So, who wants to win 1 million Euro?

[ka9q]

I've heard many of these tradeoffs between solid and liquid rockets for a long time. I'm familiar with the usual quantitative engineering tradeoffs like I_sp, etc, but not with the cost figures. Can anyone cite some reliable (i.e,. experience-based, not marketroid guesswork) figures for both NRE (non-recurring engineering) and production costs for solid and liquid rocket boosters of various sizes?

[Captain Swoop]

Succinctly, that's exactly the confusion I was trying to express.  "Compounding" a steam engine (i.e., using steam over and over again until its pressure is thoroughly exhausted) is a common device in large steam engines, and every engineer learns those techniques.  They're more appropriate to large ship engines -- e.g., the "triple expansion" designs, but I was aware the principle had been used in steam locomotives.  I just wasn't exactly sure to what extent.

That the Big Boy was articulated goes without saying.  You can't wrap something that long around a curved track without it.  I knew for a fact of the articulation, but I was unsure whether the Mallet design required both the articulation and the compounding.  Hence my guess as "Mallet" (for the articulation) but not the traditional kind (because I wasn't sure about the compounding).

Strictly speaking a Mallet loco is articulated and 'compunded' It's front Low Pressure drivers and cylinders are mountred on a pivoting truck and fed from the exhaust of the fixed HP cylinders. This means the steam pipes only deal with 40 or so psi and are not too difficult to keep steam tight at their joints. As locomotives got bigger and boiler pressures higher the size of the LP cylinders got too big fo the loading gauge and the mass of the reciprocating parts got to be a problem above about walking speed. To get round this the Chesapeake & Ohio introduced all HP 'simples'. They got round the steam pipe problem by incorperating them in to the centre of the leading truck pivot so they only moved in a radial direction making the seal a lot easier. Big Boys are 'Simples' so strictly speaking not Mallets.

Off course the 'best' articulated locomotives are the Garretts. Both engine units are articulated with the cab and boiler slung between them this frees the boiler and firebox from the size constraints imposed where they are placed over the frames and running gear. It does however result in a lot more moving steam pipes and joints that have to be kept sound.

Somewhere I have a pictures of my dad on one of the big South African GL class Garretts in the 60s. They were popular on a lot of colonial railways as they are good riders on rough track and they are  tank engines and can run both directions without turning.

[ka9q]

It seems there are few really new ideas in engineering, just a lot of rediscovered old ones. Multistage expansion has been rediscovered in a slightly differerent form as the "combined cycle" used in new, highly efficient gas-fired power plants. Medium grade waste heat from the gas turbines boils water to make steam that drives turbines to make additional electricity.

The bigger the temperature difference between the hot side and the cold sides, the greater the Carnot limit.

Large modern combined cycle power plants can hit 50-60% efficiency, which is remarkable for a heat engine. What kind of efficiency did these multistage steam locomotives achieve with their far tighter constraints on size and weight?

[Captain Swoop]

Not enough to make it worthwhile. Most compound locomotives suffered from very 'sub optimal' steam path.  A long steam cycle made made them particularly sensitive to temperature-drop and condensation of the steam during its lengthy passage from boiler, through HP cylinder, Steam Chest and then through the LP cylinder.
To get round this higher boiler pressure and increased 'super heating' is needed and in most cases this resulted in no overall increase in efficiency of fuel or water.
In the forties Chapelon came the closest, he had a good grasp of thermo and fluid dynamics and he designed very efficient flow through the system. Even he had to use inovations like re-heqating the steam between the HP and LP cylinders and added a 'hot steam jacket' around the cylinders to keep the temperature up.
On later locomotives more efficient valve gear using smalle 'cut off' achieved the same efficiencies without all the extra complication so Compounding went out of fashion.

[Noldi400]

Speaking of rediscovering old engineering ideas...

I frequently hear (read) the question, usually from HBs, that if we had the technology to go to the moon 43 years ago, why don't we have it now?  How can the technology have been lost, considering the tech advances we've made since then?

I've been pondering this question and it seems to me that it's not so much the technology that we don't have as the ability to (re-)construct the hardware that was used. We're all aware that the reason that the hardware didn't continue to be built and refined is simple - money.  Once the "national goal" was accomplished, public support and therefore budget allotments dropped off quickly and that was the end of the Apollo Program.  If there had been commercial profits to be had from lunar missions it would have been a different story, of course, but sadly that wasn't the case.

