U.S. Plans Test of Anti-Satellite Interceptor Against Failed Intelligence Satellite

The United States is planning to intercept a dying reconnaissance satellite with a missile launched from a Navy ship. The administration justifies the intercept on the basis of public safety. That is a long stretch, indeed, and thus far in the news coverage that I have seen there is virtually no mention of the political consequences of the United States’ conducting its first anti-satellite test in over two decades.

The United States, along with China, Russia, and other space-faring nations, should be working to ban anti-satellite weapons. Such a ban would work strongly in the best interests of the United States because we depend more, by far, than any other nation on access to space for our economy and security. Any measure that reduces the threats to satellites will enhance American security. The proposed test is a potential public relations bonanza, showing the public how a defensive missile can protect us from a—largely imaginary—danger from above. What follows is a simple analysis of what some of these dangers might be and a description of what might happen. These are questions that should have been asked of the administration.

In December 2006, the United States launched a 5000 pound spy satellite from the military space center at Vandenberg, California. Virtually everything about these satellites is highly classified. The government has declined to even say who manufactured it, much less give details about what it does. Most accounts seem to assume it is a photoreconnaissance satellite. It is designated as US193.

The satellite was successfully placed into a 220 mile high orbit but radio communication with the satellite was soon lost. At 220 miles, the Earth’s atmosphere, while tenuous, still exerts some drag on a satellite the size of a small school bus that is pushing through it at 17,000 miles per hour. Reconnaissance satellites are normally placed in low orbits; they are just big cameras after all and you get better resolution in the pictures if the camera is closer to the thing it is photographing. Reconnaissance satellites usually carry some propellant and small thrusting rockets, for three reasons. First, if there is a particular place on the Earth that the spy satellite needs to photograph, the orbit of the satellite will—eventually—naturally bring the satellite right overhead but the intelligence analysts, the military, or the president might not be able to wait. So the satellite can use its propellant and rockets to nudge it a little one way or the other to shift its orbit enough to bring it over the desired spot on the Earth sooner rather than later. Second, because the satellite is in such a low orbit, it will lose energy to air resistance and slowly come closer to the Earth. The rockets can be used as a booster to occasionally nudge the satellite a little higher to keep it in orbit. Third, when the propellant is almost gone and the satellite is doomed to reenter the atmosphere, the last bit of propellant can be used to intentionally slow the satellite and force it down, usually aiming for the Pacific Ocean where debris will fall harmlessly.

The propellant is hydrazine, a compound of hydrogen and nitrogen. It is not the most efficient propellant but it is extremely simple to use. It is a monopropellant, which means it can be used just by itself, there is no need for separate oxidizer and fuel. Just squirt some onto a catalyst in a reaction chamber and it decomposes, forming hot hydrogen and nitrogen gas that rush out a rocket nozzle, creating thrust. The problem with US193 is that radio control has been lost, the propellant is not being used up, the satellite is about to reenter the atmosphere, and the propellant tank is still filled with a thousand pounds of hydrazine. There is some chance that the tank will not burn up on reentry, some chance it could land on a populated area, and some chance the hydrazine could injure someone. Hence the plan to intercept the satellite.

You Can’t “Shoot Down” a Satellite.

Almost all press reports include some statement about how the Navy is going to “shoot down” the satellite. The image suggests a hunter with a shotgun shooting down a duck. Bang! The duck gets hit, its wings fold, and it falls to Earth. Not the way it works with a satellite. This is a satellite; it is in orbit. It stays in orbit because of its momentum and the balance between the centrifugal force and the Earth’s gravity. It is not being “held up” the way an airplane’s wings hold it up in the air.

When the interceptor hits the satellite, it is not like a bullet hitting a car, punching a hole in the side and coming out the other side. The interceptor will hit the satellite at about 18,000 miles per hour and the energy of the interceptor is far more than needed to melt and even vaporize the material of the interceptor. This happens so quickly it is as though it were an explosion. Shock waves will travel through the structure of the satellite and break it into pieces, some large, some as small as dust. The hope is, apparently, that the interceptor will break open the hydrazine tank so it will leak out before the tank reaches the ground.

But the interceptor is not “shooting down” the satellite. The satellite weights 5000 pounds and the interceptor weights 20 pounds. Even if the satellite breaks up into pieces those pieces are going to be moving in roughly the same direction as the satellite was moving, that is, in the same orbit. Some smaller pieces will encounter proportionately more air resistance and will come down sooner than the satellite would have. But if the propellant tank breaks free, the density of the propellant tank is higher than the average density of the satellite so the propellant tank by itself might actually stay up longer than the satellite by itself would have, had it remained whole.

