Imagine the first landing strip on the moon

[John Gogo]

What would the descent be like at 1/8th gravity?

[John Gogo]

On Tuesday, July 28, 2015 at 12:04:15 AM UTC-5, John Gogo wrote:
> What would the descent be like at 1/8th gravity?

The first thing we did when we conquered in WWII is build a landing strip.

[John Gogo]

How would they take off?

[John Gogo]

Sometimes, I truly believe that science will only advance in terms of sending unmanned- auto-mated versions of ourselves. We could get robots to colonize the moon before we ever showed up there. Battle of the Bots advanced.

[Thomas Heger]

Am 28.07.2015 07:04, schrieb John Gogo:
> What would the descent be like at 1/8th gravity?

You have two components: inertia and gravity.

Gravity is much lower on the Moon, while inertia is not.

Since the Moon has no atmosphere, a spaceship landing there had to
decelerate by reversed thrust. This is necessary to prevent the craft
from slamming into the ground.

The acceleration caused by gravity had to be compensated by thrust from
the engine, too, but this component is much lower compared to the same
effect here on Earth.

Since on Earth we have air to slow down the craft and on Moon we have
not, we need much more fuel for landing, since the inertial movement can
only be compensated by reverted thrust.

How much more the latter effect is compared to saving due to lower
gravity, that is depending on velocity. So we had to assume some sort of
velocity, like orbit velocity around the moon. This is still rather fast
and most the fuel is required, to reduce the velocity to zero and a
little to prevent the spaceship from dropping down.

TH

[wobbly]

Thomas Heger wrote:

> How much more the latter effect is compared to saving due to lower
> gravity, that is depending on velocity. So we had to assume some sort of
> velocity, like orbit velocity around the moon. This is still rather fast
> and most the fuel is required, to reduce the velocity to zero and a
> little to prevent the spaceship from dropping down.

Are you just saying that this task is not achievable without a computer?

[Thomas Heger]

No. It is possible without computers, but is difficult. Certainly the
reverted thrust is not easy to control, since you have a set of
difficult tasks:

point the engine in the right direction (opposite to the flight path)

make the spaceship slow down according to the desired flightpath
(properly control the thrust)

target the planned landing zone

have exactly zero velocity in horizontal and vertical direction exactly
at the surface

You would need to have an eye on the fuel used, since that is a critical
point.

since you have not much additional fuel, you have only one try and no
means for corrections while on descent


All of the tasks are quite difficult, but could be achieved without a
computer (even if such a device would be helpful).

But VERY difficult is the problem of the needed fuel, since the craft
cannot use a parachute to slow down. It could only decelerate by
reversed thrust and that is something, that consumes a LOT of fuel.

TH

[Thomas Heger]

Am 29.07.2015 03:14, schrieb Thomas Heger:

>>> How much more the latter effect is compared to saving due to lower
>>> gravity, that is depending on velocity. So we had to assume some sort of
>>> velocity, like orbit velocity around the moon. This is still rather fast
>>> and most the fuel is required, to reduce the velocity to zero and a
>>> little to prevent the spaceship from dropping down.
>>
>> Are you just saying that this task is not achievable without a computer?
>
>
> No. It is possible without computers, but is difficult. Certainly the
> reverted thrust is not easy to control, since you have a set of
> difficult tasks:
>
> point the engine in the right direction (opposite to the flight path)

The spaceship had to point the thrust EXACTLY into the direction, where
it is flying, since even a few degrees off would make the ship rotate.
And that would be EXTREMELY dangerous.

So the engine had to be directed very precisely into the right direction.

This is very similar to controlling the ascent of a rocket, but in the
opposite direction.

It would -at least require- some sort of guidance system and the ability
to adjust the position of the craft.

>
> make the spaceship slow down according to the desired flightpath
> (properly control the thrust)

The deceleration could not be too strong, since otherwise the thrust
would need to be very high. And this would require more precision in the
control of the orientation. Otherwise the ship would rotate.

Now this limited reverted thrust makes it much more difficult to
estimate, where the flightpath would end (compared to a steeper drop).

> target the planned landing zone
>
> have exactly zero velocity in horizontal and vertical direction exactly
> at the surface

Horizontal velocity in any direction while landing would be very
unpleasant, since it could make the spaceship tilt and land sideways.
This would be dangerous, since that would not allow to restart.

Vertical drop could only be compensated by damping legs or similar and
to a very small degree.

So in sum the ship needs to reach the surface with (almost) zero
velocity in any direction.

