A May 3 article in Air Force Times applauded the Air Force for achieving the longest ever hypersonic flight by a scramjet-powered aircraft on May 1.
The article states: “The X-51A WaveRider flew for more than three minutes under power from its exotic scramjet engine and hit a speed of Mach 5.1…”
The engine successfully operated for about 240 seconds, until it burned its 270-pounds of fuel. This established a record as the longest flight completed by a vehicle while powered by a scramjet engine. As intended, the WaveRider then splashed into the Pacific Ocean.
The most recent flight did set a time duration record for the X-51 program. It did not exceed altitude or speed records set in earlier scramjet programs. The flight, the last in the X-51A program, did not meet expectations published by the Air Force, which called for the WaveRider to “accelerate to approximately Mach 6 as it climbs to nearly 70,000 feet”.
Missourians have reason to doubt the glowing tributes made by Darryl Davis, President of Boeing Phantom Works, which built the X-51:
“This test proves the technology has matured to the point that it opens the door to practical applications, such as advanced defense systems and more cost-effective access to space.”
Not quite. While not stressed in the article, initial assistance for the WaveRider, which has an empty weight of 4,000 pounds, was provided by a 185,000-pound B-52H, which helpfully chauffeured the WaveRider to 50,000 feet and a speed of approximately 525 mph. Additional assistance was then provided by an MGM-140 solid rocket booster that, in 26 seconds, provided lift to 60,000 feet and acceleration to Mach 4.8, or 3,200 mph.
Powered by the scramjet engine, WaveRider decelerated immediately upon separation from the rocket and then accelerated by 200 mph to 3,400 mph, or Mach 5.1, while slightly gaining altitude.
Relative contributions of the two propulsion systems bear note.
The scramjet accelerated the WaveRider from 3,200 mph to 3,400 mph in about 240 seconds. The MGM-140 accelerated the WaveRider from 525 mph to 3,200 mph in 26 seconds. In comparative terms the MGM-140, developed for the United States Army and originally used in Operation Desert Storm over 20 years ago, was the clear winner.
This comparative performance was expected, because scramjet engines have very low thrust to weight levels. With larger vehicles and further development, the scramjet is expected to have a thrust to weight ratio of about two. The scramjet used in the X-51 has a thrust of between 500 and 1,000 pounds, so the thrust to weight ratio was a small fraction of one. In contrast, rockets have very high thrust to weight ratios, typically in the range of 50 to 100.
The offsetting benefit of the scramjet engine over the rocket is fuel economy and resulting lighter fueled vehicle weight.
Significance of this flight can only be understood by examining the technology and history of the scramjet engine. The middle zone of the speed envelope has always been troublesome. In 1976 the SR-71 Blackbird set the world speed record for a manned jet plane, at 2,193 mph or Mach 3.3. This is thought to be roughly the maximum speed attainable with jet propulsion, because of inability of turbine blades to slow incoming air to subsonic velocities required for combustion at higher speeds.
Rocket-powered vehicles can reach Mach 25 but are limited by need to carry huge amounts of oxidant for the combustant. The Space Shuttle demonstrates this limitation. The Shuttle, with an empty weight of 166,000 pounds, requires 226,000 pounds of liquid hydrogen and 1.4 million pounds of liquid oxygen to reach orbit. The weight of the fuel required to launch the shuttle into orbit is almost ten times the weight of the shuttle.
The quest is for a lightweight, fuel efficient propulsion system to accelerate a payload from Mach 3 upward. Scramjet provides the best solution to this problem.
The Scramjet Engine
The X-51 Program was intended to demonstrate the practicality of the scramjet engine, which would be a major technological leap because of its simplicity.
The scramjet, or supersonic combustion ramjet, is a variant of the ramjet engine and has no moving parts.
Turbojet engines use rotating inlet fans, multiple stages of rotating compressor fans and multiple rotating turbine fans. Above speeds of Mach 3 to Mach 4, the turbines are not effective and ramjet engines, in which air is rammed through the engine inlet nozzle into the compressor, are used.
Combustion in a ramjet occurs at subsonic air velocities and combustion products are accelerated through a convergent-divergent nozzle to supersonic speeds. Ramjets, since they have no mechanical air compression, cannot accelerate a vehicle from low speeds. Typically, ramjets do not achieve sufficient compression to power a vehicle at less than supersonic speeds. At high vehicle speeds, slowing incoming air to subsonic velocities results in excessive heat, so the maximum speed of a ramjet powered vehicle is about Mach 5.
