Why are the KSP rockets so small compared to real ones?

[thaflya]

Hi all,

this is my first thread in this forum. I saw Kerbal Space Program in steam 3 weeks ago and i couldn´t withstand this game. I don´t regret buying this great game. Fell in love the first second I started to play. I am not that good in english so pls forgive me my bad style.

After playing this game for 100 hours i started to ask me why all designs in KSP are so far away from the real Rockets used. For example we have nothing in this game that comes close to the solid boosters used to get the Spaceshuttle into space; same thing is the comparison to the Saturn V. Our biggest Tanks are 2.5m in diameter (with mods 3.5m ?!), Saturn V was 10m. Everything in this game is just small compared to the real ones.

Is this cause of problems with the simulation engine? Maybe it can´t handle such big things.

What do you think about this?

[iamaphazael]

Everything in the game is scaled down. The original reason was so that a trip to the moon could be done in a few hours rather than several days (this was back before timewarp had been implemented, so the game had to be played in real-time)

[Carlbergh]

Everything in the game is scaled down. The original reason was so that a trip to the moon could be done in a few hours rather than several days (this was back before timewarp had been implemented, so the game had to be played in real-time)

What he said, I think everthing is about 6 times smaller than their "real universe counterparts".

[Deadpangod3]

Isn't Jool like only the size of earth in rl?

[erkha343]

the game certainly needs some bigger boosters!

[Hocki]

What he said, I think everthing is about 6 times smaller than their "real universe counterparts".

No, infact it's eleven times smaller.

[Spatzimaus]

I think everthing is about 6 times smaller than their "real universe counterparts".

At least. The sun in this system is over a hundred times smaller than our Sun, which actually means it's about ten times too small to actually BE a star. (Minimum size for nuclear fusion is about 0.08 solar masses.) Kerbin's radius is one-tenth that of Earth, and one hundredth of its mass; this gives it the same surface gravity as Earth (9.8 m/s^2), but a far smaller orbital velocity. This makes spaceplanes easy, as it's not a lot of work to go from a cruising speed of Mach 3 to an orbital speed of Mach 5-6, whereas on Earth you need to go Mach 25 in low orbit. (It also means that Kerbin's density is about ten times as much as Earth's, which isn't actually possible.)

So while the basic laws of physics might still be reflected in KSP, it's not even close to a simulator of our own star system. It's not surprising, then, that the game uses smaller components.

[OrbitusII]

The reason rockets are smaller are because you don't need nearly as much power or fuel to get into orbit. Kerbin is 600km in diameter and space starts lower than on Earth, which is 13400 km in diameter with some atmosphere (even if it is next to nothing) up past 300-400 km, which is where things like the ISS orbit. Thus we also have to stationkeep in real life, whereas we don't have to do so in KSP since the atmosphere ends completely at a little less than 70km.

[Temstar]

Delta-V wise it takes 9400m/s to reach LEO, it takes 4500m/s to reach LKO. Given the Tyranny Of Rocket Equation that 4900m/s make a huge difference in the size of the rocket required. In fact 9400m/s is similar to the amount you need to return to Low Eve Orbit from Eve's surface, and the few people crazy enough to design Eve return vehicles will tell you that such rockets are just about as large as Earth rockets (give or take asparagus staging).

Edited April 20, 2013 by Temstar

[architeuthis]

Delta-V wise it takes 9400m/s to reach LEO, it takes 4500m/s to reach LKO. Given the Tyranny Of Rocket Equation that 4900m/s make a huge difference in the size of the rocket required. In fact 9400m/s is similar to the amount you need to return to Low Eve Orbit from Eve's surface, and the few people crazy enough to design Eve return vehicles will true you that such rockets are just about as large as Earth rockets.

Well said. I recall reading in Michael Savage's Millennial Project something loosely like 'our solar system almost seems as if was designed with ease of exploration and colonization in mind'. In the case of KSP that is literally true; 'reality, but easier'. This means that even if rockets are less powerful in absolute terms, they are way more powerful in relative terms. Except when they actually are more powerful in absolute terms as well: the PB-Ion has 5555 the thrust of most advanced current ion engine, the 10 kW NSTAR used on NASA's Dawn mission. Cf. the Rockomax Mainsail which has .22 the thrust as the Rocketdyne F1 or the LV-N which has .18 the thrust of the NERVA 2:)

[TwoHedWlf]

A lot of it boils down to, "It's a physics based game, not a simulation." And it was one of many decisions made with the goal of maximizing the fun "Realistic" bits and minimizing the boring tedious parts.

