Set in present day Earth, several space agencies and military across the globe had been closely tracking many near earth objects for many years using deep space telescopes and also an array of ground based lenses. One of the NFO has attracted several eyes and minds, it is named "Horus" after a deity worshiped by the ancient Egyptians as the name means "the distance one". Based on existing calculation on Horus's size and trajectory, it is concluded that this asteroid a hundredth the size of Moon is heading towards Earth at 23 000 mph and will impact in 720 days.

"We need a plan I want to live to see tomorrow again! any good plan?" - leader of committee.


Ensure the survival of humankind takes priority i.e given only 720 days left evacuation from Earth is unlikely.


  • Use all available resources at your disposal i.e. H-bomb, laser... etc
  • No pseudo science please
  • All methodologies must not contradict with current known physics
  • Be creative i.e make good use of your surrounding
  • Minimize casualties i.e. at least not fewer than 10% of population (2015)

[Known Description of Horus]

It is spherical and composed of rock and ice with an estimated diameter of 100Km (density is 2500 Kg per cubic meter), there is a thick layer of fully ionized plasma (measured with a whopping 1 million kelvin in temperature) enveloping Horus by a strong magnetic field (about 1000 tesla) which suggest it may come from extra-terrestrial intelligence origin.


Density = 3000kg/m^3.

Volume = (4/3)(3.14)(480000m/2)^3 = 5.79x10^16m^3

Mass = (3000Kg)(5.79x10^16m^3) = 1.74x10^20Kg

Kinetic energy while traveling at 23,000 miles per hour (10281.92 meter per sec) is (1/2)(1.74x10^20Kg)(10281.92mps)^2 = 8.95x10^23j

Type 1a supernova with 2x10^28j totally dwarfed my Horus but that is still formidable.

Time to impact is (10000m)/(10281.92mps) = 0.97s

Rate of energy dissipation is (0.97s)(7.35x10^28j) = 8.68x10^23w

Making our sun appears brighter at 3.84x10^26w

Therefore reduce size and density but maintain speed,

New density = 2500kg/m^3. New diameter = 100Km

New volume = (4/3)(3.14)(100000m/2)^3 = 5.24x10^14m^3

Mass = (2500Kg)(5.24x10^14m^3) = 1.31x10^18Kg

Kinetic energy while traveling at 23,000 miles per hour (10281.92 meter per sec) is (1/2)(1.31x10^18Kg)(10281.92mps)^2 = 6.73x10^21j

Time to impact is (10000m)/(10281.92mps) = 0.97s

Rate of energy dissipation is (0.97s)(6.73x10^21j) = 6.53x10^21w

Many times weaker than the largest nuclear weapon ever built, "Tsar Bomba" and our sun more brighter but it is acceptable in our case.

Please check my calculation, thanks.


  • Easy : Horus is compose of rock and ice, a hundredth size of Moon and you have 2 years.
  • Normal : Same as easy about double size of Easy and you have 1 year.
  • Hard : Same as Easy + plasma shield + magnetic shield.
  • Insane : Same as Hard and Horus has a twin trailing 1000 Km right behind.

[Purpose] I'll be writing books for different age groups and background so this is where the difficulty levels come in. I need unique and innovative ideas thanks.

[Note] I'll assume all answers are by default set at "Easy" difficulty level unless otherwise stated. I've scaled down the difficulty tremendously due to popular demands see Horus v2.


v2: mass=0.0128xMoon/speed=23000mph/eta=720days***New***

v1: mass=0.5xCeres/speed=23000mph/eta=720days/remove starlite

v0: mass=2xCeres/speed=24000mph/eta=30days

  • $\begingroup$ Unstable Horus makes things harder, not easier... $\endgroup$
    – John_H
    Commented Mar 27, 2015 at 7:11
  • $\begingroup$ please run the numbers again maybe there'll be a shed of light in a miasma shrouded with fear. Probably I'll be discarding this question soon, anyway thanks for all of your insights again. $\endgroup$
    – user6760
    Commented Mar 27, 2015 at 7:26
  • $\begingroup$ @user6760 The stability doesn't matter, even if you break it up, it's the same mass hurtling towards Earth at the same speed with the same energy. $\endgroup$
    – Schwern
    Commented Mar 27, 2015 at 7:41
  • $\begingroup$ The goalposts have shifted so far, this is a different question and our answers don't make sense. I would recommend putting the question back the way it was and starting a new one with your new parameters. $\endgroup$
    – Schwern
    Commented Mar 27, 2015 at 17:16

6 Answers 6


"Normal" difficulty is ridiculously hard. We clearly don't have a solution to this sitting on a shelf somewhere so we will need to:

  • Get funding to make a solution.
  • Demonstrate that the threat is credible enough to warrant a major shift in global spending to get the project off the ground.
  • Get more funding, because the project scope gets better understood.
  • Design the device.
  • Build it
  • Can't test it, so this has to be done perfectly the first time, without a single error in all million lines of code, multiple rocket motors, and a few thousand rivets and/or welds.
  • Integrate it (it's going to need to be made all over the world to get the job done fast enough)
  • Get it into space to do an intercept
  • Actually intercept.

