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2007 Planetary Defense Conference
http://www.aero.org/conferences/planeta … apers.html
State of the art asteroid deflection - lots of papers available as PDFs - some that caught my eye ...
* Evaluation of Present and Future Ground-Based Surveys and Implications of a Large Increase in NEA Discovery Rate
* An Analysis of the Correction Problem for the Near-Earth Asteroid (99942) Apophis=2004 MN4
* Near-Earth Asteroid Rendezvous Missions with the Orion Crew Exploration Vehicle
* Gravity Tractor
* Nuclear Deflection
* Impact Deflection of Potentially Hazardous Asteroids Using Current Launch Vehicles
* Blast Designs for NEO Destruction,
* Head-On Impact Deflection of NEAs: A Case Study for 99942 Apophis
* Gas-Blast Orbit Modification,
* Deflection of Near Earth Objects by Means of Tethers
* Hovering Control of a Solar Sail Gravity Tractor Spacecraft for Asteroid Deflection
* Multiple Mass Drivers as an Option for Asteroid Deflection Missions
* Sticking Thrusters into Asteroids from Permanent Bases at L1 and L3
* Impact Disaster Preparedness Planning
* Financing a Planetary Defense System
* Planetary Defense as a Major Rationale for Human Spaceflight and Exploration
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Good find!
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Yes, good to see gravity tractor at the top of the list - it's the most attractive proposal.
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A scan of the 271 page 2006 NASA NEO Survey and Deflection Study
http://www.b612foundation.org/papers/NASA-finalrpt.pdf
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This topic dates back to 2007 .... The Space Show of 05 Oct 2018 featured Dr. Jay Melosh ... According to Dr. Livingston's write-up, the "gravity tractor" was discussed as one of several impact mitigation methods. I have not yet heard the broadcast, but the write-up reminded me of something that might increase the effectiveness of the gravity tractor technique for changing the path of an asteroid ... The mass of the tractor will necessarily be small compared to the mass of the asteroid, but there would seem to be no reason why the tractor could not increase its mass over time by selecting material from the asteroid. This would have the benefit of increasing the mass of the tractor and decreasing the mass of the asteroid.
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The attraction between the tractor and the asteroid would remain the same in any case, though, so it wouldn't become any more effective. Just more complex.
"I'm gonna die surrounded by the biggest idiots in the galaxy." - If this forum was a Mars Colony
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NEA or NEO's all show up quickly and disappear just as fast which means energy and thrust if deflecting are peak levels while slow would allow for other types of propulsion that are not ION, Nuclear or fuels once attached to the object. Depending on the mass we may only be able to deflect its course.
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For most space rocks a small deflection will suffice. Only a very massive one discovered late will need more than a small force to get it to miss earth. That may require one or more nuclear weapons. Nobody saw the Chelyabinsk rock coming, so that requirement is not impossible.
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I went to the 2009 planetary defense conference in Granada, Spain, to present a poster paper. The sense I got was that detection capability is not up to snuff, which is why things like the Chelyabinsk hit still surprise us.
Things like gravity tractors or a whole series of small impactors can change the orbit of objects for which we have warning times of years. The nuclear explosives are a last ditch defense against surprises with short warning times. Anything with a very elongated orbit like a comet will inherently fall in that short warning time class.
The cohesiveness of these objects is a big unanswered question. Some appear to be non-cohesive piles of rubble only barely "held" together by faint gravity. Push on a thing like that, and it flies apart, converting a bullet strike into a shotgun blast. Not a good outcome for a last-ditch defense.
Some sort of detection satellite swarm well inside the orbit of Earth toward the sun, but looking outward, is needed to detect most or all the surprises like Chelyabinsk. No way around that unaddressed need. Some of these need to be IR sensors, as dim dark asteroids are easier to see in the IR than in the visible. No way around that unaddressed need, either.
We're going to need a whole slew of asteroid and comet sample missions to understand the (I anticipate) wide spectrum of physical properties these things really have, which (I think) will prove to range from loose, dry sand banks, to solid lumps of metal. By the end of that investigation, we will (I predict) begin to understand that there is no distinction between a comet and an asteroid, only a spectrum of objects of varying volatile ice content and cohesiveness, exclusive of the metal ones. The smaller ones will be drier, as will the ones closer to the sun.
We're going to need to experiment with deflection methods, so that we can actually push on the dry loose sand banks as well as the more cohesive ones. Today, that is a completely unaddressed need, the impactor to one comet notwithstanding. And when things don't go as expected, men will have to go and do experiments, adapting on the fly, to get the answers we need. And there is as yet no way to send them there. It's very long mission, all in zero-gee, requiring both radiation protection and spin gravity.
