The following is an excerpt from my book "Growing up with Spaceflight- Skylab/ASTP" the text is protected by Copyright 2015 Wes Oleszewski and no portion of this may be republished in any manner.
THEY ALMOST LOST THE WHOLE DAMNED VEHICLE
Launch day was set for Monday, May 14, 1973, at 1:30 in the afternoon Eastern Time. Coverage of the launch on ABC and NBC began exactly ten minutes before liftoff, and CBS came on five minutes prior to liftoff. That fact alone was symbolic of the TV network’s attitude toward Skylab. Gone were the days when the launch of a Saturn V to begin a mission garnered more than a full hour of coverage. Oddly, the best coverage came in the way of segments presented on the morning news shows such as “The Today Show.” Seeing that I was in the last few weeks of attending what I considered to be one of the worst junior high schools in the galaxy, I had no trouble getting my parents to give me the day off from school to watch the launch.
My first view of the Saturn IB booster that was to loft the crew up to the workshop came on the morning of Skylab 1’s launch. Scheduled to launch the day after the workshop had been placed into orbit, the Saturn IB was mounted on a tall pedestal called a “milk stool.” The reason for the milk stool was to allow the S-IVB stage and the Apollo spacecraft to use their regular swing arms and assorted umbilical connections on the launch tower. That tower had been built to service the Saturn V, which was 196 feet taller than the Saturn IB. So a stool was needed to elevate the vehicle. It was a unique and clever solution to allow the Saturn IB, which had not been launched since October of 1968, to utilize hardware and launch pads that had been leftover from the Apollo lunar missions. Originally, the milk stool had been called the “bar stool” until some wise person at NASA Headquarters pointed out there may be some problems with that name.
What stunned me about the Skylab Saturn IB was that, unlike every other Saturn IB that I had seen photos of, all eight tanks on the SA-206 first stage were painted white! All of the previous Saturn IBs had their RP-1 fuel tanks painted black with a white rectangle containing the words “UNITED STATES” painted in red. SA-206’s RP-1 tanks were all white with the red lettering. In fact, all of the future S-IB stages would be painted in the same manner. Why the heck had they done that? It was a question that bugged me for more than three decades. Then, while researching documents on the early Saturn IB’s, I found the answer. AS-206 through AS-210 had all of their S-IB fuel tanks painted white instead of black because on April 19, 1965, unexplained deformations had appeared in the black tanks on the very first Saturn IB’s S-IB stage. These deformations corrected themselves once the stage was taken indoors. Thus they were thought to be caused by simple sunlight heating the tank. Painting the tanks white was the fix that eliminated the deformations. Since the tanks for SA-206 were the next ones on the assembly line that had not yet been painted it was decided to make the change there and simply live with the deformations from SA-201 to 205.
As network coverage of the Skylab 1 launch began I was fully prepared with my trusty cassette recorder, a portable TV, the family TV set and naturally my models of a Skylab Saturn V and a Saturn IB; minus the all-white tanks, of course. Indeed I had my own launch control center all set up in the family living room.
The countdown was smooth, having started the previous Wednesday at two o’clock in the morning. That countdown ran in parallel with the Saturn IB’s countdown that began at eight o’clock that same morning. It was the first time since Gemini 12 in November of 1966 that a dual countdown had taken place in a NASA mission.
Overall the planning for Skylab 1’s trip up-hill was nearly identical to the previous Saturn V launches. There was, however, one planned difference and it involved the shutdown of the F-1 engines on the S-IC stage. Normally the center engine was shut down first at about 140 seconds into the boost and the four outboard engines were shut down together about 20 seconds later. In the case of AS-513 the center engine was planned to shut down at the normal time but the four outboard engines were scheduled to shut down in sets of two, 0.7 seconds apart, in order to soften the shock of staging. That shock, it was reasoned, could have damaged the Apollo Telescope Mount (ATM).
Counting down, the final seconds were familiar to us space-buffs as the big Saturn V ignited at T-8.9 seconds and roared to life. As it lifted off I had two very clear thoughts. First, I thought, “I saw you in person,” and secondly I was somewhat saddened in the knowledge that what I was looking at was the last Saturn V that would ever fly. Just 49 seconds after liftoff, Skylab 1 was swallowed by a thick layer of clouds that blocked out any view from the ground. That was unfortunate because big problems were just seconds away.
Shortly after vanishing from sight, an “anomaly” occurred aboard the Saturn V that put the entire Skylab program in jeopardy. The events began about 63 seconds after liftoff. This anomaly can be found described in historical shorthand by both NASA publications and media presentations as being the moment when the workshop’s micro-meteoroid shield prematurely deployed, was caught by the slipstream, and torn off the Skylab.
The overall results were workshop overheating and a jammed solar panel wing. The second solar panel wing had been lost off the workshop completely. Although most accounts of the launch and the Skylab program normally leave it at that; a study of the overlooked details of the 63 second anomaly is far more interesting and far more frightening. AS-513, in fact, came within seconds of becoming the first Saturn V to be lost in flight.
At 62.807 seconds after liftoff the launch vehicle began to react to an external, abnormal aerodynamic force. This was 1.707 seconds after Mach 1 (the sound barrier) was passed and was the beginning of the anomaly that was the premature deployment and subsequent loss of the workshop’s micro meteoroid shield.