Scramjet engines are similar to ramjets but do not decelerate air flow to subsonic velocities. Instead,the inlet merely decelerates inflow air to a lower supersonic speed for combustion, with resulting acceleration to a higher supersonic speed through the nozzle.
With current designs, a scramjet will not produce thrust sufficient to power a vehicle below vehicle speeds of less than about Mach 4.5. The May 2013 flight of an X-51 therefore occurred near the lower boundary of scramjet-powered vehicle speed.
History of Scramjet Development
Between 1962 and 1978, the John Hopkins Applied Physics Laboratory performed classified research to develop missiles using scramjet propulsion. Engine modules were carried aloft by rockets and tested at a series of simulated altitude/speed combinations, including Mach 10 at 88,000 feet, primarily to verify aerodynamics.
In about 1982, DuPont Aerospace proposed design of a hypersonic vehicle to DARPA. The program was funded between 1983 and 1985 as a black program named Copper Canyon. Development efforts continued as the National Aerospace Plane program, established by the Secretary of Defense in 1985.
The X-30 Program
In his 1986 State of the Union address, President Reagan called for development of a new Orient Express that could, by the year 2000, take off from Dulles Airport and either attain low earth orbit or fly to Tokyo in two hours, at speeds of up to Mach 25.
The first stage of this effort was intended to develop two X-30 aircraft to be capable of single stage to orbit flight, or alternatively capable of sub-orbital flight with horizontal takeoff and landing. The X-30 was intended to use a combination of jet, ramjet and scramjet liquid hydrogen-based propulsion systems.
In 1994 the program was canceled because of high cost, estimated at $15 billion, to build two X-30 test vehicles. Costs incurred before cancellation totaled at least $1.7 billion.
The X-43 Program
The follow-on the was the X-43A, a $230 million program to test hydrogen fueled scramjet engines in a wingless vehicle roughly 12 feet in length and weighing about 3,000 pounds. The X-43A was designed to operate at speeds greater than Mach 9.8 at altitudes of about 100,000 feet.
The program was initiated by the Air Force Research Laboratory in December 2003. The X-43 was carried aloft by a B-52 and used a modified first stage of a Pegasus rocket for initial acceleration. Three units were built and tested.
The first X-43 and rocket were destroyed mid-flight in June 2001 after they began uncontrolled oscillations about 13 seconds after release from the B-52.
The second unit was flown in March 2004. The vehicle was released from the Pegasus rocket at 95,000 feet During the 11 second period the scramjet burned, about two pounds of hydrogen fuel was used. A maximum velocity of Mach 6.83, or about 4,600 mph was achieved coincident with burnout of the Pegasus. After slowing as a result of detachment from the Pegasus, the vehicle did accelerate while gaining altitude.
The third X-43A vehicle set a new speed record of Mach 9.65, or 6,598 mph, at an altitude of 112,000 feet, in November 2004.
The X-43 program at one point envisioned development of the X-43B, a fighter plane-sized vehicle, an X-43C to test viability of hydrocarbon fuel and the X-43D, which was to be almost identical to the X-43A but with a design speed of approximately Mach 15. All models were canceled in favor of the X-51 program, which would use JP-7 rather than hydrogen as a combustant.
The X-43 holds the world scramjet speed record, having achieved approximately 7,000 mph, over Mach 10, almost twice the highest speed achieved by the X-51.
The X-51 Program
The X-51 program began in 2004 and extends scramjet engine research undertaken with the X-43, as a joint effort of DARPA, NASA, the Air Force, Boeing and Pratt & Whitney Rocketdyne, managed by the Aerospace Systems Directorate of the Air Force Research Laboratory. The X-51 engine is designed to ignite on a combination of ethylene and JP-7 jet fuel and then switch to JP-7, which was developed for use in the SR-71, about ten seconds later. This is a major change from the X-43 engine, which was designed to operate on hydrogen.
