Another Magical Space Drive Bites the Dust

The "EM Drive" is alleged to provide reactionless thrust.

Someone finally set up a sensitive and repeatable test protocol, and they measured thrust.

A small fly in the ointment though, the thrust occurred without regard of how the motor was facing.

It appears that the thrust came from the current flowing to the motor, with the magnetic field of the earth acting as a stator, and no thrust came from the motor itself, but the current was pushing against the magnetic field of the earth:

It was bound to happen eventually. A group of researchers that may actually be competent and well-funded is investigating alternative thrust concepts. This includes our favorite, the WTF-thruster EM-drive, as well as something called a Mach-Effect thruster. The results, presented at Space Propulsion 2018, are pretty much as expected: a big fat meh.

The key motivation behind all of this is that rocket technology largely sucks for getting people around the Solar System. And it sucks even worse as soon as you consider the problem of interstellar travel. The result is that good people spend a lot of time eliminating even the most far-fetched ideas. The EM-drive is a case in point. It's basically a truncated hollow copper cone that you feed electromagnetic radiation into. The radiation bounces around in the cone. And, by some physics-defying magic, unicorns materialize to push you through space.

………

The key problem seemed to be that the main proponents of crazy space thrusters may actually be pretty bad at doing experiments. All in all, I would have moved on, but others are more thorough than I am.

Let the adults have a go

A group of German scientists has now gotten a reasonable amount of money under the rubric of testing all the things. Basically, because the various space agencies have whispered that no idea is too silly to ignore, we need an effective way to quickly test all the stupid space stuff on the Internet. The Germans are currently building something that is designed to do all that testing. It is an awesome bit of equipment.

First, everything is done in vacuum. And, not just the poor vacuum that you might get by attaching a Hoover to a leaky box—they can get down to a respectable billionth of atmospheric pressure. This is not world-class vacuum, but it is certainly overkill for testing the various WTF-thrusters.

Inside the vacuum, the researchers use a torsion balance attached to a calibrated spring to measure thrust. They’ve got the whole thing automated, so they can level the balance, change the tension of the spring, run calibrations on the torsion bar (they have two methods of calibration), and do tests without ever opening the box. They can even rotate the thruster during the test. Being automated, they can repeat the same measurement under the same conditions multiple times and take the average. The current system is sensitive to around 10nN (nano-Newtons) of force.

………

Testing all the things

Instead of getting ahold of someone else’s EM drive, or Mach-effect device, the researchers created their own, along with the driving electronics. Let’s start with the EM drive.

The researchers used precision machining and polishing to obtain a microwave cavity that was much better than those previously published. If anything was going to work, this would be the one. The researchers built up a very nice driving circuit that was capable of supplying 50W of power to the cavity. However, the amplifier mountings still needed to be worked on. So, to keep thermal management problems under control, they limited themselves to a couple of Watts in the current tests.

The researchers also inserted an enormous attenuator. This meant that they could, without physically changing the setup, switch on all the electronics and have the amplifiers working at full noise, and all the power would either go to the EM drive or be absorbed in the attenuator. That gives them much more freedom to determine if the thrust was coming from the drive or not.

………

WTF-thruster is a magnetic WTF-thruster

And the winner is… Physics, without much doubt. Even with a power of just a couple of Watts, the EM-drive generates thrust in the expected direction (e.g., the torsion bar twists in the right direction). If you reverse the direction of the thruster, the balance swings back the other way: the thrust is reversed. Unfortunately, the EM drive also generates the thrust when the thruster is directed so that it cannot produce a torque on the balance (e.g., the null test also produces thrust). And likewise, that “thrust” reverses when you reverse the direction of the thruster.

The best part is that the results are the same when the attenuator is put into the circuit. In this case, there is basically no radiation in the microwave cavity, yet the WTF-thruster thrusts on.

So, where does the force come from? The Earth’s magnetic field, most likely. The cables that carry the current to the microwave amplifier run along the arm of the torsion bar. Although the cable is shielded, it is not perfect (because the researchers did not have enough mu metal). The current in the cable experiences a force due to the Earth’s magnetic field that is precisely perpendicular to the torsion bar. And, depending on the orientation of the thruster, the direction of the current will reverse and the force will reverse. The researchers made some calculations, based on the location of the experiment and the amplifier current, and got a torque that agreed quite well with the measured torque.

This is, of course, not the final word. But it is an excellent cautionary tale. The thrust that the researchers measured with just a couple of Watts of power was the same as that measured previously with 50W of power. And that was all due to a shielding problem. When the amplifiers are properly mounted and the shielding is in place, it will be even more difficult to detect the thrust, because the effects of noise will grow as well. I expect a flood of null results in the next year.

They also did similarly precise tests on something called, "Mach Effect Thrusters," with similarly dismal results.

Score one for physics.

There may be some ways to cheat the laws of physics, thought Lt. Commander Montgomery Scott has always been dubious of such things, as have I.

If you think that you have a breakthrough in basic physics on the macro level,^* check your experimental design and methodology.

You've probably f%$#ed something up.

^*Note that one does get seemingly "magical" results from some quantum mechanical effects, but these actually reflect the theory, they are just weird, they don't actually violate the laws of physics they follow it.

I'm With NASA on This

NASA has said that it is profoundly uncomfortable with man rating the SpaceX booster, because one of its core technologies, super-cooled propellants, would require that fuel be loaded when the astronauts are already in the capsule.

I agree.  Cooling LOX and kerosine well below their boiling point prior to loading does increase the total mass of fuel in the tank, but, because of thermal issues, this requires very fast loading immediately before launch, and as such is a menace:

When Elon Musk and his team at SpaceX were looking to make their Falcon 9 rocket even more powerful, they came up with a creative idea — keep the propellant at super-cold temperatures to shrink its size, allowing them to pack more of it into the tanks.

But the approach comes with a major risk, according to some safety experts. At those extreme temperatures, the propellant would need to be loaded just before takeoff — while astronauts are aboard. An accident, or a spark, during this maneuver, known as “load-and-go,” could set off an explosion.

The proposal has raised alarms for members of Congress and NASA safety advisers as the agency and SpaceX prepare to launch humans into orbit as early as this year. One watchdog group labeled load-and-go a “potential safety risk.” A NASA advisory group warned in a letter that the method was “contrary to booster safety criteria that has been in place for over 50 years.”

Concerns at NASA over the astronauts’ safety hit a high point when, in September 2016, a SpaceX Falcon 9 rocket blew up while it was being fueled ahead of an engine test. No one was hurt, but the payload, a multimillion-dollar satellite, was lost. The question on many people’s minds at NASA instantly became: What if astronauts were on board?

The fueling issue is emerging as a point of tension between the safety-obsessed space agency and the maverick company run by Musk, a tech entrepreneur who is well known for his flair for the dramatic and for pushing boundaries of rocket science.

he concerns from some at NASA are shared by others. John Mulholland, who oversees Boeing’s contract to fly astronauts to the International Space Station and once worked on the space shuttle, said load-and-go fueling was rejected by NASA in the past because “we never could get comfortable with the safety risks that you would take with that approach. When you’re loading densified propellants, it is not an inherently stable situation.”

