realism?

[jaunco325]

I got the feeling that in the game, it's pretty easy to launch payload into space. how realistic is that?

[king of nowhere]

depends on how you define realistic.

First of all, even though ksp is a pretty good simulator with a lot of complex engineering, it still leaves out all the nasty details of engineering. setting up all the pipes and pumps for the fuel, finding a metal alloy that can survive the extreme working conditions of rockets, setting up some passive heat transfer system to avoid your satellite being baked in the sun or freezing while shadowed.... there are dozens and dozens such problems that ksp simply does not address.

however, we did practice with all that for decades, and by now we're pretty good at throwing stuff in orbit, so I would say that launching to orbit is indeed relatively easy... but terribly expensive. ksp currency is very easy to come by, in real life it takes tens of thousands of dollars to send a single kg of payload in space. And for that you need a spaceport, with all the personnel working in it, and factories with the required know-how, and all that is, again, terribly expensive.

so, launching stuff in space is easy in the sense that if we want to do it, we can do it. but it has huge practical limitations.

finally, you may have noticed that the game has much smaller planets than real life. kerbin has 600 km radius, earth has 6370. kerbin orbit requires some 3400 m/s, earth orbit requires 11 km/s. On the other hand, engines and fuel tanks are less efficient, to partially compensate, and the net result is that rockets work similarly, but it takes a lot less time to orbit - else a launch would require half an hour.

however, this allows a lot of exploits that simply would not work in real life. from ssto rockets with 20% payload mass - which would simply not be possible if you need 11 km/s to orbit - to spaceplanes - which take advantage of using jet engines to accelerate at orbital speed, because 2 km/s is orbital speed, while on earth you can still use a jet engine to reach 2 km/s, but that's nowhere near enough for orbit.

So, a lot of the more optimized ways of ksp are not possible in real life.

[Davi SDF]

Like it has been already said, KSP makes a lot of things much easier to acomplish than in real life. It's a trade-off for fun.

[jimmymcgoochie]

3 hours ago, king of nowhere said:

earth orbit requires 11 km/s

Actually, getting to low Earth orbit takes a lot less than that- it tends to be 9000-9500m/s in my experiences with RSS and RO.

Kerbin being a fraction of Earth's size does make things much easier, since accelerating to hypersonic speeds with air-breathing engines takes you most of the way to orbital velocity (1500m/s out of 2200m/s) whereas on Earth you're not even close (1500m/s of 7800m/s). I once made a stock parts replica of the Black Arrow orbital launch rocket, which in real life could put a ~150kg satellite into a relatively low Earth orbit; the KSP version had nearly identical delta-V in all its stages, but managed to send a ~500kg probe to the surface of the Mun and back.

Besides the difference in scale, there are a lot of things about space travel that KSP doesn't include for the sake of making the game fun for more than the hardcore simulator-ists: ullaging, residual propellants, performance variation and engine failures, life support, speed of light delay for communications, crew health and radiation exposure, actually building and testing the rocket in the first place before launching it... There are plenty of mods out there to add realism in many different forms, but the learning curve for KSP is steep enough as it is without having to get to grips with all of that at the same time so they're not a part of KSP and to my knowledge won't be included in KSP2 either.

[jaunco325]

I was referring specifically to the ratio of payload to the total weight of the ship.
While I knew the planets here were smaller, I thought the engines would be nerfed to match. But from what I've read, maybe it's not? so the engines are nerfed but not enough to make them comparable IRL? Does that mean that the mods that make the engines more realistic would make things easier for me instead of complicating them?

Edited March 15, 2022 by jaunco325

[jimmymcgoochie]

Payload fractions in KSP are much higher than in real life because while engines and fuel tanks are worse than in real life they’re not proportionately worse- in fact stock parts are rather overpowered in the stock scale Kerbol system. It’s possible to get payload fractions of over 20% in KSP even without using any cheaty exploits that can create thrust out of nowhere or lift without drag, whereas in real life 5% is good and 10% nearly impossible.

[jaunco325]

Is there any way that the launches are more complicated in this sense without downloading the map of real planets?

[KerikBalm]

19 hours ago, jaunco325 said:

I was referring specifically to the ratio of payload to the total weight of the ship.
While I knew the planets here were smaller, I thought the engines would be nerfed to match. But from what I've read, maybe it's not? so the engines are nerfed but not enough to make them comparable IRL? Does that mean that the mods that make the engines more realistic would make things easier for me instead of complicating them?

To get more realistic payload fractions and ship performance, you need to rescale the system by 3-6x.

I currently play at 6.25x with stock parts. It's hard, but doable.

[Entropian]

1 minute ago, KerikBalm said:

I currently play at 6.25x with stock parts. It's hard, but doable.

I (normally) play RSS with stock parts, and it's definitely hard but certainly doable as well.

[jaunco325]

12 minutes ago, KerikBalm said:

To get more realistic payload fractions and ship performance, you need to rescale the system by 3-6x.

I currently play at 6.25x with stock parts. It's hard, but doable.

and how to rescale the system? can you have a problem with mods this?

Edited March 15, 2022 by jaunco325

[KerikBalm]

11 hours ago, Entropian said:

I (normally) play RSS with stock parts, and it's definitely hard but certainly doable as well.

