Apollo 13's Slickest Trick, "The Entrance"

Originally posted by decisively
When the Command Module/Lunar module combined stack separates, when the lunar module is jettisoned, the command module capsule then continues traveling toward the earth at a velocity of greater magnitude than that of the just separated Command module/Lunar module stack, and even more importantly for our considerations here, that velocity vector will be of a DIFFERENT DIRECTION THAN THAT OF THE JUST SEPARATED COMMAND MODULE/LUNAR MODULE STACK..

Nope. All things fall with the same acceleration, regardless of mass. So with no other forces than gravity working on the CM, it would continue on the exact same trajectory as when it was docked with the LM.

When an astronaut steps outside the ISS for a spacewalk, does he suddenly start moving away from the station? No, of course not. He stays in the same orbit as the station, even though he has essentially "undocked" from the station. That's because he's experiencing the same acceleration as the station, despite the fact he weighs much less.

Perhaps they had help?

www.abovetopsecret.com...

The "Contact from Planet Koldas" tells of their encounter with Apollo 13 and guiding it back to Earth.
That was after popping Apollo's tank, because they could tell Apollo 13 had a nuclear bomb onboard to explode on the Moon.
Funny, I dont think Nasa ever sent another bomb back to the moon?
Tho they certainly rammed it with enough rockets. .

reply to post by gort51

Perhaps they had help?

www.abovetopsecret.com...

The "Contact from Planet Koldas" tells of their encounter with Apollo 13 and guiding it back to Earth.
That was after popping Apollo's tank, because they could tell Apollo 13 had a nuclear bomb onboard to explode on the Moon.
Funny, I dont think Nasa ever sent another bomb back to the moon?
Tho they certainly rammed it with enough rockets.

What do you think, Doc? They agree with you on the nuclear bomb aspect....

reply to post by nataylor

No, incorrect……

A spacewalking astronaut must have a SLIGHTLY DIFFERENT VELOCITY THAN THE SPACESHIP OR HE/SHE CANNOT SEPARATE FROM THE SPACESHIP.

In order for something to move away from something else, under ANY circumstances, even a nanometer , the separating objects must have a velocity with respect to one another, otherwise, separation cannot occur. THIS BY DEFINITION IS WHAT IT MEANS TO "SEPARATE". THIS CANNOT BE A POINT IN DISPUTE.

An astronaut does not move away from a spaceship without a velocity in relation to the ship, otherwise, he/she would be stuck to the ship. The LM and CM cannot separate without their having a relative velocity, one to the other. Were this not the case, they would remain together.

In the scenario under consideration, the LM and CM approach the earth together/joined, and then at some point they separate. In their separating, they so necessarily acquire a velocity in relation to one another. Separated and actively continuing to separate, they now each occupy a unique point in space relative to the earth. By the very definition of what we mean when using the term "velocity", it is nothing less than NECESSARILY the case that the LM and CM do not have the same velocity in relation to the earth. They do not move toward the earth with the exact same speed and in the exact same direction. Each piece of equipment, the LM and the CM, travel with different, unique velocities.

Keep in mind here now, we are not talking about speed which is a scalar quantity. Velocity is a vector, and so is an entity with both magnitude and DIRECTION. The LM and CM, once separated, are at unique points in relation to the earth, and so it must be that regardless of their speed, because their direction in moving toward the earth is different, their velocities must be different. Two objects occupying distinct/unique points in space moving toward the earth under the influence of the earth's gravity cannot by definition have the same velocity. This is true by virtue of their moving toward the earth from unique respective vantages.

For those familiar with the fundamentals of physics, these points are easily seen to be, acknowledged as, points not in dispute. They are true simply by virtue of what we mean by the terms "separating", "speed", "velocity". Of course in science, these terms are defined with great precision, and to be sure, that is my very point here.

Your view could not be one any more in error here nataylor.

