How would you improve current launch vehicles?

[Nibb31]

Yeah, If it were possible, people smarter than you would have already invent it in the past. So don't bother... Thinking that way, nothing would be improved ever. We would be still sitting in a cave and chipping stones.

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.

[PakledHostage]

but how do you know the technology is mature ? Because you don't think bigger improvements are possible.

No, because I am an aerospace engineer and it is my professional opinion. Likewise, Nibb is a professional in the aerospace industry. You can accuse me of making an argument from authority, but at some point you have to trust the experts. The limitations are well understood by physicists, chemist and engineers and it doesn't take a rocket scientist to know we're already bumping up against them.

[Pipcard]

So we will never become a spacefaring species?

[Frozen_Heart]

Aerospace engineers and scientists aren't idiots. Believe me, if there was an easy and cheap way to get stuff into orbit, we would be using it by now.

However technology improves over time. Lighter materials are made and engines can squeeze out a tiny bit more thrust and ISP. 200 years ago many of the best minds were trying to work out how to even fly. They still couldn't do it for a long time.

I don't know if it is your intent but you make it sound like we are at a max technology level and nothing can be improved.

Standardization of the system. Standard tank diameters, standard engine mounts for a given load, etc.

I agree with the standardisation technique. Performance may be lost but its made up for by the cost decrease. Same technique Spacex uses currently. All tanks are the same diameter and each vehicle uses 10 of the same engine.

[MBobrik]

You can accuse me of making an argument from authority, but at some point you have to trust the experts.

Well, I flatly refuse. I will judge arguments according to their merit and nothing else. No faith in the clergy experts for me.

it doesn't take a rocket scientist to know we're already bumping up against them

Well, either that, or you just painted yourselves into some corner, like experts tend to when they start believing no new idea can come along...

[PakledHostage]

Well, either that, or you just painted yourselves into some corner, like experts tend to when they start believing no new idea can come along...

I didn't say that no progress was possible. Only that you shouldn't expect much more than incremental progress in the current paradigm of chemical rockets.

[MBobrik]

I didn't say that no progress was possible. Only that you shouldn't expect much more than incremental progress in the current paradigm of chemical rockets.

If you stretch the definition of incremental enough, everything is just incremental progress. And in the other direction, large enough accumulation of small increments may amount to order of magnitude large change.

I agree that the energy density won't change with chemical rockets, but I don't believe we are already close to the maximum physically possible engine TWR or tank fuel weight/dry weight ratio. And I don't believe at all that we are already close to the minimum physically possible manufacturing and operating costs.

Edited December 16, 2014 by MBobrik

[Dkmdlb]

So we will never become a spacefaring species?

We can become one, but it will require some changes. From Nibb's earlier comment:

That is why, as long as energy is at a premium, and as long as it's dangerous to handle huge energy sources, spaceflight is always going to be a niche business.

There are two "if" statements and one "then" statement. Change the if statements and you get to change the then.

Edited December 16, 2014 by Dkmdlb
a letter

[KerikBalm]

Air augmented rockets/Ram-rockets.

We already have solid fuel missiles that get an effective ISP of 500s

Seems to me that a 2 stage to orbit craft could be made fully reusable.

1st stage is the ramrocket stage (solid fueled? both?). If that can get it going mach 5 at 100,000 feet, the 2nd stage should be easily able to acheive orbit with a good payload.

The disadvantage of an air-augmented rocket for an SSTO is the weight of the intakes and such, which don't help at high speed and altitude. Then you need to heat shield everything for re-entry

You get around scramjet problems, because you're not combusting fuel with the intake air, the intake air is just ReMass - but don't take that deat weight to orbit.

2 stage it, so the air augmented rocket stage doesn't need so much heat shielding.

I'm imagining something like an oversize air augmented rocket powered "white night" that launches an orbital "space ship one"

[MBobrik]

There are two "if" statements and one "then" statement. Change the if statements and you get to change the then.