(emphasis mine)

Think about Autopilot.

Also notice the next bit:

SpaceX supporters say tradition and old ways of thinking can be the enemy of innovation and thwart efforts to open the frontier of space.

Greg Autry, a business professor at the University of Southern California, said the load-and-go procedures were a heated issue when he served on Trump’s NASA transition team.

Note that Musk, and the rest of the "eBay Mafia", made their fortunes by exploiting an area of regulatory forbearance, which allowed them to operate without the (expensive) consumer protections that banks were required.

And note that Greg Autry, is a f%$#ing Business Professor talking about literal rocket science.

Launching unmanned payloads is not as much of an issue, because if Musk attempts to launch something unreliable, the insurance industry will price it into their premiums.

This is not possible with a life on the line.

I would note that even with the NASA safety standard of 1 in every 270 flights with a death, it means that you have a 50% chance of death after 186 flights, and this is what the dotcom and the business types find to be an insufficiently risk-taking culture.

Seriously, this is not ordering shoes online.

A Load of Bananas Whirling Around

It does look like whirling bananas


And the 1980s predecessor

The aviation engine manufacturer Safran is looking at an open rotor engine, which was looked at, and largely abandoned in the 1980s because of issues with noise and airframe integration issues:

Safran Aircraft Engines now has clearly plotted the technological trajectory a counter-rotating open-rotor (CROR) engine can be part of, somewhere between an ultra-high-bypass-ratio (UHBR) turbofan and a boundary-layer-ingestion (BLI) configuration. Despite wavering interest from the rest of the industry, the France-based company believes its ground demonstrator here in Istres is proving the architecture is certifiable in terms of both safety and noise. It says it would be an efficient powerplant for the 2030-35 generation of narrowbody aircraft.

The CROR concept has to be evaluated long before a commercial program is launched. It would be a greater breakthrough than the UHBR, a geared turbofan with a bypass ratio of 15. The latter could be ready in the 2025-30 time frame and is Airbus’ priority. In Safran’s view, the CROR, with its bypass ratio of 30, would be next. That would proceed an engine designed for BLI, in 2040-45.

Compared to the CFM Leap’s fuel burn, the UHBR and the CROR would be 5-10% and 15% better, respectively. Being unducted, a CROR can have a greater bypass ratio, and therefore a lower fuel burn. At Mach 0.75, the CROR would require a minor concession in speed.

………

A major challenge for an unducted engine can be found in acoustics. A witness to GE36 testing in the 1980s remembers its “dreadful” noise. And, since May, no journalist has been allowed to see and listen to an actual CROR run in Istres.

Nevertheless, Safran says the problem has been solved. The pair of propellers has been aerodynamically optimized, with thin blade profiles and complex shapes. They meet the current Chapter 14 standard, according to wind tunnel-trial results. The noise level is well below that of a turboprop, Bonini adds.

The engine is in generally form remarkably similar to the GE/Snecma engine from 30 years ago.

Both are using a fighter engine in the 20,000 lb thrust class as gas generators, and in both cases the props are being driven by counter rotating free turbines without a transmission.

It's a bit of 80s technology that never seemed to find its way into production.

Maybe this time.

Russia Slams Breaks on SU-57

It looks like it will remain largely a technology demonstrator for the next 10 years as its intended engines are developed:

The Kremlin’s new state armament plan, which will run from 2018-2027, will continue modernization of the Russian Aerospace Forces. However, while Russia will continue to buy modern combat aircraft such as the Sukhoi Su-35S Flanker-E air superiority fighter and the Su-34 Fullback bomber, Moscow is not likely to make large purchases of the fifth-generation Su-57 PAK-FA stealth fighter until after 2027.

“The Su-57 is not expected to enter into serial production until upgraded engines are ready, which is unlikely to happen until 2027,” Center for Naval Analyses senior research scientist Dmitry Gorenburg wrote in a new PONARS Policy Memo. “Over the next eight years, Russia will continue to purchase small numbers of these planes for testing.”

………

During the coming years, the Russian air force is likely to focus on addressing support aircraft such strategic airlifters and intelligence, surveillance and reconnaissance planes. Moreover, the Russians will also have to address persistent problem with their aerial refueling capabilities.

“Transport and refueling aircraft, long an area of weakness for the Russian air force, will be one area of focus,” Gorenburg wrote. “Serial production of the long-troubled Ilyushin Il-76-MD90A is expected to start in 2019, and the Russian military is expecting to receive 10-12 such aircraft per year thereafter. A light transport aircraft is under development, with prototypes expected to be completed in 2024.”

Obviously, this is not an official announcement by Russia, but it makes sense.

Refueling, transport, and AEW are significant weaknesses in the current Russian aviation forces, and their fighter force is largely recapitalized, so it's a case of focusing resources on the most obvious weaknesses.

Another Step Forward for Reaction Engines

Proposed Test Stand


Heat exchanger with miles of tiny tubes

Reaction engines, whose SSTO Skylon concept has been making the rounds for nearly a decade, seems to be getting more support, specifically, it has scored a large contract with DARPA to demonstrate its precooler engine technology:

Reaction Engines has achieved a major breakthrough in the U.S. market with a contract from the U.S. Defense Advanced Research Projects Agency (DARPA). The award covers conducting high-temperature testing of the precooler technology at the heart of its proposed hypersonic air-breathing, combined-cycle Sabre rocket concept.

Reaction has seen interest grow in the U.S. about elements of Sabre, particularly the precooling heat exchanger, ever since the concept was first independently validated by the U.S. Air Force Research Laboratory in 2015 (AW&ST Aug. 3-16, 2015, p. 63). Designed to chill airflow from over 1,800F to −240 F (1,000C to −150C) in less than 1/20th of a second, the heat exchanger is pivotal to the process of extracting oxygen from the air for use by the rocket.

However, the heat exchanger can also be used more generically to precool other engine cycles and reduce heating on engine components in high-speed flight. According to Reaction, the design, dubbed HTX, “could enable new classes of vehicles and operational possibilities.” The precooler will be tested at speeds up to Mach 5 in a new high-temperature airflow evaluation facility to be built in Castle Rock, Colorado, as a base for REI (Reaction Engines Inc.), the U.S. subsidiary of the UK-based company.

It does appear that their technology is getting funding and support, so I'm hoping to see a flight test article in the next 5 years or so.

Previous posts about Reaction Engines here.

If You Can't Beat Them, Join Them

Reverse flow operation (starts at 45s)


See also this diagram


The GE Engine

GE will be attempting to challenge Pratt & Whitney in the turboprop market, where the PT6 turboprop completely dominates the market.

Of interest to me is that GE will be copying the basic operating principals of the PT6,(paid subscription required) P&W's reverse flow operation.

The inlet is at the back of the engine, and air flows forward. This allows the compressor and the compressor turbine to be completely separate from the power turbine and prop.

While the air flow is rather more circuitous than that of a straight through engine, it has a number of significant advantages:

• No need for concentric shafts while still maintaining a two spool compressor and turbine.
• A smaller and lighter starter motor.
• More easily adopted to different power levels.
• Greater simplicity and reliability.

