ESTCube-1

ESTCube-1
Company type	Satellite
Industry	Space, Satellite technology
Founded	May 7, 2013; 13 years ago
Fate	Mission ended February 17, 2015
Headquarters	Tartu, Estonia
Products	CubeSat satellite, Electric solar wind sail experiment
Website	www.estcube.eu

ESTCube-1 represents Estonia's inaugural satellite and holds the distinction of being the first spacecraft globally to test an electric solar wind sail (E-sail) concept. It was launched into low Earth orbit on May 7, 2013, aboard the Vega VV02 launch vehicle. Constructed following the CubeSat specifications, ESTCube-1 measured 10×10×11.35 cm, with a volume of one liter and a weight of 1.048 kilograms.

The mission concluded officially on February 17, 2015, having contributed extensively to academic research and business ventures: it inspired 29 bachelor's theses, 19 master's theses, 5 doctoral dissertations, and led to the creation of 4 startup companies. Unfortunately, deployment of the E-sail tether was unsuccessful, which prevented the acquisition of experimental data regarding both the E-sail mechanism and plasma braking system. The final communication from the satellite was received on May 19, 2015.

Scientific purpose

ESTCube-1 was developed through the Estonian Student Satellite Program, engaging university and secondary school students in its design and construction. Although primarily educational, the satellite carried out scientific objectives by testing an electric solar wind sail (E-sail) technology devised by Finnish researcher Pekka Janhunen. The mission aimed to extend a 10-meter-long E-sail wire ("Heytether") with a thickness between 20 and 50 micrometers. Deployment progress was intended to be monitored via changes in the satellite’s spin rate or through images captured by an onboard camera.

To regulate the interaction between the E-sail and Earth's plasma environment—particularly its influence on spacecraft rotation—two nanotechnology-based electron emitters were installed. These devices emitted electrons to positively charge the E-sail up to 500 volts. The resulting repulsion of plasma ions against this charged tether would modify the satellite's rotational speed, providing critical data for the experiment. Additionally, this tether was engineered to function as a plasma brake for deorbiting small satellites at mission end. A color CMOS camera capable of capturing VGA-resolution RAW images was onboard to photograph Earth and observe tether deployment.

Orbit

ESTCube-1 was positioned in a Sun–synchronous circular orbit at an altitude of approximately 670 kilometers to optimize both experimental conditions and communication capabilities. The satellite was deployed by Arianespace using a Vega VV02 rocket launched from Kourou’s ELA-1 launch complex at 02:06:31 UTC on May 7, 2013. After reaching orbit, successful contact with ground stations was established. The first image of Earth was taken on May 15 and transmitted via amateur radio frequencies.

Lifespan of the satellite

Following deployment on May 7, 2013, ESTCube-1’s mission unfolded as anticipated:

Within half an hour post-launch, antennas and critical subsystems were activated.
During the initial two days, the satellite broadcasted safe-mode CW beacon signals.
The early weeks were dedicated to subsystem testing and achieving full operational status.
The spacecraft was oriented so that its camera faced Earth, enabling it to capture images including those of Estonia.
It rotated around its longitudinal axis at a rate of one revolution per second, potentially making it one of the fastest controlled rotating satellites with an angular velocity reaching 841 degrees per second.
In mid-October 2014, an attempt was made to deploy the E-sail tether using centrifugal force; however, this effort failed likely because the reel became stuck. No visual confirmation was obtained from the onboard camera, leading to suspension of further E-sail experiments.
Despite this setback, cold cathode electron emitters onboard were successfully tested after tether deployment failure.

Conclusion of the mission

The mission came to an end as a result of deterioration in the photovoltaic power system combined with battery depletion. The final official signal was received on 17 February 2015, although Earth observation and environmental data gathering persisted until 19 May 2015. The intended solar sail experiment did not succeed because the deployment mechanism for the sail cable failed to endure the vibrations experienced during launch.

<imagemap> File:ESTCube-1 orbiting our colourful planet.jpg|alt=A grid of satellite photos of Earth, four wide by three high, on a black background.|center|thumb|600px|Images captured by ESTCube-1 (arranged chronologically). Hover over or click each image to identify its location.

rect 174 75 814 556 Arctic rect 844 75 1484 556 Australia rect 1514 75 2154 556 Brazil

rect 2180 75 2500 315 Bangladesh rect 2500 75 2820 315 Myanmar rect 2180 315 2820 556 Bay of Bengal

rect 174 586 814 1065 Algeria

rect 844 586 1484 1065 Peru

poly 1970 1065 2030 1040 2120 820 2154 850 2154 1065 Mauritania poly 1845 685 1790 830 1670 950 1650 930 1670 870 1735 810 1730 790 1770 740 1755 735 1800 660 1830 660 The Gambia circle 1980 670 30 Dakar poly 1970 1065 2030 1040 2120 820 1987 658 1845 685 1740 640 1514 1065 Senegal poly1740640169076015909001514840151065Guinea-Bissau poly1590900151410651514840Guinea

rect1514215421065Atlantic Ocean rect218028201065Red Sea

rect174109681481575Sudan rect844109614841575English Channel rect1514109621541575Antarctica

rect21802180210961575China–Mongolia border

</imagemap>

Dimensions and mass

The Estonian satellite utilized a standard CubeSat configuration of one unit (1U). Typically, a single CubeSat unit measures approximately100.0±0.1 mm along each edge and stands at a height of about113.5±0.1 mm, with a maximum allowable weight of1300 grams.

Communication systems

ESTCube-1 operated on two frequencies allocated by the International Amateur Radio Union:

437.250 MHz
437.505 MHz

Telemetry data was periodically broadcast via an18 WPM Morse code signal at437.250 MHz, providing essential satellite information every three to ten minutes. For higher-speed data transmission, frequency shift keying (FSK) signals at437.505 MHz enabled a9600 baud rate using the AX.25 packet protocol. Due to bandwidth constraints within amateur radio bands, transmission speeds were limited to25 kHz. This faster communication channel was activated solely upon command. Command signals were transmitted over the145 MHz amateur radio frequency.

Software architecture

The satellite’s microcontrollers ran different operating systems tailored to their functions:

FreeRTOS managed Command and Data Handling as well as camera operations.
TinyOS was employed for the communication subsystem, chosen for its low power consumption.

Development of the Mission Control System was undertaken by students from Tartu University under the guidance of CGI Group professionals.

Funding and expenses

ESTCube-1 was launched as a secondary payload aboard Vega flight VV02, which represents the European Space Agency’s most cost-effective satellite launch option. Estonia’s membership in ESA covered the majority of launch-related fees (around70,000 euros) through educational contributions, resulting in total project costs near100,000 euros.

Outcomes

The satellite successfully validated operational capabilities in orbit with an anticipated two-year mission duration. ESTCube contributed to reducing commercial expenses associated with satellite development. Nevertheless, the deployment attempt of the E-sail did not succeed, and no scientific data was obtained from either the E-sail or plasma braking experiments.

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