DID THE SATURN V NEED FINS?

Very often the question comes up, "Did the Saturn V really need those great big fins?" When this is asked on internet forums there follows assorted postings from people who really do not know what they're talking about. Here's a word of advice- beware of any comment that begins with or contains the following phrases: "I heard" or "I think" or "I seem to remember" these are dead giveaways that the person posting is sitting at their keyboard with no real factual knowledge and simply wishes to make it look as if they have some knowing of the subject.

Additionally, watch out for the myths... such as...

MYTH: "The Saturn V really didn't need those fins, they were just for decoration."

FACT = The fin decision came about in early 1961 before the first Saturn I ever flew. You can find the explanation of their purpose in NASA, MSFC document MPR-M-SAT-61-5 published July 17, 1961, Page 208, Section 13.1, which reads in part, "The actual fins were not optimized for aerodynamic properties alone  but were designed  in conjunction with control output of the swivel engines  and the environment  that the vehicle  would encounter.  With four 188K  engines  swiveled to 10°  control angle,  various amounts of wind  and sheer gradients can be tolerated.  A highly unstable vehicle in the high dynamic pressure region  of flight  is severely  restricted  unless a very large control  torque  is available.  This might have been  designed into the system;  however,  this would have created another  undesirable situation . That is,  in case of shutdown  of the engines  high divergent rates  would exist, a condition which is not desirable  for a manned vehicle."

Now, let me translate that... the key in the statement is, "a condition which is not desirable  for a manned vehicle," and the term "torque control." The concern, even early on was one of torque vs arm. By arm I mean the distance between the center of the vehicle's rotation and the point where the astronaut's hand grips the abort handle. It was concluded that if one of the gimbaled engines should go hard-over or somehow fail while thrusting in an undesirable direction, which was common in the early 60s, the Saturn was so tall that the torque applied to the upper area where the crew were located would be so great that it would pull the astronaut's hand away from the abort handle and not allow for a manual abort. Additionally, the above cited document goes on to explain that the fins add to the stability assurance in the clustered engine configuration in the case of engine failure. Keep in mind that this was the first time that an entire family of vehicles were designed totally based on the clustered concept, which, up until October 27, 1961, when SA-1 successfully flew in spite of being nick-named "Cluster's Last Stand" many so called rocket "experts" believed clustering would never work.

Thus, the fins had a real and practical purpose on the Saturn vehicles, including the Saturn V. If one of the F-1 engines went hard-over, especially in the lower atmosphere, the fins would provide a counter to the resulting torque just long enough for the CDR to turn the abort handle.

Additionally, the fins added stability during the transition through the area of maximum aerodynamic pressure as well as in the altitudes where jet stream winds could cause significant wind sheer. The ideal was to have those gimbaled F-1 engines actually need to move as little as possible.

And now some common myths about the fins...


MYTH: "von Braun was really in love with fins, so he insisted that they have them on the Saturns."

FACT = This one is so silly it actually made me laugh out loud. People who write such thing simply demonstrate that they know very little about Dr. von Braun and little about the design efforts of the several thousand people who created the Saturn V. The MSFC team that designed the original Saturn C-1 for the ARPA and were led in large part by von Braun, designed a booster with no fins and the early Saturn C-5 (predecessor to the Saturn V) designs also had no fins.

MYTH: "The Titan II didn't have fins."

FACT = Apples and oranges- two very different rockets with different initial purposes, engine configurations and most of all arm lengths.

MYTH: "The first Saturns didn't have fins, so there was really no need for the later ones to have fins."

FACT = Read the above and you'll see how silly this statement is.

MYTH: "I believe in the end they were more for show than anything; the gimbaling motors kept the rocket stable. the fins as stabilizers were pretty useless I think at the velocities used." 

FACT = Note the term "I believe" used here, on par with "I think." This person is dealing from no hard research or knowledge. But, let's take a look at the "useless" contention. During the Apollo missions weight was so critical that NASA was doing everything in their power to scrub un-needed weight of ANY kind. They went as far as offering $10,000 for every pound that could be scrubbed from the LEM! There is the famous legend that they were also limiting the number of band aids in the first aid kit (a legend that I've heard 3 Apollo astronauts restate, but have yet to find the paper work to prove it) Now, in that environment, if the Saturn V fins, which weighed in the neighborhood of 1,000 pounds,  were in fact "useless" would not they be the first thing scrubbed?