C. LM Separation After CM IMU alignment was complete (140:55 GET) the spacecraft was maneuvered to the LM jettison attitude using the LM RCS. Once the maneuver was complete at 141:02 GET the spacecraft was placed in an AGS attitude hold with wide attitude error dead bands. The LM was maneuvered to an incorrect roll (LM body frame) attitude that placed the CM IMU platform near gimbal lock. The desired LM roll was 135 degrees but the spacecraft was maneuvered to 235 degrees LM roll. While the LM –X axis had been correctly aligned along the positive radius vector during the maneuver, the vehicle was yawed (CM body frame) 45 degrees on the north side of the CM entry ground track rather than 45 degrees on the south side (Figures 26, 27, and 28). By the time Mission Control had recognized the attitude error the CM and LM hatches were being installed by the crew. The minimum LM/CM separation was predicted to be 4,000 feet at EI. The initial CM roll angle after EI would steer the CM to the north, but subsequent modulation of the lift vector would move it away from the LM orbital plane. The in-plane separation of the vehicles was judged to be adequate for a nominal entry. The separation was not optimum if the crew flew a roll right (CM body frame) constant 4g entry due to PGNCS and EMS failures, but the separation was judged to be adequate. Due to these factors and the time-critical nature of the pre-entry timeline, Mission Control chose not to correct the spacecraft attitude before LM separation.15 The maneuver to the LM separation attitude was complicated by efforts to avoid CM platform gimbal lock. This required close coordination between the commander in the LM and the CM pilot in the CSM. The maneuver consumed a considerable amount of propellant. Had a gimbal lock occurred, a recovery procedure would have been executed to re-establish platform alignment before entry. Recovering from gimbal lock would have complicated the remaining part of the pre-EI timeline.25 The docking probe and drogue hardware, along with many other items, were left in the LM as a part of the stowage plan to achieve the desired CM L/D for re-entry. Before leaving the LM the crew placed the spacecraft in an AGS controlled attitude hold with wide attitude error deadbands.29 After the hatches were in place Mission Control closely monitored the CM IMU gimbal angles. If maintenance of the attitude hold by the LM AGS drove the CM IMU close to gimbal lock the crew would have performed the separation early. LM attitude control between hatch closure and separation was nominal and the CM IMU gimbal lock did not occur. The separation used delta-velocity, imparted from air venting, from the docking tunnel at separation. The CM RCS could not be used since CM RCS propellant was required for re-entry. Before undocking, the tunnel pressure was reduced to 2.2 psi to achieve the desired delta-velocity of ~2 feet/second. Apollo 10 (May 1969) LM jettison data was used to determine the appropriate docking tunnel pressure differential to achieve the desired deltavelocity. §
The LM was jettisoned 70 minutes before EI, 10 minutes earlier than planned, at 141:30 GET (Figure 29).
Sensed velocity at LM jettison was -0.65 feet/second along the LM X and -0.02 feet/second along the LM Y axis.
The separation was stable and the LM continued to be stable within the AGS 5 degree attitude error deadband until
LM loss-of-signal at 142:38 GET.

And

After separation, the crew maneuvered away from the near-gimbal lock attitude to the entry attitude. Entry attitude accuracy and IMU platform alignment were confirmed by a sextant star check. Tracking data showed a slight change in the EI flight path angle to -6.2 degrees. However, this was within expectations and did not require a change to the normal heads to Earth orientation of the CM at the start of re-entry to re-orient the lift vector.

Source

The CM changed it's attitude after LM separation and maneuvered away for reentry.

Moving right along

As was pointed out and has been emphasized, this is not a CT thread.

We are not concerned here with what NASA has to say as they cannot explain the extended blackout time. We here, the honors physics students of ATS, are trying to do what the NASA guys could not, explain the prolonged blackout time during the Apollo reentry and so forth.

The splash was on target, but the blackout was prolonged, NASA SAYS THEY DO NOT KNOW WHY. Could it be that LM/CM/Service module separation might account for this ? Could separation have imparted a trajectory change sufficient to account for the blackout ? Since the blackout was prolonged, that suggests the trajectory was shallow, more glancing. Might that explain things ?

