Despite budget cutbacks and a lack of support, U.S. military officials have pushed through upgrades and technology insertion for the nation's land- and sea-based atomic missiles, as well as for the nuclear arsenal's multi-layer command-and-control systems.
No one is indifferent when it comes to nuclear-tipped intercontinental ballistic missiles (ICBMs). These doomsday weapons represent one of the most politically volatile and emotional issues people have faced for more than half a century. These weapons are scary, and it's not hard to see why. Each missile can deliver about 10 times the destructive power of the bombs dropped in 1945 on Hiroshima and Nagasaki. Some of these missiles also carry multiple independently targetable re-entry vehicles (MIRVs), which increases their destructive power. The very existence of these weapons has induced ordinary citizens to build underground shelters in their backyards, was behind the "duck-and-cover" drop drills in public schools at the height of the Cold War, and sparked countless public protests since the 1960s.
Nevertheless, ballistic missiles represent the two most important legs of U.S. nuclear strategy, which is the traditional "nuclear triad" of land-based bomber aircraft, ICBMs, and submarine-launched ballistic missiles (SLBMs). The land- and sea-based ballistic missiles offer the big punch, are more hardened against enemy attack than the bombers are, and can be launched at their targets from thousands of miles away. Still, the long distances to their targets and the challenging environment of ocean-going submarines makes missile-guidance and command-and-control technologies for aiming and directing ballistic missiles a daunting challenge.
|The Minuteman-III land-based intercontinental ballistic missile waits in its silo for orders to launch.|
Scary or not, nuclear missiles are as essential today for helping maintain the global balance of military power as they were during the Cold War, and arguably have helped prevent huge military confrontations since World War II. Supporters of global nuclear disarmament contend that nuclear weapons and their delivery systems are obsolete today, relics of a bygone era when the United States and then-Soviet Union were the undisputed world powers. The existence of nuclear missiles, however, still deters aggression, and forms the last line of defense during dire global military contingencies.
ICBM guidance systems
The ability to guide, control, and command the nuclear missile force is still a primary concern among U.S. military planners, despite treaties and cutbacks that have reduced the U.S. nuclear arsenal by about 75 percent since the end of the Cold War in the early 1990s. No one wants a force this powerful to be loosely controlled or less than accurate. That's the reason for a reliable command structure for the nuclear missile force (see accompanying story: Command and control of intercontinental ballistic missiles) and precise guidance systems for the ballistic missiles themselves.
Today, the guidance systems for land- and sea-based ballistic missiles rely on inertial technology-precise gyros that keep the missiles on their glide paths, periodically updated by on-board celestial navigation subsystems that watch the stars to make sure the inertial systems are functioning accurately.
Advanced navigation systems, such as the satellite-based Global Positioning System (GPS), have been considered for upgrades to the nuclear ballistic missile force, but as yet have not been adopted. Nevertheless, advanced technologies such as fiber-optic gyros (FOGs) have been inserted into the ballistic missile force to keep guidance systems as reliable and accurate as possible.
One problem with upgrading the nation's ballistic missile force has been a relative lack of money. Generally, it's a political loser for the president of the United States, Congress, or the Pentagon to push hard for upgrading the missile force. Nuclear weapons, after all, are an unpopular topic, and few in the public eye step forward to champion their improvement.
|The Autonetics D-17 guidance computer from a Minuteman I missile, shown above, was replaced with the Boeing NS-50 missile guidance computer between 2001 and 2008 as part of the Minuteman-III Guidance Replacement Program.|
Treaties have been in place since 1969 that compelled the reduction of U.S. nuclear warhead stockpiles. The U.S. inventory peaked in 1966 at 32,193 warheads. Notable treaties between the U.S. and Russia include the START II treaty; although never actually put into force, it led to major changes in the U.S. nuclear arsenal. START II, short for the second Strategic Arms Reduction Treaty, called for banning the use of MIRV warheads on land-based ICBMs.
In 2002, the U.S. on its own started withdrawing MIRV ICBMs from service, which included the complete deactivation of the LGM-118 Peacekeeper missile-popularly known as the MX. Each Peacekeeper missile was designed to carry as many as 10 separate warheads, making this system one of the most destructive weapons ever deployed. These missiles started entering service in 1986, and 50 of these missiles eventually were deployed. Largely due to START II, however, the U.S. started deactivating these missiles in 2002, and took the last one out of service in 2005. The Peacekeeper nuclear warheads, however, were retained. Russia reportedly still has from 40 to 75 R-36M2 ICBMs in service, each with 10 MIRV warheads apiece.