> You would need to have an eye on the fuel used, since that is a critical
> point.
>
> since you have not much additional fuel, you have only one try and no
> means for corrections while on descent
>
>
> All of the tasks are quite difficult, but could be achieved without a
> computer (even if such a device would be helpful).
>
> But VERY difficult is the problem of the needed fuel, since the craft
> cannot use a parachute to slow down. It could only decelerate by
> reversed thrust and that is something, that consumes a LOT of fuel.
>

The descent is quite similar to ascent (with opposite signs), hence
would require somehow similar means.

TH

[Sylvia Else]

On 29/07/2015 4:47 PM, Thomas Heger wrote:
> Am 29.07.2015 03:14, schrieb Thomas Heger:
>
>>>> How much more the latter effect is compared to saving due to lower
>>>> gravity, that is depending on velocity. So we had to assume some
>>>> sort of
>>>> velocity, like orbit velocity around the moon. This is still rather
>>>> fast
>>>> and most the fuel is required, to reduce the velocity to zero and a
>>>> little to prevent the spaceship from dropping down.
>>>
>>> Are you just saying that this task is not achievable without a computer?
>>
>>
>> No. It is possible without computers, but is difficult. Certainly the
>> reverted thrust is not easy to control, since you have a set of
>> difficult tasks:
>>
>> point the engine in the right direction (opposite to the flight path)
>
> The spaceship had to point the thrust EXACTLY into the direction, where
> it is flying, since even a few degrees off would make the ship rotate.
> And that would be EXTREMELY dangerous.

The thrust line has to pass through the craft's centre of gravity to
avoid making the craft rotate. The direction of motion (which is
ill-defined anyway) has nothing to do with it.

Sylvia.

[Sylvia Else]

On 28/07/2015 3:04 PM, John Gogo wrote:
> What would the descent be like at 1/8th gravity?
>

The essential requirement is that that vertical component of the
velocity be close to zero at the point where the craft makes contact
with the surface. The horizontal component can be anything, subject only
to the requirement that the surface be smooth enough that the craft
doesn't get shaken to pieces.

The higher the horizontal component of the touchdown, the closer the
craft is to still being in an orbit, and the lower is the amount of fuel
used in the landing.

In practice, though, to provide much of a saving, the touchdown has to
be at a horizontal velocity near to the orbital velocity. This would
require a very long landing strip, and landing gear capable of handling
very high velocities. Getting rid of the heat from braking could also be
a problem. The implied extra mass for the gear might better be used for
fuel in a conventional vertical landing.

Sylvia.

[Thomas Heger]

Am 30.07.2015 15:34, schrieb Sylvia Else:

>>>> Are you just saying that this task is not achievable without a
>>>> computer?
>>>
>>>
>>> No. It is possible without computers, but is difficult. Certainly the
>>> reverted thrust is not easy to control, since you have a set of
>>> difficult tasks:
>>>
>>> point the engine in the right direction (opposite to the flight path)
>>
>> The spaceship had to point the thrust EXACTLY into the direction, where
>> it is flying, since even a few degrees off would make the ship rotate.
>> And that would be EXTREMELY dangerous.
>
> The thrust line has to pass through the craft's centre of gravity to
> avoid making the craft rotate. The direction of motion (which is
> ill-defined anyway) has nothing to do with it.

Actually no!

There are two components: inertia and gravity.

To decelerate the craft, the thrust should point directly into the
direction, where the ships flies. (That's what I called 'direction of
motion'.) This is caused by inertia, what is not altered by the lower
gravity of Moon.

To compensate acceleration caused by gravity, the engine should generate
a force in opposite direction (up), hence the thrust should point down.

This makes two accelerations that combine to the needed thrust, (what
the crew had to direct properly).

Any minuscule error would cause a rotation or other unwanted features of
the flight (like hitting the ground).

TH

[Thomas Heger]

You certainly do NOT try to land like a plane on the Moon, since there
is no air.

It is actually possible, to fly in a very low orbit around the moon.

But you certainly do not like any kind of contact with ground at that
velocity!

Actually I'm insecure, how fast a wheel could possibly roll, but
certainly not much fast than about 400 km/h.

Orbit velocity around the Moon depends on altitude.
https://answers.yahoo.com/question/index?qid=20130914181012AABn55i
Quote:

" The minimum velocity happens at the highest orbit, not the lowest.
Depending on the orbit geometry, this could be as high as 4671 km from
the center of the moon. Higher orbits are possible, but they are not
stable -- they would end up going around the Earth-Moon system, not just
the moon.

At that altitude, the orbit speed (relative to the moon) is about 1.025
km/s = 3688 km/hr. The fastest orbit, very low to the surface, is 6048
km/hr. "

And you - definitely - do not want to land with 6048 km/h.