Again, NASA gave up on this problem, we have not. We shall not find our answer, and the NASA boys will be the first to tell you that, in rehashing their stuff. We, the honor physics students of ATS, seek our own solution, the one NASA could not provide. That said, we do assume NASA is correct in one sense. This is not a CT thread. We assume the capsule splashed right on target, and the unextended blackout time was minutes long unaccounted for. We go from there. How was that possible ?

The CM's angle of entry was off just over 6 degrees, resulting in a longer and shallower flight path for re entry.

The ionized air around the CM during re entry is what causes the radio black outs. The Gemini capsules would experience 4 minutes of this, and the Apollo capsules normally around 3 minutes (something that the space shuttle was able to over come with the building of the TDRSS, Tracking and Data Relay Satellite System. Before that, the space shuttle used to under go a 30 minute blackout).

With a longer re entry flight path, Apollo 13 experienced a longer black out period (about 1 minute 30 seconds longer I believe), as the air around the capsule remained ionized longer.

LM and CM separation had no part in this, as the CM had to maneuver after separation. The longer flight path of re entry was due to the results of those maneuvers.

Not the LM sep. Separation of the LM was achieved with 2.2 PSI of air in the docking ring. This gave a delta V of 2 feet per second between the LM and the CM.

2 feet per second of delta V is not enough to prolong the flight path. However being 6 degrees off in attitude is.

reply to post by decisively

The splash was on target, but the blackout was prolonged, NASA SAYS THEY DO NOT KNOW WHY. Could it be that LM/CM/Service module separation might account for this ? Could separation have imparted a trajectory change sufficient to account for the blackout ? Since the blackout was prolonged, that suggests the trajectory was shallow, more glancing. Might that explain things ?

No, no and no. Most likely, the diminished battery power made the radio signal weaker, so it could not penetrate the ionization envelope as readily.

Originally posted by decisively

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.

edit on 3-7-2012 by decisively because: is> was

edit on 3-7-2012 by decisively because: added "(caps mine)"

edit on 3-7-2012 by decisively because: removed "by small charges"

edit on 3-7-2012 by decisively because: momentum> momenta, comma, added "this very same"

What about this theory: of the hundreds of skilled personnel on the ground and the three in the spacecraft, somebody thought of this before the operation, just as they had to do for virtually everything in a space mission, got some quantitative numbers (as in estimate momentum transfer), and decided that the effect was too small quantitatively to matter, or was even considered in the flight plan.

I like calling it "rocket science".

Originally posted by eriktheawful
Not the LM sep. Separation of the LM was achieved with 2.2 PSI of air in the docking ring. This gave a delta V of 2 feet per second between the LM and the CM.

2 feet per second of delta V is not enough to prolong the flight path. However being 6 degrees off in attitude is.

The actual undocking imparted far less velocity than that. The undocking was designed to impart 0.4 ft/s in separation velocity between the LM and CSM. Of course, that velocity relative to the existing flight path was proportionally distributed between the LM and CM based on their masses. Which means the undocking added about a whopping 0.27 ft/s to the velocity of the CM.

A further separation maneuver, performed by the LM RCS gave the craft a separation velocity of about 2.5 ft/s. But of course that has no affect on the CM.

reply to post by nataylor


I guess my source is incorrect then as it states that the LM RCS was used to orientate the LM/CM for separation only. The CM RCS was not used because it was needed to maneuver for re entry:

The separation used delta-velocity, imparted from air venting, from the docking tunnel at separation. The CM RCS could not be used since CM RCS propellant was required for re-entry. Before undocking, the tunnel pressure was reduced to 2.2 psi to achieve the desired delta-velocity of ~2 feet/second. Apollo 10 (May 1969) LM jettison data was used to determine the appropriate docking tunnel pressure differential to achieve the desired deltavelocity.

Source

I agree

reply to post by mbkennel


I agree mbkenne, it may well shake out that the energy and so velocity/direction change imparted by separation was not significant enough to effect the trajectory. That is pretty much the way I look at it all now. But I keep playing with this, that, and the other thing. I like physics a lot. Do you ?

