Apollo 11 Lunar Lander Pre-Launch

[nomuse]

It's not at all surprising to me that some work had to be done after the LM was encased in adaptor.

It's absolutely standard.  The notion that any vehicle and its payload are rolled out the launch pad with all the parts installed is laughably naive.

Well, if it is a James Bond movie they also transport it fully fueled.

[nomuse]

I think people need to consider the deflector was 6 inches away from the nozzle and not 5 feet. To suggest the thrust would have little impact is a supposition I have seen nowhere (from a technical standpoint). And regarding the comments about the DAP, it is the partial reason why the craft may go into an uncontrollable spin. If the thrusts start to cause instability, the system may call for more thrusts in what will lead to an almost negative feedback loop. I will dig up one of the MIT papers which suggests this is a real possibility short of perfect conditions. Thanks to posters for taking the time to respond.

Was that paper by a cyberneticist and by some terrible miscarriage was he permitted to graduate? Seriously, this is control loop 101 stuff.

(Now sitting back and waiting for Jay to deliver full broadside on this one).

[JayUtah]

(Now sitting back and waiting for Jay to deliver full broadside on this one).

It's a red herring.  Sure, any PID-type controller can be coerced into unstable behavior if given wildly unexpected outputs.  But our poster's latest handwaving is based on the thrusters causing "instability" by impinging on the plume deflectors.  The only component of the deflectors' reaction force that would matter points through the LM center of mass, or close enough to it that the moment arm is negligible.  Proving how the control system would respond given certain dynamic conditions doesn't prove that the plume deflectors would produce those dynamic conditions.  He waved his hands past that part.

[jr Knowing]

I appreciate all the responses. And I understand everyone's convictions and their solid understanding on these subjects. And I respect everyone's position. First I would like to point out I meant to say positive feedback loop not negative. And for the poster who used a satellite photo to demonstrate there were no craters near the A17 LM, there are many high resolution photos of the A17 LM directly beside a crater at least  3-4 feet deep. And one of its pads is actually in a smaller crater. And not that everyone doesn't know, the entire Apollo photo catalogue is on Flickr.

With regards to the deflectors, I still think people should not dismiss this issue. As one poster rightly pointed out, because of the deflectors, stability required the engines to be fired in pairs. It also needed to be perfectly balanced (according to the MIT paper, which I will find). Do you not think that would present a problem? Changing fuel, moving astronauts etc. Also what if any of the RCS's failed? They had failed prior to A11. Yet they had no backups on these 7 flights.

And btw, given we are on the subject of RCS engines, how did the RCS's nozzles not get torn off the Saturn on liftoff. The LM's RCS's were covered but the RCS's on the CM were completely exposed. Max Q is 14km up. That is a long way up for those small nozzle cups facing up not to get torn off. Even if they were not torn off, they could have been easily damaged or compromised.  That seems quite the risk NASA took given the RCS's had no backups.  Regards jr.

[Dalhousie]

And btw, given we are on the subject of RCS engines, how did the RCS's nozzles not get torn off the Saturn on liftoff. The LM's RCS's were covered but the RCS's on the CM were completely exposed. Max Q is 14km up. That is a long way up for those small nozzle cups facing up not to get torn off. Even if they were not torn off, they could have been easily damaged or compromised.  That seems quite the risk NASA took given the RCS's had no backups.  Regards jr.

Which is why they were under the boost protective cover (BPC).  If you don't understand something, ask.  Don't assume that the people who worked on Apollo were stupid or risk takers, or that you have discovered some inconsistent detail that proves it was fake.

[Jason Thompson]

First I would like to point out I meant to say positive feedback loop not negative.

I thought that was probably the case.

And for the poster who used a satellite photo to demonstrate there were no craters near the A17 LM

No, I put the picture up to ask you to identify the 'very large one' that was supposedly a problem.

there are many high resolution photos of the A17 LM directly beside a crater at least  3-4 feet deep.

Then provide one, then explain why that would be a 'certain death' situation, taking into account the stability of the LM given it's structure and the range of slopes it could safely sit on.

And one of its pads is actually in a smaller crater.

Yes, a very small one. So what?

With regards to the deflectors, I still think people should not dismiss this issue.

They haven't. In fact you've been provided with a very detailed explanation as to why it was not an issue.

As one poster rightly pointed out, because of the deflectors, stability required the engines to be fired in pairs.

No, that is not what was said. Firing in pairs is the best way to achieve the pitch, roll and yaw regardless of the deflectors. If you wish to have an 'honest discussion' don't mis-represent the counter-arguments.

It also needed to be perfectly balanced

Do you undertand the concept of error margins? It was not necessary to 'perfectly' balance the system, just to keep it within a certain margin of performance.

