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How to Land on the Moon

113 points by NaOH 7y ago

himeexcelanta 7y ago
Always love newatlas.
netingle 7y ago
I want to know more... How does one know one is in orbit? How do you work out when to fire you thrusters to leave orbit and head towards something like the moon?
- extropy 7y ago
  Radars, star trackers and some math. Random Google link: https://timeandnavigation.si.edu/navigating-space https://timeandnavigation.si.edu/navigating-space
- Aardwolf 7y ago
  Kerbal space program helped me understand a little more of the basics. The computer aid showing the trajectories helps quite a bit and that's demonstrated quite well in KSP.
- bdamm 7y ago
  As we learned in the Hidden Figures (I did anyway) the math is Euler’s method of iteration. So a desired variable (location of touchdown!) is fixed and then the inputs iterated until a successful set of inputs are found.
- yCloser 7y ago
  you need to play Kerbal Space Program....
anonu 7y ago
I just finished watching the national geographic on Apollo. It's really well done. The drew on a lot of local news footage which gives you a unique insight into the era.
chenster 7y ago
Don't forget bringing a golf club
rkagerer 7y ago
When Neil Armstrong brought his Lunar Module, Eagle, in to land, he found that the site was strewn with boulders and had to very quickly find somewhere else to put down. I thought they overshot their intended landing site, in part because Armstrong missed some visual landmarks when his attention was taken away from the window several times by a 1202 alarm. The area beyond the site was rocky (which they knew beforehand) and by the time he located and touched down on a clear spot they had < 30 seconds of fuel remaining (leading to some clenched butts in mission control).
- dmix 7y ago
  What would have happened if they hit some boulders with the lander? Was there a real chance they could have been stuck on the moon?
  - agildehaus 7y ago
    The walls of the LM were 0.012 inches thick. A tad under 4x the thickness of a soda can. You can imagine why hitting anything might ruin your day.
    - perl4ever 7y ago
      This raised the question, for me, of just how thick is the sheet metal on a typical earth-bound automobile. It appears that steel panels in modern cars are probably something like 0.03 or 0.04 inches thick. Aluminum panels may be 0.05" or 0.06", possibly thicker or multiple layers.
  - FatalLogic 7y ago
    The lunar lander was lightweight and relatively fragile, designed for low gravity and low pressure differential. For example the aluminum alloy skin seems vulnerable to distortion and to sharp impacts, because it was 0.3mm, about 3-4x thickness of a modern soda can, though the frame supporting it was much stronger. I thought the safe take off angle was very limited, but some NASA research says that even up to 70 degrees tilt could be manageable if the crew handled it correctly. https://forum.nasaspaceflight.com/index.php?topic=32246.msg1068329#msg1068329 https://forum.nasaspaceflight.com/index.php?topic=32246.msg1... That doesn't mean 70 degrees would be safe for landing, though. Maybe it would topple or get damaged by rocket blowback. Apollo 15 was tilted about 10 degrees and that was not a problem.
jaco8 7y ago
I landed on the moon many times in 1975 using the HP-25 moonlander program. It achieved this in 49 lines of code and a few manualy supplied data points. Boulders were never a problem.
somatic 7y ago
> When the spacecraft is about 2,000 ft (610 m) from target, it switches to the landing phase. This is when the computer hands over manual control to the Commander, who guides it in for final touchdown. Slowed to a hover, the module can be steered by tilting it like a helicopter to make any necessary corrections. A rocket landing on (top of) a column of thrust and a helicopter suspended below a disc of thrust are not even remotely the same thing. Classic failure to reason from first principles. Here’s a suitable analogy: it’s like the difference between having a center of mass behind the center of pressure, and a center of mass in front of the center of pressure. For the interested layman: https://en.wikipedia.org/wiki/Longitudinal_static_stability https://en.wikipedia.org/wiki/Longitudinal_static_stability
- jacobolus 7y ago
  > Here’s a suitable analogy: it’s like the difference between having a center of mass behind the center of pressure, and a center of mass in front of the center of pressure. This "analogy" is more abstract than the original statement and is only going to make sense to someone who more-or-less also understands that one. How about “it’s like pulling a floating balloon by a string vs. pushing the balloon from the side and trying to keep it moving in a straight line in both cases” Or maybe “it’s like balancing a vertically-oriented baseball bat while holding it at the top vs. balancing a broom while holding it at the bottom.”
  - jacobolus 7y ago
    Erm, sorry, my editing was only half baked above; I tried to change my example from a broom to a baseball bat and accidentally left both in.
- aeternus 7y ago
  The idea that a rocket sitting on top of a column of thrust is significantly different than a rocket suspended underneath a column of thrust is actually a common fallacy, known as the pendulum rocket fallacy: https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy You are correct that longitudinal stability is applicable and important for most aircraft, but that is due to angle of attack and lift forces. Neither of which apply in a vacuum.
DEADBEEFC0FFEE 7y ago
One of the early games I played on either my ZX81 or possibly BBC B was a lunar lander simulator. Really just a timeline and some maths and some dials. You contolled the decent with some thrusters. Burning fuel makes it lighter, which changes the thrust. Don't run out of fuel, dont land to heavy, make sure you land vertically. Good times. Nope, that's a confabulation. https://youtu.be/jlS3fr3t4Fg https://youtu.be/jlS3fr3t4Fg

113 points by NaOH 7y ago

Always love newatlas.

