How would you improve current launch vehicles?

[Bill Phil]

This gets into why staging is a good thing. It gives you more than just the different mass loads, it lets you focus engines on their own niches. The first stage engines often have high thrust, which helps to reduce gravity losses. Not only that, but it also has to leave the ground. The more efficient a chemical fuel is, the lighter it is. This means you need more mass flow to get the same thrust as heavier fuels. And so that is why first stages are more about power, and second stages about sustaining all that power and keeping it useful.

[Frozen_Heart]

Any thoughts on the use of Aerospike or other altitude-compensating nozzles?

They might not be worth the extra cost on a throwaway launcher. If they are being reused spacex style then they may be worth it.

[cantab]

Well we can't... even if we would travel with speed of light, create star gates, make ships with artificial gravity... it won't help!

Homo sapiens can't stay for too long in space, can't even stay few years on moon or on Mars because of different gravity (not to mention radiation issues)

and after return to home, Earth's G would kill us.

Baseless speculation. And indeed what evidence we have suggests it's not the case. Valeri Polyakov spent 14 months on Mir, and when he landed back on Earth he walked right out of the Soyuz capsule and has since been perfectly healthy. Living things aren't static machines, they're dynamic and can adapt to their changing environment during their lifetime, and we humans can further improve our adaptability with technology.

With this in mind I do not expect any showstoppers problems with permanent human living in Martian, lunar, or even zero gravity. Sure, visiting a higher-gravity world will be unpleasant for a while until you get used to it, but so what.

[SciMan]

That's a good point.

So, would the be better on the side boosters or the core? I think they would be better on the core, because it has engines running thru a greater range of atmospheric pressures, while the side boosters only go part way up.

I seem to remember that there was a proposal to use some kind of altitude compensating nozzle on the Space Shuttle Main Engines, at some point.

Also, altitude compensating nozzles can be used with solid fuel rockets as well, but I'm not sure what the benefit to that would be if there is any.

[Bill Phil]

Solids are used for a very short time compared to the liquids. Unless it's a Castor stage, but then it's primarily vacuum oriented.

[Camacha]

Homo sapiens can't stay for too long in space

That is really a bit too direct. We can (probably) stay in space making use of artificial gravity or just as is, but accepting that return will not be easy or happen at all. There usually are many different options, each with its consequences.

[Camacha]

Except it does not work that way. You don't need a multi-billion facility to have an idea. And to patch together a proof of concept, it is in fact even easier to do that in the "garage" now, that it was before. 3D printing, cheap embedded processors, simulation in CAD as your tablet has now more computing power than a dedicated server a few decades ago.... Single person ? No, single person got practically no chance nowadays. Good thing that with an internet connection you aren't a single person even when you are alone in a cabin in the woods.

This is very true. It still amazes me what I can do within the space of a single desk. I can design a product, run nonlinear, thermal and frequency simulations, print a prototype, render a photo realistic image, make a presentation and print it in full colour. Each of those steps used to take a separate professional and sometimes workshops full of equipment to do, now it can be done within a couple of square metres, in hours rather than weeks and with an incredible quality too.

Not to mention the vast amounts of data everyone has access to - though I must admit half of it consists of cat pictures.

[magnemoe]

And the point flew over your head. My point was that the smart people who tend to invent new stuff also tend to get an education and find themselves working in an industry that pays for smart people like them to invent new stuff. They tend to publish papers and attend conferences where they interact with their peers, not internet forums.

It used to be possible for someone to invent a new groundbreaking technology in his garage (or in his cave). That is not really the case any more, especially when you are dealing with vast amounts of energy that require a heavy infrastructure to work with, and a technology field that is too complex for any single person to be an expert in all aspects of it. The low-hanging fruit have mostly been picked by now.

This happens for all stuff, as technology matures it become harder doing stuff better as its already good, true from everything from cars, planes, computers or software.

Its still lots of long hanging fruit, however mostly in new areas, also rooms for improvements within existing technology, integrated circuits is the best example here.

[Bill Phil]

Well, you can still build small rockets and figure out how different things work. Experimenting and whatnot.

[magnemoe]

It really seems that reusability is within reasonable possibilities, as SpaceX may soon be able to soft land their first stage. That alone should be quite a revolutionary thing, even if we are stuck with chemical propulsion. So if space launches an become cheap, I don't see what's stopping us anymore at that point.