Most media and poorly researched accounts say that the event took place at “…the point of maximum vibration…” or they will also say it happened at “Max-Q,” or the point where the vehicle experiences maximum aerodynamic pressure. But, Max-Q was a full 10.63 seconds into the future and the meteoroid shield would be long gone by then. What really happened was that as the Mach 1 shock wave passed down the vehicle a reverse flow of air along the skin of the vehicle found its way up what was called the Auxiliary Tunnel (a conduit that ran the length of the workshop). Entering through two uncapped stringers at the base of the tunnel, the high pressure air moved up the tunnel and popped the rubber boot at the top. That airflow got up under the shield structure and propagated a bulge that was just enough to lift the shield more than 2 inches into the slipstream, which was now at Mach 1.05. By 63.289 seconds into the flight, less than one second after it had started, the damage was done and the shield had torn away and its departure loosened both Solar Array Assembly (“SAS”) wings as it went. The worst of the damage, however, was not done yet.
As the two-and-a-half story tall, 22-foot-wide hunk of meteoroid shield fell, it struck the Saturn V at least twice. The first impact was on the S-IVB to S-II adapter, where the debris punched a hole in the adapter’s skin. This showed up in post flight data as the pressure in the adapter area was shown to drop at an abnormal rate. The potentially fatal blow, however, came when the shield’s remains struck the Saturn V for the second time. The impact area included the second plane separation point where the linear shaped charge was located that pyrotechnically blows the parts of the airframe apart so that the “skirt” ring can be dropped after first stage separation. This “skirt sep” often seen in videos, normally took place about 30 seconds after first stage separation. It is a critical event and, in manned Apollo flights, if the skirt failed to separate from the S-II, it was an abort situation requiring use of the escape tower.
The reason why this “skirt sep” is so critical is not one of weight, but rather it is thermal in nature. A back-flow of hot gasses from the five J-2 engines would become trapped in the confines of the skirt and the issue would become critical at center engine cut off. With the four outboard engines still firing in the near vacuum of space, and no center engine to provide its flow, the back-flow of heat would intensify. The temperatures imposed on the base of the stage along the thrust structure would quickly spike and go into the range where a “thermally induced failure” of the stage would take place. In that scenario the thrust structure melts and the burning engines push up into the LOX tank. On AS-513, that is what began to take place and the vehicle was within seconds of failure when S-II’s outboard engines finally shutdown. Had there been the loss of one engine, and the stage had been forced to burn a bit longer to compensate, they would have lost the entire vehicle. Even with the S-II engines burning normally, the estimates are that the Skylab 1 vehicle came within a very few seconds of that disaster.
So, why did the skirt fail to separate and, worse yet, why did the ground controllers not get an indication of failed separation?
Here is why: When the separation signal was sent by the Saturn V’s Instrument Unit (IU), two Exploding Bridge Wire units would fire at opposite ends of the Linear Shaped Charge (LSC) loop that passed completely around the vehicle at the separation plane. The LSC would then blow apart 199 tension straps holding the two sections together, and the skirt would thus be freed to drop away from the S-II stage. A back-up charge would fire if an electrical plug between the two sections did not disconnect, indicating that the two sections were less than ¼ inch apart. On AS-513, the meteoroid shield impacted the seam where the LSC for the skirt was located and it broke the loop. When the LSC fired, the explosion only propagated 165 degrees around the separation plane (about 89 tension straps). But that was enough to pull out the electrical plug used to indicate a separation of more than ¼ inch, so no back-up charge firing was commanded and the signal sent to the ground said that separation had taken place when in fact it had not. Because of the cloud cover, no ground cameras could be used to back up the faulty telemetry, so no one in Mission Control knew that the skirt was still attached. It was calculated that the huge meteoroid shield impacted the S-II skirt at between 200 and 1,000 feet per second. It was a close one; they almost lost the whole damned vehicle.
A second anomaly, which also is often misreported, involved the loss of SAS wing number 2. Most accounts say that it was lost with the meteoroid shield, but in fact it was not! Although loosened by the shield’s departure, SAS wings number 1 and 2 stayed connected to the work shop all the way up. At S-II shutdown, however, four solid fuel retro rockets mounted at 90 degree intervals around S-IVB / S-II forward adapter skirt fired to aid in separation of the S-II from the upper stage. SAS wing number 2 was centered just 16.8 degrees off of one of the retro rockets. The plume from that retro’s firing hit the already loose SAS wing and blew it “…completely off the bird,” as Pete Conrad later observed. SAS wing number 1 was held down by debris from the meteoroid shield which was enough to hold it against its associated retro’s plume.
Although you may see the anomaly sequences misreported in “documentaries” and even in some NASA films, the facts are as stated here. It simply shows that accounts of spaceflight history are normally written by persons too lazy to dig into the post-flight analysis. It also is important to keep in mind that normally NASA films are produced by outside contractors who know little or nothing about the subject, yet were able to make the lowest bid in order to get the project. For those of you still not convinced, perhaps because Wiki something says different, don't take my word for it. Simply find NASA report MPR-SAT-FE-73-4, August 1, 1973, Saturn V Vehicle Flight Evaluation; SA-513 Skylab 1 Saturn V... and READ IT.