Los misiles Hipers\u00f3nicos en desarrollo son de dos tipos: \u201cHypersonic Cruisse Missile\u201d y \u201cBoost Glide\u201d. Hasta hace pocos meses se debat\u00eda cual de los dos sistemas deb\u00eda considerarse prioridad en la asignaci\u00f3n de recursos, teniendo en cuenta el menor tiempo necesario para lograr su disponibilidad operativa. Para EUA, los misiles de Crucero Hipers\u00f3nicos, se presentan como la nueva prioridad.<\/p>\n
Fielding an operational scramjet-powered cruise missile has emerged as a new priority for the U.S. Defense Department\u2019s proliferating portfolio of maneuvering hypersonic weapons.<\/p>\n
Senior defense officials are putting together a program to develop an operational follow-on to DARPA\u2019s Hypersonic Air-breathing Weapon Concept (HAWC), which currently supports competing scramjet-powered missile demonstrators designed by Lockheed Martin\/Aerojet Rocketdyne and Raytheon\/Northrop Grumman Innovation Systems teams.<\/p>\n
\u201cWe are in the process of trying to figure out what [an operational program] would look like,\u201d says Mike White, assistant director for hypersonics in the office of the under secretary of defense for research and engineering.<\/p>\n
As the U.S. military rushed after 2017 to respond to Russian and Chinese hypersonic advances, air-breathing hypersonic cruise missiles fell to the bottom of the priority list. Funding for operational programs favored boost-glide technology over the seemingly less mature field of weapons powered by scramjets (supersonic combustion ramjets).<\/p>\n
But that assumption is being challenged. Along with the flight-test experience accumulated a decade ago by the Air Force Research Laboratory\u2019s (AFRL) X-51 scramjet vehicle, recent ground tests and simulations indicate scramjet technology is more advanced than previously understood. In September, the AFRL announced it had achieved thrust levels over 13,000 lb. with a Northrop-designed engine at speeds \u201cabove Mach 4\u201d in a hypersonic wind tunnel. In June, Raytheon reported the maturity of its scramjet-powered HAWC demonstrator had exceeded that of its boost-glide design.<\/p>\n
In December 2018, Michael Griffin, under secretary of defense for research and engineering, described hypersonic cruise missiles as \u201cfurther out\u201d than boost-glide weapons. But the technology advanced so quickly that another official, Air Force acquisition chief Will Roper, concluded seven months later the HAWC program would be \u201ca nearer-term not a far-term capability.\u201d<\/p>\n
\u201cWe\u2019d like to see HAWC transition to a fully operational system,\u201d says Mark Lewis, the Defense Department\u2019s director of research and engineering for modernization. \u201cIt\u2019s probably the issue that our hypersonic team is spending most time on right now.\u201d<\/p>\n
Awareness is also growing for the technical challenges still facing medium-range boost-glide missiles in the class of DARPA\u2019s Tactical Boost Glide (TBG) missile demonstrators. The Air Force\u2019s 2017 decision to launch the AGM-183A Air-launched Rapid Response Weapon (ARRW), an operational follow-on to the TBG, helped legitimize the Defense Department\u2019s revived interest in hypersonic weapons, White says.<\/p>\n
\u201cI think people underestimate the importance of this decision of the Air Force [to launch ARRW] in the hypersonic community,\u201d he says. \u201cWe\u2019ve always been kind of stuck in the [research and development] realm. The Air Force in 2017, they were the first service that said: \u2018Hey, we want hypersonic weapons.\u2019\u201d<\/p>\n
But the TBG-derived ARRW represents a particularly difficult technical challenge. The design uses a higher lift-over-drag ratio wing shape, which has never been successfully tested by the U.S. government. By contrast, the axisymmetric shape of the lower lift-over-drag glider developed for the Common Hypersonic Glide Body (C-HGB)\u2014the front-end designed for the Air Force Hypersonic Conventional Strike Weapon, the Army\u2019s Long-Range Hypersonic Weapon (LRHW) and the Navy\u2019s Intermediate-Range Conventional Prompt Strike (IRCPS)\u2014has logged several successful flight tests since the late 1970s. The winged TBG\u2019s greater maneuverability, albeit with shorter range, makes it far more challenging to design.<\/p>\n
\u201cIt\u2019s DARPA-hard, and TBG is hard,\u201d Lewis says.<\/p>\n
