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Comment by Mahn | Hacker News Reader

Does anyone else think NASA should reconsider their plans for a manned mission to Mars? With Europe, Ceres, Enceladus, Ganymede and many more promising moons out there it seems kind of a waste to spend time, effort and capital in Mars now.

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Mars would be the first long-term space based mission. If you've only made a pillow-fort (ISS), or stayed in a tent in your backyard (moon), wouldn't you try to camp in your local state park before backpacking into the wilderness?

Europa is a lot further away than Mars [1]. Every extra 4600 m/s of delta V in the mission means another factor of e in the ratio of initial to payload mass. At least until we develop better high efficiency rockets.

[1] http://i.imgur.com/AAGJvD1.png

I'm simultaneously embarrassed and proud to say that the only time I've seen a subway map like this of a Solar system, it was of Kerbal.

In practice, the ΔV differences are actually way smaller than that chart suggests. Those figures are for direct transfers (per the legend). But if you allow indirect trajectories with gravity assists [0], that makes things drastically cheaper. To intercept Jupiter, you can steal much of the needed ΔV from flybys of the inner planets (at the tradeoff of time, waiting to go around the sun multiple times). And maneuvering within Jupiter's gravity well can be practically free, by flybys of the Galilean moons. The map tells you 8,890 m/s to intercept Europa, which would be horrifying, but none of that actually needs to be propulsion.

[0] https://en.wikipedia.org/wiki/Gravity_assist

Keep in mind, for a human mission, you want to minimize time, rather than deltaV. Gravity assists will take a lot of time, as you spend a lot of time waiting for the encounter.

Furthermore, that chart is likely computed via a direct Hohmann transfer, which is one of the most efficient transfer maneuvers available. It also will take a lot longer.

For practical human travel to destinations farther way, you need to perform the so called "star wars maneuver", which is going essentially from A to B in a more or less straight line, which will cost a LOT of delta V.

> Keep in mind, for a human mission, you want to minimize time, rather than deltaV. Gravity assists will take a lot of time, as you spend a lot of time waiting for the encounter.

True, but we could throw the big ship with all the supplies into a flight path that gains a lot of momentum around the inner planets and intercept it with a much smaller craft only loaded with enough fuel to get the astronauts to the transit ship (and back, if necessary).

There is exploration and there is colonization, which to some degree are orthogonal and to some degree complementary to each other, but they are not the same thing. Manned missions to Mars would mostly be about colonization, though exploration would be a significant side benefit. Mars is by far the most promising candidate for colonization (with the potential for using local resources to enable an early level of significant self-sufficiency, increasing over time) which would help kickstart our capabilities in interplanetary spaceflight in general, both manned and unmanned.

For manned missions when a major "location" of the mission is the space in-between Earth and the destination, Mars becomes a much more lucrative first destination because the duration in transit is much shorter.

It's at least 13 months to get to Jupiter for a probe, and reasonably much longer for a man-rated craft.

Jupiter's moons are exciting, but have huge radiation concerns. Still trying to solve that for the flight to Mars.

I saw some students prove that water can be an effective radiation barrier. The only problem is that it's heavy. If we were already going somewhere with a lot of water...

Ganymede is the exception here, due to the fact that it is the only Jovian moon with it's own magnetosphere.

Absolutely. We can learn much more about life in our universe by exploring Europa, Enceladus and Titan. All can be explored for much less than a Mars mission.

They are completely separate missions. Mars is about sending humans somewhere other than the moon. It's less about scientific discovery and more about engineering and exploration discovery - we're doing it to learn about Mars sure, but moreso we're doing it to see if we can.

Mars is the next step in humanity's long term (hundred of thousands of years) survival. If we ever intend not to be at the mercy of gravity, we have to get off earth. We've been to the moon, which is gravitationally constrained to earth, and is only a three day journey (with many chances for safe aborts). We've conquered LEO and now know more about our planet than we could have dreamed up 20 years ago. Mars is a completely different challenge, and by going to Mars we'll develop the first bits of technology that will help us off our deathtrap of a cradle.

These two missions can coexist. We haven't developed the technology to send humans that far out into the solar system so we should continue to send probes.

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