Frank Møller came to Raufoss in 1984. Before that, he had been a chief engineer on a Royal Norwegian Navy submarine. Looking back to his first years at the Nammo Test Center, he feels the advances in rocket motor technology have been great. But things have not really slowed down since those early days. Frank is still part of a development team, and their work could result in new technology with a potential to revolutionize missiles.
“I like to joke that we make “fire-and-forget missiles”, while the HR department could do “hire-and-forget”, Frank Møller says, smilingly.
“Hire and forget, indeed! You do realize you’ve stayed almost 40 years in the same place?”
“I planned on staying for two or three years, but I am still here. Most people who come here like the company, and tend to take root. So did I. I like my colleagues, and in some ways the work is more exciting than before”, says the veteran.
From ammunition to early rockets
Norway’s rocket motor production has its roots in the years just after World War 2. The weapon system “Terne” was at that time developed in cooperation between FFI (the Norwegian military research institute) and U.S. Navy. Terne was an anti-submarine system in use from the late 1950s until the early 1970s. The system was based on rocket propelled sinking mines and became the foundation for further Norwegian technological development in the propulsion field. The Raufoss ammunition factory became the hub for this work.
With all its technological know-how in the propulsion field, Nammo soon became involved in the Sidewinder AIM-9 air to air missile. If we count all the various versions of the Sidewinder, no other system has been produced in larger numbers. A key production technique was the extrusion of the propellant powder. The experience with both missiles and production techniques lay the foundation for the many other systems Nammo later got involved in, like AMRAAM or EXOCET. When Nammo was established in 1998 through the consolidation of Nordic defense companies, Raufoss was still the hub for rocket motors.
Simple constructions – at least in principle
After a year and a half at the Test Center, a couple of years doing security analysis and statistics, Møller changed to rocket motor development. There, he rose through the ranks and was selected to head the development programs. One of the projects he was responsible for, was the propulsion system for the Penguin mk 2 mod 7 naval missile (launched from helicopters). And in the years after that, many other rocket motor systems, including rocket systems for the European Space Agency (ESA) and their Ariane program. Among his latest endeavours on the military side is work for the NATO-led ESSM missile program.
“Just try to visualize a balloon which you’ve blown up and then let go. That’s a rocket motor right there. It becomes a tube with an opening on one end, and there’s energy in the form of pressure in it.”
You know, rocket motors are really very simple constructions, at least in principle
While a balloon can be a decent illustration of how a rocket motor works, it is not exactly ready to be used in combat at a few times the speed of sound.
A modern rocket motor must endure extreme stress: Not only must it withstand conditions varying from warm summer temperatures on the ground to 50 degrees Celsius below zero when it’s mounted underneath a plane wing. It will also be subjected to the high burn temperatures when the rocket motor fuel is ignited, those can reach 2-3000 degrees. Strong G-forces are normal as well, and on top of that, a missile must be able to maneuver.
“In a rocket motor, the component materials are pushed to the limits. From an engineering standpoint, the materials and the propellant take centre stage”, Møller says.
New propellant technology
In the late 1970s, various NATO Air Forces acquired the new F-16 fighter jet. The new plane itself was a significant upgrade, but also brought technological change to many of its subsystems. The missiles were affected, and where older rocket motors had been powder driven, the new generation used a cast composite fuel type.
The new rocket fuel was more demanding to work with, since even a miniscule bubble or irregularity could lead to major safety issues such as explosion risk.
“At the time, this was a completely new technology. But as time passed and our experience with it increased, it has been gradually improved. Today, cast composite fuel is our workhorse solution for both missiles and space rockets”, Møller says.
One problem is that most such fuel types contain significant amounts of ammonium perclorate. When the rocket fuel burns, it releases hydrochloric acid.
“Hydrochloric acid is a less than ideal waste product, as it is both corrosive and toxic. In a time where we see increased activity in both the military missile sector and the space sector, we need to find better solutions”, Møller says.
Rocket motors for the future
Luckily, Frank Møller is part of a Nammo team working on something that might be just that – a better solution. The concept – known as ramjet – is about as old as it gets in the aviation world. French engineer René Lorin filed a patent for a subsonic design back in 1908. Another french aviation engineer, Rene Leduc, continued his research and eventually built several ramjet-powered planes (known as the Leduc planes). These would fly test flights in the late 1940s and throughout the 1950s.