I have lots of formal training as a chemist, but in terms of playing with problems, I like physics more. There are a few other pure physics problems that have come up for me studying Apollo. I may post them as time goes on. Thanks for your post.

reply to post by eriktheawful


actually i think you are correct in a sense.. by manoeuvring to a certain position they can control the descent trajectory to a certain degree during re-entry which also means they can control the seperation from the LM to a certain degree.

i think the shape of the CM was well known and thus they could predict its direction of travel depending on its orientation, so they may have used this as a method of controlling the trajectory to a certain degree during re-entry.

Originally posted by decisively

I agree

reply to post by mbkennel

 

But I keep playing with this, that, and the other thing. I like physics a lot. Do you ?

I have lots of formal training as a chemist, but in terms of playing with problems, I like physics more. There are a few other pure physics problems that have come up for me studying Apollo.

such as this simple pendulum

That is the question. How could the blackout be longer than expected and yet the landing on target? I remember watching the whole thing live as a young child. My dad explained to me that if we didn't hear from them at the expected time that it meant something was wrong and they may have burned up in the atmosphere. Time ticked away and I thought oh no... and then the camera (suddenly) showed a shot of chutes deploying on a successful on target reentry of the capsule.

To this day, I wonder about that. How did the camera cut to the chutes popping open at such a low altitude? That should have occurred much higher up? If the capsule burned up and they had a standby aboard a helo ready to deploy for the camera, that would explain the late chute and on target splash down.

Weird thing is I had a friend whose dad was in the air force told me he saw a chopper carrying a helo suspended from it traveling the area prior to the splashdown. I have no confirmation of this, just a long time ago friendship and report.

Originally posted by intrptr
That is the question. How could the blackout be longer than expected and yet the landing on target?

I have not found a detailed explanation as to why the blackout was abnormally long. It might have been low transmit-power on the spacecraft. It might have been that the Apollo Range Instrumentation Aircraft (ARIA - modified 707s) that relayed comms from the spacecraft to Mission Control (MCC) were pointed the wrong way (while circling) for their antennae to receive the first signals. Perhaps the crew just waited until they heard the call from CapCom before they answered.

I remember watching the whole thing live as a young child. My dad explained to me that if we didn't hear from them at the expected time that it meant something was wrong and they may have burned up in the atmosphere. Time ticked away and I thought oh no...

Apparently there was a bit of a disconnect between what they were getting at MCC and what the TV networks knew and reported. The transcript shows that Odyssey exited blackout and established communications through ARIA while still at high altitude. At this point, the Apollo capsule was generating aerodynamic lift (it really was an honest-to-god "flying saucer" - even if it was only gliding) and Command Module Pilot (CMP) Jack Swigert was flying it towards the recovery target area. Three minutes later, at around 24,000 feet it deployed two drogue chutes to slow the descent and orient the capsule blunt-end-forward. All of this happened out of sight of the cameras on the recovery ship, USS Iwo Jima.

...and then the camera (suddenly) showed a shot of chutes deploying on a successful on target reentry of the capsule. To this day, I wonder about that. How did the camera cut to the chutes popping open at such a low altitude? That should have occurred much higher up?

Nope. The main chutes deployed ~40 seconds after the drogues - at around 10,000 feet. That's less than 2 miles up, and 5-6 miles away from the recovery ship, so Odyssey would have been seen popping its mains ~20 degrees above the horizon as seen from Iwo Jima. Mind you, the TV cameramen were already looking towards the target area, so they very quickly acquired the capsule.

If the capsule burned up and they had a standby aboard a helo ready to deploy for the camera, that would explain the late chute and on target splash down.

As explained, the chute was not late, and - believe it or not - the pilots trained to land on-target. Even when it came to splashing down in the open ocean, it was a matter of pride and bragging-rights to be as close to the target as possible.

(Trivia Question: Which astronaut still holds the record for the most off-target splashdown in history?)

