.

The orbital speed for a circular orbit can be approximated by sqrt((GM)/r)1, where G is the gravitational constant (6.67408 × 10-11 m3 kg-1 s-2), M is the mass being orbited (for the Moon, 7.342 x 1022 kg), and r is the distance from the center of the mass being orbited (Lunar radius is approx 1740 km, so add that to your altitude above the surface).  Assuming a 200 km orbit, that gives us (very) roughly 1590 m/s.

A 200km orbit above the Earth requires a velocity of ~7800 m/s. 


  • This formula only works for objects that are much less massive than the thing they are orbiting, and when the orbit is roughly circular.  It won't work for orbits of large natural satellites like the Moon, or orbits that are highly eccentric.


so in a nut shell because the moon has 1 6th gravity of the earth the object would need to travel a lot faster around earth than it would the moon

Yup.  For any given orbit, an object has to fall "sideways" faster around the Earth than around the Moon.  So low lunar orbits look positively leisurely compared to low Earth orbits (such as the live view from the ISS).  And if you have a camera that you're just pointing out a window, you can remain fixed on one object for quite a while, so it may look like you're hovering over it, even though in reality you're screaming past it at 1600 m/s.

Offline Apollo 957

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Re: Lm hovering
« Reply #22 on: January 30, 2018, 04:38:06 PM »
I look at 22mins and I see a craft moving, not hovering. Look at the crater bottom left, the window frame is clearly obscuring more and more of the crater as the craft moves. 

Offline nomuse

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Re: Lm hovering
« Reply #23 on: January 30, 2018, 11:08:36 PM »
Urggg....okay, for the sake of the current discussion, its good enough, but it is making my skin crawl anyhow.

It's all about MASS. The Moon being "smaller" (in diameter) actually means orbit can be faster, as you can get closer to the theoretical point source (don't bring up mascons, okay? bad enough already). The mass being smaller, though, means mutual attraction is lower. Add it all up and you get, basically, slower.

Hovering, though..  != sharing orbital elements. Can you share detail on this person's arguments, or a link to where they appear? Because from here it sounds particularly non-sensical.


Offline benparry

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Re: Lm hovering
« Reply #24 on: January 31, 2018, 05:13:01 AM »
Oh it is non sensical lol i just thought i would ask here to make sure. the answers before have explained to me that lower gravity mean slower movement. also the camera is not fixed.

Offline Abaddon

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Re: Lm hovering
« Reply #25 on: January 31, 2018, 10:18:37 AM »
Oh it is non sensical lol i just thought i would ask here to make sure. the answers before have explained to me that lower gravity mean slower movement. also the camera is not fixed.
Think about it for just a moment. By the crazy logic of the claim, geostationary satellites are hovering and must all therefore be fake. In consequence, satellite TV must also be fake since it relies on those fake satellites.

That is obvious nonsense. When you set up your satellite TV dish, you point it at a fixed spot in the sky (i.e. the location of the "hovering satellite that provides your signal.) What you don't do is pay some bloke to constantly reposition your dish 24/7 like a demented WWII tail gunner.


Offline nomuse

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Re: Lm hovering
« Reply #26 on: January 31, 2018, 01:01:20 PM »
Oh, I would totally pay for that!

Offline jfb

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Re: Lm hovering
« Reply #27 on: January 31, 2018, 03:37:29 PM »
Geostationary sats are my chief retort to hard-core geocentrists (the kind who claim that the Earth doesn't even rotate on its axis).  If they're stationary with respect to the Earth's surface, and the Earth doesn't rotate - well, what's keeping gravity from pulling them back down again?  DirecTV obviously works, so geostationary sats must be a thing, so...

Same thing with polar orbits - why does the ground track of the satellite move?  If the Earth were standing still, it wouldn't. 

To be fair, there's a lot about orbital mechanics that isn't intuitive (such as lower orbits being faster), but we're not talking about the hard stuff, here.

Offline nomuse

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Re: Lm hovering
« Reply #28 on: February 01, 2018, 12:23:28 AM »
Meh. If the flat-earther stuff I was looking at is any guide, they'll just claim since there's no atmosphere around the satellites, there's no reason for them to fall. Because apparently "density" is a better explanation for why things fall than "gravity."

Yeah, I know. Talk to them. I don't think even they can understand what they are trying to say. Even if buoyancy somehow happened without gravity to drive it, how's that explain why things fall DOWN?