The PT6 has used this formula to completely dominate the market, and it looks like GE will be aping their approach, with a lot of additive manufacturing throw into the mix:

………

Then there’s the ATP, GE’s Advanced Turboprop engine (see photo, above). This is a very big deal in terms of technology and targeting.

For those cloistered monks among you, some background: Pratt & Whitney Canada’s PT6 family has reigned supreme among turboprops since, well, forever. And for good reason. The type ranges in power from 500-2,000 shp and has demonstrated rock-solid reliability through decades of operation. Its bulletproof reputation is the reason almost all single-turboprop-powered aircraft—from the Piper’s owner-flown M600 to Beechcraft’s PT-6 Texan II military trainer to the do-it-all Pilatus PC-12—are fitted with a PT-6. More than 51,000 PT6s have been produced since the engine’s introduction in the 1960s. It has been expanded to include 69 versions that power some 100 different aircraft models, including all production King Airs.

GE hopes the ATP will break Pratt’s near monopoly. Developed at the company’s “turboprop center of excellence” in Prague with a $400 million investment, this, the world’s most “printed” engine (additive manufacturing has replaced 855 parts with a mere dozen 3D-printed components)features a single-lever integrated engine and propeller control, 16:1 pressure ratio, reverse-flow combustor and output of 850-1,650 shp. The design promises 20% better fuel burn, 10% more power and longer maintenance intervals than you know what.

This is, in its own way, a tribute to the genius of the design team that first devised the PT6.

I Was Waiting for this Tech to Hit Commercial Use

We have finally seen a the first non-US commercial satellite with all electric propulsion delivered to a customer:

Eutelsat’s new 172B satellite marks a new step in the operator’s push toward widespread use of electric propulsion. Company executives believe all conditions are gradually being met to make such power both a reliable and economical option. There is more than one launcher available for this size spacecraft, a trade-off has been found between efficiency and transfer time to orbit, and an Ariane 6 feature will further reduce time to market.

Mainly thanks to electric propulsion, the weight of 172B has been limited to 3.5 metric tons (7,700 lb.) instead of 6 tons for a more conventional satellite. For that weight class, the lower position under Ariane 5’s fairing had long been the only option for launch, Eutelsat’s chief technology officer Yohann Leroy, notes. Other options that were technically feasible were not economical. Satellite operators are leery about relying on a single launcher, Leroy emphasizes, and that reluctance had stalled the advent of electric propulsion. “SpaceX’s Falcon 9 changed the game,” he says.

As a second launcher became available for the new weight class in commercial communications geostationary satellites, Eutelsat forged ahead, and in 2015 a Falcon 9 launched Eutelsat 115 West B, the operator’s first satellite using electric power for both station-keeping and orbit-raising.

The Eutelsat 115 West B was built by Boeing. But the France-based operator no longer has to depend on the U.S. industry. Thales Alenia Space and Airbus now also offer all-electric platforms, thus increasing the number of supplier options.

In 2014, Eutelsat ordered 172B from Airbus. The satellite uses Airbus’s upgraded Eurostar 3000 EOR (electric-orbit-raising) platform. “It is the first fully electric satellite not developed in the U.S.; it is a first for us and the European industry,” says Nicolas Chamussy, head of space systems at Airbus Defense and Space. Airbus was hoping to source the thrusters from Safran, in an attempt to have an entirely European spacecraft. Autonomy in space technology is a goal shared by the European Commission and the Continent’s industry.

………

Energy use onboard 172B is optimized thanks to two robot arms—two thrusters can be found at the end of each arm. Thrust can thus be precisely vectored. The axis of the thrust always goes through the satellite’s center of gravity, Arnaud de Rosnay, Airbus Defense and Space’s director for communications satellites, explains. Moreover, the arms help remove heat from the electronics hardware inside the spacecraft.

Assuming that VASIMR technology can reach a commercially acceptable state, it could provide relatively high thrust at lower efficiencies for orbital transfer, and lower thrust, and higher efficiency for station keeping, which would allow for both the advantages of Ion and Hall effect thrusters.

In either case, this promises to reduce the cost of satellites, because, much like ground round, you pay for launches by the pound.

They've Been Working This for Years

The tough part is integrating unsteady combustion in a constant flow turbine


The detonation front moves helically around the combustion chamber

Conventional turbine engines use combustors that rely on deflagration (burning).

Theoretically, if you can burn the fuel through detonation (explosions), you can get a significant improvement in efficiency.

That being said, this is hard to do, but Aerojet Rocketdyne has a new way to approach detonation technology: (paid subscription required)

For over 70 years, jet engines have powered airplanes ever more safely and efficiently. But, despite higher core temperatures and pressures, and the introduction of efficient propulsion concepts like the geared fan, conventional gas turbines may be running out of runway.

A fundamental change in the way a gas turbine combusts air and fuel in its core could open a path to a new era of jet engine development, however. Long pursued by propulsion researchers as a potential game-changing thermodynamic technology for gas turbines, the concept of pressure-gain combustion appears to be finally making headway.

………

Unlike current gas turbines in which air is compressed, mixed with fuel and combusted at a constant pressure, the air and fuel mixture in a pressure-gain engine is detonated in a wave that rapidly compresses the mixture and adds heat at a constant volume. Because detonations produce extremely high pressures, the unsteady constant volume combustion process creates pressure gain in the burner, offering potential improvements of more than 15% in thermal efficiency and fuel consumption.

But getting a detonation engine to deliver these efficiencies is extremely difficult. Despite at least two decades of experimentation with various pressure-gain combustion devices, researchers have yet to demonstrate a detonation engine that operates in a practical way, either as a means of augmenting current gas turbines or as a propulsion system in its own right.

Now, Aerojet Rocketdyne hopes to change this with the RDE. To be studied with the National Energy Technology Laboratory (NETL) of the U.S. Energy Department, the RDE is a simple combustion chamber contained in an annular ring that uses most of the compression for efficiency gains by allowing the detonation wave to propagate continuously around the curved edge of the chamber.

………

Proving the ability of the unsteady combustor to interact efficiently with the turbine is crucial to the viability of the RDE, which differs from some alternative pressure-gain concepts such as tube-configured pulse detonation engines (PDE). These configurations fire intermittently because the fuel/air mixture needs to be renewed between detonation waves. Although PDEs have been developed and even were test-flown in 2008, Aerojet Rocketdyne selected the RDE as a more promising option because it is “a very elegant solution,” says Claflin. “It has minimal moving parts and the combustion process is continuous, unlike a PDE, which has valves cycling on and off at high rates.”

Most of the work on PDEs has dealt with their being a successor to conventionally combustion ramjets, though it's rather similar to the pulse jets used on the V-1 "Buzzbombs".

The RDE comprises an annular ring with nozzles at the inlet end that inject a mixture of fuel and air axially from a high-pressure plenum. The mixture is ignited once to begin the detonation process, which propagates circumferentially around the combustion chamber. The gas expands in azimuth and axially, while the exhaust and injection systems both operate axially. Because the detonation propagates in azimuth around the annular chamber, the kinetic energy of the inflow is reduced and the RDE uses most of the compression for gains in efficiency. “It is an unsteady process, but the axial flow is continuous and we end up with very-high-power densities because of it,” adds Claflin.