MYTH: They did offer some stability but mostly it was habit. All rockets had fins so the Saturn V should too."

FACT = This was another one that actually made me laugh out loud. "ALL rockets had fins..." Hummm... the Saturn I, Block I, SA-1,2,3 and 4) had no fins. So there goes the "All rockets" part of the statement. Here's the fact- solid ENGENEERING got us to the moon with the Saturn V. Period! Nothing, and I do mean NOTHING was done out of "habit."

In fact, in the September 1964 issue of popular science, Dr. Wernher von Braun spoke specifically about rockets and fins including the Saturn V.

September 1964 Popular Science

Where he said in part: "Suppose a large vehicles such as the Saturn five has a serious autopilot (IU) failure at the most critical part of its ascent through the atmosphere (MaxQ). When the speeding rocket bucks the most severe aerodynamic forces. A failure in a swivel actuator (engine gimbal) may throw one of the five booster engines into a "hard over" deflection. In such a case, if I inherent aerodynamic instability assisted in rapidly increasing the angle of attack, structural overload might break up the rocket before the astronauts in the Apollo command module triggered their escape rocket…”

“…in the Saturn V booster, fins are not to provide perfect aerodynamic stability under all conditions-that would take fins of excess size. But the fins reduce the aerodynamic instability enough to make sure that the astronauts can safely abort, no matter what technical trouble may afflict their space vehicle. Our aim is to reduce the turning rate rotational speed at which the aerodynamically unstable Saturn V, when stricken by an autopilot failure, would turn into an angle of attack at which its structure would be bound to fail. One might say the purpose of the fins is to extend the period of grace that the astronauts have to push the "panic button."

My thanks to all of the arm-chair rocket people who made and those who will continue to make these silly remarks and internet posts- I really love you folks. This was fun.

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A TRIBUTE TO TOM MINTIER

Today I was reading the Space Hipsters Facebook page and saw that CNN journalist Tom Mintier has passed away. He is best known to space buffs as a spaceflight announcer, yet he covered many other subjects world wide. He had the unfortunate duty of being on the TV, live, when the CHALLENGER was lost in January of 1986. I did get the chance to meet him several months after the 51L accident and wrote briefly about it in my book "Growing up with Spaceflight- the Space Shuttle" and here is that excerpt...

"Later that summer I was back up in Michigan, working a summer job at Tri-City Airport, when I happened to meet CNN’s science/space anchorman Tom Mintier in the lounge at the executive terminal. He was there to cover would-be presidential candidate Pat Robertson, who was arriving and being greeted by a throng of… exactly nobody. We started chatting about STS-51L and soon everyone nearby was listening. I told him my story and he talked about being live on the air at that moment.

“There’s a few million people listening,” he said glumly, “what do ya’ say? There’s just nothing you can say, the camera tells it all. There is simply nothing you can say.”

Even six months after the accident you could see that both of us were still a bit lost by the event."

Tom Mintier broadcasting STS-51L and about to toss to the live NASA cameras for that fateful launch. Only a hand full of ATK engineers expected disaster and they were silenced by management and told to "Put on your management hat.".

APOLLO15; STAGING ANOMALY

A little-known staging anomaly took place on Apollo 15 (AS-510). When I read about it in the AS-510 launch report I nearly fell out of my seat and recently while watching news video of the launch I saw another piece of the puzzle. The following is an excerpt from my book, “Growing up with Spaceflight-Apollo Part Two” concerning the launch anomaly plus a lot of details not included in the book, especially that final piece of the puzzle; the secondary plume!

The whole story is in HERE

“Boosting Apollo 15 was a Saturn V quite a bit different from the vehicle that had boosted Apollo 14. Nearly all of the changes in the launch vehicle monikered as AS-510, had been made to save weight and add payload capability. Most apparent from the external perspective was the absence of the four ullage motors that had previously been located at 90 degree intervals around the skirt that attached the S-IC first stage to the S-II second stage.