TH

[Sylvia Else]

What I said is true. To the extent that some particular thrust direction
is required for other reasons, the crew had better ensure that the craft
is oriented so that the thrust line goes through the centre of gravity.

Sylvia.

[Sylvia Else]

There are other options, such as magnetic levitation.

>
> Orbit velocity around the Moon depends on altitude.
> https://answers.yahoo.com/question/index?qid=20130914181012AABn55i
> Quote:
>
> " The minimum velocity happens at the highest orbit, not the lowest.
> Depending on the orbit geometry, this could be as high as 4671 km from
> the center of the moon. Higher orbits are possible, but they are not
> stable -- they would end up going around the Earth-Moon system, not just
> the moon.
>
> At that altitude, the orbit speed (relative to the moon) is about 1.025
> km/s = 3688 km/hr. The fastest orbit, very low to the surface, is 6048
> km/hr. "
>
> And you - definitely - do not want to land with 6048 km/h.

Given that it's in a vacuum, on a tectonically quiet body, it's not such
a way-out idea.

Whether it could ever make any economic sense (both financially, and in
terms of mass) is another matter.

Sylvia.

[Thomas Heger]

Am 31.07.2015 03:28, schrieb Sylvia Else:

>>> The thrust line has to pass through the craft's centre of gravity to
>>> avoid making the craft rotate. The direction of motion (which is
>>> ill-defined anyway) has nothing to do with it.
>>
>> Actually no!
>>
>> There are two components: inertia and gravity.
>>
>> To decelerate the craft, the thrust should point directly into the
>> direction, where the ships flies. (That's what I called 'direction of
>> motion'.) This is caused by inertia, what is not altered by the lower
>> gravity of Moon.
>>
>> To compensate acceleration caused by gravity, the engine should generate
>> a force in opposite direction (up), hence the thrust should point down.
>>
>> This makes two accelerations that combine to the needed thrust, (what
>> the crew had to direct properly).
>>
>> Any minuscule error would cause a rotation or other unwanted features of
>> the flight (like hitting the ground).
>>
>> TH
>
> What I said is true. To the extent that some particular thrust direction
> is required for other reasons, the crew had better ensure that the craft
> is oriented so that the thrust line goes through the centre of gravity.

No, it's not true:

gravity is the force, by what the Moon attracts the craft. This force is
pointing down - of course.

The centre of gravity of that spaceship is a certain point (within the
limits of this ship), where all gravitational forces balance out and we
could assume a single centre of gravity and a single vector acting upon
this point.

The other force is caused by deceleration. This is pointing in direction
of flight and has an own centre, where the forces add together like one
single vector acting upon the spaceship.

Only: these points do not need to be the same. This would only be the
case, if the craft would be a solid homogeneous piece of material.

This is clearly not the case, hence we had two different points for
centre of inertia (in direction of flight) and centre of gravity (vertical).

Also problematic: the craft is inhabited by astronauts, who could
possibly move. Also difficult to estimate is the influence of the
decreasing amount of fuel, while slowing down the ship.

You need to direct to thrust exactly opposite to the current sum of both
points. This is a little difficult, since the craft turns in vertical
direction, what has an effect upon this centre.

To actually control direction and strength of the thrust is way too
difficult to be done manually. But a relatively simple guidance system
could eventually do this. This would continuously measure the deviation
from the desired course and adjust the engine accordingly.

This would also enable to calculate the effect of corrections on the
place of landing, the landing velocity in vertical and horizontal
direction and the consumed fuel. From this a new course could be
calculated and feed into the guidance system, while still on descent.

Its quite a challenging task, especially if you try to land at a certain
spot, but is in the range of possibilities even with a cheap rasperry
pie and a moon-based equivalent to GPS.


TH

[Thomas Heger]

There is a very high danger caused by tremendous kinetic energy of a
spaceship landing at such a pace.

Any tiny deviation from the correct path would not only leave a few
scratches, but would make the entire thing explode.

You also have problems with mountains on the Moon, since you certainly
do not like them to be in your way, while orbiting along the surface.

And: the runway needs to be fantastically long, smooth and levelled.

After contact the runway should be able to absorb that enormous kinetic
energy, without getting torn to pieces.

So my guess: that's not possible to build.

TH

[kefischer]

In 1969, it might have had to be done
manually, with the pilot watching to avoid
craters or slopes, no electronics can do
that, and the electronics then was not
capable of all the inputs necessary.