Guess how long that would take if we used the "You have to trust the experts. If it were possible someone smarter than you would already have done it" approach...

[Darnok]

So we will never become a spacefaring species?

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.

Different gravity on other planets won't allow us to colonize other worlds, we can do that only using evolution as tool to shape ourselves into multi-spiecies civilization.

Multi-spiecies because for each new planet we would have to create new branch in our evolution tree that would be adapted to new environment, but all of them would be part of same civilization.

If we ever want to travel for other stars or make permament bases on Mars we should start building space stations in Earth's orbit with G 1.0. Send there families and slowly, year after year, change gravitation on that stations, to lower or higher depends on travel destination.

After few generations homo sapiens would adapt to new environment and evolve... become something else, something that for example would be adapted better for Mars gravitation than for Earth's... space travelers species

No, because I am an aerospace engineer and it is my professional opinion. Likewise, Nibb is a professional in the aerospace industry. You can accuse me of making an argument from authority, but at some point you have to trust the experts. The limitations are well understood by physicists, chemist and engineers and it doesn't take a rocket scientist to know we're already bumping up against them.

Trust experts nope, never and making the "argument from authority" is against science because science is about research, study, observation, experiments etc etc but not about authority. Experts are not born, they are common humans like OP who are starting to ask questions about science and later they are doing their own research and booom we have new expert

Edited December 16, 2014 by Darnok

[Frozen_Heart]

How well could a Nuclear rocket work as a launcher if you disregard public hate? They have a much higher energy density but lower TWR. Solid core ones can get close to 1000m/s ISP.

Different gravity on other planets won't allow us to colonize other worlds, we can do that only using evolution as tool to shape ourselves into multi-spiecies civilization.

The buildings on the planet could be giant centrifuges. Though that's far into the realm of Sci-fi. I don't doubt its possible but well above our current capabilities.

Edited December 16, 2014 by Frozen_Heart

[MBobrik]

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.

So, to be crass, "you dont' have a phd in that area so shut up". Sorry, I don't buy that. I saw a quite a few international conferences full of blah-blah, and had a lot of extremely productive scientific debates over skype or even internet forums. Making a priori judgements based on the form of the communication channel and not on the content is simply wrong.

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.

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.

Edited December 16, 2014 by MBobrik

[Darnok]

The buildings on the planet could be giant centrifuges. Though that's far into the realm of Sci-fi. I don't doubt its possible but well above our current capabilities.

Yes you can build entire town for 100.000 people and keep them under 1.0 G, but how would they gather resources? How would they repair buildings, expand?

And after years you would want to build mega city with artifical gravity for milions of people?

I don't know like you, but I would be too afraid to sleep in that kind of city, not to mention how much power would be wasted just to keep G1.0

[Frozen_Heart]

It is very possible to do high tech things in the garden shed. My dad founded his submarine business out of a garden shed.

[Frozen_Heart]

gather resources? How would they repair buildings, expand?

It wouldn't kill you to walk onto the moons surface for a few hours or days outside of 1g. 12 people have done it.

not to mention how much power would be wasted just to keep G1.0

Quite a bit... as I said that's not even remotely within our current tech.

[Darnok]

It wouldn't kill you to walk onto the moons surface for a few hours or days outside of 1g. 12 people have done it.

Quite a bit... as I said that's not even remotely within our current tech.

You are right, but costs and efficiency of such "moon walks" makes it not worth a try IMHO.

Like I said before to colonize planets and get our hands on its resources we should change our way of thinking about "planetary colonization". The way we do this right now is too expensive and too dangerous and from both reasons we are still here with single space station few decades after 12 people were on moon.

[Alias72]

I would investigate a tandem launch system. The "rocket" contains reaction mass. A ground based laser system powered by a nearby nuclear reactor would power the lasers which would, through thermal ablation, accelerate the reaction mass out the rocket nozzle.

oooh, oooh! how about we use a reusable first stage powered by a jet engine or hybrid rocket. that way we can get a more efficient launch profile.

the possibilities are ENDLESS!!!