Well, that's harder than reality. Engines in reality have much higher twrs, tanks have better mass ratios, hydrolix engines get you 450+ Isp, but in KSP the chemical engines top out at 350 (380 with making history)

11 hours ago, jaunco325 said:

and how to rescale the system? can you have a problem with mods this?

I use Kopernicus and sigma dimensions to rescale it

[Pds314]

1. Kerbin is 10.6 times smaller diameter than Earth with proportionally lower escape energy.

2. Kerbal rockets use a common fuel which is storeable, non-cryogenic, reasonably efficient, fairly dense, hypergolic, nontoxic, does not boil off, and does not damage the physical or chemical structure of tanks or engines in any way. Few, if any, real rocket fuels have all of these desirable properties. Real life rocket fuels are diverse with many strengths and weaknesses and not interchangeable between engines.

3. Life support isn't an issue in KSP. You can literally send someone on decades long interplanetary trips in a spacesuit. IRL, life support is perhaps the main barrier to crewed interplanetary missions.

4. Kerbal Liquid-fueled rocket parts are 3-10x more durable than realistic, but arguably 3-10x heavier too.

5. Magic torque disks aren't a thing in real life. Real reaction wheels, control moment gyroscopes, and all similar devices are easily satureable, require momentum dumping, and most types are much weaker than in KSP.

6. Kerbal rocket bells can't be destroyed by using them in overly thick atmospheres that cause underexpansion. They do lose efficiency though.

7. KSP's aerodynamics are different. Lift and drag are far higher than in reality and wing shapes are far more forgiving. High mach L/D is unreasonably good in KSP. Although low mach L/D is unreasonably bad. Parachutes are stupidly effective as well.

8. Kerbin has no axial tilt and the main launch site is equatorial on an east coast.

9. All liquidfuel engines are infinitely restartable without any starting fluid, deeply throttleable, efficient when throttled, and can run for arbitrarily long periods. Some real life engines don't carry any way to start them in-flight, can't throttle below 80%, and lose efficiency when throttled.

10. Fuel flow is extremely generous. Fuel tanks in KSP can easily force fuel against the counter pressure in another tank for no added weight.

11. Fuel movement in the tank isn't modeled in KSP. Landers can aggressively rotate without having to fill their tanks with baffles to stop fuel slosh. Rockets in zero G can start with no concern for ullage.

12. Kerbal components are totally reliable no matter how long you use/abuse them. Real rocket engines often have a time before overhaul measured in minutes. Just long enough you can discard it at the end of the stage. Many also are not safe to operate continuously even if they are restartable and reuseable. Control Moment Gyros are very likely to fail IRL after years in space. Nothing ever just gets wrecked by cosmic rays or micrometeorites or X class flares either.

13. KSP has an anti-liquidfuel bias. Almost every other engine type in the game is blatantly overpowered compared to it's real life counterpart. Liquidfuel engines have 1/5th the TWR they should. Liquidfuel Tanks are 10 times heavier than necessary. Afterburning jets are twice as efficient as they should be and get vastly more thrust increase from mach than they should. High bypass jets get triple the thrust they should and don't lose efficiency with speed. All jets need way less intake than realistic. SRBs are pretty realistic. Ion engines are 1000 times as high thrust as they should be and nuclear engines don't horrifically irradiate everything that strays past the shadow shield. Monopropellant has no downsides of explosivity or toxicity and fairly reasonable performance. BG props literally violate the conservation of energy. Literally the only category of engines that perform worse than their IRL counterparts is Liquidfuel engines.

14. Gravity is always a one body problem with no mass concentrations or equatorial bulge to worry about in KSP. This means every orbit above the atmosphere is stable without any need for stationkeeping.

15. Electricity is really OP. IRL ion engines require stupid amounts of electricity to generate tiny amounts of thrust. In KSP, they can create kiloNewtons from a reasonably sized solar array.

16. Rocket launches are instant in KSP, as are technology development and facility upgrades. You can build and launch a moon lander within an hour of starting your space program. In real life these all take weeks, months, or even years.

17. Creating tooling for fast and cheap construction of parts isn't considered in KSP. Meaning there's no reason to stick with a standardized tank size or whatnot.

18. Kerbal jetpacks have 100 times the Delta-V of their IRL counterparts and weigh significantly less. Even if EVAFuel is not cold gas but a more potent chemical fuel, getting ~600 Delta-V from that little fuel is impressive.

19. There is no risk of part failure or changes in material properties from normal variations in environmental conditions. IRL, some components used in spacecraft such as the O rings in the shuttle SRB have been extremely sensitive to temperature.

20. KSP has no wind or turbulence. Air doesn't move and can't threaten the performance or safety of a vehicle in any way.

21. Kerbin's atmosphere is conveniently about the right height for a rocket to burn constantly prograde to orbit, never stopping its gravity turn as it enters low orbit. IRL, the atmosphere is close enough to Earth's surface that most efficiently-designed rockets will lack the performance to do this, and instead will launch on a trajectory noticeably above their target orbit, then use the extra time gained from higher altitude to burn somewhat above prograde, trading cosine and gravity losses for lighter stage weight.

Edited March 16, 2022 by Pds314