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flosofl posted:I don't think they were looking to push it on a straight line vector either, they're only looking to change it's vector to intercept the sun, not necessarily the speed. A hit from the Navou at a near 90 degree angle would transfer almost all of its angular momentum to Eros. I'm trusting that they did the math to figure out the velocity needed on the intercept to alter Eros's orbital trajectory. In order to make Eros deorbit the sun you have to slow its speed relative to the sun to close to zero.
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Feb 20, 2017 16:12
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I wouldn't necessarily believe what the HUD in the show says. In season 1, when they were inching closer to the Scopuli, the HUD displayed very high delta-v.
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Feb 20, 2017 16:26
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The protomatter built a mass effect drive on Eros The protomatter is the Reapers, Shepard!
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Feb 20, 2017 16:27
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Subyng posted:In order to make Eros deorbit the sun you have to slow its speed relative to the sun to close to zero. That would be if you want the Eros to fall directly into the sun on its first pass. If Kerbal space program has taught me anything, dipping into the atmosphere of an object a few times is just as good as landing on a thing. Now what the protomolecule will do with all that energy as it interacts with the suns atmosphere is a different matter.
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Feb 20, 2017 16:28
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flosofl posted:I don't think they were looking to push it on a straight line vector either, they're only looking to change it's vector to intercept the sun, not necessarily the speed. You can't change one without changing the other. To get an object to fall into the sun you need to effectively cancel out almost all of its orbital velocity, which in the case of Eros means a delta-v of drat near 24 kps. It would literally take less change in velocity to get Eros to escape the solar system entirely. everydayfalls posted:That would be if you want the Eros to fall directly into the sun on its first pass. That's what they want to do because they don't want anyone to have time to board it and cut their way in. And to get Eros close enough to the sun to pass through its atmosphere, okay, maybe you just need 20 kps of delta-v instead of 24, it doesn't help you much.
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Feb 20, 2017 16:46
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Promo for next week's episode looks nuts. This has officially become my favorite show.
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Feb 20, 2017 17:41
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Phanatic posted:You can't change one without changing the other. To get an object to fall into the sun you need to effectively cancel out almost all of its orbital velocity, which in the case of Eros means a delta-v of drat near 24 kps. It would literally take less change in velocity to get Eros to escape the solar system entirely. You are assuming that they are not using other planets / moons in the inner solar system as a reverse gravity assist and using the thick atmosphere of Venus to perform an aerobraking maneuver to shed the necessary deltaV.
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Feb 20, 2017 20:13
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welp time to fire up kerbal space program again I don't think you can use planets for reverse gravity assists, none of them have retrograde orbits. Edit: well, enough to have it fall into the sun. You can use them to decelerate. Smiling Jack fucked around with this message at 20:26 on Feb 20, 2017 |
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Feb 20, 2017 20:22
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HERAK posted:You are assuming that they are not using other planets / moons in the inner solar system as a reverse gravity assist and using the thick atmosphere of Venus to perform an aerobraking maneuver to shed the necessary deltaV. It feels like a rather safe bet that if you're close enough to Venus to use its atmosphere to break, you won't be able to get out of its gravity well (to me at least. I'll gladly admit to being an idiot)
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Feb 21, 2017 01:07
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Dancer posted:It feels like a rather safe bet that if you're close enough to Venus to use its atmosphere to break, you won't be able to get out of its gravity well (to me at least. I'll gladly admit to being an idiot) If you're going fast enough it wouldn't matter, but the consequences on Eros and Venus of it blasting through its atmosphere could be pretty damaging.
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Feb 21, 2017 01:24
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Dancer posted:It feels like a rather safe bet that if you're close enough to Venus to use its atmosphere to break, you won't be able to get out of its gravity well (to me at least. I'll gladly admit to being an idiot) Nothing is ever said in the show about using Venus or anything else to brake. Hitting something the thickness of Venus's atmosphere with Eros from across the solar system with a single impact being your only impulse to control its path with would be remarkably difficult. On the other hand, they did talk about Fred's geeks running all the math, which implies getting it right is a non-trivial task. But again, you're talking about canceling out a significant chunk of 24kps of velocity, I don't think you can *do* that with a single pass through even the thickest parts of Venus's atmosphere. Especially not with a decidedly asymmetric hollowed-out rock. Even if you can hit the narrow slice of atmosphere, there's no way to guarantee that Eros just doesn't break into big chunks that impact Venus, and I'm pretty sure when the entire point of your exercise is to safely incinerate the protomolecule you don't want to risk the unknowns of what it might do if it impacted Venus .
