Apollo 13's Slickest Trick, "The Entrance"

OK Apollo era space buffs. Put on your thinking caps, and put 'em on snugly, grab your slide rules, cuz' decisively has a STRAIGHTFORWARD Apollo 13 question that is guaranteed to stump every single one of you. Don't believe me ? Check this bad boy out.....

We all know Apollo 13 landed, if a few minutes late, right on target nevertheless. But how in the world could they have pulled it off ?

The fabled Apollo 13 "PC + 2 burn" occurred, well where else, at the good ol' PC, the pericynthion. The LM guidance system was used for that burn, and was shut down after the burn was complete. From that time on, the astronauts would fly, not blind, but nevertheless, without the assistance of their fancy guidance system.

Despite the fine result yielded by the " PC + 2 burn ", as the story goes, the Odyssey/Aquarius joined vehicle was not viewed by the boys in Houston as having the most desirable of trajectories. Some say that it was an Aquarius cooling water vent that was serving as a little jet , and so pushing the clumsy contraption off its established course.

Cold and pretty dang tired, the astronauts needed to employ a post " PC + 2 burn" burn, to yet again correct course. For this latter burn, they used the Earth's terminator as a reference, given the navigational system's having been shut down. If this "Earth terminator as reference burn" wasn't done well enough, the ship would "bounce" off into space if their approach had resulted in a "glance", or would have burned up, if the approach angle was too acute.

Here's where the whole thing gets 10 plus insanely interesting. So they have the thing lined up like they want it to, more or less anyhoo, best they can do anyhoo, but WAIT !!!! what about the effect of jettisoning the Service Module and the LM ? Each time there is separation, equal and opposite forces are imparted, one separating unit to the other. The angular momentum of the system remains constant as well, but the momenta of the components change, and perhaps markedly so. The total momentum, both angular and linear of the system remaining constant, the angular and linear momenta of each component would have changed upon separation, and in ways uncalculable, or so it seems at first blush to me.

When they first jettison the SM, the CM-Aquarius is "shoved" equally and oppositely. The angular momenta of the separating parties is altered as well, while the total linear and angular momenta of the system, the two separating parts, remains the same. Ditto for when the CM separates from the Aquarius by virtue of the latter's being jettisoned away, "jettison" of course being in a sense relative here, depending on which ship "part" CM vs Aquarius, one sits on/in.


Today as I thought about this conservation of momentum based conundrum, I realized that it was seldom , if ever discussed, and when it was discussed, it was done so in the most unsatisfactory of terms. For example; here is what astronaut Charles Duke had to say on the topic of my Honors Physics Bonus Question. From Duke's Johnson Space Center Oral History Interview, page 12-39(www.jsc.nasa.gov...);

DUKE: To reenter. That’s correct. And so, you know, it was a tense time and—during the whole procedure and—of the recovery and 99 hours of drama, or thereabouts, till they separated and reentered. John Young and I were talking last night about that, as a matter of fact; and I remember we had figured out, in the simulator, that they had a series of maneuvers to do right before reentry to—because we were—we had never separated this whole stack of the command module, service module, lunar module for reentry. It had never been designed for that.

WARD: You were going 25,000 miles an hour at that point.

DUKE: Right. And accelerating, and how—one’s going to be reentering at the wrong speed, and the dynamics and the aerodynamics of it. Could we crash them together? And so, we had to figure out what was the best attitude and we’d done that, but it required a number of maneuvers to get it in the right position. And the more we thought about that, the more concerned I became, because, I mean, we could still be maneuvering and (Excuse me)—and we’d reenter and not get it all done, or we’d get to gimbal lock if we have a problem with a jet. We’d lose our attitude.

;

(Here we of course acknowledge that the entire system is accelerating under the earth's gravitational pull. So "the system" has this external force as a constant player, gravity is of course everywhere. But for the sake of our discussion, we may acknowledge gravity as a participant, but need not include it as a major active player here. By that I mean what Charles Duke is concerned about above is a conservation of momentum based concern. So for starters, let us too focus on that, unless of course someone has a role for gravity here that clears this all up. Please feel free to comment on this important "simplification" of the problem, if/as you see the need. )


So the point is, once they do the final burn, IT IS ONLY AFTER THAT, THAT THEY JETTISON THE SERVICE MODULE AND THE LUNAR MODULE AQUARIUS. JETTISONING THESE COMPONENTS ALTERS THE COMPONENTS' ATTITUDES, ANGULAR MOMENTA AND LINEAR MOMENTA, ALTERS THE CAPSULE'S ANGLE OF ATTACK WITH RESPECT TO ITS APPROACH INTO THE ATMOSPHERE.

So how did they do it ???? Enter and so splash so perfectly after mucking everything up with their separations ????? Charlie Duke recognized it as a problem worthy of discussion with his colleague John Young, if not a problem frankly in need of explanation, and to be frank, Duke doesn't sound much like he knows what he's talking about, where to begin sorting through all of this.