Do you not think that would present a problem? Changing fuel, moving astronauts etc.

Do you really think this is beyong the engineering knowledge of the companies that built them? They knew what the craft had to do and engineered it accordingly.

Also what if any of the RCS's failed?

How many have to fail to present a problem that can't be fixed using the remaining active ones?

And btw, given we are on the subject of RCS engines, how did the RCS's nozzles not get torn off the Saturn on liftoff. The LM's RCS's were covered but the RCS's on the CM were completely exposed. Max Q is 14km up. That is a long way up for those small nozzle cups facing up not to get torn off. Even if they were not torn off, they could have been easily damaged or compromised.  That seems quite the risk NASA took given the RCS's had no backups.  Regards jr.

Again, do you honestly not think they could be engineered to withstand those forces, gven that the design obviously presented this problem in flight? You keep presenting these 'issues' as if they are insurmountable problems, but the reality is they can be solved by a team of halfway competent engineers.

[Jason Thompson]

And btw, given we are on the subject of RCS engines, how did the RCS's nozzles not get torn off the Saturn on liftoff. The LM's RCS's were covered but the RCS's on the CM were completely exposed. Max Q is 14km up. That is a long way up for those small nozzle cups facing up not to get torn off. Even if they were not torn off, they could have been easily damaged or compromised.  That seems quite the risk NASA took given the RCS's had no backups.  Regards jr.

Which is why they were under the boost protective cover (BPC).  If you don't understand something, ask.  Don't assume that the people who worked on Apollo were stupid or risk takers, or that you have discovered some inconsistent detail that proves it was fake.

The CSM RCS quads were not under the BPC, being about a third of the way down the side of the service module.



 However, that doesn't mean they can't simply be engineered to be tough enough to survive those forces. That's the kind of detail that years of design and testing fixes....

[VQ]

I appreciate all the responses. And I understand everyone's convictions and their solid understanding on these subjects. And I respect everyone's position. First I would like to point out I meant to say positive feedback loop not negative. And for the poster who used a satellite photo to demonstrate there were no craters near the A17 LM, there are many high resolution photos of the A17 LM directly beside a crater at least  3-4 feet deep.

To be clear, an unstable or rough landing was a concern during mission planning. The designers studied the dynamics of what a tipover accident on landing might look like and considered if a tilt sensor to trigger an automated abort was warranted. What they determined was that in 1/6th gravity, it takes long enough for a LM to tip over that the astronauts would have time to manually press the abort button. So even in the scenario that you imagine (which overstates the actual A17 landing danger) it was not "certain death" for the crew.

And rather obviously, the windows were adequate for the crew to visually survey the landing site and make adjustments as needed to avoid obstacles if necessary. A11 did so rather famously.

[onebigmonkey]

And for the poster who used a satellite photo to demonstrate there were no craters near the A17 LM, there are many high resolution photos of the A17 LM directly beside a crater at least  3-4 feet deep. And one of its pads is actually in a smaller crater. And not that everyone doesn't know, the entire Apollo photo catalogue is on Flickr.

Firstly, the entire Apollo photo catalogue is not in the Flickr archive - most of it is. You will find a more complete (but not necessarily high resolution) collection at the Apollo Image Atlas.

Secondly, I don't think you will find photos of the Apollo 17 LM directly beside a 3-4 feet deep crater. This is because I suspect you are actually referring to Apollo 15. It caused the crew some concern, but it was well within the safety margins of the LM design. If I am right, it is perhaps another indication of the depth of your understanding of the subject.

As well as the US's LRO, there is photographic evidence from China, Japan and India of human activity at that landing site, and a wealth of high resolution imagery taken on the surface that show details from that landing site that are confirmed by those orbiting probes. Do please show us a pre-Apollo image showing the crater next to which they landed. Can you tell us in what way a photograph of something on the surface of the moon proves that it is not on the surface of the moon?

I always get annoyed by hyperbolic and hysterical news reports featuring vox pop interviews about some easily averted minor crisis where, had events conspired differently "anything could have happened and the world could have ended". This is the same. Disaster didn't happen. How is that proof of anything?

[Obviousman]

Here is some footage of the tests they conducted to ensure the stability of the LM landing gear:

[ka9q]

Do you think that a rocket motor works by "pushing" against something?

To be fair...

While it's true that a rocket doesn't work by pushing against surrounding objects with its plume, that assumes the surrounding objects aren't attached to the rocket itself. When they are, the effect is exactly the same as a hypothetical unobstructed rocket generating the same ultimate gas flows and directions. That's why Jay said that the deflectors generate a small inward force in the process of deflecting the plume outward.

