Carmack's Throatless Rocket Engine 351
Baldrson writes "John Carmack is working a potentially disruptive technology: A throatless rocket engine. Its made from plain aluminum pipes with few machined fittings. Carmack says: "The great thing about these engines is that it only takes me two nights to machine the parts, so we can test two engines a week if necessary." It scales too: "If this line of tube engine development works out, we can make a 5,000 lbf engine with very little more effort than the test engine." This is what makes disruptive technology development work: Cheap, fast turnaround on on redesign producing technologies that scale. If this works, the NASCAR guys may really start entering space competitions like the X-Cup."
Re:There's a lot more to a rocket engine... (Score:2, Interesting)
Re:You don't understand rocketry (Score:5, Interesting)
Unfortunately, no. Chemically fueled rockets are just barely capable of making it to orbit. They're mostly fuel tankage. Single stage to orbit craft must have at least a 90% fuel fraction. At least. Any serious inefficiency or weight growth kills the design, as happened for Rotary Rocket.
Staging helps. Two stages will get you to low earth orbit. Beyond low orbit usually requires three. This reduces the fuel fraction, but by less than one would hope. The Shuttle's fuel fraction is around 89%.
So space flight is all about weight reduction. Which is why everything is so fragile and unreliable. If you could build a launch system with a fuel fraction of 50%, which is roughly where most aircraft live, it would be a straightforward job.
Re:Obscure unit (Score:5, Interesting)
As a scientist I think in SI these days though it took years to unlearn the training of my youth, and I still vascillate between F and C for my preferred temperature unit.
Nobody uses perfect units. Why aren't you measuring your car's efficiency in inverse square millimeters?
Re:Obscure unit (Score:5, Interesting)
Which is the standard, utterly nonsensical, argument. These are only measurement systems. You can use either to express anything. However, one of them (and I'll let you figure out which) makes it MUCH easier to do conversions and allows useful equations (like e=mc^2) to actually work without inventing new units to fit. So yes, something which is an inch today may be 2.54cm, which isn't as convenient to write. But guess what, that same thing in a metric country would be 2.5cm, or maybe even 3cm. Which is 1.18110236. I'll let you work out what fraction that is....
Negative connotations (Score:2, Interesting)
Re:Obscure unit (Score:1, Interesting)
More information on the current usage of imperial units can be found here: http://en.wikipedia.org/wiki/Imperial_units#Curren t_use_of_Imperial_units/ [wikipedia.org], but you knew that, right? Canada appears to be even more on board with metric usage than, say, the U.K.
Ok, I understand, you post was really just an occassion to whing...
This looks vaguely like an X-cor motor (Score:2, Interesting)
Re:Armadillo seems stalled, engine-wise... (Score:3, Interesting)