Now it is generally accepted that breaking up the asteroid is worse than actually letting it collide with earth. Many studies have shown that a hail of smaller meteors actually does more damage. The only valid solution that we have found using real modern NASA science is to push it away from Earth colliding trajectories. Now, let's assume the Ceres sized rock is on a bee-line right for the center of Earth's mass. This means we need to divert it roughly 6300km. The effect of rockets in space is often measured in "delta-V" or the ability to change velocity. The amount of delta-V we need depends on how long we have to push the rock out of the way after designing and building are done.

  • 1 day - 73 m/s
  • 10 days - 7.3 m/s
  • 30 days - 2.4 m/s

This is just simple physics. Now, ceres has a mass of rougly $900\cdot10^{18} \text{kg}$. With this, we can find the total impulse needed to cause that deflection. This is measured in N-s, but for a sense of scale, they are also provided in terms of theoretical maximum impulse of a Saturn V rocket ($5.6\cdot10^9\text{N s}$).

  • 1 day - 73 m/s - $6.57\cdot10^{22} \text{N s}$ - 11,732,142,857,143 Saturn V's
  • 10 days - 7.3 m/s - $6.57\cdot10^{21} \text{N s}$ - 1,173,214,285,714 Saturn V's
  • 30 days - 2.4 m/s - $2.16\cdot10^{21} \text{N s}$ - 385,714,285,715 Saturn V's

This should get you a sense of just how brutally unstoppable a planetoid can be.

What if we amped things up. What if we tried to use everything we have at our disposal? To push the rocks out of the way, we need to be able to exert force against something. One approach would be to magically fracture the rock in half, and then apply energy (through a mystical process) to shove the halves in opposite directions around Earth. Let's even say we can do this "now" with no innovation. We have 30 days, so a meager 2.4m/s of delta-V is required. Using $E=1/2mv^2$ we can determine how much energy we need to put into ceres to deflect it. Half of the energy will go into pushing half of the rock one way, half goes the other way. This comes out to $2.59\cdot10^{21} \text{J}$. Turning to one of my my personal favorite charts of all time, Orders of Magnitude (Energy) we see the comparisons:

  • $7.9\cdot10^{21} \text{J}$ - estimated energy contained in the world's petroleum reserves as of 2010
  • $2.9\cdot10^{22} \text{J}$ - identified global uranium-238 resources using fast reactor technology
  • $3.9\cdot10^{22} \text{J}$ - estimated energy contained in the world's fossil fuel reserves as of 2010

We would need to harness a tremendous amount of energy. Viewed different ways, it could be thought of as 1/3 of the total petroleum reserves in the world, or 3.8% of the entire world's fossil and nuclear fuel reserves just to have enough energy to do the job. This needs to be handy today, though in reality most of those reserves are still underground.

If we give our miners as much times as possible, we come across a hard limit of 24 days to mine out the entire energy reserves of our planet. That gives us 6 days to use the entire fossil and U238 energy reserves of our planet to impart the energy needed to shove both halves apart at 12.3m/s in each direction, just barely causing them to miss our planet.

Good luck!

  • $\begingroup$ It gets worse. The OP says it's twice the diameter of Ceres so likely 8 times the mass. $\endgroup$
    – Schwern
    Commented Mar 27, 2015 at 6:26
  • $\begingroup$ @Cort I'm totally impressed by your insight and same goes to Henry Tayor, but I must defense the difficulty ranking system. Take hollywood movies for example they have filmed many movies depicting similar scenario and they actually got science consultant involved. The introduction of difficulty ranking is to enable intellectual to transcend beyond the plots already discussed in most disaster movies. I need good insights and ideas such as yours so I can write good novel, thanks. $\endgroup$
    – user6760
    Commented Mar 27, 2015 at 6:28
  • 5
    $\begingroup$ @user6760 Do not use Hollywood movies and "science" in the same sentence. Giant rock space disaster movies may have a science consultant, but they usually ignore them. There's no transcending the physics here, your rock is too massive, too fast and too close to divert. You need to slow it down, reduce the mass, and open the distance to give humanity a chance to divert it. $\endgroup$
    – Schwern
    Commented Mar 27, 2015 at 6:30
  • $\begingroup$ @Schwern sorry, looks like my novel is going into "Recycle Bin". $\endgroup$
    – user6760
    Commented Mar 27, 2015 at 6:38
  • $\begingroup$ @user6760 it's still doable, you just have to trim the scale on it $\endgroup$ Commented Mar 27, 2015 at 7:04