[pcard...@volcanomail.com]

On Monday, July 27, 2015 at 10:04:15 PM UTC-7, John Gogo wrote:
> What would the descent be like at 1/8th gravity?

Without an atmosphere, a landing strip makes no sense.

[wobbly]

kefischer wrote:

> In 1969, it might have had to be done
> manually, with the pilot watching to avoid craters or slopes, no
> electronics can do that, and the electronics then was not capable of all
> the inputs necessary.

A human pilot is an adaptive filter. A slow one. Without electronics
(which are fast) flights are not possible nowadays. Disregard the flight
mode, automatic or performed by a pilot. Among all the piano movers I
know, you must be the most inexperienced one.

[kefischer]

On Sun, 2 Aug 2015 17:02:24 +0000 (UTC), wobbly <wob...@dont-email.me>
wrote:

>kefischer wrote:
>
>> In 1969, it might have had to be done
>> manually, with the pilot watching to avoid craters or slopes, no
>> electronics can do that, and the electronics then was not capable of all
>> the inputs necessary.
>
>A human pilot is an adaptive filter. A slow one. Without electronics
>(which are fast) flights are not possible nowadays.

That's what Ben Rich claimed about his baby,
but heck, anything with enough thrust and enough
control surface _will_ fly, and can be flown by man;

https://www.youtube.com/watch?v=2Q24sjLUzF4

https://www.youtube.com/watch?v=Wf9Jfa5f1FA

https://www.youtube.com/watch?v=_iqqHAWJq_0

https://www.youtube.com/watch?v=sGWF7QTZZi0

https://www.youtube.com/watch?v=aMeGqVGZcjA

Scroll to 7:00

https://www.youtube.com/watch?v=Q7ohBpNCQ5s


Now, change your name again, troll.

>Disregard the flight
>mode, automatic or performed by a pilot. Among all the piano movers I
>know, you must be the most inexperienced one.

I haven't moved a piano in 45 years.

[John Gogo]

Apollo 8 revolved around the moon umpteen times. How does a spacecraft land on the moon's surface from this position?

[pcard...@volcanomail.com]

Apollo 8 didn't land. The craft that did land, didn't use a landing strip.

[John Gogo]

Was it the best way to land and take off?

[Thomas Heger]

Am 02.08.2015 20:40, schrieb kefischer:
> On Sun, 2 Aug 2015 17:02:24 +0000 (UTC), wobbly<wob...@dont-email.me>
> wrote:
>
>> kefischer wrote:
>>
>>> In 1969, it might have had to be done
>>> manually, with the pilot watching to avoid craters or slopes, no
>>> electronics can do that, and the electronics then was not capable of all
>>> the inputs necessary.
>>
>> A human pilot is an adaptive filter. A slow one. Without electronics
>> (which are fast) flights are not possible nowadays.
>
> That's what Ben Rich claimed about his baby,
> but heck, anything with enough thrust and enough
> control surface _will_ fly, and can be flown by man;

To slow down a lander from orbital velocity to zero velocity, while
simultaneously land at a certain spot, that is fantastically difficult.


The pace was possibly about 5000 km/h in some kind of orbit at maybe 50
km above ground.

The spaceship would circle around the Moon forever, if it is not slowed
down.

Now you need to aim the engine into the right direction and fire it, to
make the craft slow down.

Since you have no air to guide the lander, the direction of the lander
needs to be manipulated into the right direction by pulses from
additional engines or by directing the main engine.

Any miscalculation would cause a rotation.

That is something, you definitely don't like, since the main engine
should point into the direction you are flying to. So, without
prevention of such rotation you could not land.

To achieve this precision of flight is certainly a challenging task.


TH

[John Gogo]

Remember the moon lander hardly weighed anything.

[John Gogo]

On Monday, August 3, 2015 at 9:32:52 PM UTC-5, Thomas Heger wrote:

I predict it will be 8 times harder than to land a plane on earth:>)

[Bohuš Matuška]

Thomas Heger wrote:

> That is something, you definitely don't like, since the main engine
> should point into the direction you are flying to. So, without
> prevention of such rotation you could not land.

Quite difficult to land and control a quadcopter with a joystick, lots of
buttons and a central processing unit. Ie

http://www.quadhangar.com/how-to-correct-a-drifting-quadcopter/

I have no idea how they did it at that time, just by looking out of a
window. I could not do it, that's for sure.

[Thomas Heger]

"How a gyroscope guides a rocket"
https://www.youtube.com/watch?v=KToggTKa9Lk

http://www.npcap.ru/en/main-directions-of-activity/inertial-control-systems/creation-of-inertial-control-systems/development-of-inertial-measuring-devices-and-systems/

http://www.clavius.org/techsteer.html


TH

[Bohuš Matuška]

Didn't look, but quadcopter are felt with all kind of sensors as well,
including 3d gyros, accelerometers and magnetic sensors.

