My Astro Photo Of The Day

[Autumnlicious]

First off, the asteroids orbit intersects with just inside Earths and Mars orbits. To get to it before it gets a gravitational assist (valid term of art), one must merely launch into a highly elliptical orbit, obviously increasing eccentricity over time, until one attains a velocity that would coincide with making landing on the asteroid.

When you are ready to land on the asteroid, you are matching the asteroid's orbit, which is an martian transfer orbit. So you've already burned all they fuel you would need to put yourself directly into your own mars transfer orbit even without an asteroid. Tada....

Nice to have a giant rock that provides living space and a cache for supplies, no?

When the asteroid does a flyby Mars, and thus a gravitational assist (calculated so as to allow the next half orbit), spacecraft merely need to disengage and aerobrake.

The majority of energy in this system to adjust the orbit comes from the planets, like two people playing catch. Another piece of the proposed enforced resonant bi-elliptic orbit is that it moves at twice the normal keplerian speed of an object.

A modified heliocentric elliptical orbit where at aphelion and perihelion the object passes out of solar sphere of influence into a local hyperbolic orbit under the sphere of influence of one of the planets is possible. But to keep this up like a tennis volley requires course planning so precise that extensive fuel burn would be required during each pass to ensure to the object pass through the correct window.

Precision is definitely a problem. The fuel burn, I am not too worried about. Then again, it would be nice then to inspect this idea in full, no?

As to twice keplarian velocity, keplarian with respect to what? If to the planet it implies no gain. You need to exceed the Keplerian orbital velocity by at least a factor of 1.4 anyway just to leave planetary sphere of influence to go into a transfer orbit to where ever you are going.

with respect to the planet.

If you manage to make your ship match the orbit of the asteroid so as to be prepared to land on it, then you would have placed your ship under exact same gravitational influence that the asteroid would be under, and your ship would thus follow exactly the same path your asteroid would have followed, even if there was no asteroid.

Yes.

So your ship would coast to mars in exactly the same way your asteroid would have. Once you are there, your ship would sling shot around mars just like your asteroid.

One needs to merely change their velocity vector just enough to graze the atmosphere of Mars such that one continues in a degenerating orbit. Aerobraking.

http://en.wikipedia.org/wiki/Aerobraking

If you plan to depart from the theoretical orbit of your asteroid so as to land, well you have to burn the same fuel to so this either way. Orbital mechanics ring a bell? Along the way if your asteroid didn't need any fuel, neither would your ship if you place it into the same orbit as you would have placed your asteroid. If your ship needed some fuel to do course corrections, your asteroid would need a whole lot more.

True. I am assuming that some significant section of the asteroid would be dedicated purely to power generation and engines to allow for course adjustments.

However, you once again neglect the primary goal of using a giant rock - radiation shielding. Yes, changing orbital parameters to ensure the appropriate windows would be met is difficult.

As to the weight of the ship's shielding, let's compare that to the fuel weight. Your ship only needs to carry fuel to make one set of orbital correction for a small ship to get into the Mars transfer orbit, and one set of correction to come out of Mars transfer orbit into either a martian orbit or a Mars aerobrake orbit.

May I point out that radiation shielding for cosmic rays is rather large and heavy for the amount of volume it would protect? May I also point out that the asteroid is a giant radiation shield. No doubt there are sections inside that are less irradiated compared to the outside, required no doubt less of that heavy ass shielding.

One of the primary issues with getting to Mars lies in defeating the radiation bath in space. So far, the prevailing idea I've heard requires the assembly of a Mars bound ship inside low earth orbit, as there would be no way to launch a complete, shielded vehicle up.

Your asteroid with its bonus shield would need to carry all the fuel for for orbital correction during each leg of its back and forth between mars and earth. One missed orbital window at either end of its elliptical orbit, and the thing slings off into the wild black yonder, needing another few dozen years to put back into correct orbit.

I keep hearing about "all this fuel", and the only thing I am thinking about is: you mean fuel for ion thrusters? Oh dear, RTG's will /never/ provide the required power.

I do concede that a fuck up in utterly missing an orbital correction window would result in a whirlwind tour of the outer solar system. Indeed, that would be "bad".

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Oh, and to follow up on the big emphasis on shielding, something that seems to be missed as a point - I must point out that one cannot get away without cosmic ray shielding. In fact, metals cause secondary radiation scatter of cosmic rays to be worse than had they (the cosmic ray) merely passed through your body. This is due to the nature of metal and light, high and low energy. So far liquid hydrogen, hydrogen rich plastics or massive magnetic fields are thought to be the solution to such a problem.

I ask, why not use a pre-existing volume and mass for intercepting that nasty shit, burrow into it, and therefore devote your resources to something else. Like changing orbital parameters and accumulate shit on the asteroid like a giant fucking space loading dock.