[astropapi1]

Ok, Kerbin is 1:11 from the earth, so you won't need 10m fuel tanks to get an orbit. I'd like to see 3.75 parts like the ones in the KW rocketry mod, but that's all, going further would ruin the game IMO. All rockets would be the same: A huge 8m engine with two giant SRBs attached to the sides, and the fun thing of the game is designing your rockets and flying them yourself.

I love KW rocketry, because now my rockets look like the real things. It has a lot of SRBs and different engines and fuel tanks. Another thing I'd like to see are fairings, I know they only add weight, but my rockets look way cooler than before, and the ones on KW rocketry are pretty cool.

Edited November 3, 2014 by astropapi1
Editing from the future like a pro!

[Brotoro]

Designing Planets

BROTORO: Tonight on Kerbal Space Program Forum I'd like to welcome our special guest, Mr. Slartibartfast, who has consented to talk to us this evening about solar system design and construction. Thank you very much for being with us today!

SLARTIBARTFAST: Well, I don't normally do interviews, but when a very important client asked for a representative from the Commercial Council of Magrathea, it happened that I was the only one who'd ever talked to an Earthman, so I got the job. It's all a bit of a bother, really.

BROTORO: A very important client? Who would this very important client be?

SLARTIBARTFAST: I'm sorry, but we do not disclose information about our clients. They are all very wealthy and powerful beings, and I'm sure you'll understand that they enjoy their anonymity. But I will say that you'd never have gotten this interview if the Mice were not very big fans of space travel.

BROTORO: Mice are big fans of space travel?

SLARTIBARTFAST: Certainly. Why else would they have arranged to be some of the first passengers ever flown in a rocket? But I've said more than enough on that subject already.

BROTORO: Ah. OK, let's get right to tonight's topic. Is there any truth to the rumor that Magratheans did the design and construction work for Squad on the Kerbol planetary system?

SLARTIBARTFAST: I've already told you, we don't discuss our clients.

BROTORO: Well then, hypothetically speaking, could you tell us if it's possible to design a solar system with these specifications?

(BROTORO hands Slartibartfast a sheet of paper. Slartibartfast glances over it briefly.)

SLARTIBARTFAST: Ah, yes... Miniature planets are adorable, aren't they? They were all the rage with a certain portion of our clientele.

BROTORO: So it's possible to construct a solar system matching those specifications?

SLARTIBARTFAST: Certainly. We Magratheans pride ourselves on being able to build any kind of planet.

BROTORO: But look at the densities of those planets. Most of them have densities greater than any known element.

SLARTIBARTFAST: That's not a problem. We use black holes.

BROTORO: Black holes? But wouldn't a black hole inside a planet just swallow it?

SLARTIBARTFAST: No, no. We use spherical force field bubbles centered around small black holes. We can adjust the mass of the black hole and radius of the force shell to get any planet density desired, then cover it with the mantle and crust material of the client's choice. It's a very flexible system.

BROTORO: So you're saying that Kerbin is mostly hollow inside, with some old rocky material thrown on top?

SLARTIBARTFAST: No. More like the inner one third is hollow. And I assure you we use only the finest ingredients when building our planets.

BROTORO: Wouldn't these force field bubbles require energy to maintain their structure?

SLARTIBARTFAST: Certainly they require energy. We just allow a small amount of matter from the lower mantle to trickle through openings in the sphere. As the matter falls into the gravity well of the black hole, the energy equivalent to a sizable fraction of its rest mass is released as radiation before it crosses the event horizon. That radiated energy is captured and used by the force field bubble, which also acts as a Dyson sphere.

BROTORO: Dyson sphere? So do Magratheans know about Freeman Dyson?

SLARTIBARTFAST: Who? You misunderstood me. I used the Magrathean term for "spherical mega-structure that captures all radiated energy from a central power source," and that little fish I put in your ear translated the concept into a term you are familiar with. I've never heard of a freemandyson.

BROTORO: Ah, so that's what the fish was for. I thought it was a quaint Magrathean greeting or something.

SLARTIBARTFAST: You're sitting there wearing a digital watch, and you think my people are quaint?

BROTORO: But wait... If Kerbin has no liquid iron core inside, how could it have a magnetic field?

SLARTIBARTFAST: Does Kerbin have a magnetic field?

BROTORO: Um... well, I'm not sure. The developers haven't given us any magnetometers yet, but I just assumed it did.

SLARTIBARTFAST: And it well might. Magnetic fields are easy. We would just need to orbit a ring of charged matter around the black hole inside the force sphere. Adjusting the charge on the matter can give the client any magnetic field desired, and the inclination of the ring can offset the magnetic pole from the rotational axis if desired. Any field strength can be tailored for the client, although it's easier for us if they want a simple dipole. Haven't you wondered why Jool has such a weak magnetic field for a jovian planet?

BROTORO: It does?

