So long Aeolus, and thanks for all the wind data

A pioneering mission comes to an end

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So long Aeolus, and thanks for all the wind data

ESA/P.Carril (2010)

On Sunday, we said farewell to a groundbreaking ESA mission… well, sort of.

As of Sunday, the Aeolus satellite transmitted its final observations. The satellite will now remain in orbit around Earth as teams finalize plans to deorbit the satellite, bringing a fiery end to its pioneering mission to chase the winds of Earth. And it really was a pioneering mission. Aeolus proved a technology that many believed impossible. It completely reimagined how vital wind data could be collected for more accurate weather forecasts. Its contributions are immense and its impact on future missions will ensure that it is not soon forgotten. 

Background

The mission was originally called the Atmospheric Dynamics Mission (ADM). It was, however, later renamed to Aeolus who in Greek mythology was appointed by the gods to be the keeper of the winds. It also does appear that there were several instances where ESA referred to the mission as ADM-Aeolus. There's even an ESA press release from October 2006 that calls it the Atmospheric Dynamics Mission ADM-Aeolus, which is a mouthful. 

Aeolus was one of four candidate Earth Explorer Core missions selected in May 1996 for 12-month Phase A studies which were completed in June 1999. However, proof of concept campaigns for Aeolus began as far back as the 1980s. Aeolus was selected in November 1999 as the fourth Earth Explorer mission. The first feasibility study phase (Phase A) of the Aeolus mission began that year. In July 2002, the mission was officially advanced to Phase B, which precipitated the primary contract for the mission being awarded to EADS Astrium in 2003. A merger in 2013 saw the programme continue its development under Airbus Defence and Space.

The original ESA press release does not have a contract value nor does Airbus have EADS Astrium press content achieved on its website. I did, however, manage to track down an archived EADS Astrium press release from October 2003 that stated that the mission would have a total cost of €300 million over its lifetime. The press release goes on to state that the value of the spacecraft itself would be around €180 million. However, at the time it was projected that Aeolus would be launched in October 2007. The spacecraft would, however, not be launched until 2018 following several years of engineering challenges to perfect the pioneering technology. According to a 2022 ESA report, the total mission cost of Aeolus was around €500 million. The satellite did, however, go on to more than pay for itself over its more than four and a half years in orbit. (more on that later).

In September 2016, ESA awarded the launch contract for Aeolus to Arianespace with the satellite being launched aboard a Vega rocket. When the contract was awarded, the rocket had already successfully launched ESA's Sentinel-2A, IXV reusable spacecraft demonstrator, LISA Pathfinder, and PROBA-V missions. It had, at the time the contract was awarded, a 100% success rate over its first seven missions.

Aeolus set sail for the launch site in French Guiana on 15 June 2018, which coincided with Global Wind Day, which is a thing I just discovered exists. Although the satellite was small enough to be transported by air, the 12-day journey across the Atlantic was selected to avoid potential damage to the sophisticated instruments caused by air re-pressurization during a possible rapid descent.

The satellite was launched aboard an Avio-built Vega rocket from the Guiana Space Centre at 21:20 UTC on 22 August 2018. Approximately 55 minutes into the mission, Vega’s AVUM upper stage placed Aeolus into a sun-synchronous orbit at an altitude of 320 kilometres and an inclination of 96.97º. Initial contact with the satellite was established through the Troll ground station in Antarctica with controllers at ESA's ESOC (European Space Operations Center) in Darmstadt, German taking over satellite operations following initial contact. This was the start of what would become a groundbreaking mission!

The mission and the tech

Globally, there are a number of technologies used to track wind speed and direction, including anemometers, weather balloons, and planes and satellites that extrapolate the characteristics of wind by tracking clouds in the sky. These methods are, however, limited in scope and are really only good for characterizing wind in specific places or specific heights under specific conditions. Aeolus changed all that.

Aeolus was the first to be able to gather wind data from the ground all the way up to the stratosphere (around 30 kilometres above Earth) around the globe. It allowed researchers to directly measure profiles of global wind patterns from space in cloud-free conditions for the first time. 

The satellite’s only instrument was ALADIN (Atmospheric Laser Doppler Instrument). The primary components of the instrument were a pair of lasers, a 1.5-metre telescope, a receiver, and a Doppler wind lidar. The satellite only required one of the two lasers to operate with the second acting as a backup.