But that force is small, because much of the plume misses the deflector. And as Jay said, the deflection angle of the gas that does hit it is fairly small.

Most people are familiar with the appearance of a rocket plume in the atmosphere: a long, thin and usually brilliant flame extending well past the nozzle. That pencil-thin plume is caused by atmospheric pressure squeezing it from the sides, and its brilliance is caused by atmospheric oxygen burning the residual fuel in the exhaust (all chemical rockets run fuel-rich for efficiency reasons).

Those factors are not present in vacuum. The gas in the plume immediately begins to expand laterally outward as soon as it exits the nozzle because there's nothing to stop it. Nozzles for vacuum engines are made longer to reduce this, but there's no confining it entirely because even a low plume pressure is still greater than zero. And of course there's no oxygen to burn the residual fuel and make it obvious where the gas is going.

You do see some of this when you watch the expanding plume of a launch vehicle as it climbs into the thinner upper atmosphere, but the viewing geometry (and the rapidly decreasing flame brightness) still make it a little difficult to see exactly what's happening.

[ka9q]

It also needed to be perfectly balanced (according to the MIT paper, which I will find). Do you not think that would present a problem? Changing fuel, moving astronauts etc.

It's amazing how persistent this misconception has become. The same thing is true for nearly every rocket launched from the earth's surface, yet few people deny that those rockets are real and actually work.

I know of two ways to passively stabilize a rocket against small undesired torques such as those resulting from imbalanced or off-axis engine thrusts. One is to spin the whole rocket around its thrust axis so the off-axis torque averages to zero. The other is to use tail fins to produce a restoring torque to drive the angle of attack toward zero.

The latter method is fine for model rockets but it obviously doesn't work in a vacuum. The former method doesn't let you fly along a programmed curved trajectory as needed when launching vertically from a surface.  (Passive spin stabilization is often used by satellites firing their apogee kick motors as steering is not needed during the burn.)

With these exceptions, rockets need some sort of closed-loop control system that can measure attitude (orientation in space) and a set of rocket motors capable of generating whatever torques are required to point the pointy end forward. If you've got several rocket engines, you can gimbal some or all of them. If you've got only one main engine (as on both stages of the LM) then you need auxiliary engines like the RCS.

So yeah, the LM was never perfectly balanced -- but it didn't have to be. During descent, the computer gimbaled the main engine to put its thrust vector directly through the center of mass. The ascent engine had no gimbal, so the computer fired the RCS engines as needed to keep the LM pointed in the desired direction. This resulted in a very pronounced "wallowing" (or rocking) motion that is clearly visible in all of the ascent movies taken from within the LM. This happened for two reasons: each RCS engine was either on or off -- only the descent engine had a throttle -- and very short RCS burns were inefficient. The control system permitted the attitude error to build up to some limit (a "deadband") before firing the appropriate RCS thrusters to push the error all the way to the other end of the deadband. Then it shut off the thruster and waited for the attitude error to again hit the edge of the deadband.

As for what happens when a rocket's attitude control system fails, see this:

[Zakalwe]

Do you think that a rocket motor works by "pushing" against something?

To be fair...

While it's true that a rocket doesn't work by pushing against surrounding objects with its plume, that assumes the surrounding objects aren't attached to the rocket itself. When they are, the effect is exactly the same as a hypothetical unobstructed rocket generating the same ultimate gas flows and directions. That's why Jay said that the deflectors generate a small inward force in the process of deflecting the plume outward.

I understand that. I was fishing to see if out erstwhile honest-discussion-seeking, just-asking-question poster is one of those that thinks that rockets only work in atmospheres as they need something to push against.

[Jason Thompson]

It also needed to be perfectly balanced (according to the MIT paper, which I will find). Do you not think that would present a problem? Changing fuel, moving astronauts etc.

It's amazing how persistent this misconception has become. The same thing is true for nearly every rocket launched from the earth's surface, yet few people deny that those rockets are real and actually work.

It amazes me too. Rockets are not dependent on a perfect set of circumstances to remain balanced and work. Passive and active correction is a common feature. Fins, grids, RCS systems, gimballed engines and gyroscopic platforms are just the ways I could think of off the top of my head to ensure that a rocket of any kind goes where you want it by either using aerodynamics during atmospheric flight phases or else reaction control systems in space.

It is somewhat less confusing than the misconception several HBs have that the LM is somehow top-heavy, despite having its fuel and oxidiser tanks in both stages set around the engine rather than stacked on top like every rocket that ever launches from Earth ever....

[Von_Smith]

I have a question for the OP:  In your opinion, why do the plume deflectors even exist?  I mean, if the missions are fake, and their presence and location somehow "give away the game", why even bother with them?