Three satellites will ride Europe's second Vega launcher into orbit Friday night, rocketing away on missions to test new technologies and examine planet Earth for research and security purposes.

The Proba-V satellite sits atop the Vespa dual-payload adapter, which houses the VNREDSat 1 satellite inside. The Vega's 8.5-foot-diameter payload fairing emblazoned with decals is visible in the background. Credit: ESA/Karim Mellab

The four-stage Vega rocket is launching the satellites for the European Space Agency, the Vietnamese government and students in Estonia.

All three spacecraft will be set free from the Vega launcher within two hours of liftoff, which is set for 0206:31 GMT Saturday (10:06:31 p.m. EDT; 11:06:31 p.m. local time) from Europe's space center in French Guiana, a French overseas department in South America.

Proba-V: Critical science on a budget

Built by QinetiQ Space in Belgium, Proba-V is designed for a mission of two-and-a-half years. It is the third in a series of European Space Agency satellites built with modest investments with highly-focused technology and scientific research missions.

Two Proba precursors launched in 2001 and 2009 to test high-tech hardware in space, including an Earth imaging payload and a revolutionary sun observation instrument.

"Now we have Proba-V ready for flight in Kourou," said Frederic Teston, ESA's Proba program manager. "Proba-V is a set of technologies, but the main mission is to provide continuity to the vegetation measurements which were initiated on Spot 4 and Spot 5. The scientists think it is very important to have continuity in long-term studies and they want to continue beyond Spot 5's observations of vegetation. Therefore, the requirements of our mission were to be compatible with the previous measurements and provide some additional performance."

Artist's concept of the Proba-V satellite in orbit. Credit: ESA

The 304-pound cube-shaped satellite isn't big - only about the size of a kitchen oven - but scientists have tasked it with continuing a 15-year record of land cover and vegetation growth which, up to now, has been the responsibility of larger, more expensive satellites.

The $65 million mission will fill a data gap between the aging French Spot satellites and the Sentinel 3 series of environment-monitoring satellites launching later this decade.

Vegetation data are useful in estimating crop yields, monitoring the effects of droughts and deforestation, and detecting changes in land use, according to scientists.

Funded primarily by Belgium, Proba-V will fly in an orbit allowing its vegetation instrument to map global land cover every two days. Proba-V's vegetation sensor provides up to a ten-fold increase in spatial resolution over the Spot 4 and Spot 5 satellites, distinguishing between different plant species and spotting the scars from wildfires, according to ESA.

VNREDSat 1: Vietnam's eye in the sky

Hidden inside the Vega rocket's enclosed dual-payload adapter for launch, the VNREDSat 1A spacecraft is starting a five-year mission to turn a sharp eye on Earth for the government of Vietnam.

Mostly financed with French government aid, with some additional funding from Vietnam's own coffers, VNREDSat 1's optical camera has a top resolution of 2.5 meters, or 8.2 feet. That is sharp enough to see cars and trucks from orbit more than 400 miles above Earth.

Artist's concept of the VNREDSat 1 satellite in orbit. Credit: EADS Astrium

The 254-pound satellite's contractor, Astrium Satellites of Toulouse, France, built the spacecraft, arranged launch services, and designed and constructed VNREDSat 1's ground receiving stations and control center in Vietnam.

Astrium will activate the satellite and hand over control to Vietnamese engineers after launch.

The French government paid Vietnam 55.8 million euros, or $73.5 million, in preferential overseas direct assistance to fund the satellite, according to the Vietnam Academy of Science and Technology. The Vietnamese government provided about $3 million for the VNREDSat 1 program.

Vietnam will use the satellite to help respond to natural disasters, promote sustainable resource development, and observe the effects of climate change, according to VAST's website.

ESTCube 1: A satellite for Estonia

Estonia's first satellite, a CubeSat built by students at the University of Tartu, will be the last spacecraft to separate from the Vega launcher.

ESTCube 1 weighs 3 pounds, and it's small enough to hold with one hand. But the diminutive will unfurl a 30-foot tether a few days after launch to test a novel method of propulsion.

The electric solar sail concept would harness the interaction of charged solar wind particles with wires deployed from a satellite. The interplay should generate minuscule levels of thrust.

The CubeSat will extend only one tether, which is compressed inside the tiny satellite for launch. But on future satellites, the electric solar sail technique could include dozens of wires carrying an electric charge to produce enough thrust to propel larger structures into deep space.

The concept should provide a gentle but consistent nudge to eventually accelerate a satellite to velocities unattainable with conventional chemical rocket engines.

Scientists in Finland conceived the electric solar sail concept, and ESTCube 1 is the first satellite to put the idea to the test in space.

It's a different concept than normal solar sails, which include a membrane that catches particles of sunlight for a push through space.