I rather think that the first applications will be for stationary equipment, power plants and the like, but until we see some real complete hardware out there doing actual work, whether it's generating electricity or powering an aircraft.

Until then, I take it as a technology that is always just around the corner.

An Inside Out Wankel

The 4 Stroke Cycle for This Engine


An animation, including P-V curves

A company called LiquidPiston has a new take on rotary engine technology, they have basically turned a Wankel engine inside out, which appears to have solved the apex seal problem while improving fuel economy.

It still has ports, instead of valves, so it's also pretty simple:

Military and other operators prefer using kerosene, rather than gasoline, across ground and air platforms, but lightweight, reliable heavy-fuel engines for unmanned aircraft systems (UAS) have proved challenging to develop.

LiquidPiston, a startup developing a novel powerplant that is smaller and lighter than piston diesel engines and more efficient than gasoline engines, has been boosted by winning Sikorsky’s Entrepreneurial Challenge.

Developing multifuel rotary combustion engines based on its high-efficiency hybrid thermodynamic cycle (HEHC), the Bloomfield, Connecticut-based company has won $25,000 and the opportunity to explore applications for its X-engine on Sikorsky products.

“We are targeting our engine to be up to 10-15 times smaller and lighter than a piston diesel engine of similar power output, and up to 2-3 times more efficient than gasoline engines, especially at part-power,” says founder and CEO Alexander Shkolnik.

I think that the claims here are a bit much, but the shape of the combustion chamber is far less prone to the thermodynamic losses that bedevil the Wankel.

In a Wankel, apex seals on the triangular rotor move in and out at high speed during rotation. “The seals are impossible to lubricate, so they mix oil into the air, but 90% of the oil burns,” says Shkolnik. “In our engines, the seals are on the stationary housing and easier to lubricate.”

HEHC is a four-stroke cycle. The fuel/air mixture enters the X-engine through the rotor and is compressed and ignited. Constant-volume combustion increases efficiency. The combustion gases are then overexpanded before being exhausted through the rotor.

The overexpanded power stroke is similar to that used by the Atkinson Cycle engine used in the Prius to achieve higher fuel economy, though it appears that it does not share the rather low power density of the Prius engine (not an issue in a hybrid, as the electric motor supplies handles need for peak power).

OK, I am Now Mildly Excited

I've been hearing about the EM drive for some time.

It's a space propulsion system which requires no reaction mass or fuel.

I've been dubious, but NASA has published a favorable report in a peer reviewed journal, which means that the concept is credible on a mainstream level.

I look forward to the tests:

NASA scientists have been daydreaming about a new kind of engine that could carry astronauts to Mars in 70 days without burning any fuel. Now, in a new paper published in the peer-reviewed Journal of Propulsion and Power, they say that it might really work.

The paper, written by astrophysicists at NASA's Eagleworks Laboratories, tested a electromagnetic propulsion system, or “EM drive,” that generates a small amount of thrust simply by bouncing microwaves around a cone-shaped copper chamber. No propellant goes in, no exhaust comes out, and yet, somehow, the engine can make things move.

If you think that news sounds too good to be true, you've got good instincts — it just might be. This “impossible” fuel-less engine appears to violate one of the fundamental laws of physics.

………

That's Newton's third law of motion. It's the principle that explains why pushing against a wall will send an ice skater zooming in the opposite direction. It also explains how jet engines work: As hot gases are expelled out the back of the plane, they produce a thrusting force that moves the plane forward.

But the EM drive doesn't work that way. Its thrust seems to come from the impact of photons on the walls of the copper cavity. That would be like moving a car forward by just banging against the windshield.

………

According to the new paper, yes. The Eagleworks scientists report that their machine generated 1.2 millinewtons of thrust per kilowatt of electricity pumped in. (That electricity could come from solar panels in a hypothetical spaceship.) That's a fraction of thrust produced by the lightweight ion drives now used in many NASA spacecraft, National Geographic noted, but it's a lot more than the few micronewtons per kilowatt produced by light sails, a proven technology that generates thrust using radiation from the sun.

I'd like to see some orbital testing, and a theoretical model explaining how it works, but I am now officially intrigued.

Might Make a Faster Pig

GE's entry


Pratt & Whitney's version

Or they might make a pig with longer range.

But it will still be a pig.

The pig in question is the F-35, and the addition of a variable cycle engine might increase its performance:

The U.S. Air Force is poised to award General Electric and Pratt & Whitney contracts for adaptive cycle technology development that will pave the way toward an active procurement program for a sixth-generation fighter engine as well as the potential reengining of the F-35 Joint Strike Fighter.

Contracts for the Air Force Research Laboratory’s (AFRL) Adaptive Engine Transition Program (AETP) are expected to be valued at up to $1 billion apiece for the two engine-makers, setting the stage for a 21st-century version of the “great fighter engine war” between GE and Pratt over dual-sourced engines for the F-15 and F-16. Although Pratt now runs both key U.S. military development programs with the F135 for the F-35 and the engine for Northrop Grumman’s B-21 Long-Range Strike Bomber, AETP opens up potential competition for both the reengining of F-35s as well as proposed sixth-generation fighters for the U.S. Navy and Air Force.

AETP is specifically aimed at maturing three-stream engine technology now considered vital to achieving the high-speed, long-endurance performance requirements of the Navy’s future F/A-XX and the Air Force’s F-X sixth-generation fighters. Although it remains unknown whether the F/A-XX will emerge as a twin-engine design, the three-stream concept is designed to be scalable across a wide thrust range. The AETP is, however, targeted initially at a 45,000-lb.-thrust-class engine baselined to fit within the existing confines of the F-35A engine bay. This makes it a contender to replace the F135 from the mid-2020s onward.

………

The third stream provides an extra source of air flow that, depending on the phase of the mission, is designed to provide either additional mass flow for increased propulsive efficiency and lower fuel burn, or additional core flow for higher thrust and cooling air. It also can be used to cool fuel that provides a heat sink for aircraft systems. The third stream can also swallow excess air damming up around the inlet, improving flow holding and reducing spillage drag.

At the heart of adaptive engines are variable-geometry devices that dynamically alter the fan pressure ratio and overall bypass ratio, the two key factors influencing specific fuel consumption and thrust. Fan pressure ratio is changed by using an adaptive, multistage fan. This increases fan pressure ratio to fighter engine performance levels during takeoff and acceleration, and, in cruise, lowers it to airliner-like levels for improved fuel efficiency. The third stream, which is external to both the core and standard bypass duct, is used to alter the bypass ratio.

I think that the cooling application might be the most important.

Both the F-22 and F-35 are basically thermos bottles which rely on their fuel as a heat sink for cooling other systems, which creates issues when the aircraft sits on the tarmac too long, or when the fuel becomes hot sitting in the sun, which has the USAF repainting all their fuel trucks white.

Any potential improvement in range or performance would be important for the F-35, which is shaping up to be a major pig.

A Little Rocketry Factoid

I was reading an article about how France is looking into creating a reusable rocket engine powered by Lox/CH₄. (Methane)

I was wondering why they would go with Methane as a fuel, so I did some reasons.

