Author Topic: Skylab injection?  (Read 17276 times)

Offline dbaker

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Re: Skylab injection?
« Reply #20 on: 02/15/2013 06:16 pm »
Further to my previous, and noting previous comment about an empty stage, S-II-513 had 22,494 lb of propellant on board at orbit insertion.

Offline John Charles

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Re: Skylab injection?
« Reply #21 on: 02/16/2013 01:09 pm »
I missed this thread in 2008 so very pleased to discover it today. Two days ago, I  toured a Russian space life sciences manager through Space Center Houston (JSC visitor center) and spent a lot of time at the full scale Skylab trainer. He asked many questions about the inflight repairs after watching the Joe Kerwin video describing the first crew's efforts. Wish I had these details then but at least I will be better prepared next time. Thanks to Rusty Barton and all for informative discussion.

(Edited to correct typo.)
« Last Edit: 02/16/2013 01:14 pm by John Charles »
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Offline zerm

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Re: Skylab injection?
« Reply #22 on: 02/18/2013 02:08 pm »
Again- there are documents that detail this event and thus off-the cuff statements from memory are not really required. From NTRS I collected, over a period of several months, read and produced the following analysis. 

I would ask user names please READ this account before posting comments or questions- do not simply computer-scan down the page picking for tid-bits and then toss out a quip before fully reading. This stuff needs to be read in full to be understood fully. I spent a long time reading and pondering and re-reading these reports in order to complete this account. At length, I reserve the right to be incorrect, all ya' have to do is find the area of the given report- tell me the page and quote where I have errored and it will be my pleasure to be corrected. I want to kep it all straight. Please don't toss Wikipeda into this- let us stick to the real reports and not the cliff-note version.

Launch of the Skylab Saturn V took place on May 14, 1973 and is best remembered for some events that 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 and was caught by the slipstream and torn off of the Skylab. The overall results were workshop overheating and a jammed solar panel wing. The second solar panel wing had been lost off of the workshop completely, but it was not until later than it would be discovered just how that happened. The first crew to go up to the workshop performed repairs and the next two missions were conducted as planned. 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 are far more interesting and far more frightening. AS-513 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 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 was 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. The airflow then 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 at the same time loosened both Solar Array Assembly (“SAS”) wings as it went. The worst of the damage, however, was not done yet. As the three 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-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 potential fatal blow 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 shaped charge was located that pyrotechnically blows the parts of the airframe apart so that the “skirt” ring can be dropped. This “skirt sep.” often seen in videos, normally takes place 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. 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. Then with the four outboard engines still firing in the near vacuum of space, and no center engine to provide its flow, a back-flow of heat would occur. 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 as 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 engine shutdown occurred. Had there been the loss of one engine, and the stage had been forced to burn a bit longer to compensate, they’d have lost the entire vehicle. So, why didn’t the skirt sep.? Here is why- when the separation signal was given, two Exploding Bridge Wire units fire at opposite ends of the Linear Shaped Charge (LSC) loop that passes completely around the vehicle at the separation plane. Then LSC would blow apart 199 tension straps holding the two sections together and the two sections would come apart. 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 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 the electrical plug used to indicate separation out more than ¼ inch, so no back-up charge firing was commanded. It was calculated that 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 entire vehicle.

  A second anomaly, which is also often misreported involved the loss of SAS wing number 2. Most accounts say that it was lost with the meteoroid shield- in fact it was not. Although loosened by the shield’s departure, SAS wings #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-II forward adapter skirt fire to aid in separation of the S-II from the upper stage. SAS wing #2 was centered just 16.8 degrees off of one of the retro rockets. The plume from that retro firing hit the already loose SAS wing and blew it “…completely off the bird.” as Pete Conrad observed. SAS wing #1 was held down by debris from the meteoroid shield which was enough to hold it against its associated retro’s plume.

Offline Archibald

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Re: Skylab injection?
« Reply #23 on: 03/12/2013 04:05 pm »
Doing further research I've found that, had Skylab A not been (heroically) salvaged, delay to launch her twin sister was 10 months - if all went well.

Google books had NASA hearings - when Congressmen literally grilled NASA officials with very precise questions.

Quote
(Congressman)
What is sacrosanct about having a backup launch ready within 10 months from a go ahead decision. In fact, there might be no decision to go ahead and if there was a technical failure in the Skylab project, it would take a good deal longer before you would want to launch again, isn't that correct ?
(NASA official answer)
The ten month response time for the launch of a backup workshop was a planning decision based on the following considerations :
1. Ten months is considered the minimum response time for the backup launch and, as such, has been designated for planning as the decision/launch interval ;
2. From an economic standpoint, a minimum preparation time for a backup launch eliminates the costly manpower phase-down-rehiring-retraining- buildup cycle and/or long-term sustaining effort costs.
3. The current ten month planning interval schedules EREP experiment data collection during the optimum growing season time period.

The actual time interval between decision and launch would depend on the type of failure experienced.

In the case of a clear-cut, easily identifiable cause for failure, e.g, launch vehicle anomaly, it is feasible to plan for the backup launch within ten months of the decision date.
or
A failure in the Workshop after launch could result in a far longer delay of launch.


First, it place Skylab B hypothetical launch around March 15, 1974 in the best case.

Now a question that haunt me is: would NASA had been given the budget to launch Skylab B ? FY74 and the shuttle ramping-up are not encouraging.
But $2.5 billion spent on an orbital wreck ? really ?

what do you think ?
« Last Edit: 03/12/2013 04:07 pm by Archibald »
Han shot first and Gwynne Shotwell !

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