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<p>All,</p>
<p>OK, I'm going to give this a go! Spoiler alert and lots of
whitespace before my attempts at answers (please be gentle if I'm
in left field! hi hi).....................................<br>
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<p>-------------------------------------STOP READING IF YOU DON'T
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<p>------------------BEGIN ANSWER---------------------<br>
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<p>So first off, this is a Motor Firing set of questions....which
lead me to the LIU set of schematics (marked page 129b, PDF page
number 158). The first question plus hints leads towards a hunt
for a hardware timing error. The golden nugget I believe is the
indication of a 1.68 factor (longer burn time than
expected).....which I'll get to in a second.<br>
</p>
<p>Bit of my logic/attempt at understanding the schematic: <br>
</p>
<p>I think I narrowed things down to the 4015 chip (U4, dual 4 bit
serial to parallel shift registers, configured to be an 8 bit
shift register) and the pair of 4029 chips (U2, U3) near the top
center of the page (with the 'burn counter' lines coming out).
Also relevant is the 4029 chip (no 'U' label) below U2/U3 that I
think is the 'kick' to start the firing sequence by setting the
'JAM' signals (aka preset enable) on U2/U3 to initialize the
countdown values in U2/U3 that are loaded into U4. The 'kick'
signal out of the 4029 is tied to Q4, so 8 cycles of the
undecimated clock passes before this bit is set (and stopped since
its also tied to the inhibit), allowing the serial to parallel
registers to be clocked in (from the pn sequence decoders) before
the 'kick' that takes their values and maps them to the U2/U3
chips. The 4040 Chip (U11) looks like its being used for clock
decimation. The 4022 chip (U5) looks like it is the valve
sequencer that controls the order and repetition rate of the
opening and closing of the helium, UDMH, and N2O4 valves,
ultimately controlling the rate at which fuel and oxidizer flows
to the motor.<br>
</p>
<p>If I'm reading the schematic correctly, it looks like U2/U3
comprise an 8 bit timer with 256 (0 - 255) possible countdown
times. U2 is the low nibble, U3 is the high nibble. Every time
U2 reaches the all zeros state, the U2 Carry Out toggles Low for
one clock period, which allows U3 to decrement by one count. U2
is fed by the 'B' side of U4 and U3 is fed by the 'A' side of U4.
Via a sequence of NAND gates, it looks like the initial 'kick'
signal triggers a Monostable multivibrator (aka a 'one shot') on
the U21 555 Timer that is the 'START' of the burn. When the
countdown finishes, it looks like another monostable multivibrator
555 (U9) fires the 'STOP' command. This is where my understanding
begins to break down, because it could be that the 555s are
astable multivibrator configurations (maybe some kind of charge
pump for the ignition coils?, or maybe the ignition is being fired
in sync with the valve sequencing?) that are being toggled on and
off rather than actual one shots, and I'm not positive about how
the valves are actually 'actuated' by the control circuitry. I am
sure that I am missing lots of details, but I think I have a
pretty good understanding of what the 'regions' of the schematic
are responsible for.<br>
</p>
<p><br>
</p>
<p>To the point......<br>
</p>
<p>Answer to Question 1:</p>
<p>I think there is a transposition of the high nibble and the low
nibble when transferred from the 4015 to the respective 4029s for
the countdown. The bits are 'mirrored' about their 4 bit lanes
when transferred. More specifically, the 4015 clocks in the
serial data on the 'B' side first, and then those bits are
transferred to the 'A' side as four more bits are moved into the
'B' side. I think the fundamental problem is that what becomes
the least significant bit of each nibble in the 4015 becomes the
most significant bit in the respective nibbles of the overall
countdown timer. Lets say that the intended 8 bit sequence that
is clocked into the 4015 is the following: 0010 1111, where the
0010 is the High Nibble, side A of the 4015 and 'jammed' into U3
on 'kick' and 1111 is the Low Nibble, side B of the 4015, and
'jammed' into U2 on 'kick'. When the 'kick' signal is applied,
the 0010 of the 'A' side of the 4015 then becomes 0100 in U3. A
similar process happens on the Low Nibble, but since it is 1111,
the transposed result is also 1111.</p>
<p>Why did I pick that bit sequence?...This is where the 1.68 factor
comes in. I'm not sure of the actual clock period, so lets assume
for the moment that the clock frequency is 1 Hz, or a rate of 1
clock period per second. For an intended countdown of 0010 1111,
this would result in a 47 second burn. With the transposition of
the high nibble, the actual countdown timer is then 0100 1111,
which results in a 79 second burn. 79/47 = 1.680851064. Thus the
motor burns longer than expected by a factor of 1.68. I figured
out the bit sequence using a giant excel spreadsheet and listing
out all 256 combinations of 'expected' sequences and the resulting
'transposed' sequences, with the associated burn times for each,
and thus the ratio of burn times and only one bit sequence shows a
factor of 1.68 of Actual burn time over expected burn time
(programmers reading this.....please don't throw any rotten
tomatoes, copy and paste is quick in excel...hi hi).<br>
</p>
<p>Answer to Question 2:</p>
<p>IF a maximal length burn was tested on the ground, the
transposition in the 'jamming' from the 4015 to the 4029s would
not have been detected. 1111 1111 with each of the nibbles
transposed is 1111 1111. Still works! The most OCD test (and