The satellite is not being controlled but this intercept is going to trade one big uncontrolled satellite for several uncontrolled pieces of a satellite. If that helped it burn up in the atmosphere, that might be useful but the first thing that happens when a large satellite enters the atmosphere is that the structure fails and it breaks into pieces anyway. Recall the sad photos of the Columbia reentering the atmosphere: it was not a single hot streak across the sky but several huge pieces moving together; and that was a vehicle that was specifically designed to survive reentry.

The Pentagon tells us that the hydrazine tank will survive reentry. I remain unconvinced. Deorbiting something is not easy. The tank may not burn up entirely from the heat of reentry but the heat should be enough to vaporize the hydrazine, creating a high pressure in the tank that would rupture the tank, spilling the hydrazine harmlessly at very high altitude. Also keep in mind that this is not a sealed tank, there will be pipes going in and out and these will absolutely be sheered off by the reentry, allowing the hydrazine to vent. Finally, intercepting the satellite will not necessarily destroy the tank. Most likely the interceptor will break the satellite into pieces, one of which will be the hydrazine tank, which will reenter the atmosphere independently but keep in mind that the satellite would have broken up quickly upon reentry anyway.

And if the tank makes it to the surface? Well, we are told it might cover an area the size of two football fields with hydrazine and if someone remained in the area they could get a fatal dose. (If I were outside and a large tank of strange material fell from outer space, I confess, it would never occur to me to leave the area.) Well, if “two football fields” is as large at 100 meters by 100 meters, that is 10,000 square meters or just less than one ten billionth of the surface of the Earth. That makes winning the lottery seem like very good odds, indeed. To put this in perspective, the United States produces 36 million pounds of hydrazine every year, the world produces 130 million pounds of it. (It is used in, among other things, the production of plastic.) Most of this is transported around the industrial world by trucks and rail. At any given time, vastly more hydrazine is in transit around the world than is in this satellite. If the government were interested in public safety it would be better to take the $3 million cost of the Standard-3 missile and pay for a traffic light at a bad intersection or pay for children’s vaccinations.

So what is going on? When control of the satellite was first lost, the risk from the satellite was dismissed as trivial, not worth any real concern. Now we need to “shoot it down.” I cannot attribute motives without being able to read minds but a normally skeptical person could be forgiven for at least suspecting that this satellite is offering a chance for the Navy to test its missiles in an anti-satellite mode for the first time since the end of the Cold War. I have seen virtually no discussion of the arms control implications of this. Are we fueling an anti-satellite arms race? Who knows, but I don’t think anyone in this administration cares.


Two other good articles, here and here.

18 thoughts on “U.S. Plans Test of Anti-Satellite Interceptor Against Failed Intelligence Satellite

  1. One website I saw (sorry, can’t find the link) had a far more plausible proposal – the satellite might be projected to land in a foreign country. Since it’s a highly classified satellite, the spy agencies don’t want anyone to be able to analyse and learn from it, so they proposed shooting it to mangle the classified bits, with the hydrazine being a cover story.

  2. The anti-satellite arms race you refer to has already started. What we are doing is essentially no different that what the Chinese did last year when they destroyed a defunct satellite in orbit by ramming it with a rocket. I find it interesting that you did mention that once in your article. Frankly, this is a military exercise we must engage in if we are to learn anything about developing a strategy to protect our satellites from enemy attack. The current political consequences are meaningless in comparison to the potential consequences of having our vital civilian and military satellite system disrupted by an attack from China or Russia.

  3. Ivan, Is hydrazine any more dangerous than gasoline? Spilling 1000 lbs of gasoline over an area of 2 football fields would be a bad thing, but hardly something the Pentagon usually worries about.

  4. Very good article, only facts, no spin. It is not going to be taken well by those who think that we are shooting a duck. And for those who know that we are not shoot a duck, they are in for the shooting, anyway. As Chairman Mao put it, “Power comes from the gun barrel.” If the United States does not shoot, how will it be certain that the gun barrel is not rusty. The mass only needs to know about the ducks and they can be assured that Dick Cheney is not firing the gun this time.

