Tag: Propulsion

And the UDF is Back

If you followed avaition in the 1980s, you probably remember GE’s GE36 Unducted Fan

It was an F-404 derived core powering counter rotating free turbines attached to props.

There is now a Safran And GE are working another version of what was fondly referred to a load of bananas whirling around.

With sustainability front and center on the aerospace industry agenda, plans are firming up on both sides of the Atlantic for a new wave of ambitious large-scale technology demonstrators to pave the way for ultraefficient next-generation commercial airliners.

Ranging from advanced propulsion and airframe concepts to new systems, structures and fuels, the main demonstrators will form part of the proposed Clean Aviation initiative in Europe and the next round of NASA X-plane projects in the U.S. Clean Aviation, which is expected to succeed Europe’s long-running Clean Sky program, supports the European Union’s broader Horizon Europe research and innovation framework effort for 2021-27 and will feed technology into new civil aviation projects later this decade and into the 2030s.


Open rotors, also known as unducted fans or propfans, were initially developed in the U.S. in the 1970s and 1980s amid concerns over rising fuel costs. Although two concepts—GE’s GE36 and the Pratt & Whitney/Allison 578 DX—were flight-tested, both were shelved by the early 1990s after oil prices fell. Although development of propfans continued in Russia, it was not until greenhouse gas emissions became a legislative factor in the 2000s that Western interest in the concept was revived.

In the U.S. NASA, GE and the FAA collaborated between 2009 and 2012 on wind tunnel tests of an open rotor with blades developed using modern computer-based design methods. The tests showed up to a 3% improvement in net efficiency relative to the best 1980s design, while nominally achieving a 15-17-EPNdB noise margin to Chapter 4 limits.

Around the same time, two open-rotor concepts were evaluated in Europe under the SAGE effort, with a Rolls-Royce-led team evaluating a direct-drive propulsor system while a Safran-led group developed the geared pusher CROR. The Rolls project was later rescoped to focus on lean-burn combustion, while Safran developed a CROR ground demonstrator using its M88 military engine as a gas generator.

So the direct drive free turbine is not a part of the equation this time around, which is kind of a pity.

 I liked the elegance of that arrangement.

Interesting Tech

Solid fuel for ramjets and rockets is generally some sort of plastic or rubber, oxidizer, and powdered aluminum.  (The devil is in the details, don’t try this at home)

A new technology involving replace the aluminum particles aluminum-lithium alloy particles.

It prevents the formation of large aluminum droplets and corrosive combustion by-products: (paid subscription required)

A Purdue University spinoff will test an improved propellant for solid-fuel ramjet propulsion systems in hypersonic weapons under more than $1.1 million in contracts from the U.S. military.

Adranos is developing a solid rocket fuel, called Alitec, which uses aluminum-lithium (Al-Li) alloy powder instead of aluminum in the propellant mix, increasing fuel efficiency and reducing corrosive effects.


Aluminum powder is used in solid propellants as an additive to increase their density and combustion temperatures and stabilize the burn. But the metallic fuel forms large molten droplets that burn slowly. This results in a performance loss of up to 10%, which prevents a rocket from realizing its full range and payload capacity. The fuel also emits hydrochloric acid, which damages the environment and corrodes launch equipment.

Aluminum-lithium fuel has demonstrated increased performance through better combustion and higher efficiency. The large difference in boiling points between aluminum and lithium causes microexplosions of the metallic drops, reducing agglomerates. In addition, Al-Li virtually eliminates hydrochloric acid production while also improving theoretical specific impulse. Adranos calculates that Alitec could increase missile range by up to 68% and booster payload by 65%.


The latest contracts have been awarded by the Army’s Aviation and Missile Center and the Defense Department’s Rapid Reaction Technology Office. Under the contracts, tests at Purdue’s Zucrow Labs will use a heated air system capable of simulating a Mach 4 flight environment to determine Alitec’s functionality within a solid-fuel-ramjet hypersonic propulsion system.


Today in Neat Tech

Reaction Engines’ precooler has successfully run at Mach 5 temperatures, validating for the first time the capability of the novel heat exchanger design to operate at hypersonic flight conditions for atmospheric and space access applications.

The breakthrough test is pivotal to Reaction’s goal of using the lightweight heat exchanger (HTX) to boost high-speed turbojets for supersonic and hypersonic vehicles as well as for developing the company’s Synergistic Air-Breathing Rocket Engine (Sabre), which is targeted at low-cost, repeatable access to space.