“Those four solid propellant rocket motors were designed to fire .5 seconds after shutdown of the first stage as triggered by the Saturn V’s Instrument Unit (IU). Then .2 seconds later the IU commanded the firing of the shaped charges that would separate the first and second stages. The Ullage motors would continue to burn for a total of about 3.87 seconds producing about 22,900 pounds of thrust each. The objective of the motors was to apply a continued acceleration to the S-II stage and thus seat the fuel and oxidizer in the bottoms of their tanks. Data from past flights indicated that those four Ullage motors were not needed, so they were deleted from all future Saturn V launch vehicles beginning with AS-510. Internally, the S-II stage had another ullage system change when fixed orifices replaced its ullage pressure regulators.

“Meanwhile, down on the huge S-IC first stage, four of the eight solid-fuel retro rockets were deleted. The retro rockets aided the separation of the stages by countering any residual impulse from the spooling down of the F-1 engines and helped to counter the stage’s inertia. Data indicated that four retro rockets could do the job as easily as eight. Additionally the F-1 engines were “reorificed” beginning with AS-510 bringing the Saturn V’s total thrust up from 7.5 million pounds to 7.68 million pounds. All of these changes, although sounding somewhat large, only increased AS-510’s payload capability by 1,410 pounds, but 400 of those extra pounds allowed the Lunar Rover to ride to the Moon.

“At 136 seconds into first stage burn, the IU commanded the center engine on AS-510 to shut down. Then, 22.56 seconds later the IU commanded the outboard engines to shut down and the staging sequence to begin. It was at this point that the concept of eliminating four of the eight S-IC retro rockets and those four ullage motors nearly bit NASA in the butt. The problem began with the “shutdown” of those new up-rated F-1 engines.

“For those of you reading who are not familiar with turbine engines (and engineers reading please excuse me for simplifying), when you shut down a high-speed turbine, you do not just stop it suddenly. Doing so would cause the turbine’s own inertia to rip itself apart and it would explode like a fragmentation bomb- sending chunks of shrapnel flying in all directions at very high velocity. The F-1 engine had at its heart ultra high-speed turbines pumping fuel and oxidizer. In order to safely shut it down, the ignition source was removed and it was allowed to “tail-off” or spool down to an eventual stop while LOX and RP-1 continued for a time to flow through it. That outflow was still at a fairly high rate and caused some residual impulse.

“In the case of AS-510 the engine tail-off of the outboards lasted longer and was of a greater residual impulse than experienced from analysis of the previous version of the F-1 by 10.8 %. To compound the problem the elimination of the four ullage motors on the interstage skirt subtracted 91,600 pounds of S-II stage posigrade thrust as well. Normally, with an eight retro rocket and four ullage motor staging, the S-IC and the S-II stages would be slightly over 100 feet apart by the time the five J-2 engines in the S-II came up to full thrust.

“Predicted separation with just four retro rockets and no ullage motors was just short of 70 feet. In reality the separation distance of the two stages on AS-510 at full S-II thrust was just short of 40 feet!

“In fact when the plume of the S-II engines contacted the S-IC it was so powerful that it knocked out the telemetry being transmitted from the departing stage. The Radio Frequency (RF) signal continued, but the antenna gain was muted. Such RF signals without gain would indicate that the cable bundles had been blown away, or that the RF canister itself had been damaged or blown away. This loss had no impact on the mission since the S-IC had already been jettisoned.

“The real alarm was sounded after the mission at MSFC when it was calculated that if one of the four S-IC retro rockets had failed to ignite the two stages could have re-contacted during the staging sequence. That would have resulted in a catastrophic failure of the S-II and a mission abort using the escape tower. It was immediately decided that the four retro rockets that had been deleted from the S-IC would be reinstated for the next mission; Apollo 16.”

Now- here is the part that I could not put into the “Growing up with Spaceflight- Apollo Part Two” book, because there is no NASA documentation to prove it, there is only my own comparison of TV video.