Of course, common people won't have their own personal spaceships, but I think we have a good change of having thousands of people living in space by the end of century.

Yes, first stage reuseability should work, no huge technical problems left.

Second stage might be harder. Makes me wonder if an cheap solid fuel upper stage would be practical? However I assume they plan to use aging first stage engines on upper stage.

As I understand the engines are the same. You would still need the same control systems.

[Kryten]

Except it does not work that way. You don't need a multi-billion facility to have an idea. And to patch together a proof of concept, it is in fact even easier to do that in the "garage" now, that it was before. 3D printing, cheap embedded processors, simulation in CAD as your tablet has now more computing power than a dedicated server a few decades ago.... Single person ? No, single person got practically no chance nowadays. Good thing that with an internet connection you aren't a single person even when you are alone in a cabin in the woods.

But you haven't got 'an idea', and you haven't done the slightest bit of research to see if such an 'idea' is even possible. Radically increasing the performance of chemical rockets from what we have now isn't going to work not because of lack of 'ideas', it's not going to happen because we're already close to the limits imposed by physics and chemistry, and have been since the 60s or 70s.

[Pipcard]

It's not only about physical limitations, it's also about economic issues such as the "there isn't a large enough market for reusable/cheap launchers and vice versa" problem

[MBobrik]

But you haven't got 'an idea', and you haven't done the slightest bit of research to see if such an 'idea' is even possible.

Great. Now are we into mind reading and clairvoyance.

Radically increasing the performance of chemical rockets from what we have now isn't going to work not because of lack of 'ideas', it's not going to happen because we're already close to the limits imposed by physics and chemistry, and have been since the 60s or 70s.

[Evidence ?]

[Kryten]

[Evidence ?]

The theoretical maximum I_sp for a Hydrolox engine is about 470 seconds; RS-25 (developed late 70's) has 450 seconds. Kerolox maximum I_sp is about 360, NK-33 has 331. There is plenty of room for innovation and ideas in spaceflight but chemical engines isn't it, at least if you're expecting some massive breakthrough in efficiency.

[MBobrik]

The theoretical maximum I_sp for a Hydrolox engine is about 470 seconds; RS-25 (developed late 70's) has 450 seconds. Kerolox maximum I_sp is about 360, NK-33 has 331. There is plenty of room for innovation and ideas in spaceflight but chemical engines isn't it, at least if you're expecting some massive breakthrough in efficiency.

ISP is only a part of overall rocket efficiency. I specifically acknowledged that we are already maxing out when it comes to energy density of chemical fuel (and thus ISP ). I also specifically named a few other areas where I am reasonably sure we aren't. But you can still show me wrong, for example by showing me where someone computed the theoretical maximum/minimum for those, because, AFAIK, no one has done that. Unless you do, I would also strongly suggest avoiding claims like "you haven't done the slightest bit of research"

[asmi]

Kerolox maximum I_sp is about 360, NK-33 has 331. There is plenty of room for innovation and ideas in spaceflight but chemical engines isn't it, at least if you're expecting some massive breakthrough in efficiency.

I_sp of RD-0124, the most efficient KeroLOx engine in the world, is 359 sec! Right - just one second below what's theoretically possible!

The only realistic way of making more than marginal improvements is to hit into material science hard. By that I mean inventing materials that are 1) stronger 2) lighter 3) cheaper all at the same time. Also ORSC engines are very heavy due to extremely harsh conditions they need to withstand, so making them lighter would also help.

[Kryten]

ISP is only a part of overall rocket efficiency. I specifically acknowledged that we are already maxing out when it comes to energy density of chemical fuel (and thus ISP ). I also specifically named a few other areas where I am reasonably sure we aren't. But you can still show me wrong, for example by showing me where someone computed the theoretical maximum/minimum for those, because, AFAIK, no one has done that. Unless you do, I would also strongly suggest avoiding claims like "you haven't done the slightest bit of research"

Plenty of people have done that-here's one good example. You get somewhat differing results depending on assumptions like chamber pressure and O/F ratio, note, but nobody is saying there's a huge load of untapped potential. Note it also gives direct energy efficiency for a good few engines-all above 90%.

