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back to article LOHAN to suck mighty thruster as it goes off, in a shed

Our piece earlier this week on possible power plants for our Low Orbit Helium Assisted Navigator (LOHAN) rocket-powered spaceplane got you lot thinking about how one would go about testing a rocket motor which needs to fire at altitude and -60°C. Click here for a bigger version of the LOHAN graphic To recap, experts gathered at …

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Paris Hilton

Seems fitting

HERPES (Hypobaric Experimental Rocket Performance Evaluation System).

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Happy

Damn, you beat me to it. I was going with "Propulsion" though....

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Anonymous Coward

With `power'.

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Propellant. There seems to be a consensus though.

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Flame

MILLINGTON!

Moderately Interesting, Low Level, Indoor, Negative Gravity Test Of igNition?

This is a British mission isn't it?

^^^^ Successful test.

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Grrr took me ages to come to that...

...before I looked at the comments.

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Possible leaks?

At -60C, could the different rates of shrinkage of the three metals be a problem?

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Thumb Up

Agree with Rich 11

The different materials struck me as potentially troublesome. Is there any reason why it can't all be e.g. steel?

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Happy

Not a problem

In the design, the only place steel touchs aluminium is at the base. Differential expansion would only pose a problem where physical connection was tight, not here. Copper pipe will no doubt be passing through rubber/silicone gaskets.

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Boffin

Simulated EXplosive Temperature And Pressure Experiment (SEXTAPE)

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>> HERPES (Hypobaric Experimental Rocket Performance Evaluation System).

Gets my vote :)

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Coat

Where's Linda {lovelace} then?

Ok, Ok, I'll get me coat.

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Headmaster

Ada of course...

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Anonymous Coward

TITTIES

Thermally Insulated Tubular Tropospheric Ignition Evaluation Station

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Coffee/keyboard

Keyboard

That is all...

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REHAB

Rocket Environment Hypobaric Assessment Bunker

struggled with the 'B' - maybe Battery, Bid or Building instead

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'Bucket' or 'Barrel'?

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Go

A big water tank around it would be a good idea to catch the shrapnel.

Have you considered condensation and then ice formation as an issue ?

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Thumb Up

Easily sorted, just bung a couple of bags of dessicant in there a day before the experiment and put a partial vacuum on it to seal it against ingress

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Happy

But what about real life as the balloon goes up, will it get wet, potentially dampening the load

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MrT
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Depends...

Pick the right day - higher temperature means the atmosphere can carry more water vapour before it condenses. As the pressure drops with altitude, the boiling point of any condensation will lower and most should evaporate before firing if it hasn't frozen out already.

Things happen gradually as the balloon rises - this rig seems to be designed to place the rocket 'at altitude' quite quickly unless the dry ice pellets and vacuum pump are applied over a longer time to simulate the ascent.

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The pressure issue

Once you ignite the motor, pressure in the chamber will increase very quickly, so unless you have a monster vacuum pump (or a fairly large hypobaric chamber), you won't be able to reliably assess the burn (e.g. does the motor burn properly, or does it fizzle enough to raise the pressure in the chamber and only then burn properly).

Two things spring to mind:

- a large-ish tank of some variety, connected to the test chamber via a pipe to effectively increase the available vacuum (similar to the expansion tank on your central heating system)

- a pressure sensor under the motor to measure the engine thrust, particularly during the first one or two seconds - to be compared against a similar burn performed with the chamber at normal pressure.

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Mushroom

Or...

move the seal to below the rocket exhaust?

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Anonymous Coward

> move the seal to below the rocket exhaust?

The air inside the rocket motor would be at ambient pressure; the test would not tell you anything.

How about just putting a hole in the top plate for the exhaust and losing the vacuum pump?

The exhaust rushing out might cause enough of a venturi effect to suck out the air in the main cylinder.

No idea how effective this would be and it still would not tell you if the rocket fired under low pressure, but it might tell you if it runs properly.

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Boffin

Ignition test

Note: "It doesn't really matter if the rig does blow its lid, as we're only testing the motor's ability to fire, not its performance across the entire burn."

*IF* it fizzles at first, there will be little exhaust and a a consequence only a un-energetic lid-blowing. So that aspect of the ignition sequence will be noticed.

But once such a solid fuel motor ignites, its resulting internal pressure will make the outside ambient pressure totally irrelevant.

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Facepalm

Ignore me.

That's bollox isn't it?

The igniter cable goes in there.