Until all of that is done, we are vulnerable and mostly helpless. The ICBM's we have cannot reach an incoming NEO as a last ditch defense, and do not have the kind of guidance systems necessary for that kind of a mission. We have the bombs, but not the right fuses. We have some big launch rockets, but no guidance on them for an NEO intercept, and no adapters to carry the bombs. Nobody is working on any of this equipment.
The conference I attended was years ago, but little has changed since then, except that most (but not all) of the 140-m+ objects have been found. Not those sunward of Earth, certainly. Chelyabinsk was one such. We have found very few of the smaller ones (and a 10 m object can be a city-buster), because the necessary equipment to do so is still not in place.
Lots to do. Little has been done. The threat is real. It could happen at any time. And governments do little or nothing about it.
Sleep tight!
GW
Last edited by GW Johnson (2018-10-08 10:31:19)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For GW #9 ...
Thanks for your notes and observations from the 2009 conference in Spain. Is your poster paper visible on the web somewhere? (th)
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GW has his own blog web site at http://exrocketman.blogspot.com/
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That poster might be out there somewhere, I don't know where. It was about augmenting significantly the gravity tractor force with electrostatic attraction. I don't think I ever posted that concept on my "exrocketman" site. There are a few posts about the space program that mention asteroid defense as a very good reason to have a space program.
In my poster idea, I strung a wire with a swivel joint or two from the tractor spacecraft to the asteroid. At the asteroid, a spear or stake at a pole of rotation attaches the end of the wire. Then you charge up to several hundred to a few thousand volts, at a rather close tractor (and wire length) range. The electrostatic attraction force should greatly exceed the gravity force.
As you hold position with neutralized-beam ion propulsion in the spacecraft, those two attractive forces (gravity and electrostatic) are the tow cable for the "tractor". The force direction is toward the spacecraft. Electrostatics is potentially a far stronger tow cable, that's all.
GW
ps -- the warning time for small (under 10 m) objects is 0-6 hours, often no warning at all. They can come from most any direction. We can only look effectively away from the sun (meaning at night). I haven't looked to see what the B612 Foundation wants to do now. They were the proponents of a swarm of IR telescope satellites looking outward from the orbit of Venus. I think that plan is now defunct, though.
pps - Got to each lunch in Granada with Rusty Schweikart the astronaut, who used to run B612. Also had drinks with Dumitru Prunariu, the head of Romania's space program, who was a cosmonaut on one of the Salyut stations, and a delightful man to talk with. And I got to chat on the plane with the guy from Sandia Lab who does the computer impact modeling, Mark Boslough. He's done some TV work about the impact problem since then.
Last edited by GW Johnson (2018-10-08 13:02:40)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For GW #12:
Interesting concept !!! I hope your poster caught the eye of a few attendees. This is the first time I've heard the idea, so I'm guessing it has not been widely publicized. A consideration is having to pull along the axis of rotation, which would be a factor in plotting a course change. Without knowing the answer before hand, is it practical to divide the tractor into a component that lands on the object and charges it one way, while the tractor remains separated and charges itself to the opposite polarity? Then the tractor could position itself wherever might be best for the needed course change.
Or, (come to think of it), the tractor might use the wire to achieve a significant charge and then disengage the wire, so it can move to where it is needed.
Another (probably minor) technical consideration is managing distance between the object and the tractor ... if electrostatic force builds up to any significance, it might achieve closure between the object and the tractor, so the tractor would have to start all over again.
Neat Ps and pps !!!
(th)
SpaceNut: Thanks for the tip about the rocketman blog ... that site will absorb some reading time, for sure! (th)
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Here is the topic for Saving the Earth - the B612 Foundation
ya its a bit thin...but it has the member information
bobunf from Phoenix, AZ
"Rusty Schweickart
"B612 Foundation
"Co-founder, Chair Emeritus"
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The main problem I see with a gravity tractor is that the impulse can't be applied fast enough in most cases. It is limited by the gravitational attraction, which is quite low. And you need to avoid creating a pressure gradient with the gasses colliding into the asteroid which would partially neutralize the effect. So...., in my mind, there's nothing like nuclear weapons to provide massive impulse in a split second, plus the potential advantage of splitting it if there's a weakness. Spin isn't much of an issue since the bomb would trigger only a few meters off the surface or instantly on impact. Not enough to affect the result much as long as the angle is right. No need to try to use a tug when a nuclear bomb has so much more power.
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The other issue with a gravity tractor is that unless your calculations are dead on a year or more out, you could actually be doing more harm than good by pulling the object towards Earth.
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All the deflection schemes have advantages and disadvantages. Here is what I do know. The usual velocity change is directed pathwise along the orbit: either speed it up or slow it down, just a little bit. This changes the orbit aphelion and perihelion values and locations, thus causing a threatened hit to actually miss.
