the ion engine is way too OP

[WafflesToo]

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"I don't like that other people have fun, ..."

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Funny, I remember saying exactly the same thing months ago.

I just checked; using the upgraded ion engine my gossimer craft have the exact same performance as my nuclear powered ones.

Congradulations, the uniquness of different challenges is being drained away one feature at a time.

IH8U;DIAF

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Gameplay >>>> Realism.

Whilst I agree, Current Ions aren't very realistic, They improve the Gameplay by quite a decent sized margin, You might find an hour Long burn fun and exciting, But most don't.

Nuclear engines worked just fine.

[Kerbart]

While on the subject of overpowering and 5hr burns. I think that time-acceleration is way overpowered and unrealistic as well. It should be 10×, max. More is completely unrealistic and thus removes the fun from the game.

[Killerdude8]

Funny, I remember saying exactly the same thing months ago.

I just checked; using the upgraded ion engine my gossimer craft have the exact same performance as my nuclear powered ones.

Congradulations, the uniquness of different challenges is being drained away one feature at a time.

IH8U;DIAF

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Nuclear engines worked just fine.

They're also a lot more powerful and don't take hours to burn.

Ions take literal Real time hours to make burns, That's a bit ridiculous for a game.

[jmiki8]

Gameplay >>>> Realism.

Whilst I agree, Current Ions aren't very realistic, They improve the Gameplay by quite a decent sized margin, You might find an hour Long burn fun and exciting, But most don't.

Totally agree with this.

[Rusty6899]

I hadn't realised it had been used extensively for interplanetary travel. I had vaguely remembered reading an article saying that there was a proposed mission which was the first to use Ion propulsion for an interplanetary transfer. I must have misremembered. I had thought they were mainly used to counter orbital decay.

[Hans Dorn]

While on the subject of overpowering and 5hr burns. I think that time-acceleration is way overpowered and unrealistic as well. It should be 10×, max. More is completely unrealistic and thus removes the fun from the game.

You can accelerate time?

Dang, I've been waiting for my launch window since 0.13.

[Pockrtplanesairways]

Quit all your bellyaching. I like das new Ion engine. And the LV-1s

[maccollo]

The SLS is expected to have a 5% higher payload fraction to LEO than the Saturn V (4.2% vs. 4.0% for the heaviest configuration), while being significantly more cost-effective. If cost-effectiveness was not a factor, that payload fraction could increase significantly.

Engine technology peaked in the 70s. Fuel fraction hasn't improved either.I recommend you watch this presentation by Antonio Elias on the subject.

[Albert VDS]

^Really? Then why does the Merlin 1D have the highest TWR. It's not an engine from the 70's.

[rkman]

^Really? Then why does the Merlin 1D have the highest TWR. It's not an engine from the 70's.

The primary measure of performance is not engine twr but Isp.

The Merlin 1D has lower Isp than the space shuttle main engine (310 vs 450), which was developed during the 70's.

[maccollo]

^Really? Then why does the Merlin 1D have the highest TWR. It's not an engine from the 70's.

The RD-270 had a sea level TWR of 188 and it was made in 1960s, and it also had better ISP than the Merlin engines.

Granted, it only did ground tests, so the Merlin 1D is the engine with the most TWR that has flown.

Edited April 5, 2014 by maccollo

[Red Iron Crown]

I'm surprised than newer rocket motors aren't all that much better. We have better materials available, and more importantly, better computational and modeling tools for designing them.

[cantab]

The primary measure of performance is not engine twr but Isp.

The Merlin 1D has lower Isp than the space shuttle main engine (310 vs 450), which was developed during the 70's.

Well that's not really a fair comparison since they use different fuels. The Merlin 1D has a higher specific impulse than the F-1, despite both using RP-1/LOX and the (simple, but not so efficient) gas-generator cycle. Of course, the F-1 gave around ten times the thrust.

In the real world, what matters isn't pure performance but cost-effectiveness. Someone could conceive the best engine ever in every possible way, but if it costs a fortune to design and another fortune to make each engine it won't be getting off the drawing board.

[Streetwind]

I'm surprised than newer rocket motors aren't all that much better. We have better materials available, and more importantly, better computational and modeling tools for designing them.

Better materials and better construction techniques aren't going to change the fact that you can only make chemical engines so good. It's the chemical reaction itself that can't get much better. It doesn't matter what material you're building an engine out of, and what level of precision goes into it; if it's a kerosene/LOX engine, you're getting roughly the same performance as other kerosene/LOX engines. When Antonio Elias says that engine technology has peaked, that is what he means: people have already exploited just about all the capabilities of known rocket fuels in engines that existed 30-40 years ago. There simply is no more power left to extract out of the chemical reaction.

