Earth defense from asteroid and comet hazard using super-power gamma-laser

[Olga]

Dear all,

We are launching a new web-site concerning several projects in Russia. Among those projects there is one called “A system for Earth defense from asteroid and comet hazard on the base of super-power gamma-laser”. We would appreciate your feedback on the related document: http://rufund.ru/Docs/laser/Doclad_laser_ENG.zip

[khallow]

Glancing through the document, I see that this appears to be a one-time emergency device (among other things, it appears that use of the device results in a small nuclear fission explosion). Namely, it's intended for a case where a collision with the threatening comet or asteroid is near at hand and large changes in the trajectory are needed. There are several problems that seem relevant here. First, there is the possibility that the device would need to be used near Earth. EMP mitigation might need to be considered. Second, this could generate a lot of debris which is one of the reason explosions (which are similar in effect) aren't considered desireable. Even if the debris isn't an issue for Earth, it greatly increases the risk of impacts in near Earth space. Third, this device has some obvious uses as a weapon (in addition to the considerable ability to deflect asteroids) and that would be an obstacle to its deployment.

Come to think of it, there's also a technical matter (assuming I understand the operation of this device sufficiently well). Given that there's a lot of natural neutron sources both on Earth and in space, it appears to me that you'd want to store this device in a subcritical (and stable) configuration and somehow snap it together just prior to firing. But the alignment of this process would appear to me that it needs to be very precise. Given that among other things, the device will probably experience both large acceleration loads (from getting launched into space) and heating cycles (from solar radiation), you need to have an alignment process that can handle that.

[Olga]

Dear khallow,

Thank you for your posting. I’ll try to be consecutive in my answer.

First of all, energy of the beam is equivalent to about 1 megaton at a trinitrotoluol. A thermonuclear explosion (at 30% coefficient of efficiency) is about 3 mt. Is there someone who considers it is a small explosion? :-)

Secondly, the device is not only for close in interception cases. It is for ANY case, including super difficult cases when a dangerous object has an embarrassing trajectory.

The assumption that there will be needed an explosion near the Earth is incorrect. In the Earth’s magnetosphere, to be precise, closer than one million kilometers from the Earth (according some sources – 5 million kilometers) it is acceptable to perform such “small” explosions as a last resort. The reason is not an EMP only. An appearance of an artificial radiation belt is more harmful.  

Thirdly, the device does not destroy a big object. We can talk about an object’s destruction if it’s dimensions are tens meters, in which case, its debris will be destroyed in the atmosphere.

Fourthly, yes, this device could be used as a weapon, a space weapon. Its use against objects on the Earth would not be effective because the atmosphere would absorb the beam’s energy. The effect of such a weapon on the Earth’s surface would be similar to the effect of the explosion of a 3 megaton bomb in space. The question of deployment of a “space weapon” is a political one and should be solved internationally. ANY deflecting asteroid device could be used as a weapon just by deflecting some asteroid toward an “Evil Empire”.

As for technical issues: issues of thermoregulation, acceleration loads, protection from high-energy particles are solved in many variants. The precise of alignment for such devices is a solvable task (a precise of alignment is not a big issue).  One real problem, however, is maintaining precision at the moment of the explosion.  To overcome this problem a precession of the device could be used at the fire moment.

[aftercolumbia]

It would be effective against targets on Earth unfortunately, if used in two manners:

1. Shoot the gamma beam at Earth.  The atmosphere will absorb energy, that's for sure, but the energy is still there, in the atmosphere.  If the atmosphere absorbed all the energy, you'd wind up with a Tunguska like explosion.  It is more likely that several hundred kilotons worth would make it to the ground (where it would actually have a smaller area of effect.)

2. Use the physics package as a "normal" nuke.  This results in a plain Jane 3MT nuke.

Chelomei might consider this a "small explosion"...the guy who origininally designed Proton as a 100MT class missile.

[joema]

...Use the physics package as a "normal" nuke...

Based on that, I don't see the utility of the laser device. We already have nuclear warheads that can be launched into space that could achieve the same result without the intermediate step of generating a laser beam.

If the asteroid is discovered far enough out (years), various non-nuclear methods could be employed: gravity tractor, kinetic impactor, etc.

If it's discovered close (weeks-months), an ICBM modified for a precision stand-off detonation could deflect it without fragmentation. Virtually all ICBMs can reach earth escape velocity with a reduced payload. If that failed, you have a redundancy factor of several hundred. Just try again. By contrast if the laser is a highly specialized very complex device. Presumably you'd have only one, or maybe a single backup? If malfunctioned, underperformed, or the launch vehicle failed, it's "game over".

It's technically interesting. The purpose of this forum is to discuss items like that. However it would appear to have very high development costs and limited redundancy relative to other options.

