STS-114 Mission Update Thread (Part 2)

emerrill · Jul 20, 2005

"No, the aft fuselage which is the engine compartment." Yeah. Woops. After I re-read, I just thought *d'oh* <img src="/images/icons/smile.gif" /> -Eric <div class="Discussion_UserSignature"> </div>

emerrill · Jul 20, 2005

"I believe the JSC group in Houston identified a potential for EMI, by analysis. not testing." I wasn't completely sure. One of the quotes from John Muratore implied to me that there were physical tests but I guess it isnt very clear about that (when I read 'lab' it makes me think of a physical test): "Testing of the (point sensor) box ... in the lab in Houston suggested electromagnetic interference could interfere with the box" The full article is at http://www.spaceflightnow.com/shuttle/sts114/050720newdate/ for full context. -Eric <div class="Discussion_UserSignature"> </div>

emerrill · Jul 21, 2005

Are there any non-flight spares lying around that they could have gotten their grubby fingers on <img src="/images/icons/smile.gif" /> or do you guys have everything? <div class="Discussion_UserSignature"> </div>

w3a53735 · Jul 21, 2005

How about the possibility of a bad BATCH of the sensors in the tank? Considering both tanks, are they all from the same manufacturing lot?

w3a53735 · Jul 21, 2005

Grounding issues, improving the grounding. I've been there. Also EMI. I've been there too. However ... They said the sensitivity (whatever is the correct word) of the system was in the order of .1microseconds. They also said that the sensor reading remained in the failed state for something like 15 minutes or if memory serves during the scrubbed launch until they drained the tank. So why were they not seeing failed indications of just .1microsecond. Not for the longer times. -steve-

emerrill · Jul 21, 2005

"So why were they not seeing failed indications of just .1microsecond. Not for the longer times." In the conference, they said that those transients would cause the circuit to lock up. With my EE experience, it seems like this could very well be grounding/EMI. Those problems tend to be VERY difficult to diagnose and reproduce. <div class="Discussion_UserSignature"> </div>

w3a53735 · Jul 21, 2005

If the box is subject to LOCKUP (like long term) then it would not be able to give individual and continuing real-time readings at whatever the sampeling rate is, if the circuit were to lock up. Very bad design but only IF this IS the case. -steve-

emerrill · Jul 21, 2005

"If the box is subject to LOCKUP (like long term) then it would not be able to give individual and continuing real-time readings at whatever the sampeling rate is, if the circuit were to lock up. " I think you are interpreting 'lockup' wrong. I beleive that just some of the conditioning sort of circuits (just basic transistors/controll logic and what not, not the actually controller) lock into a particular state. -Eric <div class="Discussion_UserSignature"> </div>

emerrill · Jul 21, 2005

"Probably TOTALLY unrelated, but there was plenty of lightning generated RF in the area too if something wasn't shielded from an induced charge...." True, but i dont think that would expain the first tank test, and I would think the source would need to be internal, since I would assuming the entire aft compartment is a shielded box. <div class="Discussion_UserSignature"> </div>

dougbaker · Jul 21, 2005

If I understand correctly; there was only two power supplies for the psb and it was identified as a potential problem where a power supply failure could cause the failure of more than one sensor. So it was changed to have 4 power supplies to provide more redundancy and this is the first flight for this orbiter with this upgrade. How ironic, if it proves to be a grounding problem, that may have been caused by the additional power supplies with a ground difference between the now 4 instead of 2 power supplies. I often troubleshoot software problems, and it also happens that by adding extra code or processes to make something more reliable, it can have the side affect of breaking something else. So the harder you try to make something better, it can cause other unexpected problems. A classic example is the airbag, that has saved many lives, which is great, but because of the airbag, some children have been killed when it deployed for a low speed impact. So now we have 2nd generation air bags. Of course I still think they will find the problem when they cryo load the et tank.

montmein69 · Jul 21, 2005

This is my first post on this forum. Thank you for all the information you give. /> However the sensor is simply a resistor which changes />resistance with temperature. The sensor is not a likly /> source of the problem. As the problem gives a headache to all the engineers, could this hypothesis defintly be excluded ? Which material is the wire ? (platinium ? carbon ? alloy ?). Do you think there is no possibility to have some physical or chemical effect of the liquid hydrogen on the material ? The cryo conditions are actually related to the erratic anomaly .... Can we exclude the behaviour of the sensor even if it is inside the tank and not easily accessible ? <div class="Discussion_UserSignature"> </div>

shuttle_rtf · Jul 21, 2005

Seems to me that if on the countdown we lost ECO Sensor 4, then they'll turn that off/ignore and go with the others. If we lose ECO Sensor 2 then it'll be a scrub.

najab · Jul 21, 2005

This thread is officially too long now! This looks like a good place to split it. On second thought, I'll split it when you guys pick up the count.