Four vehicles were constructed and tested to intentional destruction. Flight One occurred in May 2010. The rocket boosted the craft to Mach 4.5 and separated and the scramjet engine took the X-51 to an altitude of 70,000 feet and a velocity of Mach 5, with an engine run time of 140 seconds. The intended maximum speed of Mach 6 was not achieved because acceleration at a lower altitude was quicker than anticipated, presumably causing overheating.
Flight Two occurred in June 2011. After separation from the rocket, the scramjet ignited on ethylene fuel, but failed to fire on JP-7 fuel.
Flight Three occurred in August 2012. The flight failed because of unspecified problems with the control fin, which resulted in loss of control 16 seconds after separation from the rocket.
The May 1 flight ended with intentional destruction of the last of the four vehicles constructed.
The End Product Vehicle
The end product of these programs is not difficult to discern, and it will not be a scramjet vehicle used to deliver tacos to Toledo or tourists to Tokyo in record time.
The end product will be a vehicle that will deliver explosives to facilities of foreign governments that do not strictly conform to America’s exacting standards in record time.
That has always been the goal – to deploy a hypersonic aircraft that will take off and land on runways in the United States that can reach any point on the planet within one to two hours. This goal was published in 1957 as the Dyna-Soar program, which would have used a rocket to launch a glider to reach the target.
After the Dyna-Soar program ended in 1963, space-plane programs went black, but a little information is publicly available. Around 1965, the CIA began work on a high-Mach spyplane called Project Isinglass. This morphed into Rheinberry, a design for a Mach-17 air-launched reconnaissance vehicle. This was replaced in 2003 by Falcon, or Force Application and Launch from the CONtinental United States.
Falcon furthered development of both a hypersonic vehicle and a small launch vehicle. Lockheed Martin was awarded a contract in 2004 to develop hypersonic vehicle technology. DARPA and the Air Force later continued development work on the X-41 Common Aero Vehicle, a classified military spaceplane, described as an experimental maneuvering re-entry vehicle capable of carrying a 1,000 pound payload at hypersonic velocities.
Other FALCON projects include Hypersonic Technology Vehicle 1, or HTV-1, which was tested in April 2010. The flight ended about nine minutes after launch due to unspecified technical difficulties. This project has apparently been canceled.
Hypersonic Technology Vehicle 2, or HTV-2, is an experimental crewless rocket glider capable of flying at 13,000 mph. HTV-2 first flew in April 2010 after being launched by a Minotaur IV Lite rocket. The plan was for the vehicle to separate from the rocket, level and glide over the Pacific at Mach 20. Contact with the vehicle was lost nine minutes into the 30-minute mission after the vehicle began to violently roll.
A second flight was undertaken in August 2011. Again, contact was lost about nine minutes into the mission, and the vehicle was intentionally splashed.
HTV-3X, also called Blackswift, was proposed to use a combination turbine engine and ramjet to power a vehicle from horizontal takeoff to Mach 6. Blackswift was not funded for fiscal year 2009.
Work apparently continues on the Hypersonic Cruise Vehicle, or HCV, which is intended to traverse over 10,000 miles in two hours with a 12,000-pound payload at speeds up to Mach 20.
FALCON is part of an overall program called Prompt Global Strike, or PGS. In a parallel program managed by the Army, in November 2011 the Advanced Hypersonic Weapon, a glide vehicle, was tested as part of the Prompt Global Strike Program. The vehicle traveled about 2,300 miles in less than 30 minutes and struck its target.
A hypersonic cruise missile is the next step but not the final product. Obviously emboldened by the test flight, the program manager for the Air Force Research Laboratory Aerospace Systems Directorate on May 9 told us the Air Force is:
“trying to get the technologies mature enough that in the 2020 timeframe we would like to be able to show the warfighter that we would be ready to start a development program of record sometime around that time.”
Two aspects of the scramjet programs should trouble all of us. One is limited progress achieved in the scramjet program.
The X-30 program began in the mid-1980s. After over twenty-five years of X-30, X-43 and X-51 programs that splashed seven test vehicles into the Pacific, all we have to show is a jet engine with no moving parts that does little more than maintain initial velocity and altitude of a 4,000 pound vehicle during a design burn time of four minutes.
Contrast this achievement with the X-15 program. Twenty years after Chuck Yeager piloted the first supersonic flight in the Bell X-1, the X-15 set a speed record of Mach 6.72, or 4,520 mph, considerably faster than the X-51. That was in 1967, almost fifty years ago, four years after the X-15 reached an altitude of 354,200 feet.
