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Gravitational attraction is determined using G (m1m2)/r^2

Which indicates the force is inversely proportional to the square of separation of the bodies

Of the terrestrial planets Mercury, Venus, Earth, and Mars - Venus and Mars are immediate neighbours to Earth. Any quantity of missions have studied either.

Venerean gravity is almost 90% of Earth's own. Venus is also closer to Sol than Earth - figuratively downhill that is. All three bodies (Venus, Earth, Mars) being in motion there may be occasions when Mars is perhaps physically closer. Yet Venus appears to have the following advantages -

  • Further downhill in the Solar System
  • Masses almost the same as Earth; ergo larger sphere of influence
  • Average separation from Earth ~25 M Miles (Mars average distance from Earth is ~140M Miles)

Does a mission to Venus orbit require less propellant than a similar mission to Mars with the same payload?

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    $\begingroup$ Round trip or one way? $\endgroup$ – TildalWave Sep 25 '13 at 12:30
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    $\begingroup$ @TildalWave: Does it really matter that much? $\endgroup$ – PearsonArtPhoto Sep 25 '13 at 12:49
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    $\begingroup$ @PearsonArtPhoto You can use aerobraking to drop from transfer orbit speed to orbital speed, only a small circularization burn is needed. You can't leave orbit that way, though. Thus the Δv requirements are not symmetric. $\endgroup$ – Loren Pechtel Nov 24 '14 at 21:01
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    $\begingroup$ @PearsonArtPhoto: the cost to land on venus is quite low but the cost to leave is enormous, because of the very dense atmosphere. $\endgroup$ – njzk2 Jan 14 '15 at 21:31
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I'm going to only start calculating delta v from Earth Escape, using this Delta V table. Furthermore, I'll assume we are starting from LEO, and we want to get in to a low orbit of the appropriate planet. The numbers turn out to be:

  • Venus- 3.5 km/s to Venus, 3.3 km/s to Low Venus Orbit
  • Mars- 3.6 km/s to Mars, 2.1 km/s to Low Mars Orbit.

Bottom line is, it takes more Delta v to orbit Venus because of it's higher gravity. But what if you are willing to accept a higher orbit? The minimum orbit is a capture orbit. Venus has a delta V of 0.4 km/s, while Mars requires 0.7 km/s. Thus, the minimum orbit is slightly easier for Venus than Mars, but if you want to get in to a better orbit, Mars is easier. If you use aerobraking, then Venus becomes slightly easier.

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    $\begingroup$ Thanks for using my cartoon delta V map! Also of interest are capture orbits. From Venus Hohmann to Venus capture is .4 km/s and from Mars Hohmann to Mars capture is .7. Both of these capture orbits can have periapsis in planet's upper atmosphere. Each time a ship makes a periapsis pass through upper atmosphere, apoapsis is lowered. Thus aerobraking can lower a capture orbit to a low circular orbit. That's what I attempted to indicate with the red vines. $\endgroup$ – HopDavid Mar 28 '14 at 22:54
  • $\begingroup$ It's a fantastic map, I've used it frequently! Thanks for making it! $\endgroup$ – PearsonArtPhoto Mar 28 '14 at 23:07
  • $\begingroup$ @HopDavid And aerobreaking is going on at Venus right now! Venus Express ends its mission by trying it out, which will be helpful for future (much needed!) Venus missions. $\endgroup$ – LocalFluff Nov 24 '14 at 18:56

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