The Strategic Offensive Reduction Treaty (SORT) was in place between the U.S. and Russia from 2003 to just last year, and called for the two countries to limit their nuclear arsenals to between 1,700 and 2,200 operationally deployed warheads each. The latest nuclear-arms reduction treaty is New Strategic Arms Reduction Treaty, or New START, which was signed in April 2010 and should be in place until early 2021. New START seeks to reduce the number of strategic nuclear missile launchers by half, does not limit the number of inactive stockpiled nuclear warheads, and does not place limitations on MIRV warheads. New START further limits the number of U.S. and Russian deployed strategic nuclear warheads to 1,550 each. It would limit the number of ICBMs, SLBMs, and heavy bombers that carry nuclear weapons to 700 in each country.
|The Trident II submarine-launched ballistic missile is designed to launch from under the ocean's surface from Ohio-class ballistic missile submarines.|
Largely due to these treaties, U.S. military leaders look to maintain and upgrade their best ballistic missile systems for the long term. The only land-based ICBM the U.S. keeps on active deployment is the LGM-30G Minuteman-III. Previous versions of this missile-the Minuteman-I and Minuteman-II-were in service from 1962 to 1997. First deployed in 1970, the Minuteman-III ICBM guidance is based on a gimbaled inertial guidance system. Although the Minuteman-III carries only one warhead per missile, it is capable of carrying three MIRV warheads.
The Minuteman-III originally was equipped with a Rockwell Autonetics D37D flight computer, but as of 2008 has been upgraded as part of the Minuteman-III Guidance Replacement Program (GRP). The Boeing Co. acquired Rockwell Autonetics in 1996, and the Boeing Integrated Defense Systems segment in Heath, Ohio, was in charge of the GRP initiative. Boeing experts installed the NS-50 missile guidance computer (MGC) based on a 16-bit, high-speed microprocessor, which helps the missile correct positional errors and generate steering signals.
Minuteman-III computer programs are stored on a magnetic tape cartridge. The computer also controls the alignment of the inertial measurement unit, and performs test and monitoring of the missile's guidance & control system. Other parts of the Minuteman-III's latest guidance system include the Gyro Stabilized Platform (GSP), Digital Control Unit (DCU), Missile Guidance Set Control (MGSC), and the Amplifier Assembly.
|The Peacekeeper ICBM, shown above, was the most advanced U.S. land-based ballistic missile until it was deactivated in 2005.|
Trident II D-5 SLBM
The UGM-133 Trident II D-5 is the primary U.S. sea-based nuclear ballistic missile, and is deployed aboard U.S. Navy Ohio-class ballistic missile submarines. The Navy operates 14 of these ballistic missile submarines, each of which can carry as many as 24 Trident II ballistic missiles. Although the Trident II is designed to carry as many as 12 MIRV warheads, current treaties reduce this number to four or five. Each missile has a range of 4,000 to 7,000 miles. The Trident II D-5 was first deployed in 1990 and is scheduled to remain in service until at least 2027.
U.S. military officials are not letting the Trident II design atrophy, however. The U.S. Navy started the D-5 Life Extension Program in 2002 to replace obsolete components using as many commercial off-the-shelf (COTS) parts as possible to keep costs down and to enhance the missile's capability. The Charles Stark Draper Laboratory Inc. in Cambridge, Mass., is in charge of upgrading the Trident II's guidance system, and has been working on this project since 2005.
In practice, the Trident II missile's inertial measurement system receives targeting data from computers aboard the submarine. The inertial measurement unit, in turn, transmits signals to the D-5 flight-control computer and converts them into steering commands to keep the ballistic missile on target. Its post-boost control system maneuvers the missile in flight to observe stars for the missile's celestial navigation subsystem, which updates the inertial system in flight.
Draper Lab received a $130.6 million contract in late 2005 to maintain and improve the Trident II's MK-6 guidance system. Awarding the contract were officials of the Navy Systems Programs office in Washington, which is in charge of Navy ballistic missile technology. In that effort, Draper Lab experts developed an open-architecture strategic inertial guidance technology synthesizer to help them evaluate alternatives to the missile's gyroscope, and appropriate radiation-hardened electronics for the missile.
One year later, Draper Lab received another Navy contract to repair and recertify the Trident II's MK-6 guidance system, including its pendulous integrating gyroscopic accelerometers, inertial measurement units, electronic assemblies, and inertial measurement unit electronics. In February 2010, Draper Lab started work to acquire circuit card assemblies for the Trident II guidance system as a part of the MK-6 life-extension program.
