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.
SKYLAB 1:
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.
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