There are only a few days left before our planned "Punch" and "Judy" flights on Saturday 5 April, so a slightly sooty Low Orbit Helium Assisted Navigator (LOHAN) team is pleased to report that we've wrapped the final ground-based rocket motor tests in the Rocketry Experimental High Altitude Barosimulator (REHAB) hypobaric chamber.

The Punch flight is dedicated to finally determining if we can get an ammonium perchlorate composite propellant (APCP) motor to breath fire at altitude. Previous forays into REHAB - where we stuck small motors into our shed-built REHAB chamber - demonstrated that off-the-shelf igniters simply weren't up to the job.

Between them, LOHAN chaps Rob Eastwood and Paul Shackleton have battled to come up with an explosive mix guaranteed to get APCP burning. In September last year, they managed to get a custom brew to go pop at 20,000m, although for safety reasons that flight did not carry a motor.

Since then, the lads have come up with no less than three flavours of igniter, and all that remained was to see how they performed on the ground before the forthcoming fiery finale to the motor ignition saga.

So, last Sunday, Middle England trembled before a fire-breathing LOHAN as we cranked up REHAB for the last time. We're obliged to Rob's parents for allowing us the use of their garden, and for the copious supply of top-quality tea.

Paul was joined by his son Harry, who proved a useful "skivvy" (Paul's rather unkind description of his lad), and is seen here with Rob (left) and his dad.

As some LOHAN fans have noted, our previous REHAB experiments have been done at ambient temperature, much higher than those we'll encounter in the stratosphere.

Cue a big box of dry ice...

...and a very chilly REHAB chamber:

Dry ice sublimates at -78.5°C, so after an hour or so of chamber chilling, the internal temperature had dropped to a level more than brass monkeys enough to simulate an altitude of 20,000m. Then, it was just a matter of sticking some bits inside and firing up the vacuum pump...

...And standing back before pressing the red button:

We wanted to test APCP and igniters under the most extreme conditions possible, so we first dropped both into dry ice for 30 minutes before use. The result was that while the igniters shrugged off the nasty nip in the air, APCP will not burn if it's frozen:

However, an uninsulated APCP motor which has merely undergone cooling from ground ambient temperature to around -50°C, over roughly 30 minutes, is quite happy to perform:

All in all, a roaring success. Since our full-fat Vulture 2 spaceplane motor has an external heater (more here), and a greater volume of propellant (and therefore more thermal mass), we're not overly concerned that it'll suffer to anywhere the same degree as our test APCP did.

Regarding the igniters, we now have the luxury of three proven blends to choose from. All of these will go aloft on Saturday, and we'll make our final choice based on that flight.

That's the summary of last weekend's REHAB tomfoolery, and when we've got the results of the final high-altitude blast, we'll bring you full details of the whole epic process. In the meantime, we leave you with this image of what happens in REHAB when LOHAN checks in for the day:

You'll now have to excuse us, because we've got prepare for the imminent hot vinyl wrapping of the Vulture 2. That's happening on Thursday, and will mark the end of the rocket ship livery job. Watch this space for magnificent snaps of the finished result...®

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.