As part of the Trident II guidance system life-extension program, Draper Lab experts went to Nufern in East Granby, Conn., to gain rugged optical fiber for use in the Trident II's guidance system. Nufern is the lead optical fiber supplier supporting Trident II upgrades, and supplies optical fiber to Honeywell Inc., maker of the Trident II missile's fiber-optic gyroscope.
Command and control of intercontinental ballistic missiles
Overall control of the U.S. arsenal of land-based intercontinental ballistic missiles (ICBMs), its submarine-launched ballistic missiles, as well as its nuclear-capable bomber aircraft, comes from the Nuclear Command and Control System (NCCS), which describes an infrastructure of fixed-site locations, aircraft, and land vehicles-all with strategic radiation-hardened communications capability.
Only the president of the United States has final authority to authorize use of strategic nuclear weapons like the ICBMs and submarine-launched ballistic missiles. The NCCS, however, helps the president communicate with his top military commanders to direct nuclear forces. The architecture of the NCCS takes into account the possibility of enemy strikes that disable or destroy some of its installations and platforms, and plans for handing off authority and tasking in case of enemy attack.
Primary parts of the Nuclear Command and Control System are the National Military Command Center (NMCC), the U.S. Strategic Command Global Operations Center, and so-called Site-R. Mobile components of the NCCS include the E-4B National Airborne Operations Center, the E-6B Airborne Command Post, and the Mobile Consolidated Command Center.
|The E-6B Airborne Command Post is a converted Boeing 707 jetliner, and serves as a backup strategic command post and as a communications link with submerged ballistic missile submarines.|
Today's Nuclear Command and Control System emphasizes strategic communications, intelligence, and planning, as well as the traditional triad of nuclear forces consisting of land-based ICBMs, submarine-launched missiles, and strategic bomber aircraft.
The National Military Command Center-perhaps the single most important command-and-control node of the nation's nuclear forces-is the primary day-to-day location for nuclear command and control. It is staffed around the clock, and is located in a shielded room in the Pentagon just outside of Washington. This site is responsible for monitoring nuclear forces and national military operations.
The U.S. Strategic Command Global Operations Center serves as a backup for the National Military Command Center in case of the latter's destruction or damage. It is located underneath U.S. Strategic Command headquarters at Offutt Air Force Base outside Omaha, Neb. The center is protected against electro-magnetic-pulse (EMP), and has its own emergency power supply. It is staffed around the clock.
Site-R is a standby strategic command post at Fort Ritchie, Md., outside of Washington, and can be brought online quickly if necessary.
Several specialized and radiation-hardened aircraft also take part in the Nuclear Command and Control System. Chief among these is the National Airborne Operations Center, represented by a fleet of modified Boeing 747-200B jumbo jets functioning as survivable mobile command posts called the Boeing E-4B Advanced Airborne Command Post.
The E-4B is the aircraft that in case of nuclear war would be the airborne command post for the president of the United States, the secretary of defense, and other high government officials. These aircraft are based at Offutt Air Force Base, Neb.
The E-6B Airborne Command Post, a modified Boeing 707 jetliner, serves as a backup to the U.S. Strategic Command Global Operations Center should the ground-based site be unable to fulfill its mission. The E-6B Airborne Command Post has a crew of 22, including pilots, communications operators, and battle staff personnel.
The E-6B is designed to be a versatile command-and-control aircraft in times of nuclear confrontation. Acting as the Airborne Command Post, it can serve as the Airborne Launch Control System with its ability to communicate launch codes directly to land-based ICBM sites. The E-6B aircraft could command ICBM launch if the launch control centers are unable to perform their missions.
The E-6B, in addition to its ability to communicate with land-based ICBM sites, can communicate with deployed U.S. Navy ballistic missile submarines in the aircraft's additional role as the Take Charge and Move Out (TACAMO) communications relay. As the TACAMO aircraft, the E-6B can deploy a 2.5-mile trailing wire antenna to give orders to submerged submarines over the vessels' very-low-frequency/low-frequency (VLF/LF) communications systems, which can receive information through the water at very slow data rates.
The E-6B aircraft also can communicate over UHF and EHF military satellite links. The E-6B fleet is based at Tinker Air Force Base, Okla.
The final node in the Nuclear Command and Control System is the Mobile Consolidated Command Center, which is a convoy of trucks that can deploy in a nuclear crisis as a road-mobile backup to the Global Operations Center or Airborne Command Post, if circumstances warrant a mobile land-based strategic command post.