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Scientists Map Out How to Nudge Small Asteroids into Earth?sOrbit
On Sep/5/2018 at 21:13, Sylvia Else wrote :
On 6/09/2018 6:18 AM, Alain Fournier wrote: On Sept./4/2018 at 06:44, Jeff Findley wrote : In article , ess says... On 4/09/2018 9:29 AM, wrote: "The notion of an asteroid headed for Earth is typically seen as a bad omen. On the flip side, some scientists and entrepreneurs increasingly see this scenario as a potential opportunity. Deliberately redirecting asteroids to our planet?s vicinity could enable us to study them up close, or even mine them. Given that these objects are packed with valuable resources, building a collection of them nearby could spark major advances in spaceflight, to say nothing of the scientific research that might result from easy access to these extraterrestrial bodies. A recent paper published in Acta Astronautica suggests that asteroids could be captured in Earth?s orbit with aerobraking, a maneuver that uses atmospheric drag to decelerate and position objects in stable trajectories around a planet. Aerobraking has helped place interplanetary spacecraft in orbit around Mars and Venus, and to slow down spacecraft returning to Earth. Led by Minghu Tan, a PhD student at the University of Glasgow, the paper immediately addresses the most obvious concern with this scenario: What if there?s some mistake in the redirect process and an asteroid accidentally impacts Earth? It?s bad enough that the dinosaurs were oblivious to their doomsday space rock, but it would be especially embarrassing if we humans smack ourselves in the face with one." See: https://motherboard.vice.com/en_us/a...o-earths-orbit After the aerobraking pass, you need to raise its perigee quite a lot, or it's just going to come back and burn up, either on the next pass, or some subsequent pass. The article doesn't say how the perigee would be raised.* Unless they're planning on using a lunar flyby, I don't see how you can do this without a sufficiently large rocket engine. If you can nudge it enough to get it to do aero-braking, it shouldn't be a problem to raise the perigee. One can imagine an extreme case where the asteroid was going to pass 200 km above Earth's surface and you can just barely nudge a little lower for aero-braking and then aren't able to raise the perigee fast enough. But a big asteroid being on such a trajectory isn't very likely. And those deciding to capture it being smart enough to be able to nudge into the atmosphere, yet too stupid to notice the danger isn't likely either. (People too stupid to see the danger aren't hard to find, it's the combination with smart enough to be able to nudge it that isn't likely.) A small nudge a long way out can be enough to direct it towards the Earth. But after the aerobraking, you don't have that option. You need to raise its perigee quite a lot. But you would probably want to nudge it millions of kilometres for it to go towards Earth. You only need to raise perigee a few kilometres per orbit. Yes, you do have to know what you are doing. And make sure that you can raise the perigee. But in most cases, raising the perigee should be easier than sending it to Earth's atmosphere, maybe not all cases, but most cases. And those who would do this are most likely people who understand the difficulty of the task and the risks. You don't send an asteroid towards Earth without understanding orbital mechanics and rocketry. Alain Fournier |
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Scientists Map Out How to Nudge Small Asteroids into Earth?sOrbit
On 6/09/2018 11:37 AM, Alain Fournier wrote:
A small nudge a long way out can be enough to direct it towards the Earth. But after the aerobraking, you don't have that option. You need to raise its perigee quite a lot. But you would probably want to nudge it millions of kilometres for it to go towards Earth. You only need to raise perigee a few kilometres per orbit. Yes, you do have to know what you are doing. And make sure that you can raise the perigee. But in most cases, raising the perigee should be easier than sending it to Earth's atmosphere, maybe not all cases, but most cases. And those who would do this are most likely people who understand the difficulty of the task and the risks. You don't send an asteroid towards Earth without understanding orbital mechanics and rocketry. Alain Fournier That's really not how orbital mechanics work. It's not distances that are a problem, but velocities. A small change in velocity for an object a long way out can translate into a large change in distance by the time the object arrives in the vicinity of Earth. By contrast, raising the perigee requires a significant change in velocity, and there's no getting around that. For a massive object, that implies a correspondingly large rocket. Putting a large rocket into space is difficult and expensive. Sylvia. |
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Scientists Map Out How to Nudge Small Asteroids into Earth?s Orbit
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Scientists Map Out How to Nudge Small Asteroids into Earth?sOrbit
On 7/09/2018 5:10 AM, Alain Fournier wrote:
Raising the perigee in Earth orbit a few kilometres is much easier than raising the perigee in Sun orbit by a few million kilometres (especially that here, for Earth orbit, we are talking about a highly elliptical orbit). And if you are going to make a plane change to move a few million kilometres instead of raising perigee it isn't easier. It is kind of true that you can use highly efficient low thrust engines to make easier the change in Sun orbit. But keep in mind that ion engines are fired for long periods of time to move spacecrafts weighing a few tons. Are you going to fire an ion engine for centuries to move an asteroid? Once again, it is possible that one would find an interesting asteroid that would need only a very small push to do an Earth aerobraking manoeuvre, it just isn't bloody likely. So if you plan on capturing an asteroid, be prepared to give it some sizeable delta-V. Clearly one isn't going to choose a random asteroid. The whole scheme is only remotely practical if the asteroid already approaches Earth, and only needs a nudge to bring it into the atmosphere. Sylvia. |
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Scientists Map Out How to Nudge Small Asteroids into Earth’s Orbit
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Scientists Map Out How to Nudge Small Asteroids into Earth?sOrbit
On Sep/6/2018 at 21:04, Sylvia Else wrote :
On 7/09/2018 5:10 AM, Alain Fournier wrote: Raising the perigee in Earth orbit a few kilometres is much easier than raising the perigee in Sun orbit by a few million kilometres (especially that here, for Earth orbit, we are talking about a highly elliptical orbit). And if you are going to make a plane change to move a few million kilometres instead of raising perigee it isn't easier. It is kind of true that you can use highly efficient low thrust engines to make easier the change in Sun orbit. But keep in mind that ion engines are fired for long periods of time to move spacecrafts weighing a few tons. Are you going to fire an ion engine for centuries to move an asteroid? Once again, it is possible that one would find an interesting asteroid that would need only a very small push to do an Earth aerobraking manoeuvre, it just isn't bloody likely. So if you plan on capturing an asteroid, be prepared to give it some sizeable delta-V. Clearly one isn't going to choose a random asteroid. The whole scheme is only remotely practical if the asteroid already approaches Earth, and only needs a nudge to bring it into the atmosphere. You also want it to be passing by not too fast, as your typical Earth crossing asteroid would do. If you attempt aero-braking a sizeable asteroid passing by at 25 km/s you risk causing damage on Earth even if the asteroid performs perfectly as planed its aero-braking manoeuvre. Asteroids passing close to Earth are rare enough, if you also want them to pass by at an appropriate speed, you risk waiting an awful long time for such an asteroid. One would probably be less picky on the choice of asteroid. You just use a more powerful rocket to nudge an asteroid that will be available in a timely manner rather than wait centuries for the asteroid with the perfect trajectory. Alain Fournier |
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