91–100 of 100 posts
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Because the SI unit is meters per second, so maintaining the “second” gives people with that understanding a basis in which to compare the delta-V.
Okay but they didn't give it in meters per second, they gave it in micrometers per second. Converting to micrometers per second is exactly as much arithmetic as converting to meters per day.
Multiplying/dividing by 1 million is way easier than by 86400 though.
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If I were holding earth hostage with my Space Battleship - I would sit in a lunar orbit. Also, I am not kidding about tug-boating - if I fly up, match an asteroids speed and velocity, why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a lit…
> I would sit in a lunar orbit Ah, so by "orbit" you were talking about orbit around Earth specifically? > why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a little slower than the earth. Again, from a high-level orbital mechanics perspec…
I may be confused but I dont mean a "larger orbit than the earth" -> I mean the exact identical orbit, the exact path that earth takes around the sun -> ahead (or behind, it does not matter) of where we are and instead of 365 days to circle the sun, the asteroid is moving at a rate that will take MORE days -> so the earth will smash into the asteroid, bc it can't do anything else. I dont mean "park" in the sense that I stop its movement, nor would I select an asteroid that has such an orbit that it couldn't be manipulated into position with little difficulty.
Like, imagine the solar system was a record on record player (I've never used one either) and the earth is on a line/groove - a choice asteroid is moving in the same direction on an immediately adjacent line/groove - the asteroid only needs to move onto the earth's groove (anywhere on that specific groove the earth occupies on the record works) and then the asteroid is then sped up or slowed down (not much tho) on that exact orbit -> either will result in a collision with earth.
The only real way to stop such activities is with spaceships. That is my entire argument - you are saying that is less feasible than making a missle out of an asteroid? I appreciate the explanation fr
Tbh, it wasn't until the game Terra Invicta that I really considered the solar system, as it actually is. That game has no other relevance to this particular conversation - good game, very different kind of 4x that I recommend but unrelated.
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> I would sit in a lunar orbit Ah, so by "orbit" you were talking about orbit around Earth specifically? > why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a little slower than the earth. Again, from a high-level orbital mechanics perspec…
I absolutely will check out Kerbal - I have done nothing more than thought experiments - which I'm sure is obvious, its obvious to me. I'm sure I am saying things exactly wrong - the idea is to save fuel and remove all of the difficulties that may arise with timing or aiming. Using more fuel is exactly opposite intent. I may be confused but I dont mean a "larger orbit than the earth" -> I mean the exact identical orb…
Unfortunately that's not really possible. To a first approximation, Earth's orbit is a circle with the Sun at its center, and the size of that circle is determined entirely by Earth's orbital speed around the Sun. Assuming you're also in a circular orbit, if you move at Earth's speed, the size of your orbit will be the same as that of Earth's. If you move faster or slower, your orbit will be smaller or larger, respectively, unless you wish to continuously burn fuel to maintain your distance from the Sun. That's why I said the asteroid's orbit must be slightly larger than that of Earth's for an Earth-catches-up-to-asteroid-in-similar-orbit scenario.
Obviously things get more complicated once you consider non-circular orbits, but the end result is similar - you can't continuously hang out in Earth's path while moving slower than the Earth around the Sun without burning a stupendous amount of fuel.
> you are saying that is less feasible than making a missle out of an asteroid? I appreciate the explanation fr
I think it's more that I think that "making a missile" is likely to require less fuel since you only need to adjust the asteroid's orbit ~once (only need to get it on a collision course) instead of ~twice (get the asteroid on a near-collision course, then adjust it again for the "right" kind of collision).
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If I were holding earth hostage with my Space Battleship - I would sit in a lunar orbit. Also, I am not kidding about tug-boating - if I fly up, match an asteroids speed and velocity, why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a lit…
> I would sit in a lunar orbit Ah, so by "orbit" you were talking about orbit around Earth specifically? > why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a little slower than the earth. Again, from a high-level orbital mechanics perspec…
The speed doesn't have to be much different - 366 days and earth will eventually hit asteroid - 364 days and it will eventually hit the earth.
Ahh, Im still having a hard time figuring out why that would take more energy - I'm going to be researching this all morning tomorrow.
Thanks for the help!
