Science!! Fucking magnets, how do they work?

  • Guest, it's time once again for the massively important and exciting FoH Asshat Tournament!



    Go here and give us your nominations!
    Who's been the biggest Asshat in the last year? Give us your worst ones!
Void

Void

BAU BAU
<Gold Donor>
9,806
11,721
It has been years since I got my degree, but we worked up a bunch of different ideas for such a problem in one of our classes. It wasn't Voyager specific, but same concept. If you go on the assumption that everything will start at the same speed through a gravity "slingshot" or detachable boosters or whatever method you want, and that cost or getting it into orbit isn't an issue, it essentially comes down to a tradeoff in weight vs. the potential for acceleration. Most of the calculations were beyond the scope of even my degree in aeronautical engineering, unfortunately, because you have to compare something simple like a chemical rocket to something extremely complex like the density of potential fuel/solar power over the distance from earth, the efficiency of the propulsion device, etc. In theory a solar sail or ion scoop can work for much, much longer (if not indefinitely) than a simple chemical rocket, but is it enough to overcome the initial advantage the rocket has before the vehicle is so far from earth that it doesn't really matter?

I'm sure that data is available somewhere, but as I mentioned most of it is extremely complex, not to mention theoretical. We didn't have the internet and such when we were trying to figure all that out, but even now it is a pretty daunting task. I'd say that in general we should be able to improve that speed simply through minor advancements in chemical rockets (they are there, even if they are pretty minor), but for any significant improvements via other methods I really have no idea where to get that kind of data.

I know this is basically a bunch of "I don't know" but I've actually spent a lot of time dealing with that question, so I'm saying it is a fairly huge "I don't know." Someone at NASA or elsewhere has an idea I'm sure, but I haven't seen anything mentioned really.
 
T

The Ancient_sl

shitlord
7,386
16
Xasten_sl said:
Ideally, you run an Ion engine constantly at the "optimal" output. Think about it like driving on the highway at 55 (or whatever the most fuel efficient speed is these days). You can gun your accelerator and maybe get there faster, but you'll burn more fuel.
Click to expand...
Are you saying that because you know an Ion drive in space operates the same way as a car on the highway or because you are guessing? I don't think the reason the combustion engine in our car is more efficient at 55 is because of how steady we are adding gas to the engine.
 
TheBeagle

TheBeagle

JunkiesNetwork Donor
8,741
30,371
The Master_sl said:
The important thing to remember is that you're always accelerating with an Ion drive. It doesn't matter that it is accelerating you at 1/1000 gravity, after a year of that you're at 69,2742 mph if you start from zero (you're not starting from zero). Constant acceleration makes a big difference.

Recent article:

http://www.gizmag.com/improved-ion-e...ifetime/26323/
Click to expand...
This is the only guy that's actually known what he's talking about in the past dozen posts.
 
X

Xasten_sl

shitlord
83
0
The Ancient_sl said:
Are you saying that because you know an Ion drive in space operates the same way as a car on the highway or because you are guessing? I don't think the reason the combustion engine in our car is more efficient at 55 is because of how steady we are adding gas to the engine.
Click to expand...
It was a crude analogy, but the principle is the same. That's essentially how it was explained to me. I clerk for the attorney who patented the VASIMR for the Ad Astra company, so I've been enjoying my exposure to these topics. My technical understanding is very basic, but I believe that my explanation was proper, if not overly generic.

From the Wikipedia: "By varying the amount of energy dedicated to RF heating and the amount of propellant delivered for plasma generation VASIMR is capable of either generating low-thrust, high?specific impulse exhaust or relatively high-thrust, low?specific impulse exhaust." With Specific impulse being defined as efficiency with respect to the amount of trust per a unit of mass over time. IE: You can squeeze a lot of energy out of your fuel over a long time, or you can gun it for a quick but drastically less efficient acceleration.
 
iannis

iannis

Musty Nester
31,351
17,656
Well that's pretty simple math, all you need to know is the speed of voyager, the acceleration, how far from earth it is, and the acceleration of the ion drive.

Voyager2 is escaping the solar system at a rate of about 3.3 AU per year and is at a distance of ~102 AU from the sun, according to a nasa page. No direct quote to acceleration, but from other quotes it seems to be contant enough for this purpose. 1 AU ~150 million km according to no one but an astronomer, astrophysicists, or jeopardy contestant knows that offhand.

Sooooo..... I'm not gonna even hit the calculator button. A while. A long while. But it would catch up.

Edit: Then again, Voyager has a 30 year headstart.
 