Several aspects of these ramjet planes were very promising. For example the Leduc 0.22 had an astonishing climb rate: 39.000ft per minute. No jet planes in existence at the time could compete (the contemporary US F-100 jet fighter plane could climb at 16.400ft per minute). Even today, the Leduc would climb only slightly slower than, say, an F-16. But even with these promising prototypes, more conventional planes would be chosen by militaries around the world.
– In a ramjet, the oxygen that is needed for combustion is taken from the air. It is driven through air ducts at high speeds, compressed, heated, and becomes part of the combustion process, Møller explains.
The ramjet concept is simple, and maybe obvious in some ways. And building a working ramjet? Definitely doable, even 70 years ago. But getting it to work well? Almost impossible. Conventional rocket motors or jet engines were just easier to make.
Building a working ramjet? Definitely doable, even 70 years ago. But getting it to work well? Almost impossible.
Efficiency has long been the key factor. Until now, getting to that peak potential is a feat no-one has achieved. And then there are the practical questions: How do you make an efficient ramjet plane if the motor needs very high speeds to even start operating? How do you land such a plane safely?
On the missile side the ramjet troubles were less pronounced. Successful 1950s and 1960s designs such as the UK Bloodhound and Sea Dart missiles or the RIM-8 Talos missiles all worked well. But so did conventional designs.
“Cast composite rocket fuel became the workhorse technology powering both missiles and spacecraft. Solid fuel ramjets were at times something exotic, half-forgotten. So were liquid fuel Ramjets, only even more complex and expensive. Many engineers probably saw the potential, but still ended up using more standard concepts”, Møller says.
Massive performance increases
However Møller feels that this type of propulsion may have plateaued now – with further major efficiency gains unlikely.
“As I see it, conventional rocket motors have two problems. Firstly, they release hydrochloric acid as part of the combustion. Secondly, getting much more performance from them seems unlikely”, Møller explains.
Ramjet technology may, on the other hand, still offer very substantial performance increases.
“Our testing so far indicates ramjets can massively outperform conventional rocket motors. Additionally, missiles built around ramjets will be more maneuverable. And last but not least: no hydrochloric acid emissions”, Møller says.
He also believes Nammo engineers are finally on the treshold of unlocking the true ramjet potential.
“The combustion has always been a problem. No-one was really able to control it well. But with new tools, we can do just that today. At around mach 3, we are seeing just the right pressure and temperatures. Armed with new analysis tools, we can also optimise any other aspect of the rocket motor.”
As much as 80% of current rocket fuel is oxidiser (solid oxygen). Just 20% is actual fuel. With an optimal combustion process, one could remove the oxidiser entirely from ramjets.
“Obviously, if the amount of fuel is increased from 20 to 100% – that’s a win. How do you use all that extra propulsive energy? Range – much more range – could be one answer. I believe the ramjet is the rocket motor of the future. And it’s not a far-into-the-future concept. We are going to demonstrate long range flight this year, in 2022, Frank Møller states.
Our testing so far indicates ramjets can massively outperform conventional rocket motors.
A new paradigm in warfare
If ramjets are successful, what implications will we see on the battlefield? Møller believes artillery could see drastic changes. Gun-fired ramjet projectiles could massively extend artillery range – possibly well beyond 100km. If combined with precision or guiding systems, some artillery projectiles could end up looking more like missiles.
Then again, if ramjet motors become widely used in missiles, they too might change. More range, higher altitudes and the ability to strike an opponent while out of his range are all likely.
“Ramjets can increase missile range by several times. In addition, I believe we’ll see more maneuverable missiles. The tactical and strategic potential? It’s hard to say, but it could be very significant. Maybe we’ll see foundational changes to NATO and US air defense paradigms? In any case: The work on ramjets will come almost last in my career, but could still define it. During these decades, we always thought we were really successful if we could improve a system by a few percentage points. Now we see a hundred times that. This is a once in a lifetime-thing”, I believe, Frank Møller concludes.