Gravity tractor:
Potentially the most accurate means of adjusting asteroid velocity, although the weakest and slowest effect. High accuracy requires only well-determined masses and an accurate range measurement.
The technological requirement is for a space vehicle design that does not yet exist: a rather large craft with big ion engines featuring canted neutralized beams. It will have to have conventional rockets, too, to effect the rendezvous. The canted exhaust streams must miss the asteroid, lest their impact force undo the gravity tractor effect.
Gravity is the weakest force available to us, which is why it takes months-to-years of hovering, to effect the needed velocity change in the asteroid. Absolutely unsuitable for short-warning situations!
If augmented with electrostatic attraction, as in my poster paper, I’m not at all sure that ion propulsion, as we know it, has the thrust capability to maintain hover against the much-increased attractive pull. These thrusters as we know them make only Newtons of thrust for tons of thruster and power supply equipment.
Impactors:
We lack the carrier spacecraft and its homing guidance, to be the payload for the big launchers required to reach the target. Nobody is working on such designs. Potentially, this could be a fairly accurate method, were it not for two crucial shortfalls in our science.
We do not know how to accurately predict the spalling reaction (that is the velocity-modifying thrust) within the best part of an order of magnitude. That is because we do not yet understand the internal properties of the target bodies. The scientists admit to that shortfall.
However, the same shortfall means that we also cannot predict when an impactor creates a crater and a spall reaction thrust, versus simply disrupting the body into a spreading cloud of fragments. In other words, self-cohesion is not understood. That disruption turns a short range event from a bullet strike to a shotgun blast, doing more damage. The scientists largely still don’t admit to that risk.
We can tolerate disruption only for long range events, so that most of the spreading cloud of fragments misses the Earth. The rest become a widespread meteor storm, of total mass lower than the original object. These will likely be recurrent meteor storms. Some of this will hit the surface.
A long warning event can be dealt with by a series of small impactors delivered over time, with far less risk of disruption. A shorter-warning event will require a single (or a very few) very large impactors. That greatly increases the chances of disruption. Which means the chances of deflection get reduced; does the impact energy go into deflection or disruption? We don’t know.
Either way, the unpredictable spall reaction means deflection results cannot be predicted with confidence. You must make the attempt, and then measure the actual result afterward. If it is not enough, you must make another attempt. If you have the time.
Nuclear devices:
There is no blast wave in a vacuum, except way down a deep well, where the gasified bomb fragments get confined. In space, there is only a super-bright flood of radiant energy. This energy vaporizes adjacent material, which (like a steam explosion) jumps violently off the surface it came from. This creates a spallation reaction of large size. You don’t “hit the asteroid with nukes”, you explode them right alongside as you pass by, at just the right range and time. Or it doesn’t work at all.
Because we do not yet understand the internal properties of these objects, we cannot yet predict how big the spallation reaction will be , or whether the body is self-cohesive enough to resist disruption. It’s just the biggest “thump” that we know how to apply.
Existing ICBM’s with nuclear warheads do not have the capability to reach threatening asteroids, precisely because they are sub-orbital systems. Period. That means you must load the warheads onto much bigger launch rockets.
We do not currently possess the guidance systems or the warhead fuzes for the near-surface burst this deflection approach requires. Nor do we possess the adapter hardware for those warheads to ride those large launch rockets. And nobody is working on any of that equipment.
It takes really big launch rockets to do this, because you simply do not have the time to wait several years doing gravity assist passes. You only have a few years warning at most, so you have to get your warhead there quickest, in order to have time to make a second attempt, if the first fails.
If the warning time is weeks or days, there is no second attempt. There is only the straightest, highest-speed shot to take. That requires a really big launch vehicle. Something like Falcon-Heavy or SLS, for just a single thermonuclear warhead. If that.
GW
Last edited by GW Johnson (2018-10-09 14:03:22)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW,
So basically what you're saying is that we need to get Bruce Willis and his team of NASA rejects to "drill baby, drill", drop a nuke down the hole, and let firecracker physics take over?
I saw this movie before, but it didn't end particularly well for us, even though Earth survived... sorta.
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Well, no, not usually. Exploding a nuke in a well is a way to disrupt the object into an intense meteor storm, especially if a last ditch defense at close range. That's a shotgun blast, usually more damaging than a single bullet strike.
I'm no expert, but usually they want to increase or decrease speed along the orbital path, and let the overall orbital parameter changes provide the miss. Most of the time, this takes less of an impulse than a direct diversion with a lateral impulse. Orbital plane changes are the highest cost of all. Angle is inverse tan of dV/V, and V is just enormous. You get the least angle that way for a given dV.
