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Using Gravity To Tow Asteroids
cryptocom writes "Space.com is reporting that two scientists at NASA are proposing using a 20-ton spacecraft to pull asteroids off a possible collision course with Earth, using the spacecraft's own gravity as an attractor. This idea would not only be cheaper, but have a much higher chance of success, due to not having to actually land on the asteroid's surface."
mir weighed 135 tons and it burned up just fine on its way down. 20 tons, relatively speaking, isn't really all that much.
Wouldn't that would be 10^8 Newtons of force pulling the spacecraft toward the asteriod? The asteriod is much more massive and would have a gravity well of it's own. Wouldn't that attractice force have to be overcome for 20 yrs, plus a slight acceleration in the direction the asteroid needed to move? The 20 ton spacecraft would have a higher force of gravity on the 'roid than that of the Sun for 20 yrs (or however long the tractor lasts) so it could gradually change to orbit, How do we make things that can stay in space for 20 yrs w/o repair? How do you get that much fuel on-board? Solar Cells are not an option that far from the Sun. A nuclear reactor maybe but they would have all sorts of issues there, even if the "tractor" was not launched from Earth, the fission elements would have to be launched as I don't think you find Uranium just floating in space. And heaven forbid someone mis-calculates and they push it onto a collission course..they it takes another 20 yrs to fix that! This article sure makes a LOT of assumptions and figure on new ideas/technologies we don't have. It is a neat idea but IMHO it belongs under the topic of Science Fiction not in a journal like Nature.
Sounds to me like it will be travelling in parallel with the asteroid, but being that it is using gravity, it will lose "altitute" relative to the object and need to regain it by thrusting away from the object without pushing the object or damaging it, thus bending the orbital arc toward the craft ever so slightly.
No conformist ever made history.
Launching the craft. How much fuel would it take to get escape velocity on something this massive? Probably not a small amount.
20 ton spaceship. That's actually smaller than the Space Shuttle.
I can't remember the source now, but the Shuttle can lift about a 30ton payload. The boosters themselves can lift far more but of course have to carry the Shuttle too (which is something like 120tons).
The Saturn V rocket was capable of lifting 118 tonnes (with the 3 stage versions).
The Shuttle Derived Launch Vehicle will have a capacity of 125 tonnes.
All seem plenty to lift a 20ton spaceship if it's the only thing being launched. Even with a Shuttle it should be doable, or we can have another up there waiting to deploy it or use the ISS team.
Since we're able to use existing launchers to get the spaceship into orbit, it shouldn't cost any more to launch than any existing mission. All your left with is the pricetag for building it and giving it enough fuel to reach the asteroid.
The crew. The time the crew would be away from earth would be how long? 10 years? 20 years? Managing and provisioning crews for such a long amount of time is probably among the major challenges facing the extension of our space travel abilities.
Coming home. What happens when a ship this large is re-entering Earth's atmosphere? That sucker will have a lot of force coming down.
Due to the distance it would have to travel a robotic mission remote controlled from Earth would make the most sense. Just in case anything breaks which isn't workaroundable/fixable it would probably make sense to send more than one.
In this case it'd be best to leave it out there - without enough fuel to return it'd be cheaper and without a crew to bring home there's no real reason to.
Shelf life. So we make a ginormous space tractor. Maybe we don't face an asteroid threat for 15,000 years. That's a lot of upkeep.
The launchers are already around, and it wouldn't take long to build a ship which is essentially a remote controlled engine with a lot of metal attached.
Assuming that we'd know of the threat in enough time to send this to the asteroid, as long as we still have the launchers to get it into space in the first place it shouldn't be unreasonable that we can build them as we need them.
If we don't have that kind of timescale then we're probably in trouble even if we could send it straight away. Since the launchers seem capable of lifting more than 20 tonnes though, we could just build a 40 tonne version and half the time we'd need (disclaimer: not linear, i think it'd be more like 3/4?).