Periodic Reporting for period 1 - EDDA (European Direct-Drive Architecture)
Période du rapport: 2019-12-01 au 2022-05-31
Spacecraft propulsion works on an action/reaction principle. When air is expelled from the exhaust, the balloon moves in the opposite direction. In the case of spacecraft, the thrust comes from either a chemical reaction, or from an ionized gas strongly accelerated by an electric field (at several tens of km/sec). While chemical propulsion systems store their energy in the propellants (fuels), energy required by electric propulsion is generated by solar panels onboard.
H2020 HV-EPSA demonstrated that the voltage delivered by solar array to the electronic units on board a spacecraft could be as high as 400V with limited effort, with respect to current 100V systems. Some thrusters are compatible with this maximum voltage: Hall Effect Thruster (HET) (currently the most used on spacecraft), as those manufactured by Sitael in Italy, and High Efficiency Multistage Plasma Thruster (HEMPT) made by Thales-D. Both types of thrusters have been the subject of research & innovation programmes which benefitted from the financial support of the European Commission, as CHEOPS (https://www.epic-src.eu/cheops/) for HET, and HEMPT-NG (https://www.epic-src.eu/hempt-ng/) for HEMPT.
These thruster developments provide a fertile ground for EDDA (European Direct Drive Architecture) which aims to demonstrate the feasibility to provide power from photovoltaic panels directly to several thrusters at the same time and at higher voltage levels than today. Normally, electronic components called power converters are needed to deliver the right voltage and current to electric thrusters. Yet, these power converters are heavy, result in thermal losses as power conversion is not 100% efficient and highly increase the costs associated with spacecraft launches (sending one kg to space costs 15-30 k€). Direct drive is a concept connecting the power source directly (without conversion) to the user to remove these limitations associated with power electronics. Used in space environment, this disruptive concept is expected to enhance propulsion capabilities either for staying in orbit around Earth (satellites) or in the frame of space exploration missions (to the Moon or to other planets within the inner Solar system namely Mercury, Venus, Mars or Asteroids).
H2020 HV-EPSA demonstrated that the voltage delivered by solar array to the electronic units on board a spacecraft could be as high as 400V with limited effort, with respect to current 100V systems. Some thrusters are compatible with this maximum voltage: Hall Effect Thruster (HET) (currently the most used on spacecraft), as those manufactured by Sitael in Italy, and High Efficiency Multistage Plasma Thruster (HEMPT) made by Thales-D. Both types of thrusters have been the subject of research & innovation programmes which benefitted from the financial support of the European Commission, as CHEOPS (https://www.epic-src.eu/cheops/) for HET, and HEMPT-NG (https://www.epic-src.eu/hempt-ng/) for HEMPT.
These thruster developments provide a fertile ground for EDDA (European Direct Drive Architecture) which aims to demonstrate the feasibility to provide power from photovoltaic panels directly to several thrusters at the same time and at higher voltage levels than today. Normally, electronic components called power converters are needed to deliver the right voltage and current to electric thrusters. Yet, these power converters are heavy, result in thermal losses as power conversion is not 100% efficient and highly increase the costs associated with spacecraft launches (sending one kg to space costs 15-30 k€). Direct drive is a concept connecting the power source directly (without conversion) to the user to remove these limitations associated with power electronics. Used in space environment, this disruptive concept is expected to enhance propulsion capabilities either for staying in orbit around Earth (satellites) or in the frame of space exploration missions (to the Moon or to other planets within the inner Solar system namely Mercury, Venus, Mars or Asteroids).
On spacecraft, Direct Drive for electric propulsion consists in supplying the thrusters at their nominal voltage, above 250V for HET and HEMPT, far above the usual satellite voltage (100V). This requires a new power electronic unit development, carried out by Thales Alenia Space Belgium.
Special care shall be taken to avoid electric arcing caused by high voltage and very low pressure. Arc is due to mobile particles which are coming either from deep Space or from the thruster (ionized gas and electrons). The characterization of the gas discharge in the magnetically shielded design of Sitael’s HET were analyzed with advanced numerical models by University of Carlos III from Madrid, in order to determine characteristics for power electronics and propulsive performances.
Depending on the spacecraft missions (around Earth, or Interplanetary), defined by Thales Alenia Space, their duration, the power available (according to Solar Array size), one or several thrusters can run simultaneously. EDDA study determines the capability of a large number of thrusters to be run simultaneously, and 2 thrusters of 5kW were tested simultaneously to verify it by experiment.
For the power electronic part, various ways to proceed (architectures) were analyzed to find one compatible with expectations and compatible with several thrusters. Then, it was built and tested, in particular control loops for voltage, current, and flow rates. As it is not easy to get a large constantly sunny solar array, a SAS (solar array simulator) was developed based on an existing one by a European SME (AXID System), which provides the necessary power in representative conditions of currents and voltage.
The final test, repeated several times with different conditions and one or two thrusters, was to simulate a Space mission, with its different phases: launch, electric orbit raising, and on station. It worked perfectly and gave some relevant measurements to design and build robust electronics solutions.