  5. You Wrote “…This is a satellite; it is in orbit. It stays in orbit because of its momentum and the balance between the centrifugal force and the Earth’s gravity. It is not being “held up” the way an airplane’s wings hold it up in the air.” and “Even if the satellite breaks up into pieces those pieces are going to be moving in roughly the same direction as the satellite was moving, that is, in the same orbit. …”
    I am sorry to be so blunt, but your physics is deplorable. An orbit = momentum (mv) and centrifugal force balanced by gravity? The force on the orbiting object = the force of gravity and this is the centripetal force that causes the object to move in a circular path. No balancing act required. (centrifugal force is a pseudo force and has no place in a discussion of the physics of motion.) The pieces will move in the same direction? Um, the momentum of the system (satellite and missile) will be conserved. If the missile arrives from “below” the total momentum of the satellite/missile system will now have an “outward” component. (a little hard to describe w/o a set of coordinate axis, but you get the idea.) Further if there is an explosion (hydrazine doesn’t need much to burn), the momentum will be still be conserved (a piece can go flying in any direction as long as a piece flies in the other direction.) My high school physics teacher would be embarrassed if one of his students said this. This is a website supported by the Federation of American Scientists? You should have talked to someone who took high school physics…

  6. A question that sticks out in my mind is: How long before the Russians test an ASAT of their own?

    Regardless of the reasons for the US action, it seems as if this will provoke the inevitable exploitation of space for warfare.

  7. why it will fail.

    missile is designed to work in earth’s atmosphere— aeronautics

    satellite– is space– astronautics

    only way they can successfully shoot down is when satellite enters earth’s atmosphere

    satellite when in space— and when missile reaches space— how the missile will react in space is mathematically unpredictable. sometimes by luck it will hit.

    if U.S. shoots down satellite when it enters earth’s atmosphere… it is no different than shooting an airplane…— this is not a big feat.

    unless u.s. testing a special aero/astro missile….. even if u.s. successfully hits the satellite in space using regular missile, it has to attributed to luck,.

  8. u.s. is apparently modifying a standard missile,— its software& guidance system—- to operate in space. this is definitely an aero/astro missile test. very good work. i totally support this.

  9. in warfare, in the event of a major war between any 2 countries, if satellites are knocked down, — your communication backbone– is broken. this affects united states especially, because u.s. is reliant on sateliites & high technology more than any other country. imagain a scenario when another nation knocks down a bunch military communication satellite during a war? what happens?

    world has to co-operate to ban asat. but u.s. will not back & should not back after china has demostrated its asat capability. world should be subservient to usa. world should trust usa… because usa will not unnecessarliy detonate nuclear warhead.

  10. <p>Associated Press – U.S. to try to shoot down spy satellite<br />
    Reuters – ANALYSIS – U.S. satellite shooting to raise space weapons worry<br />
    USA Today – U.S. to shoot down failing spy satellite<br />
    Newsday – U.S. to shoot down satellite<br />
    Navy Times – Navy tasked with destroying satellite<br />
    Detroit Free Press – Missile will be shot at satellite</p>
    <p>in the above navy times headlines is most accurate—they used the word “destroy” or disable as opposed to shoot down. (shooting, exploding a bomb—all this is applicable in earth’s atomosphere—not space</p>

  11. I cant see how we could hit a satellite from below with a missile. This satellite is only a few meters across, and going 17,000 miles an hour or so; can U.S. guide a missile that precisely?

  12. Has it occurred to any others that this missile launch comes just a few weeks after Iran launched it’s new design? It serves to show Iran that the U.S. will act against any Iranian attempt to deploy anti-American spy satellites using their new missile. It also allows a comparison of debris fields against the Chinese test of January 2007 which can indicate circumstantially that the guidance controls are as good as equal to U.S. models. I reasonably suspect the PRC stole U.S. guidance soetware.

  13. a tip for concerned u.s. scientists/engineers

    a standard missile— that has integrated sub-missile—with special guidance system to operate in space— (use ingenuity from space space shuttle)–to control the submissile when in space— sensors on sub-missile that seeks said sensor on satellite (eg heat or anything else) . when submissile hits satellite, only colliding force will/should dismantle/disable satellite. (higher the speed, the great the chance for satellite to get dismantled/disabled)

    U.S., has the technology (in standard missile & space shuttle)– everything that is needed for ASAT weapon- u.s. didn’t bother to put together a peice of technogy to call something an asat weapon. this will happen on thurday.

  14. Certainly it was not required to hit and destroy the satellite in its orbit for the wellbeing of the mankind but to show the American superiority in space particularly after the China had done so few months earlier. And why did it China? Simply, balance of powers. To show the US that her spy satellite are not really safe. That was a big blow to the US. Thus the US had to come up with the same results if not better. Further it was a valuable chance to test the capabilities of the navy. …To serve the mankind is not the character of Americans. They always seek superiority by shedding the blood of the innocent.

  15. A few years back, while the F 14 tomcat was operational, it did carried a missile called the Phoenix and the F15 at that time carried a missile called ALMV ASAT. What happened to those missiles?

    Reply: They are probably in storage. HK

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