Phillip Pournelle
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According to AP News: Russia Claims Superiority in Hypersonics
By Phillip E. Pournelle
The incoming and outgoing Chief of the US Indo-Pacific Command (INDOPACOM) have identified hypersonic weapons as a priority, as discussed in the incoming Admiral’s testimony during his confirmation hearing. Additionally, a US Navy-commissioned study identified hypersonic weapons as a requirement of an effective Future Fleet Architecture. Why are hypersonics suddenly getting so much attention from Navy brass?
Here are the trends and developments that seem to be compelling attention to hypersonics: It appears that we are in an offense dominated environment, a critical feature of which is the proliferation of long range missiles (either independently or as proxies of great powers such as China and Russia). Questions about the adherence of Russia to some arms control agreements and the utility of the agreements in light of the competition with China recently drove the United States to initiate departure from the INF treaty. There are also questions about the effectiveness of defensive weapons in combat and the inventory that we will have available. These trends raise the possibility that the costs associated with remaining on the defense could force us out of power projection, or even great-power competition. Meantime, Putin demonstrated a hypersonic weapon over the Christmas break while the Chinese have brandished their own weapon in response to American and British ships operating in the South China Sea. The development of hypersonic weapons by both China and Russia potentially signal an arms race.
Judging by leadership rhetoric, the US Navy is attracted to hypersonics as a way of redressing unfavorable trends or at least maintaining parity. We might therefore ask: What are their strengths and weaknesses? and, How do they compare with alternative options, such as B-21s carrying short-range weapons, conventional theater range weapons (now that the US seems to be leaving INF), and maybe even conventional ICBMs.
Trends in air defenses
Modern air defense systems have greatly improved over the years and those deployed by Russia and China have been designed to engage the weapon of choice employed by the United States, the Tomahawk cruise missile. Similarly, the US has deployed it own air and missile defense systems but the cost of those defensive weapons have been prohibitively high when compared to the weapons they are intended to defend against.
These advanced air defense systems are also proliferating either by export by the great powers or by domestic development (possibly supported by a great power).
China has made its own claims that it can engage US stealth platforms with advanced air defense systems, the effectiveness of which is disputed by both those who operate US stealth aircraft and those who advocate more conventional methods of eliminating those threats.
The development of advanced air defense technologies now includes the use of Directed Energy Weapons such as High Energy Lasers (HEL) and advanced High Power Microwave (HPM) weapons to defeat missile raids. While recent demonstrations show current HEL and HPM weapons are effective against lightweight drones and perhaps swarms of them, it will take much more energy than currently available to cause sufficient damage to cruise and ballistic missiles than can currently be deployed.
In the competition between missiles and directed energy weapons a critical factor is the dwell time, the amount of time the weapon must be direct its energy onto the missile to have the desired effect. A hypersonic weapon traveling more than five times the speed of sound would absorb less than a fifth of the energy directed by a laser in the same amount of time than a subsonic cruise missile would.
Thus, the benefits of hypersonic weapons could include both survivability and timeliness due to the nature of the speeds they travel.
Types of weapons
There are three main types of hypersonic weapons: ballistic missiles, boost glide missiles, and cruise missiles employing scramjet engines. Part of the ongoing debate include some related high-speed weapons. There are weapons which employ a sub-sonic cruise missile body which then launches a sprint vehicle in the terminal phase. Supersonic ramjet missiles travel at speeds of Mach 3 to 5 and have been in use for over 90 years and while slower have greater range per pound (ISP) than Scramjets (which in turn are more efficient than the solid rocket motors of ballistic or boost glide missiles).
While ICBMs are technically hypersonic weapons, most of the discussion on hypersonics is about boost glide and scramjet weapons. Both of these follow different flight profiles and pose their own challenges to defenders. Optimizing air defenses against one will not necessarily enable defense against the other.
Basing and Employment
In addition to the issues of selecting the type of weapon there is the issue of where to base them and what platforms to launch them from. These factors include responsiveness, basing, and costs.
Figure 1 (click to view in separate tab) provides a means for comparing the different employment options for a scramjet weapon. In the first column is the platform, the second the base closest to our target of choice (China), the third is the number of weapons carried in each platform, the fourth is the time until the weapon can reach most of the potential targets of interest. The fifth column contains the number of platforms required on station to meet a baseline requirement while the sixth includes the number required to have in inventory in order to rotate them forward to maintain a constant presence. The second to last column includes the cost for the required inventory; these costs include an annualized acquisition cost, yearly operations and sustainment costs, and annual cost for require personnel to operate and maintain the system. The last column is the percentage of the planned inventory (for existing or program or record systems) the fifth column would take up. Using Figure 1, we can assess the advantages and disadvantages of each of our options.
We begin with a surface ship, an important topic as the US Navy looks into the next generation surface combatant. The Arliegh Burke class destroyer is the current workhorse of the surface navy and provides a baseline for understanding the probable low end cost of future destroyers. The Mk 41 Vertical Launch system on the Burke could potentially employ a ramjet or scramjet weapon system atop a solid rocket motor booster, but the small size of its cells would greatly limit the range and payload of such a weapon. The much larger Mk 57 VLS cells, currently carried on the Zumwalt class destroyer, would be capable of carrying a much larger weapon able to meet the mission requirements, as was in the original designs for the platform before cancelled in the “Peace Dividend.” Because only three were purchased, the cost per ship is inflated. However the lessons learned from the Zumwalt design may very well show up in future destroyers, giving us a good high end estimate of future surface ships and the baseline for our comparison. Each Zumwalt has 80 Mk 57 VLS cells capable of carrying the next generation of Ramjet or Scramjet missiles. For the purposes of analysis, we will assume only half of the total cells are devoted to a Scramjet powered cruise missile.
