Large astroid hitting earth

[Armitage]

Originally posted by: Soccerman06

Originally posted by: Armitage

Originally posted by: Soccerman06

Originally posted by: Armitage

Originally posted by: Soccerman06

Originally posted by: AbsolutDealage
Quit feeding this guy. Seriously.

If there were ever an argument for being able to hide posts from a specific user, it would be him. Just read around his HT posts and you will see what I mean.

I'll shutup now, b/c this forum is not for flaming.

-----

Back on topic, everyone else is right piddle. You cannot use E=MC² in this case, because you are not going to be turning the asteroid into energy. What you are essentially calculating is the energy of the asteroid if it were travelling at c... which means nothing. What you really want is the kinetic energy of the asteroid, which any high school physics book will tell you, is K=mv^2/2.

I hope you meen Ke=mv^2.

The thing is with asteroids, meteors, comets and whatnot is if one was going to hit Earth, and if we detected and launched some device as early as say 10 milion miles away

10 million miles isn't that far on this scale - only about 3.8 degrees of the earths orbital path. If that's the soonest we can intercept, I suspect we're toast. If you have less then the orbital period of the asteroid to work with before impact you want to do your manuever about 180 degrees away from the impact point for in-plane manuevers, or 90 degrees away for out of plane (inclination) manuevers. Out of plane takes alot more energy, so forget about it for the moment. In this in-plane case case you are hoping to raise or lower the orbit of the impactor by at least half the radius of the earth.

Let's pick a very simple case - an asteroid with a aphelion @ 300,000,000 Km and perihelion @ the earth - 150,000,000 Km. So let's say we want to raise the perihelion so the object no longer crosses earth orbit - make it an even 13,000 Km.

The energy of the asteroid orbit is: E = -u/2a = 1.3271544e11/(2*225000000) = -294.9232 km^2/s^2

Orbital velocity is given by E = V^2/2 - u/r

For the initial orbit:
Vaphelion = 17.173328157 Km/s
Vperihelion = 34.34665631 Km/s

for the raised orbit:
Vaphelion = 17.173824254 Km/s
Vperihelion = 34.34467197 Km/s

So the dV needed at aphelion is 0.4961 meters/second

Let's assume a 1Km diameter spherical stone asteroid. Given a density of 2 g/cm^3 its mass will be approximately 8.3776e12 Kg

So the energy needed to give it that dV will be 1/2 M V^2 = 1.0309e12 kg m^2/s^2

This works out to 0.2464 kilotons

Quite a bit less then I was expecting - I better check my math . However, when you consider bombs, I suspect that setting off a bomb next to an asteroid will be a very inefficient & unpredictable way to change the velocity of a rock in space. If the asteroid has a lower perihelion, the energy is higher, so anything you do with it will take more energy as well.

Now if you have several revs to deal with it, you can get away with less dV. You don't have to raise the orbit by that amount, but simply alter the period enough so that even though it crosses earths orbit, the timing is changed and the earth isn't there at the same time as the asteroid. This is left as an exercise for the reader

, we would easily be able to deflect it out of the way. Even if you nudge it less than 1 degree, that is still way more than enough deflect it out of Earths path.

One degree of what?

1 degree if you think about the earth and the meteor/asteroid on an xy axis.

But I ment 10 billion sorry bout that.

Sure, what's a few orders of magnitude between friends! But how do you plan to spot an earth impacting asteroid or comet at a distance more then double the radius of Neptunes orbit?

There is another thing you can do besides using nukes. Basically launch many rockets into space and put them on an intercept course with the meteor/asteroid. Once they have gotten into the proper position, they would shoot out a tow hook which would ancor into the asteroid. Then powerful chemical jets would propel the rock out of our way. There would have to be many rockets depending on which direction you would want the rock to go, but the farther away, the less required. This solution could only work if the rock was not rotating at a major speed.

Sure, that'll work.
Using an Isp of 465 which is about what the space shuttle main engine gets and is pretty good for a chemical rocket I get a mass ratio of 1.00011 for the 0.5 m/s dV above.

So you just need 0.00011 times the mass of the asteroid in fuel - that's just shy of 1 billlion Kg Any plans on how to get that much gas up there?

Other alternatives include solar sails, solar panels with ion engines, etc. But these are very low thrust, so you beter get there early!