These days, there are 4 basic options for launcher fuel, Liquid Hydrogen, Kerosene (RP-1), Hydrazine, and Methane.

Hydrazine has fallen out of favor for boosters, though it is still used in thrusters of various sorts. It has low impulse, and it's toxic, but the fact that it can be used as a monopropellant means that it is convenient to use for orbital maneuvering, since it requires half the parts, and you don't need to make sure that the flow of a separate fuel and oxidizer are synchronized for short the "blip" that would be needed for an orbital rendezvous or station keeping.

The commonly used propellants are LH₂ and RP-1 each have distinct advantages:

• Hydrogen has the highest impulse (fuel economy).
• RP-1 is denser, and requires smaller tanks.
• RP-1 can be stored at room temperature.

Methane falls in between Hydrogen and RP-1. It's less dense than RP-1, and more dense than LH₂, and is more fuel efficient than RP-1 and less so than LH₂.

Methane is also a lot easier to handle than LH₂, with hydrogen condensing at -252.9°C, while liquefies at a relatively balmy -161.6°C, much closer to the boiling point of LOX. (-183°C)

Additionally, for reusable and restartable engines, Methane has the advantage that it does not coke up, so recycling the engine for another use is more straightforward than RP-1.

Additionally, if you want to go to Mars or the outer planets, it is relatively trivial to manufacture or extract Methane, while manufacturing LH₂ would be extremely difficult, and manufacturing RP-1 would be nigh impossible.

So, now you know more than you want to about why a number of rocket manufacturers are looking into Methane as a propellant.

It Took Long Enough

SpaceX has finally managed to safely land a first stage on their booster:

SpaceX engineers and on-board software maneuvered the first stage of a Falcon 9 launch vehicle back to a steady, tail-down landing at Cape Canaveral Monday, 10 min. after returning the kerosene-fueled rocket to flight following an ascent explosion on a mission to the International Space Station in June.

Success in recovering the stage, after two unsuccessful attempts to land on a barge in the Atlantic, marks a major step toward the long-sought dream of reusable commercial space launchers. While Blue Origin brought its liquid-hydrogen/liquid oxygen New Shepard vehicle back from a suborbital launch to space on Nov. 23, Monday’s SpaceX recovery was the first known landing for an unmanned orbital launcher.

Silicon Valley venture capitalist Steve Jurvetson, an early SpaceX backer, tweeted “Congrats @SpaceX for landing the rocket back on land!!!! Incredible!!! One giant leap!”

The landing at a surplus launch pad on Cape Canaveral AFS, Florida, came in the middle of three significant milestones for commercial spaceflight. For SpaceX, it marked a return to flight for the Falcon 9 launch vehicle that is the linchpin of the company’s business in the near term. For its customer, Orbcomm, it completed launching of a 17-spacecraft low Earth orbit (LEO) constellation of second-generation Machine-to-Machine “OG2” satellites.

Although only a secondary test objective on the Orbcomm-2 mission, landing the Falcon 9 stage at Launch Complex 13 on Cape Canaveral — a surplus Atlas launch site designed “Landing Complex 1” by SpaceX — was a major achievement for the Hawthorne, California-based company.

I am dubious as to the ultimate significance of the reusable stage.

At least some of the potential savings is eaten up by the additional fuel that needs to be carried to fly home, as are any arrangements for a landing site, with its associated blockhouse and firefighting equipment.

We'll see.

I Did Not Think that You Could Use Roller Bearings for This

There are a number of reasons why roller bearings (ball bearings, cylindrical roller bearings, spherical roller bearings, tapered roller bearings, etc.) find use.

They provide a low drag solution, and, particularly for low speed applications, like turret rings, they tend to be the favored solution.

For higher speed applications, things like crankshaft bearings and bearings though, they are not used, because they tend to shake themselves to pieces.

Instead, fluid bearings are used, where the bearing moves with respect to the journal supported on a thin film of a fluid, typically some sort of oil or air. (Think air-hockey puck)

There is more drag in the system, but it functions at much higher speeds.

This is why you do not see roller bearings in jet enginse, at least that was why until now: (paid subscription required)

A recent development in Germany by FAG Aerospace and MTU Aero Engines could affect turbofan engine operations in three key areas: oil consumption, fuel economy and power generation.

The companies designed a main-shaft ball bearing that exceeds, reportedly for the first time, an operational speed parameter of 4 million mm/min. (160,000 in./min.)—66% greater than the 2.4 million mm/min. generated by most conventional bearings during takeoff.

At maximum speed, the bearing reportedly consumes the same amount of oil and generates identical temperatures as conventional bearings. At normal speed up to 50% less oil—6 liters/min. (1.6 gal./min.)—is needed for cooling, temperature is 25C (77F) lower and power loss drops as much as 25%.

Peter Glockner, head of product design at FAG Aerospace, attributes the reduction in oil consumption to, among other features, outer-ring cooling technology and an “integrated squeeze-film damper” that mitigates vibration load. The benefits of lower oil consumption and reduced vibration include power-loss savings, which “increase[s] the mechanical efficiency of the engine” and thus lowers fuel consumption, he adds.

The fuel savings are low: FAG Aerospace estimates the technology could save 200,000 tons of fuel annually for global turbofan fleets. In 2015, total fuel consumption for all aircraft is forecast to be up to 230 million metric tons.

Nevertheless, the technology appears to have clear engine-power advantages, and even minuscule savings add up for large operators, including the military.

Assumign that the price comes down, I would expect to see this in automotive turbocharger bearings, and (eventually) main engine bearings.

When I was in E-school, this was the sort of application for roller bearings that we were basically told, "Don't even think about it".

And now someone is trying to sell it.

I am impressed

Son of the PT6

Click for slide show

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The PT6 Bass Ackwards Air Flow


No connection between the gas generator and power turbine


Note the adjacent engines


The reverse flow prevents one engine failure from taking out another

In my pre-engineering school days, I always wondered why the Pratt & Whitney PT6 turboprop had its intake in the rear, and its exhaust in the front.

I also could not understand why this arrangement, which has the airflow reversing course was so popular. as it seemed to add a lot of complexity, as well as losses into the system.

After the my time in engineering school, I actually understood that this.

The reverse airflow scheme allowed for the use of a free turbine, where the meant that the power turbine is not attached to the compressor, etc.

It makes for a simpler layout. You don't need any concentric shafts, and starting the engine requires much less "oomph".

Well, it now looks like a very similar arrangement for advanced airliner configurations. (Yes, this is a few months old. I came across this while doing digital housecleaning)

Not bad for an engine design that is over 50 years old:

As designers of future airliners look increasingly beyond traditional tube-and-wing configurations to meet the high efficiency goals of the 2030s and beyond, new territory is being carved out in the critical area of airframe-engine integration.

Unusual features ranging from recessed inlets to pylon-mounted upper-surface engines have become familiar sights in wind tunnels, but even seasoned researchers are surprised by a new engine architecture proposed by Pratt & Whitney. The concept not only physically separates the propulsor from the gas generator, but also mounts the core backward and at an angle. This novel arrangement is aimed at overcoming installation challenges in new configurations like the D8 double-bubble airliner concept under study by NASA and the Massachusetts Institute of Technology (MIT).