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Feb 21, 2017 01:27
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They don't have to stop Eros, just slow it down enough that it's orbit falls into the sun eventually.
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Feb 21, 2017 01:54
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Cojawfee posted:They don't have to stop Eros, just slow it down enough that it's orbit falls into the sun eventually. Which is basically zero
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Feb 21, 2017 02:13
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Not really. There are several things they could do to alter the orbit of Eros. They could hit it in a way that would be equivalent to a radial burn to move the orbit so it hits the sun.
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Feb 21, 2017 02:18
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Cojawfee posted:Not really. There are several things they could do to alter the orbit of Eros. They could hit it in a way that would be equivalent to a radial burn to move the orbit so it hits the sun. All we've really learned is that not enough people in this thread have played Kerbal Space Programme.
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Feb 21, 2017 02:21
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Cojawfee posted:Not really. There are several things they could do to alter the orbit of Eros. They could hit it in a way that would be equivalent to a radial burn to move the orbit so it hits the sun. That’s not any easier, though.
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Feb 21, 2017 02:23
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man Thomas Jane has been in a lot of bad movies.
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Feb 21, 2017 02:27
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Throwing things into the sun is one of the most "expensive" things to do in space.
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Feb 21, 2017 02:52
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Luckily they had a free spaceship with a bunch of magic drives.
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Feb 21, 2017 03:00
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Cojawfee posted:Not really. There are several things they could do to alter the orbit of Eros. They could hit it in a way that would be equivalent to a radial burn to move the orbit so it hits the sun. That's the *same thing*. Eros has an orbital velocity of about 24 kps. The sun is small. To put Eros into an orbit that actually intersects the sun, you need to cancel out about 24 kps. That's what we're talking about. It doesn't matter what you do to alter its orbit, it doesn't matter what timescale you do it over, how *long* it takes you to alter its orbit: if you don't cancel out its orbital velocity almost entirely it won't hit the sun. Anything less than that, any orbit which does not actually intersect the sun, will just be a highly eccentric orbit that doesn't culminate in Eros impacting the sun. If it's close enough to pass within the Roche limit, it will disintegrate and wind up as a short-lived ring. Anything further then that, it will just keep on orbiting in a highly eccentric orbit that will give other people plenty of time to land on the surface and cut their way in. As will any kind of gravitational slingshotty trick to get it to fall into the sun eventually, some day years or decades in the future.
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Feb 21, 2017 03:17
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From now on everyone wanting to argue about orbital mechanics has to post a screenshot showing their KSP experience.
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Feb 21, 2017 03:20
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withak posted:From now on everyone wanting to argue about orbital mechanics has to post a screenshot showing their KSP experience. Platystemon posted:
SSTO on monopropellant Yes, I know that was rhetorical request.
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Feb 21, 2017 03:27
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withak posted:From now on everyone wanting to argue about orbital mechanics has to post a screenshot showing their KSP experience. 
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Feb 21, 2017 03:31
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Not the same.
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Feb 21, 2017 04:24
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Maybe someone should model this scenario in KSP and demonstrate what can go wrong? Orbital physics is way over my head, so count me out.
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Feb 21, 2017 04:44
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Short version: you need to gently dock with the giant rear end space rock and then burn your engines in a retrograde orbit until it falls into the sun Any collision strong enough to make the velocity change would be catastrophic and lead to the destruction / fracturing / partial vaporization of Eros
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Feb 21, 2017 04:48
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Will someone do the math on how long it'd take Eros to hit the sun if you cancelled out its orbital velocity? I'm getting between 99 and 196 days, depending on where in its orbit Eros was at the time. Does that sound right? I don't feel like I have a good frame of reference for something falling straight into the sun.
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Feb 21, 2017 05:17
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Smiling Jack posted:Short version: you need to gently dock with the giant rear end space rock and then burn your engines in a retrograde orbit until it falls into the sun It’s also more efficient, but it’s not as cool and you can’t have a “DON’T TOUCH ME!” moment. If it’s true that the Nauvoo’s engines can accelerate one hundred million tonnes of steel at 1.79 km⁄s², they could accelerate present‐day Eros at a blistering 0.0268 m⁄s². That sounds bad, but it would only take a week or two to null its orbital velocity. If the lesser figure is correct and the Nauvoo can only accelerate at 65 g, then it would take over a year.