expensive if actual propellant was used during the test) would be
to test all 256 potential burn periods (one of them would be '0'
and thus the cheapest!). Measuring the burn time of each burn and
comparing against the expected burn times for the sequence loaded
would have revealed the problem.</p>
<p>Answer to Question 3:</p>
<p>No idea really. Zero experience with how these kinds of valves
work. I'm guessing if the problem is 'electrical' in nature it
maybe has something to do with the timing between the 4040 clock
decimation chip ('pyro speed' indicators here, without remote
control of the selector, suggesting the developers were testing
various rates, and then settled on a jumper for the fastest rate)
and the 4022 valve sequencer that is 'self inhibiting' (maybe
another step of clock decimation?). It looks like the Helium
control valve is the first valve in the sequence at one of the
lower bit values (bit '2') relative to the higher bit values. So
maybe the helium valve is getting 'toggled' more frequently,
meaning less 'time open' and thus reduced helium pressure in the
propellant/oxidizer tanks (like maybe it was getting 'stuck' and
the toggle rate was too rapid to allow sufficient helium to make
it into the tanks?). Maybe this was less of a problem earlier
before the big burn because the propellant/oxidizer tanks had
sufficient pressure on their own when they were more full
(requiring less helium to pressurize them sufficiently)? Last
shot in the dark.........The 4022 is tied back into the pn
sequence decoder reset lines.....so maybe some kind of reset
occuring relatively quicker than expected even when the right pn
sequences are sent. maybe the 4022 hits the reset condition,
which clears the pn sequences from the registers, requiring some
number of clock periods (8?) before they are 'reloaded' with the
correct pn sequence, reenabling the process.....so sort of a 'stop
and go' situation with the valve sequencing.....again, maybe not a
big deal when the tanks were full and had their own pressure, but
more of a concern later when more helium is needed to pressurize
fully?</p>
<p><br>
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<p><br>
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<p>That's it.......again, I'm sure I screwed up a lot of the
details, but that's my best guesses for the three questions. Fun
game! I look forward to partial credit!<br>
</p>
<p><br>
</p>
<p>-Zach, KJ4QLP<br>
</p>
<pre class="moz-signature" cols="72">Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305</pre>
<div class="moz-cite-prefix">On 6/11/2018 9:31 AM, Douglas Quagliana
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:6788F2AA-EAF9-466F-B65A-04B43A5C3EDB@gmail.com">
<meta http-equiv="content-type" content="text/html; charset=utf-8">
<div>Friends,</div>
<div><br>
</div>
<div>Even if you know the history, you might not have seen the
actual blueprints, and you still have to find it in the
blueprints. <br>
<br>
Regards,
<div>Douglas</div>
</div>
<div><br>
On Jun 11, 2018, at 6:59 AM, Michelle Thompson via
Ground-Station <<a
href="mailto:ground-station@lists.openresearch.institute"
moz-do-not-send="true">ground-station@lists.openresearch.institute</a>>
wrote:<br>
<br>
</div>
<blockquote type="cite">
<div>
<div dir="auto">Good question - post with a generous spoiler
alert style header. Cc Phil for a faster reply.</div>
<br>
<div class="gmail_quote">
<div dir="ltr">On Mon, Jun 11, 2018, 04:52 Zach Leffke via
Ground-Station <<a
href="mailto:ground-station@lists.openresearch.institute"
moz-do-not-send="true">ground-station@lists.openresearch.institute</a>>
wrote:<br>
</div>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>Do you want answers (or attempts at answers) on the
list or direct to you?</p>
<p><br>
</p>
<p>-Zach, KJ4QLP<br>
</p>
<pre class="m_6306829133418286794moz-signature" cols="72">Research Associate
Aerospace Systems Lab
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305</pre>
<div class="m_6306829133418286794moz-cite-prefix">On
6/8/2018 10:36 PM, Michelle Thompson via
Ground-Station wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">
<div>
<div class="m_6306829133418286794gmail_signature">
<div dir="ltr">
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<div>
<div>Phil Karn KA9Q has been
working on something fun for us.
If you enjoy this quiz, please
feel free to share it and let
him know!</div>
<div><br>
</div>
<div>Given the documents that you
can find at: <a
href="https://github.com/phase4space/AO-10-blueprints"
target="_blank"
rel="noreferrer"
moz-do-not-send="true">https://github.com/phase4space/AO-10-blueprints</a></div>
<div><br>
</div>
<div>Quiz for fans of the AMSAT
Phase IIIB/AO-10 blueprints</div>
<div>Phil Karn, KA9Q</div>
<div><br>
</div>
<div>Question 1: AO-10 carried a
400-newton kick (rocket) motor
that used hypergolic
propellants. It was fired only
once, but the burn duration was
1.68 times longer than planned.
Why? (Note: the burn did *not*
end because of propellant
depletion.)</div>
<div><br>
</div>
<div>The cause can be discerned
from the prints; i.e., it was a
hardware problem, not a software
bug or operational mistake.</div>
<div><br>
</div>
<div>Optional hint 1: The burn was
timed in hardware.</div>
<div><br>
</div>
<div>Question 2: The ground test
of the hardware consisted of
successfully executing a maximal
length burn. What tests could
have revealed it?</div>
<div><br>
</div>
<div>Question 3: Although the
first burn did not deplete the
propellants, it was not possible
to fire the engine again because
of insufficient helium pressure.
Why? (Hint: the cause was not
insufficient helium loading
before launch.)</div>
</div>
</div>
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