@CortAmmon covers well why you're not going to be able to shove this thing out of the way, at that speed, mass and distance it will hit Earth. There is nothing we can do to change that in 30 days or even a year.

Let's get a rough idea of the scale of this impact, because its a lot bigger than you think.

The volume of a sphere is 4/3 pi r^3. If you double the diameter, you increase the volume by eight times. Your object has eight times the mass of Ceres or 8e21 kg.

How much energy will this impact have at 24,000 MPH? That's .5 x mass x velocity^2 or 4.6e29 J. How much energy is that?

The Chicxulub impact that wiped out the dinosaurs is estimated to have been 4.2e23 J, your impact is one million times stronger.

The Sun outputs 3e26 J per second which is a tremendous amount of energy. Your impact is as much energy as the Sun puts out in 20 minutes! Not what strikes the tiny Earth, the Sun's total output for 20 minutes.

The energy required to destroy the Earth, to overcome its gravitational binding energy and blow it up, is 2e32 J or only 500 times more than your impact.

It's fair to say your impact will do damage the Earth likely hasn't seen since it was smacked by a planetoid which tore off enough material to form the Moon. Basically, there is no hope for life or anything to survive on the Earth, underground, or in orbit. Everyone and everything is dead. The surface of the planet is molten. Large chunks of molten Earth are blown into space and orbit. The only evidence our civilization ever existed will be our space probes.

You might want to scale things back.

Note that kinetic energy scales linearly with mass, but exponentially with velocity. Double the mass, double the energy. Double the speed, quadruple the energy. Making it smaller isn't as important as making it slower. For example, changing to "easy" mode where our object is half the diameter of Ceres reduces the volume, and thus mass, by 64 times. That reduces the energy of the impact by 64 times. Sounds like a lot, but it's still 7.2e27 J which is "only" 17000 times stronger than the impact that wiped out the dinosaurs. Everything on Earth is still dead.


So this is your idea of a "normal" difficulty level?

  • Present day, so we can't use anything we don't already have.
  • Thirty days, so we can't develop anything new.
  • 9 billion-billion tons of rock flying at us at Mach 31.
  • only 18 million miles away, so the only thing between it and us is our moon.

Dude! We're world-builders, not miracle workers.

Fortunately, although you ruled out most of our favorite tools (pseudo-science, playing fast-and-loose with the physical laws, and planet-scale evacuations), you overlooked one of my personal favorites... alternative history.

Let me let you in on a few state secrets. Given that the world is about to end, there is no reason to keep up the charade. Most of the history which you were taught in school was actually an elaborate lie. The cold war, the space race and the star wars missle defense programs, those were all just cover stories, created to hide the most ambicious undertaking in human history. Welcome to Project Star Shield.

For the last fifty years, the Unified Governments of Earth, the covert shadow empire which rules every occupied acre om our planet, has been funnelling a large percentage of our gross planetary profit into preparing for something like Horus. We have amassed thousands of high mass projectiles in lunar orbit. Each projectile masses only a couple of tons, but each is equipped with frozen carbon dioxide tanks which can be vented to sublimate in controlled bursts, impelling and steering these objects through intricate patterns. Recent advances in these trajectory control systems have elevated these projectiles' mobility to the level of surgical instruments.

So here is the plan. We don't have nearly enough projectiles to destroy or even deflect Horos; but we are able to slow it down just a little, enough to change exactly when that massive rock passes across our moon's orbital path. We've done the math repeatedly, and we are now certain that we can arrange a collision between Horus and our moon. With luck, the point of contact will be such that both bodies will be deflected from their current paths, falling into parrallel, sunward-plummeting trajectories. We will loose our moon but we might just save our lives...