Have you considered putting this thing on the back of the moon?  There's no atmosphere to get in the way, and it's always pointed away from the earth, so there are fewer political ramifications.  Whatever damage you do to the back side of  the moon would be considered acceptable, if it saved the earth.

[stargazer777]

As Olga mentioned, any device sufficiently powerful to change the trajectory of a onrushing comet or asteroid would, inevitably, make a powerful weapon that could be used against Earth.  That is a risk we are just going to have to take.  I can't make a judgment on its scientific or engineering feasibility, but I wouldn't close the door on any option that might enable us to save our collective derriers from such a catastrophe.  When it comes to the survival of our species -- remember, "pride cometh before the fall."

[Olga]

aftercolumbia - 23/3/2007  1:01 AM

It would be effective against targets on Earth unfortunately, if used in two manners:

1. Shoot the gamma beam at Earth.  The atmosphere will absorb energy, that's for sure, but the energy is still there, in the atmosphere.  If the atmosphere absorbed all the energy, you'd wind up with a Tunguska like explosion.  It is more likely that several hundred kilotons worth would make it to the ground (where it would actually have a smaller area of effect.)

2. Use the physics package as a "normal" nuke.  This results in a plain Jane 3MT nuke.

Chelomei might consider this a "small explosion"...the guy who origininally designed Proton as a 100MT class missile.

1. Unfortunately, an interaction of a gamma-beam of such energy with a medium is not researched enough. There is a set of nuclear, quantum, wave and thermodynamic processes. According to the modern estimations it is possible to say that, indeed, a shoot of the beam to the atmosphere will create appearances similar to the processes of Tunguska but scales of them will be in 50-100 times less.    Just to remind, energy of the beam is about 1 megaton and the energy in the region of Podkamennaya Tungusska according to the modern estimations was about 40-50 mt.


Yes, in top layers of the atmosphere, starting from 80-100 km when the beam will pass in a target direction there appears a wisp of hot plasma. More there, a part of exposure’s products concentrated in a beam as well will reach the target.  However the most part of the energy will be scattered in top layers of the atmosphere in contrast to Tungusska’s phenomenon where a part of substance (the beam has no any) reached lower layers of the atmosphere. An air blast is the basic damaging factor and it can not be powerful coming from a great height. The result will be a zone of total destruction on the Earth’s surface with dimensions of about one half of a football ground. Don’t forget that to do it you will need to set off a charge of 3 mt in the nearest space which will destruct your satellite system as well as will make impossible any space missions for months or even years because of powerful artificial radiation belts in the magnetosphere. Do you think a destruction effect costs that?


2. For what? There are mentioned by you “normal” nuke which besides more effective and cheaper. Let’s agree that a space vehicle with the device will be based on the Earth in a subcritical and stable configuration under an international control. At Baikonur  might be guarded by American, Chinese and Russian military,  at Franch Gviana  or at Canaveral – Japanese, French, Indian and so on. Systems of international controls ate technically and organizationally are developed.  

[Olga]

joema - 23/3/2007  3:47 PM

...Use the physics package as a "normal" nuke...

Based on that, I don't see the utility of the laser device. We already have nuclear warheads that can be launched into space that could achieve the same result without the intermediate step of generating a laser beam.

If the asteroid is discovered far enough out (years), various non-nuclear methods could be employed: gravity tractor, kinetic impactor, etc.

If it's discovered close (weeks-months), an ICBM modified for a precision stand-off detonation could deflect it without fragmentation. Virtually all ICBMs can reach earth escape velocity with a reduced payload. If that failed, you have a redundancy factor of several hundred. Just try again. By contrast if the laser is a highly specialized very complex device. Presumably you'd have only one, or maybe a single backup? If malfunctioned, underperformed, or the launch vehicle failed, it's "game over".

It's technically interesting. The purpose of this forum is to discuss items like that. However it would appear to have very high development costs and limited redundancy relative to other options.

In one Russian comedy film there is one scene when one of the heroes looking to a meadow turns to another hero and asks: “Do you see the gopher?  No?  But it exists.” I mean if you don’t see something it doesn’t mean the thing does not exist.

Existing ICBMs can NOT be launched so far into deep space for interception purposes. They can NOT even achieve 0.01 of a result which is achievable by the proposed laser. To do that you would need a superpower thermonuclear charge which would go deep into an object. A stand-off detonation is absolutely ineffective because of lacking an air blast in space – the base for destroying an object.  Also such charges should be constructed before so they could withstand accelerative forces of tens of thousands of G’s.

The laser beam in fact settles a rocket engine on an asteroid and combines a power of deep thermonuclear explosion with advantages of a remote impact.  The issue of utilization of normal nukes was discussed broadly by specialists. You can easily find information about that in the Internet.