What the Merlin engine does to get its great TWR is the fact that advanced materials and construction techniques make the engine lighter. So it weighs 450kg instead of who knows what, maybe an engine from the 70's with that kind of size and performance would have weighed 600kg. That looks great on paper, because it's a 25% improvement in TWR. But ultimately, whether you have 4.5t or 6t of engine mass on a 505t Falcon 9 v1.1 rocket doesn't make that big of a difference.

Now I'm not agreeing with all of Mr Elias' ideas in the video, because he more or less cherry-picks specific metrics that support his point while ignoring those that don't, but I'm fairly convinced myself that advances in engine technology that actually reduce launch costs will not come from improving existing engines but rather from changing the fuel used, and from using economies of scale in production and refurbishing (for those parts that are meant to be reusable). SpaceX and NASA both are developing methane/LOX rocket engines at the moment, because that reaction offers more Isp than kerosene/LOX but costs only a fraction of cryogenic LH2/LOX. They're hoping to get an engine that costs the same (or slightly less) to fuel as existing kerosene/LOX engines but has 15%-20% more Isp, thereby reducing fuel consumption and decreasing the price of launch stages. There's also an added incentive in ISRU because methane is relatively easy to make on-site on Mars for example.

And there's actually a fairly good reason for SpaceX to be doing what they're doing with the Merlin engines in terms of mass production. A few years ago, when it was announced that they would be building 40 engines per year, people were shaking their heads and saying "what the hell could they possibly use even half that many for, they can't launch often enough" because they were used to rockets like the DeltaIV Heavy that makes do with four engines. But look at the Falcon 9: 10 engines per rocket. If they keep up producing 40 engines per year, that would be enough for 4 launches per year. That's not all that much. SpaceX is already launching more often than that, so they had to ramp up their engine production. Then comes the Falcon Heavy, to premiere this spring: 28 engines per launch. Twenty-eight. Almost three quarters of the amount that people thought totally overblown, for just a single launch. What SpaceX is doing here is an attempt to combine the added safety of engine-out capability, where they can lose an engine inflight and still have enough thrust to make it to orbit, with a sort-of mass production program for rocket engines. Never before has any company anywhere built so many engines per year. They're doing this to lower cost. Does it work out for them? I have no idea, I don't work there. But that's their strategy at least.

And wow, this thread sure went off topic in a hurry

Edited April 5, 2014 by Streetwind

[rkman]

And there's actually a fairly good reason for SpaceX to be doing what they're doing with the Merlin engines in terms of mass production.

Sure there are. But the point of the video and of several arguments in this thread is that from a technical performance point of view, modern engines are not better than older engines.

That's why other factors such as overall reliability and project overhead cost are as important as they are, and the gains from improvements there are marginal compared to what people are wishing for, such as the ten-fold reduction in cost predicted by the NASA director quoted in the video.

That will remain so until there is a major breakthrough in rocket engine technology, which probably first requires a major breakthrough in fundamental science.

[Red Iron Crown]

Sure there are. But the point of the video and of several arguments in this thread is that from a technical performance point of view, modern engines are not better than older engines.

That's why other factors such as overall reliability and project overhead cost are as important as they are, and the gains from improvements there are marginal compared to what people are wishing for, such as the ten-fold reduction in cost predicted by the NASA director quoted in the video.

That will remain so until there is a major breakthrough in rocket engine technology, which probably first requires a major breakthrough in fundamental science.

Or enough of a change in political climate to permit nuclear rockets.

[Streetwind]

Yeah, nuclear engines, now those still have a ton of improvements left. The NERVA program didn't come close to maxing that tech out.

However, those aren't launch engines, and we're talking about launch engines here. Not sure you can get a clean NTR to a useful thrust-weight-ratio for launches even with modern technology. In-space usage really isn't a problem, you don't need much dV up there and electric propulsion is still making major steps forward. Wish I knew what the holdup with the VF-200 is...

[rkman]

you don't need much dV up there and electric propulsion is still making major steps forward.

I suppose you mean we don't need much thrust up there, it is dV where electric propulsion excels. Which brings us back to the OP, about which i actually do not have much of an opinion..

[Jouni]

Sure there are. But the point of the video and of several arguments in this thread is that from a technical performance point of view, modern engines are not better than older engines.

The primary technical performance metric is the cost of launching 1 kg to LEO. The engineers have been optimizing that for decades, instead of some artificial targets like ISP. Reducing fuel usage by optimizing ISP is rather pointless, unless it also reduces costs.

[karolus10]

I personally like the buff of ion engine, I would not mind having stock 1 meter version as well . Ions are good with better thrust as long as their energy consumption is on legitimate levels... Electric propulsion is all about getting enough power to run them.

From other hand energy requirements and output of all stock parts need some serious balancing IMHO... command pods and probes (stack guidance units also they need lager batteries than regular probes) should need more energy to run them making batteries and power generation parts (also we could use of having APU burning RCS fuel and fuel cells) more important.

