JDAM Joint Direct Attack Munition is an outstanding representative of the U.S. military’s precision guided air munitions in the past two decades. It has fully demonstrated the charm of air-to-ground precision strike tactics in many actual combats such as the Iraq War. However, with the improvement of the performance of air defense weapon systems and the extension and expansion of air defense combat networks, the range of JDAM has gradually become a weak point, and air defense weapons have posed an increasing threat to aircraft that drop JDAM. In order to deal with new threats, the best way is undoubtedly to increase the effective range of JDAM. For this reason, the research and development unit has launched the "Extended Range Joint Direct Attack Munition" (JDAM-ER) program, which increases the range of JDAM by adding a new glide range extension component. However, this improvement is limited after all. In order to fundamentally increase the range of JDAM, it can only be "powered". This is the new generation of "powered joint direct attack munitions", the English name of which is P-JDAM. In October 2023, Boeing and Kratos’s Technical Direction Company (TDI) signed a memorandum of understanding (MoU), the main content of which involves installing the TDI-J85 small turbojet engine of the Technical Direction Company on the 227 kg (500 lb) "Joint Direct Attack Munition" (JDAM) and converting it into a "Powered Joint Direct Attack Munition" (P-JDAM).
From JDAM, JDAM-ER to P-JDAM
JDAM precision-guided bombs (Joint Direct Attack Munition, referred to as JDAM), JDAM guided bombs are made by adding corresponding guidance and control devices to the current aerial bombs. Because of the use of autonomous global satellite positioning/inertial navigation combined guidance, the aircraft has day and night, all-weather, outside the defense zone, and launch and forget, multi-target attack capabilities.
JDAM was jointly developed by Boeing for the US Navy and the US Air Force. It transforms the traditional uncontrolled aerial bomb into a controllable precision-guided weapon that can be used in adverse weather conditions.
The guidance function of the ammunition is provided by the bomb tail control attachment and the global positioning system or inertial navigation system, which is compatible with the fire control system of various military aircraft such as the US military’s B-2 Spirit stealth strategic bomber. IDAM has high strike accuracy on the one hand, and is inexpensive on the other. At that time, the price was only about 20,000 US dollars per bomb, which greatly reduced the threshold for the use of precision-guided munitions.
In April 1994, the bomb began to be produced in small batches. In June 1995, the US Air Force conducted an air drop test with the B-2A stealth bomber for the first time. In July 1995, the US Navy conducted an air drop test with the FA-18 for the first time. In January 1996, the US Air Force conducted an air drop test with the B-1B and at the end of the year, it conducted an air drop test with the F-16. The overall effect of the test met the predetermined requirements. It passed the test between 1998 and 1999. With the assistance of GPS, the "circular error" (US military test standard) of JDAM can reach 13 meters. In the Kosovo War in 1999, this ammunition was used in actual combat for the first time. B-2 bombers taking off from the United States dropped more than 600 JDAMs during the war. In the 2003 exercise, a B-2 bomber could drop 80 500-pound (230-kilogram) JDAMs at a time, showing a strong "precision saturation attack" combat capability. JDAM was also put into use in the Afghanistan War in 2001 and the Iraq War in 2003.
JDAM-ER, the full name is the winged extended-range joint direct attack explosive. Developed by Boeing, on the basis of aerial bombs, by adding guidance control components and extended-range components, it seeks to achieve the purpose of all-weather and longer-range precision guidance at a low cost-effectiveness ratio.
In order to get closer to actual combat and improve bomb performance, the designer combined the interests pursued by the navy and the air force. By strengthening the use of GPS means and combining the guidance system, the free-falling bomb has been transformed into a precision-guided bomb. JDAM-ER has a conventional inertial autopilot, satellite GPS and laser gyroscope, which can solve the shortcomings of the "Paveway" guided bomb GBU-15EOGB bomb by relying on positioning through non-direct observation means-the former uses laser semi-active guidance, and the latter uses electro-optical contrast guidance, but both rely on good weather conditions. If it encounters rainy and foggy weather, the advantages of these two bombs are gone, and they even become "blind". Coupled with the simple and direct tail fin installation, the flight distance of the bomb and the steering wheel control accuracy can be greatly improved. Inertial units, GPS, laser gyroscopes and tail fins make JDAM-ER better than other guided bombs.