Special care shall be taken to avoid electric arcing caused by high voltage and very low pressure. Arc is due to mobile particles which are coming either from deep Space or from the thruster (ionized gas and electrons). The characterization of the gas discharge in the magnetically shielded design of Sitael’s HET were analyzed with advanced numerical models by University of Carlos III from Madrid, in order to determine characteristics for power electronics and propulsive performances.
Depending on the spacecraft missions (around Earth, or Interplanetary), defined by Thales Alenia Space, their duration, the power available (according to Solar Array size), one or several thrusters can run simultaneously. EDDA study determines the capability of a large number of thrusters to be run simultaneously, and 2 thrusters of 5kW were tested simultaneously to verify it by experiment.
For the power electronic part, various ways to proceed (architectures) were analyzed to find one compatible with expectations and compatible with several thrusters. Then, it was built and tested, in particular control loops for voltage, current, and flow rates. As it is not easy to get a large constantly sunny solar array, a SAS (solar array simulator) was developed based on an existing one by a European SME (AXID System), which provides the necessary power in representative conditions of currents and voltage.
The final test, repeated several times with different conditions and one or two thrusters, was to simulate a Space mission, with its different phases: launch, electric orbit raising, and on station. It worked perfectly and gave some relevant measurements to design and build robust electronics solutions.
The main improvements of the direct-drive concept beyond the state-of-the-art are related to the gain in power efficiency (close to 100% of the power extracted from the solar panels, no thermal losses due to power conversion, converter mass saving). As a consequence of these significant performance improvements, cheaper and lighter spacecraft can be envisaged, or identical ones with enhanced performances. The socio-economic impacts of EDDA can be appraised in 3 main market applications: GEO telecom satellites, Deep Space Exploration (as interplanetary missions), or the novel On Orbit Servicing.
For the large geostationary (at 36000 km altitude) telecommunication satellites, removal of power converters will result in significant cost and mass reductions, opening the way to less expensive space launches or additional payload onboard (more functionalities / capacity). Direct drive can also provide a reduction of transfer orbit duration.
On-orbit services is an emergent market. Such services include: life extension, end of life deorbiting , debris removal, relocation, transportation… and they can address both GEO and (smaller) LEO satellites. On one hand, a moderate increase of the number of GEO satellites (devoted to telecommunication) is anticipated, and they can require maintenance/repair/upgrading services. On the other hand, the LEO satellite market is currently experiencing deployment of large constellations and mega-constellations. They are meant to provide full Earth coverage of communication networks and Earth observation services in the next years. LEO satellites will therefore increase the already large number of objects orbiting close to the Earth, thereby triggering the needs for services such as debris removal, asset relocation, and deorbiting.
In Deep Space Exploration, development of direct-drive for electric propulsion will be an important enabler for future Deep Space Exploration phases, either on Moon, Mars or Asteroids, where large amount of power to supply electric propulsion is recognized.
The first two markets are related to telecommunications networks which are vital in mankind’s daily life. They can help to protect the planet and the environment (satellites provide data on climate change, measure pollution, monitor natural disasters,…) with downstream impacts on biodiversity, agriculture,…. Besides, Space technologies improve products we use every day, weather forecasts, and communications worldwide.
Advances in Deep Space Exploration, as shown by Artemis Moon missions, holds many promises. On one hand, it enhances safety on Earth (e.g. asteroid aversion such as the DART mission) and it supports defining appropriate risk management strategies. On the other hand, scientific discoveries nurture human curiosity by pushing our boundaries by exploring the unknown and inspiring future generations.
For the large geostationary (at 36000 km altitude) telecommunication satellites, removal of power converters will result in significant cost and mass reductions, opening the way to less expensive space launches or additional payload onboard (more functionalities / capacity). Direct drive can also provide a reduction of transfer orbit duration.
On-orbit services is an emergent market. Such services include: life extension, end of life deorbiting , debris removal, relocation, transportation… and they can address both GEO and (smaller) LEO satellites. On one hand, a moderate increase of the number of GEO satellites (devoted to telecommunication) is anticipated, and they can require maintenance/repair/upgrading services. On the other hand, the LEO satellite market is currently experiencing deployment of large constellations and mega-constellations. They are meant to provide full Earth coverage of communication networks and Earth observation services in the next years. LEO satellites will therefore increase the already large number of objects orbiting close to the Earth, thereby triggering the needs for services such as debris removal, asset relocation, and deorbiting.
In Deep Space Exploration, development of direct-drive for electric propulsion will be an important enabler for future Deep Space Exploration phases, either on Moon, Mars or Asteroids, where large amount of power to supply electric propulsion is recognized.
The first two markets are related to telecommunications networks which are vital in mankind’s daily life. They can help to protect the planet and the environment (satellites provide data on climate change, measure pollution, monitor natural disasters,…) with downstream impacts on biodiversity, agriculture,…. Besides, Space technologies improve products we use every day, weather forecasts, and communications worldwide.
Advances in Deep Space Exploration, as shown by Artemis Moon missions, holds many promises. On one hand, it enhances safety on Earth (e.g. asteroid aversion such as the DART mission) and it supports defining appropriate risk management strategies. On the other hand, scientific discoveries nurture human curiosity by pushing our boundaries by exploring the unknown and inspiring future generations.