Forming the culmination of a DARPA contract awarded in 2017, the Mach 5 run took place in the second week of October at the company’s TF2 test facility at the Colorado Air and Space Port near Watkins. Established on an all-new site just 22 months ago, the high-speed test comes seven months after the heat exchanger demonstrated operation at supersonic conditions equal to Mach 3.3. Heated air for the tests is generated by a General Electric J79, which operated at military power for the supersonic runs and in maximum afterburner for the tests up to Mach 5.


The precooler is made up of 16,800 thin-walled tubes (equal to more than 27 mi. of tubing) through which helium is pumped to remove heat. In the Colorado tests, the heat is rejected into water that boils off to the atmosphere, but in a Sabre it would be cooled by a hydrogen heat exchanger. “In the Mach 5 test, the temperature was reduced from around 1,000C to roughly 100C in less than 1/20th of a second,” says Dissel.


For high-speed turbojet applications in the nearer term, the HTX significantly reduces compressor delivery temperature (T3). This maintains sea-level conditions in front of the compressor over a wider range of speeds, thus maximizing net thrust. For space access applications, the HTX will pass chilled air to a turbo-compressor and into a rocket thrust chamber, where it will be burned with subcooled liquid hydrogen fuel.

I find this technology really cool.

While right now, they are testing with liquid hydrogen fuel for launches to orbit, I’m think that liquid methane would likely be used for any potential hypersonic transport or air breathing weapon.

Something Bad Happened Near Severodvinsk

In Russian

There was some sort of event, involving a significant release of radiation, at the Nenoksa naval base:

On the morning of Thursday, August 8, something exploded at the Nenoksa Naval Base in Russia, not far from the city of Severodvinsk. This article is a good summary of what we knew by Friday. Since then, the Russian government has said that a radioactive source was involved in the explosion, along with liquid rocket fuel. Reports have gone back and forth on whether radiation detectors in Severodvinsk detected anything. Five more people have been reported dead. Sarov/VNIIEF, one of the Russian nuclear weapons laboratories, has released a statement, which some folks are rushing to translate.

The translation that I have seen of this video shows it not to be particularly informative, but it does reveal that there was an incident, and there were fatalities.

The New York Times coverage is similarly anodyne, though it does reveal a spike in radiation, albeit one that stays below recommended limits, at a nearby town.

The indications are that this is not a nuclear warhead, both Russian and US nuclear warheads have been designed to survive things like a rocket motor explosion, so it would imply that it was a test of some sort of nuclear propulsion system, along the lines of the 9M730 Burevestnik nuclear powered cruise missile announced by Putin last year.

What is DARPA’s Endgame Here?

Nuclear thermal rockets typically have around twice the Isp (basically fuel economy) of chemical rockets, on the order of 800—1000, which is a lot less than than electric propulsion, which is typically ten times that of chemical rockets, but the available thrust produced is far greater, 100-1000 kilo-newtons for nuclear thermal vs. 10-500 milli-newtons for the various electric rockets.

For longer missions, Mars and the further, it’s clear that electric propulsion is better and faster, so the only applications that I see are some sort of manned moon base, or an as yet undisclosed military mission:

DARPA plans to demonstrate a nuclear thermal propulsion (NTP) system that can be assembled on orbit to expand U.S. operating presence in cislunar space, according to the Pentagon advanced research agency’s fiscal 2020 budget request.

The agency is seeking $10 million in 2020 to begin a new program, Reactor On A Rocket (ROAR), to develop a high-assay low-enriched uranium (HALEU) propulsion system. “The program will initially develop the use of additive manufacturing approaches to print NTP fuel elements,” DARPA’s budget document says.

“In addition, the program will investigate on-orbit assembly techniques (AM) to safely assemble the individual core element subassemblies into a full demonstration system configuration, and will perform a technology demonstration,” the document says.

In a nuclear thermal rocket, propellant such as liquid hydrogen is heated to high temperature in a nuclear reactor then expanded through a rocket nozzle to produce thrust. Propulsive efficiency, or specific impulse, can be twice that of a chemical rocket.

Given the advances in electric propulsion, I do not see where nuclear thermal will have an advantage, except possibly for supplying a moon base or some as yet undisclosed military program.

Wicked Bad Day at the Office

Look to the left

The moment it goes pear shaped

We now have video of the Soyuz failure, and it was booster separation that caused the mishap:

On Thursday, Russian space officials held a news conference to lay out their findings into an October 11 accident that involved the launch of a Soyuz FG rocket and its spacecraft. The crew of NASA astronaut Nick Hague and Russian cosmonaut Aleksey Ovchinin escaped safely, but the rocket was destroyed.

