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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

Is there a limit to how fast you can go using gravitational boosts from the sun and planets?

NASA frequently uses the gravitational slingshot method to boost the speed of spacecraft destined to travel to the outer planets. If the satellite passes close enough to a planet on the right trajectory, it can get a boost to its speed that would send it to its destination at a higher speed. Like a ball being thrown up in the air, to reach greater distances from the sun you need higher speeds. For a single encounter, the amount of speed boost depends on just how strong the gravitational field is that the planet can provide before the spacecraft enters its atmosphere or crashes to its surface. The deeper it penetrates the gravitational field, the larger the boost increment. For Jupiter, its mass and size are so great that a pretty big boost can be gotten from only a moderate encounter. For the earth, or one of the other planets, the spacecraft would have to swing by within a few thousand kilometers of the surface to get an appreciable boost. So, yes there is a limit to the maximum speed or 'delta-V' you can get from each planet without impacting its atmosphere or surface.

Off hand, I do not know what these values are for particular planets, but I would guess that using Jupiter, the largest delta-V is probably somewhere near 100,000 miles per hour ( 160,000 kilometers/hour). Perhaps someone out there on the NET that works in astrodynamics could give me a better estimate!

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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.