1019Re: [GPSL] Last Weekend's ISU Flight
- Oct 5, 2004Hi Mark,
Congrats on a near-bushel-basket recovery!
Not sure whose email from U. Idaho that you were quoting (Paul V?), but
I ran a post-mortem on the line that separated above the six bottom
payloads on EOSS-81. The line separated in the middle of the 2-ft open
span between the knots separating the the two adjacent payloads. This
span could never have come in contact with the ends of the thru tubes;
it appears that the 240# tensile dacron line separated due to excessive
tension during post-burst chaos.
Note that some of the separated payload housings had the aerodynamic
characterisitics of a shoe box, thus exacerbating post-burst chaos. On
most flights, we put a streamlined (fast-falling) beacon at the bottom.
but on this one, I foolishly decided to move the beacon up the payload
line and to let someone else's box take the parachute drag drubbing.
EOSS has used this method successfully on many payloads, and we use
threaded plastic dress caps drilled thru to prevent abrasion. Mating
nuts make interior access to the clamshell housings fast and easy.
We have also seen a number of student payloads using less robust
attachments arrive at the recovery site with nothing but a plastic
thru tube left on the line. The payload housing must be secured firmly
to the thru tube, as this is all that is keeping it from solo flight.
One EOSS payload uses a 0.38" diameter HDPE toilet fill tube as the
thru tube. This tube has a molded-in flange at one end that provides
a large-area surface to support the bottom of the housing. But it's
very had to cut decent threads into this material to accept a nylon
nut agt the top. I finally got it right using a very sharp lathe tool
and the single-point threading method.
Building-grade styofoam board can be useful for payload housings, but
it is difficult to make precise cavities into, and nearly impossible
to seal the air gap between the housing and a removable cover. And it
doesn't tolerate a rough parachute drag without leaving gouged-off
bits behind. The EOSS CW/cutdown beacon foamcore housing has endured
well over 20 flights and recoveries; altho it's a bit "cosmetically
compromised" from all the landing dings, it's still quite functional.
Those poster paper shear layers are surprisingly robust, especially
when treated with a couple of thin coats of Krylon.
EOSS's first two Shuttles used a four-cord bridle attached to the
corners and tied off a few feet above and below the housing. Although
this scheme does support the package well while conferring some
reducdancy, it also translates line tension into radial crushing forces
that the walls of the housing must withstand. One Shuttle had to be
re-built after a flight where it supported a 50# USAFA at the bottom
of the line. And that flight did not incur post-burst chaos.
The thru-tube method completely isolates the payload structure from the
line tension, and that was our purpose in developing it.
73 de Mike W5VSI
> > I ran out into the field as the balloon landed and missed grabbing
> > it by about 3 feet.
> > The plowed field was uneven and I couldn't change my running
> > direction fast enough
> > without tripping.
> Very cool. We haven't quite been able to do that here yet, though we have had good luck being within a couple hundred yards as the payloads come down.
> > Another topic. BalloonSats are popular with college students.
> > The University of
> > Idaho recommends using the plastic tube of a ball point pen to run
> > the load line
> > through. ISU says they saw metal pipe (from lamps) being used at
> > Boulder. We lost
> > three BalloonSats when the metal tube of one BalloonSats abradied
> > the load line. I
> > recommend using plastic tubing from hobby shops for the loal line
> > and three cord
> > suspension system. I'll post photos of the design shortly. I
> > would also recommend
> > using 1/2" thick styrofoam in place of the foam core. I'll write
> > up an article on this for
> > Nuts and Volts for early next year. I'm planning on getting Boise
> > School District
> > students to make a bunch of BalloonSats for launch.
> For the UNO BalloonSat flight, I believe the students used plastic tubing used to run water to things like ice makers in refrigerators, etc. Easily obtained from a hardware or home improvement store. To keep the tubing from sliding through the cube, a metal retaining clip (looks like a "C" with flanges that grip the tube) was placed on both sides of the cube. This worked pretty well for us. The tube was flexible enough to keep the line from abrading. We also put a separate line from the top tracking payload to the bottom one so that if one of the BalloonSats did cut the load line, the tracking payloads would remain tied together. There were no cameras in our BalloonSats so there were no issues with obscuring their view with another line.
> Has there been an issue with foam core satellites? I think foam core mount board would be a lot easier for the students to cut cleanly than styrofoam.
> 73 de Mark N9XTN
> Yahoo! Groups Links
Mike Manes manes@... Tel: 303-979-4899
"Things should be made as simple as possible, but not more so." A.
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