"Scott Lowther" wrote:
Charleston wrote:

From your read of the data what is the data rate for xducers 1302 and
2302?

!2 samples per second.

I know what the data rate was supposed to be and my question pertains to the
STS 51-L data I put on my website not data from post 51-L flights. NASA
repeatedly and throughout the five volumes of the Presidential Report,
stated that the data rate for those same xducers was 12.5 samples per
second. The cycle is completed every two seconds when the 25th sample is
finished. NASA reported the sample period as 80 milliseconds. That would
make sampling at a rate higher than 12.5 samples a bit difficult. If you
look at the first second of data again you will see that there are 25 data
points. That first second of data is farcical and NASA has since admitted
as much to me.

From the Executive Summary of the PC Report
http://history.nasa.gov/rogersrep/v1ch3.htm scroll down to pages 37-39 where
we have the following:

Channel Identifier Sample Rate Sample Period Description
(Samples/sec) (sec)
B47P1302C 12.5 0.080
LH SRM CHAMBER PRESSURE
B47P2302C 12.5 0.080
RH SRM CHAMBER PRESSURE

So again I ask what is your read of the data rate for the STS 51-L flight
data on my website?

How about the other two sets of xducers?
One and five samples per second. 1, 5 and 12 sps are what we run with to
this day. Likely to change sometime around STS 115 or after, though.

And back then on 51-L it was 1, 2, and 12.5 samples per second respectively.

*Precision* may be down to milli-psi, but *accuracy* is another matter. As
a general rule of thumb on these, expect on the order of a percent
variability between smae make and model xducers in this application.
Vibration, heating and whatnot.

Ah yes precision and accuracy, first year chemistry, thanks. Accuracy is
indeed another matter. I expect that NASA would have a standard and indeed
they did. The CEI requirement was +- 15 PSI but there was no requirement to
actually calibrate the pressure transducers. There was a requirement to
discard the transducers after three flights or so. I'd have to go look up
that number of flights to be sure. I think you would agree that if the
accuracy requirement was 15 PSI, that any interpretation of that data should
be caveated with an engineering disclaimer to that effect. No such
disclaimer exists anywhere that I have ever seen in any volume of the PC
Report. I find it quite nauseating that NASA suggested that their data was
quite accurate without ever addressing the issue of the accuracy
specification, nor lack of a calibration requirement. I guess it would be
embarrassing to admit that the measurements NASA relied on most were not in
fact reliable. It was like pulling teeth just to get the CEI document for
the HPM and even then NASA did not give me the figures or tables for the
document. You can verify what I have stated is true through MSFC's RSRM
project office. You will have to find an engineer who was there at the time
of the accident. I know one. The SRM chamber pressure accuracy debacle led
directly to the requirement to place all future SRM pc measurements under
configuration control.

Not back then, I must agree. Does that make it okay during steady state
burn?
Yup. 1,5, and 12 sps is more than adequate for post-flight ballistic
reconstruction. Kinda stinks for blips and ignition transient, so that's
why we're lookign at bumping it up by more than an order of magnitude.

Yes for the ignition transient, the data rate for STS 51-L was wholly
useless. To this day NASA can not definitively state what really happened
pressure-wise in that first 600 milliseconds other than the boosters did
ignite and pressurize. NASA used data from other flights in their charts
pertaining to the ignition transient. IIRC they never showed a single
chamber pressure data point from 51-L data for that time when the black
smoke first appeared.


Today I sort of doubt you have those spreads between the xducers.
Same data rates today. Our traces don;t have the jagged appearance because
int he data you've presented, the 3 xducers are displaying data at all
time points. To clean up the data, just delete the cells that have the
extraneous data (such as, say, B14-B16, B19-B21, C14-C25, etc.)

Ya, I know. I have done much more than clean up that data. I have actually
gone in and separated out the two different data streams that NASA used to
generate the first second of 51-L data following T=0. I have also treated
the rest of the data the same way and the results are quite interesting.

Quality high rate data is three things:

1. Expensive
2. Heavy
3. Processor intensive

Nevertheless, if one is going to stake a report on data like that to which
I have referred, it should be honestly presented, accurate within a
tolerance that makes the data truly relevant,

The data presented looks to be fully in compliance with what would have
been actually recorded. You can't present data that *wasn't* recorded.

Okay, we can discuss this more later, but if it is compliant then how come
the data is recorded at a variable data rate throughout the flight?


Now one more thing, looking at the data, what interpretive value would you
place on it during the first second following T= 0?

I'm not sure what you're after. If you're askign if it looks right... yes,
it does. A spike followed by a dip in pressure follwed by a climb back up.
This is normal in *many* solid rockets: the igniter fires and quickly
pressurizes the case; the case begins to blow down, and then the main
propellant gets up to speed and drives the pressure back up.

Umm, I just wondered if you noticed the data rate was 25 samples/second and
that it changes many times thereafter?

If you delete the extraneous data, you'll see that the transducers aren't
grabbing data at the same time, but are offset by some milliseconds. This
also addes to the apparent lack of co-ordination between them, as the
pressure was constantly changing, and they weren;t reading it at the same
time.

I wish it were so simple. Of course I hope others here will look at the
data too, and add their comments.

Daniel