LOHAN is heading towards REHAB

LOHAN to REHAB

Oh you guys!

I just love ...

... how this project (and the previous one) is such a mix of proper science and advanced engineering on one hand and just a bunch of guys who turn up with a plastic sheet and a couple of carrier bags on the other. I guess that just makes it "engineering" - getting it done with what you need to get it done and no more.

Basic Physics

Just how much have you thought about this? How far is that rocket motor actually going to get you? So far the thinking seems to be, "Ah, but gravity is much less at 100,000ft so it'll get us a lot further." I've got news for you.

The radius of the earth is 6,387km. Add 100,000ft to that, and you get 6,409km - the difference could be politely described as "bugger all". Because gravity is proportional to the inverse square of distance, the acceleration due to gravity is about 9.7 m.s^-2, a whole 1% change from the usual 9.81.

Based on the test firing, that 100Ns seems to actually be about 16N for 8 s. Suppose that your rocket weighs 500g, then the force from gravity will be 0.5 * 9.7 = 4.85 N, so the net force on the rocket is ~ 11N, producing an acceleration of 11 / 0.5 = 22 m.s^-2.

That acceleration over 8s will produce a distance of 713m. It'll then be doing 178 m.s^-1, and before gravity overhauls it that will carry it another 1640m or so. So you gain a total extra 2350m. It's not trivial, I guess, but it's not exactly a big gain when you've already reached 30,000m. Less than 10% extra. And if the thing actually weighs 1kg, you're down to 333m additional height. If you can get the thing down to 200g then it starts to get respectable, an extra 18.5km of height.

All this assumes no drag losses, which may or may not be reasonable at 100,000ft, I'm not sure. It also hasn't taken into account how the weight of the rocket changes as the fuel is used up, which may be quite unrealistic. But how realistic is a goal weight for the rocket of 200g?

Uhm..

Is this not just a low temperature/condensation ignition type problem?

Assuming the rocket supplies its own oxidant, which it will, then I would have thought sucking the air out would not matter too much. Condensate, low temperature, will be worst case at ground level so if your rocket ignites at the expected temperature at ground level it should be good to go at altitude.

Have a word with your 'local' mil-spec power supply developer/supplier, or indeed UoS. They should be able to loan you an environmental test box. They come with holes including the top where you can mount your rocket so it vents to atmosphere and controllers to dial an appropriate time/temperature curve. They are also 'portable' so you can stick things in the car park for testing.

Plus, and this might be a biggy, you can place the ignition box inside the chamber to check its performance out as well. At the moment you have it sitting outside of your present contraption.

Failing that just stick the whole thing in a bucket of dry ice for an appropriate amount of time and give it a wang. As I say... if it works at ground level it will/should go at altitude.

Beer because you can buy some with the money saved.

Maintain thrust, blow its load early, or fall flaccid

There's no air filling the gaps and defects in the rocket that would otherwise slow and cool hot exhaust gasses, so it could explode. There's also less maintained exhaust gas pressure against the propellent so it could fizzle. Either way,wear goggles and be prepared to tell the rocket that it could happen to anyone.