[Thomas Heger]

Such model copters are actually a good example for the problems of rocketry.

The first landers had gyroscopes to guide the crafts.

First use of gyroscopes was in the rocket 'V2', build by Germans under
direction of Wernher von Braun. He was also the head of the 'Apollo'
program of the NASA, hence we can safely assume, he would use gyroscopes
if necessary.

Those Apollo landers had only one engine, hence the deceleration is
similar to balance a broom-stick on an ascending rocket. (certainly
difficult)

The other problems are:

a LOT of fuel is required

the velocity should be zero (vertically and horizontal) exactly at
surface level (not a few meters above or below).

the landing zone has influence on the subsequent rendezvous, hence it is
important to manage to land at a certain spot.

All of the tasks are interwoven, since e.g. corrections would require
time and that would make the lander land somewhere else. It would also
consume fuel.

To figure out the various consequences of a certain activity would
require a fast calculator, who could do such calculations several times
per second.


TH

[John Gogo]

Here's a moon nerd joke. If landing on the moon is too harmful for mankind then why don't we just land on its' dark side?

[Thomas Heger]

Am 06.08.2015 07:24, schrieb John Gogo:
..

>> the velocity should be zero (vertically and horizontal) exactly at
>> surface level (not a few meters above or below).
>>
>> the landing zone has influence on the subsequent rendezvous, hence it is
>> important to manage to land at a certain spot.
>>
>> All of the tasks are interwoven, since e.g. corrections would require
>> time and that would make the lander land somewhere else. It would also
>> consume fuel.
>>
>> To figure out the various consequences of a certain activity would
>> require a fast calculator, who could do such calculations several times
>> per second.
>>
>>
>> TH
>
> Here's a moon nerd joke. If landing on the moon is too harmful for mankind then why don't we just land on its' dark side?

Would be too dark. And it's actually quite cold there.

After sunrise, that would change very quickly and it gets really hot.
Also sunlight is VERY bright there and completely unfiltered.

So, you could chose between being boiled or getting frozen. And you
could chose between pitch black nothing and blazing brightness.

TH

[kefischer]

There is no "dark side", there is a "day side"
and a "night side".

[Thomas Heger]

Am 07.08.2015 08:41, schrieb kefischer:
>>> Here's a moon nerd joke. If landing on the moon is too harmful for mankind then why don't we just land on its' dark side?
>> >
>> >Would be too dark. And it's actually quite cold there.
>> >
>> >After sunrise, that would change very quickly and it gets really hot.
>> >Also sunlight is VERY bright there and completely unfiltered.
>> >
>> >So, you could chose between being boiled or getting frozen. And you
>> >could chose between pitch black nothing and blazing brightness.
>> >
>> >TH
> There is no "dark side", there is a "day side"
> and a "night side".
>

You certainly have noticed, that 'dark' was used as synonym for 'night'.

Well, maybe English more strict in such cases (compared to German).

But a 'day' on moon is not really a day (more month), hence I would like
to call the dark side 'dark side'. (if you allow)


TH

[Poutnik]

On 08/07/2015 08:41 AM, kefischer wrote:
>
> There is no "dark side", there is a "day side"
> and a "night side".

Day side is supposed to be bright,
same as night side to is supposed to be dark.

Physically, dark/bright side is even more appropriate,
referring to physical attributes,
than day/night, that is more human and social centric.

--
Poutnik ( the Czech word for a wanderer )

[kefischer]

On Fri, 07 Aug 2015 10:29:50 +0200, Poutnik <Poutni...@gmail.com>
wrote:

>On 08/07/2015 08:41 AM, kefischer wrote:
>>
>> There is no "dark side", there is a "day side"
>> and a "night side".
>
>Day side is supposed to be bright,
>same as night side to is supposed to be dark.
>
>Physically, dark/bright side is even more appropriate,
>referring to physical attributes,
>than day/night, that is more human and social centric.

Nonsense, the moon rotates about 13 times
a year, the words dark and light do not denote
a changing condition in light, day and night does.

[Poutnik]

Dark and bright is not black and white,
they do denote light conditions
as amount of light reflected.

Day and night are human centric terms.

[Emmerich Schultheiß]

Poutnik wrote:

>> Nonsense, the moon rotates about 13 times
>> a year, the words dark and light do not denote a changing condition in
>> light, day and night does.
>>
>>
> Dark and bright is not black and white, they do denote light conditions
> as amount of light reflected.
>
> Day and night are human centric terms.

