Original URL: http://www.theregister.co.uk/2011/11/22/lohan_pump/

Got a few minutes to help LOHAN suck?

Home-made vacuum pumps... bright ideas invited

By Lester Haines

Posted in SPB, 22nd November 2011 14:28 GMT

As we recently reported, El Reg's Low Orbit Helium Assisted Navigator (LOHAN) team has taken delivery of an AeroTech RC 32/60-100NS rocket motor – the proposed power plant for our Vulture 2 spaceplane.

Click here for a bigger version of the LOHAN graphicHowever, no one – including AeroTech – is sure whether the thing will fire while freezing its 'nads off at the intended launch height.

Accordingly, we've devised a cunning plan to put together a Rocketry Experimental High Altitude Barosimulator (REHAB – full details here) device to test the motor under the required low temperature and pressure conditions.

As we speak, trained botherers of steel down at my local metalworks (now dubbed "LOHAN's Anvil") are considering just how to make this concept a reality...

Our revised hypobaric test rig concept

...and while the lads are worrying some tubing, we've been busy sourcing the bits and pieces we'll need to complete this magnificent garden-shed contraption.

We've managed to sort a robust glass top plate*, along with its rubber seal, plus a viable temperature sensor. We are, however, scratching our heads about the vacuum pump. These babies don't come cheap, and we really don't want to blow a wad of cash for a single experiment.

So, it's over to you, our beloved and tech-savvy readers. Got any bright ideas for putting together a home-made vacuum pump that can create and hold a vacuum of 15 mmHg? Let us know... ®

Bootnote

*Yes indeed – we're going to put a mirror (not shown in diagram) at 45 degrees to the top plate so we can reflect an image of the motor firing and capture the drama with a high-speed video camera.

To clarify, the top plate isn't fixed to the inner tube, but is pulled down onto the rubber seal as the vacuum forms. When the motor fires, the plate will act as a pressure release "valve", to prevent the REHAB beast exploding. So, it's likely that the viewing mirror will be sacrificial, but it's better that it takes the force of the plate popping rather than the video camera.

It's so simple, it's hard to imagine what could possibly go wrong...