Aimed at NASA’s N+3 performance goals for an airliner that could enter service around 2035, the D8 is designed to burn at least 60% less fuel than the current generation of narrowbody airliners. The secret behind this leap in performance is a configuration that clusters the engines together atop the wide tail of a flattened fuselage. Besides providing a clean high-aspect-ratio wing for low drag, this enables the engines to reenergize to slow-moving boundary layer flow over the fuselage, increasing efficiency.

But such a configuration creates several issues. The engines lie so close to the upper surface of the fuselage their fans must be sufficiently robust to cope with flow distortion from ingesting the boundary layer. Fan size will also be large because the engines envisioned for the D8 will have a bypass ratio of at least 20:1, and be targeted at extremely low noise levels of -52 EPNdb below current Stage 4 limits. Scale tests conducted at NASA of a distortion-tolerant fan developed by United Technologies Research Center show the boundary-layer challenge has been met, but other key questions remain.

Because engine cores are becoming more efficient and operating at higher pressure ratios, they are also shrinking and becoming disproportionately small compared to the propulsor section as bypass ratios increase. This leads to blade heights of 0.5 in. or less at the exit of the high-pressure compressor. At this small scale, tip clearances not only become harder to maintain, but there is little space within the core through which to run the driveshaft connecting the fan to the low-pressure turbine. Additionally, because the core is proportionately longer and thinner, designers face the issue of backbone bending which further affects clearance control.

“So that’s when we had the breakthrough idea of turning the core backward,” says Pratt & Whitney Technology and Environment Vice President Alan Epstein. Air enters the engine through the fan as normal, but instead of continuing directly into the compressor, it is ducted around the side and back of the core to enter from the opposite direction. In an arrangement similar to Pratt & Whitney Canada’s PT6, in which air flows forward through the engine, hot gas will be discharged forward through a power (low-pressure) turbine connected to the fan via a gear system. The turbine, gearbox and fan will be connected via “a really short shaft, and because the core is not connected to the power side, you can take the core off easily for maintenance,” Epstein explains.

The concept also overcomes another challenge. The idea of nested engines, as in the D8, does not meet current FAA certification criteria under the “1 in 20” rule. This states that there should be only a 1 in 20 chance of debris from an uncontained engine failure causing a second engine to fail. However, because the core and propulsor are no longer mechanically linked, “the designers have come up with an extraordinarily clever arrangement in which the cores are angled relative to each other,” Epstein says.

“We cant them at around 50 deg. and the exit from the core turns via a 50-deg. duct to go into the power turbine. So now they are more than 90 deg. off from each other. It’s simple geometry,” he says. “It enables you to have a large bypass ratio, and you are not turning much of the airflow if you are turning just the core flow, so pressure losses are low.”

I love it when advanced technology goes all retro.

I Need Some Pictures to Understand This

Click for big honking image slideshow

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Skylon
Saber Engine


Schematic of engine

Reactions Engines, the British company working on a partially air breathing cryogenic engine which would power a single stage to orbit spacecraft, Skylon, as well as a hypersonic transport, the A2.

This project has taken a major step forward with both the European Space Agency and the Air Force Research Laboratory (AFRL) have found the basic concept sound, including a heat exchanger that cools the incoming air by hundreds of degrees in a fraction of a second without choking up without being choked with frost:

It is a well-established truism in aerospace that leaps in propulsion technology almost always precede major advances in spacecraft or aircraft design.

As the clamor for affordable access to space continues to grow, there is mounting interest in the Synergetic Air-Breathing Rocket Engine (Sabre) concept under development by U.K.-based Reaction Engines. This hybrid powerplant is designed to bridge the infamous power gap between air breathers and rockets, potentially enabling a vehicle to accelerate from a standing start on the runway all the way to low Earth orbit.

Such an engine could power high-speed aircraft, suborbital craft or even multi- and single-stage-to-orbit vehicles. Even more encouraging to Sabre proponents is that, while earlier attempts to harvest oxygen from the atmosphere succumbed to thermodynamic reality, the Reaction design continues to pass muster with experts in Europe and the U.S. The company’s most recent—and possibly most valuable—vote of confidence comes from the U.S. Air Force Research Laboratory (AFRL), which analyzed Sabre under a cooperative research and development agreement.

AFRL’s validation followed a detailed study of the entire concept, particularly the precooler heat exchanger technology, which allows for the practical extraction of oxygen from the air without clogging up the mechanism with frost and ice. Reaction unveiled initial details of the methanol-based frost-control system at the American Institute of Aeronautics and Astronautics Hypersonics and Spaceplanes conference in Glasgow in early July.

AFRL program manager Barry Hellman says analysis “confirmed the feasibility and potential performance of the Sabre engine cycle. While development of the Sabre represents a substantial engineering challenge, the engine cycle is a very innovative approach and warrants further investigation.” As a result, Reaction Engines and AFRL plan to continue collaborating on Sabre, with potential follow-on work focusing on evaluation of various air-breathing-powered vehicle concepts and testing of specific engine components.

The AFRL study will also evaluate other potential uses for the Sabre’s heat exchanger technologies, including looking at broader defense applications. “The question to answer next is what benefit the Sabre could bring to high-speed aerospace vehicles compared to other propulsion systems,” says Hellman. “AFRL is analyzing vehicle designs based on the Sabre engine concept. We are also considering testing their heat-exchanger technology at Mach 5 flight conditions in a high-temperature wind tunnel.”

While AFRL acknowledges that Sabre’s original target—a single-stage-to-orbit space access vehicle dubbed Skylon—remains technically “very risky as a first application,” Hellman says: “Sabre may provide some unique advantages in more manageable two-stage-to-orbit configurations.”

………

The precooler chills the incoming air from more than 1,000C (1832F) to -150C in less than 1/100th of a second, before passing it through a turbo-compressor and into the rocket combustion chamber, where it is burned with subcooled liquid hydrogen fuel. For higher altitude operation and the jump to orbit, the engine switches to an onboard liquid oxygen supply and runs as a conventional closed-cycle rocket engine (AW&ST Nov. 26, 2012, p. 47).

What this means in the short term is not space travel, but it does mean that they are far more likely to get government and private sector funding.

Good folks at Av Week have a description of how Reaction Engines made this work, but I cannot make heads nor tails of it:

………

But after endorsement of the basic technology from the European Space Agency and, more recently, the U.S. Air Force’s Research Laboratory, the company’s synergetic air-breathing rocket engine (Sabre) concept is being taken far more seriously. Designed to power a vehicle from a standing start to Mach 5.5 in air-breathing mode, and from the edge of the atmosphere to low Earth orbit in pure rocket mode, the Sabre engine with a heat exchanger at the heart of the design is attracting widespread interest for potential application on a range of atmospheric and space vehicles.

With patents pending and negotiations with new industrial partners apparently at an advanced stage, Reaction Engines has made the surprise decision to unveil the first details of the critical technology at the core of its hybrid hypersonic propulsion system.

