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An answer to the following question mentions a free online calculator for long-distance space travel.

Software to ease my interstellar travel calculations

I'm looking for a 3d simulator that accurately and visually shows transition from orbit and other aspects of interplanetary (rather than interstellar) travel.

I don't care about trading between planets or social interactions or wars - just the travel aspect.

I'm thinking of purchasing Kerbal Space Program, https://www.kerbalspaceprogram.com/en/ which although it has cartoon green aliens as an extra, does, I've heard, have accurate physics.

Does anyone have experience of this software? Will it serve my purpose?

Does anyone have other recommendations?

Requirements

I'm hoping for software that shows heavenly bodies and spacecraft visually and in 3d from variable points of view, preferably with a zoom facility. The graphics don't have to be ultra-high-definition, just easy to recognise. I want to take account of amounts of thrust/fuel needed with realistic rocket equations built into the software (so I don't have to do them!) and to be able to travel from orbit around the home planet to orbit around the destination with course corrections where necessary. Takeoff from the planetary surface would be a bonus but not vital.

Worldbuilding - I want to build a fictional solar system with fictional planets but that has exploration and so on with realistic physics.Therefore the ability to place fictional planets around a fictional sun is highly desirable.

NOTE: There is a tag especially for software-recommendations so I don't believe this question should be closed as 'opinion based'.

There has been some difference of opinion about whether to use 'hard-science' or 'science-based'. I've finally settled on the latter. I don't want rocket equations in the answers, I just want the software to be as true to real physics as reasonably possible on your average Windows 10 machine.

EDIT: I suppose I was hoping for something where I would say, "I'm in orbit on planet X and I'd like to be in orbit on planet Y - Please show me what fuel I need to carry, how long it will take me and the optimum trajectory". Judging by the answer by PSquall, I guess that's a very big ask. If that's not available then the nearest approximation will do nicely.

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    $\begingroup$ "does, I've heard, have accurate physics." - accurate enough for most purposes, but it does not perform full N-body simulation. Instead, it uses Sphere of influence model. Difference in results is small, but it is there. $\endgroup$
    – Mołot
    Commented Nov 26, 2018 at 12:12
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    $\begingroup$ You might want to put your pruposes into en enumerated and possibly weighted list of requirements. makes this easier to answer $\endgroup$
    – dot_Sp0T
    Commented Nov 26, 2018 at 12:29
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    $\begingroup$ Software recommendations have previously, at least, been considered on topic if there is a clear connection to worldbuilding. This seems to me to qualify. $\endgroup$
    – user
    Commented Nov 26, 2018 at 12:44
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    $\begingroup$ Obligatory xkcd $\endgroup$
    – adaliabooks
    Commented Nov 26, 2018 at 21:29
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    $\begingroup$ "in orbit on planet X and I'd like to be in orbit on planet Y - Please show me what fuel I need to carry, how long it will take me and the optimum trajectory" with "realistic rocket equations built into the software (so I don't have to do them!)" get Kerbal Engineer Redux and MechJeb. Those make your job in KPS just building rockets or spaceplanes, which you can fly manually if you want to. $\endgroup$
    – Mazura
    Commented Nov 27, 2018 at 4:42

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Kerbal Space Program is an homage to the developments in the Space Race of the Cold War. You will see names like Wernher von Kerman or Gene Kerman to remember the old Apollo and Gemini flights, but even near-future propulsions are implemented, although the game doesn't take itself too seriously.

The simulations are, as Mołot stated in his comment, not n-physics based, but work with Sphere of Influence. On top of that, the Kerbal System (the equivalent of the Solar System) is roughly 1/10 downscaled to the real solar system, but still with the same surface gravity. Overall, I would say the feeling is much the same, the orbital mechanics are the same, but with many differences in technology. I recommend it, if you want to learn the basics of orbital mechanics in a practical way.

Two points I need to add:

  • The game is not easy. It is literally rocket science.
  • If you don't like the simplifications made in the simulation, there are mods that overhaul the complete game. Real solar system, accurate planets and rocket engines with equivalents in the real world, even an n-body simulation. But, all these modifications make the game even more complicated and harder. The game on its own is very laggy, depending on the size of the simulated rocket, so modding it even further most likely won't make it any better.

And if you really want to take a look at planetary transfers, look for the Hohmann Transfer. That is the basic for every current interplanetary transfer

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    $\begingroup$ Note - there always been at least one "active" mod that changed Kerbol into our solar system, with correct distances and gravity. forum.kerbalspaceprogram.com/index.php?/topic/… $\endgroup$
    – Mołot
    Commented Nov 26, 2018 at 13:12
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    $\begingroup$ @chaslyfromUK Kerbal is hard, but then, so is space travel. It doesn't have a simple learning curve, but it is really the best way to get intuition about how space travel really works. $\endgroup$
    – kingledion
    Commented Nov 26, 2018 at 13:16
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    $\begingroup$ @chaslyfromUK start with in-game, then switch to real one and see how harder it got. Then see how mod was done and mod it again to suit your needs. At least that's how I would go around it. On the other hand, I have KSP license anyway, bought for fun, so it doesn't cost me anything. $\endgroup$
    – Mołot
    Commented Nov 26, 2018 at 13:19
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    $\begingroup$ @chaslyfromUK There is a mod, KSP Trajectory Optomization Tool, which will do those calculations of "I'm in orbit on planet X and I'd like to be in orbit on planet Y - Please show me what fuel I need to carry, how long it will take me and the optimum trajectory." $\endgroup$
    – Skyler
    Commented Nov 26, 2018 at 15:30
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    $\begingroup$ Also with regard to the patched conics: even N-body modeling isn't quite accurate. That's why we have models such as EGM96 which model spherical harmonics in gravitational effects on Earth out to degree 360. No matter what you do, there's always going to be some corner case you didn't plan for. So might as well start with something easy (like patched conics) until you know enough to realize that you need to go to the next step. $\endgroup$
    – Cort Ammon
    Commented Nov 27, 2018 at 1:53
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If you are content with flying around our solar system, I'd recommend the NASA trajectory browser.

