Finally, some news about ENVISAT, a massive European satellite that has mysteriously stopped communicating with Earth. On April 8th, it unexpectedly stopped sending data to Earth. Now it has been spotted by another satellite in orbit.
On 15 April, the French space agency CNES turned Pleiades satellite to capture images of Envisat passing within about 100 km. This remarkable feat was possible thanks to the exceptional agility of Pleiades. France’s new Pleiades satellite normally provides very high-resolution images of Earth, but is now focusing on Envisat to shed more light on the situation. Optical, radar and laser observations of the Envisat satellite show that it is still in a stable orbit. The Fraunhofer Institute for High Frequency Physics and Radar Techniques in Wachtberg, Germany, is also providing images to help determine Envisat’s orientation. Images from the TIRA ground-based tracking and imaging radar show the satellite’s body, solar panel and radar antenna.
Flight specialists and engineers are using the images to determine the orientation of Envisat’s solar panel – the satellite’s power source. If the panel is in a suitable position for sufficient exposure to the Sun, enough power is being generated to put Envisat into safe mode, and could allow for re-establishing communications with Earth. Basically, ‘safe mode’ would be a starting point for revival.
Information on Envisat’s orbit is being provided by the US Joint Space Operations Center. In addition, multiple laser ranging stations on the ground are providing information to verify the stability of the satellite’s orbit.
The first sign that there was a problem came on April 8th when contact with the satellite was unexpectedly lost, preventing the reception of any data as it passed over the Kiruna ground station in Sweden. While it is known that Envisat remains in a stable orbit around Earth, efforts to resume contact with the satellite have, so far, not been successful.
The $2.9 billion satellite is one of the most expensive ever built and the largest non-military satellite to observe the Earth from orbit. It is about 10 meters long (30 feet) and 5 m wide (16 feet), with a huge solar array that is about 5 m wide (16 feet) and 14 m long (46 feet). The 10-year-old spacecraft weighs about 8,000 kilograms (17,600 pounds).
Envisat orbits the Earth at an altitude of about 782 kilometers (486 miles) and it completes one trip around the planet every 100 minutes. Since it was launched in 2002, this remarkable satellite has orbited Earth more than 50 000 times delivering thousands of images and a wealth of data to study and understand our changing planet, establishing itself as a landmark success in observing Earth from space.
An analysis of the space debris environment at Envisat’s orbit suggests that there is a 15 % to 30 % chance of the satellite colliding with another piece of junk during the 150 years it remains in orbit. But that likelihood is based on the current population of space debris in low Earth orbit remaining constant during the period – a scenario no one believes is remotely possible.
Envisat’s primary mission has been to study the Earth with 10 sensitive instruments to map the planet’s land, oceans, ice and atmosphere in extreme detail. It has been used by more than 4,000 projects representing 70 different countries. The sudden interruption of Envisat services has disrupted data provision to the international Earth observation user community, which relies on data continuity. The launch of the upcoming Sentinel series being developed for Europe’s Global Monitoring for Environment and Security (GMES) programme has become even more urgent, according to ESA. The Sentinels will provide the data needed for information services to improve the management of the environment, understand and mitigate the effects of climate change and ensure civil security.
Envisat’s last image before loss of contact
Featured image: An artist’s illustration of the Envisat satellite in orbit (Credit: ESA)
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