So violent was the close proximity ignition of the five J-2 engines of the S-II stage that not only did it wipe out the telemetry RF units but it also ruptured the LOX tank dome on the S-IC stage. This is clearly seen in the staging footage as a secondary plume erupts from the S-IC that is not seen on any other Saturn V staging. In order to prove this I watched the staging videos from all of the Saturn V stagings where the event can be seen (Apollos 9, 12 and Skylab 1 were obscured by weather and Apollo 17 was a night launch so no plume was visible) and none have the brief secondary plume.

At staging there was 31,135 pounds of residual LOX in the tank, under pressure. At that point the S-IC was ~72Km or 44 miles in altitude and well outside of most of the earth’s atmosphere. The release of 31,135 pounds of LOX could easily account for the secondary plume seen in the video. That would mean that the upper LOX tank dome was compromised by the staging event.

Presented here is a side-by-side of the Apollo 14 staging sequence and the Apollo 15 sequence. The images are matched frame-by frame so you can see the difference.

That said, the crew was not really in any danger. The departing LOX, as seen in the ground and flight tests for SA-2 and 3, simply turned to ice crystals instantaneously. It could not burn or explode, because there was no fuel to combust. Instead what it did was to expel outward and very rapidly down the side of the S-IC and away from the departing S-II and Apollo spacecraft. Although the close proximity of the staging did wake up the engineers when the post-flight data was reviewed, in aviation we have a saying about vehicles moving too close to one another: “As long as you don’t get into those negative inches, there’s no problem.”

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SKYLAB'S MONIKERS

Ever wonder why the Skylab mission patches and the mission number don't seem to match? Well here's the complete explanation quoted from my book "Growing up with Spaceflight, Skylab/ASTP"

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When the missions for Skylab were first being finalized it had been decided that the launch of the workshop would be called “Skylab I” and the three crew launches were to be given monikers of Skylab II, III and IV, or SL-2, 3 and 4.

As the program progressed, however, someone in NASA management decided to re-designate the manned missions as SLM-1, 2 and 3. Thus, when it came time to make the mission patches there was some confusion as to which number should be applied to which mission. The crews were told that they should use 1, 2 and 3 to designate their individual missions and the process moved ahead with artwork being done for patches and stickers all using 1, 2 or 3.

As launch dates drew near, NASA management, of course, decided to change that decision back, drop the “M” from the manned missions and, again, number the Saturn V launch as “Skylab-1” and the manned flights as 2, 3 and 4.

Unfortunately, it was far too late for the mission patches and other items already branded with those numerals. So, Skylab 2 launched with a patch that said “I” and Skylab 3 launched with a patch that said “II” and so on. This confused the hell out of the news media as the Skylab 3 launch approached. They were given a press kit for the second manned mission that said “Skylab 3” on it, but were given mission patches, stickers, mugs, and assorted other mission items that said “Skylab II.” They did not know what in the world to call the mission! NASA, however, managed to side-step the problem by simply referring to the mission as “Skylab.” You may note that in this text we will use the original designations of Skylab 1, 2, 3 and 4. In aerospace it is always simpler to avoid management decisions in the first place.

By the way, the wives of the Skylab 3 astronauts had a secret mission patch of their own created that spoofed the one that their husbands were wearing.

COOL Videos and stuff area

This is the section for assorted cool videos and stuff

Some folks post their cool photos, videos and drawings on FaceBook,  but there is a catch. You see when you post a photo on FaceBook you give licence to everyone else on that site to use your photo any way they wish anyplace on that web site. I prefer to control my own photos. So, you are welcome to see my cool photos and stuff here... where I still own them. All photos and images here are copyright Wes Oleszewski and all right are reserved.

 WHAT I WAS DOING ON THIS NIGHT, JULY 25th, 1971
THE EVE OF THE APOLLO 15 LAUNCH

"SHERIDAN PARK, WE HAVE A PROBLEM!"

(From Growing up with Spaceflight- Apollo Part Two")

"Late into the evening prior to launch-day I decided to do a flight readiness test of my recording equipment. Suddenly- A GLITCH! My, or rather- my sister's, external microphone had failed! This was before they started putting built-in microphones on recorders- so I was really screwed. It was 9:45 at night- there wasn't a store in the Saginaw Valley that was open- especially not one with a microphone. Worse yet, I had spent my last dime on the tapes! I scrambled for a solution. Wiggle the wires... no use. Tap on it- no good. Take it apart... now it's REALLY busted! Sheridan Park- we have a problem!

