Cunning Reg reader cracks LOHAN hot coupling condundrum
Lightbulb moment in quest for spaceplane motor heater connect
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's rocket motor casing, lest the power plant catch cold during its ascent to launch altitude.
The temperature is monitored by a thermistor connected to a cheap aquarium thermostat, and juice is provided by a 12V LiPo battery. The rig - seen here with an outer coat of heatshrink around the motor case - works a treat, and performed splendidly during a recent test flight to a tad under 28,000m.
Of course, the battery and thermostat will ultimately be inside the electronics enclosure of our fantastical flying truss launch platform. Accordingly, we and our beloved readers have spent quite some time fretting as to the best way to hot couple the whole shebang in a way that allows a clean release at launch.
Along the way, we've had some ingenious suggestions, all of which had their pros and cons, but just as we were about to have a serious sit-down to make a final decision, this idea popped up in Reg forums:
A suggestion for attaching electrical connections between the plane and the truss.
For each connection a short length of backward facing copper tubing would be fixed to the plane (or even inside the body with the tail end of the pipe outside). The front of the copper pipe is soldered to the internal wire.
On the truss a cable hangs down to the plane with a small piece of steel wool soldered to the end. To make the electrical connection the steel wool is then pushed into the copper tube on the plane. The springyness of the steel wool will hold it in place but should slide out of the tube as the plane launches.
The amount of grip needed inside the tube can be varied by soldering more or less steel wool to the end of the wire. Install one tube/wire combo for each required connection.
Well, we thought this was an excellent idea, but reckoned it could be simplified further. Here then <portentous drumroll> are four pieces of 2mm copper tube, into which wires can be inserted:
The amount of physical resistance to extraction is adjusted by simply pushing more or less wire into the tube, which means we don't really need the wire wool.
Having soldered connectors to the copper tubes (male for the battery, female for the thermistor), we glued them through the plane's rear fuselage...
...bent them backwards, and with the rocket motor inserted into the spaceplane's rear end, ran a quick test:
You can see the reason for the male/female connector ruse: they hook up to their opposites connected to the motor heater and thermistor. That way, there's no chance of accidentally swapping the connections, and we have been known suffer moments of absent-mindedness.
Finally, as an extra precaution, we colour coded the tubes and feed wires and voilà:
The Styrofoam blocks are to keep the exposed wires apart after launch, although the thermostat handily cuts the battery power to the heater if the thermistor disconnects, so it's not really an issue.
It just remains to tweak the lengths of the inserted supply wires, to adjust the resistance to the point where they're firmly inserted, but will detach as planned. Once the flying truss is wrapped, we'll mount the Vulture 2 on its launch rod, connect the heater and give the whole thing a good shake, rattle and roll, to check it's good to go.
Thanks to all of you who chipped in suggestions on this vital mission element, which is now pretty well crossed off the rapidly diminishing "things left to do" list.
As ever, your input is welcomed, and in this case, essential. ®
More from the lovely LOHAN:
- You can find full LOHAN coverage right here.
- If you're new to LOHAN, seek out our mission summary for enlightenment.
- There are photos our our magnificent Vulture 2 spaceplane here, and detailed structural plans here.
- For your further viewing pleasure, we have all our photographic material stored on Flickr.
- Our LOHAN and Paper Aircraft Released Into Space (PARIS) videos live on YouTube.
- We sometimes indulge in light consensual tweeting, as you can see here.