The X-15 empty weight was less than four times that of the X-51, and carried a pilot who maneuvered conventional landings. The X-15 was even equipped with a ejection seat that allowed pilot exit at speeds up to Mach 4 or altitudes up to 120,000 feet. The contrast becomes even more glaring with recognition that the X-15 was designed by a small crew of dedicated engineers using awesome supercomputers called…. slide rules. The X-15 design crew clearly had fervent desires to enhance national defense and space exploration capabilities.
These types of contrasts might lead to suspicion that the X-30, X-43 and X-51 programs were little more than high-tech self-licking ice cream cones, whose only purpose was to sustain themselves, at substantial cost to the Treasury Department. The primary objective of development programs such as the X-51 may be providing defense industry employment opportunities for retiring generals and improvement of the wealth of shareholders of major defense contractors rather than improvement of the defense capabilities of the United States.
The second problem has two aspects, both more substantial: Lack of time for verification and risk of catastrophic reaction.
Pentagon generals perceive the existence of a dangerous gaping chasm in our defense capabilities – the inability to deliver non-nuclear weapons over long distances very quickly. Substitute service is currently provided by Air Force Hangar Queens, sometimes called B-2s.
Their most recent mission was a March 2013 flyover of the Jik Do target range in South Korea to drop dummy ordinance. A pair of B-2s were delicately tugged out of their luxurious air-conditioned quarters at Whiteman AFB in Missouri and flown over 6,500 miles. The cruise speed of the B-2 is 560 mph, so this flight required roughly twelve hours of air time. So did the flight back to Missouri, all at an operating cost of over $135,000 per hour per plane, not including the considerable costs of four mid-air refueling operations.
The proposed solution to this perceived chasm in national defense is the hypersonic cruise missile. In a show of strength, dummy ordinance could have been dropped upon South Korea in less than two hours rather than twelve hours. But drastically lower response times also means drastically reduced time for verification that the intelligence being acted upon is correct.
The Pentagon offers a single target in which use of a hypersonic vehicle would have been beneficial. In August 1998 American warships in the Arabian Sea fired more than 60 Tomahawk cruise missiles at suspected training camps near Khost in eastern Afghanistan. At 550 mph, the missiles had a two-hour flight time. During those two hours, the primary target, Osama bin Laden, left the target area.
He also was reported to have been located in Afghanistan on two occasions in September 2000 but was not fired upon.
Note the word “suspected”. Verification apparently was not achieved in any of these three cases.
The August 1998 destruction of an alleged VX nerve gas plant in Khartoum, Sudan, which actually was a pharmaceutical plant, is a prime example of need for additional time for verification. The plant manufactured ninety percent of the country’s most widely used medicines and left the country with no supplies of chloroquine, the standard treatment for malaria. This was the only plant in the country manufacturing drugs to treat tuberculosis for over 100,000 patients.
After numerous revisions, the official justification for the attack became the CIA’s reliance upon a single laboratory analysis of a single soil sample obtained by an unidentified agent from an unidentified foreign country taken from an undisclosed location somewhere outside the factory that seemed to indicate the presence of a commercially available non-lethal precursor of a chemical used in making VX nerve gas.
A CIA agent later admitted that their choice of an operative for the mission likely did not lend itself to ensuring entirely objective results, a polite way of saying the sample could have been intentionally tainted.
Subsequent analysis suggested the chemical detected, EMPTA, can easily be confused with FONFOS, an agricultural insecticide commonly used in Africa. The substance thought to be detected also is chemically similar to several other widely available pesticides and insecticides, including the weedkiller Roundup.
The recent fiasco in Benghazi provides another example of confusing and conflicting intelligence that typically evolves in fast-moving events where rapid response might worsen an already bad situation. Pulverization of meetings of Taliban warriors that are later learned to be female attendees of Pakistani wedding ceremonies are examples of rapid action undertaken based upon intelligence that proves to be flat-out wrong.
In all these cases, delay in response rather than acceleration would have been advantageous. And availability of a rapid-response cruise missile will dramatically decrease the odds of level-headed delay. As then-Secretary of State Madeleine Albright said to then-Chairman of the Joint Chiefs of Staff Colin Powell: “What’s the point of having this superb military that you’re always talking about if we can’t use it?
