Artists impression of CryoSat-2 in space. Image courtesy of ESA – P. Carril.
Earth Observation (EO) satellite launches are currently few and far between, so today we’re going to celebrate one that’s hit ten years in space, and commiserate with two satellites that have reached end of life.
The celebration is for ESA’s CryoSat-2 satellite which last Wednesday, 8th April, marked its tenth anniversary in space. Launched in Kazakhstan CryoSat-2 was the second version of the satellite, as the original CryoSat was lost during a launch failure in 2005. It has a non-sun-synchronous low earth orbit at just over 700 km with a 369-day ground track cycle, imaging the same area on the Earth every 30 days.
The main instrument onboard is a Synthetic Aperture Radar Interferometric Radar Altimeter known as SIRAL. It sends out bursts of radar pulses, at an interval of 50 μs, covering a 250 m wide strip of the Earth and measures the time of the return signal to determine the height of the satellite above the planet. It requires a very accurate position measurement, and so it also carries a Doppler Orbit and Radio Positioning Integration by Satellite (DORIS) instrument to determine its orbit. The SIRAL instrument can detect millimetre changes in the elevation of both ice-sheets and sea-ice.
CryoSat-2’s mission is dedicated to the measurement of polar ice – both the vast polar ice sheets and sea floating in the polar oceans. Over the last decade, it has provided several valuable datasets including:
- first complete assessment of Arctic sea-ice thickness
- measurements of the ice sheets covering Antarctica and Greenland
- showing how 200, 000 mountain glaciers have succumbed to climate change
- monitoring the thickness of ice on lakes in winter
- producing bathymetric charts
Although originally designed as three and half year mission, it’s moving towards tripling that lifespan. However, the risk of component failure means it could reach end of life at any time.
Sentinel-3 can undertake some similar measurements, and whilst there is unlikely to be a direct replacement it’s hoped that the Copernicus Polar Ice and Snow Topography Altimeter (CRISTAL) operational mission, currently being developed, will carry on collecting polar ice datasets.
The first of the two satellites to reach end of life is the RapidEye constellation as Planet confirmed its retirement last week which they’ve done proactively and the satellite will no longer collect data. Launched on the 29th August 2008, the five satellite constellation offered commercial imagery for use at a spatial resolution of approximately five metres. Planet noted that since it’s launched the constellation has:
- Orbited the Earth more than 305,000 times
- Travelled almost 13,500 million miles.
- Acquired more than 660,000 images of the Earth’s total landmass.
It has also been confirmed that Diwata-1, the Philippines first EO microsatellite, was on a decaying orbit where it will burn up in the atmosphere. Launched on 27th April 2016 from the International Space Station, the 53-kilogram microsatellite had three instruments:
- High-precision telescope with a 3-metre spatial resolution with visible a near-infrared band.
- Multi-spectral imager (SMI) with an 80-metre spatial resolution, again with visible and near-infrared capabilities.
- Widefield camera with a spatial resolution of 7 kilometres.
The aims of this satellite included studying natural disasters, vegetation changes, ocean productivity, and cloud patterns. According to the Department of Science and Technology – Advanced Science and Technology Institute (DOST-ASTI)  during its time in space Diwata-1:
- Orbited the planet over 22,500 times
- Passed over the Philippines almost 5,000 times.
Its last image of the Philippines was acquired on 28th December last year, whilst its successor, Diwata-2, continues to collect data.
