Estonian satellite to photograph Earth from 600 kilometres

Photo: SCANPIX

Estonia’s second satellite project pulled by Tallinn Tech (TUT) innovation centre Mektory and partners will in 2018 (latest) send a cube 600 kilometres into space with main job to scan Earth in visible and presumably in infrared light.

«The cube will weigh about a kilogram, with measurements approximately 10 x 10 x 10 centimetres. It will fly at almost eight kilometres a second, covering its orbit 14 to 15 times in 24 hours, and – this is fun – will fly over Estonia at least once in 24 hours thus providing for daily communication window,» enthused Mart Vihmand, head of the space programme.

Definitely featured on board will be a line-scan camera focussed on a very narrow line while shooting pictures of an exceeding wide area of height of a couple of pixels. Of that, a very sharp image will afterwards be constructed.

With the Estonian project, the resolution of the pictures ought to be about 200 metres on the ground per pixel. Meanwhile, within space projects of much larger budgets and staff, photos come with one metre per pixel. «Thus, for starters we will definitely not be entering space photo business. However, we’d like to raise up a generation of competent students who will afterwards bring home added value from the world,» explained Mr Vihmand.

They are also considering the option of installing a near-infrared camera to monitor vegetation and other things organic.

«While unable to send up expensive technology for ultra-sharp pictures, we intend to compensate by daily pictures of good time-consistency,» said Mart Vihmand.

Energy need enormous

In the programme, TUT stands not alone – close cooperation is ensured by Tartu Observatory while contracts have been signed with Telegrupp AS building a station on Earth, and the software developer CGI Eesti AS.

«The time for data exchange with Earth is very short, during which loads of data need to be sent down at once. The key issue is building pixels into pictures while in space, which might prove complicated considering the limitations of energy and computing capacity. But when sending «unpacked» info from space, data volume would need to be considerably boosted,» said Telegrupp chief Ivo Remmelg.

For that very reason, the UHF connection used on Estonia’s initial ESTCube-1 will no longer suffice, its frequency falling between 300–3000 MHz.

In the project at hand, extra X-strip connection channel will be created to work at 10 GHz and will allow for data exchange speed of 500 Kbit/s – 5 Mb/s .

«Not a bad result at all, with the minimal distance between the station and the satellite 600 km and maximal 3,000 kilometres,» observed Mr Remmelg.

On top of that, it needs to be considered that to catch the signal, the satellite needs to be at right position towards the station on Earth with accuracy of two to five degrees, while the satellite antenna on Earth is at one degree accuracy the satellite in space.

«Quite a challenge, with all these positions. On the one hand, the cameras need to be precision-directed towards the photographed objects; secondly, the directional antenna properly positioned regarding station on Earth; and thirdly the solar panels in relation to the Sun,» explained Ivo Remmelg. «Lots and lots of technical challenges.»

«The satellite needs massive amounts of energy, due to the functions differing and at times more complicated than on ESTCube,» said the Telegrupp chief Mr Remmelg.

Mr Remmelg said the satellite has not the energy to spray signals everywhere. The more so that at frequencies like 10 GHz, close to 80 percent of capacity will be lost as heat. Therefore, from the Earth – i.e. from the antennae at roof of Mektoriy in Mustamäe, Tallinn – the satellite needs to be super precisely monitored during the minutes and seconds it flies overhead. «Miss two degrees and we will no longer see anything,» summarised Mr Remmelg.

No one song band

Mart Vihmand said Estonia might easily study space from a satellite sent from ISS, but that does not fly across Estonia. However, the programme is educational by nature – the main aim being to connect highly varying fields of technology within a single project. 

Also importantly, the university appreciates the massive loads of work accomplished at development of technology and – should all go well – the subsequent exports of the technology and knowhow when cooperating with other universities in the world etc.

The project involves close to 20 academic supervisors from various institutes, leading nine sub-teams at the side of main job. The students involved – mainly from TUT – are over 30 and from nine nationalities.

«From the beginning, my idea was to do a programme – if we have a band, we’ll not play one song only. To get the space domain going, it takes more resource than to keep it going afterwards. The perspective could be to send up a satellite from Estonia every couple of years,» said Mr Vihmand.

Why communication at various frequencies?

UHF – two direction communication; if needed, satellite can be coded from Earth and commands issued.

X-strip – for the sole purpose of bringing large volume «web camera» picture down from space.