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back to article LOHAN rolls out racy rocketry round-up

In response to requests from several Reg readers who've been following the progress of our Low Orbit Helium Assisted Navigator (LOHAN) ballocket mission, we've put together a round-up of just where we're at with the various aspects of the project. Click here for a bigger version of the LOHAN graphic The LOHAN team is fighting …

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Pint

carbon fibre?

Can't see much details on the tessellated trussy thing, someone point me at the right article, all these daft titles are impossible! Interested to see how the joints work.

So when the rocket fires, isn't the whole truss thing going to rock about like crazy under the balloon?

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Boffin

Re: carbon fibre?

"So when the rocket fires, isn't the whole truss thing going to rock about like crazy under the balloon?"

Probably, but the rocket will be long gone by then. Also depends on where the thrust is aimed, if it's not aimed at something attached to the truss, then impulse on the truss should be minimal.

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(Written by Reg staff) Bronze badge

Re: carbon fibre?

The joints will be revealed in due course...

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Let's hope the titanium rod doesn't fall off during the rocket launch - that'd do some damage falling from 20 km.

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Happy

James Van Allen had similar issues

I was only reading recently that when James Van Allen(he who the radiation belts are named after) had similar problems getting his test "rockoon" to fire at altitude due to extreme cold he solved the problem by heating cans of orange juice, attaching it to the firing mechanism and then wrapping the whole lot in insulation.

Of course those mechanism's were clock work and we have progressed a long way since then. For instance we now have pot noodles

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Bronze badge

Re: James Van Allen had similar issues

This being El Reg I suspect vodka and orange might be more appropriate.

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To supply power to the heater in the rocket a couple of pads would do on the base of the rocket contacting some pads on the truss (a bit like a cordless phone sitting in a charging unit). It wouldn't matter if it gets jostled about and loses contact momentarily as it's only a heater.

Alternatively perhaps (since we're all IT types) an RJ45 connector with the little tab broken off? They come disconnected easily.

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Or...

Posted this idea to the 'main' forum; use something like the Magsafe connectors...

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Vic
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> a couple of pads would do on the base of the rocket contacting some pads on the truss

Or you could wire it with gold wires passing behind the rocket motor...

Vic.

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Tail

You are fitting a tail to orientate the truss in the wind?

If the truss is floating from a balloon then it would be travelling at the same speed as the wind and so cannot work. Or am I not thinking this through properly?

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Silver badge

Re: Tail

Sadly, I fear you are correct. I think we will have little rotational control of the truss once launched. However, it's possible that a large fin will provide some stabilisation simply by friction - though in what passes for air at high altitude, I'm not sure I'm thoroughly convinced.

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Re: Tail

I guess it will provide some resistance to rotation as the side of it would have to push against air to rotate.. Perhaps it will work, just for different reasons!

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battery disconnect from heater

Risking a pattent lawsuit from Apple, find an old Apple computer and take the magnetic power coupler out of it along with tail to the wall wart.

This should provide a fairly easy disconnect for the batteries from the heating unit.

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Re: battery disconnect from heater

How about a 1 inch audio jack plug and socket? Have used this technique to power a dress made of fairylights (before leds) on stage. 2 x 12volt lead acids desguised as a 'dougal' dog on wheels, cable up the lead to jack / socket which pushed together to turn on the dress, pull apart for off. Inbetween lots of prancing around so connction had to be impervious to shaking etc but easily separated with a straight pull.

Only thing to remember is the socket should be conected to the batteries - doing it the other way round can cause at least a one octave shiftt higher in your local panto dame's voice....

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Thumb Up

Jolly good, chaps

We are waiting for the take off

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estes scissor wing

I remembered this (http://www.rocketrytoday.com/scissorwing.html) design from my childhood. Some variation on this seems a more practical design than a fixed wing. I am guessing they already looked at something like this.

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Wouldn't a simple metal switch connector suffice for the connection

The Thermaltake Spedo PC case has a little bent metal spring thing to metal contact switch between the door and case which cuts out the fan when the door is removed and removes the need for a cable connection between the two. Simple and effective with no moving parts. Would do the same job and pretty easy to knock up your own similar kind of thing.

http://techreport.com/r.x/2008_11_23_Thermaltakes_Spedo_Case/in-02-600.jpg

http://images.hardwarecanucks.com/image/lemonlime/cases/thermaltake_spedo/spedo_inside9_sm.jpg

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Vic
Silver badge

Re: Wouldn't a simple metal switch connector suffice for the connection

> a little bent metal spring thing to metal contact switch between the door and case

Remember we're looking at a situation where there might be icing...

Vic.

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WTF?

rubber band??

The design appears to include a rubber band from the titanium rod to the truss. Why? If you actually intend to use a real rubber band, you have a problem: it will become brittle at low temperature. Remember Challenger's O-rings.

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Chilly up there

no chance the v2 wont freeze onto the titanium rod?

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you need to see this

http://www.dailymail.co.uk/news/article-2197089/Sorry-Lilo-ve-got--Lohan-celebrity-EVER-evicted-notorious-Chateau-Marmont-refusing-pay-29-000-hotel-bill.html

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Make Lohan a swinger

Center of gravity aft when supersonic that then moves forward for a long session of gliding?

Why doesn't she have swing wings? These can be spring loaded to be pushed back by launch forces, thrust and supersonic drag then swing forward when she's gliding.

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Truss as a tension/compression structure

The truss appears to use only rods. Rods provide both tension and compression. A well-designed truss can use rods for compression, and (much lighter) wires for tension. In this application, you can use carbon-composite rods for the compression members and truly light-weight fibers for the tension members. I suspect that the thinnest available Kevlar fibers will suffice for the tension members of the truss. So: a triangular truss would have three long composite rods, Nx3 very short rods, and 2Nx3 fibers. Or if you are brave Nx3 fibers. But this application does not need Symmetric triangular truss, because the forces in the three dimensions are not symmetric.

The trick here is to ensure that the rods and fibers have roughly the same coefficients of expansion (change in length with temperature.) Increased distiane between the rods will add weight but will reduce any warpage. Acceptable truss warpage, in turn, depend on how the truss orientation affects the mission parameters.

If all we need it a truss that points (approximately) "up", then at the extreme we need a single carbon rod. If we need more rigidity, then we need two or three rods. it is not clear why we need mor than two: gravity workss, after all.

Consider a two-dimensional truss of (say) one metre. Two 1-metre rods, separated at (say) 20-cm intervals with 100 mm rods. The rods are turn connected by digaonal Kevlar fibres at each junction. This two-dimensional structure is in turn stabilized at its midpoint by triangular outriggers in the third dimension, connected to each end of the truss with more kevlar fibres.

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