-- edit in response to comments --

Glancing Collision Survival Plan

  • $\begingroup$ nice plan for a normal difficulty, ever heard of kobayashimaru a sci fi vessel in the star trek universe in which the captain must maintain absolute composure and clear thinking in the face of an eminent death. Do you agree that during times of natural or man made disaster a good leader is the one who make others believe in miracle after they managed to pull through. Survival isn't for the fittess rather a common goal and that is the plan. $\endgroup$
    – user6760
    Commented Mar 27, 2015 at 6:00
  • $\begingroup$ I ran the numbers, and the "normal" mode Horus has enough energy to destroy the Moon three times over. Horus has so much energy left over the trajectory of its debris field will not be altered. The pulverized Moon and Horus are now heading towards Earth like an interplanetary shotgun and will arrive about 10 hours after impact. $\endgroup$
    – Schwern
    Commented Mar 27, 2015 at 6:50
  • $\begingroup$ @user6760 - I would definitely agree that you have created a kobayashimaru here, even in "easy" mode. And I guess that measuring our world's leaders' coolness in the face of unavoidable death is an interesting way to spend our last 30/365 days. Schwern, you hard science guys amaze me! I met my match trying to put the mass of Ceres into human readable words. But why does your equation only involve the moon? Shouldn't two times the mass of ceres and 24k MPH be in there too? $\endgroup$ Commented Mar 27, 2015 at 11:47
  • $\begingroup$ @HenryTaylor Normal Horus is 8x the mass of Ceres (2x diameter of a sphere means 8x the volume). It still doesn't matter. Normal Horus has so much energy, and the Moon is so much more massive than Horus, they'll shatter each other and still have so much energy left over that Horus' original trajectory will not be significantly altered. It says something about the scale of the problem the OP has set up when you can effectively ignore the mass of a Dwarf Planet. With easy Horus your plan could have a chance, but I haven't done the math. $\endgroup$
    – Schwern
    Commented Mar 27, 2015 at 17:09
  • $\begingroup$ I'm far from being knowledgeable about space physics, but I kind of see Horus as a bullet aimed for earth. $\endgroup$ Commented Mar 27, 2015 at 19:46

This answer is a gutsy one. It doesn't actually answer the original question. The original question asked for realistic solutions to an extinction event asteroid impact on a timeline. However, there is a problem. There are entire teams of Astrophysics PhDs paid to do nothing but solve a simpler version of this problem where all of the design and construction can be done before the asteroid is detected (as opposed to this question, which needs to lump design and implementation into the same timeline) Their answer: we don't really know how to do it. You are not going to get any better scientifically feasible answer than the officially accepted answer in the scientific community that "you simply can't do it."

However, that's boring. This is worldbuilding. We have a bit more flexibility to bend and/or break the laws. So I instead am going to latch onto two words out of the entire original question, "be creative," and ignore the fact that I am probably being a wee bit too lenient in my interpretations of the original question. Enjoy

The v2 Horus is still a ridiculously formidable foe with no real win scenario. However, I think it is getting close enough to being a Kobayashi Maru scenario: no win case, but we might be able to cheat a bit to create a win case.

Using similar logic as in my previous answer for the v1 Horus, we can find that we need to apply a delta-V of .1m/s to the asteroid to deflect it enough to miss earth if we magically had the correct apparatus in place right at the 2 year mark (no surprise, that's 24x less than the velocity needed to deflect the asteroid in the original 1 month timeframe). Unfortunately, even with the decreased mass, we're still looking at $6.55\cdot10^{15} \text{J}$, which is the total energy output of about a million Saturn-V rockets. Realistically, since you'll have to build the craft and send it out, there wont be a full 2 years for deflection, so that number is a gross underestimate.

However, your new numbers got me thinking: 2 years is a long time. Its a time period that allows us to draw on other players besides our self. The general case is "Earth goes squish," but there's no particular reason we have to look at the general case. What if we could come up with a specific case where the geometry lends itself to something more hospitable?

Gravitational slingshots are a well understood force-multiplication tool. In short, a vessel steers near a planet so that its gravity well accelerates the vessel. The vessel can effectively rob some momentum from the planet or planetoid to impart an acceleration or change in direction.

What if, in the specific Horus situation, Horus wasn't actually heading straight towards us, but was actually on a trajectory that bent around a planet to hit us. If so, we might be able to tweak its trajectory to hit that slingshot slightly different. This would be a very effective force multiplication: a small change in entrance velocity into the slingshot would result in a marked difference in trajectory. Why burn a million Saturn V rockets, when you can just use the raw energy of an orbiting planet!