………

“It is pretty mind-bending stuff,” says Reaction Engines technical director and chief designer, Richard Varvill. Speaking at the American Institute of Aeronautics and Astronautics International Space Planes and Hypersonics conference here, he says the system counters the frost that precipitates out of the air as it becomes saturated with increasing relative humidity during the rapid cooling process. The precipitation “looks like the white feathery frost you’d see on a cold winter’s day. Unfortunately, that frost is sufficiently mechanically strong that it can bridge the gaps between the tubes and will block the matrix solid in about 3 sec. flat if you don’t do anything about it.

“So—surprise, surprise—we use an anti-freeze, and in this case it is methanol. But we use the methanol in a rather sophisticated way, with the objective of minimizing the amount you need. Also we don’t want to spray the methanol in and leave it in the air flow because we are actually cooling down the air to the point at which the methanol would freeze itself,” he says.

To do this, Reaction Engines has “borrowed a trick from the chemical process industry,” says Varvill. “We inject the methanol at one of the coldest points, and we effectively get the mix of water and methanol to flow forward in the matrix—against the direction of the airflow.” He concedes this seems counterintuitive, but explains the system generates an effective reverse flow by catching the water-methane mix and reinjecting it further upstream. “We have multiple injection and extraction points in the matrix, but the overall effect is the mix of methanol and water is actually flowing forward in the matrix against the airflow direction.”

The reasoning, he says, is that the condensate composition at the cold end of the matrix is nearly all methanol, and as it flows forward the methanol picks up the water. “At the inlet [of the matrix] it is nearly all water, so the composition is more methanol-concentrated at the cold end than it is at the warm end," Varvill says. "That then reduces because you have extracted most of the water at the warm end, and that reduces the absolute amount of methanol you need to throw into the pre-cooler to stop it freezing.” And because the amount of liquid water reduces so does the relative humidity. “Eventually you end up with a situation where you have extracted all the water vapor as liquid from the airflow, and that leaves you essentially with dry air below 215K. The partial pressure of the water vapor at this point is so low that you can allow it to pass through the heat exchanger and it does not freeze.”

………

Reaction Engines decided to go public on the frost-control technology because of pending patent applications. “The trigger for patenting was the awareness that to execute this program we are going to have to involve other companies,” says Mark Thomas, the former chief engineer for technology and future programs at Rolls-Royce and now managing director at Reaction Engines. “You can’t keep trade secrets very long in that situation, so it is better to be protected formally and legally on the clever stuff.”

This is all going on while the engine is moving faster than mach 5, though it is slowed to subsonic speeds (the cooling allows the system to avoid the complexities of a scramjet, the shock cone in the inlet is the tell here).

I would really like to see an animation of this, because for the life of me I cannot see how they get coolant to flow forward against that sort of air flow.

It's weird, but it is a good kind of weird.

Sorry to Harsh Your Warp Drive Buzz ………*

The reports of the EM Drive appear to be greatly exaggerated:

………

Perhaps we should take a long cool drink at this point. Let’s start with the “NASA validates” part. NASA is a huge agency, with more than 18,000 employees. The testing was done by five NASA employees in a lab devoted to exploring unorthodox propulsion ideas. The team leader is a researcher named Harold “Sonny” White, himself a proponent of ideas about faster-than-light warp drives that most of his colleagues have classified as physically impossible. The lead author is one of White’s Eagleworks teammates, David A. Brady. Calling this group “NASA”—as almost every popular news story has done—is a gross oversimplification.
till, science is science: What matters are data, not motivations or semantics. Did White et al actually validate Fetta’s version of the EmDrive? The abstract of their paper, which was presented at a propulsion conference in Cleveland, is freely available online. Reading it raises a number of red flags. The methodology description makes it unclear how much of the testing took place in a vacuum—essential for measuring a subtle thrust effect. The total amount of energy consumed seems to have been far more than the amount of measured thrust, meaning there was plenty of extra energy bouncing around that could have been a source of error.

Worst of all is this statement from the paper: “Thrust was observed on both test articles, even though one of the test articles was designed with the expectation that it would not produce thrust.” In other words, the Cannae Drive worked when it was set up correctly—but it worked just as well when it was intentionally
disabledset up incorrectly. Somehow the NASA researchers report this as a validation, rather than invalidation, of the device.

Did I say that was worst of all? I may have  take that back. In the paper by White et al, they also write that the Cannae Drive “is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma.” That last bit stopped me. What’s a quantum vacuum virtual plasma? I’d never heard the term, so I dropped a note to Sean Carroll, a Caltech physicist whose work dives deeply into speculative realms of cosmology and quantum theory.

Carroll wrote back immediately, with a pointed message: “There is no such thing as a ‘quantum vacuum virtual plasma,’ so that should be a tip-off right there. There is a quantum vacuum, but it is nothing like a plasma. In particular, it does not have a rest frame, so there is nothing to push against, so you can’t use it for propulsion. The whole thing is just nonsense. They claim to measure an incredibly tiny effect that could very easily be just noise.” There is no theory to support the result, and there is no verified result to begin with.

………

That’s part of why this space-drive story bothers me so much. Abandoning known science when it feels good to do so is a dangerous proposition. As Carroll later tweeted, “The eagerness with which folks embrace sketchy claims about impossible space drives would make astrology fans blush.” I am personally a huge space enthusiast; I would love to see a new type of propulsion that would make it easier to explore the universe. But having your heart in the right place is no excuse to walk away from normal critical thinking. It is not materially different than the approach of people who reject science when they don’t like what it says about climate change, vaccines, or genetically modified organisms.

(Emphasis Mine)

Let's be clear here:  The tests are dubious, the detected "thrust" being, "Between 30-and-50 microNewtons, where the limit of the measuring device is 10-to-15 microNewtons," which makes the setup vulnerable to subtle errors and confirmation bias.

I am not saying that it's true, but I am saying that we don't have even the vaguest model to describe this phenomenon, and the scientific method requires skepticism, and this sounds like the Pons and  Fleischmann cold fusion fiasco of the late 1980s.

There needs to be a lot more testing, and some theories that could actually reliably predict the results, before we should start buying Star Trek uniforms.<sup>†

*</sup>Actually, I do want to harsh your buzz. Seriously. This appears to be complete bullsh%$, or at least irresponsibly immature, and I can feel virtuous by shooting it down.
^†On my part, I will not be buying a Star Trek uniform. As an engineer, I would be wearing a red shirt. I do not like those odds.

Interesting Development in Ion Drives

Iodine looks promising as a replacement for Xenon for the propellant in ion drives: (paid subscription required)

A high-efficiency radio-frequency (RF) ion microthruster in development could give engineers another approach to solar-electric propulsion (SEP) technology for deep-space exploration, particularly for the tiny CubeSat-based probes just coming into their own.

While large-scale SEP is considered necessary to preposition supplies on Mars for human explorers, work is underway at NASA and in universities on CubeSat-class missions to the Moon, Mars and other deep-space destinations as well. Of particular interest is SEP technology that uses iodine as a propellant instead of xenon.

Iodine is easier to integrate into spacecraft and costs much less than the xenon typically used today. Although they sit next to each other in the periodic table, iodine is a solid that sublimates into a useful gas at relatively low temperature, while xenon in its ambient state is a gas that must be contained in a pressure vessel.