It lets you find realistic flight paths to many large and small objects in the solar system, for example starting from LEO and inserting into an orbit around Europa. The browser assumes standard rockettry, meaning flight plans using discrete burns with a defined delta-V to reach your destination. Sci-Fi stuff like constant acceleration rockets cannot be modelled. By playing with the maximum allowed delta_V you can simulate more powerful rockets.

You'd still need to calculate fuel loads manually ina spreadsheet or similar, using this form of the rocket equation for each burn (start your calculation with the last burn, as the fuel for the last burn is part of the payload for the second to last etc.): $M_f=1- e^\frac{\Delta v}{v_e}$, with $M_f$ the propellant mass fraction and $v_e$ the exhaust velocity. $v_e$ is another parameter you can play with to get more science-fictional rockets.

How does this stack against your requirements?

  • 3d view - no
  • graphic representation - yes, simple/abstract
  • travel times - yes
  • fuel demand - only with the help of a spreadsheet
  • fictional solar system - no
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  • $\begingroup$ That looks good. Perhaps it might be used to check the correctness of my Kerbal journeys in our solar system. This will give me a feeling for other planetary systems. $\endgroup$
    – chasly - supports Monica
    Commented Nov 26, 2018 at 16:08
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    $\begingroup$ "Sci-Fi stuff like constant acceleration rockets" are not that fictional. Ion propulsion has low enough thrust that approximating burns as impulses no longer works. $\endgroup$
    – Phil Frost
    Commented Nov 27, 2018 at 3:27
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STK, https://www.agi.com/products/engineering-tools , is a tool used in creating many such visualizations by NASA, SpaceX, etc.

It's an engineering tool, so it's very realistic, but it might be a bit too much for a lay person.

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  • $\begingroup$ Had a quick look. Seems worth pursuing. $\endgroup$
    – chasly - supports Monica
    Commented Nov 26, 2018 at 21:21
  • $\begingroup$ They have a free version (limited, not sure if what you need is included), and also a full 1 month trial version. Also, I would suggest reaching out to them, they might be able to set you up with a longer trial or something. They are very friendly and accommodating. $\endgroup$
    – ventsyv
    Commented Nov 26, 2018 at 22:52
  • $\begingroup$ I use STK professionally, and +1 this answer. $\endgroup$
    – cms
    Commented Nov 28, 2018 at 20:05
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Universe Sandbox

https://store.steampowered.com/app/230290/Universe_Sandbox/

Very pretty, and as accurate as you are going to get on physics without a supercomputer doing detailed sums.

A little bit short on autosolving transfer orbits and such unfortunately.

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I can't believe no one's mentioned Orbiter 2010! Its similar to KSP, but without the building part, and with full-scale, n-body physics. There is a mod for it called Interplanetary which allows you to input your location, your destination, and the maximum time you have to get there, and it will tell you how much dV you need and give you a trajectory.

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I would go for Kerbal Space Program as well, but here's a game I recommend you have a look at alongside KSP:

Rogue System

I like this game because it tries to do something new and different. It brings a DCS-style level of simulation, but to a space game.

Yes, this means that it simulating something that doesn't exist, but the game's author has produced something that, to me, feels real.

Unlike KSP, with moveable cameras and views, in this game you only see the world through the eyes of your character.

It's still in early access, but in my view there's plenty in the game to keep you occupied.

I still haven't completed an orbital transfer in this game. In KSP I've sent manned missions to Duna (KSP's Mars), have landed multi-part bases on the Mun and Minmus, and remote probes to all corners of its solar system without problem.

In Rogue System I still have trouble turning on my engines.

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    $\begingroup$ "In Rogue System I still have trouble turning on my engines." Haha! Sounds like my abortive and abandoned efforts to play Tomb Raider beyond the first obstacle. $\endgroup$
    – chasly - supports Monica
    Commented Nov 26, 2018 at 17:11
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Goddard Mission Analysis Tool

GMAT is free software from Goddard SFC that can do most of what you are asking to do, provided you already know a little about orbital mechanics. You can find it here.

It has Windows and Linux binaries, and can be run from a GUI or in script mode (you want the GUI, I would imagine). I use it occasionally at work for some geocentric orbits, but it is specifically designed for interplanetary missions.

The documentation is pretty good too, and there are several examples you can tweak to meet your needs. I used their Earth-Mars transfer example and got it running in about 5 minutes. Here are the screenshots: enter image description here enter image description here enter image description here

The celestial bodies can be customized (planets added, removed, moved, increased in size, etc) so it should be good for a fictional solar system.

Good luck!

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If you're just looking for required thrust, then take a look at some of the calculators created specifically for Kerbal Space Program, like this one: http://ksp.olex.biz/

Here's a comprehensive list:

https://wiki.kerbalspaceprogram.com/wiki/Calculation_tools

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