I havent thought of getting it there, thats not my job, I think of things, others figure out the problems

So what good is thinking of things if they can't work?
Our largest launch vehicle can put about 23,000 Kg into low earth orbit. Assuming the entire payload is fuel (ie. no structural weight), it would take over 43,000 launchs just to get that fuel to LEO. Getting it to the asteroid is another whole issue.

Solar sails would work but the problem is it would have to be soo big to counteract the weight of the rock that it would be easier to just use rockets, and you cant put it at an angle because there would be too little oomph from other sources, so the only real direction you could use would be slowing the rock down, but that also creates a problem of it might hit the earth at a later point in time.

A solar sail would have very low thrust, which is why you need it up there for a very long time. But it doesn't just slow it down. If you deploy it on the outbound half of the orbit, it speeds it up. On the inbound half, you could furl it or such. But it doesn't really matter whether it is slowing it down or speeding it up - the goal is to change the period so that the phasing WRT the earth is changed and it doesn't hit. Faster or slower will work. The example I gave above of raising the perihelion above earth's orbit is completely contrived in that respect - it's very unlikely that you would have a situation like that. A big problem with the solar sail idea is the spin of the asteroid though.

Maybe I'll try a phasing example a bit later.

Ion drives would be an intriging thought but they need a nuclear reactor to be of any use, because batteries would die way too soon and solar panels would barely put enough energy off at that great of distance.

Nasa has been thinking up ways to use nukes as a propulsion device, but that would require large amounts of testing before we could actually use one. But think about using many small nukes as a way to give a meteor a nudge in the right direction. They also are thinking about using plasma as a propulsion but how do you heat up gasses above millions of degrees without using a nuke and for a very long time, in space? :laugh: someone stop my babbling

 

[Jeff7]

Originally posted by: Gibsons
So what's 3 orders of magnitude between friends?

Yeah, in 5 years, you're working with astronomers, watching for incoming objects.
"Psh, who cares about that asteroid? Your report said it's only 1 meter wide."
"Oops, I mean 1 kilometer wide. What's 3 orders of magnitude between friends?"




I loved doing calculations in physics class - something like if you'd slam a golf ball into NYC at half light speed, you'd still devastate most of the city. Relatavistic speeds were fun.

 

[egkenny]

You would still need a delivery system. The farther out you hit it the bigger deflection you can make in its path. This means a spacecraft that has to go millions of miles from the earth. Coming up with the bomb and rocket in a few months may not be possible. Even then there would no time to test it. We all know how reliable rockets are. Then there is the posibility of needing multiple warheads to achieve the needed effect. Then there is the repercussions of it going off course and causing more problems...

 

[Soccerman06]

No not really, Its quite easy to get a delivery system that far, we already have technology to get that far like ion drives and solar sails. Do a little research before you post egkenny

 

[Armitage]

Originally posted by: egkenny
You would still need a delivery system. The farther out you hit it the bigger deflection you can make in its path. This means a spacecraft that has to go millions of miles from the earth. Coming up with the bomb and rocket in a few months may not be possible. Even then there would no time to test it. We all know how reliable rockets are. Then there is the posibility of needing multiple warheads to achieve the needed effect. Then there is the repercussions of it going off course and causing more problems...

It's not to bad to get there, though not foolproof as the various mars missions have demonstrated. But it takes time to develop a mission like that, lots of flight time to get there, and there are only so many launch windows. For example, you only have a feasible launch window to mars about every two years. Of course, unlike the Mars missions, you don't neccesarily need to rendevous - if you can pass by at the right proximity & orientation you can pop the bomb as you fly by. Of course you'll only get one shot at it, though that isn't much different then anything else in deep space operations.

All of this points to the need to spot it early - on the order of years early - decades is better.

 

[egkenny]

Originally posted by: Soccerman06
No not really, Its quite easy to get a delivery system that far, we already have technology to get that far like ion drives and solar sails. Do a little research before you post egkenny

I know a little about propulsion systems. I used to work for a contractor for the Space Shuttle's Propulsion Divsion at NASA's MSFC.

Ion drives and solar sails are very cost effective but provide only limited thrust. Sure the thrust is steady but speed builtup is slow. You really need something with a lot more thrust to get you to the target in minimal time.

