Three satellite concepts are competing to be the next mission of ESA’s Earth Explorer programme:
- Stereoid, to measure surface movements, particularly of glaciers, active areas on Earth and its oceans.
- Daedalus, to study the physical properties of the upper reaches of the atmosphere.
- G-Class:H2O, to survey the water cycle over Africa and the Mediterranean.
Each proposed mission would tackle a different aspect of planetary research. The proposals will now be the subject of a feasibility study, after which ESA’s Advisory Committee on Earth Observation (ACEO) will assess their science value. At the end of the selection process, the chosen mission will join the six satellites already in orbit, the most recent being Aeolus launched on 22 August. Like the previous missions, it will be orbited in 2027-2028 from the Kourou spaceport by a European Vega launcher.
“The principle driving ESA’s Earth Explorer programme is to undertake highly innovative missions addressing big challenges and scientific ambitions,” explains Juliette Lambin. “All three missions are original in their own way, and this 10th selection has chosen to go for more technically innovative concepts designed to pursue broader, less focused science goals. We’re talking about unprecedented, first-generation concepts with higher potential. Personally, I have to say the selection surprised me, but the innovation approach is very appealing.”
Stereoid would measure small shifts in Earth’s oceans, glaciers and crusts. Two satellites, Stereoid A and B, would orbit in formation with one of the Sentinel-1 satellites of the Copernicus programme, separated by less than 250 km. “Stereoid will take advantage of Sentinel-1’s radar, distributing the reflected signal from the surface to the other satellites. The two companion satellites are therefore passive sensors, thus dispensing with power-hungry transmission functions. A mission like this was studied and proposed 15 or 20 years ago, but the technological advances made since then make it more feasible today.”
The two Stereoid satellites flying in formation with Sentinel-1 D from the Copernicus programme.
Daedalus would probe the largely unexplored area between the Earth’s upper atmosphere and space from a highly elliptical orbit taking it between altitudes of 150 and 1,000 km. It would release four instrumented nanosatellites into the atmosphere.
“Daedalus is original in that it would acquire local measurements, whereas other Earth-observing satellites are looking down at the surface,” says Juliette Lambin. “In this sense, it would obtain ‘in-situ’ measurements, rather like CNES’s DEMETER mission in the 2000s. This is an unusual configuration for an Earth-observation mission, as the science goals are most often focused on Earth’s surface or near it. Here, it’s a more exploratory approach: we’ll see what we find when we get there, and every measurement will be a discovery in itself, in a region that’s still poorly understood.”
Daedalus and its suite of instruments designed to acquire local measurements in the upper atmosphere.
G-Class:H20 is a radar imaging concept capable of identifying water on Earth and in its atmosphere. It would thus improve forecasting of rain, availability of water resources, flooding and landslides.
“It’s a really new radar imaging concept,” notes Juliette Lambin. “A radar emits radio waves, receives the signal reflected from the surface being observed and then processes it to produce an image. Such missions are generally in low Earth orbit, to get as close to the observed surface as possible and take advantage of the satellite’s forward motion to build up the image. But G-Class:H20 would be in a geosynchronous orbit, at very high altitude, almost geostationary (35,800 km), tracing out a figure of eight above Africa on either side of the equator. That means a lot of transmission power is needed, with a large receiving antenna and sufficient dwell time although the satellite is in motion. So it’s a combination of technical trade-offs. If it works, it would be an imaging radar capable of acquiring several images of the same point every day, unlike most other satellites. This detection capability would serve to survey the water cycle in Africa, complementing other satellites already operating from low Earth orbit.”
G-Class:H20 in near-geostationary orbit, in a figure of eight above the Mediterranean.
Earth, Environment and Climate programme manager
E-mail: juliette.lambin at cnes.fr
Tel : +33 5 61 28 31 74
Centre National d'Etudes Spatiales, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 9, France