Rockets

Remember model rockets when you were in middle school? The biggest engines I ever launched were Es. These guys started with Is and ended up using Os.

What strikes me as odd about this stuff, though, is why all these rockets are mainly subsonic. They go transonic or slightly supersonic at the end of the boost stage, but they really aren't getting into the many thousands of feet per second that even suborbital stuff would. And why not? These engines deliver around 200 seconds of impulse, which is a pretty serious amount of bang. If they could get their rockets down to less than the weight of the engine, they should be good for 4500 ft/sec in a vacuum. Surely a few seconds of air drag wouldn't wipe out 70% of this delta V?

What I'd really like to build would be a solid fuel ignited propane ramjet. The idea is to use Kelly Johnson's design for the back end of the Blackbird engine, but with gas pressurized propane for the afterburner and a solid rocket motor instead of the turbojet as an ignitor. Getting proper mixing of the exhaust, air, and fuel might be tough... I think it's significant that those SR-71 motors are so long.

...and you gotta love the web. Georgia Tech has a web-based design tool for just this kind of thing. They call what I want to do a Supercharged Ejector Ramjet. Can't handle a solid-fuel core, but what the hell, let's try a O₂-JP5 engine instead.

Work the specs:

C3H8 tank: 5cm dia 100cm long - 1900cc
  Energy:   48 MJ
  Fuel Mass: 1.1 kg
Solids: 200 seconds impulse, 2 kg fuel
  Burn time: 10 sec
  Thrust: 392 N  (4 G acceleration off the pad)
  Delta-V: 294 m/s
Rocket: 6.9 kg mass

Required thrust?   1000 N (about 10 G acceleration)
Inlet area?        45 cm^2
Cowl height?       3 cm
Nose to cowl?      100 cm
Compression angle? 10 degrees
Forebody friction? 0  (uh oh)

Primary Area ratio? 15
Chamber pressure?   6000 KPa  (Can't be as high as the swoopy stuff)
Fan pres ratio?     1 (no fan)

Defaults after this...

ALIVH

One of things that makes HPC (High Performance Computing, i.e. weather, aerodynamic, vehicle crash and nuclear bomb simulation) so expensive is the huge memory systems on these machines. There is an old saying in the field that latency is hard, bandwidth you just pay for. Anyway, the cost of a memory system isn't the memory itself -- Pricewatch puts a stick of 512MB of 200 MHz DDR memory at $137, or $274K for a terabyte. The cost has generally been in the plumbing necessary to connect that memory to the CPU(s)*. You need lots of very fast wires, which has historically required exotic packaging.

Things change. I just read that half of all cellphones are made on circuit boards with enough density to make an HPC architect drool. Chuck the unobtainium and use ALIVH -- this stuff is cheap! It makes me want to design a hobby HPC.

* Well, actually, the prices mostly come from market dynamics. You have consumers (big companies and government labs) with deep pockets and little ability or incentive to ensure they get real value for their money, and producers who try hard to lock their consumers into proprietary hardware and software to avoid real competition. The HPC money well is drying up as (a) defense budgets have been slashed and (b) many customers have realized that racks of commodity PCs will do the job just as well.

National Missile Defense

I watched a Frontline program on the National Missile Defense program recently, while waiting to feel tired enough to go to bed.

When Reagan started the Strategic Defense Initiative, the idea was to build a defense against nuclear missiles coming from the USSR. Frontline went over the history of SDI and NMD, but totally missed the fact that the insights and policy turnarounds during those two programs had all happened before. Summary: we've been trying to build ABMs ever since the 1950s. Every time we have a system ready to deploy, either the Congress or the President kills it, and then funds yet another system design. We actually had a working defense from 02-Oct-1975 to Feb-1976, about five months, before that last one, Safeguard, got killed.

Once again, after a few years everyone has realized that defending against incoming missiles is so hard that stopping thousands reliably, the first time, is impossible. Also, the USSR has evaporated. Russia still has the missiles, but we're buying their warheads from them slowly, and they seem less of a strategic threat somehow. So the folks in Washington have changed the emphasis, just as the Johnson administration did in the late 60s. SDI is now NMD, and the idea is to shoot down just a few incoming missiles from "rogue states". They're still trying to do it with "hit to kill" vehicles, basically, hit a warhead travelling 15,000 MPH with another missile travelling 15,000 MPH in the other direction.

Progress so far: since the mid-80s, they've spend $50 billion, they've decided they want to take out incoming warheads by smacking straight into them, but they can't quite hit the target, and they have no idea how to select the warhead from a cloud of decoys bursting from the same missile.

What bugs me most about all this waste is that now that the program goal has been changed, we could achieve that goal by redeploying the Safeguard system we had in 1975! Why screw around with entirely new research and development? I think we should do a cost reduction pass on the Sentinel system design, and then deploy the damn thing and be done with it. Yes, this means I think we should build more nuclear bombs. (The warheads on the Sprint and Nike Zeus missiles are thermonuclear, which gets rid of most of the accuracy and decoy selection problem.)

It would appear that policymakers in Washington have consistently concluded that it is important to do R&D on ABMs, but not important to actually have ABMs. Which makes you wonder if ABMs are supposed to shoot down warheads or keep a bunch of middle class voters in important districts employed.

If you want to find out how nuclear weapons actually work, check the Nuclear Weapons FAQ. It scared the piss out of me. I had previously assumed that nuclear weapons were a bit like a little piece of the Sun, but here. Nope. The Sun is a great big lazy ball of hydrogen with the odd thermal fusion reaction happening here or there. Nuclear weapons operate with an intensity that puts our Sun to shame. I find the notion of forcing reality so far away from it's normal course terrifying to read about.

Gas Guzzling

I just got back from a trip to the UK to show my new baby off to all the relatives. The highlight, perhaps, was driving around Northern Ireland with my parents, wife, and daughter, and having my parents point out where they got married, had their honeymoon, etc. I'm entering a stage in my life which is very analagous to the stage my parents were at when I first entered the world. Somehow I can relate better to their experiences of the late 1960s as newlyweds and new parents than I can to their experiences as children. And though getting older does have it's downsides (getting fatter, slower, and creakier), I'm enjoying my relationships with family even more than I did when I was young.

I got a ride in my uncle's new BMW 525d. My wife drives an older 525i, so it's interesting to compare the gasoline and diesel variants. Bottom line: that diesel rocks. Colin says he gets 34 MPG, equivalent to 27 MPG here (their gallons are bigger). Martha gets maybe 22 MPG, and I seriously doubt a new 525i does any better (probably worse: EPA says 18 / 26 MPG).

What I have wanted for a long time is a better minivan: The powertrain should be a 25 MPG front drive hybrid diesel, with electric low-speed RWD for getting around on steep, slippery roads that snowplows haven't visited recently. All I need is 10 HP on each wheel, but I need that at 5MPH. I'd like a suspension and transmission more like the 525i's automatic and decidedly less like that of the Dodge Caravan I have now. The rear seats should stow like the Odyssey, the roof rack should lever over the side so my wife can get skis off the roof, and a dog fence behind the middle seats that doesn't tear up the interior should be a dealer option. Oh, and that roof rack should be good for more than 200 pounds -- I tried putting four kayaks on the Caravan's rack and the thing just sagged down onto the roof!

(For my other car, I want an S2000R. :-))