There is a catch: at the speeds Horus is moving, it is only .42AU away from earth when detected. (Poor show, NFO -- missing a small object at larger distances is reasonable, but this is a beast!) Mars has an orbit of 1.55AU, which means even the best case scenario wont let us use any of the outer planets. The closest mars will get to us is still .55 AU away. However, Venus has an orbit of .72AU, which means if the planets align in our favor, Venus could be between us and Horus.

So its time to hack the Kobayashi Maru scenario: when nobody is looking, change any of the randomization features to happen to cause us to detect the asteroid hurtling towards us from the inner solar system. Maybe play it off as though the unspecified ET's that may have sent the asteroid at us wanted to use the effects of the sun to hide the asteroid from NFO, explaining their poor response time. Now, when nobody is looking, change the stardate -- *ahem* I mean Julian date of the scenario to occur when Venus is along the path of Horus, and its gravity well bends Horus into its final lethal trajectory.

Now wait until morning, and lets take the test. We can do some quick linear approximations on the slingshot to figure out what is going on. Seat of the pants approximations ignoring a lot of details suggest that there may be a path as short as .28AU between Venus and the impact point of Earth at some perfect time. I'll leave it to others to figure out if this matters. This means that T-480 days Horus would leave the gravity slingshot of Venus. A deflection in velocity in any direction of .15m/s at this point will be sufficient to cause Horus to miss Earth. The change in velocity through a slingshot is:

$$V_{Horus}^\prime = \sqrt{4V_{Venus}^2 + V_{Horus}^2 + 4V_{Venus}V_{Horus}\cos\theta}$$

Where theta is the angle of incidence Horus has with respect to Venus. We want a change in velocity caused by changing Horus's velocity (changing theta would also work, but is hard to do because it takes far more energy), differentiating with respect to $V_{Horus}$ we get

$$ \frac{d}{dV_{Horus}} V_{Horus}^\prime = \frac{V_{Horus} + 2V_{Venus}}{\sqrt{4V_{Venus}^2 + V_{Horus}^2 + 4V_{Venus}V_{Horus}\cos\theta}}$$

This is a small-perturbation model for how much the final velocity changes with respect to changes in the initial velocity. This is our force multiplier term. If it equals 10, it means that a .01m/s change in initial velocity comes out to a .1m/s change in velocity as it hurtles towards earth. The higher this number is, the less effort it will take us to move Horus; Venus will do the rest of the work.

So how much did we have to cheat the Kobayashi Maru? Lets plug in some numbers to get:

$$ \frac{d}{dV_{Horus}} V_{Horus}^\prime = 30.322/\sqrt{5011 + 1400\cos\theta}$$

Thus our force multiplier is dependent on the incidence angle. A plot shows this varies from 1.0 at a 0deg angle (perfectly glancing) to 1.34 at a 90deg angle.

This means even with the gravity slingshot, we don't quite get enough oomph to be a useful force multiplier.

But now let's really cheat. This is Kobayashi Maru after all. What if you don't think anybody is looking at the velocity of Venus. After all, they didn't plan for it to be part of the test. What could we do to sneak a solution in to maximize our force multiplier?

Clearly the best solution will be at a 90deg incident maneuver, so we're looking to maximize

$$ Multiplier_{cheating} = \frac{V_{Horus}+2*(\mu V_{Horus})}{\sqrt{4(\mu V_{Horus})^2+V_{Horus}^2}} = \frac{1+2\mu}{\sqrt{5}} $$

where $\mu$ is a ratio between the velocity of Horus and our hacked mass of Venus. A large $\mu$ yields better multipliers, implying Venus is moving at a substantial rate. Venus naturally moves at a rate of roughly .00011 times the speed of light. Venus is supposed to move roughly 3x faster than Horus, so I think they'd notice if we made Venus move at relatavistic speeds, but we should be able to make Venus move 100x faster without anyone noticing. Now $\mu$ is 350, for a multiplier of 150.

A force multiplier of 150 means we now only need $4.3\cdot10^{13}J$, which is only about 750 Saturn-V rockets. This is also on the order of the amount of energy in Little Boy, implying that this multiplier has now brought the problem into the realm of a brute force solution. Kirk will love it.

As long as nobody is checking Venus's velocity, we'll get away with it too.