Suppose you have the luxury of six months warning. That give you only weeks to get the whole thing launched to intercept it only a few months from the earth. That would require a rocket more powerful than we currently have. Remember without the luxury of a minimal energy launch window you need as much thrust as you can get.

All this assumes a minimal orbital plane change. If the asteroid is in a different orbital plane then that ups the fuel requirements tremendously. As an example the Space Shuttle with all it's onboard fuel can only change it's orbital plane by a few degrees.

It would also require very precise timing for intercept because without braking it would aproach at maybe 10-20 km per second.

You can't just order a booster rocket and the required upper stages to boost a payload into interplanetary space. The whole thing must be carefully integrated and tested or the final result will have very little chance of succeeeding.

 

[the splat in the hat]

lets face it , if its as big as a footy field and is headed straight for us, fast , we are f@#$K#@D, we cant stop it at the moment, the fact is EARTH or its humans have NO international plan to prevent or stop these things yet.
Everything else is just speculation , or guestimation.
Humans can also only watch a small percentage of the sky at any given moment, even with our computors we really need more of them places looking for them, and internationally, some rocks we know to be travelling so fast we cant track them, what do we do there ?
And if a body the size of our moon comes straight for us next week ? Even at low velocity l dought we could stop something with so much mass.

 

[imported_Dimicron]

Originally posted by: Soccerman06
No not really, Its quite easy to get a delivery system that far, we already have technology to get that far like ion drives and solar sails. Do a little research before you post egkenny

...and how many probes have been lost heading to Mars?

 

[Armitage]

Originally posted by: the splat in the hat
lets face it , if its as big as a footy field and is headed straight for us, fast , we are f@#$K#@D,

We might stand a chance of doing something about stuff that size.

we cant stop it at the moment, the fact is EARTH or its humans have NO international plan to prevent or stop these things yet.
Everything else is just speculation , or guestimation.
Humans can also only watch a small percentage of the sky at any given moment,

While I'll agree that we need more & better surveillance, you don't have to look at the whole sky all the time. You just have to survey it well enough & often enough to map whats out there. Asteroids and comets to just materialize out of nowhere.

even with our computors we really need more of them places looking for them, and internationally, some rocks we know to be travelling so fast we cant track them, what do we do there ?

The fastest thing out there are comets and we can track those well enough to run a probe into them.

And if a body the size of our moon comes straight for us next week ? Even at low velocity l dought we could stop something with so much mass.

There is nothing out there even remotely close to the size of our moon that could ever hit us.

 

[Soccerman06]

Originally posted by: Dimicron

Originally posted by: Soccerman06
No not really, Its quite easy to get a delivery system that far, we already have technology to get that far like ion drives and solar sails. Do a little research before you post egkenny

...and how many probes have been lost heading to Mars?

I said nothing about the payload reaching the rock, just said its easy to get out that far.

 

[DrPizza]

To answer your question more directly, google for shoemaker-levy. We've seen a comet break into pieces and smash into Jupiter. IIRC, the largest "explosion" was larger than the earth.

Tons of stuff from here: http://www2.jpl.nasa.gov/sl9/sl9.html

 

[the splat in the hat]

''There is nothing out there even remotely close to the size of our moon that could ever hit us. ''


omg we are so smart ,we know so much about whats out there, come on, really we have seen and found things beyond our wildest imagination, never say never , there is a theory our moon was born though a body the size of mars hitting earth , whether its true or not , who knows , but we cant sit here and say 100 per cent we know theres nothing remotely close to the size of the moon could ever hit us , we just dont know, can we see everything out there ?
Just because it hasn't happened for a long long time that we know off, does not mean its not a real possability of happening when its very possible physicly , we cant even rule out if a black hole we dont know about strays our way and wipes our solar system out, ever since we discovered they were real.

Hell whos to say, a body the size of Jupitor made of rock and ice doesnt scream into our solar system at a higher speed than we have ever seen or imagined, cant happen...

The universe is so full of suprises its just not funny, and when it comes to rocks , at speed , we just dont know everything.......yet....

