[AR] Re: "How Hard Can It Be" rocket episode
- From: Rick Maschek <rickmaschek@xxxxxxxxxxxxxx>
- To: "arocket@xxxxxxxxxxxxx" <arocket@xxxxxxxxxxxxx>
- Date: Wed, 20 Nov 2013 03:43:56 -0800 (PST)
I was at the 'How Hard Can It Be' episode when we also flew our second
MiniSShot for the Sugar Shot Project. Those three guys did an awesome job for
not having built rockets before and to take on such a large project in such a
short time period; I've known people to take longer to do far less. While under
the pressure of the show's production schedule they spent many days and nights
working and during this time unknowingly accidentally drilled holes into the
CO2 ejection system that prevented the nose cone from deploying.
Shortly after their launch that same day, we flew the MiniSShot with the first
time our dual pulse motor successfully flew. Unfortunately, with one second
left in the second burn the airframe failed at the recovery section aft of the
nosecone/avionics and the chutes were shred. That was in mach+ speed and over
15,000'. During free-fall it continued recording data and transmitting its
location after impact with the ground. It was still transmitting when recovered
and data about the motor and vehicle from the flight computer was also
recovered. This data was used to help determine the probable cause of the
airframe failure. On future Sugar Shot flights, data will be stored on board in
addition to telemetry as a backup.
In 40+ years of amateur experimental rocketry I've seen many rockets impact and
destroy their payloads and avionics. When I launch my personal rockets, I now
encapsulate the electronics in a strong free floating pod within the rocket
airframe and cushion that with foam in the event of a ballistic landing. So far
this has saved the electronics on one ballistic landing with full data
recovery. I also have one flight computer potted in silicon. Earlier this year
on one of the student teams I mentor, a flight with a hard landing had the
microSD card pop out and was difficult to find on the lake bed. A short
brightly covered streamer would have helped but that has been rectified by
securing the card with tape.
Rick
______________________________________________
Date: Tue, 19 Nov 2013 14:26:06 -0800
Subject: [AR] Re: "How Hard Can It Be" rocket episode
From: George Herbert <george.herbert@xxxxxxxxx>
Personally, I believe in engineered crush structures. A lot.
If you can establish the G-load limit (and possibly, if applicable, jerk
and jounce limits) for the electronics, you can mount it so it can slide
vertically, with a known resistance foam or honeycomb above it for some
distance.
Combining that with how hard you think the lawn dart impact will be (tank
length, expected terminal velocity, etc), you can use calibrated
foam/honeycomb to keep loads safely below the established limit. You need
enough space for that to happen over the impact event, with some margin
(and some higher resistance foam / honeycomb as a final bumper in case of
mistake / exceptional situation).
These are rockets; 10, 20, 50 cm of cylinder for it to decelerate in is
probably Just Fine...
Some of my lawn-dart style manned capsule landers kept G-loads to 10 Gs or
less for the crew. That should be within tolerance bands for electronics,
though one needs to look at the specific equipment.
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