 Perhaps, I pondered, when the store opens at 9:00 in the morning, I could get there and, after negotiating some sort of a lawns-to-be-cut-later deal with my parents, I could buy a new microphone, and make it back home within the 26 minutes between the time the store opens and the launch takes place... okay... that was nuts. There was no way that was going to happen, just the negotiating the lawn-cutting part with my parents alone was on a par with negotiating with North Vietnam. I sat there looking at the disassembled microphone and I thought "What would Gene Kranz do?" Simple- he'd call a meeting of his engineers and controllers and he would tell them to go out and find a solution to the problem with what they had.

 With what they had... hummm...

It was then that the thought struck me that several months back I had accidentally stuck an earphone into the microphone jack and it fit; in those days both had 1/8 inch jacks. And an earphone had the same basic elements to it as the microphone that was now laying in pieces in front of me. I knew that because I had dissected plenty of earphones. In short order I was rooting through the family “junk drawers” and had scrounged up an earphone that I had not yet dissected.

I tested it in the microphone jack; IT WORKED!

Sure the sound had a lot of tin in it and some 60 Hz hum, but it recorded! Using a four inch by six inch railroad “pounding card” that Dad had brought home from work, some masking tape and a hand full of tissues I had a microphone that the boys in the backroom at Houston would be proud of. I added a small measuring stick to give me the optimum distance from the TV speaker and I was "Go for the launch of Apollo 15!"

Copyright 2014 Wes Oleszewski- all rights reserved

THE COOLEST OPENING THEME EVER (IMO)

In my opinion the coolest opening TV theme for any Apollo flight was the NBC one for Apollo 15.

So, after more than a decade of searching, I now have a copy of it. Here it is...

(In keeping with the "Internet Users Who Are Occasionally Dense Act of 2009" we now advise you to click on the video and NOT the picture of the TV set. Thank you.)

By the way... my second book on spaceflight, Growing up with Spaceflight- Apollo Part Two can how be had in both eBook and PRINT! Get your print version today... because this one has Apollo 15 in it, as well as Apollos 14, 16 and 17.

Growing up with Spaceflight- Apollo Part Two, paperback

THE DAY OF THE APOLLO 11 LAUNCH

Here is a sample of my account of the Apollo 11 mission and this is how we saw it back in 1969

It was a fine summer morning in Saginaw, Michigan on the 16th day of July, 1969 and by nine o'clock that morning, most of us kids had already been outside playing for a while. I had no idea that the events that were up-coming would have a profound effect on my life. Sure, I'd been told a zillion times that history would be made that day, but in the mind of a 12- year- old, that meant little.

There was no escaping the TV coverage of the Apollo 11 mission as all of the networks had been on the air live since before dawn. Bergman did some of his best space savvy droning on ABC in contrast to the outward disdain for the space program presented by Chet Huntley and his otherwise indifferent partner David Brinkley on NBC. Over on CBS they had pulled out all of the plugs for this mission. Cronkite had been teamed up for the first time with astronaut Wally Schirra in pairing that would become nearly as legendary as the flights they would cover.

All three networks ran the standard clips of the astronauts, eating, suiting up and walking out... although a close look at the suit-up video would have revealed that the event shown was actually taped during the Countdown Demonstration Test back in the first week of June. The tell-tale clue to that is the fact that in the "suit-up" footage, the astronaut's suits are missing the Apollo 11 mission patch.

My Mom called me to the TV less than two minutes before Apollo 11 lifted off. At the time I had watched, with a growing kid's interest, all of the previous flights. In my mind, NASA could do anything. Now I stood by the TV and watched as Apollo 11 counted down to zero. The images of the Saturn V roaring to life were now, for me, as familiar as were the images of the ascent and staging. I recall that as Apollo 11 cleared the tower, my Mom said,

"Oh God... they're taking such an awful chance."

Looking at her I said to myself "What chance?" I thought that NASA had this all planned out so completely that every detail was covered. I recall feeling that my Mom's concern just showed that she did not understand how good NASA was at doing this. When the coverage showed Apollo 11 in Earth orbit, I went back outside to play.

