Lewis and T. Minimum propulsion for a given range is achieved with a reentry angle closer to 22 deg than to 45 deg because the range is not small compared with the radius of the Earth. Of course, the atmosphere of depth 10 tons per square meter exerts a substantial drag on the ballistic missile as it rises, so that a practical design does not achieve intercontinental speed within the dense atmosphere; this is accomplished by limiting the thrust and hence the acceleration of the missile.
This also limits the "dynamic pressure" and the skin heating on ascent. But too low an acceleration implies excessive "gravity loss", since it is only the excess of vertical component of thrust over the force of gravity that actually results in acceleration of the missile. Even so, a typical large liquid-fueled missile may have a thrust of 1. The kinetic energy of the RV, which is a good fraction of the total energy of the propellant of the entire ICBM, must be dissipated on reentry.
ICBM warheads must be protected by a reentry vehicle RV against the heat and deceleration of the atmosphere. A typical peak deceleration is on the order of 60 g. However, only a small fraction of this energy need be absorbed by the material of the RV-- the rest being carried off by the wake of the reentry.
Although initial ICBM RVs used a heat-sink approach, this was soon superseded by a much lighter protection system that uses ablative material that gradually sacrifices its heated surface layer and erodes in a controlled fashion on reentry.
The RV shape approximates a sharp cone with a small nose radius. It might need to be removed via horizontal tunnel and erected before launch, or it might be stored vertically, and launched in that position after opening a protective door. The missile can 3 See footnote re MIT charts. The first-stage booster, when fuel is exhausted, is then separated by explosive bolts, as are eventually the second stage and the third stage, so that the warhead travels on its own to the reentry point.
In order not to prejudice accuracy because of the uncertain orientation of the warhead on reentry, the warhead can be fitted with monopropellant rocket jets to force it to pitch over to assume the appropriate orientation for reentering along its longitudinal axis.
It is then often "spun-up" by additional jets, in order to maintain that orientation for the remaining 20 minutes or so of flight. Alternatively, the alignment with velocity might be delayed until the beginning of reentry, and the RV spun up at that time. The United States and other countries with multiple warheads or "penetration aids" often use a "bus" more formally a PBV, for Post-Boost deployment Vehicle which carries the guidance unit for the missile and which has the job of accelerating each of the warheads or decoys or penetration aids sequentially to the proper velocity so that it will fall to its particular target.
Bussing may take five to ten minutes in order to distribute the warheads and appropriate decoys to accompany them. A ballistic missile defense system could interfere with the ICBM either before launch, or in boost phase during the operation of the first, second, or third-stage engines during the bus activity, or it could counter a warhead either above the atmosphere or on reentry, until it achieved its detonation altitude.
The United States tries to learn where all potentially threatening missiles are based. It could destroy them preemptively in the case of hostilities. However, some ICBMs are mobile, and if they are out of garrison and not otherwise observed, they are not vulnerable to such attack. Even if the location of the mobile launcher were known at the time of launch of ICBM, if it were in motion it would be safe from destruction by the nuclear warhead on a ballistic missile.
The United States maintains in high-Earth orbit a set of Defense Support Program satellites DSP which for decades have reported in real time every ballistic missile launch of significant size. It was revealed officially that the U. With a element linear infrared sensor that rotates once every ten seconds, DSP can determine the launch point with an accuracy on the order of a kilometer.
Since a typical ICBM burns for about s, multiple observations are possible and pretty good trajectory information can be obtained in this way. In the early seconds of boost, an ICBM is vulnerable to a command-detonated mine adjacent to the site or to a rocket-propelled grenade. Even short-burning Scuds could be destroyed by small homing interceptors launched by radio from as much as 50 km distance from the launch site.
Normal ICBMs would be vulnerable in boost phase to ground-based interceptors GBI or sea-based interceptors from anywhere within a region of about km of the launch site. Such an interceptor would be launched by command on the basis of DSP data, without there ever having been a radar detection of the ICBM. Fitted with a sensor capable of detecting the missile flame, it could direct its limited field of view in the direction commanded according to the data from DSP, and accelerate toward a predicted intercept point.
The prediction would need continued refinement, by observation from the interceptor of the current position of the ICBM booster. But the interceptor would have to be launched from a site sufficiently close and have sufficiently high performance in order to reach the missile while it was still burning.
Furthermore, the interceptor could not simply home on the flame but in the late stages of intercept would need to look "ahead" of the flame, in order to strike the solid missile and not sail harmlessly through the tenuous flame.
This could be done either by blind reckoning because of the known shape of the flame, or by actual detection of the solid missile with a proper design of the interceptor seeker. Specifically, it should be possible to use an interceptor of the same gross launch weight as the GBI of the NMD program about 14 tons, with A simple calculation shows that the sea-based interceptor could be deployed as much as km downrange from the launch site and still be able to catch the ICBM while it is still burning.
Because the interceptor must rise vertically in the lower atmosphere, it probably moves only about km toward its target while it is burning, and then in the remaining seconds moves some km. So in the burn time of the ICBM, the interceptor can reach out a total of km from its launch site.
The interceptor could be deployed km east or west of the ICBM trajectory, about km downrange. So there is plenty of room for U. The ships need have no missile-tracking radars. Such a sea-based boost-phase intercept system is not compliant with the ABM Treaty; but Russia and the three other parties to the Treaty might well agree to a specific exception, especially if this were combined with progress on lower missile levels in Russia and the United States. My own judgment is that the ABM treaty plays a valuable role in U.
Alternatively, Russia and the U. It is a chemical oxygen-iodine laser mounted in a Boeing aircraft that has the task of focussing through the turbulent atmosphere further disturbed by the passage of the laser beam itself in order to weaken or melt the structure on a missile during boost phase.
The ABL laser operates at 1. The ABL will operate at an altitude of 13 km-- most of the time above the clouds and, assuming that the laser works as planned and that laser beam propagation is as assumed, Forden assesses the range for "decisive engagement" from km for the al-Husayn to km for the North Korean Nodong km-range missile. This assumes that a substantial arc of the missile skin must be softened so that the missile collapses. For a less catastrophic criterion, Forden estimates the range limit from the missile launch point to be km, and km or more for an ICBM assuming the ABL downrange from the ICBM launch and so can attack at closer range.
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Learn more and compare subscriptions content expands above. Full Terms and Conditions apply to all Subscriptions. Or, if you are already a subscriber Sign in. It's just like throwing a ball; the faster you throw it at a given angle, the farther it will travel," Wright said, adding that the burn-out velocity -- or speed an ICBM reaches when it shuts off its engines in space -- isn't known, among other variables. Given the correct angle of launch and some modifications, he thinks North Korean ICBMs might be capable of reaching between 3 and 4.
The Hwasong missile test reportedly flew some 2, miles into the sky, for a total flight time of about 47 minutes. It also lofted a reentry vehicle -- a device that protects one or more warheads from burning up when plowing through Earth's atmosphere -- but it's uncertain if the dummy vehicle accounted for the weight of an actual warhead. The lighter a payload, the faster, higher, and farther a missile can go.
There's also evidence that the reentry vehicle failed and broke into pieces on its way back down. It rotates underneath the missile," Wright said. This not only requires over- or under-shooting a missile, but also makes the physics of targeting far more complex.
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