Good Morning or Good Evening, depending on where you are in the world— I hope that all is well in your world and the week has not been to taxing on the spirit. Last week I talked about the British concept vehicle called the Skylon. I also said that we would move forward with a series of articles on UAVs. However, before I do that I really need to address “The Future and Beyond,” one more time.
NASA is also addressing the issue of Mach 5 vehicles but in a different way. Their money/research is on scramjets and the project is called the “Hyper-X-Program.
NASA made aviation history with the first and second successful flights of a scramjet-powered airplane at hypersonic speeds – speeds greater than Mach 5 or five times the speed of sound. Compared to a rocket-powered vehicle like the Space Shuttle, scramjet (supersonic combustion ramjet) powered vehicles promise more airplane-like operations for increased affordability, flexibility and safety for ultra high-speed flights within the atmosphere and into Earth orbit. Because they do not have to carry their own oxidizer, as rockets must, vehicles powered by air-breathing scramjets can be smaller and lighter – or be the same size and carry more payload. A modified Pegasus booster rocket ignites moments after release from the B-52B, beginning the acceleration of the X-43A over the Pacific Ocean in March of 2004. The X-43A vehicle is mounted on the nose of the rocket.
Researchers have worked for decades to demonstrate scramjet technologies, first in wind tunnels and computer simulations, and now in an airplane in flight. Ultimate applications include future hypersonic missiles, hypersonic airplanes, the first stage of two-stage-to-orbit reusable launch vehicles and single-stage-to-orbit reusable launch vehicles.
The eight-year, approximately $230 million NASA Hyper-X program was a high-risk, high-payoff research program. It undertook challenges never before attempted. No vehicle powered by an air-breathing engine had ever flown at hypersonic speeds before the successful March 2004 flight. In addition, the rocket boost and subsequent separation from the rocket to get to the scramjet test condition had complex elements that had to work properly for mission success. Careful analyses and design were applied to reduce risks to acceptable levels; even so, some level of residual risk was inherent to the program.
Hyper-X research began with conceptual design and wind tunnel work in 1996. Three unpiloted X-43A research aircraft were built. Each of the 12-foot-long, 5-foot-wide lifting body vehicles was designed to fly once and not be recovered. They are identical in appearance, but engineered with slight differences that simulate variable engine geometry, generally a function of Mach number. The first and second vehicles were designed to fly at Mach 7 and the third at Mach 10. At these speeds, the shape of the vehicle forebody served the same purpose as pistons in a car, compressing the air as fuel is injected for combustion. Gaseous hydrogen fueled the X-43A.
After the first flight attempt in June of 2001 failed when the booster rocket went out of control, the second and third attempts resulted in highly successful, record-breaking flights. Mach 6.8 was reached in March of 2004, and Mach 9.6 was reached in the final flight in November of 2004.
The first X-43A hypersonic research aircraft and its modified Pegasus booster rocket were carried aloft by NASA’s NB-52B carrier aircraft. At nearly 5,000 mph, the March flight easily broke the previous world speed record for a jet-powered (air breathing) vehicle. The X-43A research vehicle was boosted to 95,000 feet for a brief preprogrammed engine burn at nearly Mach 7, or seven times the speed of sound. During its third and final flight – at nearly Mach 10 – the X-43A research vehicle flew at approximately 7,000 mph at 110,000 feet altitude, setting the current world speed record for an air-breathing vehicle.
The Mach 10 research vehicle featured additional thermal protection, since expected heating was roughly twice that experienced by the Mach 7 vehicle. Carbon-carbon composite material, for instance, was added to the leading edges of the vehicle’s vertical fins to handle the higher temperatures.
Both flights began with the stack being carried by a B-52B aircraft from NASA’s Dryden Flight Research Center to a predetermined point over the Pacific Ocean, 50 miles west of the Southern California coast. Release altitude from the B-52B was 40,000 feet for both successful flights. At that point, each stack was dropped from the B-52B, and the booster lifted each research vehicle to its unique test altitude and speed.
Other than differences of altitude, speed and distance covered, the Mach 10 flight profile followed that of the Mach 7 flight: The Mach 10 research vehicle separated from the booster and flew under its own power and preprogrammed control. It was separated from the booster rocket by two small pistons. Shortly after separation, its scramjet engine operated for about ten seconds obtaining large amounts of unique flight data for an airframe-integrated scramjet. The engine thrust was very close to its design value in each flight – sufficient to accelerate the vehicle during the Mach 7 flight and to allow the vehicle to cruise at constant velocity in the Mach 10 flight.
In each case, when the scramjet engine test was complete, the vehicle went into a high-speed maneuvering glide and collected nearly ten minutes of hypersonic aerodynamic data while flying to a mission completion point, hundreds of miles due west (450 miles at Mach 7, 850 miles at Mach 10) in the Naval Air Warfare Center Weapons Division Sea Range off the southern coast of California. Each vehicle splashed into the ocean, as planned, and was not recovered.
Guinness World Records has recognized both the Mach 6.8 and Mach 9.6 accomplishments and has listed the flights on their web site and in the 2006 edition of their book of records. Prior to the 2004 X-43A flights, the previous record was held by a ramjet-powered missile that achieved slightly over Mach 5. The highest speed attained by a rocket-powered airplane, NASA’s X-15 aircraft, was Mach 6.7. The fastest air-breathing, crewed vehicle, the SR-71 achieved slightly over Mach 3. The X-43A more than doubled the top speed of the jet-powered SR-71.
