1. ASCMD,
2.2 CRUISE MISSILE THREATS
The weapons referred to in this study under the generic title of cruise mis- siles can be ground- or air-launched. Ground-launched cruise missiles are gen- erally multistage missiles, with the first stage being a rocket. At some predeter- mined altitude, the rocket booster is discarded and wings or canards are deployed to provide aerodynamic lift. Simultaneously, a motor is activated to provide propulsion. Air-launched cruise missiles are carried to launch altitude by an aircraft. In this case, too, tail fins, wings, and/or canards may be deployed to provide trajectory control surfaces.
A cruise missile may be accelerated to cruise speed by a rocket booster and might be designed to employ rocket thrust for a high-speed terminal attack. For most of its flight, a cruise missile is propelled by air-breathing turbojet or ramjet engines and relies on aerodynamic lift to carry its weight and maintain altitude.
Cruise missiles remain within the atmosphere and under power during their cruise phase. Hence, their range and general flight characteristics are similar to those of an airplane.
Payloads carried by cruise missiles may include large, unitary, high-explo- sive warheads, submunitions, runway penetrators, or weapons of mass destruc- tion (nuclear, chemical, or biological). In the past, successful cruise missile attacks succeeded in sinking warships or causing severe, mission-limiting dam- age to them. Cruise missiles that are configured to carry and dispense submuni- tions constitute a particularly severe threat to troops in the field and to nonar- mored vehicles such as trucks. When the submunitions that are dispensed by a cruise missile are high-performance, self-propelled devices that are equipped with terminal engagement sensors, they can even constitute a significant threat to armored vehicles. Thus, cruise missiles are a significant threat both to plat- forms at sea and to forces ashore.
Cruise missiles can be classified according to the altitude and velocity of their cruise segment, as well as their launch-to-target range. Cruise altitudes fall into three categories: high altitude, low altitude, and surface skimming. High- altitude cruise extends the range by improving fuel-use efficiency, but it makes the cruise missile more likely to be detected. At lower altitudes, such missiles can take advantage of the decreased line-of-sight horizon for trackers in the vicinity of the target and of terrain features that mask the approach path. Surface skimmers, which are practical only over the ocean or extremely flat and desolate terrain, descend to within a few meters of the surface and may go undetected until very close to the target. Cruise missiles may cruise at subsonic, supersonic, or hypersonic velocity. Because lift-to-drag ratios decrease with increasing speed above the maximum endurance speed, a range penalty is paid for supersonic or hypersonic flight. However, since the time of flight is inversely proportional to speed, the intercept problem becomes more difficult as the speed of the target missile is increased. Of course, a cruise missile’s flight path may be broken into
PRESENT AND PROJECTED THEATER MISSILE THREATS 27 segments with different altitude-speed characteristics to maximize the probabili- ty of mission success.
A cruise missile is not constrained to follow a single path to its target and can, in fact, follow a devious route to avoid obstacles and terrain, to hide below the tracker’s line of sight, and to deceive defenders. While the thrust-to-weight ratio need not be large to maintain cruising flight, a cruise missile is easily designed to pull significant g load factors, allowing it to change direction quick- ly. Hence, it can jink, S-turn, and feint on the way to its target. It can approach its target a few meters above the surface or pull up and dive on its target at a high angle. To limit the ability of defending forces to maintain its trajectory in track, a given cruise missile can be programmed to choose apparently random ap- proach maneuvers.
Unlike a ballistic missile engagement, a successful intercept of a cruise missile before it approaches its target virtually assures that the cruise missile will fail to accomplish its mission. Furthermore, less damage may be necessary to defeat a cruise missile than to defeat a ballistic missile. Such a missile need not always be totally destroyed—degraded performance in the form of diminished accuracy for the guidance sensors or a partial loss of aerodynamic control authority may be enough to cause it to miss its intended target.
Cruise missiles can attack both stationary and mobile targets. If a movable target is stationary for an extended period of time, the missile may be pro- grammed to fly to the global positioning system (GPS) coordinate where the target is known to be located. Worldwide open access to the GPS and GLO- NASS (the Russian equivalent of GPS) networks simplifies the navigation and guidance systems for cruise missiles designed to attack fixed targets. Ten-meter navigational accuracy to any latitude-longitude pair is readily obtainable now that GPS selective availability (SA) has been turned off. One-hundred-meter accuracy is available with SA operating. In a major conflict, the United States might take measures to restrict the local availability of GPS to its adversaries.
However, there is no precedent to indicate that during low-intensity operations, the operation of GPS will be restricted.
Cruise missile attacks on moving targets are multistep processes. First, the missile must be guided to fly to a point where, based on a target track developed by an external sensor, there is reason to expect that the terminal sensor on the cruise missile will be able to acquire the intended target. If the intended target is within the acquisition basket of the missile’s seeker, the seeker can acquire the target and the missile can guide itself on a collision course to the target. A wide variety of seekers have been developed to support the terminal engagement phase of cruise missile attacks. If the cruise missile does not have a data link back to an individual who can evaluate the output of the cruise missile’s sensor and control the terminal engagement, it must be guided to the target autonomously.
