Methods for mitigating impact of a large high speed cloud of dust in space

Question

Vaughn Heppner wrote a science fiction series in which humans have to defend against a growing cyborg threat. The star of the series, Martin Kluge, comes up with a way to destroy a group of military spacecraft by sending a high speed cloud of sand into the ships. Traveling at significant speeds, each mote of dust blasts a huge hole into the oncoming ships, effectively winning the battle.

What are some methods of defending against this weapon? Detonating nuclear blasts wouldn't have any effect since there is no blast wave, right? I can imagine high speed focused lasers, but it would take an enormous amount of power to actually destroy something with a laser - albeit at the zetajillion times you'd have to do it against a large sand cloud.

Any other theories out there that are (somewhat) scientifically feasible?

This was originally posted in sci-fi, but they suggested that it might be better suited for this forum. Assume that each particle of dust varies between 1µm - 100mm, the cloud measures 20 x 20 x 20 km in size, and the particles are traveling at 30 km/s. The density of the dust cloud is 0.125 g / cubic meter.

Answer 1

the cloud measures 20 x 20 x 20 km in size, and the particles are traveling at 30 km/s. The density of the dust cloud is 0.125 g / cubic meter.

That's about a million tonnes of debris there, with a total kinetic energy of 450PJ (about 100 megatonnes TNT equivalent, more or less). Each square metre of the front of the dust cloud has 2.5kg of dust behind it, giving a yield of ~1.125GJ/m²... that's about a quarter of a tonne of TNT equivalent. A ship with a 400m² cross-section would be hit with the equivalent of a hundred tonnes of TNT, pasted all over its nose.

I'm not going to say that's not very much, but it is a fairly small proportion of the energy of the cloud. Ships are not going to be within 20km of each other, so that's a fair amount of overkill to throw at one ship, especially given that a) the acceleration mechanism is going to be very energetic (and therefore visible from far away), the cloud is going to occlude things behind it (and therefore be visible from far away) and is going relatively slowly compared to the vastness of space and so the target ship is going to have plenty of time to see it coming, and will not have to manoeuvre very hard to evade it.

What are some methods of defending against this weapon?

Given that its only working out as 2.5kg of mass per square metre of cross-sectional area of the ship, simple dumb armoring will be pretty effective. A sheet of aluminium 1m x 1m x 1mm weighs a little more than that, and might be reasonably expected to absorb a decent amount of the impact. A multilayer Whipple shield made of successive thin layers of suitable materials will protect the ship behind it quite effectively, and without an unreasonable mass penalty.

Obviously, this only works a limited number of times, but given the difficulty of generating the dust cloud in the first place and the good chance of the target seeing it and evading it, the shooter might not be able to hit the target enough times to take it out.

Detonating nuclear blasts wouldn't have any effect since there is no blast wave, right?

Well. A nuclear blast in space does generate a lot of radiation, and as MadScientist already observed you might reasonably expect the dust cloud to absorb a reasonable amount of that radiation which will vaporise some of it and deflect some of it. Remember the whole cloud doesn't have to be disrupted, only enough to limit the amount that hits the Whipple shielding (or other armor) that the target spacecraft has. If you hit the cloud far enough away, the deflected dust grains (and the gas expanding from the vaporised grains) will act like a blast wave and disrupt the cloud further.

However. Not all nukes are created equal! Behold the Casaba Howitzer, or even its non-militarized cousin the Orion drive pulse unit. These act as directional nuclear blasts in space, absorbing a substantial portion of the radiation emitted by the blast into a propellant disk which is turned into a dense plasma cloud that flies towards the target. This is very much the sort of blast that can disrupt the gas cloud, to the point where I feel that this might be the ideal defensive option.

Note that Orion propulsion units are potentially non-military devices (they may be nuclear warheads, but they're far from optimised to be weapons) and so could be used in defence by non-warships.

I can imagine high speed focused lasers, but it would take an enormous amount of power to actually destroy something with a laser - albeit at the zetajillion times you'd have to do it against a large sand cloud.

As with the nuclear radiation pulse above, you don't have to completely destroy a dust grain to reduce or eliminate its damaging capability. The dust cloud is optically thick, so a laser weapon might reasonably expect a large proportion of the energy of the beam to be absorbed. Some of the grains may be wholly vaporized, some will be partially vaporized which will deflect them, and for others it may be that the radiation pressure of the beam can provide a useful amount of deflection or slowing-down. Remember that deflected (or slowed) grains can collide with other parts of the cloud, further disrupting it. You're only limited by the cycle time of the laser, and the distance at which you can detect the dust cloud (which is likely to be far away).