I guess my point is that, as a non-engineer on the outside looking in, it seems to me that the current "technology", in terms of knowledge, is not the bottleneck to future manned lunar missions so much as - once again - money.  We've gained a tremendous amount of experience in spaceflight since 1969. In other words, if Congress would open up the expletive deleted pocketbook, we could get off the ground in relatively short order.

So my question is directed at those of you in the industry, who actually know what out current tech level is. If the practically unlimited budget of the 60s were available, are there many new things we need to learn, questions we need the answers to, as it was during Gemini-Apollo when almost everything was an unknown? Or would it be pretty much a matter of putting what we already know to work. Obviously there's an HLV to build, whether the Space Launch System or something else, but how difficult would that be if the cash river was flowing?

Stupid questions, maybe, or at least naive, but some of us laymen can't help wondering.

[raven]

I am willing to bet a lot of relearning would be involved. With so many engineers from that era dead or retired, a lot of hard won practical wisdom has been lost.

[Allan F]

Maybe the cheapest would be to use known technology, the Saturn 5, as the basis. Many small incremental improvements in alloys, power generation, power consumption, computer control, automation, cameras, fluid dynamics, aerodynamics (to name a few) would allow quantum leaps in reliablity, and make it possible to land on the moon with much increased weight (=increased capabilities). Extended stay, greater crew comfort, new landing spots away from equator and many other things. And having the basic functioning hardware available, will shorten the development time and cost. Ben Johnson (Lockheed Skunk Works, while developing Oxcart) said, "The first 90% takes 10% of the time, the last 10% takes 90% of the time). Basically, soon it will be "good enough", but trying to achieve "perfect" is a waste of resources. Already having "good enough" leaves time and money to get a step closer to "perfect".

[raven]

With manned space though, you need to be just about perfect. If a satellite or probe goes wrong, if a rocket explodes on the pad, it sucks and it's heartbreaking, but it's 'only' money and man-hours gone. No one is dead.

[Allan F]

Yes, you need perfect reliability on the not-blowing-up bit, but as Apollo 13 showed, perfect is not always available. Second stage had an engine failure, but they achieved their parking orbit anyway (later something else broke, I know). Apollo 12 had a lightning strike, which tilted all the electronics in the capsule, but the booster continued anyway, since it's guidance was separate and adequately shielded. Where I'm saying "perfect" is too much, is in weight, guidance, life support and other places, where human interaction can correct small errors. And where the mission has space and time to be corrected. Mid-course corrections using attitude thrusters were planned, but some weren't necessary.

[Allan F]

Just a small thing like interior lighting. On Apollo, the crew cabin were lighted by flourescent tubes. The instrument panels had hundreds of small lightbulbs. Replace all with diode lights, and you save a lot of weight and electrictiy consumption. Also diodes are more robust than other light sources, and don't break as often. Less electricity consumption could mean you could simplify the wiring, saving weight again. I don't know about fuel cell efficiency, but I suspect they're lighter and more reliable now, again saving weight. The guidance computers and gyros also lighter, less energy, more reliable, more flexible. All these gains could be translated into greater crew comfort, safety, endurance, capabilites.

[raven]

You couldn't just copy things for the cooling then, or you'd end up as cold as Apollo 13, or be wasting a lot of energy on heating.

[Allan F]

Cooling - again weight saved. And since there's all the sun in the world (!) on the way out there, just paint the capsule an appropriate color in some places. Sun energi is free.

Of course a lot of things should be reworked. It's a synergy after all. Everything has an impact on everything else.

[Grashtel]

Of course a lot of things should be reworked. It's a synergy after all. Everything has an impact on everything else.

And this is exactly why trying to rework an existing design like the Saturn V isn't likely to be practical, you are very likely to end up with snowballing design changes until you would have been better off starting out making a new design.

[raven]

Of course a lot of things should be reworked. It's a synergy after all. Everything has an impact on everything else.

And this is exactly why trying to rework an existing design like the Saturn V isn't likely to be practical, you are very likely to end up with snowballing design changes until you would have been better off starting out making a new design.

That was pretty much my basic point. Modern tech would mean a lot of changes. Which is one reason why the conspiracy theorists are so wrong when they ask 'Where are the blue-prints?'

[gillianren]

With manned space though, you need to be just about perfect. If a satellite or probe goes wrong, if a rocket explodes on the pad, it sucks and it's heartbreaking, but it's 'only' money and man-hours gone. No one is dead.

There's a long distance between "just about" and "actually."  If you're waiting for perfect, you're never going to get anything done.