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-   -   That asteroid... where's it going? (http://www.physicsforums.com/showthread.php?t=151609)

Jenab6 Jan16-07 01:36 AM

That asteroid... where's it going?
 
Here's an assessment of the feasibility of diverting asteroid 1981 Midas into a collision with Earth in the year 2018. I'm posting this to show the potential military-political advantage to controlling access to space.

Note the relatively small size of the divert delta-vee. Only about 301.5 meters per second will cause the asteroid to shift into a collision course.

Elements used for Earth.
a = 1.0000001124 AU
e = 0.0167102192
i = 0
L = 0
w = 103.078101 degrees
T = JD 2454468.667 (4:00:29 UT, 3 January 2008)

Elements used for 1981 Midas.
a = 1.7761208686 AU
e = 0.6501608192
i = 39.835472411 degrees
L = 357.03080224 degrees
w = 267.74138625 degrees
T = 2453926.666 (3:59:02 UT, 10 July 2006)

Midas divert delta-vee.
dV = 301.4552 m/s
RA = 17h 19m 45.192s
dec= -48.6042 degrees
Td = JD 2457809.620 (2:52:48 UT, 25 February 2017)

Transfer orbit is an ellipse with aphelion at departure.

Elements of the Midas transfer orbit.
a = 1.776419 AU
e = 0.6495124
i = 39.82184 degrees
L = 356.6238 degrees
w = 267.1621 degrees
T = JD 2457377.22 (17:16:48 UT, 20 December 2015)

Minimum distance between Earth's orbit and the Midas transfer orbit: 97.8 km
Minimum distance occurs at heliocentric longitude: 176.623768 degrees

Transit time = 384.379 days.
Impact on Earth at JD 2458194.0 (12h UT, 16 March 2018)

Midas approaches Earth from approximately
RA = 14h 2m
dec= +35.1 degrees
Facing Midas on arrival is: The North Pacific Ocean.
A vertical impact could occur: NE of Hawaii, S of Valdez AK, W of Los Angeles CA.

Midas' diameter: 3.4 kilometers
Assumed density: 2200 kg/m^3
Estimated mass: 4.5E+13 kilograms
Arrival speed in transfer orbit: 28.304 km/sec
Impact speed: 30.432 km/sec
Impact energy: 2.1E+22 Joules = 5.0 teratons TNT equivalent.

Jerry Abbott

cesiumfrog Jan16-07 01:58 AM

You're talking about taking building the world's biggest cannon, and pointing it roughly in the direction of your enemy's continent. You don't have the accuracy to know you won't instead hit your own country and regardless you risk globally extinguishing human civilisation. It will be extraordinarilly costly, and the target will launch a massive (nuclear) counterstrike prior to the impact (M.A.D.). There is indeed a military advantage to space control, but this capability is not it.

Jenab6 Jan16-07 09:14 PM

Quote:

Quote by cesiumfrog (Post 1214335)
You're talking about taking building the world's biggest cannon, and pointing it roughly in the direction of your enemy's continent. You don't have the accuracy to know you won't instead hit your own country and regardless you risk globally extinguishing human civilisation. It will be extraordinarilly costly, and the target will launch a massive (nuclear) counterstrike prior to the impact (M.A.D.). There is indeed a military advantage to space control, but this capability is not it.

I wasn't recommending it be done. I was only pointing out the possibility of doing it. The energy involved in diverting Midas is 488 megatons TNT equivalent, about equal to five of the largest hydrogen bombs.

PeterFries Jul15-07 01:21 AM

Please excuse me for bumping this half-year old thread, but I'm working on a science fiction story with a similar premise to the idea being proposed here and was curious about the feasibility of my premise (I'm no physicist or mathematician)...

What if, rather than diverting an asteroid or similar Near Earth Object into a collision with our planet, the goal was to push it into a collision course with a specific spot on the lunar surface?

I confess to not even knowing how to begin trying to calculate or even to portray convincingly the orbital mechanics, the needed mass of the object in question, the size of a payload required to divert the NEO, and other factors required to pull off such a feat.

mgb_phys Jul17-07 06:01 PM

You can in theory divert the asteroid to hit anything you like, the moon has a predctable orbit and so you can calculate where it will be at any future time with reasonable accuracy.

Diverting an asteroid just involves giving it a push in the right direction!
The earlier you give it the push the less force you will need to get a given degree of movement, ideally you would give it a small nudge this time round the sun so that it had moved the correct amount the next time it came round. However the period (time needed for an orbit) of such an asteroid is 1000s of years so instead you probably want your Bruce Willis team to head out toward it while it is a decent distance away but heading toward us and attach rocket moters to give it a nudge in the right direction.

PeterFries Jul18-07 11:56 PM

Quote:

Quote by mgb_phys (Post 1380502)
You can in theory divert the asteroid to hit anything you like, the moon has a predctable orbit and so you can calculate where it will be at any future time with reasonable accuracy.

