Orbiter Data Recording & Power Systems

The following text describes how the operational data recorders and power systems aboard the Space Shuttle Orbiter function. Authored by experts at NASA, these descriptions also address what happened to these systems during the Challenger disaster and provide supplemental evidence to contradict the Challenger Transcript Hoax.

Newsgroups: sci.space.shuttle
From: Brian Welch
Date: Jan 29 1996
Subject: Challenger transcript history

I am posting this message in response to the continued interest in the Challenger transcripts, and in the hopes that a detailed listing of events will help quell a persistent myth. There are no "partial" Challenger transcripts, and there are no voice tapes recorded after the breakup of the vehicle. Even ten years after the accident, this continues to be the source of myth and speculation. It probably will continue to be for some years to come. I hesitate to even revisit the topic, but the continued misinformation, including completely false stories appearing on many "news" radio stations around the country in recent months, suggest that perhaps a detailed accounting of what did and did not happen will at least arm some responsible souls out there with the real data. I hope some of you will save the following and pass it on in the weeks, months and years to come when someone on the 'net asks about it.

The Challenger onboard intercom was recorded on one of two operational recorders (hereafter, "ops" recorders) aboard the orbiter.

Shuttle orbiters have several onboard components with memory-saving capacity: the General Purpose Computers (GPC), Ops recorders, a payload recorder, and a Modular Auxiliary Data System (MADS) recorder. Personal cassette recorders are available to crews for note taking, but it is thought that they were not in use during Challenger's launch.

The ops recorders store Shuttle ascent telemetry data and air-ground voice channels. Ops recorder 1 records the 60 kilobits/second (KBPS) data stream from the three main engines; Ops recorder 2 records at 128 KBPS the Shuttle downlink/downlist data and the two air-ground channels. Circa 1986, the Ops recorders were played back after reaching orbit to bridge gaps in real-time telemetry to ground stations or through Tracking and Data Relay Satellite coverage.

On March 19, 1986, NASA announced that four of five Challenger General Purpose Computers (GPC) had been recovered from the Atlantic and moved to the IBM Federal Systems Division facility in Owego, NY. The GPCs were cleaned under controlled conditions and submerged in deionized water at Kennedy Space Center prior to air shipment March 16, 1986, to Owego. The GPC ferrite core memories were examined for any possible residual data -- a process that at the time was expected to take several months. This information was in the form of data--not onboard voice--and this path was pursued to add any possible additional information to the accident investigation. Many weeks later, it was found that the additional data frames did not measurably add to the information already gathered during the investigation.

Both Ops recorders and the MADS recorder were recovered and were taken to the Marshall Space Flight Center, Huntsville, AL, for cleaning in clear, cold water and for subsequent drying in a thermal vacuum chamber. The cleaning/drying of recorder tapes took about two weeks, after which the tapes were taken to the Johnson Space Center for extraction of any usable data.

On April 30, 1986, JSC announced that it had so far been unable to extract data from the tapes. "Because the long exposure to salt water has deteriorated the tapes such that they cannot be unwound from the reels without total loss of the data, all attempts to date to recover information from then have been unsuccessful." JSC also reported that one of the personal cassette recorders available to crew members for note-taking had been recovered, but it was still in its stowage container, indicating it had not been used, and the recording tape was too severely damaged to be played back.

On July 16, 1986, JSC announced that additional efforts had been made to salvage the tapes from the Ops recorders. The tapes underwent treatment at IBM's facility in Tucson, Arizona, to remove magnesium oxide caused by seawater reaction with magnesium tape reels. The tapes were first treated with diluted nitric acid, and then rinsed in methanol. Earlier treatment immediately after recovery had included submersion in clear, chilled water until methods for salvaging the tape could be devised.

Through these types of intensive efforts, it ultimately was possible to listen to the tapes and provide a transcript of them to the media. The transcript was made available on July 28, 1986 at 4:30 p.m. EDT. Initially, NASA had concluded that the crew was unaware of the events preceeding the breakup of the Challenger. But detailed analysis revealed a final comment, providing "the first potential indication of awareness on their part at the moment when all data was lost at 73 seconds into the flight," NASA announced. That comment was "Uh oh," attributed to Pilot Michael Smith.

There is no transcript after the 73-second point because once the Challenger began to break up, power was lost and the recorders stopped running.

Out of respect for the families of the crew, NASA felt strongly that the voice tape audio should not be released. A transcript was released and the contents were widely reported for several days. Later, the New York Times sued NASA for release of the tape audio itself, a case which ultimately went to the Supreme Court, with the court ruling in NASA's favor.

In the July 28 news release announcing the transcript and the release of a report from astronaut Dr. Joseph Kerwin on the cause of death of the crew members, Rear Admiral Richard Truly, then head of NASA's Office of Space Flight, thanked all of the people involved in the massive salvage effort. "Their work deserves the admiration and thanks of the American people, and I believe their efforts have now closed this chapter of the Challenger loss," he said. "We have now turned our full efforts to the future, but we will never forget our seven friends who gave their lives to America's space frontier."

Brian Welch
Chief, News & Information
NASA Headquarters
Washington, DC

Newsgroups: alt.folklore.urban
From: Steve Patlan
Date: Jan 31 1996
Subject: The 'Last Word' on that Challenger Transcript

Where does the Shuttle's power come from?