JDAM-ER’s guidance system acts as the "brain" to escort the bomb’s precision strikes. The "brain" is divided into three parts. The "sensory center" of the "brain" is the inertial unit HG1700 with a Honeywell laser gyroscope! The inertial unit is responsible for tracking the bomb’s movement speed and travel distance in space, and providing the system with information related to calculating exchange rate deviations. The "visual center" of the "brain" is the standard military GPS navigator Rockwell GEM. This is the device responsible for inputting target coordinates and the current coordinates of the bomb. The "language center" of the "brain" is the controller of all GCU microprocessors. Its job is to calculate the current position of the bomb based on the data from the inertial unit and the navigator, and calculate the flight trajectory based on the altitude and speed. The coordinated operation of each central system makes the control system of JDAM-ER digital and multi-terminal.
At the same time, when designing JDAM-ER, American engineers continuously made innovative improvements to the attack process. Designers installed the communication antenna at the tail of JDAM-ER. This installation method can shield the radiation and signals emitted by the ground air defense system, and at the same time can guarantee the normal operation of the "brain" to the greatest extent possible, and ensure the stable attack of JDAM-ER. The original JDAM was designed to achieve the purpose of precision guided bomb flight. But the JDAM series is more than that. Boeing has expanded and developed JDAM-ER because it wants to increase the flight range of guided bombs. JDAM-ER adds two deployable wings and spring devices for deploying wings to the bottom of the kit on the basis of the plastic sleeve that the JDAM series already has.
The normal operation of the "brain" ensures the stable attack of JDAM-ER. The original JDAM was designed to achieve the purpose of precision guided bomb flight. But the JDAM series is more than that. Boeing has expanded and developed JDAM-ER because it wants to increase the flight range of guided bombs. JDAM-ER has two deployable wings and spring devices for deploying wings at the bottom of the kit based on the plastic sleeve that the JDAM series already has.
After the bomb is dropped, JDAM-ER flips in the air, and the spring device extends the wings. In this way, the range of bombs equipped with JDAM-ER will be greater. This upgraded device makes the bomb three times faster than ordinary bombs. When dropped at an altitude of 14,000 meters, the bomb can fly up to 75-80 kilometers.
Facts have also proved that JDAM-ER has also emerged in several recent local wars in the Russian-Ukrainian conflict. In recent months, the United States has shipped these precision-guided bombs to Ukraine. Reports show that Ukraine has previously used four JDAM-ERs to attack a Russian military warehouse in Bakhmut in eastern Ukraine. The bombing caused huge losses to the Russian army.
However, due to the continuous development of modern air defense weapon system technology, the 80-kilometer flight distance of JDAM-ER guided bombs has become unsafe for carrier aircraft, which means that the carrier aircraft needs to risk dropping bombs within the range of the enemy’s air defense system. In order to solve this problem, it is urgent to further increase the range of JDAM-ER. Then the solution can only be to install an engine and use power to greatly increase the range.
Components of the ammunition
The "Powered Joint Direct Attack Munition" is mainly composed of four key components: a power kit containing the TDI-J85 engine and additional fuel tanks, a gliding wing kit that is the same as the "Extended Range Joint Direct Attack Munition" (JDAM-ER), a guidance kit on the traditional JDAM, and a 227 kg MK82 bomb body.
The power system of the "Powered Joint Direct Attack Munition" is a separate kit and cannot be directly combined with the ordinary "Joint Direct Attack Munition" JDAM, but other than that, the guidance and other components of the two ammunition are the same. The TDI-J85 micro-turbojet engine in the power kit has a thrust of 0.89 kilonewtons. When combined with the gliding wing kit, the ammunition can reach a range of up to 300 nautical miles (about 550 kilometers), which makes P-JDAM a "standoff precision strike weapon" in the full sense. Since the flight time of P-JDA M is much longer than that of ordinary JDAM, the demand for power for navigation, guidance, data link and other mission avionics is also greater. The generator equipped with the TDI-J85 engine can generate a maximum of 1.5 kilowatts of AC power, which can meet the long-term operation requirements of the electronic equipment on the missile.
