Graduation projects

Project I

Glider soaring using reinforcement learning

Reddy, G., Wong-Ng, J., Celani, A. et al. Glider soaring via reinforcement learning in the field. Nature 562, 236–239 (2018)

Soaring birds often rely on ascending thermal plumes (thermals) in the atmosphere as they search for prey or migrate across large distances1,2,3,4. The landscape of convective currents is rugged and shifts on timescales of a few minutes as thermals constantly form, disintegrate or are transported away by the wind5,6. How soaring birds find and navigate thermals within this complex landscape is unknown. Reinforcement learning7 provides an appropriate framework in which to identify an effective navigational strategy as a sequence of decisions made in response to environmental cues. Here we use reinforcement learning to train a glider in the field to navigate atmospheric thermals autonomously. We equipped a glider of two-metre wingspan with a flight controller that precisely controlled the bank angle and pitch, modulating these at intervals with the aim of gaining as much lift as possible. A navigational strategy was determined solely from the glider’s pooled experiences, collected over several days in the field. The strategy relies on on-board methods to accurately estimate the local vertical wind accelerations and the roll-wise torques on the glider, which serve as navigational cues. We establish the validity of our learned flight policy through field experiments, numerical simulations and estimates of the noise in measurements caused by atmospheric turbulence. Our results highlight the role of vertical wind accelerations and roll-wise torques as effective mechanosensory cues for soaring birds and provide a navigational strategy that is directly applicable to the development of autonomous soaring vehicles.

Project II

Chemical sensing using small drones

Javier Burgués, Santiago Marco, Environmental chemical sensing using small drones: A review, Science of The Total Environment, 2020

Recent advances in miniaturization of chemical instrumentation and in low-cost small drones are catalyzing exponential growth in the use of such platforms for environmental chemical sensing applications. The versatility of chemically sensitive drones is reflected by their rapid adoption in scientific, industrial, and regulatory domains, such as in atmospheric research studies, industrial emission monitoring, and in enforcement of environmental regulations. As a result of this interdisciplinarity, progress to date has been reported across a broad spread of scientific and non-scientific databases, including scientific journals, press releases, company websites, and field reports. The aim of this paper is to assemble all of these pieces of information into a comprehensive, structured and updated review of the field of chemical sensing using small drones. We exhaustively review current and emerging applications of this technology, as well as sensing platforms and algorithms developed by research groups and companies for tasks such as gas concentration mapping, source localization, and flux estimation. We conclude with a discussion of the most pressing technological and regulatory limitations in current practice, and how these could be addressed by future research.

Project III

High-flying pseudosatellites

Satellites pass over a city once a day at most, notes Fehr. “You get a very interesting view of the chemistry which is around, but only once a day,” he says. With a HAPS hovering at 20 kilometres over a city, researchers could see how emissions wax and wane throughout the day. They could also better connect the satellite observations with those from ground-based pollution-measuring stations.

See related newspiece article.

Is it a bird? Is it a plane? No, it’s a High-Altitude Pseudo-Satellite (HAPS) — an unmanned airship, plane or balloon watching over Earth from the stratosphere. Operating like satellites but from closer to Earth, HAPS are the ‘missing link’ between drones flying close to Earth’s surface and satellites orbiting in space.

See ESA exposition of the concept.

Atmospheric satellite (United States usage, abbreviated atmosat) or pseudo-satellite (British usage) is a marketing term for an aircraft that operates in the atmosphere at high altitudes for extended periods of time, in order to provide services conventionally provided by an artificial satellite orbiting in space. Atmospheric satellites remain aloft through atmospheric lift, either aerostatic/buoyancy (e.g., balloons) or aerodynamic (e.g., airplanes). By contrast, conventional satellites in Earth orbit operate in the vacuum of space and remain in flight through centrifugal force derived from their orbital speed. To date, all atmosats have been unmanned aerial vehicles (UAVs).

See Wikipedia article.

Project IV (completed.)

Effects of contrails on cloud formation and global warming

This project is about using Google Earth satellite data to quantify a link between cloud formation and air traffic. 