To believe that the transcript is valid assumes that it was receiving power after the explosion. The electrical system of the shuttle is designed to be fail-safe - i.e, doubly redundant. There are three Fuel Cell Powerplants (FCPs) which feed the three main electrical distribution buses - MNA, MNB, and MNC. Some equipment is powered by redundant feeds from two main buses. The FCPs are fed from multiple sets of cryogenic H2 and O2 tanks - at least three, and typically four. A failed fuel cell is shut down and taken off-line, and a leaking cryo line can be isolated from the rest of the system by closing valves (isolating the tank in the process). The design philosophy of the shuttle assumes that at most two FCPs could be lost before making an emergency landing, so there is no "need" for battery backup-power, which is also p rohibited by weight considerations. (The shuttle uses 28V dc power. A typical on-orbit current level is 570 amps. That's an awfully big battery.)

How is the Ops-2 recorder powered?

I consulted the Space Shuttle Systems Handbook (publication JSC-11174, Revision E of October 28, 1994) Drawing 16.18, entitled "OPS RCDRS" shows that power is applied to Ops-2 by Switch 12 on Panel A1A3. The recorder has redundant feeds from the MNB and MNC buses, so at least one of FCPs 2 and 3 would need to be on-line after the accident.

So where are the FCP's located?

In the Rockwell shuttle body-axis coordinate system, the X axis is along the vehicle length, positive out the tail. It is measured in inches, with Xo236 at the nose and Xo1613 at the end of the bodyflap (aerosurface between the elevons and below the main engines.) The aft bulkhead of the crew compartment is at Xo576. So, here are the FCPs:

        FCP1: Xo650        FCP2: Xo620        FCP3: Xo680
Here are the cryo tanks:
                        H2         O2
      Tankset 1    |   Xo890  |   Xo780  |
      Tankset 2    |   Xo830  |   Xo720  |
      Tankset 3    |  Xo1010  |  Xo1100  |
      Tankset 4    |   Xo890  |  Xo1070  |
All these are located beneath the payload bay. Tanksets 1 and 2 are used on Ascent. Now, in the explosion video that I have seen, the crew compartment can be unambiguously identified. It is clearly *not* attached to 22 feet of keel. In fact, it does not appear to be attached to much of anything. It is definitely *not* trailing a tangle of plumbing and cryo tanks. (FYI, the O2 tanks are 33 inches in diameter and hold 781 lbs. The H2 tanks are 41 inches and 92 lbs. I don't think I would have missed seeing them.) There are two cryo pressure regulators for each FCP. The first drops the line pressure from the tanks down to 120 psia, and the second drops that down to 60 psia. Since the lines were severed during the explosion, there wouldn't have been an appreciable amount left between the regulators and the FCP. For reference, in the first 2 minutes and 30 seconds after liftoff, the shuttle uses 3.58 lbs of H2 (0.82 cubic feet) and 28.6 lbs of O2 (0.42 cubic feet). So, the FCPs were not receiving cryo after the vehicle broke up.

Yeah, but won't the FCP's "keep going"?

Well, this assumes that they were still attached. It's been a while since I saw the video, but I don't recall seeing an extra five feet of payload bay attached to the rear of the crew compartment. But I will address this issue for the sake of completeness. In a nominal, non-explosion scenario, an FCP will still operate if the flow of one of the reactants is shut off. If H2 is cut off, the FCP will fail within 20 seconds. That's "fail" as in zero power - it will begin to drop off immediately. If both H2 and O2 are cut off, I would expect it to drop to zero in less than 20 seconds.

Making the shaky assumption that the FCP survived the explosion intact, there is another consideration: Each FCP contains three substacks, each with 32 fuel cells. The walls within and between these small cells are rather thin. A regulator within the FCP keeps the coolant pressure the same as the O2 pressure - if the O2 pressure is much greater than the coolant, the walls will fail, destroying the internal structure. The coolant line between the FCP and the heat exchanger would have been severed in the explosion, so its pressure would have dropped to zero. However, the O2 is still at 60 psia beyond the stage 2 regulator. Picture a bear swiping a paw through a honeycomb. The FCP's water lines would also have been severed in an explosion, causing another pressure differential. It is not really reasonable to assume that the FCPs produced electricity for more than a couple of seconds after the vehicle broke up. But they weren't attached to the cabin anymore anyway, so it matters not.

Hey, we all know flight recorders have batteries. Sheesh!

Well, the systems drawing I mentioned earlier did not show any external batteries. Besides, the Ops-2 recorder is not an airline-type "black box", although it records the same type of data. I consulted the Communications Systems Section head (who I've known for 15 years and is no government shill) and his Ops Recorder system expert. They confirmed that the recorder contains no internal batteries. Keep in mind that the shuttle was designed in the early 1970's and uses a lot of old technology. The Ops recorder is a large, heavy piece of equipment, and weight and space are both at a premium on the shuttle. Given that the shuttle's power system is assumed to be reliable, there is no reason to believe that the Ops-2 recorder contains a battery. If you don't believe that last sentence, re-read this article until you do. Thank you.

Steve Patlan
NASA JSC/Electrical Power Systems

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