Proposed solution(s) to an on-going issue.

submitted by Tom_Bombadil from self.AskSaidIt

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[–][deleted] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (12 children)

Oh wow. Those rockets do look quite unstable. They're very tall and have those short legs, those would be hard to land under human control. I wonder why number 4 exploded.

But the lunar module looks quite stable to me. It's short, and its legs stick out.

And according to this article, the lunar module DID have computer assistance:

On final descent, Armstrong noted that the automatic landing system was guiding Eagle toward the boulder-strewn floor of a crater the size of a football field (”West Crater,” not shown below). Armstrong took manual control and skimmed over the crater, landing in a flat plain beyond. Eagle had only about 30 seconds’ worth of fuel left at touchdown.

Do you have any other reasons why landing a lunar module would be impossible, other than the instability of SpaceX rockets?

[–]Tom_Bombadil[S] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (11 children)

The fundamental challenge to landing is the inherent instability of landing any/every rocket.

Can you name a single rocket type aircraft that a human has ever landed on Earth; and walked away from? I'd like to see a video of this if you can find one.

Every person to ever take a flight in a rocket landed by some other means.
The rocket was abandoned at some point in flight, and the pilots parachuted down, etc. The pilots never landed using the thruster. Ever.

The obvious reason for this is landing a rocket propelled craft by controlled thruster descent was literally impossible, at the time.

[–][deleted] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (10 children)

I found a video, but first: Why are rockets inherently unstable? Are jets and propellers inherently stabler?

[–]Tom_Bombadil[S] 3 insightful - 1 fun3 insightful - 0 fun4 insightful - 1 fun -  (9 children)

Aircraft use wings for lift and stability.

There's no atmosphere on the moon, so wings are useless for stability. Beyond the rocket power there's no stabilizing forces. It's 100% thruster controlled.

[–][deleted] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (8 children)

Oh, so you mean like how if you use the thrusters to rotate a spaceship it keeps turning until you manually cancel the rotation? (or turn on a killrot autopilot)

[–]Tom_Bombadil[S] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (7 children)

Manually cancelling the rotation of a freely floating object would be close to impossible.

[–][deleted] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (6 children)

I suppose I can agree with you about that. I've tried it myself in Pioneer and Orbiter and I can bring the rotation close to zero but I'm always still drifting just a bit.

Here's the closest thing I've found to a rocket powered vehicle that somebody landed on Earth. However, it's also powered by a jet that gimbals. I wish I could fly one. [Wikipedia article on said vehicle](https://en.wikipedia.org/wiki/Lunar_Landing_Research_Vehicle

[–]Tom_Bombadil[S] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (5 children)

I've seen that gimbal contraption. dangerous as heck, and he's barely keeping it together.
I think I read somewhere that it was a terrifying experience.

Also, there not appear to be sufficient thrust going on there, and it looks like there's a propeller on the underside (like a upside down helicopter). This could be a hoax video intended to appear like a

Notice the designed horizontal distribution of this vehicle. It's nothing like the ladder, yet it's teetering with instability.

Imagine traveling thousands of miles an hour; careening blindly towards the moon.

Then rotating the craft around perfectly and engaging the thrusters in perfect opposition against the momentum of the craft (and the increasing gravity of the moon on approach).

Perfect control of the craft in all rotational directions; flying completely blind.

Then gently landing the lander on uneven surfaces, but without any negative incident; 6/6 times, within 3 years... Impossible. ;-)

[–][deleted] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (3 children)

Imagine traveling thousands of miles an hour; careening blindly towards the moon.

Then rotating the craft around perfectly and engaging the thrusters in perfect opposition against the momentum of the craft (and the increasing gravity of the moon on approach).

Perfect control of the craft in all rotational directions; flying completely blind.

Then gently landing the lander on uneven surfaces, but without any negative incident; 6/6 times, within 3 years

Why do you say blindly, and perfectly? How do you know that this is impssible, other than that you believe it would have to be done blindly and perfectly? If you learned they used computers, readouts, and a small window to accomplish this feat to a sufficient accuracy, would you reconsider your belief that this is impossible?

[–]Tom_Bombadil[S] 1 insightful - 1 fun1 insightful - 0 fun2 insightful - 1 fun -  (2 children)

Why do you say blindly, and perfectly?

Blindly, because if rocket propulsion is used to land, then the pilot needs to see through the rocket's thruster exhaust (assuming there's a window) to see where to land.
It's extremely unlikely that the exhaust is transparent during the final moments of descent, so it would be essentially landing blindly through smoke.

Perfectly, because landing a rocket on it's thrusters requires functional perfection. Top of the line 2018 tech is still crashing in double-digit figures.

Belief is the issue at hand. There are too many successively improbable (impossible) challenges to overcome for a single successful landing.

We haven't even addressed the fuel required to leaves the moon to connect to the orbiter, or how all of the alignment/rotational challenges also exist for recoupling the lander and orbiter (again this is close to impossible).
Consider the challenges of aircraft in-flight refueling, and then add in theall of the subtle rotational challenges as difficulty multipliers.

Realistically consider how many second chance they would have to realign and reconnect in orbit??? If the approach is to fast, then reverse thrusters are engaged, but that created a rotational moment, and now the craft is rotating in a combination of i-j-k directions.

You have seen the inside of the lander module, right?
Primitive CRT screens, lights, dials, switches, buttons, etc.
How do they determine the precise rotational speeds, and precise rotational directions (yaw, pitch, roll) with any degree of precision? How do they precisely correct the movements???

Success at any of these extremely challenging situations is a miracle.

Performing each of these challenges.
Flawlessly.
6/6 times to the"moon".
In 3 short years???
That is... impossible. :-/