While the weapons on a Zumwalt tied to the pier in Japan could hit many targets in China, it would take about 19 hours to cruise to an optimal position where it could reach a large portion of the targets of interest. In a crisis such a ship would sortie, reducing response time. If two destroyers were station in Japan and alternated to stay on station continuously, then the response time would be reduced to zero. Similarly, four destroyers based in San Diego could rotate to a forward deployment station to have the same effect, but with increasing associated costs. The deployment of these destroyers would be a detectable deterrent force, but they would not necessarily be easy to track. These multi-mission destroyers would be executing more than just a strike deterrence role during a crisis.
The US Navy has considered the use of hypersonic weapons from the Block V variant of the Virginia class submarine carrying 12 submarine launched ballistic missiles or boost glide variants. Figure 1 includes data for the Virginia Block V carrying either the ballistic missile weapon or the scramjet weapon. As Figure 1 illustrates, deploying these weapons on a submarine comes at a premium. However, it is currently very difficult to track them, and commanders could place them in positions which other platforms cannot reach, and thus the weapons could arrive from an unexpected direction.
Submarines sailing from Guam at 20 knots would take 74 hours to get on station to enable the weapon to reach a large portion of the target set. It would take four submarines stationed in Guam to keep two submarines constantly on station, and eight in alternating deployments from San Diego to maintain two in permanent presence with at least forty weapons on hand.
Several rows represent different bombers operating from various forward operating bases. The cost estimates include operating from Elmendorf or Diego Garcia with proportional cost for tanker support. Where the response time is zero, a constant presence is being maintained. For the columns listing the B-21, assumptions have been made based on the Congressional Research Center cost estimate for the program and using the O&M costs of the B-2 as a stand in. Similarly, the weapons load estimate is based on public data on the B-2.
As we can see maintaining a constant presence with bombers is an expensive proposition. If commanders can accept a delayed response of at least three hours the requirements can be met with bombers forward deployed to Andersen AFB in Guam. In a crisis these bombers could then be placed on a higher operating tempo. Additionally, these same bombers can be reloaded after their first mission and conduct follow on missions in less than twelve hours while ships and submarines would take days to reload.
A single stealth bombers such as the B-2 or the B-21 could carry more than enough bombs to address forty potential target in a single sortie, but then it would be operating in a challenging air defense environment and subject to potential attrition.
One option is to deploy converted merchant ships as Auxiliary Missile Cruisers (ACM). Merchant ships taken from trade can be converted to carry 40 Mk 57 VLS cells loaded with the larger ramjet missile. The proposal assumed these ships can be purchased and improved for $100M, crewed with seventy sailors and civilian mariners, and have an annual O&M costs similar to other hybrid Maritime Sealift Command (MSC) vessels. Since these ships are converted from older ships in trade, we assume the ACM will have only 20 years of expected service life, though many MSC ships have had much longer service lives after conversion.
(There is another lower cost option offered by Captain Wayne Hughes, not assessed here, which takes a cue from the New Navy Fighting Machine: the development of a single mission stealthy missile platform based on the Sea Shadow to carry 20 of these missiles.)
Land based Medium Ranged Ballistic Missiles (MRBM) are the least expensive option and if stationed in Japan could range all of the targets of interest in North Korea and a large portion of those targets in China. However, as we discovered during the Cold War, stationing of such missiles in allied countries has been controversial and would probably be today. In addition, land-based mobile systems would have a larger area to maneuver and hide in Europe than in small densely populated islands like Japan.
The use of Conventional Intercontinental Ballistic Missiles (CICBM) would avoid controversies of overseas deployment. However, in addition to being prohibitively expensive, they would also be indistinguishable from their nuclear armed cousins in flight.
Figure 1 illustrates the tradeoffs between responsiveness and costs. Having platforms armed with penetrating hypersonic weapons constantly on station provides regional commanders and the national command authority the ability to rapidly respond to a crisis or aggression by revanchist powers and maintain deterrence by denial or punishment. In addition to responsiveness and costs, we must also consider the factor of Distributed Lethality for the joint force. Placing all of the joint force’s hypersonic strike capabilities in a small number or single type of platform gives our competitors leeway to focus their efforts to respond. Increasing the number and type of platforms by even a small effort greatly complicates the ability of a potential adversary to track and plan on how to counter that force and can be enhanced by other methods.
Conclusion
There is a range of supersonic and hypersonic weapons that exist today and will be available in the near future. These weapons can be difficult and costly to defend against. Our competitors and others are investing in these weapons. Our regional military commanders have declared there is a requirement for future forces to possess this capability. Defending against them can be a difficult and expensive proposition, particularly if different weapons have different flight profiles. As we deliberate on how best to meet these needs, it is important to examine the full range of opportunities of weapons types, carrying platforms, and their impact on our competitors.
These weapons can be placed on a range of platforms in the joint force that exist today, will soon be in the program of record, or other innovative options. The deployment of these weapons will require a tradeoff between timely response, distributed lethality, and costs in support of a deterrence posture towards our competitors. Some weapons such as land-based missiles can be cost effective on the Eurasian continent (subject to political factors) others are more effective in a maritime environment. While deployment of a single weapon from a single platform may be efficient, such actions would provide our competitors the ability to focus on a single threat. A more effective cost imposing strategy is the deployment of a range of weapons across the breadth of the joint force. As we consider the alternatives for the replacement and recapitalization of our forces, we need to consider how the current and next generation of platforms will employ these weapons.