I'd much prefer the Casaba Howitzer to a laser, though.

You might also be able to use laser driven lightsails... a series of featherweight sheets blown forwards by light pressure alone, but it seems difficult to get enough mass moving quickly enough to make a difference. A magnetic sail driven by a particle beam might be more effective, both in term of delivering mass and getting projectiles launched and accelerated quickly. By way of a bonus, these things might reasonably be carried for non-military purposes, which might be plot-relevant.

What are some methods of defending against this weapon?

Why not fight fire with fire? Generate your own high-speed clouds-o-doom, and fly behind them, relying on them to help sweep opposing clouds, drones, missiles and ships out of the way. Obviously you can't easily carry a million tonnes of grit around with you everywhere, but you should be able to do it at least once.

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Honestly though, I'm not sure that this is a very useful weapon. It is difficult to produce, not practically portable, and is too easy to spot at extreme ranges and avoid. It also appears to be possible to defend against without undue difficulty.

Send your weapons engineers back to the drawing board.

Answer 2

Whatever the ship already uses to protect from interstellar dust

A dust particle hitting the ship at 30 km/s is no different from a ship travelling at those speeds hitting a stationary dust particle; which ships would already routinely do on their travels. It is true that this cloud would be far denser than the interplanetary or interstellar medium, but each particle and impact is still discrete; a ship that can tank a million particle impacts over the course of its travels before it needs a hull replacement, is probably a ship that can tank a million of those impacts in a second.

It is true that many successive impacts would heat up the hull and weaken it for the next impact, but also consider the fact that 30 km/s is a very slow speed for a sci-fi spaceship; that's slower than some of our real-life solar probes, and sets a travel time of years just between planets in the same system. A faster space-ship, particularly one that goes faster than light, would need some defense against particles far, far more energetic than anything this weapon can muster.

What defense do ships use against space dust? For a very "hard" sci-fi answer, consider using the beryllium disc which was thought up in the 70's for Project Daedalus. This is an erosion shield; it is meant to ablate over the course of the journey. An omnidirectional equivalent would be a thicker hull that needs replacement after battle.

Other ideas include strong magnetic fields (anything is magnetic if you try hard enough), or the warping of spacetime itself. Basically whatever FTL mechanism you have, it should have dust protection built into it.

Answer 3

Small size means that strong flow is relatively effective at blowing the grains off course, or even stopping them. Spacecraft have rockets. A rocket should be able to blow the sand away. However ...

• The exhaust plume of the rocket plume will be far smaller than the cross section of a large spaceship, for grain clearing duty you would probably change the nozzle geometry to create a wider exhaust plume at lower velocity. Probably need to sweep an area with gimbaled rockets

• This also means that a craft in "defensive mode" needs to have it's main rockets pointed at the dust cloud, limiting it's maneuver options

• The exhaust of the rocket dissipates, so the effect will be short range - possibly a few hundred meters

• This will burn huge amounts of fuel. The main offensive use of dust: To force opposing craft into spending valuable fuel on "grain blowing"

As for detection of the dust, I'd assume IR or active laser scanning of suspect areas. Not sure how good we are at detecting dust clouds in near space.

Answer 4

I would not be so quick to dismiss good old fashioned nuclear weapons.

It's true that there is no blast wave for a nuclear detonation in a vacuum. Most of the energy is output in the form of a staggeringly intense flash of soft X-rays.

As a very rough order of magnitude calculation, the average nuclear weapon X-ray photon energy is around 12Kev, which corresponds to an attenuation coefficient of about 100 microns. This is well within the bounds of the grain size specified, meaning a reasonable percentage of the X rays that pass through the sand will be absorbed by the grains.

This will apply radiation pressure on the grains, and may even be enough to partially vaporise the sand grains, causing an ablation-recoil away from the blast. It seems plausible that a sequence of powerful detonations leading into the cloud would blow out a "bubble" in it. If correctly timed, this may allow a defender to punch a hole in the cloud that they could dodge through.

I make no guarantees as to the efficiency or number of weapons required. I would happily defer to anyone actually willing to run the numbers, but that is a non-trivial exercise.