SLARTIBARTFAST: Of course. If it didn't, the planet would have powerful radiation belts, and any kerbal you sent in there for aerobraking would be late.

BROTORO: Late?

SLARTIBARTFAST: Yes. As in, "The late Jebediah Kerman." Ah hum.

BROTORO: . . .

SLARTIBARTFAST: I don't understand why Earthmen always stare at me blankly when I use that line.

BROTORO: I'm just wondering how you know about Jebediah Kerman.

SLARTIBARTFAST: It's the Babelfish again. I just used the Magrathean word for "bad-ass space pilot," and the fish did the rest in conjunction with your primitive brain.

BROTORO: Well. What about Kerbol, the sun of the system? How could something with that low of a mass possibly support thermonuclear fusion?

SLARTIBARTFAST: I'm not part of our stellar division... I work on the planets, and I specialize in doing coastlines... but there are two different ways we handle miniature stars.

BROTORO: One way involves black holes?

SLARTIBARTFAST: Both ways do. In one method, we simply make the force sphere around the black hole small enough that the density and pressure in the overlying hydrogen-rich material is sufficient to maintain thermonuclear reactions at the rate needed for the desired luminosity. The second way involves simply letting sufficient matter flow through the force sphere and into the black hole to provide the desired luminosity.

BROTORO: Which method did you use for Kerbol?

SLARTIBARTFAST: I didn't say we made Kerbol. I was speaking hypothetically. Why don't you just measure the neutrino flux coming out of Kerbol... then you could tell if there are fusion reactions going on inside of it.

BROTORO: Well... again... we don't have any neutrino detectors as yet.

SLARTIBARTFAST: You really do need to take more interest in your greater environment. If you're not paying attention to things outside your planet, terrible things could happen to it.

BROTORO: Yes, thank you. But what about Minmus?

SLARTIBARTFAST: What about it?

BROTORO: The developers tell us that it's made of ice, but that can't possibly be the case given its distance from the sun, can it?

SLARTIBARTFAST: Kerbin, like your own planet Earth, is located at a distance from the sun where the equilibrium temperature is below the freezing point of water. If not for their natural greenhouse effects, the oceans on both bodies would be frozen over. The temperature is even lower when you are dealing with a surface that has a very high albedo, like ice, since that reflects away most of the incoming energy.

BROTORO: Yes, yes, I know all that. But Minmus has no atmosphere. Its surface is in vacuum. And water ice would sublime directly into a gas and escape into space at the equilibrium temperature of Minmus. Minmus should be a gigantic comet!

SLARTIBARTFAST: Ah, I see. Young Hargledertfirst of our small moon department solved that problem.

BROTORO: Did he?

SLARTIBARTFAST: She. She engineered a microorganism that was active in the small moon's water during its early warm phases. The organism excretes a clear polymer as a waste product...kind of like a resin. All of the ice on the small moon contains a small percentage of this polymer. When the ice is exposed to vacuum, the water will indeed sublime away, but the polymer is left behind and forms a barrier to further sublimation. And any future impacts or landing rocket flame scars on the surface are self-healing once the vapor clears.

BROTORO: Really? And that's what you did for Minmus?

SLARTIBARTFAST: I was speaking hypothetically.

BROTORO: And I suppose you'll tell me that Eve is purple because of a little food coloring.

SLARTIBARTFAST: Indeed. It takes a very small percentage of certain chemical compounds to give a planetary surface or atmosphere a desired color. You'd be surprised how many clients are upset if they don't get just the right shade of purple or some other color in their skies. We are very good at this, and all the chemical stains and particulates are USDA approved.

BROTORO: You know about the USDA? Oh, wait...it's the Babelfish again, isn't it.

SLARTIBARTFAST: Indeed.

BROTORO: So... if you had to do it all over again, are their any changes you'd make to the Kerbol system?

SLARTIBARTFAST: Well, yes, now that you've asked. I think Kerbin would look much better with more fjords on the coastlines. I always try to put a lot of fjords on a planet, but the managers always say it's too much. A lot of my work got erased. I was quite incensed about that.

BROTORO: Hypothetically speaking, you mean.

SLARTIBARTFAST: Um. Yes. Of course.

BROTORO: Well, our time is up. We really appreciate you coming here today. So long, and thanks for the fish.

SLARTIBARTFAST: No, I'm afraid I must take the Babelfish back with me.

BROTORO: Oh, please? I think it would be very useful *arrgh* Hey!

SLARTIBARTFAST: Flerti slark tilligert sibilas fer torrn. Ser fasto gerhs.

BROTORO: Yeah. Whatever.

Edited February 19, 2016 by Brotoro

[Logan.Darklighter]

**APPLAUDS**

You sir, are indeed a hoopy frood who knows where his towel is!