You say that ICBMs can reach earth escape velocity with a reduced payload. That is true. And how long they will travel at this velocity to a interception point? At which distance do you want to intercept an object? And when a rocket is there what will you do with the “reduced payload”? What will it be enough to do? Don’t forget that the aim of the “reduced payload” is to give a stone mountain an additional velocity which should allow this mountain to miss Earth by at least 6400 kilometers (one Earth radius) within days before a collision. If you fail, there are no second chances?

Have you ever seen a “plain” nuclear device or a space device?  Even the first satellite was not so “plain”. Any specialized and complex device may be tested including its elements if you can develop it to a certain reliability.

Nobody says we are talking about one device. A group of such devices would be about in 100 times cheaper than gravity tractor, kinetic impactor, etc.

[Olga]

Dear stargazer777,

Thanks  

[joema]

Olga - 23/3/2007  4:40 PM
Existing ICBMs can NOT be launched some far deep into space for interception purposes.

That is incorrect. An ICBM is simply a launcher with a payload sized for suborbital delivery. Many such ICBMs have (or had) 10 warheads of of 300 kiloton EACH, plus a post-boost maneuvering bus, plus a heavy inertial guidance platform.

Striped down to a single 300 kt warhead, a Peacekeeper-class ICBM could easily achieve earth escape velocity. In fact the Titan II ICBM launched the Clementine probe into lunar orbit, which included the additional propellant burden of lunar orbit insertion: http://en.wikipedia.org/wiki/Clementine_mission

Olga - 23/3/2007  4:40 PMA stand-off detonation is absolutely ineffective because of lacking an air blast in space – the base of sticking factor.

A stand-off detonation is very effective -- the immediate X-ray and neutron burst simply vaporizes a thin layer of material from the asteroid surface which propulsively nudges the body in the opposite direction, without fragmenting it.

Olga - 23/3/2007...what will you do with the “reduced payload”? What will it be enough for?...

This has already been studied in great detail. For an asteroid the size/mass of Apophis, a stand-off detonation of a small 30 kiloton nuclear warhead would deflect it (without fracturing) about 15 centimeters/second, which is enough move it out of the gravitation "keyhole" (about 640 meters wide) in 1.2 hours (1.2 MB .pdf): http://www.llnl.gov/planetary/pdfs/I...n/04-Solem.pdf

If an asteroid the mass/speed of Apophis is detected closer, missing the keyhole isn't sufficient -- you have to alter the trajectory to totally miss earth. A single 30 kt detonation 1 year out would do it in most cases. For closer detections, multiple detonations would be required, each changing the asteroid velocity about 15 cm/sec. In theory you could deflect it sufficiently (without fracturing) with only a few weeks advance notice by using 10-20 such stand-off detonations. There are many variables, but the technology already exists and could be deployed within weeks or months if necessary.

[Olga]

joema - 24/3/2007  3:16 AM

Olga - 23/3/2007  4:40 PMA stand-off detonation is absolutely ineffective because of lacking an air blast in space – the base of sticking factor.

A stand-off detonation is very effective -- the immediate X-ray and neutron burst simply vaporizes a thin layer of material from the asteroid surface which propulsively nudges the body in the opposite direction, without fragmenting it.

If you insist I’ll try to give more arguments.  
At first let’s consider a high altitude thermonuclear explosion. Utilization of a thermonuclear explosion for defense from hazardous space objects was suggested for the first time in Hyde R. A., 1984. Cosmic bombardment. - Special report UCID-20062, Lawrence Livermore Nat. Lab. Resulted from the thermonuclear explosion decay products, X-ray and gamma-radiation and a neutron flux arrange an air-blast. The main role belongs to the neutron flux (Hammerling P., Remo Y. L., 1992. NEO Interaction with X-ray and neutron radiation. - In: IW-92, p. 186.), which gets at a depth of 20 cm under a surface of an object at a density of ?=2g/cm3 and average atom weight of a substance equal to 25. A part of substance will be “blown-off” (here is a source of origin English terms “blow-off” and “stand-off” for this type of thermonuclear explosions) and a space object will get an additional impulse.

At an optimal height of explosion over a surface (Ahrens Th. J., 1992. Deflection and fragmentation of Near-Earth- As-teroids. - IW-92, pp. 89-111) equal to


h=D((v2 - 1)/2)˜0.2D

0.3 of its surface will undergo radiation. For all that explosion energy equal to f=0.28 gets to the surface. A share of explosion energy transmitted to a neutron radiation is equal to e=0.32. For all that a velocity of a blown-up particle is equal to v =feW/CP, where W is a power of thermonuclear explosion in kilotons; CP = 2 km/s – is a velocity of spreading a neutron blast wave, and a velocity v is directed orthogonally to the object’s surface. At accepted values v = 44 m/c for each of kiloton of the charge. A reduction of v for a direction of object’s motion gives  vr =0.7 v = 31 m/c for each of 1 kt of the charge (for D = 100 m a drift speed is 5.3 cm/s).