I_sp of RD-0124, the most efficient KeroLOx engine in the world, is 359 sec! Right - just one second below what's theoretically possible!

It depends on the assumptions you've made in the calculation-but the site linked above, the least conservative I've seen with these assumptions, gives about 390. There's room for improvement, but not revolutionary improvement.

[asmi]

It depends on the assumptions you've made in the calculation-but the site linked above, the least conservative I've seen with these assumptions, gives about 390. There's room for improvement, but not revolutionary improvement.

My point is that - despite what some people are saying here - scientists and engineers do make incremental improvements to existing technologies (RD-0124 first flew in 2001). But nobody in their right mind expects anything revolutionary coming out of this, since we came very close to limits already. And talking about ORSC engines - it's material science is what's limits improvements (for higher efficiency we need higher pressure, but existing materials are not strong enough to withstand these conditions). Just to make it clear - we're talking about the kind of conditions that burn steel in a split second.

[MBobrik]

Plenty of people have done that-here's one good example.

Did you even bother reading what I wrote ? I specifically said I am not talking about stuff related to fuel energy content and its utilization. I specifically acknowledged that we are maxing out in this area. I also pointed out that there are other parameters that too determine overall rocket efficiency. And you just keep going about engine efficiency.

[Kryten]

Did you even bother reading what I wrote ? I specifically said I am not talking about stuff related to fuel energy content and its utilization. I specifically acknowledged that we are maxing out in this area. I also pointed out that there are other parameters that too determine overall rocket efficiency. And you just keep going about engine efficiency.

You specifically asked me to point out where somebody had computed those values, now you're complaining that I did.

EDIT: And where else is this revolutionary increase in performance supposed to come from? We already have stages that can't even hold up their own weight without pressurisation, so you're not going to majorly improve dry mass without running out of rocket-all that leaves you is economic factors, which Nibb acknowledged. Did you actually read his post?

Edited December 17, 2014 by Kryten

[MBobrik]

You specifically asked me to point out where somebody had computed those values, now you're complaining that I did.

I was asking whether someone computed theoretical maximums of the other parameters, not ISP.

[Kryten]

I was asking whether someone computed theoretical maximums of the other parameters, not ISP.

For dry mass, theoretical maximum is effectively Atlas-Centaur, without poking into materials that don't really exist yet. Both stages were thin enough to collapse without pressurisation-you can't improve dry mass significantly from that without running out of rocket to shave off. We're already at the point where engine T/W is good enough for them to be only a few percent of dry mass; what other parameters could their be?

[MBobrik]

without poking into materials that don't really exist yet

So either no new materials will be invented ever, or this isn't the theoretical maximum after all.

what other parameters could their be?

Cost of manufacture and operating costs. Good luck finding the computation of theoretical minimum of that.

[Kryten]

So either no new materials will be invented ever, or this isn't the theoretical maximum after all.

It's about the theoretical maximum without nanotubes or somesuch. Nobody even builds their rockets with balloon tank first stages since Atlas due to the manufacturing and handling costs, they're not going to be making rockets out of nanotubes.

Cost of manufacture and operating costs. Good luck finding the computation of theoretical minimum of that.

I've acknowledged there's room for improvement in economic a good few times, as has Nibb, including in his original post. Again, did you actually read it?

[MBobrik]

It's about the theoretical maximum without nanotubes or somesuch.

So no new materials except nanotubes or somesuch ever ? O RLY ?

I've acknowledged there's room for improvement in economic a good few times, as has Nibb, including in his original post. Again, did you actually read it?

No he didn't. Quite the opposite. Quoting his first post.

If you want to reduce costs, then there are no other choices than to increase demand. A larger market allows economies of scale, lower unit costs, and reusability. A small market increases infrastructure and manpower costs. There is no way around that. The problem is that there are no viable business models that lead to increasing demand for space access.

Emphasis mine.

So there are no other cost reduction options than increased demand, and no options to increase demand, in short, there are no cost reduction options.

And, as a matter of fact, neither have you.

Your first post:

But you haven't got 'an idea', and you haven't done the slightest bit of research to see if such an 'idea' is even possible. Radically increasing the performance of chemical rockets from what we have now isn't going to work not because of lack of 'ideas', it's not going to happen because we're already close to the limits imposed by physics and chemistry, and have been since the 60s or 70s.