Dark and bright side of the Moon, doesn't mean those parts or regions are
always in dark or light. Kefisher is stronger than you in dvergent matter.

[Poutnik]

Read once more what you have just written
and learn from that for the future.

Dark side is in dark, otherwise it is not dark side.
Bright side is in light, otherwise it is not bright side.

As these regions are dynamic, defined wrt to light source position.

Sure, Kefischer is stronger than anybody in DM nonsense.

[Emmerich Schultheiß]

Poutnik wrote:

> On 08/07/2015 03:01 PM, Emmerich Schultheiß wrote:
>> Poutnik wrote:
>>
>>>> Nonsense, the moon rotates about 13 times
>>>> a year, the words dark and light do not denote a changing condition
>>>> in light, day and night does.
>>>>
>>>>
>>> Dark and bright is not black and white, they do denote light
>>> conditions as amount of light reflected.
>>>
>>> Day and night are human centric terms.
>>
>> Dark and bright side of the Moon, doesn't mean those parts or regions
>> are always in dark or light. Kefisher is stronger than you in dvergent
>> matter.
>
> Read once more what you have just written and learn from that for the
> future.

I don't need to learn that for the future, since as you say, it was
written by me.

> Dark side is in dark, otherwise it is not dark side.
> Bright side is in light, otherwise it is not bright side.

Only a cretin would feel the need to specify that.

> As these regions are dynamic, defined wrt to light source position.

The point in this discussion is that there is no "dark side of the Moon".

[kefischer]

On Fri, 07 Aug 2015 13:42:51 +0200, Poutnik <Poutni...@gmail.com>

wrote:

>On 08/07/2015 12:21 PM, kefischer wrote:
>> On Fri, 07 Aug 2015 10:29:50 +0200, Poutnik <Poutni...@gmail.com>
>> wrote:
>>
>>> On 08/07/2015 08:41 AM, kefischer wrote:
>>>>
>>>> There is no "dark side", there is a "day side"
>>>> and a "night side".
>>>
>>> Day side is supposed to be bright,
>>> same as night side to is supposed to be dark.
>>>
>>> Physically, dark/bright side is even more appropriate,
>>> referring to physical attributes,
>>> than day/night, that is more human and social centric.
>>
>> Nonsense, the moon rotates about 13 times
>> a year, the words dark and light do not denote
>> a changing condition in light, day and night does.
>>
>
>Dark and bright is not black and white,
>they do denote light conditions
>as amount of light reflected.
>
>Day and night are human centric terms.

The moon rotates relative to the sun
and stars, and the same side is not dark
all the time, there is a near side and a
far side, no "dark or light" side.

[Poutnik]

On 08/07/2015 05:20 PM, kefischer wrote:
>>
>> Dark and bright is not black and white,
>> they do denote light conditions
>> as amount of light reflected.
>>
>> Day and night are human centric terms.
>
> The moon rotates relative to the sun
> and stars, and the same side is not dark
> all the time, there is a near side and a
> far side, no "dark or light" side.
>

There are near, far, bright and dark sides.

None of them is stationary.

Borders of the former 2 oscilate
while borders of the latter 2 circulate around the Moon.

[Thomas Heger]

Am 07.08.2015 16:11, schrieb Emmerich Schultheiß:

>>>>> Nonsense, the moon rotates about 13 times
>>>>> a year, the words dark and light do not denote a changing condition
>>>>> in light, day and night does.
>>>>>

...

>>>> Day and night are human centric terms.
>>>
>>> Dark and bright side of the Moon, doesn't mean those parts or regions
>>> are always in dark or light. Kefisher is stronger than you in dvergent
>>> matter.
>>

..

>
>> Dark side is in dark, otherwise it is not dark side.
>> Bright side is in light, otherwise it is not bright side.
>
> Only a cretin would feel the need to specify that.
>
>> As these regions are dynamic, defined wrt to light source position.
>
> The point in this discussion is that there is no "dark side of the Moon".

Well, that's just fighting for words.

You have certainly noticed, what I have meant by 'dark side'.

Maybe there exist some better terms among cosmologist and Moon lander
scientists, by what what they distinguish lit and dark areas of the Moon.

Also a 'Moon day' could be named other than the similar effect on Earth
(maybe not).

On the other hand: it's not really fun to discuss proper use of English
language, since that wasn't the topic of this thread.


TH

[Emmerich Schultheiß]

kefischer wrote:

>>Day and night are human centric terms.
>
> The moon rotates relative to the sun and stars,

No, it only rotates relative to Earth.

