# Can you go over the asteroid belt rather than through it?

If the asteroid belt is a disc, couldn't you go above or under it rather than through it? Or does it form a sphere around the terrestrial planets orbits? Edit: I know the chance of hitting an asteroid is extremely low, so just think of it theoretically

• Note that every outer-planet mission so far launched has done so with zero concern for the locations of small asteroids in the belt, and thus far none have hit anything. Feb 5 '18 at 22:41
• Movies depict asteroid belts as places that are densely packed with boulders. This depiction is so very far removed from reality that it isn't even funny. It's just sad. Feb 6 '18 at 1:22
• @DavidHammen: The one movie getting a passage through the asteroid belt right, is 2001: A Space Odyssey. You can see one single boulder flying by. Feb 6 '18 at 8:12
– uhoh
Oct 31 '18 at 3:40
• However if you are sure your question is not answered by the other Astronomy answers, then it's better to mention that question in your question and explain why you can not find an answer there yet, or if there is something else that needs to be addressed. On the other hand, maybe nothing will happen. The number of possible outcomes is astronomical! ;-)
– uhoh
Oct 31 '18 at 3:42

Yes, you could go "over" or "under" the asteroid belt. However, plane changes are expensive, and as pointed out in the comments, the asteroid belt is not very dense (average distance of 600,000 miles [1 million kilometers] between objects) so there isn't much to avoid.

• Never tell me the odds! Feb 5 '18 at 23:50
• So... You're telling me there's a chance...... I hear you loud and clear. Feb 6 '18 at 0:47
• Mind you, even if the asteroid belt was a solid disk of material, the plane change involved would be tiny - you only need a small impulse when you're traveling so far. It's not worth even that with how sparse the belt is. Feb 6 '18 at 14:26
• @Luaan That would be true if the asteroid belt was uniplanar, but it is not. If the asteroid belt were solid, it would actually be toroidal and you would need around 20 degrees of inclination to get over it--not cheap. Feb 6 '18 at 14:32
• @called2voyage It's a risk-benefit calculation. How much of the mass of the belt is within a 1 degree (actual question, no idea where to find that kind of data)? It's not like a single asteroid at 2 AU in a polar orbit around the Sun would make you say "yup, the belt is spherical, no way to avoid it" - you'd say "it's roughly planar, with 10% outliers" or something. Not to mention that more material in the belt (to make the encounter chance high enough to matter) would probably tend to make it flatten out even more. Feb 6 '18 at 16:17

Purely propulsive plane changes are expensive, but a much smaller adjustment followed by a swing-by maneuver over the pole of a planet a bit like Voyager 1 did at Saturn, (which in this case I guess would have to be Venus, Earth or Mars), might be much less expensive.

Or you could just leave Earth orbit in a direction that doesn't happen to be in the Ecliptic plane to begin with.

In either case if the mission were to visit a body in the ecliptic, you'd then have to make a large $\Delta v$ maneuver to get back to the ecliptic, and a second swing-by of perhaps Jupiter to stay there.

However, if the mission were to a body that wasn't in the ecliptic to begin with, then the rocky-planet swing-by's or initial out-of-plane trajectories would be all you'd need.

• Humm... I suppose you could do a gravity-assisted plane change at say Venus, with the new orbit figured to rendezvous with Jupiter and reverse the plane change? Feb 6 '18 at 4:29
• Come to think of it, the first one degree of plane change isn't that bad. How tall is the asteroid belt anyway? Feb 6 '18 at 6:30
• @jamesqf how? Leaving Venus and going out-of-plane and over/under much of the asteroid belt, what would bring you back to the ecliptic to pass near Jupiter? Besides thrust, there isn't any way that I'm aware of.
– uhoh
Feb 6 '18 at 7:11
• @uhoh: That's easy. Jupiter. You have to cross the ecliptic twice per orbit. Feb 6 '18 at 14:37
• @uhoh: If you use Venus' gravity to go "up" out of the ecliptic plane, then assuming you haven't achieved solar escape velocity, you must come down and cross the ecliptic plane again somewhere, no? So with proper aiming, it seems like it should be possible to re-cross the plane at the point occupied by Jupiter. IOW, the new orbit is an elipse with the sun at one focus, and Venus & Jupiter at opposite ends. I am not an orbital mechanic, though :-) Perhaps someone who plays with a simulator could try it? Feb 8 '18 at 2:59

It would be a bit like sailing your ship from Spain around the cape of Africa rather than through the Mediterranean sea to get to Egypt just because you were worried you may hit off Malta or Sicily.

There would be significantly more to avoid within a significantly smaller space in low earth orbit than out in the asteroid belt which is extremely empty compared to the image movies and tv shows have presented us with.

The cost of going around or "over" it would mostly be measured in time and would be a completely worthless endeavor. You would also have to figure out how to then correct your course as space navigation is not the same as on earth where you apply force in the direction you want to go. 99.999' % of the force acting upon any object in space is gravity and propulsion systems are not used to cover distance so much as to adjust trajectories so that gravity and angular momentum propels the craft in the desired direction. As for where you are going that also has to be worked out ahead of time as everything is moving, you need to aim for where the thing will be at the time you get there rather than aiming at where it currently is. If you take the time to go around something then the thing you are aiming for will have moved. You cant travel to another planets location, you have to intercept it at a certain point along its path.

The asteroid belt ranges from 2.2 to 3.2 astronomical units (AU) from the Sun and is 1 AU thick, see. So it is a very long way to go over it and too much fuel would be necessary. All the very sucessful spacecrafts to the outer solar system would have been impossible if they had to use a trajectory over the belt.