Boeing has also recently signed a memorandum of understanding (MOU) with Ferra Engineering of Australia to produce the gliding bomb wings of JDA M-ER, indicating that the research and development and production preparations for P-IDAM are proceeding in an orderly manner. In addition, Boeing has completed a round of wind tunnel testing of P-JDA M in August, and used the collected data to create a "digital twin" of the missile, which will be used to support the further development and improvement of the missile in a virtual environment.
Capability characteristics of ammunition
Like the existing JDAM, P-JDAM also uses the standardized MK80 series bomb shape as its warhead, which provides significant flexibility for the further design of the missile. The move to install a power system for JDAM is one of the latest moves to create long-range munitions for ground and sea attacks. For example, the U.S. Air Force is testing an active radar/infrared dual-mode guidance system installed on the head of JDAM for the "QuickSink" project, which is the maritime strike version of JDAM. In response, Boeing said that the power kit can provide P-JDAM with optional modular strong functions to further improve performance using the open system architecture interface. JDAM in the "QuickSink" project can also integrate the power kit to become an anti-ship weapon with a range of 300 nautical miles (about 550 kilometers). In addition, P-JDAM also has the potential to be converted into an air-launched decoy. In this configuration, the warhead of the bomb will be replaced by electronic equipment and additional fuel tanks, and its range can reach at least 700 nautical miles (about 1,300 kilometers).
There is no news on whether the P-JDAM concept can be applied to 454 kg (1,000 lb) or 907 kg (2,000 lb) bomb bodies. If applied to such larger bomb bodies, a more powerful engine will be required, and the bomb will also be larger, which may be difficult to mount in the internal bomb bay of a stealth fighter. In addition, since the P-JDAM is self-powered, a ground-launched P-JDAM similar to the "Ground-Launched Small Diameter Bomb" (GL-SDB) may appear in the future.
Boeing positions the P-JDAM as a cruise missile-like weapon that is flexible and low-cost. The price of the tail kit of the guidance system of an ordinary JDAM is between 20,000 and 30,000 US dollars. Although TDI refused to disclose the cost of the TDI-J85 engine, it said that its engine research and development focused on the use of low-cost technology. By comparison, the F107 small turbofan engine used in the AGM-158B missile costs $190,000. The F107 engine has a thrust of "thousands of Newtons" and a more complex structure. Therefore, the price of the TDI-J85 engine may be only a fraction of that of the F107. The cost of a P-JDAM without other additional guidance systems may be only a few hundred thousand dollars, while the cost of a P-JDAM version equipped with a multi-mode seeker in the "Fast Sinking" project may be hundreds of thousands of dollars.
A few opinions
As an improved ammunition based on JDA M, P-JDAM provides multiple potential advantages.
The first is the flexibility of use. The bomb provides a kind of standoff ammunition for front-line troops. It can be easily reset for different targets to adapt to different mission environments, and even become an air-launched decoy when necessary. Compared with larger missiles such as AGM-158,
227 kg bombs are smaller in size, so P-JDAM can be carried in the internal weapon bay of stealth fighters such as F-35, or can carry more bombs when installed on the outside of fighters.
Secondly, P-JDAM has a low cost, which can achieve low-cost strikes on medium and low-value long-range targets in great power wars, thereby freeing up high-value missiles such as AGM-158 to attack higher-value targets. The US military has recently focused on low-cost strikes. The Mitchell Institute for Aerospace Studies once issued a report stating that the US military needs an ammunition with a range of about 250 nautical miles (about 460 kilometers) and a cost of hundreds of thousands of dollars to carry out the task of striking a large number of targets (refer to the previous article "Affordable Precision Strike" in this public account). P-JDAM meets the above requirements in terms of range and cost, but the missile is not a stealth shape, which may limit its penetration capability.
Third, the commonality of P-JDAM and ordinary JDAM components can also help countries equipped with JDAM to easily increase their inventory of standoff ammunition. Boeing said that there are currently about 35 countries equipped with JDAM. P-JDAM can create potential cooperation opportunities for these overseas allies. In addition, for some countries that cannot purchase AGM-158 series missiles, P-JDAM can meet their needs for long-range strikes. Q