The problem, the officials said, boiled down to a “bent” sensor on one of the rocket’s four boosters that failed to properly signal stage separation. This caused one of the booster stages to improperly separate from the rocket, which can be seen in the video released by the space agency. This booster then struck the core of the rocket, causing a significant jolt and triggering one of the Soyuz spacecraft’s automatic escape systems.

According to the officials, the sensor rod was bent by a little more than 6 degrees, and this happened during assembly of the rocket. The Russian space corporation, Roscosmos, has classified this as a handling error. To fix the process, Soyuz rockets already assembled for launch with their booster packs will be disassembled and reassembled to assure that similar mistakes have not occurred.

It should be noted that, by the standards of man-rated boosters, the Soyuz is quite safe, and the escape system functioned as it should have.

Still, a bummer for the astronauts/cosmonauts and ground crew, no doubt.

One Way to Deal With Limited Launcher Capacity

Israel is working to sharpen its eyes in space, enlisting Israel Aerospace Industries (IAI) to improve the optical and radar payloads of the spy satellites serving the nation’s intelligence community.

The company is developing a new generation of satellites for even more complex missions, using nanosatellite production and electric propulsion concepts.


In addition to the imagery, Doron says the low weight and a unique set of reaction wheels in IAI’s satellites enable them to capture more usable images of an area of interest in every pass. Special reaction wheels also enable Israeli satellites to carry a smaller amount of hydrazine gas, usually used to enable the satellite’s maneuvers in space and to keep it at the designed altitude.

An ion thruster or drive is a form of electric propulsion used for spacecraft. It creates thrust by accelerating positive ions with electricity for satellites with optical and synthetic aperture payloads. The resolution will be improved, and the way the images are processed on the ground also will be enhanced with very advanced ground stations.

Reaction wheels are basically gyroscopes, and it means that there is no propellant expired to change orientation.

They are also looking at adding electric propulsion for orbital maneuverability:

To further prolong the life of full-size Israeli satellites, the division is evaluating the use of electric propulsion to replace the use of hydrazine. The system will use xenon gas to operate on thrusters, he says. According to Doron, the use of xenon will enable the satellite to orbit the Earth at a lower altitude but give it enough power to correct any loss of altitude that will be caused by greater friction with the atmosphere.

An ion thruster or drive is a form of electric propulsion used for spacecraft. It creates thrust by accelerating positive ions with electricity for satellites with optical and synthetic aperture payloads. The resolution will be improved, and the way the images are processed on the ground also will be enhanced with very advanced ground stations.

An ion drive provides much less thrust than a rocket or a thruster, but it’s ISP (basically fuel economy) is far greater, with about 250 seconds for a thruster, and 3000 seconds for an ion thruster, which means a lot more delta-V with a lot less propellant, which means greater maneuverability and greater time on station.

I’m Kind of Dubious of This

Blah, blah, blah!

The German research lab Bauhaus Luftfahrt is proposing replacing the high pressure turbine and combustor with a piston engine.

It sounds like a step beyond the turbo-compound engines that were the final stage of piston engines before jets took over.

The reason that I am dubious is for the same reason that turbines beat out pistons for at that time: Maintenance costs.

Even a first generation turboprop would deliver 10 times the time on the wing, which outweighed the much higher fuel economy of a piston engine, at least at higher power levels.

Still, it is an interesting technology:

The Composite Cycle Engine (CCE) concept incorporates piston engines into the core of an aircraft turbo engine. The piston engines increase thermal efficiency by using non-stationary isochoric-isobaric combustion, which enables higher peak pressures and temperatures within the core engine. In the current design, the piston engine is connected with the high-pressure spool and powers the axial-radial high-pressure compressor. The low-pressure system is similar to a conventional geared turbofan (GTF) architecture. This way, the outstanding power-to-weight ratio of low-pressure turbines can be fully utilised and an ultra-high bypass ratio is realised. Assuming an entry into service in 2050, fuel burn improvements up to 50 per cent relative to year 2000 turbofan technology (11 per cent relative to year 2050 advanced GTF technology, respectively) can be reached. 

In fact, pistons have better fuel economy to this day, though the fuel is harder to find, and you really don’t find aviation piston engines at the higher power levels of turbines.

I could see this being applied in some areas, expendable drones and the like, and possibly private aircraft, where the additional range might be more significant than the engine time on the wing.

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

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.