I went back to my room that evening and got out my model CSM and LEM that I had built with my remedial modeling skills. I practiced some docking and undocking and did a lunar landing on my bedroom floor. For the first time in my 12 years of life, I recall having the strong desire to find out, not just more, but a lot more about Apollo and spaceflight in general. I wanted to do so before the astronauts, now headed toward the moon, arrived there.

The complete account of  Apollo 11, as well as Apollos 7,8,9,10,12 and 13 can be found in my book. It is available in hard copy or in e-book form at the following links:

Growing up with Spaceflight- Apollo Part One- print version




Growing up with Spaceflight- Apollo Part One- eBook











A PART OF APOLLO/SOYUZ THAT YOU DIDN'T SEE
This video contains a segment of the Apollo/Soyuz launch day that you probably have not seen. Tom Stafford had a lot of trouble approaching the S-IVB as the sun glare off of the Pacific Ocean was so bright that it blotted out his COAS (Crew Optical Alignment Sight).
CAUTION: This clip is rated "PG" for language- Pilot guidance is advised...

Here is a short video about the fiber optics and the camera pods...

(Photos: Space World Magazine and NASA)

If you like this sort of detailed stuff, check out my book series "Growing up with Spaceflight"

You can't miss 'em, they're shamelessly splattered all over this blog.
Growing up with Spaceflight






"WE CAME IN PEACE"

"Don't you ever bring that book to this classroom again!"

This is a sample from Growing up with Spaceflight- Apollo Part One:

"Several weeks after the Apollo 11 splashdown, my Dad stopped into a Gulf station for gas. He came back from paying and he handed me something- it was a book. When I opened that book, titled "We Came In Peace," it was as if someone had injected liquid hydrogen into the sparks of my new-found spaceflight passion. Even looking at the publication today, it is likely one of the finest illustrated and composed presentations of the nuts and bolts of the effort to get to the moon and space in general that had ever been produced up to that time. Yet, it was sold at gas stations! All of the other spaceflight books in my school’s library were illustrated with early representations of von Braun’s 1950s exploration plans or Project Mercury missions with looks “forward” to Project Gemini, but this book was about Apollo and it was up-to-date. The book was free if you “filled up,” but my Dad rarely filled the car up with gas. Instead, along with his “dollar’s worth” of gas that he normally bought, he probably paid the full price for the book; that price was one dollar.

I lived in that book to the point where my sixth grade teacher told me never to bring it to school again."

Here is the CBS opening for Apollo 15

Here is the CBS News intro for the Apollo 15 mission:

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My story of the Apollo 15 mission can be found here; in Growing up with Spaceflight- Apollo Part Two. The book can be found exclusively on Amazon Kindle.

APOLLO PART TWO: eBook version

COULD SNOOPY LAND ON THE MOON?

No matter when the subject of Apollo 10 comes up, space-buffs always seem to ask the question as to if or not the Apollo 10 crew could have landed on the moon and been first.

Dubbed the “dress rehearsal” Apollo 10 was much more; it was a critical step toward mankind’s first landing on the lunar surface. The media, however, seemed relentless in their efforts to portray Apollo 10 as an excess step leading up to Apollo 11. Even the use of Pad 39B was slanted as somehow being frivolous. The fact was there were plenty of navigation, communication and hardware issues that needed to be explored and solved before a landing attempt could be made. Even Cronkite speculated that considering Stafford and Cernan were going to be just 50,000 feet above the lunar surface, perhaps they may be tempted to. “…just ease her down and be the first ones to land…”

Thus, to this day the question is still batted about as to if the crew could have "pulled a fast one" and just landed SNOOPY and the correct and simple answer is, "No."

The cold hard fact was that SNOOPY, LEM 4, which the crew would be flying, had not gone through Grumman’s Super Weight Improvement Program also known as SWIP. That program saw NASA offering a bonus of $10,000 for every pound that could be scrubbed off of a LEM. Of course that meant that a clever Grumman engineer could have made a cool $1.85 million if he could have figured a way for Stafford to not take Cernan along. The first vehicle to go through SWIP was LEM 5 that would fly on Apollo 11. So, the Apollo 10 LEM was actually too heavy to lift off from the lunar surface and make it into any sort of orbit where it could rendezvous with a CSM.

