Truly a KISS moment
Simple and efficient it is. Have one and celebrate. ------------->
We invite fans of our Low Orbit Helium Assisted Navigator (LOHAN) project to raise a glass or two today to the Reg reader who finally cracked the problem of just how to hook up our Vulture 2 spaceplanes's rocket motor heater. To summarise, we've got a space-grade Polyimide Thermofoil flexible heater wrapped round our aircraft' …
Could you not use thin strips of sticky metallic tape for the break point, it would provide good continuity between the tubes and the cabling but still have the ability to shear off cleanly on launch?
Alternately a reverse cloths peg style of clip that provided the connection onto the inside of the tube by sprung assisted friction alone and the thrust would again draw the clips out of the tube.
I wondered about simply using a piece of 70C alloy, similar to Chipquik (tm) but with slightly less indium so it doesen't go brittle at low temperatures.
Only thing I'd do is add triple redundant contacts so if any two things break the failsafe still operates.
ie physically separate contacts encased in heatshrink to avoid shorting.
The conductive grease sounds like a good idea. Note that Copper oxidizes, producing Copper Oxide (I or II), which is either non-conductive, or a semiconductor. The conductive grease should prevent the oxidation. One could also get fancy and Silver plate the interior of the Copper tubes (Silver Oxide is a conductor); consider some of the electroless Silver plating solutions, which will deposit a few Angstroms of Silver (Cool-Amp is one maker (I have no connection, etc.).).
You might also consider ensuring that the end of the Copper tube has a slight flare to it, or, at least, is deburred. Cutting Copper tubing tends to produce a burr, or slight squeezing of the tube at the cut point, and, if you're counting on a dependable release, you don't want anything binding at the end of the Copper tube.
You could also consider some type of spring contact that would be inserted in the Copper tube. I'm thinking of something along the lines of a piece of Beryllium Copper that is folded and soldered to the wire.
Good luck with it!
P.S. Remember that any landing you can walk away from it a success.
Well, we've got to have some of this, if only for the name: http://www.cool-amp.com/conducto_lube.html
The open end of the tube has indeed been deburred, with a very fine drill bit which created the desired slight flare.
I don't think we're going to get a spring contact inside, and it's an unnecessary refinement, to my mind.
This may be quite unnecessary, but:
Improved connection contact behavior, if necessary. Clean the inside of the copper with a mild acid or cleaner of choice. Maybe a bit of abrasion.
Coat wires to be inserted and the inside of the copper tubing with a material called Stabilant 22. This improves the contact between the materials and protects from oxidation/corrosion. Plain copper generates an oxide film fairly quickly. This insures max current flow for the circuit. The Stabilant actually conducts under pressure.
This may change retention force to a bit lower.
I use this stuff on any electrical connections. PC connections to power connectors. It is similar to magic.
At the risk of making a brilliantly simple thing a bit less so, would a small magnet on the outside of the copper tube help keep the inserted steel wire pressed against the inside of the tube until the point of release? Seems like it would provide a little friction to help stop the wire from being vibrated out of the tube during ascent but not really impede disconnection.
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