As a result the object with a mass M will get a velocity DV (m/s) equal to


?V=?D²d?fv_reW/M=2*10⁷?D²W/M

 where W in kt, D in m, in g/sm, M in g.  

The consequence is that by explosion equal to 300 kt you will give to a “medium” in his density asteroid with a diameter of 1 km increase of velocity about 2-3 cm/s.

Variants of stand-off and immediately surface explosions give similar results in a diapason up to 20 mt. I will save you your calculations of different variants. You can use an average value of 10⁶-10⁸(t m/s)/Mt. For the rest be so kind as to calculate yourself. If you meet any difficulties I can provide you with diagrams for explosions of various power and asteroids of various dimensions, just to save you from a necessity to use sources like http://en.wikipedia.org or kids’ encyclopedias.

As for ICBM I consider the format of this forum is not appropriate to give lectures on space ballistic and etc. It requires some time to invent a situation with a dangerous space object where this carrier would be useful and when it would be worthy to use it (heavy space types of it for instance 3C has better chances). And if you care a little about consequences for ecology after ICBM utilization then it’s better to forget about military toys all together.  

Here is a typical, even optimistic case: a long-period comet-type object from a remote area of the Solar system is discovered. The core’s diameter is about 8 km. An inclination to ecliptic’s plane is 65 degrees. A direction of revolution round the Sun is reverse to the Earth revolution at its orbit. A velocity relative to the Sun while crossing an Earth orbit is about 30 km/s. Time to a possible collision is 6 months (we were lucky). Estimations of collision’s probability are 60% (after 10 days of observation). After three months from discovering the comet became active, a trajectory is corrected; the core’s decay is predicted for one large (90% of mass) and few small fragments. Estimations of collision’s probability become higher up to 90% (after 90 days of observation).
Is there anything incredible?  Now let’s suggest NASA use Titan. Can you guess where they will advice you to allocate it? I can’t use rude words here, but you can ask me via private mail. Or do you hope that we will need to deflect only those objects which will be “comfortable” to deflect? May be you would ask asteroids to be polite and check with us their trajectories and dimensions in advance?

[Olga]

I’ll start with a fact that Apophis is not a limitation. Secondly, data from “one year out” taking into account a required precise will not allow you to answer a question “in what direction to deflect”? Deflecting “somewhere” may push it directly to the Earth, when without yours interference it would pass beside the Earth. And this is only one reason. You said “A single 30 kt detonation 1 year out would do it in most cases”. I’ve suggested one situation in the previous posting – try to push it from “falling down” trajectory.

To deflect “with only a few weeks advance” in fact means that at a point from where there are few weeks before a collision there is already a group (10-20) of space devices (which need to be designed, constructed, launched, to fly) which will consistently (“just” 10-20 nuclear explosions) deflecting an asteroid. For all that the devices were not tested because they were made “quick and dirty” within “few weeks or months”. Who will win do you think? I would stake on asteroid

I’ll try to give a graphic example. A difference between mentioned by you nukes and the proposed laser is the same as between infantryman with a grenade and infantryman with a bazooka in a fight against a tank. At certain circumstances, if fortunate, the first one with a grenade can shoot down the tank, however, is it reasonable for his commanders to expect he succeeds?

Sorry for short answers. Reaction to all aspects would end up with very long texts.

[Olga]

bhankiii - 23/3/2007  5:15 PM

Have you considered putting this thing on the back of the moon?  There's no atmosphere to get in the way, and it's always pointed away from the earth, so there are fewer political ramifications.  Whatever damage you do to the back side of  the moon would be considered acceptable, if it saved the earth.

I confess that we did not consider this variant

I should remind you that a theoretical firing distance of the device is about 100 000 km (one third of the Moon orbit’s radius). A real firing distance taking into account difficulties with pointing and keeping stable the beam is unlikely to be more than 30 000 km. Asteroids in their turn have an annoying property not to take into consideration our preferences regarding their trajectories and won’t go straight “to ambush”  (then it is better just to hope that the Moon will be on their way). With the same result you can allocate a nuclear mine somewhere in a deep space hoping to detonate it if some asteroid will pass close by.

[aftercolumbia]

joema - 23/3/2007  6:16 PM

Striped down to a single 300 kt warhead, a Peacekeeper-class ICBM could easily achieve earth escape velocity.

The Minotaur IV manual at www.orbital.com does not agree with you.  The Minotaur IV is a booster derivative of the Peacekeeper MX with Orbital's Orion 38 added as a fourth stage.  The highest energy performance quote is 2246m/s short of escape speed.