That being said, the dV along the path does take at least some time to have enough effect to miss (meaning a diverted distance greater than an Earth radius or diameter). Direct angle diversion might be required at extremely close range in a truly last ditch defense scenario. That would be a huge-yield bomb going off to one side of the asteroid, as it goes by the asteroid.
GW
Last edited by GW Johnson (2018-10-09 16:02:36)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW,
Is it realistic to deliver small thermonuclear devices attached to SEP-enabled kill vehicles that intercept or chase down the offending space rocks?
How practical would it be to "chain detonate" a series of devices to magnify the "push"?
How about breaking the big rock apart with one warhead and then using smaller warheads to take care of the stragglers?
As it pertains to bore hole nukes, I was wondering if there's any way to determine the composition of the core and how the asteroid would fracture, such that there's a chance of blowing it to bits small enough to not have an extinction-level effect on Earth. Obviously this would have to be tested, but our nukes aren't really doing anything useful here on Earth.
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Much like the nukes for Armagadan the hole is a time factor we may not have to chase a rock with SEP to deliver them.
Blast radius is a function of the size of the nukes for the clear zone wave that will come back at you.
Bruce had lots of data on what it was made of but its still a drill and place time limit.
This all sounds like the nuke rocket boiler plate/ blast plate / pusher plate for the rock to move from once they are detonated.....
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What about the mass driver device? It might go something like this>>>>A lander descends to the surface with power source, railgun with captive bucket and a regolith collection arm. Put rocks/ sand/ ice in bucket, aim the railgun in the opposite direction to the desired delta v and fire the contents away at high velocity. Return bucket to filling point. Repeat as necessary.
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I'm not sure I know the answers to the questions Kbd512 and Elderflower posed in postings 20 and 22. I'm not sure anyone knows yet. The answers depend fundamentally on a good understanding of interior properties and self-cohesion. None of that is yet known.
mass driver?
A mass driver as propulsion might be another good deflection concept. I think we need to know a lot more about the properties and cohesion before we could design an effective regolith miner for the "gun". So far, we hardly know how to touch down or move about.
breaking up the body?
Monolithic particles of silicate mineral striking Earth's atmosphere ablate by 1/8th of an inch radially, on the average. What that means is a solid object more than 1/4 inch in dimension will neither burn up nor explode in the air, but will strike the surface. It's the ices, and the poorly-bound small chunks merely bundled together, that burn and explode up in the air.
A few inches in size is a few meters of crater diameter. It goes up exponentially from there. So when I say that disrupting one of these NEOs, whether by design or by accident, will create a violent meteor storm, I'm talking about an exceedingly destructive event, not a light show in the sky. So I do think disruption is a really bad thing, to be avoided if at all possible.
sequenced nuclear explosions?
Chaining multiple smaller explosions as a sequence of pushes would likely work, if the guidance and fuzing is good enough to actually get the job done precisely enough. There might be a risk of spall debris destroying the following warheads, I don't know. I don't think anybody does know.
This sequenced multiple event concept would apply to impactors as well as nuclear devices, I'm pretty sure. If the self-cohesion is low, that is definitely the way the job has to be done, to stay below disruption force levels.
As for the guidance and fuzing, none of the requisite kinds are available off-the-shelf, or being worked on. Those are items requiring considerable development testing. Adapters to fit these craft to a huge launch rocket are not a development problem, just a design verification problem.
SEP to send the interceptor?
I would imagine that SEP might be used during the transit to achieve higher speeds and to finely-tune the transfer trajectory for precision intercept, although I myself don't really know. But I don't see it as the departure propulsion from Earth's vicinity onto whatever transfer trajectory is required. If there's no time for doing gravity assists, there's also no time for vanishingly-small accelerations onto the transfer trajectory.
GW
Last edited by GW Johnson (2018-10-10 13:09:10)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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I'm sure the Pentagon is already all over the idea of nukes in space "to deflect asteroids" (or blow up Earth, whichever). A penetrating tactical nuke might be nice. A nice long sequence of them hitting them from a single side, all launched by a single mother ship that positions them and keeps on firing. Not sure why a BFS-C couldn't be coopted. Get the weapons system in place, then start targeting, timing and releasing the missiles. Not that we're in any serious danger of being hit. We're far more likely to get into a nuclear war and do it ourselves.
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"Penetrating tactical nuke"? To disrupt the asteroid? One of my main points was why you do NOT want to do that!
You want to detonate alongside at a small standoff distance, and use the flood of radiant energy to create a violent thermal spallation event. The reaction to that spallation is the deflective thrust, provided the body does not break up. Remember, in a vacuum, there is NO blast wave!
GW
Last edited by GW Johnson (2018-10-11 09:50:42)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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