As surely as the sun sets in the west, any hypersonic cruise missile that is available will be used. And, given that speed is the weapon’s primary attribute, the weapon will be used quickly – meaning without time for contemplation of whether the weapon should be used, and without time for approval by top-level officials. The hypersonic cruise missile program in effect will be a drone assassination program on crystal meth operated by lower level unidentified and unaccountable CIA or Air Force personnel. Sane minds can easily conclude that these strikes will make the United States less rather than more safe.
Launch of the hypersonic cruise missile poses an even more serious risk. The combination turbine-ram-jet-scramjet engine does not appear to be technically feasible. The alternative is initial boost by either a B-52 or a rocket. Again given that the primary advantage of the weapon is speed, selection of the rocket over the bomber is a given.
Supporters say the hypersonic cruise missile will reduce reliance on nuclear weapons in conventional conflicts. But their use will increase the risk that other nations will use nuclear weapons in response.
When development of the weapon was being considered under the George W. Bush administration, the idea was rejected because of fears that a rocket-launched cruise missile would trigger a Russian nuclear launch warning system, potentially provoking a nuclear war, since Russia would not be able to ascertain that the launched rocket is carrying a conventional and not a nuclear weapon.
An example of this type of situation occurred in April 2013, when a scheduled routine test launch of a Minuteman III missile from Vandenberg Air Force Base in California was postponed to avoid any misperception or miscalculation on the part of the Democratic People’s Republic of Korea. In plain language, the missile test was aborted so North Korea would not conclude it was about to be subjected to preemptive nuclear attack.
The obvious solution to risks of retaliation by Russia is advance notification. But notification would require that Russia trust that the United States was being truthful and straightforward. If that trust does not exist, Russian concerns could heighten and their finger on the big red “Execute Launch” button could tense rather than relax.
And United States actions around the world in recent years have in all too many cases not been conducive of developing the required trust.
Like so many of the problems that plague the world today, this problem has no military solution. Which brings us to the ultimate issue that should be considered as we strive to develop hypersonic cruise missiles:
What should be the functions of the United States armed forces and will the hypersonic cruise missile further those functions?
A Humane Alternative to the X-51
Only a handful of American citizens would support an unnecessary attack such as was waged on a non-threatening Sudanese pharmaceutical factory based upon erroneous intelligence. Even fewer would support such an attack with conventional weapons that could trigger nuclear war with Russia or China or both simultaneously.
Remaining citizens, in President Obama’s era of Hope, should fervently hope that the X-51 program and follow-on programs are nothing more than sophisticated, expensive self-licking ice cream cones. Yes or no, my point is that the military is concentrating efforts and resources on the issue of whether the hypersonic cruise missile can be produced. I submit the real issue is whether the missile should be produced. Or whether the military should instead be concentrating its efforts and resources in more humane areas, such as rehiring thousands of teachers who have been laid off because of budget limitations or assisting the 247,000 veterans of wars in Iraq and Afghanistan with PTSD the military has produced based on…. incorrect intelligence.
Astute readers will note that the Veterans Administration rather than the Air Force has responsibility for the care of our veterans. I respond with the “Pottery Barn Rule” reportedly uttered by then Secretary of State Colin Powell in the summer of 2002 when warning President Bush of the consequences of military action in Iraq. In simple terms, the rule is: “If you break it you own it.”
Department of Defense avoids this rule. they break our veterans and then claim they have no responsibility. This reasoning is the heart of all that is lacking in our care for our veterans and must change if we are ever to stand up for the soldiers who stood up for our nation, with their care assigned a higher priority than is given to defense industry cost-plus contracts that might develop ever-faster means of killing people.
The hypersonic cruise missile is but one example. Costs of the X-43 and X-51 programs are classified. We do know the X-30 program cost $1.7 billion before cancellation. The X-43 was at least $230 million. Including indirect costs, a $4 billion total for all three programs seems a reasonable estimate.
$4 billion for a 4,000-pound unmanned vehicle with an engine with no moving parts that basically maintains altitude and velocity for a four-minute run time before crashing. Wiser minds would have used that $4 billion in a wiser manner. And wiser minds will work to kill the X-51 successor programs.