Diverting an asteroid just involves giving it a push in the right direction!
The earlier you give it the push the less force you will need to get a given degree of movement, ideally you would give it a small nudge this time round the sun so that it had moved the correct amount the next time it came round. However the period (time needed for an orbit) of such an asteroid is 1000s of years so instead you probably want your Bruce Willis team to head out toward it while it is a decent distance away but heading toward us and attach rocket motors to give it a nudge in the right direction.

Thanks for the response!

Is it conceivable that the "nudge" could be done remotely, via some sort of small near-NEO nuclear detonation? I don't need a Bruce Willis team for my story, and the intended lunar target is relatively small, nowhere near the size of a city or anything, so my inclination is that the asteroid or similar object wouldn't need to be very massive at all.

Ideally, I wouldn't want to affect a change that needed centuries or eons to take effect; something far more immediate would be much better dramatically. :smile:

That's good input that the farther out from the target, the better, as far as orbital manipulation goes.

mgb_phys Jul19-07 11:07 AM

The problem is a nuclear blast in space doesn't really give you very much force. You do get quite a lot of heat energy released and so the damage caused to a city on earth is largely due to this superheating the air which then expands and creates a shock wave that generally lowers proprty values for a considerable distance! This is why for maximum inconvenience you detonate a device a couple of km above the target - so that the spherical shock wave slams down onto it.

In space the only force on the asteroid would be the energy from the device heating some part of the surface which would then evaporate a jet of material and create a force in the opposite direction. You could improve the efficiency by burying the device into the asteroid and so vaporising a volume of rock, some of which would fly outward giving a force in the opposite direction.
It would be tricky to get an accurate amount of "push" and so an accurate final orbital path from these methods. I would have thought it was better to land a few big rocket engines nose-first in a few places on the asteroid and then you can nudge it into any path you like.

There are probably lots of web sites devoted to dismissing the science in the bruce willis movie - some of these probably have good descriptions of how you would do it.

What kind of SF are you writing? The Robert Heinlein/Larry Niven type where you give the orbital calcs in the appendix or a more modern free style.

PeterFries Jul19-07 02:39 PM

Quote:

Quote by mgb_phys (Post 1381824)
The problem is a nuclear blast in space doesn't really give you very much force.

In space the only force on the asteroid would be the energy from the device heating some part of the surface which would then evaporate a jet of material and create a force in the opposite direction. You could improve the efficiency by burying the device into the asteroid and so vaporising a volume of rock, some of which would fly outward giving a force in the opposite direction.

What kind of SF are you writing? The Robert Heinlein/Larry Niven type where you give the orbital calcs in the appendix or a more modern free style.

Ha, I'm no Heinlein or Niven -- I was just trying to gauge the believability of the plot device at the heart of my story, that a Near Earth Object could be weaponized by a repurposed system meant to divert such objects. I was surprised when I found this thread because the original poster's concept wasn't too far off from mine.

Again, thanks for the input. It gives me some stuff to mull over.

mgb_phys Jul19-07 02:48 PM

Quote:

repurposed system meant to divert such objects
Easily - but if I was building a sytem to divert such objects it would either be a station out past the orbit of mars with either:
1, A very big laser to heat a carefully calculated small patch of the surface which would vaporise giving a jet of material which would push the asteroid the other way.
2, A kinetic impact weapon, basically a big lump of metal (tungsten/uranium) accelarated to a very high speed (google railgun) which would slam into the asteroid and nudge it in the right direction.

It's completely plausible that a defence system like this could become a weapon, see Niven's ringworld engineers.

turbo Jul19-07 03:15 PM

The masses involved need not be huge. Theoretically, you could gather lots of modest-sized objects from the asteroid belt, tug them to orbit around your "target" and launch them in the right direction with a rail-gun and let your target body's gravitational pull accelerate your projectiles. If you wanted to make a get-away during your attack, you could use the recoil of your mass-driver for propulsion.

PeterFries Jul19-07 03:26 PM

The problem with a railgun as the potential deflection system is that if you have railgun tech already in space, couldn't that instead be used as the lunar-targetting weapon, skipping a step in my scenario?

Hmmmm. I was hoping for a tech solution not too far removed from current know-how, sort of a garage-kit weapon used in a way no one expected...

zorgon Dec24-07 01:01 AM

Quote:

Quote by Jenab6 (Post 1214321)
Here's an assessment of the feasibility of diverting asteroid 1981 Midas into a collision with Earth in the year 2018. I'm posting this to show the potential military-political advantage to controlling access to space.

Fascinating work :cool:

One has to ask why would such calculations be needed? Well I suppose you could use it to apply for a job with these gentlemen

Rand Corporation
NATURAL METEOROIDS AS WEAPONS
http://www.rand.org/pubs/monograph_r...R1209.appc.pdf

LURCH Dec24-07 03:35 PM

Maybe you could use other objects near your intended weapon, rather like a billiard "bank-shot." Find a small object that will pass relatively close to the main object at a high closing speed. Use a bunker-busting nuke to deflect the small object (easier to deflect because of its lesser mass), and let it collide with the larger object, which will be diverted toward your target.

As for hitting a location on the moon, it would be easier than hitting a location on Earth, because of the Moon's tidal locking with Earth. The moon is rotating much more slowly, so a couple of seconds error results in much less distance off target.


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