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Feb 21, 2017 05:18
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Toast Museum posted:Will someone do the math on how long it'd take Eros to hit the sun if you cancelled out its orbital velocity? I'm getting between 99 and 196 days, depending on where in its orbit Eros was at the time. Does that sound right? I don't feel like I have a good frame of reference for something falling straight into the sun. That sounds about right. You need multiple integrations to do it exactly but if you just treat it as a very highly eccentric elliptical orbit with the sun at one focus, you can just use Kepler's laws and figure out what half the period would be based on the semimajor axis.
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Feb 21, 2017 05:31
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Guys. Guys. Calm down and enjoy the ride or else you all will loving have an aneurysm soon. Like maybe tomorrow. Let go of your preconceived notions or biases or expectations and let Space Jesus take the wheel.
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Feb 21, 2017 05:43
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Phanatic posted:That sounds about right. You need multiple integrations to do it exactly but if you just treat it as a very highly eccentric elliptical orbit with the sun at one focus, you can just use Kepler's laws and figure out what half the period would be based on the semimajor axis. My last physics class was a long time ago, but my approach was to take the masses of Eros and the sun to find the gravitational force between them (once for aphelion and again for perihelion), then assume the sun wouldn't move appreciably and use that force and Eros's mass to find its acceleration toward the sun, and then use that acceleration and an initial velocity of zero to find travel time from aphelion and perihelion. How backwards was my approach?
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Feb 21, 2017 05:48
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Toast Museum posted:My last physics class was a long time ago, but my approach was to take the masses of Eros and the sun to find the gravitational force between them (once for aphelion and again for perihelion), then assume the sun wouldn't move appreciably and use that force and Eros's mass to find its acceleration toward the sun, and then use that acceleration and an initial velocity of zero to find travel time from aphelion and perihelion. That approach only works in a uniform gravitational field. Near Earth’s surface, that’s a fine approximation, but it falls apart when you try to drop things into the Sun. The Sun’s gravity, like that of all other masses, gets stronger as you approach it. You need calculus to account for that. Platystemon fucked around with this message at 05:53 on Feb 21, 2017 |
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Feb 21, 2017 05:51
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Phi230 posted:Guys. Let us nerds have fun
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Feb 21, 2017 05:54
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Toast Museum posted:My last physics class was a long time ago, but my approach was to take the masses of Eros and the sun to find the gravitational force between them (once for aphelion and again for perihelion), then assume the sun wouldn't move appreciably and use that force and Eros's mass to find its acceleration toward the sun, and then use that acceleration and an initial velocity of zero to find travel time from aphelion and perihelion. That'll give you the instantaneous acceleration at the start but as the distance between them decreases the gravitational force will increase, which means so will the acceleration. Really you can just use the sun's mass and ignore Eros, but you can't ignore the decreasing distance/increasing force. A precise solution needs a double integral but it's not a really complicated one, the initial equation of motion is d^2r/dt^2=-GM/r^2 M = mass of the sun, G = the gravitational constant, r=distance from the sun, you're differentiating wrt time. So plug in those values, double-integrate, and see how long it takes r to go to 0.
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Feb 21, 2017 06:00
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Docking a ship to Eros then accelerating it to the Sun is stupid because that leaves a bunch of time for UN/MCRN ships to investigate and get contaminated with the protomolecule. Not everything is about energy efficiency. 
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Feb 21, 2017 06:05
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Josh Lyman posted:Docking a ship to Eros then accelerating it to the Sun is stupid because that leaves a bunch of time for UN/MCRN ships to investigate and get contaminated with the protomolecule. Not everything is about energy efficiency. The amount of energy needed to do it through collision would probably vaporize Eros Somebody with more nerd ability than me please express the amount of energy needed in megatons, TIA
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Feb 21, 2017 06:08
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Not to mention Eros is spinning like a bottle
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Feb 21, 2017 06:09
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Phanatic posted:That'll give you the instantaneous acceleration at the start but as the distance between them decreases the gravitational force will increase, which means so will the acceleration.  I can't believe I overlooked something so obvious. I need to take a refresher course or something.Thanks for the explanation.
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Feb 21, 2017 06:11
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Smiling Jack posted:The amount of energy needed to do it through collision would probably vaporize Eros How fast do you want it to reach the sun? Like, what's enough time for someone to get in board, cut their way in through the slagged docks, get infected and leave again? Because yes. Just just having it infall to the sun will take weeks at least, if you want it there faster then the Nauvoo impact willl have to propel it, which is an even more ridiculous impact. If you're hitting it that hard and the protomolecule can survive then even the sun isn't a reliable disposal method.
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Feb 21, 2017 06:21
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Minimum required to fall into the sun. Still a staggeringly large amount of energy to transfer in a collision
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Feb 21, 2017 06:24
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