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.

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

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

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.

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.

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.