T

The Ancient_sl

shitlord
7,386
16
Xasten_sl said:
From the Wikipedia: "By varying the amount of energy dedicated to RF heating and the amount of propellant delivered for plasma generation VASIMR is capable of either generating low-thrust, high-specific impulse exhaust or relatively high-thrust, low-specific impulse exhaust." With Specific impulse being defined as efficiency with respect to the amount of trust per a unit of mass over time. IE: You can squeeze a lot of energy out of your fuel over a long time, or you can gun it for a quick but drastically less efficient acceleration.
Click to expand...
But what if you use intermittent low thrust pulses?
 
X

Xasten_sl

shitlord
83
0
The Ancient_sl said:
But what if you use intermittent low thrust pulses?
Click to expand...
What do you mean exactly? Where do the low thrust pulses rate in terms of efficiency? I'm not certain, I would think that each individual pulse would be just as efficient as its equivalent setting for constant thrust, just that it doesn't last as long. So whether it's set on low, medium, high, or 11, each second the pulse lasts would be roughly as efficient as an equal amount of time as if the engine were constantly burning. The only reason for the pulses, it seems, is that they just don't have enough electricity to power the engine on the space station, otherwise they might employ the engine on a constant thrust scheme on its most efficient setting. There may be some energy costs in starting/stopping the engine, but that answer is beyond me.

A key thing to keep in mind is that efficiency is measured as a balance between thrust per unit of fuel, thrust per a unit of energy spent, and acceleration / arrival time. If you can burn the whole tank to get to where you're going quickly, then that's most efficient. If you want the object to go as fast a possible for an indefinite period of time, you'll want to burn low and long with your limited fuel and unlimited time.

If I can remember, I'll ask for clarification next time I'm in the office.
 
T

The Master

Bronze Squire
2,084
2
The Ancient_sl said:
So if we launched one now using the trickle to pulse the ion drive how long would it take to overcome Voyager 1?
Click to expand...
2.8 years at 1/1000 gee acceleration. Quick search didn't show me numbers for where it'll be in three years, but it is at 125 A.U. so I just rounded up to 130 A.U., which is actually too much, so a little less.

Time on Earth: 2.8227 years
Time on Ship: 2.8222 years
Speed: 0.0014565293569740161 of C or 19,937,605.746012 m/s or 4.45992 x10^7 mph.

Constant acceleration makes a huge difference in how we'd approach long distance space flight.
 
iannis

iannis

Musty Nester
31,351
17,656
The Master_sl said:
2.8 years at 1/1000 gee acceleration. Quick search didn't show me numbers for where it'll be in three years, but it is at 125 A.U. so I just rounded up to 130 A.U., which is actually too much, so a little less.

Time on Earth: 2.8227 years
Time on Ship: 2.8222 years
Speed: 0.0014565293569740161 of C or 19,937,605.746012 m/s or 4.45992 x10^7 mph.

Constant acceleration makes a huge difference in how we'd approach long distance space flight.
Click to expand...
How can that possibly be correct if it's not reaching a matching velocity in that time? I'm not trying to contradict you, I'm actually asking. If one year is .7AU of acceleration or so, it doesn't make a lot of sense that 3 would be enough to overtake the voyager as well as make up the 100+ distance already covered.
 
T

The Master

Bronze Squire
2,084
2
It isn't a matching velocity, you'd fly right past Voyager once you caught up to it. If you wanted to match velocities you'd need to flip over and accelerate in the other direction to slow down at some point. Add ~14 months for that. The key point is you are constantly accelerating and nothing is slowing you down. Imagine if you were in a car that went 1-60 in 6 seconds. At 12 seconds you're at 120 mph. At 18 seconds you're at 180 mph. And, of course, you've been traveling this whole time. That sounds unreasonable for cars, it is the reality in space.

The key thing to remember is Voyager isn't getting any faster. It doesn't have any significant acceleration and hasn't for years. It is going the same speed. You're not, you're accelerating. Voyager is traveling at 17 km/s. Our hypothetical constant boost ship is traveling at 20,000 km/s when it catches up. 1,172 times as fast.
 
W

Wuyley_sl

shitlord
1,443
13
So when they shot out Voyager back in the day, do they try to calculate where all the planets, comets etc will be so it doesn't smash into them or do they just toss it out there and hope for the best? I know space is vast and quite empty, but there has to be all kinds of random shit up there floating around.
 
T

The Master

Bronze Squire
2,084
2
Wuyley_sl said:
So when they shot out Voyager back in the day, do they try to calculate where all the planets, comets etc will be so it doesn't smash into them or do they just toss it out there and hope for the best? I know space is vast and quite empty, but there has to be all kinds of random shit up there floating around.
Click to expand...
They calculated where each of them would be. Because they wanted pictures, because they used the gravity of said objects for acceleration, etc. Space is basically empty. To say that this was computationally difficult in an era where people were still regularly using slide rules is to vastly understate the case, but they got it done. Mass tends to clump together or become otherwise location stable because of larger masses, or the pull between two masses, etc. Even if you don't know where each and every large object is, although I think people would be surprised at how many objects we've located in our solar system, you know where objects like that will be, because there are only so many places they'd be stable, either orbiting a planet, a moon, falling into the sun and not being an issue, stuck in the asteroid belt, what have you.
 
iannis

iannis

Musty Nester
31,351
17,656
They def. did that for the planets. You don't get to use gas giants as a gravity version of VTech kicking in without knowing where they'd be beforehand.
 
