Ship Killers From Low Earth Orbit

By Kenneth Roy

Also for the past 50 years, the measure of a nation's sea power has been the number and quality of its carrier battle groups—and the U.S. Navy has had an almost unchallenged monopoly on these weapon systems. The sheer cost in treasure, skilled manpower, technology, and time required to build a fleet of carrier battle groups able to contest control of the seas with the U.S. Navy is so great that other nations would not willingly attempt it, and could not attempt it without some response from the United States.

Before the carrier battle group, battleships were the measure of a nation's sea power. The battleships of 1940 were the culmination of a long and complex development process. They were, by any measure, remarkable fighting machines that were better in every way than their predecessors. They were manned by skilled and dedicated crews who benefited from long naval traditions. Any ship, except another battleship, that ventured within range of their big guns survived only because the battleship allowed it. They did not, however, decide the question of sea control during World War II. In due course, aircraft carriers, planes, and air crews emerged as the final arbiters. World War II's naval battles proved to all that the battleship era was over.

To understand the transition from the battleship to the carrier battle group as the arbiter of sea power is to recognize the possibility that yet another weapon system could evolve to replace the carrier battle group. That so many naval officers of the 1930s failed to anticipate the battleship-carrier transition is not encouraging.

Consider the Mark 7 16-inch/50 gun mounted in the Iowa (BB-61)-class battleships. Now move this gun 150 miles straight up and place it into a circular orbit. When it fires a 2,700-pound Mark 8 armor-piercing shell at 2,500 feet per second against its direction of orbit (downrange), the shell impacts a point 2,280 miles up range, nine minutes later. Because of atmospheric drag and the pull of gravity, its trajectory becomes steeper as it nears its target. It impacts at an angle of 10o at 8,750 feet per second (Mach 7.7). The kinetic energy at this speed for a 2,700-pound projectile is roughly equivalent to 2,100 pounds of trinitrotoluene (TNT).

If the gun is pointed straight down and fired, the shell impacts 1,541 miles from the aiming point, five and a half minutes later. The impact angle is 8.So at a speed of 7,730 feet per second (Mach 6.8). The kinetic energy at this speed is equivalent to some 1,600 pounds of TNT. 1

Although there would be a certain symmetry (and some battleship advocates might say poetic justice), no one is seriously proposing to put such a gun in orbit. Any 2,700 pound object that can give itself a 2,500 foot per second 'kick' while in a low earth orbit and survive re-entry can inflict the same havoc. A 400-pound solid-rocket motor could be substituted for the 100-ton Mark 7. Indeed, there is nothing special about 2,500 feet per second. If the change in velocity is reduced to 1,000 feet per second, the results are about the same. The range and flight time are longer but the impact parameters are similar. Also, the Mark 8 projectile is just a starting point. Its ballistic and destructive characteristics are understood and are useful to illustrate the advantages of starting from low earth orbit. The projectile mass could be increased while the drag coefficient and diameter were reduced to yield something that could actually survive earth reentry while being far more deadly.

What I propose is technically a smart, hypersonic, ballistic guided missile or projectile, launched from low earth orbit. The term "missile," however, implies a somewhat delicate vehicle with a warhead attached while the term "projectile" implies a dumb warhead. These proposed hypersonic missiles/projectiles would be neither delicate nor dumb—and need not have a warhead. They would be shipkillers.

Orbital mechanics dictate that anything in low earth orbit circle the earth while the earth turns beneath it. Depending on the inclination of the orbit with the earth's equator, the ship-killers would overfly some, or all, of the earth's oceans. There would be no refuge for any medium-to-large ship except underwater, or possibly in storm systems. There would be no safe harbor. The possible orbital configuration of this weapon system is beyond the scope of this essay, except to note that it would be complex and ever-changing as hundreds of ship-killers and other satellites in different orbits criss-cross the globe. Their orbits could be changed at random to confuse anti-satellite weapons.

The ship-killers would require cueing from sensors that can clearly see the ocean's surface. Earth orbit is the ideal location for these eyes, although the intelligence behind them could be located elsewhere. Ocean reconnaissance satellites, using thermal and visible light as well as radar, are nothing new. They would assume a targeting function as well as a reconnaissance role. Once they identified a target anywhere on the earth's surface, the target could be hit and destroyed within minutes, provided a ship-killer was in position.