Autonomous guidance sensors are subject to jamming, deception, and de- coys. ECMs against missile guidance and navigation systems have been em-
ployed since World War II, as have electronic counter-countermeasure (ECCM) techniques that are designed to negate the effects of defensive countermeasures.
The ECM-ECCM battle is open-ended and will continue indefinitely into the future. The sensors on the newest missiles that are entering into the operational inventories of potential adversaries appear to have extremely robust ECCM ca- pabilities against current ECM techniques. Advances in techniques related to automatic target recognition (ATR) tend to make seekers robust against distrac- tion decoys. On the other hand, the fidelity with which modern decoys or repeat- ers can replicate the signature of the target of a cruise missile is impressive.
Clearly, the Navy must continue an aggressive ECM program so that as new advances in seeker technology are fielded, new countermeasures will be avail- able to negate them.
Aside from the threat that improved cruise missile seekers pose to Navy ECM techniques, there are many trends in cruise missile design that the commit- tee found to be a source of concern, including the following:
• Greater missile speeds, which limits the engagement time;
• Lower RCSs, which limits the range within which a missile may be de- tected once it has crossed the horizon of defensive radars;
• High maneuverability, which limits the ability of a defensive system to track and engage the missiles;
• Trajectories that make maximum use of terrain obscuration and clutter masking in littoral situations; and
• Sea-skimming flight paths, which keep incoming missiles below the ho- rizon of defensive radars for as long as possible.
Worldwide, cruise missile designs abound. Many of these designs already stress the capabilities of U.S. defensive systems. Table 2.1 lists some of the worst-case parameters of currently operational missiles and the committee’s pro- jections for the parameters that may be encountered in the next 15 to 20 years, based on its assessment of trends in technology.
The first four attributes listed in Table 2.1 are intended to limit the options for engagement by defensive missiles. The fifth and sixth attributes attempt to defeat defensive ECM techniques. The committee’s estimates for 2020 are ex- trapolated from current trends in missile technology. The sixth could leapfrog future ECM efforts. Although some members of the committee doubt that accel- erations of 20+ g will be feasible, all of them concur that future cruise missiles will possess greater agility than currently deployed threat missiles. As missiles become more agile, the data rates of defensive systems must be increased and the track association algorithms of defensive sensors will require major modifi- cations. Even if the RCS values of threat missiles do not decrease, their greater agility and speed will challenge the tracking algorithms and data rates of existing defensive systems.
PRESENT AND PROJECTED THEATER MISSILE THREATS 29
Under optimum conditions, these systems employ a defensive shoot-look- shoot (SLS) doctrine to conserve interceptors. If the defensive time line is com- pressed by some combination of changes in missile RCS altitude, ECCM, speed, and maneuverability, the capability of the defensive system will be reduced suc- cessively from shoot-look-shoot, to shoot-shoot, to shoot and, in the worst case, to no shot possible. The effects of RCS and Mach number are illustrated con- ceptually in Figure 2.1.
The figure shows that for a sea-skimming incoming cruise missile attacking a defended ship equipped with only a surface-based sensor (or for such a missile at any given altitude), there will be a large area in the RCS-missile velocity plane where it is not possible to launch a defensive round. If the altitude of the attacking cruise missile is low enough and if its velocity is high enough, there may be no way to shoot the missile, even if it has a large RCS. In other areas of the RCS-missile velocity plane, defensive systems have an opportunity to launch either one or two defensive missiles or may even be unable to launch a single defensive missile.
Most current cruise missile threats do not lie in the no-shot region. Howev- er, unless elevated sensors are used, or unless significant improvements in defen- sive capabilities are achieved, missiles with the attributes in the third column of Table 2.1 will generally fall into the no-shot region of Figure 2.1. In such a situation, the defense will have to depend entirely on the Navy’s ECM capabili- ties to defeat the terminal guidance system.
If elevated radars are used in lieu of surface-based radars, the radar horizon will increase significantly, somewhat negating the advantages of high speed. Of course, elevating the radar will not offset a reduction in the RCS value of the threat missile. The RCS value of a missile varies with both frequency and missile orientation. Thus, low-RCS missiles can only be defeated by using radars that operate at lower radar frequencies and/or by using some form of TABLE 2.1 Attributes of Current and Projected (2020) Cruise Missile Threats
Attribute Current Estimated for 2020
Agility 6 to 8 g maneuvers 10 to 20+ g maneuvers
Nose-on radar cross –10 to –30 dBsm –20 to –40 dBsm
section
Altitude (sea skimmers) 2 to 5 meters 2 to 5 meters
Terminal speed Sub- to supersonic Up to hypersonic
Electronic countermeasure Moderate Improved
robustness
Guidance Global positioning system GPS and target recognition (GPS) and radar/infrared
xx
multistatic operation that allows the missile to be viewed from orientations where its RCS value has significant peaks.
2.3 THEATER BALLISTIC MISSILE THREATS