Void

Void

BAU BAU
<Gold Donor>
9,806
11,721
The Master_sl said:
It isn't a matching velocity, you'd fly right past Voyager once you caught up to it. If you wanted to match velocities you'd need to flip over and accelerate in the other direction to slow down at some point. Add ~14 months for that. The key point is you are constantly accelerating and nothing is slowing you down. Imagine if you were in a car that went 1-60 in 6 seconds. At 12 seconds you're at 120 mph. At 18 seconds you're at 180 mph. And, of course, you've been traveling this whole time. That sounds unreasonable for cars, it is the reality in space.

The key thing to remember is Voyager isn't getting any faster. It doesn't have any significant acceleration and hasn't for years. It is going the same speed. You're not, you're accelerating. Voyager is traveling at 17 km/s. Our hypothetical constant boost ship is traveling at 20,000 km/s when it catches up. 1,172 times as fast.
Click to expand...
As I mentioned in my post, I basically said a lot of "I don't know," but it isn't as simple as saying that you get to constantly accelerate until you pass Voyager unless you know for a fact that you can carry enough fuel onboard to do it, because eventually you run out of the fuel you brought and you have to rely on the particles in space to fuel the ship, which is a) pretty hard to do with any real accuracy, and b) tends to diminish the further you get from the solar system.

Obviously you never have to worry about slowing down, so eventually you ARE going to pass Voyager no matter how rare the fuel gets, but as I stated, the real issue is would it do so where you wanted it to? Or would it do so somewhere out beyond our capability to reliably communicate with it anymore? Even if your mission isn't to catch Voyager, but just to leave our solar system as quickly as possible, it still might be faster to use conventional propulsion systems because something like an ion scoop or solar sail wouldn't reach that same speed until much later in the journey. I don't know that is the case, but my point is that just because you can choose a constant acceleration system doesn't mean it is the best one for the particular mission. If the mission is to get to point A the fastest, rockets might be the best. If the mission is to get to another solar system, and we somehow have a way to maintain communications, ion scoop is probably the best. And even if we know the particular mission, without all of that data I mentioned earlier, none of us here are ever going to be able to calculate which system is best.
 
Big Phoenix

Big Phoenix

Pronouns: zie/zhem/zer
<Gold Donor>
46,372
98,475
The Master_sl said:
They calculated where each of them would be. Because they wanted pictures, because they used the gravity of said objects for acceleration, etc. Space is basically empty. To say that this was computationally difficult in an era where people were still regularly using slide rules is to vastly understate the case, but they got it done. Mass tends to clump together or become otherwise location stable because of larger masses, or the pull between two masses, etc. Even if you don't know where each and every large object is, although I think people would be surprised at how many objects we've located in our solar system, you know where objects like that will be, because there are only so many places they'd be stable, either orbiting a planet, a moon, falling into the sun and not being an issue, stuck in the asteroid belt, what have you.
Click to expand...
Wonder how many physicists and mathematicians they would have going over their calculations and equations. Pretty amazing to think there hasnt been a navigational failure with a probe sent to Jupiter or beyond.
 
T

The Master

Bronze Squire
2,084
2
Vvoid_sl said:
As I mentioned in my post, I basically said a lot of "I don't know," but it isn't as simple as saying that you get to constantly accelerate until you pass Voyager unless you know for a fact that you can carry enough fuel onboard to do it, because eventually you run out of the fuel you brought and you have to rely on the particles in space to fuel the ship, which is a) pretty hard to do with any real accuracy, and b) tends to diminish the further you get from the solar system.