> and the same side is not dark all the time, there is a near
> side and a far side, no "dark or light" side.

Exactly, this happens to be correct.

[pnal...@gmail.com]

On Friday, August 7, 2015 at 10:18:36 AM UTC-7, Emmerich Schultheiß wrote:
> kefischer wrote:
>
> >>Day and night are human centric terms.
> >
> > The moon rotates relative to the sun and stars,
>
> No, it only rotates relative to Earth.

The very first scientific statement that you write... and you get it wrong! completely backwards!

\Paul A

[Emmerich Schultheiß]

Another standartenführer in Physics. No brain required. The Moon rotates
relative to Earth, the Earth rotates relative to Sun, the Sun relative to
the center of the Milky Way.

The rotation of the Milky Way, relative to the "center" of this Universe,
is not known to take place, since the large paths and distances are
getting convoluted non-locally in a curved 4d manifold.

[pnal...@gmail.com]

On Friday, August 7, 2015 at 10:49:57 AM UTC-7, Emmerich Schultheiß wrote:
> pnalsing wrote:
>
> > On Friday, August 7, 2015 at 10:18:36 AM UTC-7, Emmerich Schultheiß
> > wrote:
> >> kefischer wrote:
> >>
> >> >>Day and night are human centric terms.
> >> >
> >> > The moon rotates relative to the sun and stars,
> >>
> >> No, it only rotates relative to Earth.
> >
> > The very first scientific statement that you write... and you get it

> > wrong! Completely backwards!

>
> Another standartenführer in Physics. No brain required. The Moon rotates

> relative to Earth...

If the moon rotated relative to the Earth we would eventually see its entire surface, but we don't, we only see its librations. The moon rotates relative to everything in the universe except for the Earth... because the moon's rotation is tidally locked to the Earth.

[Emmerich Schultheiß]

pnalsing wrote:

> On Friday, August 7, 2015 at 10:49:57 AM UTC-7, Emmerich Schultheiß
> wrote:
>> pnalsing wrote:
>>
>> > On Friday, August 7, 2015 at 10:18:36 AM UTC-7, Emmerich Schultheiß
>> > wrote:
>> >> kefischer wrote:
>> >>
>> >> >>Day and night are human centric terms.
>> >> >
>> >> > The moon rotates relative to the sun and stars,
>> >>
>> >> No, it only rotates relative to Earth.
>> >
>> > The very first scientific statement that you write... and you get it
>> > wrong! Completely backwards!
>>
>> Another standartenführer in Physics. No brain required. The Moon
>> rotates relative to Earth...
>
> If the moon rotated relative to the Earth we would eventually see its
> entire surface, but we don't, we only see its librations.

That's turning around own axis, which is called "revolving", a special
case of rotation.

revolve (rɪˈvɒlv) vb
1. to move or cause to move around a centre or axis; rotate
2. (intr) to occur periodically or in cycles
3. to consider or be considered
4. (intr; foll by around or about) to be centred or focused (upon):
Juliet's thoughts revolved around Romeo.

> The moon
> rotates relative to everything in the universe except for the Earth...
> because the moon's rotation is tidally locked to the Earth.

Cretin.

[kefischer]

I would like to see if it is known if the rotation
of the moon is indexed to the Earth, or to the moon's
path (not rotating relative to the path through space).

[pnal...@gmail.com]

On Friday, August 7, 2015 at 11:31:19 AM UTC-7, kefischer wrote:

> I would like to see if it is known if the rotation
> of the moon is indexed to the Earth, or to the moon's
> path (not rotating relative to the path through space).

I don't know what you mean by 'indexed'. The concept of tidal locking is well understood...

https://en.wikipedia.org/wiki/Tidal_locking

https://www.youtube.com/watch?v=R-z1oSqivu8

... it is also called 'gravitational locking', with which you will undoubtedly vehemently disagree... just predictin'...

[kefischer]

On Fri, 7 Aug 2015 11:46:37 -0700 (PDT), pnal...@gmail.com wrote:

>On Friday, August 7, 2015 at 11:31:19 AM UTC-7, kefischer wrote:
>
>> I would like to see if it is known if the rotation
>> of the moon is indexed to the Earth, or to the moon's
>> path (not rotating relative to the path through space).
>
>I don't know what you mean by 'indexed'.

The Earth rotates at a regular rate,
the moon does present the librations, is
it because of the moon following an ellipse
that allows us to see more than half of the
hemispheres of the moon facing and following
the moon's path, or something else?