[architeuthis]

are you saying that being able to launch Whackjobian skyscraper towers of unaerodynamic fuel tank stacks strung together with spiderwebs of struts and square girders on chemical booster stacks is somehow not a "little too cartoony" by this measure? people have always been able to use ion engines in this game for purposes that would be ridiculous in real life; landing on minmus, gilly, landing at all, etc...

people innovate given their tools, if you don't want to land on a moon with these ions, then don't... if you want to wait for your satellite to complete its 20 minute burn with your thruster that was only balanced for sandbox gameplay, go ahead, it's just a config file change... ion engines IRL even have been seriously considered for launching huge interplanetary crewed missions, so your claim of "should not be able to launch this or that" is complete nonsense

I remember a few years ago a friend of mine asserted that there would never be a space game with Newtonian physics that would gain any form of mass popularity. People wouldn't like that they couldn't swoop around in their spaceships as if they were WW2 fighter planes, and would therefore grow bored. I'm pleased that KSP seems to disprove the notion that space-based realism cannot also be fun. So you can probably tell that I don't care much for the "who cares if it's crazy unrealistic, it's just a game" argument. Nobody here is saying KSP should completely mirror reality, also nobody is saying we should ditch everything that makes KSP realistic. I think most everybody would like some combination of realitic-ish, and fun to play, so the discussion is about what that means to the game. It is fine to discuss that. It is also fair to discuss balance for single player games. The main thing I dislike about ion engines in KSP is that we get bored so easily we have to fundamentally alter them to basically be just another high-isp rocket engine, and force them to be something they are not. All ion engines are used for long duration burns, this is what defines them. KSP ions can only ever be aesthetically like RL ions.

Engine technology peaked in the 70s. Fuel fraction hasn't improved either. I recommend you watch this presentation by Antonio Elias on the subject.

http://youtu.be/oY3GclS5VUQ

Interesting video. Thanks for linking that.

[rkman]

The primary technical performance metric is the cost of launching 1 kg to LEO. The engineers have been optimizing that for decades,

Except that factors other than material- and engineering cost are a major factor in cost/kg, and are non-technical in nature (project overhead cost, politics).

instead of some artificial targets like ISP. Reducing fuel usage by optimizing ISP is rather pointless, unless it also reduces costs.

Higher Isp generally does reduce cost because it does not only save on fuel (by itself a relatively small saving), but also reduces fuel mass and structural mass - and thereby reduces thrust requirements (meaning you can use smaller/fewer engines). That reduces material- and engineering cost considerably, and thus Isp is one of the main technical avenues of reducing cost/kg of payload. With these things there is always diminishing returns; at some point cost vs improvement makes it no longer worth the effort. But that does not mean Isp is not very important.

Edited April 5, 2014 by rkman

[Jouni]

Except that factors other than material- and engineering cost are a major factor in cost/kg, and are non-technical in nature (project overhead cost, politics).

The same can be said for all other engineering challenges as well.

Improving ISP is essentially an academic problem. You have a nice, well-defined task with some real-world relevance, and a metric that tells you how your proposal compares against the alternatives. Still, the engineers in the industry might not use your improved engine proposal, if the improvements in efficiency don't translate into improvements in cost-effectiveness, given real-world constraints.

Higher Isp generally does reduce cost because it does not only save on fuel (by itself a relatively small saving), but also reduces fuel mass and structural mass - and thereby reduces thrust requirements (meaning you can use smaller/fewer engines). That reduces material- and engineering cost considerably, and thus Isp is one of the main technical avenues of reducing cost/kg of payload. With these things there is always diminishing returns; at some point cost vs improvement makes it no longer worth the effort. But that does not mean Isp is not very important.

The main reason for real-world SSTO proposals is that fuel is cheap but rockets are expensive. It could be a good trade-off to waste a lot of fuel, if it means that that you can salvage and reuse the rocket/ship, or at least a good portion of it. With similar reasoning, people can decide to build bigger rockets with cheaper engines, instead of smaller rockets with more expensive engines.

[rkman]

The main reason for real-world SSTO proposals is that fuel is cheap but rockets are expensive. It could be a good trade-off to waste a lot of fuel, if it means that that you can salvage and reuse the rocket/ship

But as of yet it is not. The reason why those are for the most part proposals, and why the one example that went beyond proposal was not cost effective, is the non-techical factor of relatively high overhead cost due to lower-than-hoped-for demand for its services. (the break-even point for the Shuttle was at 50 to 60 launches per year)

The reason why the Merlin engine is good for SpaceX is not that its technical performance is better than older engines. And although it is worth the effort, the positive effect on launch cost is marginal.

The bottom line is that for the time being we're essentially stuck wrt launcher technology.

[Red Iron Crown]

The bottom line is that for the time being we're essentially stuck wrt launcher technology.

True, we're basically working on commoditizing existing technology.