A cleaner future for flight — aviation needs a radical redesign, Nature, 2022.

Aviation is a big polluter. Globally, the industry generates roughly one billion tonnes of carbon dioxide per year — comparable to that produced by Japan, the world’s third-largest economy. Although many governments are regulating emissions from cars and trucks, such as by phasing out internal-combustion engines and switching to electric vehicles, air transportation is technologically rooted in old patterns. Apart from a pause during the COVID-19 pandemic, emissions from flights have risen by 2.5% each year for the past two decades. Over the next 30 years, the industry’s impact on global warming is set to exceed that of its whole history1, since the Wright brothers’ first flights in the early 1900s.

Cutting the sector’s impact on global warming is high on the agenda of the triennial assembly of the International Civil Aviation Organization (ICAO) in Montreal, Canada, this month. Ministers from 193 nations will try to negotiate an industry-wide target for cutting emissions, in line with the goals of the Paris climate agreement. There will be much talk about the need for action. However, the preparations indicate that most of the focus will be on familiar ideas, such as cleaner forms of jet fuel and schemes to offset carbon emissions. It is no coincidence that these ideas are also the least disruptive to how the industry operates today.

We know that aircraft engines burn fossil fuels, releasing CO2, a warming gas. But high temperatures in engines also produce nitrogen oxides, and they release aerosols that alter the composition of the atmosphere. Burning hydrocarbons generates water vapour that, by mingling with aerosols, produces contrails.

The biggest wild card concerns cloud formation — a fast-evolving aspect marked by huge uncertainties. Some simulations warn that ‘contrail cirrus’ might have caused almost twice as much warming as CO2 from the aviation sector up to 20188 (see ‘Current warming and cooling effects of aviation’). Other satellite-based studies suggest a much lower figure9. Because of these additional effects, even if biofuels replace conventional jet fuel and reduce CO2 emissions, they might not fully fix the climate.

No easy solutions for aerospace, Nature Materials, 2016

Civil aviation is known to be a significant contributor to global warming, with high-altitude CO2 and condensation trails being important factors1. With the number of passengers ever increasing — China for example is forecast to experience an average year-on-year growth rate of 5.5% (ref. 2), the largest of any country — this contribution is likely to rise. .

Formation and radiative forcing of contrail cirrus, Nature Communications, 2018

Aircraft-produced contrail cirrus clouds contribute to anthropogenic climate change. Observational data sets and modelling approaches have become available that clarify formation pathways close to the source aircraft and lead to estimates of the global distribution of their microphysical and optical properties. While contrail cirrus enhance the impact of natural clouds on climate, uncertainties remain regarding their properties and lifecycle. Progress in representing aircraft emissions, contrail cirrus and natural cirrus in global climate models together with tighter constraints on the sensitivity of the climate system will help judge efficiencies of and trade-offs between mitigation options.

Condensation trails (contrails) are line-shaped ice clouds generated by jet aircraft cruising in the upper troposphere at 8–13 km altitude. Depending on surrounding atmospheric conditions, contrails can be short- or long-lived. Long-lived contrails are those that remain for at least 10 min—defined by the World Meteorological Organization as Cirrus homogenitus1—and are the only man-made type of ice clouds. Depending on whether or not they retain their linear shape, they have been referred to as persistent contrails and contrail cirrus, respectively, or together as aircraft-induced clouds (AIC). A change in global cloudiness due to AIC creates an imbalance between incident radiation from the Sun and upwelling radiation from the Earth’s surface and atmosphere, resulting in a radiative forcing (RF) of climate that induces a tendency to change the temperature structure in the lower atmosphere.

Project V

Building with drones

Aerial additive manufacturing with multiple autonomous robots, Nature 2022.

