Twenty years after entering service, the Raytheon AIM-120 AMRAAM is still one of the most feared weapons in air warfare, yet it may also be among the most endangered.
China and Russia are developing new air-to-air missiles with possibly longer ranges, adding to the overall threat posed since 2010 by the appearance of the Sukhoi T-50 and Chengdu J-20 prototype stealth fighters.
Moreover, a new generation of surface-to-air missile systems are extending their reach, making a strike by fighters armed with anti-radiation missiles - the 27-year-old Raytheon AGM-88 HARM - an ever more perilous mission for the air crews.
Twenty years ago the Raytheon AIM-120 AMRAAM entered service. It's still one of the most feared weapons in air warfare, and perhaps the most endangered
The US Air Force has already decided that the AIM-120 and the AGM-88 must be replaced with a new weapon - now called the next-generation missile (NGM). "Doing nothing is not a viable option," according to Air Combat Command, which submitted written responses to questions by Flight International. "The operational risks would be unacceptable."
But the cost of the new acquisition programme will not come cheap. The AIM-120 alone has cost US taxpayers more than $20.4 billion. In 2008, the Charles Rivers Associates consultancy estimated that the cost to develop and produce a next-generation air-to-air missile would be at least $15 billion.
Air-to-air combat also may seem to be an unlikely area to attract investment funding. In the first nine months of this year, the USAF released 3,836 weapons on targets in Afghanistan. None of them were AIM-120s or AGM-88s. Raytheon has delivered more than 16,000 AIM-120s to the USAF and US Navy since 1991, but fewer than a dozen have been fired in anger in more than two decades.
The Department of Defense, meanwhile, is facing budget cuts of nearly $1 trillion over the next decade. It may not be enough to justify investing in new capabilities on their merits alone. To launch a new programme, it may be necessary to take money away from other accounts.
Also not helping the USAF's case for the NGM is the absence of any public support from the USN. In the late-1970s the two services partnered to develop the "launch and leave" missile that became the AIM-120, but have chosen to take separate paths on a replacement.
While the USAF pursues a single new weapon to replace the AIM-120 and AGM-88, the USN has devoted its resources to developing the Alliant Techsystems (ATK) AGM-88E AARGM for the air-to-ground mission and buying more AIM-120s for the air-to-air mission.
The USAF also is constrained from making its best case for the NGM in public. Most capabilities of air-to-air missiles, including their precise speed and range, are considered secret. USAF officials declined requests for interviews for this article, but the ACC, which is developing the requirements for the NGM, agreed to answer questions in writing.
MEET THE ADVANCES
The ACC did not deny the near-absence of air combat over the past two decades, but the officials argued this is irrelevant.
"Lack of recent [air-to-air] engagements does not equate to a lack of an advanced [air-to-air] threat," the ACC said. "Continued advances in threat aircraft, sensors, jamming, and Air Defense technologies require advances in US weapons. For the foreseeable future, the US must continue to meet those advances in order to assure air superiority."
Two of the "advances" the USAF may meet some day are the Chinese PL-21 and the Russian RVV-BD air-to-air missiles, said Douglas Barrie, senior fellow for military aerospace at the International Institute for Strategic Studies.
Both countries do not trail far behind the radar-guided capability of the AIM-120 missile. Russia has fielded the RVV-AE, or R-77 missile, and China has kept pace with the PL-12. With the emergence of the possibly ramjet powered PL-21 and rocket-powered RVV-BD missiles, China and Russia appear poised to meet or even surpass the range and performance of the AIM-120D.
"The US was way, way ahead in fighter design," said Rebecca Grant, director of the Mitchell Institute for Airpower Studies, the independent research organisation founded by the US's Air Force Association.
"But the gap in missile design was never as big, There are good, non-US missile makers out there."
To be fair, the USAF has not been idle either. Even as it developed the AIM-120D, the USAF has been funding technology development projects for a next-generation missile.
It is clear the USAF wants a weapon with an even longer range than the AIM-120. At the same time, the NGM must fit inside the internal weapons bay of the F-22 and Lockheed F-35. Since both weapons bays were sized to support the AIM-120, the NGM has a difficult design challenge: more range without more payload volume.
This requirement may be the key driver for a series of demonstration contracts awarded by the Air Force Research Laboratory since 2008. Their goal is to combine or scale down other components inside an air-to-air missile, which possibly allows the NGM designers to add space for more fuel to achieve the extra range.
The seeker integrated target endgame (SITES) contract combines the missile's radar and the fuze into a single device. Additionally, if the SITES radar is transformed into a conformal array, Barrie suggests, more internal fuel volume could be added.
The multi-role responsive ordnance kill mechanism (MR ROKM) is seeking to invent a directional warhead.
Instead of scattering shrapnel in all directions, this warhead would channel the damage in a single direction.
This technology also may create more room for fuel by allowing the missile designer to install a smaller - but more lethal - warhead. Finally, the AFRL also has awarded the dual-role air-dominance missile technology (DRADM-T) contract, which is developing a new propulsion system.
Propulsion is one of the critical questions that the USAF must decide upon. The NGM may be the first air-to-air missile in the USAF inventory to be partly ramjet powered - like the MBDA Meteor.
Contracts awarded by the Defense Advanced Research Projects Agency (DARPA) offers the key evidence. The triple-target terminator (T3) programme is developing a ramjet-powered missile, and the technology is designed to transfer directly into the NGM programme, according to the ACC.
PEAK ENERGY STATE
Compared with a solid rocket booster, a ramjet offers some key advantages, Barrie said. The rocket motor has a higher overall speed, but its energy drops off rapidly near the end of its range. The ramjet, however, may be slightly slower, but it maintains its peak energy state for a longer period, Barrie said.
With Raytheon already established in the air-to-air missile business, the USAF invested heavily to strengthen Boeing as a challenger. Boeing received all three AFRL contracts - SITES, MR ROKM and DRADM-T. DARPA has also handed Boeing and Raytheon separate demonstration contracts to launch the T3 programme.
Meanwhile, a Lockheed Martin/Northrop Grumman team also plans to compete for the contract, having invested internal research and development funding to keep pace with Boeing and Raytheon. The ACC also confirmed that MBDA would be allowed to compete as a prime contractor.
But first the USAF has to clarify the acquisition plan for the NGM programme. Two years ago, USAF budget-justification documents submitted to Congress laid out a concise schedule for the programme, which was then named the joint dual-role air dominance missile. A required analysis of alternatives would begin next September.
The first technology-development contracts would be awarded in 2014, which would allow the first NGM missiles to enter operational service around 2020.
But something has happened to muddle the USAF's planning for NGM. Recently, when the ACC was asked to provide an up-to-date acquisition schedule for the new missile, the command tersely responded: "Undetermined at this time."