Incidentally, your scenario has the glaring problem of the "black helicopter" showing-up on the radars of the entire recovery task force, and possibly on the civilian TV cameras as well. And where did it come from? If there was another ship that it staged off of, that is a whole 'nother crew that would be in on the deception. Sailors - even those paid by the CIA - are famous for not being able to keep their mouths shut when there's a good sea-story to be told (Disclaimer - I was in the Navy for 10+ years).

Weird thing is I had a friend whose dad was in the air force told me he saw a chopper carrying a helo suspended from it traveling the area prior to the splashdown. I have no confirmation of this, just a long time ago friendship and report.

A helo carrying a helo? It's possible, though hardly suspicious. My real problem with that anecdote is that the recovery task force personnel were all Navy. The only Air Force guys in the area were on the ARIA planes, and they were too high and too far away to have seen what was described to you. As you say, no confirmation...

I would dearly love to see some unedited news coverage of the Apollo 13 landing. Both the Ron Howard Movie and at least two documentaries I've seen cut it so that there seems to be no contact, then the main chutes are spotted and everyone cheers. The timeline & transcripts (and at least one other documentary I've seen) show that there was considerable time (~4 minutes) between acquisition of signal and the visual sighting. I'd like to know how it was reported at the time.

reply to post by Saint Exupery

Thank you for that most in depth and informative reply. You helped me answer an old mystery and I will clarify my spelling mistake about "helo carrying a helo" up front. It was too late to go back and edit. I meant a helo, I was told a Chinook, carrying a "standby capsule" suspended beneath it to drop in case of reentry failure. Ok, that is the heresy part told second hand to me in my youth.

I have not found a detailed explanation as to why the blackout was abnormally long. It might have been low transmit-power on the spacecraft. It might have been that the Apollo Range Instrumentation Aircraft (ARIA - modified 707s) that relayed comms from the spacecraft to Mission Control (MCC) were pointed the wrong way (while circling) for their antennae to receive the first signals. Perhaps the crew just waited until they heard the call from CapCom before they answered.

Me neither. That is the million dollar question. Lot of perhaps answers. Thing is I watched it live. Back then they still gave us LIVE feed . In the background was News announcer (was it Cronkite?) giving "explanations". Then you also heard Capcom, calling out, "Do you read"?, and the camera was on the control room. Screens were in background showing the ocean and helos hovering... view from carrier I think? Time ticked painfully slow to add minutes to expected recovery of signal from blackout.

I remember the call being made from the capsule just prior to the mains being deployed. There was static and then pop, pop like a mike being keyed. Having watched all the reentry's up to that time (it was a big deal in our household), it seemed surprising that they caught all that on camera right off the recovery ship. Especially after the extended blackout. Did anyone test those depleted batteries or measure signal strength or explain how the manual corridor adjustment to reentry glide slope was made with such precision, before firing of explosive bolt(s) to jettison LEM prior to reentry?

When you add it up...

At this point, the Apollo capsule was generating aerodynamic lift (it really was an honest-to-god "flying saucer" - even if it was only gliding) and Command Module Pilot (CMP) Jack Swigert was flying it towards the recovery target area.

Wait. What? He was flying it after reentry and prior to chute deployment? How could he know where they were? And what on the capsule provided aerodynamic control? You lost me there.

Nope. The main chutes deployed ~40 seconds after the drogues - at around 10,000 feet. That's less than 2 miles up, and 5-6 miles away from the recovery ship, so Odyssey would have been seen popping its mains ~20 degrees above the horizon as seen from Iwo Jima. Mind you, the TV cameramen were already looking towards the target area, so they very quickly acquired the capsule.

If you say so. I sawer it with my eyes. You provide one solution to the sudden chute and how low they were, but that cut it close didn't it? Better even than the guidance computer.

I'd like to know how it was reported at the time.

Just like I saw and you say. My memory about when they saw the chute is that that appeared on screen just after the "we read you" from the capsule. Then the response was almost immediate. "we see you on the mains" and massive cheering in the control room. The screen in the control room showed the capsule suspended from chutes. Did they hold back cheering till then to be sure? Dunno.