[Scotius]

*Gives a standing ovation to Brotoro* Man, that was HILARIOUS! Do you write fanfics by chance? Because i would totally read them. LOL.

[Itsdavyjones]

That was amazing. +1:D

[0jam3290]

Brotoro, that is by far one of my favorite Kerbal fan-fiction stories EVER! (Believe me, I've read alot)

[Giggleplex777]

I like my rockets really small.

[Flixxbeatz]

Actually with the parts in-game, you can now already make some real-scale rockets, like Delta-II, which has a 3m-wide core.

If you want real-scale rockets, then ask the add-on developers to mod 4-meter wide tanks and engines, which is roughly the same diameter as the Atlas V. Don't even get me started on real heavyweight rockets (Delta IV, Proton, Ares V, SLS), which have cores ranging from 6 to 8-meter, which will be deemed too powerful for Kerbin System.

Edited April 20, 2013 by Flixxbeatz

[magnemoe]

The reason rockets are smaller are because you don't need nearly as much power or fuel to get into orbit. Kerbin is 600km in diameter and space starts lower than on Earth, which is 13400 km in diameter with some atmosphere (even if it is next to nothing) up past 300-400 km, which is where things like the ISS orbit. Thus we also have to stationkeep in real life, whereas we don't have to do so in KSP since the atmosphere ends completely at a little less than 70km.

I did an "landing" with an manned balloon probe on Jool and got back into orbit.

Much harder than Kerbin even harder than Eve, as you had to reach the orbital speed of 5.800 m/s at 200 km height.

The balloons took me up to 40 km after I dropped the science platform, the transfer stage and other stuff not needed for takeoff.

[thaflya]

Ty for the many answers and Brotoro for his creative story.

So the next question is. Is it possible in this game-engine to expand the Solar System with all its parts and distances and also the Rockets to match their real counterparts (maybe as an alternative option for later releases)?

Don't missunderstood me, i love this game as it is. But it is a bit disapointing when i show this game to a friend and i have to note that all the planets, distances and rockets are just toys compared to the real ones.

[Netris]

Not to mention that kerbals are about 64% the size of humans. That's why their rockets are smaller.

[Murchadh]

I am late to the party, but..

Fantastic Hitchhiker inspired post. I thoroughly enjoyed reading that. Lots of creativity there.

[nats]

Hi all,

this is my first thread in this forum. I saw Kerbal Space Program in steam 3 weeks ago and i couldn´t withstand this game. I don´t regret buying this great game. Fell in love the first second I started to play. I am not that good in english so pls forgive me my bad style.

After playing this game for 100 hours i started to ask me why all designs in KSP are so far away from the real Rockets used. For example we have nothing in this game that comes close to the solid boosters used to get the Spaceshuttle into space; same thing is the comparison to the Saturn V. Our biggest Tanks are 2.5m in diameter (with mods 3.5m ?!), Saturn V was 10m. Everything in this game is just small compared to the real ones.

Is this cause of problems with the simulation engine? Maybe it can´t handle such big things.

What do you think about this?

Mods can give you 5m tanks but I havent used them myself yet - with drag the way it is it isnt a good idea to use massive tanks like that.

[Technical Ben]

At least. The sun in this system is over a hundred times smaller than our Sun, which actually means it's about ten times too small to actually BE a star. (Minimum size for nuclear fusion is about 0.08 solar masses.) Kerbin's radius is one-tenth that of Earth, and one hundredth of its mass; this gives it the same surface gravity as Earth (9.8 m/s^2), but a far smaller orbital velocity. This makes spaceplanes easy, as it's not a lot of work to go from a cruising speed of Mach 3 to an orbital speed of Mach 5-6, whereas on Earth you need to go Mach 25 in low orbit. (It also means that Kerbin's density is about ten times as much as Earth's, which isn't actually possible.)

So while the basic laws of physics might still be reflected in KSP, it's not even close to a simulator of our own star system. It's not surprising, then, that the game uses smaller components.

Yeah, I'm happy for handwavium. Like perhaps the Kerbin sun is a neutron star enclosed by the remnants of it's twin?

Ty for the many answers and Brotoro for his creative story.

So the next question is. Is it possible in this game-engine to expand the Solar System with all its parts and distances and also the Rockets to match their real counterparts (maybe as an alternative option for later releases)?

Don't missunderstood me, i love this game as it is. But it is a bit disapointing when i show this game to a friend and i have to note that all the planets, distances and rockets are just toys compared to the real ones.

I could see this as a proper (I won't use the other word) "sequel" to KSP. Once KSP is finished, take everything learned and the engine, and scale it up. By that time, hopefully timewarp and automated flights will mean your not waiting hours for each flight.