Founded at MIT in 2010, the mission of Altaeros is to deliver the next generation of infrastructure to rural and isolated communities. Altaeros has developed a tethered aerial platform that can be used for a range of applications in energy, telecom and agriculture. Its first commercial product, the SuperTower, delivers high-speed mobile broadband to hard-to-reach rural communities around the world. Deploying one SuperTower provides coverage equivalent to 15 conventional cell towers at 60% lower cost.

Overcoming headwinds

During the development of any complex, large-scale system, prototyping and testing is an expensive proposition. For a start-up company like Altaeros, developing a prototype of its autonomous airborne SuperTower, the risk of failure was particularly acute.

To ensure safety and reliability, the SuperTower’s balloon must remain aerodynamically stable, even in variable wind conditions. Although it is designed to passively align itself to point into the wind, changing conditions can cause short-term stresses and mechanical loads capable of damaging the platform.

Aerodynamically, the challenge for Altaeros’ airborne platform comes down to the variability of wind. The system passively weathervanes to point into the wind. However, in terms of mechanical loads and flight dynamics, the balloon can experience high angles of attack or sideslip on a short-term basis, which must be accommodated.

Altaeros needed to create accurate models that enabled early designs to be tested through simulation, before material is ordered or cut — enabling Altaeros to minimize risk.

How new ideas take flight

Altaeros uses a model-based design approach to design the aerodynamics and control systems for stable flight at operating altitude, during autonomous launch and recovery, and in extreme conditions. This requires high-fidelity modeling capability, including the development of an extensive aerodynamic database.

Altaeros uses Ansys Fluent to model dozens of different operating conditions, performing computational fluid dynamic (CFD) simulations. These simulations leverage high-performance computing resources delivered via cloud by Nimbix, an Atos company. Using cloud computing enables Altaeros to perform the simulations with manageable turnaround times while maintaining high fidelity.

The CFD results of these SuperTower simulations were used to develop load cases for the mechanical design of the system and to identify the best location of key sensors such as windspeed sensors. However, Altaeros’ use of simulation doesn’t stop there.

Altaeros models the complete system — the rotating ground station, tethers and balloon — in its proprietary flight dynamics simulation tool. The CFD results from Ansys Fluent are a key component, serving as the aerodynamic database from which aerodynamic forces and moments are determined. The flight dynamics simulator allows:

• Development and tuning of flight control software
• Verification of the design for conditions at the limit of the design envelope, which would be difficult to replicate in prototype testing
• Training for operators of prototype systems

A viable model for the future

For Altaeros, its initial investment in modeling capabilities and simulation has provided significant payback in terms of reduced iterations of physical prototypes and in-flight tuning of the control software.

Altaeros’s previous flight prototype accumulated autonomous flight experience across a wide range of conditions, validating the design approach. This enabled the design of the company’s first commercial system at a significantly larger scale.

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