When Aeolus was in operation, ALADIN’s laser pulsed ultraviolet light down into Earth’s atmosphere. The telescope then collected the light backscattered from particles of gas and dust in the atmosphere and directed it to the receiver. The time that elapsed between sending the light pulse down and receiving a signal back determined the distance to the scatters and therefore the altitude above Earth. It’s basically sonar but with light. As the particles move in the wind, the wavelength of the scattered light shifts by a small amount as a function of speed. This allows the Doppler wind LIDAR to measure this change so that the speed and direction of the wind could be determined. With these data points combined, the spacecraft is able to generate a map of wind patterns below it.

The spacecraft

In 2003, when EADS Astrium was awarded the Aeolus contract, the company stated that the spacecraft would be based on the Mars/Venus Express platform design. Later references state that the platform was based on ESA’s CryoSat and Rosetta missions, among others. So, Aeolus had some impressive heritage behind it.

The satellite had a launch mass of 1,357 kilograms. The satellite platform accounted for 650 kilograms, the fuel 266 kilograms, and the payload 450 kilograms. Interestingly, the satellite was originally envisioned as being significantly smaller. Early design specifications had the satellite with a launch mass of 800 kilograms with 300 kilograms of that being the payload.

In its launch configuration, the spacecraft measured 4.6 metres in height, 1.9 metres in length, and had a width of 2.0 metres. Once in orbit, a pair of three-panel solar wings were deployed. The satellite's two solar wings were capable of producing 2,400 watts of end-of-life power. The average power demand for the satellite during operations was 1,400 watts. An 84 Ah lithium-ion battery was equipped for use during eclipse phases and LEOP (Launch and Early Orbit Phase). The Power Conversion and Distribution Unit was manufactured by Patria in Finland.

Now, if you really want to get into the weeds, all onboard data was handled by an ERC32 radiation-tolerant processor which was developed by Temic in Germany (which had been purchased by Atmel by the time Aeolus was being built) under contract from ESA. Bear with me here because I went down the rabbit hole a bit with this component of the satellite. The ERC32 processor is kind of an amazing story unto itself. It was just the second time that ESA had pursued developing a microprocessor following on from the MA31750 processor which powered the agency’s Rosetta mission notable as the first spacecraft to ever orbit a comet. ERC32 has been the beating heart of many important ESA missions including the Automated Transfer Vehicle which was used to deliver cargo to the International Space Station (ISS). An upgraded version of the processor was also utilized aboard the Herschel and Planck space observatories and as part of the Ariane 5 guidance system. Russia even utilized a version of the processor to help run its segment of the ISS. The processor was replaced with the LEON2-FT in the early 2010s. 

With the huge amount of data being collected by the ALADIN instrument, Aeolus had a solid-state hard drive that provided it with 8 GB of onboard data storage. This ensured that no data was lost between downlinks.

The spacecraft was designed to be highly autonomous in all mission phases with ground contract required no more than once every five days in the case of an anomaly. Additionally, the spacecraft’s orbit had a seven-day repeat cycle so that the complete operational timeline was repeated on a weekly cycle, thus minimizing the effort for mission planning. The satellite’s Command and Data Management Unit was manufactured by RUAG (now Beyond Gravity).

The spacecraft was three-axis stabilized with AOCS (Attitude and Orbit Control Subsystem), reaction wheels, and magnetorquers as actuators, and magnetometers (developed at LusoSpace, Portugal), coarse Earth sun sensors, inertial measurement units, rate measurement units, AST (Autonomous Star Tracker manufactured Terma in Denmark), and a GPS receiver as sensors. The satellite’s orbit was maintained by four 5 N hydrazine thrusters. Interestingly, in 2006 the design of the vehicle called for ten 5 N thrusters.

The payload

The laser system for ALADIN instrument was developed by Galileo Avionica along with an array of subcontractors. An extensive pre-development evaluation and assessment program of the ALADIN laser component technology was started in 2000. Manufacturing of the laser began in late 2004. According to an ESA article at the time, the team faced multiple obstacles during the development and design phases of the project with more than 500 designs being produced. In September 2005, a transmitter-laser prototype emitted its first light pulses in ultraviolet.

In 2010, an in-depth review from "independent laser experts" identified the need for several modifications to the laser's design. The modifications were required to ensure adequate performance margins for the three years of in-orbit operation. The most signification modification was a change of the operational baseline from "burst" to "continuous" mode. This change meant that the complete version of the end-to-end simulator and ground payload data processing software needed to be upgraded to support the new mode. This change alone delayed the launch by approximately two years.

In 2015, ESA director of Earth observation Volker Liebig explained that one of the biggest challenges faced in developing Aeolus was a lack of knowledge about ultraviolet-laser-induced damage on optical surfaces in a vacuum. According to Liebig, ESA asked NASA for assistance and was told that "when you find out the answers, please let us know." It should be noted that this response is what was characterized by Liebig and is not a quote from an official NASA response.

