Ken,
Interesting data - that's the kind of information I was looking for.
Thanks for sharing it.
-Bob
On 12/24/2015 06:08 PM, KEN BIBA wrote:
A bit of experimental data.
The 17 years of the ARLISS (A Rocket Launch for International Student Satellites - www.arliss.org <http://www.arliss.org>) program has some interesting data to contribute to this discussion. This is the first and oldest CanSat competition - begun by Professor Bob Twiggs (CubeSat co-inventor) and continued by AeroPac in partnership with Unisec Global (unisec-global.org <http://unisec-global.org>). Each year we fly about 50 flights of 15 kg airframes with 1 kg university student payloads to about 3k meters on M motors … where the payloads are deployed at apogee for autonomous return … each payload is an autonomous robot. Most land to crawl home across the Black Rock playa floor, but some fly in various ways. Each payload has a rather complex DIY electronics payload as well as the flight avionics … subject to boost acceleration of up to 8 Gs plus deployment shock (from either black powder or CO2). We now have about 800 flights on M motors with this flight profile during the program - on a fleet of very similar airframes, on essentially the same motor - the Aerotech M1419.
In 2013, we decided to investigate more deeply about the flight dynamics of our student payloads and designed a custom flight recorder with 3x accelerometer + 3x gyro with a recording rate of ~1.3 kHz to examine these dynamics. A team of our members, led by Bob Feretich, designed and implemented the custom datalogger and post processing software (http://www.rafresearch.com/rocketdatalogger/index.html) to implement this data collection and analysis. A portion of the database of these flights from 2014 can be found here (http://www.rafresearch.com/arlissdatalogger/flightdata/ARLISS2014/index.xml) including spectral analysis of the experienced by the payloads during boost and deployment.
One of the surprising results of the analysis is that while there are some very large magnitude shocks (up to 50g! - particularly from black powder deployment) - there is little correlation with payload electronics failure. Remember these are student payloads … so build quality is highly … variable. We speculate that while the absolute magnitude of the shock can be high, the duration is very short … so the total energy in the shock is modest.
We think this will correlate well to the shock profile for ARLISS Extreme suborbital flights as well. We will fly one of these recorders this coming season to confirm - but the motors and deployment methods are not dissimilar.
A paper describing an overview of this recorder can be found here (https://www.dropbox.com/s/1kpkt3dg6038pbx/ARLISS%20Data%20Logger%20Project%20Part1.pdf?dl=0). Bob Feretich has these recorders for sale as well.
Here is an overview of the ARLISS program. https://www.dropbox.com/s/5f6sl7dsr5lrdl8/Sport%20Rocketry%20ARLISS%201.2014.pdf?dl=0
A copy of Dnepr user manual is enclosed … this has some standards for testing payloads on a big solid to LEO - note pages 54-58 for specs on typical payload acceleration and deployment shock.. https://www.dropbox.com/s/ncnk03oly4eodxu/Dnepr_User_Guide.pdf?dl=0. To my eye, the boost acceleration magnitude and the deployment shocks are not dissimilar between Dnepr and ARLISS and perhaps might be extrapolated to other solid fueled systems.
We see very few flight avionics failures (three out of 800 flights - and we ascribe those to pilot error) and most of the student failures seem to be from connector failure on landing shock.
Ken