Ongoing studies by the Air Force\u2019s Warfighting Integration Capability are also starting to highlight the operational benefits of cruise missiles compared to medium-range boost-glide systems. A cruise missile still requires a booster rocket to accelerate to hypersonic speed, but it does not need to carry as much oxidizer and fuel as a boost-glide rocket because it remains within the atmosphere. Air-breathing cruise missiles\u2019 smaller size means a single aircraft, such as a Boeing B-52, can carry them in much greater numbers.<\/p>\n
\u201cFor a hypersonic boost-glide vehicle you can get two, maybe four, on a B-52,\u201d White says. \u201cBut you can get 15 or maybe 20 hypersonic cruise missiles [on a B-52] because the size is much smaller.So you can carry them internally in the rotary rack. There are significant advantages for the air breathers, but they offer different technical challenges.\u201d<\/p>\n
The smaller size and increased packaging advantages of air breathers would give the Air Force significant tactical advantage, Lewis adds. \u201cThe No. 1 question we should be asking is: \u2018How do we deliver lots of these things?\u2019 In my mind, one way to do that is to fit a lot of them in a weapons bay. Getting 15-20 per bomb bay is a lot, but if I\u2019m [launching them from] a single mobile launcher, I\u2019m not sure I can deliver the numbers I need. We are not interested in capability when we build two and declare it a success\u2014that doesn\u2019t do anything.\u201d<\/p>\n
The Pentagon\u2019s hypersonic weapons portfolio emerged in a blur of bureaucratic activity between 2017 and 2018. The first step was the Air Force\u2019s decision to launch the medium-range ARRW program in 2017 as the follow-on to TBG. Shortly afterward, the Air Force also decided to launch the longer-range HCSW. In November 2017, the Navy conducted a successful test of the proposed C-HGB, which prompted the Navy and the Army to support funding toward the operational prototypes of the IRCPS and LRHW\u2014for submarine and ground launch, respectively.<\/p>\n
As it stands now, the portfolio includes air-launched medium-range and long-range boost-glide systems, an intermediate-range submarine-launched missile and a long-range weapon launched from a tractor trailer. If an operational follow-on of the HAWC is approved, with Air Force and Navy concepts under consideration, new air- and surface-launched options for medium-range targets could become available.<\/p>\n
In addition to the offensive programs, the Defense Department\u2019s road map also includes development of a counter-hypersonic system\u2014starting with the Missile Defense Agency\u2019s Regional Glide-Phase Weapon System as well as multiple programs for booster development and continued funding of basic science and technology. Additional DARPA programs include the ground-launched Operational Fires, which seeks to integrate a TBG front-end on a two-stage booster stack that includes a throttled upper stage, and the Advanced Full-Range Engine, a dual-mode ramjet that could power a future hypersonic aircraft.<\/p>\n
Such a diverse yet overlapping road map has prompted criticism. In July, the chairman of the House appropriations subcommittee on defense, Rep. Peter Visclosky (D-Ind.), warned defense officials that they \u201cneed to better define the strategy for the investment in these systems.\u201d Visclosky\u2019s committee proposed cutting some funding for the Army\u2019s hypersonic program, but a joint conference committee of Congressional appropriators ultimately restored the funding and added more for other hypersonic programs.<\/p>\n
Lewis believes the development of a multitude of hypersonic missile programs is justified.<\/p>\n
\u201cToo many people think hypersonics is just one thing,\u201d Lewis says. \u201cThey think, for example, [it\u2019s just for the long-range, conventional prompt strike mission]. But no, it\u2019s a range of capabilities.<\/p>\n
\u201cEven at the tactical level it\u2019s, for lack of a better phrase, a high-low mix,\u201d Lewis adds. \u201cWe should probably have a mix of air breathers and boost-glide systems. They probably have different capabilities, different ranges and so on. We have F-16s and F-15s, and they have different roles, and that should be the same with tactical hypersonic systems as well.\u201d<\/p>\n