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September 2, 2021

Reaching Low Earth Orbit on Short Notice with Aevum’s Ravn X

The Aevum Ravn X autonomous launch vehicle

Space missions typically have long lead times. If you want to launch a payload into low Earth orbit, you have to find a place on a rocket that is due to launch months or years in the future.

Aevum, Inc., a member of the Ansys Startup Program, plans to change all that with low Earth orbit autonomous transport services that can be ready for takeoff in as little as three hours.

Jay Skylus, founder and CEO of Aevum, realized that there was no way to quickly respond to the need for supplies to cope with a natural disaster somewhere far away on Earth, or to rapidly deploy a surveillance satellite to better understand the dangers of a military situation anywhere around the globe. In these cases, waiting months or years to hitch a ride on a scheduled rocket simply isn’t fast enough.

It was clear that limited access to space was stifling technologies that could save millions of lives. Spurred in part by having a brother in the military, Skylus resolved to democratize the access to space by founding Aevum in 2016. Four years later, on Dec. 3, 2020, Aevum unveiled the world’s largest UAS (by weight), its Ravn X autonomous launch vehicle. Aevum has been selected by the United States Space Force for its Agile Small Launch Operational Normalizer 45 (ASLON 45) mission. ASLON 45, which is designed as a building block toward responsive launch, calls for the launching of multiple 3U and larger U.S. government cubesats into low Earth orbit at a 45-degree inclination. Ravn X is designed to launch in as little as 180 minutes from the initial order to launch.

Realizing early on that simulation would be needed to design the system he had in mind, Skylus discovered the Ansys Startup Program through Ansys’ Elite Channel Partner, Simutech, which makes Ansys simulation software available to startups for a fraction of the list price.

“Being able to generate analysis results to justify the margins of safety for different components of Ravn X using Ansys simulation software was very helpful,” says Ovidiu Mihai, Chief Engineer at Aevum. “We would not have been able to do that without the Ansys Startup Program.”

The autonomous drone is only the first stage of a three-part system. It carries a two-stage rocket underneath it.

It’s a Plane, It’s a Rocket … It’s Both

The Ravn X autonomous drone looks like an airplane, and it can take off like one from a runway as short as 1 mile long. It can launch and land at many locations on the planet, including a farmer’s field near a disaster site or battle zone, making it versatile for quick deployment wherever help is needed.

But this autonomous drone is only the first stage of a three-part system. It carries a two-stage rocket underneath it, which is activated in the air when the drone has reached a velocity of roughly 650 mph at an altitude of about 60,000 feet. The rocket drops away and ignites the kerosene-liquid oxygen engines of the second stage, while the 100 percent reusable drone flies back to the landing strip and parks itself in the hangar, ready for reuse.

The second stage accelerates the rocket, then the third stage, carrying a satellite or other payload, separates from the second and fires its engines to reach escape velocity (over 17,000 mph) to put the payload into low Earth orbit. The third stage might contain a cargo module that carries 264 smaller drones for personalized delivery of much needed supplies to devastated areas on Earth.

Designing the Ravn X

Aevum’s design scheme from the start has included minimizing risk, maximizing flight efficiency and leaving no space junk behind.

“By operating autonomously, there's no risk to human life,” says Mihai. “The ignition of the rocket engines and the actual rocket flight happen far away from human beings, unlike traditional rockets that lift off from a launch pad on land.” And there are no humans onboard who might be at risk if something goes wrong in space.

Additionally, by removing a human pilot from the launch equation, Aevum can take full advantage of the laws of physics and has designed Ravn X for optimum efficiency, which include significant fuel savings. Unlike other horizontal launches, where the plane acts like a carrier vehicle, Ravn X operates as a true first stage, contributing delta V, to the rocket’s momentum. Delta V is the difference between the initial velocity and the final in-orbit velocity.

Ravn X is currently subsonic, though there are future plans for supersonic options. Finally, Aevum is determined to be a steward of the low-Earth orbit environment.

“Our end goal is that every system of the Ravn X will be reusable,” Mihai says. Right now, the first stage drone is 100 percent reusable, and the two stages of the rocket are designed to burn upon re-entry into Earth’s atmosphere. “We are aware of the challenges that we are facing today as a planet, of so many companies and so many people launching satellites and launching payloads,” he adds. “We look to leave the low-Earth orbit space clean, as clean as possible. Space is infinite, but low-Earth orbit is not.

Simulating Space Solutions

A major initial challenge in designing multiple-stage rockets is determining the mass fractions for the different stages. The goal is to maximize the mass fraction, which is the ratio of the payload mass to the total vehicle mass.

“Determining the optimal mass fraction is always a challenge,” Mihai says. “We investigate structures made of very advanced composite materials. We make an effort to optimize fiber placement and fiber direction for all the structural components. Obviously, we can't get away with only composites — we'll have some metallic structures as well — but even then, there's always a way to make sure that we only carry the necessary structural weight in the vehicle.”

While investigating composites, he has used Ansys Mechanical ACP Prep-Post to predict the margins for different failure criteria of composites.

“Using the Tsai-Wu interaction constants is  easy with Ansys Mechanical,” he says. “Setting up external data cloud points with pressure fields or any other described loads is simple compared to other simulation products I have used.” He also uses simulations to determine Hertzian contact stresses, which are localized stresses that develop as two curved surfaces come in contact and deform slightly under the imposed loads.

Mihai has also used Mechanical to design Marman clamps, which hold two cylindrical objects together end-to-end with a ring clamp. Generally, a Marman clamp consists of a circular strap with an interior V-shaped groove. Tension is applied to the strap with a threaded bolt and nuts connecting to the ends of the strap. Mihai describes the design work as “normally very tedious,” but he got results quickly and easily using finite element analysis.

“Most of my experience has been doing mechanical simulations and checking them with hand calculations,” he says. “If you get similar results, people get so much confidence in the results that it's easier for upper management to say ‘go ahead and build a prototype and run a test.’ With Ansys simulations, I get correlation of results within 5% all the time.”

Mihai and his colleagues at Aevum have their work cut out for them. From the online unveiling of the Ravn X in December 2020 to the award of a patent for its technology on May 4, 2021, to its scheduled first commercial mission in 2022 is a quick turnaround time. But providing a quick turnaround are what Ravn X — and Ansys simulations — are built to do.

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