Answer 5

Some old shower curtains

(or any other thin, flat, cheap material you have on hand)

The toughest part of defense here is knowing the attack is coming. I take that as part of the premise of the question. Perhaps there is a cloud of tiny drones surrounding your fleet in all directions to relay a warning.

Now if we know the attack is coming, and from where, we don't need to block the entire 20 x 20 km "attack formation" of sand grains. We only need to block a ship-sized area of it. So if we can jettison an opened bale of old shower curtains that were on board, and maneuver the ship(s) some kilometers directly behind them, the sand grains will ravage that bale of curtains, and send dangerous soft plastic shrapnel in all directions ... but barely any of the sand or plastic will actually hit your flagship. And all the other ships are stacked up at odd intervals behind it, safely in its "shadow".

If you are short on shipboard luxuries (or hygiene), you could press a solar sail into use for this purpose. Hopefully you packed a spare in case something went wrong with it ... right?

Answer 6

30km/s is not much in space (voyager is travelling faster than 17km/s). Your visibility is millions of km in space. Blasting sand too late means sand blasters will be in effective weapon range before fired, risking getting attacked.

Thus, simply dodge the incoming blast. If they wait until you get close enough so you cannot dodge, take out the blasters before they fire. As long as you know they are going to do this attack, it won't be effective.

If you don't know about it, then you are in trouble. If you want it to be more challenging increase the speed to a few % of the speed of the light. Now it will travel a million km in a few minutes and then the attackers will be scrambling to defend themselves using interesting tactics.

Answer 7

Ionize the dust? Depending on available power, and no hard science tag content here. you could using an ion beam ionize the dust field and generate a powerful magnetic field around the ship to divert the dust around your ship. In effect a reverse Bussard ramjet. One could imagine (sculpting) configuring the magnetic fields in a way that the force lines would efficiently divert the particles taking into account the overall shape of the space craft.

I cant math that well, but for my own curiosity, I would like to see how much energy over a given time it would take to divert the kinetic energy of the sand cloud around the spacecraft.

EDIT Bonus, depending on your universe tech etc. Devices like this or something to modify from could be in place on your ships already to protect from solar radiation / flares / space herpies of any sort.

Answer 8

Detonating nuclear blasts wouldn't have any effect since there is no blast wave, right?

You may have heard of Project Orion, that designed spaceships that would use the blast from atomic explosions to push on a pusher plate that would transfer momentum to the ship.

And the plan was to use the blast from the atomic explosions to not only launch the spaceship from Earth with its dense atmosphere but also to launch the spaceship from airless moons and planets and to propel the spaceship through the vacuum of space.

But how can atomic explosions create a blast in the vacuum of space where there is no air to be blasted against the pusher plate of the spaceship?

The explosive devices would have to provide their own "air", actually solid material on the outside, arranged on the side facing the pusher plate so that the vaporized mass would be hurled against the pusher plate to propel the ship.

And similar designs of explosive devices could be used to vaporize material and fling it against the approaching clouds of dust.

the missile swould be launched from the defending space ship, and thus would have its velocity, before being fired toward the cloud of space dust, thus increasing their velocity toward the cloud of space dust. And when the bombs exploded behind the stored particles of matter, the bombs would add considerable velocity to thevaporized matter, so that it would be approaching the dust at several times the speed of the dust.

So when dust particles were struck by gas particles from the bombs in the missiles, the dust particles would slow, and stop, and then be pushed backwards, away from the incoming space warships.

I don't know how well such a system would work, but someone interested could check the math to see how well it might work.

Answer 9

Use blocks of ice that are formed into a shield. Yes, this likely requires being able to resupply from a planet afterwards, but there's also plenty of ice in space, too.

I was going to suggest spraying water to form a wall of water ahead of the spaceship, but that has problems of vaporizing and reduced density.

There's plenty of ice in the form of comets, asteroids, and various other space debris. Just pick (or make) a suitably sized shield and push it where you want to go. The sand will either wear away only the ice, bounce off, or stick to the ice and make a better shield.

If you want something of specific size, you can have the ship manufacture or otherwise shape the shield by harvesting water or ice from a planet or that space debris, forming it inside the ship, letting it freeze under pressure (to avoid vaporization and loss mentioned earlier), and moving it to the front of the ship.

An ice shield is nothing new in science fiction, so you shouldn't have to justify it.