The first flight attempt of the X-43A was in June of 2001. Unfortunately, the booster failed and had to be destroyed early in flight. As a result, the research vehicle was not tested because it never reached test conditions. Although no single contributing factor was found, the root cause of the problem was identified as the booster’s flight control system. The booster failed due to inaccurate design models that overestimated the capability of the flight control system to operate within predicted flight conditions.
The Hyper-X program has significantly expanded the boundaries of air-breathing flight by being the first to fly a “scramjet” powered aircraft at hypersonic speeds. Numerous actions were taken in response to the findings. Wind tunnel tests were conducted to provide data to reduce atmospheric loads on the booster’s control surfaces, more powerful booster fin actuators were added to overcome aerodynamic loads, and propellant was machined out of the Pegasus booster to enable launch at its normal launch altitude of 40,000 feet instead of 23,000 feet – as on the first flight – in order to reduce aerodynamic loads.
A ramjet operates by subsonic combustion of fuel in a stream of air compressed by the forward speed of the aircraft itself, as opposed to a normal jet engine, in which the compressor section (the fan blades) compresses the air. Ramjets operate from about Mach 3 to Mach 6.
A scramjet (supersonic-combustion ramjet) is a ramjet engine in which the airflow through the engine remains supersonic. Scramjets powered vehicles are envisioned to operate at speeds up to at least Mach 15. Ground tests of scramjet combustors have shown this potential, but no flight tests have surpassed the Mach 9.6 X-43A flight. See illustration below.
So we know now that hypersonic flight is possible, and we will probably have a working model flying commercially before the end of this decade – but what about beyond. Where do we go next – Warp Drive? Let’s see what NASA thinks……….
Warp Drives”, “Hyperspace Drives”, or any other term for Faster-than-light travel is at the level of speculation, with some facets edging into the realm of science. We are at the point where we know what we do know and know what we don’t, but do not know for sure if faster than light travel is possible.
The bad news is that the bulk of scientific knowledge that we have accumulated to date concludes that faster than light travel is impossible. This is an artifact of Einstein’s Special Theory of Relativity. Yes, there are some other perspectives; tachyons, wormholes, inflationary universe, spacetime warping, quantum paradoxes…ideas that are in credible scientific literature, but it is still too soon to know if such ideas are viable.
One of the issues that is evoked by any faster-than-light transport is time paradoxes: causality violations and implications of time travel. As if the faster than light issue wasn’t tough enough, it is possible to construct elaborate scenarios where faster-than-light travel results in time travel. Time travel is considered far more impossible than light travel.
Ever since the sound barrier was broken, people have been asking: “Why can’t we break the light speed barrier too, what’s the big difference?” It is too soon to tell if the light barrier can be broken, but one thing is certain — it’s a wholly different problem than breaking the sound barrier. The sound barrier was broken by an object that was made of matter, not sound. The atoms and molecules that make up matter are connected by electromagnetic fields, the same stuff that light is made of. In the case of the light speed barrier, the thing that’s trying to break the barrier is made up of the same stuff as the barrier itself. How can an object travel faster than that which links its atoms? Like we said, it’s a wholly different problem than breaking the sound barrier.
Here is a snap shot of the theory that sums up the problem: “Special Relativity”. Actually Special Relativity is pretty simple in its construction… Just start with 2 simple rules:
Rule Number 1: The distance you’ll travel (d) depends on how fast you move (v), for how long you’re moving (t). If you drive 55 mph for one hour, you’ll have covered 55 miles. – simple.
Rule Number 2: — This is the mind boggling one — No matter how fast you’re moving, you’ll always see the speed of light as being the same.
When you combine these together and compare what one traveler “sees” relative to another traveler at a different speed – that’s when the problems come into play. Let me give you another way to picture this. Close your eyes. Imagine that the only sense that you had was the sense of hearing. All that you know is sounds. You identify things by how they sound. So when a train goes by, did its horn really change? We know that the horn was always tooting the same tone, but it was the train’s motion that made it appear to change because of something called the Doppler shift. Its a similar situation with light. Everything we know around us we know by light, or more generally electromagnetism. What we see, what we feel (the air molecules bouncing off our skin), what we hear (air molecules bouncing off each other in waves of pressure), even the propagation of time, are all governed by electromagnetic forces. So when we start moving at speeds approaching the speed by which we are getting all our information, our information gets distorted. In principle it’s that simple. Understanding it well enough to do something about it, well that’s a different matter.
One of the consequences of this Special Relativity is the light speed barrier. Here’s another way to look at it. To move faster, you add energy. But when you get going near the speed of light, the amount of energy you need to go faster balloons to infinity! To move a mass at the speed of light would take infinite energy. It appears that there is a distinct barrier here.
I feel certain that if Einstein was still alive he could help NASA resolve the problem; however, with that not being possible I think we will have to wait until we can copy the technology of an alien spacecraft.
Next week we will talk about the future of UAVs so until then, have a good weekend, remember to protect yourself, your family, and your profession.
January 9, 2015