SpaceKiwi · Jul 21, 2005

Okay, we've got a new launch date. And, we've got a potential cause of the ECO sensor problem. My question would be this:- Tanking proceeds nominally and the ECO sensors read correctly WET. Do they 'risk' running the test signals again to set them to DRY? I would be tempted not to if they correctly read WET and you know there is propellent in the ET. <div class="Discussion_UserSignature"> Who is this superhero? Henry, the mild-mannered janitor ... could be!-------------------------------------------------------------------------------------------Bring Back The Black! </div>

shuttle_rtf · Jul 21, 2005

Thanks SG, any ETA on how long the delay is?

dougbaker · Jul 21, 2005

They are not platinum. But early in the program they were a different material that did react to the o2. See a post by me, with a link to a document that describes the early welding problems and the steps they now take to make sure the sensor is good. If you can't find my earlier post, I can post the link to the 2001 document again.

Testing · Jul 21, 2005

In the news conference yesterday they said they would be testing the ECO sensors at every opportunity. Specificly when things that were different such as new equipment was turned on or off. One item mentioned was bipod strut heaters or anything else that could cause an EMI spike. If it is an EMI related problem they can nail down the source by testing the ECO repeatedly. <div class="Discussion_UserSignature"> </div>

dougbaker · Jul 21, 2005

oops, I should read my post before sending it. They are now platinum.

shuttle_rtf · Jul 21, 2005

My round up on this is as follows: (SG please correct if I have anything inaccurate here): Sensor curcuits 2 and 4 will be swapped in the point sensor box (PSB) Should Sensor 4 fail, fault will be shown as the Sensor 2 circuit path Should Sensor 2 fail, fault will be shown as the PSB Any other failure will be a UA (Unexplained Anomoly) Grounding in works to sort EMI (Electro Magnectic Interference) EMI test to be completed. Line testing, fault tree, and common cause analysis in works and continuing S0007 CTS on Saturday with a planned launch time of Tuesday at 10:34 AM EDT PTB Friday - L-2 Sunday Attempts 7/26, 7/27, 7/29, and 7/31 ECO 3 of 4 rationale will be acceptable for indicated fault in wire/ET - allowing launch to proceed Will scrub for PSB failure or new failure

emerrill · Jul 21, 2005

"That is not what I was told... Are you sure that they are not platinum?" He corrected himself, top of this page: "oops, I should read my post before sending it. They are now platinum. " <div class="Discussion_UserSignature"> </div>

dougbaker · Jul 21, 2005

I read the following from : http://www.spaceflightnow.com/shuttle/sts114/050718options/ When I made my comment about more power supplies, it was based on the following: "As it turns out, NASA's original launch commit criteria called for three-of-four operational ECO sensors. But in the wake of the Challenger disaster, a review of shuttle systems revealed that two of the sensors were powered or controlled by a single component in an electronic black box "upstream" of the sensor system. Because the failure of that component could take down two sensors, the rule was changed to require four-of-four at launch. A modification was proposed several years ago and implemented during Discovery's last major overhaul, eliminating the single-point failure mode. This will be the first flight for the modification. In the downtime after the 2003 Columbia disaster, engineers discussed changing the LCC back to three-of-four, but ultimately decided to let the rule stand as is. "

dougbaker · Jul 21, 2005

From the following: http://www.jsc.nasa.gov/news/columbia/nsts08399/book00/part4/031042703.pdf OPEN CIRCUITS OF THE LOX ECO POINT SENSOR TRANSDUCERS OCCURRED DUE TO USE OF MOLYBDENUM/RHENIUM SENSING WIRE WHICH OXIDIZED IN AN OXYGEN ATMOSPHERE (REFERENCE CAR AB6852 AND AB6853 AT MPTA AND AB5397, AB6613 AT KSC). CORRECTIVE ACTION FOR ALL VEHICLES CHANGED THE SENSING ELEMENTS TO PLATINUM.

dougbaker · Jul 21, 2005

Thanks for the clarification. My main point was a change in the box may have caused the grounding problems.

emerrill · Jul 21, 2005

"With one snag, a Delta IV is ready to go. the range will normally give each guy 2 trys and then they have to stand down for the next guy inline. The Delta guys may give us some of their days" What days do they currently have the range? Have they officially given up any days yet? I imagine they must be itching to get off the pad too (as would anybody who as a spacecraft just waiting to go) <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

shuttle_rtf · Jul 21, 2005

Thanks SG, I'll add that to my info. Much appreciated.

STS-114 Mission Update Thread (Part 2)

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