Obviously you never have to worry about slowing down, so eventually you ARE going to pass Voyager no matter how rare the fuel gets, but as I stated, the real issue is would it do so where you wanted it to? Or would it do so somewhere out beyond our capability to reliably communicate with it anymore? Even if your mission isn't to catch Voyager, but just to leave our solar system as quickly as possible, it still might be faster to use conventional propulsion systems because something like an ion scoop or solar sail wouldn't reach that same speed until much later in the journey. I don't know that is the case, but my point is that just because you can choose a constant acceleration system doesn't mean it is the best one for the particular mission. If the mission is to get to point A the fastest, rockets might be the best. If the mission is to get to another solar system, and we somehow have a way to maintain communications, ion scoop is probably the best. And even if we know the particular mission, without all of that data I mentioned earlier, none of us here are ever going to be able to calculate which system is best.
Click to expand...
Fuel isn't an issue for constant boost technologies, that is the point. Chemical rockets are fuel+reaction mass, rolled into one. Ion engines use solar power for fuel but still need to carry a reaction mass to ionize. But this makes a massive difference. You could carry enough reaction mass for an ion engine to last for years in the same amount of space as a few minutes of rocket burn. Solar sails use zero internal resources, but are not a good return technology (tacking against solar wind is slow). Comets in the Oort cloud have their tails pointing away from the sun still, plenty of solar radiation pressure out there. There are plans for nuclear drives going as far back as 1964 that use a vacuum (not hard to find in space) and are otherwise completely self-contained and will last for 30-40 years of constant operation. Heinlein wasn't kidding when he said if we wanted 1/1000 gee constant acceleration we could start later this afternoon (and he wrote that in 1980). There are things we know work that would just cost a fortune to build in space. That is why people are excited about the VASIMIR drive, because it is actually being tested in space. 39 days to Mars, parking orbit to parking orbit, including the flip over and slow back down maneuver.

Constant acceleration of any reasonable speed (I'll cap that at 1/1000 gee or higher, arbitrarily) is always the best choice for traveling in space. It just isn't, technologically, a choice we can make yet. Even if we have engineers who have been working on this for forty years telling us something will work, we need to get it into space and test it. Even to some place as close as the moon it'd be faster then a conventional rocket. Note the chart earlier that said Mars was 45 days away at 1/100 gee. The VASIMIR gets us to Mars in 39 days. So just a smidge faster than 1/100 gee acceleration.

Phoenix:http://www.honeysucklecreek.net/dss44/voyager.html

You might like that.
 
F

fucker_sl

shitlord
677
9
The Master_sl said:
Fuel isn't an issue for constant boost technologies, that is the point. Chemical rockets are fuel+reaction mass, rolled into one. Ion engines use solar power for fuel but still need to carry a reaction mass to ionize. But this makes a massive difference. You could carry enough reaction mass for an ion engine to last for years in the same amount of space as a few minutes of rocket burn. Solar sails use zero internal resources, but are not a good return technology (tacking against solar wind is slow). Comets in the Oort cloud have their tails pointing away from the sun still, plenty of solar radiation pressure out there. There are plans for nuclear drives going as far back as 1964 that use a vacuum (not hard to find in space) and are otherwise completely self-contained and will last for 30-40 years of constant operation. Heinlein wasn't kidding when he said if we wanted 1/1000 gee constant acceleration we could start later this afternoon (and he wrote that in 1980). There are things we know work that would just cost a fortune to build in space. That is why people are excited about the VASIMIR drive, because it is actually being tested in space. 39 days to Mars, parking orbit to parking orbit, including the flip over and slow back down maneuver.

Constant acceleration of any reasonable speed (I'll cap that at 1/1000 gee or higher, arbitrarily) is always the best choice for traveling in space. It just isn't, technologically, a choice we can make yet. Even if we have engineers who have been working on this for forty years telling us something will work, we need to get it into space and test it. Even to some place as close as the moon it'd be faster then a conventional rocket. Note the chart earlier that said Mars was 45 days away at 1/100 gee. The VASIMIR gets us to Mars in 39 days. So just a smidge faster than 1/100 gee acceleration.

Phoenix:http://www.honeysucklecreek.net/dss44/voyager.html

You might like that.
Click to expand...
jesus fuck. i didnt know about the imminent test of the Vasimir

from wiki

Testing on the space station[edit source | editbeta]On December 8, 2008, Ad Astra signed an agreement with NASA to arrange the placement and testing of a flight version of the VASIMR, the VF-200, on the International Space Station (ISS).[19] As of June 2012[update], its launch is anticipated to be in 2015,[20] the Antares rocket has been reported as the "top contender" for the launch vehicle.[21] Since the available power from the ISS is less than 200 kW, the ISS VASIMR will include a trickle-charged battery system allowing for 15 min pulses of thrust.

Testing of the engine on ISS is valuable because it orbits at a relatively low altitude and experiences fairly high levels of atmospheric drag, making periodic boosts of altitude necessary. Currently, altitude reboosting by chemical rockets fulfills this requirement. The VASIMR test on the ISS may lead to a capability of maintaining the ISS or a similar space station in a stable orbit at 1/20th of the approximately $210 million/year present estimated cost.[9]

VF-200[edit source | editbeta]The VF-200 flight-rated thruster consists of two 100 kW VASIMR units with opposite magnetic dipoles so that no net rotational torque is applied to the space station when the thrusters are firing. The VF-200-1 is the first flight unit and will be tested in space attached to the ISS.[7]
Click to expand...
please dont be a hoax or failure. Stuff like this is what we fucking need for humanity
 
You must log in or register to reply here.