[Karriz]

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.

[Idobox]

Current chemical launch vehicles run on either LH2/LOX, Kerosene/LOX, N2H4/N2O4, Aluminium/Ammonium Perchlorate (used in solid rockets), or any combination of them. If the agencies/companies were a little more adventurous (foolish!), they'd probably switch the aluminium fuel in solids with powdered beryllium, which is more energetic. Liquid-fuel rockets can improve their specific impulse by switching to more energetic oxidizers, like liquid fluorine, or better (worse?) yet, chlorine trifluoride. Liquid hydrogen is already tops in being a high-performance fuel in the mix, but the density is rather dismal, so you can replace some of it with a higher-density fuel that is at least as energetic, or possibly more, like liquid mercury or lithium.

When I read this, I imagined a ClF3 - LiAlH4 hybrid rocket, and my palms started to sweat. I would feel safer with a lit stick of dynamite.

Also, think of the damage to the infrastructure is the thing blows up, and rockets tend to do that.

More seriously, mass drivers are an actual option. Ram accelerators and light gas guns have accelerated stuff to orbital speeds in labs before, of course tiny projectiles only, but scaling them up is not that difficult (compared to building SLS or the ISS for example). In particular, a RAM accelerator is more or less a 2km long steel tube filled with an explosive mix of gas, a remarkably simple machine.

Of course, the acceleration would be too high for humans or delicate instruments, but smart ammunition go through much worse, so small rockets, electronics, solar panels, antennas, optics, solar sails and inflatable structures could very well survive.

Then you have the issue of traveling at 6 or 7km/s in the lower atmosphere. There is remarkably little data about this kind of things, and we can assume there will be loud bang, some serious negative g, and lot of compression heating. The deceleration would probably not be worse than the acceleration, and ablative heatshields could deal with the heat at the cost of mass fraction.

The other exciting technology is momentum exchange tethers. Basically you have a station in LEO spinning a long tether. You grab ships on suborbital trajectories (for example one thrown from a mass driver) and release them at a higher velocity, putting them into orbit.

By doing so, you slow down your station, so you need to compensate for the lost momentum. This can be done by putting high ISP thrusters, or by slowing down other stuff (stealing their momentum), for example by deorbiting satellites, or by catching and slowing down projectiles sent at very high velocities (from your mass driver).

This one is a lot less ready, since we have little experience with long tethers in space (there are concerns about wear due to micro-collisions), and having a rendezvous and docking between a ship on a suborbital trajectory and the end of a fast moving, fast spinning tether would be quite hard. Docking is normally done with ships that are on the same orbit and still takes hours, here your objects would have very different trajectories, and you would have minutes, or maybe even seconds to do it.

Still, it's a very exciting prospect.

[SciMan]

Chemically fueled rocket engine technology still has one area that hasn't been researched much. Engine nozzle geometry.

A standard De Laval rocket nozzle can only be optimized for a certain range of altitudes. If you optimize for sea level performance you lose out on vacuum performance (under-expanded for vacuum use), and if you optimize for vacuum performance you usually get combustion instabilities at sea level (over-expanded at sea level).

These problems are solvable by using one of the several types of altitude compensating nozzle.

The Aerospike (in both linear and toroidal flavors) is probably the best known to KSP players, but there are also Stepped bell, Extendable bell, Plug, Expansion-Deflection, and a few other types.

Several of them are not much heavier than a standard rocket nozzle, which is the prime complaint against Aerospike nozzles.

A few have been tested, but none have actually flown on a launch vehicle.

I'm certain that using one of these types of rocket nozzle would measurably improve first stage performance, which would likely have a disproportionate effect on overall rocket performance.

It might even have enough of an effect to make a pure rocket SSTO possible. Possible, not necessarily cheaper. Reusable rocket SSTO, also not necessarily cheaper.

Another idea is propellant crossfeed. Yes, exactly like Asparagus staging.