2015 also saw another of Aeolus' most significant contributions, although this one was not one that would have been celebrated. Because of the schedule delays and cost overruns of Aeolus and EarthCare, ESA modified the way it contracted the development of satellites carrying unproven technology. New procedures implemented in 2015 introduced a delay between contracting for the development of an instrument and the overall satellite program. This change allows ESA to ensure that an instrument like ALADIN is ready for deployment before the agency commits full funding for the entire satellite programme.

If you’re interested in learning more about the challenges ESA faced when developing the laser for Aeolus, this presentation from October 2018 does a great job of breaking the whole development process down.

Even once the satellite was in orbit, the laser continued to be a challenging component of the satellite. In May 2019, ESA announced that the satellite's laser was losing power at a rate of around one millijoule per week. Luckily, the team had prepared for an eventuality just like it with the satellite carrying a backup laser that was turned on and commissioned in July 2019, allowing it to continue its mission.

In late 2022, degradation of optics utilised in conjunction with the second laser forced the team to examine alternative solutions. After two months of troubleshooting, ESA and industry project teams were able to switch back to the primary laser and managed even to improve its original performance.

Kayser-Threde in Germany was responsible for all the payload’s optics including the main telescope with the primary mirror being polished at Opteon in Finland. Contraves Space was in charge of the receiver and a whole bunch of other companies were involved in bringing Aeolus from its design to an operational satellite. As a side note, it’s pretty astonishing how many of the entities that worked on this satellite have been acquired or merged with other companies. This made tracking down specific contractor information more than a little difficult. 

The satellite’s impact

Over its more than four years of operation, Aeolus orbited the Earth 16 times a day and covered the entire globe once every week. Altogether, ALADIN beamed down over seven billion laser pulses. The satellite's ground services were equally as efficient, enabling 99.5% of the data collected to be accessed by users within just three hours.

In November 2018, the retired head of ESA’s Opto-electronics section, Errico Armandillo explained that just months after it was launched, Aeolus began returning more wind data than all ground-based measuring systems put together - just one satellite. 

In May 2019, Dr Florence Rabier, director general of the European Centre for Medium Range Weather Forecast (ECMWF), was already pushing for additional Aeolus missions to be launched.

"It's already had a positive impact in our numerical weather system,” Rabier told the BBC. “You know, most new satellites can take months, even years, to have a positive impact. The fact that Aeolus has already had an impact is very encouraging, and I can confidently say we'd like to see more of these satellites."

Since ECMWF began utalising Aeolus data, the satellite has become one of its highest impact-per-observation instruments ever. The satellite's capacity is particularly effective where data from more traditional methods is scarce. For instance, when planes were grounded during lockdowns imposed by the pandemic, Aeolus became an invaluable tool to fill in the gaps. 

Data collected by Aeolus has been used by major weather forecasting services worldwide, including the ECMWF, Météo-France, the UK Met Office, Germany’s Deutscher Wetterdienst, and India’s National Centre for Medium Range Weather Forecasting.

The satellite has also had a measurable euro-value return on investment. In late 2022, ESA published a report that showed that Aeolus had brought in €3.5 billion in economic benefits to Europe. This figure includes €0.8 billion in primary benefits through direct users of Aeolus data and information based on the average willingness-to-pay contribution and 4,000 EUMETSAT (European Organisation for the Exploitation of Meteorological Satellites) users. A further €2.8 million in wider benefits included improved forecasting accuracy. 

Aeolus also had a significant impact on the European institutional infrastructure dedicated to utalizing lasers in space. “In the end, we had to set up two new labs, call in additional DLR German Aerospace Center support and produce entire new technical standards, which are now being applied to all follow-on laser missions,” explained Armandillo. “The commercial space industry by itself could not have gone to the lengths we took.”

What’s amazing about all this is that Aeolus is essentially a pre-operational mission. Its function is to demonstrate new laser technology and pave the way for future meteorological satellites to measure the Earth's wind. At the ESA ministerial meeting in November 2022, member states approved funding for a second Aeolus mission. This follow-on mission is expected to be launched within a decade. It is expected to have mission costs of €1.8 billion and remain operational for over 10 years. ESA is estimating that this second Aeolus mission will bring in €7.1 billion in benefits, of which €1.5 billion will be primary benefits.

Conclusion

Aeolus isn’t celebrated enough, in my humble opinion. The mission showed that ESA can take on a seemingly insurmountable challenge and conquer it. The mission also had a tangible and continuing impact on the present and future of weather forecasting. And although never the most desirable outcome for a programme, it also had a positive impact on how the agency contracts future missions by ensuring that technology is ready for flight before assigning it to a mission. When you consider all of this, that €500 million price tag looks more and more like a bargain.

