Talk:Rich Purnell/@comment-31131540-20170124000050

Ok, I am not professor in astrodynamics, but I do fly to Dres in Kerbal Space Program without any assists.

This "maneuver" is a joke simply because of two things:

1) in order to make orbital rendezvous, the speeds and directions need to match. The distance can be matched by burning at proper time, so its not relevant. That means, to match asteroid, the spaceship must match its orbit. In order to catch food from Earth, the food transport NEEDS to match the ORBIT of flying by spaceship. That means - food transport will have to burn the equal amount of fuel! Virtually its irrelevant if spaceship takes something from food transport or not - they will be flying together side by side. So - why match orbits? Just to match SPEEDs. In astrodynamics - total orbit size = speed. If orbits are not matched on rendezvous, the spaceship will SMASH the food transport.

2) The very same applies to "Mars slingshot". Either spaceship burns retrograde to drop speed and enters stable orbit around Mars - or it will SMASH into capsule.

I am not a genuos to tell this is one huge BS.

More points:

- it is just fine to burn in Earth proximity to increase engine efficiency due to oberth effect. However, its completely useless, because the ship was on the way from Mars and the transfer window is long closed - meaning it will take either years and years to get to Mars - or burning lots and lots of fuel for "bruteforce" maneuver closer to Sun proximity. So any benefits of oberth effect are gone. They could however do oberth burn, say, near Mercury - provided its somewhere on the other side of the Sun. It will still take years to get back though - because they would be nearly out of fuel.

- more popcorn - pause in the scene where spaceship recieves these new calculations, in that exact scene - the spaceship engines are shown burning the fuel! This is again total nonsense, because there are three burn periods for interstellar travel: injection burn(to match orbit intersection with target), correction burn (midway to target, its usually very small) and deacceleration burn (to decrease apoapsis and take stable orbit). So why are they burning the engines mid-flight?! Mid flight the engines are DEACTIVATED.

- Now, let me go back to planting more potatoes in Mars useless dust. Because its dust. Its not soil. Soil and dust are different in composition.

The film is a total facepalm, I am damn speechless. Just buy KSP and learn it instead of paying for this waste of film. They could reduce the orbit near earth to stable orbit, rendezvous with fuel and supplies, then burn bruteforce to Mars. That is realistic.