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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."
2000 lbs in a ton
20 ton spacecraft
$10,000/pound to get to geosynchronous transfer orbit
$400,000,000 just to launch this thing into a geosynchronous transfer orbit (not counting construction costs). I assume the fuel to move it isn't included in the 20 ton estimate either (since it will burn off on the way) so that would need to be lifted as well. I wonder if a huge nuke would be cheaper and easier to construct and launch? Then again, with the current U.S. national debt at over 8 trillion (with which we could pay for the launch costs of 20,000 of these things) maybe the launch costs aren't unreasonable.
I Am My Own Worst Enemy
Crew? Not a chance. There is absolutely no reason to send crew on a mission like this. It would just complicate a mission that computer controls could already do more than well enough, and send the price through the roof. We're already doing completely automated asteroid *landings* (harder than it sounds, because they have very irregular gravity fields). There's no way that the 20 tonnes includes a human payload and all of the associated baggage.
No humans, no coming home. Also, they mention 20 years prep time - i.e., they're not planning to build it until a threat is discovered, and the couple billion dollar cost would be amortized over that time to perhaps 100 mil per year, split around the world's space agencies. I'm sure that's more than enough time and low enough cost. Also, a 200 meter asteroid is hardly a worldwide cataclysmic event if it hits; it's like a single large nuclear weapon hitting a random place on the planet, if you can trust the impact calculator.
He's just being nice so my real father won't freeze him in carbonite and sell him for spice.
Considering the number of asteroids etc that only get seen on the way out, asking for decades of warning is perhaps unrealistic.
Engineering is the art of compromise.
Launching the craft. How much fuel would it take to get escape velocity on something this massive? Probably not a small amount.
Why would you launch it from earth??? It's just weight for weight's sake, so build it from stuff already in space, or at the very least, on the moon. Only the engines, control module, etc would need to be lifted from earth. My personal opinion would be to find a nearby asteroid or similar of the appropriate size, shape it as needed, and slap some thrusters on/in it.
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.
What crew? Why on earth would you crew it? Remote operation should be just fine.
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.
OK, now you're just being stupid. What possible reason would there be for landing this contraption on earth?
Actually the force is much less than that.
F = GmM/r^2
For a 20000kg object, and a 9e19kg object (Hygiea), with a distance of 205km between them (1 km away from the asteroid, but the distance between is the centre of masses is much greater, Hygiea has a radius of 204km), the force is 2870N. In comparison, the force of gravity from the Earth will be that much 3.53e12 km away (471 times the distance of Pluto from the Sun at it's farthest point in orbit). It's just more than the gravitational force of four 70kg people standing on the ground.
In other words, if a big asteroid comes at us, we are royally boned.
I often refer people to look at unmanned Mars missions, and determine how many of the huge number of failed Mars missions could have been saved by people. The answer is almost none. Most were booster failures, calculation errors (which humans couldn't have noticed until it was too late), failures in critical hardware, even explosive depressurization of pressurized parts (and you better believe that you have a lot more pressurized area with people!). Only two in which the computer was shut down but recoverable could realistically have been saved by humans. On the other hand, one of the missions which was salvaged likely would have killed any human crew onboard; a solar panel used for aerobraking at Mars was damaged, and they had to make it take many months longer to get into Mars orbit. This would have been fatal to the crew (unless they were equipped to do spacewalks and metal repairs, which raises the price and complexity even further).
Adding humans will around 20x your cost. So, take your pick: 20 completely different designs, or one manned mission with a significant chance of failure, for the same price. It's a pretty simple call; there's a reason why almost all probes that we launch are unmanned. The manned space program gets funding. The unmanned space program does the research.
He's just being nice so my real father won't freeze him in carbonite and sell him for spice.
Actually, it would take precisely the same amount of fuel - either way, you're moving the tug plus the asteroid. The whole idea with this method is simply that gravity is a very gentle force. Pushing the asteroid by attaching a rocket to it or exploding something next to it are both very sharp, uneven forces that could very well break it up in to little pieces. Some of those pieces would probably hit the earth, even if the main bulk didn't.
Yeah but don't you think there will be a boatload of people screaming
about an unmanned mission if the fate of the world hangs in the balance?
From a political point of view I can't see anyone supporting a robot probe
mission to save the earth.
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