I want to know more... How does one know one is in orbit? How do you work out when to fire you thrusters to leave orbit and head towards something like the moon?

extropy 7y ago
Radars, star trackers and some math. Random Google link: https://timeandnavigation.si.edu/navigating-space https://timeandnavigation.si.edu/navigating-space
Aardwolf 7y ago
Kerbal space program helped me understand a little more of the basics. The computer aid showing the trajectories helps quite a bit and that's demonstrated quite well in KSP.
bdamm 7y ago
As we learned in the Hidden Figures (I did anyway) the math is Euler’s method of iteration. So a desired variable (location of touchdown!) is fixed and then the inputs iterated until a successful set of inputs are found.
yCloser 7y ago
you need to play Kerbal Space Program....

anonu 7y ago

I just finished watching the national geographic on Apollo. It's really well done. The drew on a lot of local news footage which gives you a unique insight into the era.

chenster 7y ago

Don't forget bringing a golf club

rkagerer 7y ago

When Neil Armstrong brought his Lunar Module, Eagle, in to land, he found that the site was strewn with boulders and had to very quickly find somewhere else to put down. I thought they overshot their intended landing site, in part because Armstrong missed some visual landmarks when his attention was taken away from the window several times by a 1202 alarm. The area beyond the site was rocky (which they knew beforehand) and by the time he located and touched down on a clear spot they had < 30 seconds of fuel remaining (leading to some clenched butts in mission control).

dmix 7y ago
What would have happened if they hit some boulders with the lander? Was there a real chance they could have been stuck on the moon?
- agildehaus 7y ago
  The walls of the LM were 0.012 inches thick. A tad under 4x the thickness of a soda can. You can imagine why hitting anything might ruin your day.
  - perl4ever 7y ago
    This raised the question, for me, of just how thick is the sheet metal on a typical earth-bound automobile. It appears that steel panels in modern cars are probably something like 0.03 or 0.04 inches thick. Aluminum panels may be 0.05" or 0.06", possibly thicker or multiple layers.
- FatalLogic 7y ago
  The lunar lander was lightweight and relatively fragile, designed for low gravity and low pressure differential. For example the aluminum alloy skin seems vulnerable to distortion and to sharp impacts, because it was 0.3mm, about 3-4x thickness of a modern soda can, though the frame supporting it was much stronger. I thought the safe take off angle was very limited, but some NASA research says that even up to 70 degrees tilt could be manageable if the crew handled it correctly. https://forum.nasaspaceflight.com/index.php?topic=32246.msg1068329#msg1068329 https://forum.nasaspaceflight.com/index.php?topic=32246.msg1... That doesn't mean 70 degrees would be safe for landing, though. Maybe it would topple or get damaged by rocket blowback. Apollo 15 was tilted about 10 degrees and that was not a problem.

jaco8 7y ago

I landed on the moon many times in 1975 using the HP-25 moonlander program. It achieved this in 49 lines of code and a few manualy supplied data points. Boulders were never a problem.

somatic 7y ago

> When the spacecraft is about 2,000 ft (610 m) from target, it switches to the landing phase. This is when the computer hands over manual control to the Commander, who guides it in for final touchdown. Slowed to a hover, the module can be steered by tilting it like a helicopter to make any necessary corrections. A rocket landing on (top of) a column of thrust and a helicopter suspended below a disc of thrust are not even remotely the same thing. Classic failure to reason from first principles. Here’s a suitable analogy: it’s like the difference between having a center of mass behind the center of pressure, and a center of mass in front of the center of pressure. For the interested layman: https://en.wikipedia.org/wiki/Longitudinal_static_stability https://en.wikipedia.org/wiki/Longitudinal_static_stability

jacobolus 7y ago
> Here’s a suitable analogy: it’s like the difference between having a center of mass behind the center of pressure, and a center of mass in front of the center of pressure. This "analogy" is more abstract than the original statement and is only going to make sense to someone who more-or-less also understands that one. How about “it’s like pulling a floating balloon by a string vs. pushing the balloon from the side and trying to keep it moving in a straight line in both cases” Or maybe “it’s like balancing a vertically-oriented baseball bat while holding it at the top vs. balancing a broom while holding it at the bottom.”
- jacobolus 7y ago
  Erm, sorry, my editing was only half baked above; I tried to change my example from a broom to a baseball bat and accidentally left both in.
aeternus 7y ago
The idea that a rocket sitting on top of a column of thrust is significantly different than a rocket suspended underneath a column of thrust is actually a common fallacy, known as the pendulum rocket fallacy: https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy https://en.wikipedia.org/wiki/Pendulum_rocket_fallacy You are correct that longitudinal stability is applicable and important for most aircraft, but that is due to angle of attack and lift forces. Neither of which apply in a vacuum.

DEADBEEFC0FFEE 7y ago

One of the early games I played on either my ZX81 or possibly BBC B was a lunar lander simulator. Really just a timeline and some maths and some dials. You contolled the decent with some thrusters. Burning fuel makes it lighter, which changes the thrust. Don't run out of fuel, dont land to heavy, make sure you land vertically. Good times. Nope, that's a confabulation. https://youtu.be/jlS3fr3t4Fg https://youtu.be/jlS3fr3t4Fg