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Old 11-05-2019, 01:51 PM
Little Nemo is offline
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Join Date: Dec 1999
Location: Western New York
Posts: 82,773

Can somebody explain these space travel physics to me?

I was reading Randall Munroe's new book How To and he talked about launching something from the Earth into the sun. And he said that the best way (assuming you're not in a hurry) would be to launch it away from the sun. The sun's gravity would pull on your item and eventually slow its speed down to zero and then begin pulling it back towards the sun where it would eventually end up. He said that launching the item directly towards the sun would be quicker but would require more energy.

He did not elaborate on this point. And I am confused. I'm assuming he's right - he used to work for NASA and I'm sure he knows a lot more about space travel than I do. But I don't see why it would take more energy.

I'm assuming (perhaps wrongly) that it takes the same amount of energy to launch an item off the Earth regardless of which direction it's being sent to. And it seems to me that if you launched towards the sun initially, your launch speed would be working with the sun's gravity rather than against it.

Can somebody tell me where I'm wrong?


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