Data Acquisition System
John Scott
about time I became more active.
For my thesis topic we designed and built a data acquisitions system
for a zuni launch, although because of the scheduling for launches
that year we never got to launch it. There were two parts to the
system, an on-board module with telemetry and an automatic tracking
antenna which would track the rocket in flight. The antenna was
directional and needed to be aimed as there were severe limitations to
the transmit power ASRI would let you transmit from their rocket.
I have to say that our electrical design for the on-board module was
quite bad. Our supervisor had a thing for basic stamps, so that's what
we used, but because there wasn't a stamp with multiple serial inputs
(there were 3 sensors that talked via serial) we ended up with 4
stamps all talking to each other via I2C which complicated
programming, which makes things unreliable. The mechanical design was
quite good, there were three layers of PCB connected via threaded rod,
in a housing which connected to the motor at its bottom and the nose
cone at its top. I can dig up some pictures of the on-board module if
any one is interested.
The main thing we learnt when designing the ting is that it needs to
be really really really reliable. launch accelerations are high (can
be up to 80g's) so if there are any components or connections loose
they will just pull apart. I was told a story (not sure how true it
is) that the Zuni rockets originally had modest accelerations of
40g's, but because they have been sitting around for so long the fuel
grains developed cracks which causes them to burn much faster. At uni
they use EEPROM's to record information. EEPROM isn't the fastest
thing, so I don't think bandwidth is a limitation (there is usually
not much information to record). Before they launch they usually any
electronics in epoxy to stop things coming loose, so although a SD
card would be good the epoxy would make it difficult to remove.
Luke Weston
Hmm, did my post just then go to the mailing list or did it just go to John?
If only you received it, John, could you copy it over to the mailing list as well?
Cheers,
Luke
Mark Blair
ASRI is bound by strict Australian DoD requirements for the safe storage and use of the Zuni rocket motors.
I'm not sure where you got your information from, but I can assure you that the Zuni rocket motors do not have propellant cracks. If they did, they would fail their surveillance life assessments conducted on a bi-annual basis. The propellant sampling and the motor static test firings are all within specification.
The in-flight acceleration is a function of the payload mass. ASRI recoverable payload modules are typically < 20kg, whereas the military warhead was significantly more than this - thereby significantly reducing the flight acceleration in the military version.
I hope this clarifies the 'rumor' :-)
Regards,
Mark Blair
ASRI
email: mark....@optus.com.au
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