Japanese outfit's private Moon mission enters Lunar orbit The possibility of the world's first successful privately funded and operated Moon landing is looking a little more likely after Japanese aerospace outfit ispace announced its Hakuto-R lander successfully completed a lunar orbit insertion maneuver on Tuesday. The lander took a three-month journey to the Moon after launching …
My first thought would be - How does going nearly 4 times the distance past the Moon give a lower energy transfer than going direct?
My best guess would be that out there you can start thrusting sideways to gain orbital velocity, and then by diving in toward the Moon's orbit you can more cheaply match the Moon's orbital speed and position than if you try to gain all of the orbital speed whilst on the way out to the Moon.
If that's the case then hats off to the boffin that came up with that one.
I'm no orbital mechanics expert (much the opposite, in fact). But bear in mind that it takes energy to speed up, and energy to slow down, that your destination isn't just a place, it's an orbit, and that the Earth and the Moon are in motion. Going the shortest *distance* to the Moon would mean leaving Earth orbit at a point where you are travelling at ninety degrees to the Moon's orbit, powering out radially to the Moon's orbital path, and then decelerating, timing it so you reach that orbit when the Moon is actually there. But if you did that, you wouldn't be in orbit around the Moon; the Moon would flash past you and off into the distance, and you'd be left sitting there like an idiot. I imagine you want to leave Earth's orbit on a curved path such that you're expanding out towards the Moon's orbit and maybe catching up to it, such that when you catch up to it, you minimize the burns needed to put yourself in orbit around it, but I wouldn't want to be too specific, because I don't know any of the orbital velocities involved off the top of my head.
> travelling at ninety degrees to the Moon's orbit, powering out radially to the Moon's orbital path,
There are no straight lines in space. Everything moves in a curve.
> timing it so you reach that orbit when the Moon is actually there. But if you did that, you wouldn't be in orbit around the Moon; the Moon would flash past you and off into the distance
You get captured by the moon's sphere of influence (gravity) which adjusts your trajectory - this is how slingshot flight plans work. Then once at your moon periapsis you burn retrograde (backwards) to slow down and enter orbit. This is the insertion burn mentioned in the article.
Orbital mechanics is actually quite simple. Its the getting things there such that they don't explode / implode / freeze / etc that is the hard part.
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