  • $\begingroup$ This needs more upvotes... ₊₁ for me! $\endgroup$
    – user22613
    Commented Nov 6, 2016 at 14:19

For "normal" asteroids and comets, there is a slim possibility that we could build a version of the ORION nuclear pulse spacecraft and use it as a missile. The details are here:


The money quote is here:

Get to high velocities with only a few explosives and small shock absorbers or no shocks at all. Launch against a 100 meter chondritic asteroid coming at 25 km/sec. 1000 megatons if it hits. Launch when it is 15 million kilometers away and try to cause 10000km deflection. A minimal Orion weighing 3.3 tons with no warhead would do the job. 115 charges with a total of 288 kiloton yield. Launch to intercept in 5 hours. Ample time to launch a second if the first failed.

So a frantic build program by every nuclear capable nation on Earth could launch a fleet of these missiles at the incoming body, with each missile impacting with a Gigaton of energy. Assuming this is a relatively solid body and every missile was programmed to hit at the same slightly off axis point, there could be enough energy transfer to deflect the main body, although Earth would still be hit with a spectacular meteor swarm.

The main issue is that cranking out nuclear warheads on an assembly line basis is not going to be easy or cheap, and for the most part the existing stock of nuclear weapons isn't suitable for making pulse units for the missiles. As well, given the time limits, it would be very difficult to mine, refine and enrich enough uranium (or produce enough plutonium) to make all the pulse units needed; existing stockpiles would have to be used, and existing nuclear weapons stripped down to access their fission cores for material.

Political factors will also be in play; would you hand over your stock of plutonium or highly enriched uranium to the United States to build all the pulse units? Would you willingly disarm yourself by surrendering all your current stock of nuclear weapons to be repurposed into pulse units? For that matter, if the Americans (or anyone really) were entrusted to build the thousands of pulse units needed for a fleet of missiles, why stop there? In a world with few or no nuclear weapons, having hundreds of 2.5Kt bombs would be quite advantageous, (and of course they could easily be used as the triggers for more powerful thermonuclear bombs). And of course, if anyone were to try to do this unilaterally, they would be accused of trying to take over the world with their huge stockpile of nuclear weapons.

So the solution would almost be as bad as the problem....

  • 1
    $\begingroup$ You can't apply that much energy to the rock--it breaks up, you're worse off than when you started. While I agree that Orion is the only possible option I think it's going to have to be a rendezvous mission. Get close and rain nuclear fire on the optimal point (you'll probably spread it around to avoid fratricide, it's just not quite as efficient), using the target itself as a crude pusher plate (acceptable as you don't care how badly it is eroded) and the bombs fused for the ideal standoff distance. $\endgroup$ Commented Nov 6, 2016 at 20:13

I'm not the math minded type that the people above are so I can't quite do the calc's they are capable of, but the most efficient method of stopping this impact is to use gravity...theory isn't mine by any means, but if we put an object travelling at the same speed in the same direction beside Horus of a significant enough mass, the two bodies will attract one another, eventually altering Horus's course ever so slightly...which is all we really need.

Steps for it:

  • Launch a ship for the asteroid belt and find a suitable object. Begin accelerating it so when Horus nears, it's already close to it's velocity as horus.

  • Drag the asteroid so the ship and it is parallel to Horus. Let gravity do it's trick and allow horus and this new asteroid to pull towards each other.

  • When they get too close, the ship drags the asteroid slightly further away from Horus and allows the process to continue.

  • You don't need much of a deflection angle for this to work since the time frame is extended.

  • A magnetic Horus might make this easier as the attraction from gravity and magnetism (assuming you can find an iron asteroid) will just increase the rate horus is moved from it's current course.

  • Earth is moving incredibly fast as well...the same concept can be applied where the ship with asteroid in tow is positioned in front of or behind Horus either speeding it up (so it flies by earth infront of it) or slowing it down (so Earth passes the point where it would collide). This is all dependant on the angle Horus is coming at to earths orbit to apply.

My unknowns of course are:

  • I don't think current humans can build a ship and get it to the asteroid belt within a year

  • I don't know how big of an asteroid over how big of time frame would be needed to either deflect or speed up or slow down horus enough to miss us.

  • How much fuel / energy would it take for the ship to constantly preposition itself and the asteroid in tow toi ensure they don't collide with horus.

Asteroid is actually optional, the mass of the ship might be enough over a long enough time frame.

  • $\begingroup$ your idea is good no worry about the math they are highlighting the magnitude of difficulty faced with my Horus(v0) and it's decessors which is totally due to my ignorant and underestimation of numbers, $\endgroup$
    – user6760
    Commented Mar 28, 2015 at 1:20
  • $\begingroup$ What you're describing is a gravity tractor. $\endgroup$
    – Schwern
    Commented Mar 28, 2015 at 15:23

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