"but aerodynamics doesn't like pancake rockets!" True.

You don't need pancake rockets to make propellant crossfeed work.

Even something like the Delta-IV or Falcon-9 Heavy could use it. Even better, since the 2 side boosters and the core are the same (minus payload adapter or nosecone), it can be standardized.

All you need is valves on the center tank that can switch over from crossfeed to own tanks without introducing air bubbles or cavitation into the propellant line.

That shouldn't be too terribly hard, as the fuel is already under pressure to ensure an even flow into the engines. Especially with modern computer design and simulation tools.

At a first glance, it seems like it would require a total of 4 valves in the propellant lines of the center tank for a 2 side boosters, 1 core setup.

It would use 2 "shuttle valves" per side booster (one for fuel, one for oxidizer).

Shuttle valves are a logical "OR" gate for hydraulics or pneumatics, automatically routing the input that has the most pressure to the output.

This means that if the side tanks are run at a higher pressure than the core, the propellant shuttle valves will automatically switch to the core tank when ever the lines to the side tanks are severed during staging, or if the pressure of the side tanks goes lower than the core. The pressure difference doesn't have to be very high to make the valve switch over, but it might affect how fast the valve operates.

This propellant cross feed idea was proposed sometime in the 60's, and declared impractical due mostly to reliability and complexity concerns.

Care does have to be taken to ensure that the engines do not get propellant feed pressure fluctuations during the staging event, but I doubt that it is an insurmountable task, especially with the power of modern computers. Using computational fluid dynamics simulations, it should be possible to ensure that the system behaves as expected even before real-world tests.

If a launch vehicle could be made to use altitude compensating nozzles and propellant crossfeed, I expect that it would offer significantly better raw performance than current rockets, at a similar cost (not counting development cost)

Obviously it would cost money to design a rocket using these technologies, but the rocket itself would not need to cost more than anything currently available.

Even if it ends up costing the same as a Delta-IV, it would almost certainly be capable of putting a greater payload in orbit.

That means it would be cheaper on a $/kg basis, even if it's not cheaper on a $/rocket basis.

Edited December 16, 2014 by SciMan

[shynung]

Propellant crossfeed needs more powerful pumps. That is, the engines on the side boosters of a crossfed Delta IV Heavy needs bigger pumps than its center-mounted cousin, because it has to pump more fuel in the same timeframe. Designing a new pump may require designing a new rocket engine, since the two is closely-linked.

That said, SpaceX's upcoming Falcon Heavy do plan to use crossfeeding.

[Bill Phil]

Well...

If you look at cars, or motherboards, or anything heavily complicated, there's a standardization. Motherboards have specific slot types, cars have different axles and motors they can use, etc. But rockets don't have as much of a luxury. If you do the research, the first car was in 1812 or so. But no one wanted it. It took a century for cars to hit it off. What does that mean for rockets?

[Bill Phil]

Propellant crossfeed needs more powerful pumps. That is, the engines on the side boosters of a crossfed Delta IV Heavy needs bigger pumps than its center-mounted cousin, because it has to pump more fuel in the same timeframe. Designing a new pump may require designing a new rocket engine, since the two is closely-linked.

That said, SpaceX's upcoming Falcon Heavy do plan to use crossfeeding.

If you're smart about it, you use the core engine's pump as well. The pipes would have to be half volume for the individual boosters, and then come together in a pipe that's the appropriate size.

The pipes would spring from another area in the prop tanks.

[SciMan]

I had a feeling that there might be something involving the pumps, but why aren't the center engine's pumps enough? Flow restrictions or something?

Also, I didn't know (or didn't remember) that the Falcon Heavy plans to use crossfeed. That's interesting, because it seems to be the option that has the highest potential to increase payload capacity (or reduce costs, take your pick).

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

Better vacuum specific impulse on the first stage isn't a bad thing, considering how rockets are designed to quickly leave the lower atmosphere, right?