 

[DrPizza]

splat's got a decent point. The words "ever hit us" should probably be changed to "in the near future on a geological time scale"

 

[Armitage]

Originally posted by: DrPizza
splat's got a decent point. The words "ever hit us" should probably be changed to "in the near future on a geological time scale"

I don't think so, though I guess it falls into the realm of splitting hairs. There is nothing anywhere close to the size of the moon unaccounted for in the inner solar system. It's just to big - about 50% bigger then Pluto in radius (1738 Km radius vs. 1160 Km) and consequently over twice the volume. You'd see it by gravitational perturbations of other objects alone.

As far as rouge extrasolar planets cruising through the solar system - none have ever been observed. Doesn't mean they don't exist, but the incidence must be so low that the risk is extraordinarily low. If one were to pass through though, you'd only get one shot at it as it goes on it's way. Considering that anything we might do against an asteroid would likely only be effective if we had a few revs to work with, there likely is nothing we could do against this.

 

[the splat in the hat]

ok , and what are the odds of life on Earth.................?
still never say never, to presume to know everything is to put yourself behind the 8 ball.
There are millions of things we have never seen but we know all do we ?
Ok the odds are small , but life on earths odds, can we even get a guestimate thats accurate ?
I dont think so, its such a small number, when you consider all the events that have brought humans to here and now, i can argue that its as likely as life arising and NOT be wrong, the odds are so small ay ?
And to be as bold to say we are going to see the gravitational pull when we cant even track all the objects out there is pretty far fetched i recon, especially if its moving very fast, heck we may not even see it at all.....just die.........
Space is the one frontier we DONT

 

[the splat in the hat]

ok , and what are the odds of life on Earth.................?
still never say never, to presume to know everything is to put yourself behind the 8 ball.
There are millions of things we have never seen but we know all do we ?
Ok the odds are small , but life on earths odds, can we even get a guestimate thats accurate ?
I dont think so, its such a small number, when you consider all the events that have brought humans to here and now, i can argue that its as likely as life arising and NOT be wrong, the odds are so small ay ?
And to be as bold to say we are going to see the gravitational pull when we cant even track all the objects out there is pretty far fetched i recon, especially if its moving very fast, heck we may not even see it at all.....just die.........
Space is the one frontier we DONT know everything about , and until we actually go out there in numbers l suspect the Universe will still have some wikid secrets for us to find ..........

 

[the splat in the hat]

wtf

 

[DrPizza]

Originally posted by: Armitage

Originally posted by: DrPizza
splat's got a decent point. The words "ever hit us" should probably be changed to "in the near future on a geological time scale"

I don't think so, though I guess it falls into the realm of splitting hairs. There is nothing anywhere close to the size of the moon unaccounted for in the inner solar system. It's just to big - about 50% bigger then Pluto in radius (1738 Km radius vs. 1160 Km) and consequently over twice the volume. You'd see it by gravitational perturbations of other objects alone.

As far as rouge extrasolar planets cruising through the solar system - none have ever been observed. Doesn't mean they don't exist, but the incidence must be so low that the risk is extraordinarily low. If one were to pass through though, you'd only get one shot at it as it goes on it's way. Considering that anything we might do against an asteroid would likely only be effective if we had a few revs to work with, there likely is nothing we could do against this.

I did say "in the near future on a geological time scale" meaning it's not going to happen in the next few 10's of millions of years. It's nothing that humans have to worry about. How long ago was it that a new "planet" was found that's bigger than pluto? I don't know how the new object compares in size to the moon, whether it's bigger or smaller. But, the planets orbits are chaotic, and out in the kuiper belt, it's far from unrealistic to believe that a passing interstellar object could give a tug sending a few of those objects into the inner solar system.

 

[Vee]

I was going to say that I'm all with DrPizza on this.
Now I'm not so sure, because I think it's quite likely that it is going to happen within the next 10 million years. Never mind Moon sized objects, it takes far, far less than that.
And I do think it is something that humans need to worry about.
You see the probability of an extinction or near extinction collision is so high that it's more a question of absolute certainty than a "probability" or "risk".
The only question is when. And it's just as likely to happen next month, or next year, or next decade, as it will be millions of years from now.

The possibilities of intervening and stopping such a disaster are probably quite good, as long as we have preparations ready and get sufficiently early warning.

If the trajectory can be manipulated very early, it may take only a small impulse to make it miss Earth.