>The concept of tidal locking is well understood...
>
>https://en.wikipedia.org/wiki/Tidal_locking
>
>https://www.youtube.com/watch?v=R-z1oSqivu8
>
>... it is also called 'gravitational locking', with which you will undoubtedly vehemently disagree... just predictin'...

Maybe not, but according to you, everything
is well understood.


http://www-istp.gsfc.nasa.gov/stargaze/Smoon4.htm

"Actually, if this is the part of the orbit closest to Earth, with the
moon advancing fastest, it would already have raced ahead to position
"B"--although its rotation at the same time would still be the one
appropriate to "A."

If that happened, the long axis of the Moon would make a small angle
with the Earth-Moon line (as drawn), allowing astronomers to peek past
the western edge of the visible Moon ("east" and "west" are defined with
respect to Earth, so the western edge is the one closer to the western
horizon of the observer.)

Similarly, when the motion of the Moon is extra-slow, by the time
the rotation of the Moon brings it to the orientation in position "A",
the orbital motion has only managed to reach position "C." Now an extra
little sliver near the eastern edge becomes visible. While the first
type of libration adds to our coverage near the poles of the Moon, this
type increases coverage at the east and west edges, by about 7.7 degrees
(out of 360)."

[Thomas Heger]

Am 04.08.2015 02:05, schrieb John Gogo:

>>>>> What would the descent be like at 1/8th gravity?
>>>>
>>>> Without an atmosphere, a landing strip makes no sense.
>>>
>>> Apollo 8 revolved around the moon umpteen times. How does a spacecraft land on the moon's surface from this position?
>>
>> Apollo 8 didn't land. The craft that did land, didn't use a landing strip.
>
> Was it the best way to land and take off?

The ONLY way possible (at time of the Apollo program) was vertical
landing, because they had no landing strips then.

To try similar as 'rough landing' and to land horizontal without a
landing strip could easily make the craft end up at a rock or in a crater.

To avoid landing altogether was certainly easier. But if landing on the
Moon was the task, than the spaceship had to land.


TH

[John Gogo]

Ha ha, that was the answer I was looking for.

[pnal...@gmail.com]

On Friday, August 7, 2015 at 12:58:20 PM UTC-7, kefischer wrote:
> On Fri, 7 Aug 2015 11:46:37 -0700 (PDT), pnal...@gmail.com wrote:
>
> >On Friday, August 7, 2015 at 11:31:19 AM UTC-7, kefischer wrote:
> >
> >> I would like to see if it is known if the rotation
> >> of the moon is indexed to the Earth, or to the moon's
> >> path (not rotating relative to the path through space).
> >
> >I don't know what you mean by 'indexed'.
>
> The Earth rotates at a regular rate,
> the moon does present the librations, is
> it because of the moon following an ellipse
> that allows us to see more than half of the
> hemispheres of the moon facing and following
> the moon's path, or something else?

No, you've got that correct, the varying rate of the moon along its elliptical orbit, when combined with its very steady rotation rate, is why we can see more than 50% of the moon's surface.

> >The concept of tidal locking is well understood...
> >
> >https://en.wikipedia.org/wiki/Tidal_locking
> >
> >https://www.youtube.com/watch?v=R-z1oSqivu8
> >
> >... it is also called 'gravitational locking', with which you will undoubtedly vehemently disagree... just predictin'...
>
> Maybe not, but according to you, everything
> is well understood.

Nonsense, I've never claimed that 'everything' is well understood, you are exaggerating... but the few times I've made that claim, the subject matter was really basic and fairly simple...

> http://www-istp.gsfc.nasa.gov/stargaze/Smoon4.htm
>
> "Actually, if this is the part of the orbit closest to Earth, with the
> moon advancing fastest, it would already have raced ahead to position
> "B"--although its rotation at the same time would still be the one
> appropriate to "A."
>
> If that happened, the long axis of the Moon would make a small angle
> with the Earth-Moon line (as drawn), allowing astronomers to peek past
> the western edge of the visible Moon ("east" and "west" are defined with
> respect to Earth, so the western edge is the one closer to the western
> horizon of the observer.)
>
> Similarly, when the motion of the Moon is extra-slow, by the time
> the rotation of the Moon brings it to the orientation in position "A",
> the orbital motion has only managed to reach position "C." Now an extra
> little sliver near the eastern edge becomes visible. While the first
> type of libration adds to our coverage near the poles of the Moon, this
> type increases coverage at the east and west edges, by about 7.7 degrees
> (out of 360)."

Great explanation! Wish I had said that :>)

[John Gogo]

About 56% of the tidal locked moons' surface can be seen from Earth.