Aeolus: More than a Mission
As promised in our Top 10 Stories of EO from the ESA, in this article we’ll be exploring more on the Aeolus Wind Mission. We thought this is a great way to look more into how space can be leveraged to support a deeper and actionable understanding of our climate and weather and dive into two other interesting topics: space re-entry and space debris.
The Aeolus satellite was launched in 2018 on the rocket Vega by the European Space Agency (ESA) loaded with one instrument, a Doppler wind LiDAR, with the aim of acquiring profiles of the Earth’s wind on a global scale. It was the first wind LiDAR in space, spent five years in orbit, delivered 7 billion pulses and is estimated to have provided €3bn in societal benefit (report here by London Economics). Importantly, it was a pioneering mission: it demonstrated the working of new Ultraviolet (UV) laser technology and was a first for assisted re-entry that limited space debris pollution.
Aeolus measuring cyclones. Credit: ESA/ATG Medialab
Climate and Weather
The Doppler wind lidar called Aladin worked by firing laser pulses of UV light towards Earth’s atmosphere. This light bounced off air molecules and particles such as dust in the atmosphere and the small fraction of light that scattered back towards the satellite was collected by a large telescope. By measuring the shifts in the return signals, the horizontal speed of the wind in the lowermost 30 km of the atmosphere was derived, making Aeolus the first satellite mission to deliver profiles of Earth’s wind on a global scale (article).
The technology of the Doppler proved that it was possible to measure wind speed, and this had a great impact in contributing to climate research and supporting operations in weather forecasts. With the updated measurements, scientists could use these to update their numerical models and improve forecasting. This was really useful during COVID lockdowns when the aircraft who normally flew these missions were grounded. In addition, it improved our understanding of how wind, pressure, temperature and humidity are related, enhancing climate research and weather forecasting. Actionable examples include its use to track real time events such as the Hunga Tonga volcanic eruption, track ash plumes to warn aviation industry of hazards to visibility and aircraft engine damage and predict extreme weather in Europe and North America.
In summary, a game changer. A mission showing the way for future meteorological satellites to deliver actionable insights and social, environmental and economic benefits. You can visit here for the data plus tools for data visualisation and satellite and orbit visualisation. Well worth a look.
Space Re-entry
Bringing satellites back down to Earth presents a danger to infrastructure, the environment and people so there is a requirement to minimise this risk. This would typically be achieved by most of a satellite burning up on re-entry or through a controlled re-entry at the end of their life in orbit. However, when Aeolus was designed back in the late 1990s no such regulations were in place. So, after running out of fuel and without intervention, Aeolus would have re-entered Earth’s atmosphere naturally – but with no control over where this would happen.
So, the team at ESA’s ESOC mission control centre in Germany created simulations to test the re-entry and managed to use the satellite’s remaining fuel to carry out a series of burns to lower Aeolus and place it in the best position to re-enter. This was faced with challenges both technical and environmental that could affect success:
- Current high levels of solar activity, for one thing, are creating unpredictable fluctuations in the thickness of the atmosphere, speeding up Aeolus’s return
- series of never-before-performed manoeuvres that should steer Aeolus on a return path over the most uninhabited regions possible, i.e. the ocean
- minor issues surfacing, such as losing contact with Aeolus or parts of the spacecraft reaching unexpected temperatures
They pulled it off of course, through a series of complex manoeuvres that lowered Aeolus’ orbit from an altitude of 320 km to 120 km to re-enter the atmosphere and burn up. Crucially, this ensured Aeolus’ position to avoid any pieces that may not have burned up in the atmosphere falling within the satellite’s planned Atlantic ground tracks (article) and re-entering in line with current regulations end-of-life disposal.
A key benefit was that this supported ESA’s wider commitment to the long-term safety and sustainability of space activities, one of which is zero debris – a topic of hot debate and much work in the sector. Let’s have a deeper look.