 

[DrPizza]

Oh sure, go ahead and change the size of the object

As far as the argument that extrasolar planets are rare, "because we've never seen one" is quite silly. We've only been looking for a few hundred years. It's impossible from our data to conclude their incidence must be low. (again, on a geologic time scale) I'd think that one every couple million years would be considered relatively frequent.

 

[egkenny]

Some estimates:

4143 Object will come within 0.2 AU (18.6 million miles) of the earth within the next 33 years
6 will come within the distance of moon (238,855 mi) within the next 33 years:

These six objects are:
Name/ID | Date closest| Distance
2005 BS1 | 2005 Jan 13 | 0.001772 AU
2005 FN | 2005 Mar 18 | 0.0009627 AU
2001 WN5 | 2028 Jun 26 | 0.001670 AU
Apophis | 2029 Apr 13 | 0.0002318 AU
2004 MN4 | 2029 Apr 13 | 0.0002506 AU
2000 SB45 | 2037 Oct 07 | 0.001418 AU


Definitions:

Vimpact - Velocity at atmospheric entry
Diameter - Estimate diameter (accurate within a factor of 2)
Mass - Estimated mass (accurate within a factor of 3)
Energy - The kinetic energy at impact: 0.5 * Mass * Vimpact^2. Measured in Megatons of TNT.
Megaton of TNT = 4.184 × 10^15 joules

Examples:

Example 1: Impact Energy for "2000 SB45"
Vimpact = 13.45 km/s = 8.357 mile/sec
Diameter = 0.050 km = 164 feet
Mass = 1.3e+08 kg = 286 million pounds
Impact Energy = 0.5 * 1.3e+08 kg * 13.45 km/s * 13.45 km/s
Impact Energy = 2.8 megatons of TNT

Example 2: Impact Energy for "Apophis":
Vimpact = 12.59 km/s = 7.823 mile/sec
Diameter = 0.320 km = 1050 feet
Mass = 4.6e+10 kg = 101 billion pounds
Impact Energy = 0.5 * 4.6e+10 kg * 12.59 km/s * 12.59 km/s
Impact Energy = 871 megatons of TNT

Comparisons of energies:

Little Boy weapon dropped on Hiroshima = 13 kilotons of TNT
Typical H-bomb today = 1 megatons of TNT
Largest nuclear weapon ever detonated = 50 megatons of TNT
Eruption of Mount St. Helens = 350 megatons of TNT
Eruption of Krakatoa = 5250 megatons of TNT
Impact of 15 km wide meteor or comet with Earth = upwards of 100 million megatons of TNT

 

[the splat in the hat]

um that we know off..........

 

[Vee]

Originally posted by: egkenny
Impact of 15 km wide meteor or comet with Earth = upwards of 100 megatons of TNT

There's got to be something wrong here.

A comet that is in elliptical orbit around the sun can reach us with an impact velocity of 50km/s. A parabolic comet would come at any, higher, speed.

So the impact energy from 15km wide objects should be more like
upwards of 100 million * million * megatons. You seem to have lost a factor of 10^12 somewhere?


Edit: removed assumption that near Earth objects in examples came from the asteroid belt.

 

[egkenny]

Originally posted by: Vee

Originally posted by: egkenny
Impact of 15 km wide meteor or comet with Earth = upwards of 100 megatons of TNT

There's got to be something wrong here.

A comet that is in elliptical orbit around the sun can reach us with an impact velocity of 50km/s. A parabolic comet would come at any, higher, speed.

So the impact energy from 15km wide objects should be more like
upwards of 100 million * million * megatons. You seem to have lost a factor of 10^12 somewhere?

Edit: removed assumption that near Earth objects in examples came from the asteroid belt.

The number for the 15km wide object is only a typical value. Actual values vary widely depending upon many factors including mass and velocity. The best documented values are for lower speed objects in periodic orbits that come near the earth. Objects in parobolic and elliptic orbits are harder get data on unless someone is lucky enough to detect it while it is inbound. If we get enough positional data we can compute orbital elements. With these we can compute estimates of velocities.

I did my calculations using published mass and velocity values. Even these are estimates based on observation data and can be off by a factor of 2 or 3. If you have better data values for known objects please post them.

 

[the splat in the hat]

who cares about the perfect maths on it, ya can never get it without the variables you mention , so just round it out n say if its big / fast/ headed straight for us/ TOAST.

hahaha drinkin again , go sunday....