Obviously, such systems could not be deployed any time soon. The development process will face several serious engineering obstacles. Deployment will require a space launch capability that does not yet exist. But engineering obstacles can be overcome and space-launch technology will improve.

The biggest challenge is the required pinpoint accuracy required for the weapons to be useful. The flight of the ship-killer begins five to ten minutes before impact when it fires its re-entry rocket. As the ship-killer encounters the atmosphere it will begin to ionize the gases around it, creating a plasma wall that is difficult for electromagnetic signals to penetrate. Somehow, the plasma wall must be eliminated or penetrated for the ship-killer to use radar or visual sensors to find its intended target. Ablatives, cooling systems, low-drag technology, slower speed, strong magnetic fields, or some combination of these might provide the answer. Using its own on-board sensors, possibly with help from sensors in orbit, the ship-killer must locate its target and then adjust its trajectory to hit it. It must be smart enough to hit the right target at an angle and from a direction designed to inflict the maximum damage. Is such a capability possible? Unknown, but there is no scientific reason it cannot be done. 2

Can a hypersonic object survive the heat and stress of re-entry? A sharp ship-killer has less drag but absorbs more heat; a blunt one dissipates heat better but has more drag and less terminal velocity. The heat absorption and stress increase as the atmosphere becomes more dense. By the time all the engineering tradeoffs have been made, the ship-killer may not be hypersonic. It might be required to make a high approach over the target area, say at 40,000 feet—where the air density is only one-quarter that at sea level—locate its target and dive vertically to minimize time spent in the lower, denser atmosphere. But even if the final approach velocity is a leisurely Mach 2 or 3 directed straight down, the overall concept remains valid. The ship-killer simply would be more massive and make use of greater quantities of conventional high explosive.

Could such a weapon inflict serious, or even fatal, damage to a large ship like a carrier or a supertanker if it were able to hit it? The weapon's assets lie in its kinetic energy and any high explosive carried. These could be put to best effect by having the projectile fragment into a shower of large supersonic, or even hypersonic pieces and sub-munitions just before impact; each non-explosive piece would be capable of punching all the way through the ship, and the sub-munitions would be fuzed to explode inside it. The hull, fuel tanks, fuel and water lines, electrical cables, parked aircraft, boilers, reactors, munition stores, all would stand a fair chance of being punctured. The shock wave caused by a ship-killer impact could itself be very damaging. If the target survived, another ship-killer would begin its short but exciting flight. There is no reason a salvo of ship-killers could not make a coordinated attack against a formation of ships.

Command and control would be challenging. There will be hundreds of ship-killers and dozens of reconnaissance and targeting satellites. All will be in slightly different orbits with constantly changing relative positions. There will be ground control stations. There may be craft in orbit, either manned or unmanned, to service and maintain the ship-killers and their support satellites. All of these will have computers that must be linked by a communications network that must allow for the loss of any single node, or even multiple nodes, without impairment of the network's ability to function. This is very similar to the proposed "digital battlefield" technology presently under development.

Communications would consist of real-time images from the reconnaissance satellites to the ground control stations, orders and information from ground control stations to the ship-killers, and status and position reports from everybody to everybody else. In space, the links between nearby nodes could be short-range, narrow-beam radio signals or even lasers. Either would require each node to "know" where to aim its communications equipment so that it could remain in contact with four or five other nodes. These would change as orbital motion moved some out of range and others into range. Each node would accept information, authenticate it, take information addressed to it, and pass on what is addressed to other nodes, much like the Internet operates today. Here, the limiting technology is encryption. There is no point in building such a system if a hacker can turn it against its builders. The hardware and software needed are not too far off the beaten path, but can they be made hacker-proof? Countermeasures are feasible. Evasive actions will probably not be practical because of the high speeds of the incoming weapon. If radar guidance is employed, various countermeasures are possible although success is a function of relative technical sophistication and raw power. Flares could confuse thermal targeting systems. Robotic vision could prove a very difficult sensor to counter. On a clear day, it could see almost forever.