Additive manufacturing methods1,2,3,4 using static and mobile robots are being developed for both on-site construction5,6,7,8 and off-site prefabrication9,10. Here we introduce a method of additive manufacturing, referred to as aerial additive manufacturing (Aerial-AM), that utilizes a team of aerial robots inspired by natural builders11 such as wasps who use collective building methods12,13. We present a scalable multi-robot three-dimensional (3D) printing and path-planning framework that enables robot tasks and population size to be adapted to variations in print geometry throughout a building mission. The multi-robot manufacturing framework allows for autonomous three-dimensional printing under human supervision, real-time assessment of printed geometry and robot behavioural adaptation. To validate autonomous Aerial-AM based on the framework, we develop BuilDrones for depositing materials during flight and ScanDrones for measuring the print quality, and integrate a generic real-time model-predictive-control scheme with the Aerial-AM robots. In addition, we integrate a dynamically self-aligning delta manipulator with the BuilDrone to further improve the manufacturing accuracy to five millimetres for printing geometry with precise trajectory requirements, and develop four cementitious–polymeric composite mixtures suitable for continuous material deposition. We demonstrate proof-of-concept prints including a cylinder 2.05 metres high consisting of 72 layers of a rapid-curing insulation foam material and a cylinder 0.18 metres high consisting of 28 layers of structural pseudoplastic cementitious material, a light-trail virtual print of a dome-like geometry, and multi-robot simulations. Aerial-AM allows manufacturing in-flight and offers future possibilities for building in unbounded, at-height or hard-to-access locations.

Project VI

Electric aircraft

Bu proje ile elektrik itkili uçuş teknolojisi araştırılacak, pilotaj eğitiminde kullanılan hafif eğitim uçağının itki sistemi olan içten yanmalı piston motoru ve sıvı yakıt yerine, elektrik motoru ve enerji depolama aracı olarak da şarj edilebilir Li-ion batarya ve aksesuar sistemler kurulacaktır. Elektrik itki (electrical traction) teknolojileri ve destekleyen alt teknolojiler son 10 yılda artan bir hızla araştırılmaktadır. Elektrik itkinin havacılıkta atmosfer içi uçuş için kullanılması bir ideal olarak benimsenmiş, bu amaçla elektrik motorlarından büsbütün başka teknolojiler de araştırılmaktadır, örneğin hareketli bir parçanın olmadığı (solid state propulsion, ionic wind) sistemleri. Elektrik itki ve elektrikli uçuş konusunda temel bilimsel araştırma ve teknoloji araştırmaları iç içe geçmiştir, bir yandan alt sistemlerin verim ve güvenliği araştırılırken diğer yandan bu sistemler uçuş platformlarında kullanılarak metodolojik yenilikler üzerine temel araştırmalar yapılmaktadır. Örneğin, aşağıda detaylı bir şekilde inceleyeceğimiz, NASA X-57 Maxwell elektrikli uçak dönüşüm projesi, bu proje önerisiyle önerilen kavramsal ve metodolojik temel bilgi üretimi amacıyla 2016 yılında başlatılmış olup  açık kaynak bilgi ve know-how paylaşımında bulunmaktadır.

Bu projenin araştırma sorusu, uçuş için elektrikli itki kavramı temelde hangi imkan, potansiyel, inovasyon  ve zorlukları barındırmaktadır, konularını içermektedir. Bu sorulara  kavramsal, metodolojik ve teknolojik cevaplar aramanın en iyi yolunun, bir elektrifikasyon dönüşüm projesi ile olduğunu düşünüyoruz. Örneğin bu proje ile geliştirilen know-how ile doğruca dağıtık itki (distributed propulsion) potansiyellerini araştırmak mümkün olacaktır. Elektrifikasyonun sağladığı dijitalleşme potansiyeli, yine bu proje ile üretilen temel bilgi üzerinde, takip eden başka bir projeyle, araştırılacaktır. Bu yönüyle projenin amacı teknolojik bir ürünün montajı olmayıp, inovatif başka projeler için gerekli bilimsel ve teknolojik bilginin üretilmesi, hazır uzman pratiğinin ve metodolojisinin oluşturulmasıdır.

Potential for electric aircraft, Nature Sustainability, 2019.

NASA X-57 project

Technological, economic and environmental prospects of all-electric aircraft, Nature Energy, 2018.

The challenges and opportunities of battery-powered flight, Nature, 2022.