too heavy to fly clean

Problem statement

Decarbonizing commercial aviation — responsible for about 2.4% of global CO₂ emissions (2018) — requires all-electric or hybrid-electric propulsion for the workhorse single-aisle aircraft segment (150–200 passengers, Boeing 737 / Airbus A320 class). The best-in-class commercially available electric motor achieves a power density of about 5 kW/kg — a figure often quoted without counting the weight of the motor's thermal management system — while fully packaged wide-bandgap inverters are approaching 20 kW/kg. ARPA-E's ASCEND program sets a specific power of ≥12 kW/kg at ≥93% efficiency for the fully integrated all-electric powertrain (motor, drive, and thermal management together) as the benchmark for a viable 150–200 passenger electric aircraft. That leap over today's integrated systems cannot be achieved by incremental improvements to existing motor topologies — it requires fundamental advances in motor design, thermal management, and power electronics integration.

Why this matters

Commercial aviation emitted roughly 920 million tons of CO₂ in 2019 and is one of the hardest sectors to decarbonize. Narrow-body (single-aisle) aircraft such as the Boeing 737 constitute the majority of commercial aircraft flying worldwide and are responsible for nearly half of aviation-related greenhouse gas emissions. Sustainable aviation fuels (SAF) address emissions but face feedstock constraints, and SAF prices currently exceed fossil-based jet fuel by a factor of two — and up to a factor of five in mandated markets. Battery-electric flight is energy-limited by battery specific energy (150–250 Wh/kg for current Li-ion cells vs. an equivalent ~13,000 Wh/kg for jet fuel), but for short-haul routes (500–1,000 miles), high-power-density electric propulsion could enable hybrid architectures using smaller, lighter fuel loads. Without the powertrain breakthrough, the aviation industry has no credible pathway to net-zero for its largest fleet segment.

What’s been tried and why it hasn’t worked

Existing high-power-density motors (e.g., those used in Formula E racing or aerospace actuators) achieve impressive specific power but sacrifice efficiency or thermal endurance. Superconducting motors offer very high power density but require cryogenic cooling systems that add weight and complexity. Conventional motor topologies (permanent magnet synchronous, induction) have already captured the easy loss reductions through low-loss steels, high-energy permanent magnets, and better conductors — pushing losses lower has proven difficult at current operating temperatures. The motor, its drive electronics, and thermal management system are typically designed by separate teams, leading to sub-optimal integration: ARPA-E notes that cooling technologies for motors and drives have fallen behind the rapid progress made in microelectronics cooling, and that quoted motor power densities often omit the thermal management system's weight entirely. GE Aerospace and NASA have tested a megawatt-class, multi-kilovolt hybrid-electric propulsion system in simulated altitude conditions, but no powertrain yet reaches the required specific power with integrated drives.

What would unlock progress

ASCEND's approach of co-designing the motor, drive electronics, and thermal management as a single synergistically cooled system could eliminate the weight penalty of separate cooling loops. Advances in wide-bandgap semiconductors (SiC, GaN) enable higher switching frequencies and operating temperatures in the drive, reducing passive component sizes. Novel motor topologies (axial flux, transverse flux) and direct-drive architectures could reduce mechanical transmission losses. Additive manufacturing of motor components with integrated cooling channels represents a fabrication breakthrough that enables geometries impossible with conventional manufacturing.

Entry points for student teams

A team could model the thermal-electromagnetic co-design of a motor segment, optimizing winding geometry and cooling channel placement simultaneously using multi-physics simulation. Alternatively, a team could benchmark emerging wide-bandgap power electronics for aviation duty cycles and identify the thermal derating factors that limit real-world performance. Electrical engineering, aerospace engineering, and thermal science skills are most relevant.