Wind profile from Aeolus 6 May 2020; Aeolus Re-Entry; Space Junk; Orbital Debris around Earth. Credits: ESA/VirEs, ESA, ESA, NASADebris
So why is space debris such a hot topic? Well, the general growth of space exploration since the late 50’s and the recent increase of low orbit missions, has formed a large body of what we can colloquially call ‘space junk’. And it could increase as our global economy is now increasingly reliant on space services for everyday activities (think of plane navigation systems or your mobile phone network).
With 6,300 rocket launches and 15,000 satellites, 10,000 are still up there and one-third of them are either inactive or defunct. Add to this nearly 32,000 trackable smaller objects floating around (spent rocket bodies, protective shields, covers, and other incidental hardware items) and nearly 131 million untracked fragments, often less than 10cm and hurtling at high speeds (twice the speed of a bullet!), there is a worry that collisions can become more frequent threatening operating satellites and orbiting infrastructure and the safety of astronauts working in orbit.
In addition, the problem could grow as the collisions of these lightning-fast fragments with larger objects can theoretically cause a cascading effect, generating ever-more debris. This is known as the “Kessler Syndrome”, named after NASA scientist Donald J. Kessler, who first proposed in 1978 the possibility of such a self-sustaining chain reaction of space debris collisions (https://www.space.com/kessler-syndrome-space-debris).
Therefore, with satellites playing a key part in our day to day lives and with no signs of slowing down, so reducing orbital debris and making the space environment more sustainable is crucial for the future of our society, environment and the global space business - even living in space!
As a result ESA has declared that by 2030, all their ESA missions will be ‘debris neutral’ – thanks to the Zero Debris Charter, supported by Airbus Defence and Space, OHB and Thales Alenia Space, which aims to achieve global consensus that space technology and solutions can enable safe and sustainable space operations.
So how are they aiming to do this? Practically, we have seen:
- deorbiting kits launched with missions to bring them down safely
- contributing to flagship missions like Clearspace-1 (led by UK Space Agency and SPECTRE) to capture stranded spacecraft in orbit and use advanced technologies (including AI) to limit risks on the ground
- commercial services like:
o SpaceDots, a company providing quicker, reliable testing materials that can ultimately reduce space debris and improve sustainability
o Astroscale, a company providing space debris docking and removal and satellite re-entry transport
From a policy perspective, we have seen:
- The WEF and ESA collaborating to publish the Space Industry Debris Mitigation Recommendations to try and make space more sustainable. Launched at the Summit for Space Sustainability, it was organized by the Secure World Foundation and has set goals including specific percentages for post-mission disposal success rates and target number of years as object should remain in-orbit at the end of it’s life. It calls for increased collaboration to reduce space debris, more transparency among operators, acceleration of technologies and practices for disposal of spacecraft at end of life and removal of existing space debris already in orbit. Key players such as GHGSat, Planet, Airbus, Astra, Axiom Space, Astroscale and Voyager Space Holdings have contributed (article).
Funding from ESA, UK Space Agency and others to the UN Office for Outer Space Activities (UNOOSA) guidelines for the long-term sustainability of outer space.
Wrap Up
In summary, this mission was a game changer with regards to our understanding of climate change and ensuring a safer, cleaner space. For us at Minesat, it is a great example of how we can leverage space within a wider remote sensing ecosystem to provide positive social and environmental outcomes – more on this soon!
The follow up mission Aeolus-2, will be developed with Eumetsat, Europe’s Organisation for the Exploitation of Meteorological Satellites, with an improved Doppler radar aim to reduce error on wind speed and provide better resolution meaning more significant results for global weather forecasting going forward. This is alongside benefits of wider societal benefits of up to €5.6bn, an acceleration to reach Net Zero and increased use of the data for solving challenges.
This looks promising, as with the ever increasing changes in climate and the devestating impacts seen, it can support more investment, awareness and action to support us solving these challenges. We can also look to a more sustainable space, a place that we do need to run our society and one where, one day, we may very well live.
For all the exciting articles that this blog is based on see below:
