If you could tether a comet as it passed you, in space, would this be practical?

Question

So a comit is wizzing by 5 million miles from earth, traveling much faster than any rocket. If a spacecraft shoots a tether into the comet as it passes, releasing some slack as the comet goes by (to avoid a giant jerk) and therefore matching the speed of the comit, could this be an efficiant way to hitch a ride into deep space?

Answer 1

Comets are loose collections of ice and rocks they are not solid. So your idea probably wouldn't work very well, now if you used an asteroid that could make a better tractor.

If you try to hit a comet with a spear-gun like tether then you will probably end up with a small piece of ice and rock and a very small acceleration; while the rest of the comet goes on by.

The asteroid express wouldn't be all that fast though, the original speed of asteroids aren't that fast, but when you combine the speed of a an orbiting object and then positioning that comet on the top of a gravitational slide into a planet is what makes them so dangerous.

Still if you got an asteroid conventionally orbiting between say Mars and Earth then you could build the Asteroid Express, of course you will have to adjust for the varied gravity situations in the problem, especially Jupiter.

Most of the NEO (Near Earth Orbiting) objects come from way out in space in the Kiper Belt or the Ort Cloud. The asteroids in the Asteroid Zone are in a firmer orbit and rarely both Earth. It is those that are way out there that cause us the most problems, like the famous Dinosaur Killer Asteroid. Most of these NEOs are put on their dangerous course by Jupiter's gravity. Of course Jupiter also has the side effect of sucking most of them in as Comet Shoemaker-Leavy Nine showed.

No a much better use of a passing comet or asteroid would be to put it into a stable far Earth orbit. If you did then you would have all that raw material up in space to work with. Water is very dense and that means heavy, a gallon is about 5 pounds. We need water to survive so when you have to push it up into space you need to pay a lot in rocket fuel. It is much better if you can find a source of water already up there and use it. That's why NASA is hoping for water at the poles of Mars and the Moon. If they find water ice there then they can establish a moon base or Mars Base. If not then the problem becomes much harder. It is just too expensive to push things into orbit by rocket.

A better way would be to use a Space Elevator, and DARPA along with NASA held a DARPA Challenge at the New Mexico Spaceport to see if there were any good ideas out there. Several contestants did come up with good ideas, but none took the prize because they were too slow.

A space elevator uses a huge counter-weight in orbit and drops a very long line down to the Earth. If established at or near the equator then the orbit can be pretty stable and transportation to orbit could be easier. The major problem is that we don’t have a material strong enough to make the cable. Simple steel would snap too easily. Carbon Nano-fiber tubes are a good idea and they may make the design practical.

Answer 2

It may work, if you can ensure that the anchor at the tether's end will stay lodged in the comet's nucleus. We've successfully sent "comet chasing" probes that catch up with a nearby comet. We've landed on a comet and returned a sample of the tail's material. So we could land a larger probe powered by radio isotopic battery (lasting decades) on a stable part of the nucleus, and over time receive reports from the comet outpost as it departs for the Oort Cloud. This would be a good way to study the heliopause, the boundary between the Sun's realm and the interstellar medium. The mission could last 100 years if properly planned.

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Answer 3

Probably the biggest problem is that comets aren't all that massive compared to what we would need. Just one assist from such a body would send it on a completely different course, most likely into the inner solar system since you would have stolen a lot of its momentum. Do we want more stuff crossing Earth's orbit? Probably not.

By the time you've achieved a high enough speed to escape Earth's gravity and be out there in the solar system, chances are, a gravity assist from Jupiter would be a much better choice than grabbing an asteroid or comet. Its gravity is enormous, and you can approach it from pretty much any angle in order to achieve the desired speed and trajectory, and nothing we could currently get into space would have enough mass to even come close to disturbing its orbit enough to even measure in a thousand years.

Answer 4

It wouldn´t be very practical. Comets aren´t that fast. As they move away from the sun they are constantly slowing down as they too orbit the sun. It takes a comet centuries to make one orbit around the sun and they only travel out to about the orbit of neptune.

Answer 5

The force required to dampen the acceleration from the comet would approach the force required to accelerate the body to that speed on its own. You might not gain very much. Then again, if your craft and cable could tolerate a giant jerk, maybe you're on to something.

Answer 6

No.