One of my best friends who is an academic/university based physicist, and by the way, finds my preoccupation with proving Apollo fraudulent, an activity worthy of only a fool, told me he found my little "discovery", "the most challenging "problem" he had ever been presented with", with respect to sorting through Apollo's mysteries. I honestly think my friend is working on the problem now. He really got off on it.

So to be absolutely clear here, this is NOT a CT thread. In this thread, we all assume, at least I do, that the Apollo 13 Mission was real, was authentic. The idea here is for "both sides" to have fun with a straightforward, but surprisingly deep conservation of momentum problem. Whether Apollo be authentic or inauthentic, a reasonable explanation must exist for how this MAY HAVE occurred, even if we wind up concluding luck to be that which was/is most reasonable in terms of an explanation.

For this thread, let's all do some physics, plain and simple. Let's assume Apollo authentic here and see what we come up with. I honestly do think a few high school honors physics students could do better than Charlie Duke. His answer borders almost on not really trying.

Originally posted by decisively
what about the effect of jettisoning the Service Module and the LM ? Each time there is separation, equal and opposite forces are imparted, one separating unit to the other.

Give us some numbers.
By this video an undocking procedure is quite gentle.

I'll make a ballpark estimate of 5mph.
At a speed of 25000 mph, thats a extra 0.02 percent.
0.02 percent!
OMG they're all gonna die.

Edit - but wait!
The LM and SM are on opposite sides of the command module. Maybe it all cancels out to zero.

reply to post by alfa1


What about the angular momentum issue alfa1 ? Duke seems concerned about that, or so I read it that way.

Baring an incomplete decompression of the docking mechanism, there is no force imparted to the CM when the LM was jettisoned. The craft are decoupled, THEN the RCS system moves the LM away from the CM. There's no force acting on the CM in process, so no change in trajectory.

I have nowhere near the depth of knowledge or education to answer this, except to posit "by the seat of their pants." These guys were test pilots; and I expect that, like many of the things they did, they used more intuition than formal physics. They just "eyeballed" it, and tweaked it as best they could, and Devil take the hindmost. Or, as Charlie Duke put it: "And so, we had to figure out what was the best attitude and we’d done that, but it required a number of maneuvers to get it in the right position. And the more we thought about that, the more concerned I became, because, I mean, we could still be maneuvering and (Excuse me)—and we’d reenter and not get it all done, or we’d get to gimbal lock if we have a problem with a jet...."

That's probably the best answer he's capable of giving for what they actually did. He might as well have said: "Well, we held our mouth just right and wiggled the stick little and pulled back some and then let 'er go."

Originally posted by decisively
What about the angular momentum issue alfa1 ? Duke seems concerned about that, or so I read it that way.

I'm sure there were a lot of things to be concerned about, but

1. You cant have it both ways.
If Duke's concerns are real then the Apollo 13 flight was real.
If Duke's concerns are fake, then you cant use them as evidence about an undocking procedure.

2. You are the one who spends their whole life thinking about this stuff.
Are you really asking your detractors for information about the magnitude of the forces involved? Why havnt you done your own numbers already?

reply to post by nataylor


What about the angular momentum concern, it seems that Duke is letting us know that he was worried ? And as you'll read in going further along in the oral history interview, such was the case. I'll post that part later, more text from the relevant part of Duke's interview. I decided not too post it all up front so as not to make the post, already long, longer still. But read on into the oral history thing nataylor. I haven't looked at what John Young says specifically about all of this, but they were obviously CONCERNED ABOUT SOME UNPREDICTABLE EFFECTS SEPARATION WOULD HAVE.

reply to post by decisively


He's not talking about angular momentum. He's taling abut orienting the craft such that when the LM and SM were separated, they would not impact the CM on reentry. There was the possibility that if they were in the wrong orientation during the separation, the LM or SM could catch up to the CM as it entered the atmosphere and slowed down. As he said, it took a number of maneuvers to orient the craft correctly, and they were worried about getting the maneuvers complete in time.

reply to post by alfa1


I like physics. I honestly am simply playing with this problem outside of my CT concerns. I am a physician and focus mostly on that stuff, medical concerns, when it comes to Apollo authenticity/inauthenticity. .

Also, as any credible debater, I always assume the side of my opponent/assume his/her role in my mind if not in writing, with every post really.

Here, in this thread, I am having fun with physics, nothing more. There is medical evidence much stronger than this type of stuff that favors Apollo's inauthenticity. This sort of material, at least for me, a non physicist, would be second tier type stuff.

reply to post by nataylor



My point exactly....and then some...... If they don't crash, what does that mean about their respective momenta, what has happened to them ?

Originally posted by decisively
reply to post by nataylor

 

What about the angular momentum concern, it seems that Duke is letting us know that he was worried ? And as you'll read in going further along in the oral history interview, such was the case. I'll post that part later, more text from the relevant part of Duke's interview. I decided not too post it all up front so as not to make the post, already long, longer still. But read on into the oral history thing nataylor. I haven't looked at what John Young says specifically about all of this, but they were obviously CONCERNED ABOUT SOME UNPREDICTABLE EFFECTS SEPARATION WOULD HAVE.