Busek Co., a privately held 50-person space-propulsion business in Natick, Massachusetts, has just demonstrated an RF gridded-ion thruster that uses iodine as a propellant and measures only 3 cm across. With iodine, the “BIT-3” thruster demonstrated a specific impulse of 3,500 sec. and a thrust measured at more than 1.4 mN. Designed to propel advanced CubeSats from geostationary to lunar orbits, using 60 watts of power it can generate a Delta-v (velocity change) of 2.5 km/sec. (1.5 mi./sec) with 1.5 kg (3.3 lb.) of fuel in a 13-kg spacecraft, the company says.

“Iodine is a substance that is stored as a solid on a spacecraft, because it has very high density,” says Vlad Hruby, founder and president of Busek. “It also stores in small volume, in a zero-pressure tank. That means the tank can be conformal. You can stick it anywhere in the spacecraft, wherever you have space, and then you heat it up a little bit and it generates enough available pressure to feed [the propulsion system].”

Busek also has used iodine as a fuel in Hall-effect thrusters, and holds NASA small-business contracts for advanced technology development work aimed at deep-space smallsat SEP. The BIT-3 approach uses an RF coil to ionize the sublimated iodine gas, and electrically charged grids to accelerate the ions to the high velocity needed.

While the Hall thrusters are good for “Earth-centric” missions, the efficiency of the gridded-ion thruster makes it more attractive for deep-space applications.

“They have different niches, really,” says Michael Tsay, chief scientist on the BIT-3 project at Busek. “The Hall thruster has very high thrust to power, so you can get higher thrust, but with slightly lower Isp [specific impulse]. The RF ion can give you very high Isp, but you get lower thrust. So it’s mission-dependent.”

For either application, iodine has another advantage over xenon that makes it more attractive as a secondary payload. Since it doesn’t require a high-pressure tank, iodine is safer and less likely to damage a high-priced primary payload if something goes wrong.

………

“It eliminates the need for a high-pressure tank, and it stores more compactly, so it takes up less volume,” says Andrew Petro, NASA program executive for the Small Spacecraft Technology Program within the STMD. “Those two features are especially important because of the small size of the small satellites we are trying to develop.”

………

Iodine has advantages for small satellites, including much lower cost as industry finds new uses for xenon in fields as disparate as photography flashes and surgical anesthesia. But it may not be as scalable as xenon for the large-scale, multi-kilowatt applications NASA’s human-spaceflight engineers are pushing as a way to move habitats, cargo carriers and other large payloads toward Mars (AW&ST June 23, p. 44).

“The challenge with iodine is feeding the propellant,” says Petro. “With the xenon gas it is very simple; it’s a pressurized gas, It will come out through a valve if you open it. The iodine has to sublime into a gas and be fed, and the larger amount of it you have, the more challenging it might be to engineer a tank that will feed that propellant in a consistent and reliable way. It certainly is possible, but it will probably take some more engineering to work that out. I haven’t really seen much. I think the real attraction of the iodine is in the smaller spacecraft, because they already have the problem of limited volume. It is not as much of an issue for the bigger spacecraft.”

Iodine sublimates at 113.7° C, and being a halogen, it is rather corrosive, but I don't see these as particularly daunting engineering issues in implementing an iodine based system.

First, You Eliminate the Competition, Then You Refuse to Release Price Data for Competitive Reasons

I knew that the taxpayers would come to regret cancelling the alternate engine for the F-32, the F136, but I did not expect it to happen so soon:

After a long battle to edge rival General Electric out of the F-35 engine market, Pratt & Whitney succeeded in 2011. GE announced it would shelve the F136 after the Pentagon refused to fund it for four years, leaving Pratt in the coveted position of a sole-source engine supplier for the largest international fighter program ever.

Three years later, though, Pratt states that its position with its F135 engine is so potentially competitive it cannot comply with the customer's request to publicly share the target contract pricing data. At issue is Pratt's hope for more government funding by garnering a piece of a $1 billion next-generation fighter engine. Although proposed by the Pentagon, this program has yet to be funded by Congress.

“We have already made significant progress in advancing this technology and anticipate a competition will be held to develop this engine. Releasing engine pricing and cost data on the F135 would impact our ability to compete for this potential next-generation fighter engine program,” says Pratt spokesman Matthew Bates.

Senior Pentagon officials have, however, been urging Pratt to release at least some data in a transparency push for the highly scrutinized F-35. Bates cites a 40% drop in engine pricing since the first low-rate-initial-production (LRIP) lot in 2006. But the rate of cost reduction “slowed down when [Pratt] got the monopoly,” said Rear Adm. Randy Mahr, deputy program manager of the F-35. “We are trying to get that information out . . . But, I can't force somebody to go ahead and report something that by law they are not” required to report. Mahr made his comments at the Sea Air Space 2014 conference here this month. “This is a subject of legal debate but the Department of Defense feels this information should be in the public domain,” according to one defense official who requested to talk on background owing to the sensitivity of the issue.

The last known engine price for the F135 was cited by Air Force Lt. Gen. Christopher Bogdan for the third lot. The F-35A/C propulsion system cost $14 million. The F-35B, which includes a Rolls-Royce lift-fan designed for short takeoff and vertical landing, cost $38 million. He is frustrated at Pratt not bringing down F135 costs as predicted. “Pratt is not meeting its commitment,” Bogdan says. “It is as simple as that. Some of their business base has dried up on other programs and projects [and] they are spreading them right where they can, and I don't like that.”

Pratt & Whitney has declined numerous requests from Aviation Week over many months to release either its pricing data or its contractual cost targets.

I predicted that the long term budget consequences of eliminating the 2^nd engine would be negative, and that the F-35 advocates' desire to lower front end costs would be swallowed up by the price increases resulting from creating an engine monopoly.

Cessna Jumps on the Diesel Band Wagon

They will be putting a diesel in the model 182 Sklylane: (Paid Subscription Required)

While avgas consumers and suppliers fret over the future of their leaded fuel, Cessna is partially weaning itself of that toxic brew by equipping its popular Model 182 Skylane with a Jet A-burning diesel engine. Others are likely to follow.

Unveiled at the Experimental Aircraft Association's recent annual gathering in Oshkosh, Wis. (see p. 35), the Turbo Skylane JT-A (photo) is fitted with the new SR305-230E engine built by SMA, a subsidiary of Snecma of France. The four-cylinder, 227-hp powerplant is already certificated by both the European Aviation Safety Agency and FAA , and Cessna hopes to begin deliveries of its newest model in early 2013.

While Austria's Diamond Aircraft has been producing aircraft powered by Austro Engine diesels for several years, the entry into that market by the much-larger Wichita aircraft maker with wide name recognition and a global support network is significant and likely to find favor, particularly in lesser-developed regions where avgas is scarce and expensive. Visitors at the Oshkosh introduction told Cessna personnel that the per-gallon price of 100LL avgas at some remote locations had topped $22.

Austro is a former Diamond Aircraft subsidiary (they spun it off) founded to replace the Thielert engine after that company's implosion.