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Another return vehicle enters the race - ArianeGroup announced its Space Case service which will host and return experiments from orbit aboard a small return vehicle. According to the company, the SC-X01 demonstrator capsule was developed with support from ESA and the Way2Space innovation centre. The small simple reentry capsule is designed to be launched aboard multiple vehicles including Ariane 6, Vega, and even smaller launch vehicles and sounding rockets. Features of the operational capsule will include monitoring of environmental and flight parameters, real-time recording to onboard memory, and real-time telemetry for safe recovery. It's not clear when ArianeGroup intends on launching the SC-X01 demonstrator.

Whoops, wrong side - A sound rocket launched from the Esrange Space Center in Sweden touched down 40 kilometres northwest of its planned landing site which was inside the borders of Norway. According to a statement from a spokesperson for the Norwegian Ministry of Foreign Affairs, the country was not pleased with the incident. “The Norwegian authorities take any unauthorised activity on the Norwegian side of the border very seriously.” The rocket carried three experiments for ESA.

ESOC, we have a problem - ESA revealed that the ice-penetrating RIME antenna aboard its JUICE satellite has not yet been deployed as planned. During the first week of commissioning, an issue arose with the 16-metre-long Radar for Icy Moons Exploration (RIME) antenna, which is preventing it from being released from its mounting bracket. The agency is currently troubleshooting the problem and has stated that there are various options available to “nudge the important instrument out of its current position.”

The rabbit steams ahead - In a MaiaSpace LinkedIn post covering a visit from Bruno Bonnell, general secretary of the France 2030 investment plan, and a delegation from parent company ArianeGroup, the company revealed that it had completed a full-scale stage prototype model for its Maia launch vehicle. This is a pretty astonishing achievement considering the company was founded just 12 months ago. The prototype will be used for cryo tests at ArianeGroup testing facilities. In a second post, the company revealed that in 2023 it planned to perform upper-stage cryo-testing, ground testing of the company’s Colibri kick stage sub-systems, and pave the way for launch site activities at Kourou.

Is it just me or is it hot down there? - Finish Earth Observation data provider ICEYE announced the Beta release of its Wildfire Insights product. According to ICEYE, the product is a first of its kind and will provide “building-level data” for a wildfire event in near real-time based on satellite imagery and a combination of advanced analytics and machine learning. The company will select insurers to participate in the final testing of the product as part of the Beta phase. The General Availability released is planned for the third quarter of 2023.

A fiery end to April - HyImpulse completed its eighth engine test campaign in the Shetland Isles, Scotland last week. The HyPLOX75 hybrid motor that was tested during the campaign will power the company's SR75 suborbital demonstrator which it expects to launch for the first time later this year. It will also power the company’s SL1 orbital-class vehicle which will utilize the motor in clusters aboard the first and second stages of the rocket. The smaller HyPLOX10 engine will be utilized aboard the rocket’s third stage.

That’s a lot of minutes! - The European Data Relay Service, built under a Partnership Project between ESA and Airbus Defence and Space, has reached one million minutes of relayed communications. Since 2016, two GEO nodes (EDRS-A and EDRS-C) have been providing secure high-speed data transfer services to the European Union’s Copernicus Programme and, since 2022, a fully European communication capability to the International Space Station.

It's like that 90s movie with Angelina Jolie but real - Thales Alenia Space successfully seized control of an ESA demonstration satellite. The exercise occurred at the third edition of CYSAT, a European event dedicated to cybersecurity for the space industry which took place in Paris. During the event, ESA challenged teams to seize control of OPS-SAT, a nanosatellite test bench operated by the agency for demonstration purposes. The Thales team was able to compromise the data sent back to Earth by modifying the images captured by the satellite’s camera while concealing their activities to avoid detection by ESA. 

Now, that’s a name: SPACE FACTORY - Thales Alenia Space announced that it had won an Italian space agency (ASI) contract to conduct the development of Italy’s Space Factory 4.0 programme. In March, ASI announced that it had set aside €57 million in PNRR funds to pursue the project. Thales will lead a consortium of companies that includes Argotec, CIRA, and Sitael to develop an interconnected system of facilities located across Italy, set to start operations by 2026. The system will consolidate the country’s expertise in the design, production, and testing of satellite components calling on automation and digitalization methods to build advanced satellites.

South Korea gets some French power - French space mobility startup Exotrail signed a contract with South Korea's Satrec Initiative to supply its spaceware micro XL propulsion system for use aboard a Satrec Earth observation satellite for a South Korean governmental R&D mission.