Wild that we went from "can we even deflect an asteroid" to measurably changing a solar orbit. 150 milliseconds sounds tiny until you realize compounding over decades makes that a meaningful trajectory shift. The engineering confidence this gives for actual planetary defense is massive.
I find it mesmerizing how predictable orbital mechanics are. We can tell where celestial body will be years ahead with meter accuracy.
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> I would sit in a lunar orbit Ah, so by "orbit" you were talking about orbit around Earth specifically? > why cant I just throw a tow strap on that, accelerate, and park it an area that only has to be accurate enough for a planet to hit it - I dont need to stop it, or have it flying at the earth, it only needs to be in the way, moving a little slower than the earth. Again, from a high-level orbital mechanics perspec…
I cant reply to your other comment - that is what I assumed you were saying but it does not make sense to me outside the process that naturally occurs - I'm assuming the suns gravity simply cant move objects of such different mass, at the same rate, and thereby the orbit and position changes accordingly? The speed doesn't have to be much different - 366 days and earth will eventually hit asteroid - 364 days and it wi…
Kind of? An object moving in a circular motion at a constant speed must have an acceleration towards the center of the circle of (velocity^2)/(radius). This means that two objects in the same circular orbit moving at different speeds must be experiencing different accelerations towards the center of the circle.
In the simplified case of orbits around the Sun, that acceleration towards the center of the orbit is due to the Sun's gravity. However, gravity accelerates everything at a given distance at the same rate. As a result, you can't have two objects solely influenced by the Sun's gravity that orbit around the Sun with the same orbital shape but moving at different speeds. You'd need something in addition to the Sun's gravity to pull that off.
> The speed doesn't have to be much different - 366 days and earth will eventually hit asteroid - 364 days and it will eventually hit the earth.
Sure. When I said slightly-larger-than-Earth-sized orbit, I really meant it. Kepler's third law of planetary motion states (approximately) that (orbital period)^2 is proportional to (radius)^3. Assuming I did my math correctly, if your orbital period goes from 365 to 366 days your orbital radius gets ~0.18% larger, which is roughly 274000 km increase over the radius of Earth's orbit. That would fit inside the Moon's orbit (~385000 km from the Earth)!
> Ahh, Im still having a hard time figuring out why that would take more energy
At least the way I was thinking, the short answer is that one alteration to an orbit is likely to be cheaper than two, especially if you aren't particularly concerned in what manner the asteroid eventually collides with Earth.
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It only worked in the Expanse because they expertly choose a special trajectory that made the rocks hard to detect and some questionable (but plot necessary) "stealth coating". By this point UN and MCR have been in cold war for 100+ years staring each other down with region killer nuke arsenals and an absurd amount of interceptors always ready. See than one time Mars actually fired a barrage - only like two warheads…
Ok. The Expanse is a show/book - that doesn't actually portray any of this very well, but its very important to note - there are no satellites in orbit, with nukes or any kind of missiles - if you want to pretend they are, they are most definitely pointed at the earth. I'd love to buy into that plot armor but there is too much to take seriously by S6. The reality is, the first time a colony decided to it was independ…
That would be far too big to not be spotted by the many UN aligned sensor platforms all around Sol, well before it is actually on a collision course as changing the trajectory of something this massive could take a long time, not to mention for it to actually travel all the way to Earth on that trajectory.
I am sure that Belter Cheguevara was not the first one to get these ideas, so any major power not tracking most asteroid orbits in almost real time at this point would be stupid. The technology they demonstrated to have should easily allow that.
And by that point one of the many Ships UN has all around the system would just go there and shoot anyone working on the big rock to pieces. Possibly deploying tugs to change the trajectory to a safe one afterwards.
So I think they had to use rock small enough not to be easily tracked, that could be quickly accelerated + that special stealth coating from the Martians. Enough to kill a city and devastate a region but not much else.
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I'm not sure this is actually a necessary explanation...but while propellers technically COULD function in space (not a perfect vacuum, right?)...they're basically going to be useless.
He probably misuses "propeller" which is strangely restrictive to "rotative blade propulsion" in English whereas "to propel" is generic in its meaning.
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Okay but they didn't give it in meters per second, they gave it in micrometers per second. Converting to micrometers per second is exactly as much arithmetic as converting to meters per day.
Yes, it's one multiplication in both cases. Multiplying/dividing by 1 million is way easier than by 86400 though.