Additionally, the computer in LEM 4 was not programmed for the landing. This was mainly because the full landing procedures had not yet been written. Additionally, the Moon's mass-cons, or mass concentrations of material that cause a sort of gravity lump and certain areas, were not fully understood and how they may effect the approach trajectory needed to be studied.

Finally, SNOOPY's ascent stage was shorted on fuel. This was not an effort to prevent those pesky astronauts from pulling a fast one- rather it was done so that the ascent stage would have exactly the same mass as Apollo 11's ascent stage on its trip from 50,000 feet to rendezvous with the CSM. Again, this was to simulate the same conditions as the lunar landing mission. 

Wes' Apollo Part One
volume of the Growing up with Spaceflight series
 has many more interesting details about Apollo 10.

Or for the e-book...

 Growing up with Spaceflight- Apollo Part One

All of that piled onto the fact that humans had only flown to the moon once prior to Apollo 10. This would make a landing attempt on that flight look like pure madness and speculation about such a thing actually sounded like nonsense. Yet still the media speculated on a sneak landing. Cronkite reported that whenever Stafford was asked the question about being tempted to "just ease her down" he, "always had a twinkle in his eye as if he was really planning to do something like that." Of course Tom Stafford has always had a twinkle in his eye normally.

SATURN V S-IC FLOW SEPARATION

The questions always come up on the Internet about the strange back-flow of the Saturn V first stage's exhaust plume. What made it happen? Were the engineers surprised to see it? Was it a concern? Did it happen on every Saturn V or just a few? How high did it go? Was it a danger to the vehicle? And often the answers given on the assorted forums and threads are mostly right or over simplified or even completely wrong.

In fact, the flow separation and resulting back-flow WAS expected. It was seen on the early Saturn I and IB launches. If you get the chance to watch the extended on-board staging films from SA-6 as presented by SpacecraftFilms "The Mighty Saturns- Saturn I and IB" DVD set, you can actually see the sooting of the LH2 vent lines on outside of the S-I inter-stage as the back-flow creeps up. It was no hazard to any of the vehicles and yes, it did happen on EVERY Saturn launch vehicle to one extent or another. The Saturn V was the most visually noticeable.

What made this happen? Well, seen below is the reason as stated by the Saturn V engineers. Now you may see folks argue that their classes in rocket engineering says this or that, but to me, the best answer is here, as stated by the folks who designed, built, flew and studied ALL of the data from the actual vehicle. Thus, it is, in my opinion, the best explanation. Highlighting of items are by me in order to bring to greater light some points of the report. The report itself can be fount on the NASA Technical Reports Server.

"Flow separation (from NASA MSFC MPR-SAT-FE-68-3, June 25, 1968; Apollo 6)

Flow separation was observed on the Saturn I and IB flights and was anticipated on the Saturn V.

Flow separation results from the expansion of the F1 engine plume at the higher altitude. The plumes create what could be considered a solid wall to the oncoming free stream. At lower altitudes, the free stream flow can be deflected around the exhaust plume by the exterral plume shock; but as the plumes increased in size, the free stream flow can no longer turn near the plume service. Consequently, the flow on the side of the vehicle separates or begins to turn before it reaches the plumes. Figure 17 – 18 illustrates the flow field which is obtained after separation occurred. 

Hot gas is fed into the separation region from the base region and plume interface. The base region hot gas results from the engine exhaust flows impinging upon one another and forcing some of the hot gases toward the base heat shield. Separation, once induced, will continue until outboard engine shutdown. As the plume diameter expands with altitude, the point of flow separation moves forward along the vehicle.

Flow separation on the AS-501 and AS-502 flights was first observed between 105 and 110 seconds. Measurements have been made of the point of flow separation for various flight time and are shown in figure 17-18. It is noted in this figure that the separation region extended beyond the top of the S-IC forward skirt just prior to stage separation. The observed blackness on the stage may be a carbon deposit rather than paint being burned."

Note that the "Forward Location" in drawing is incorrect and is corrected in the text. Photos of the Saturn V also shows the back-flow extending beyond the FORWARD S-IC skirt.

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