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TIMBERLAKE

Temperature Ihibited Main Body Evacuated Rocket Launch Activity KPI Evaluator

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Coat

Problems with dry ice

If you are using dry ice for cooling make sure that you have facilities to exclude goths from the system. They go crazy for that stuff.

Mine's the black trenchcoat...

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Coffee/keyboard

C'mon, man.

Making me guffaw at work is uncool...

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Some kind of temperature sensor attached to the motor would be handy, as in view of the vacuum around it it will take a while to get down to -60.

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Mushroom

You've probably already considered this, but...

Put the vacuum pump tube near the top, then you don't need to go through the outer tube.

Get the temperature low before pumping out the air - the thermal conductivity of a vacuum is pretty low.

And as mentioned above, make sure your lid doesn't get frozen on. I've seen rigs like this blow their top due to frozen relief valves and it gets pretty violent.

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" ...make sure your lid doesn't get frozen on"

That was the second thing I thought of (after the different materials) - some suitable grease on the rubber seal is imperative to stop things freezing together.

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A correction...

Surely, the "Thrust" arrow sould be pointing down and not up (unless the motor sucks, of course)?

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(Written by Reg staff) Bronze badge

Re: A correction...

Fair point. Should read "Exhaust"...

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Here there be dinosaurs

Sealed Partially Evacuated Arctic Rocket Rated Ignition Test Tube

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Mushroom

Depressurised Evacuated Explosive Pyrotechnic Temperature and Hyperbaric Regulated Organic Accelerant Testing

D.E.E.P.T.H.R.O.A.T

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Joke

No atmosphere

Looking at that design, I can see at least one place where it sucks.

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Looks like a...

Pyrotechnic Environmentally Non-compliant Ignition System Enhancer

err, or so I've been told.

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Dang it.

I was going to go for 'Pressure Evacuation aNd Ignition Speed Enlarger

I'm sure there must be a better 'N'.

I was also going to suggest a weight on the lid and some means of measuring the acceleration of the lid as a guide to thrust.

ttfn

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air inside the rocket

You should slowly evacuate the inner tube, so that any air inside the rocket itself can diffuse through its materials. Otherwise the pressure difference might deform the rocket, or the residual air help support the burning.

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Boffin

So when you fire this thing off into the heavens, I'm assuming the air pressure will drop at an equally slow rate to avoid similar deformation? :-p

perhaps you should evacuate at the same rate as the air pressure will drop, this way you get a 2 for 1 one test :-)

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Holmes

The first phase of assent will be by balloon. The rocket is the second phase. So yes, the pressure drop will be pretty gradual. The whole point of the test is that the rocket will not be fired from ground level.

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pyr

It would be a good idea to tether the metal top to prevent unwanted damages.

I expect the motor will not ignite at that altitude. You might be able to retain enough air in the rocket housing by surrounding the rocket tube in a couple of layers of some sort of sheathing material. Latex might be best - provided you can find something that would fit your tiny rocket.

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Alert

> It would be a good idea to tether the metal top to prevent unwanted damages

and to be careful when re-admitting air if it doesn't ignite. Never return to a lit firework, and all that.

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Anonymous Coward

A complaint

Sirs,

I wish to complain in the strongest terms about the misleading nature of this article.

You can imagine my disappointment when I learned that the content related to some mildly interesting space technology instead of the article I was led by the headline to expect.

Yours faithfully,

I.M. Disgusted Col. (Rtd)

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Anonymous Coward

Well said sir!

Thanks to the every more fiendish wordplay of the sub eds, I am now in a state or semi-perpetual confusion.

I am no longer able to tell if the stirrings I feel upon reading the headlines are excitement at the anticipation of a technological revelation, or of a baser nature provoked by the lewd punning.

yours (on the bus, at the back, near the engine, about to spill more than his coffee)

D. E. Viant

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Anonymous Coward

AIR BAGS

Atmospheric

Ignition

Rig

Burn

And

Gauge

System

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Boffin

Two thoughts

1. Sit the motor on top of an electronic set of scales, logged appropriately so that you get a record of actual thrust over time.

2. Make sure that the rocket stays cold, and at low pressure, for an appropriate length of time, based on how long the balloon will take to reach altitude. Half that time if you are in a hurry, equal if you want to be certain.

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Facepalm

Do'h!! Hypo, not Hyper

Depressurised Evacuated Explosive Pyrotechnic Temperature and HypObaric Regulated Organic Accelerant Testing

D.E.E.P.T.H.R.O.A.T

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