With antimissile and automatic cannon defenses, we enter the arena of game theory. The problem for the defender is that individual ship-killers are cheap and the attacker must succeed only once where the defense must succeed every time, or lose a very expensive asset. Also, the technical problems in actually hitting a small, maneuverable, hypersonic object are not minor.

Despite the orbiting ship-killers in its arsenal, a nation will need traditional naval escort ships to counter submarines, aircraft, cruise missiles, and small, fast, or stealthy surface ships that seek to attack his shipping or defend their own. The ship-killers can ensure that these escorts won't face any large surface combatants.

The ability to place ship-killers and reconnaissance and targeting satellites in orbit in sufficient numbers to be effective is not possible with today's launch vehicles. Current costs to put a pound into orbit is about $6,000 with a Titan IV, although the Air Force hopes to lower this number by 25% to 50% with its Evolved Expendable Launch Vehicle (EELV) Program. Lockheed's Skunk Works is currently developing the X-33, a prototype reusable launch vehicle that may lead to the VentureStar single-stage-to-orbit, reusable launch vehicle. The VentureStar's payload is projected at 59,000-pounds; cost to low earth orbit could be as low as $500 a pound. Turnaround time between flights is expected to take 2,500 man-hours over a period of one week, as opposed to the current space shuttle's 50,000 man-hours over two months.

The picture that begins to emerge is unexpected. Existing and emerging superpowers could be expected to develop a space launch capability for perfectly legitimate reasons. If this space launch capability is equivalent or superior to the projected VentureStar launch system in capability and cost, then development and deployment of a nonnuclear, space-based, ship-killer weapon system could occur relatively quickly. After that, control of the seas would belong to the nations that controlled these weapons, whether or not anyone fully understood the fact. If, in the course of several hours or days, they reduced the United States' surface navy to insignificance, how could the United States respond short of employing nuclear weapons?

There is no strong incentive for the United States, with its existing carrier battle groups, to develop and deploy such a weapon system. The desire by an emerging superpower that is frustrated by the U.S. Navy, in achieving what it considers its legitimate national objectives, however, could be intense.

Deployment of such a weapon system would mark the end of the carrier era. Unlike the battleship-to-carrier transition, this transition would not just swap out weapon systems that define sea power, it also would usher in the era of space power.

Alfred Thayer Mahan identified the major effect that sea power—or the lack of it—can exert on the outcome of campaigns ashore. A Mahan for space power has not yet emerged, perhaps because it is too early, but space power can be expected to influence land conflicts both indirectly by affecting sea power as discussed in this essay, and directly in ways yet to unfold. Ships are ideal targets for ship-killers because they are complex, compact, and expensive collections of steel, fuel, and ordnance. Fully fueled space launch vehicles sitting on the ground, however, are even better target. A country with a few deployed ship-killers easily could prevent other nations from deploying similar systems if it were willing to use its shipkillers to attack the launchers. Low earth orbit is the ultimate high ground, and taking it away from a nation determined to hold it will be very difficult.

The civilian and military leadership within the United States can ignore this coming transition or they can develop a long-term strategy to allow the nation to benefit from it. Either choice has important implications. Unless we choose to make it happen, there is no particular reason why the nation that will become the world's first space power need be the same nation that was the world's last sea power.

1 These numbers are based on a computer simulation that makes a number of assumptions: The world's atmosphere conforms to the 1962 U.S. Standard Atmosphere, lift forces are ignored, earth and atmospheric movement during flight are ignored, and most amazingly, the ballistic shield and the projectile behind it withstand re-entry while facing backward or sideways as they hit the atmosphere. This last assumption has no basis in reality, but that is not the point.

2 The very serious issue of pin-point accuracy used for reentry vehicles carrying weapons of mass destruction is understood. Kinetic energy weapons fired from orbit are not weapons of mass destruction and anyone who deployed them would have to ensure that everybody else understood this fact. First use of nuclear weapons will continue to invite response in kind for some time to come. But what response is appropriate to first use of kinetic energy weapons from space directed against military targets?

Mr. Roy is an engineer with the Lockheed Martin Energy Systems Corporation in Oak Ridge, Tennessee.


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