Concern for an effect does not mean there is an effect to be concerned about. Just because they BELIEVED an effect would POSSIBLY take place does not mean the effect took place. Prove to me that the effect is real, and someone having concern does not make the event real. I know plenty of children who are concerned about the monster in the closet.

Originally posted by decisively
reply to post by nataylor

 

My point exactly....and then some...... If they don't crash, what does that mean about their respective momenta, what has happened to them ?

Show me the physics that proves they would crash, if the physics does not come to the conclusion they would I fail to see anything to discuss.

A bit more from the Charlie Duke Interview here

reply to post by decisively


From page 12-40 of the Charlie Duke JSC Oral History. Here's Charlie;

And so it was a real moment of decision, if you will. If I—as I recall it, John and I went to (I think it was Gene Kranz) and said “Gene,” you know, “why don’t we just take what we got and just separate and let’s just go?” And we did one or two little maneuvers, but we cut out some of them and that’s what we agreed to do. And sure enough, everything came back in; and we didn’t have any problems at all with collisions and things like that.

I'll see if I can find a John Young based reference on this.

What's odd about the above statement of Duke's is that for what it is worth, it seems this should be coming from Bostick types, TRENCH guys, and not Young and Duke astronaut guys, the bit about biting the bullet more or less and proceeding on with the separation.

At any rate, would seem to be the case that I need to read up more on the separation stuff, the logistics, what happens. Is it in fact the case that the separate units do simply unlock and one jets a bit to push away from the other, or one simply floats away from the other after unlocking/disconnecting ????

Would seem the key is simply knowing how the components separate, the logistics, the mechanism of that.

Thanks for the comments so far.

reply to post by OccamsRazor04



The point is that Duke does not know what might or might not happen. This is an unknown. That is why Duke and presumably Young as well expresses worry. See the post just above with reference to their going to Kranz and saying, "enough cutting bait, let's fish".

Maybe this has something to do with the unexplained "Blackout"

reply to post by OccamsRazor04


This is from Flight Officer Jerry Bostick's Johnson Space Center Oral History Interview, page 12-59;

So here on Apollo 13 we've gone through the most tiring, excruciating time in our history, working twenty-four hours a day and pulling off four or five miracles in a day, you know, and here we've got them back home and…this impossible thing has worked out, and they're coming back and everything's fine, and we lose them in blackout. Then the end of the blackout comes and we call them, there's no answer. There's no answer. We're all saying, "Oh, no." I mean, "No, no, no, not after all of this." You know, it's done. It's over. We've done the impossible. It went on for like another minute and a half and we couldn't contact the crew, and then all of a sudden we hear them. To this day, to my knowledge, nobody's figured out why the blackout lasted as long as it did.

BUTLER: Really?

BOSTICK: No. It's one of those things that nobody seems to understand.

If the prolonged "blackout" was not communication based, then it had to have been trajectory based. And if the latter was the case, perhaps it was grounded in the dynamics of separation.

Lunar Module Jettisoning was an ACTIVE EVENT

This is from NASA's own website;

spaceflight.nasa.gov...

Quote from the NASA site above(caps mine);

The lunar module is jettisoned BY FIRING SMALL CHARGES around the CSM docking ring.

That says it all right there. The CM and Aquarius were blown away from one another via an ACTIVE mechanism, the firing of charges. The CM's attitude, angular and linear momenta, would thereby all be changed and so affect the trajectory of this very same CM, its angle of attack, and its orientation/attitude coming in.

reply to post by decisively


Yet you show no proof. If the charges were of identical force they would offset one another if fired in opposite directions. So how about some evidence.

Originally posted by decisively
reply to post by OccamsRazor04

 

The point is that Duke does not know what might or might not happen. This is an unknown. That is why Duke and presumably Young as well expresses worry. See the post just above with reference to their going to Kranz and saying, "enough cutting bait, let's fish".

Exactly, an unknown, as in it is unknown it will have an effect. You jump from unknown to it will have an effect, a known. Sorry unknowns stay unknowns until evidence shows they would have an actual, not feared risk. The monster in the closet is an unknown, prove its real.

No proof of a change in linear momentum is needed

reply to post by OccamsRazor04


If the objects separate, then by definition, the linear momentum has changed, and with it, so has the angle of attack.

Originally posted by OccamsRazor04

Originally posted by decisively
reply to post by OccamsRazor04

 

The point is that Duke does not know what might or might not happen. This is an unknown. That is why Duke and presumably Young as well expresses worry. See the post just above with reference to their going to Kranz and saying, "enough cutting bait, let's fish".

Exactly, an unknown, as in it is unknown it will have an effect. You jump from unknown to it will have an effect, a known. Sorry unknowns stay unknowns until evidence shows they would have an actual, not feared risk. The monster in the closet is an unknown, prove its real.

He doesn't have to prove it's real - it IS an Unknown variable. Virtue of this itself is enough to make the astronauts stop dead in their tracks and get more data before making any kind of maneuver. Otherwise your saying NASA plays fast and loose with men's lives - after they had planned for months and had contingency after contingency in place for everything. I just can't see NASA doing this.. that's way out of the ballpark. It's very unscientific and dangerous.