NIGRAN, Spain, March 7 (Reuters) - Spanish space startup Sateliot is raising cash to send 100 microwave oven-sized satellites to the orbit, entering a crowded race for a slice of a market potentially worth $100 billion to offer cheap data connections via space.

The company, which already has two test satellites in orbit, seeks 100 million euros ($109 million) in equity and debt from private equity investors, funds and banks, CEO Jaume Sanpera said in remarks cleared for publication on Thursday.

Sateliot expects to launch its first four commercial satellites by June, he said.

"With just four satellites, we will be able to invoice, to go commercial in the second half of this year," Sanpera told Reuters at the Sateliot facility in northwestern Spain where his teams are manufacturing the nano-satellites.

Sateliot has an order book worth about 187 million euros in annual revenue, and its clients are mostly from countries with vast areas not covered by mobile networks, including Canada, Brazil, South Africa, Indonesia or Australia, Sanpera said.

Sateliot has spent about 25 million euros to develop, build and send in orbit, through SpaceX, the two test satellites and the first four commercial ones.

The space industry is going through a market revolution as new technologies have reduced the cost and the size of space devices to a fraction of what they used to be, with many startups joining the fray.

Lucas Bishop of investment firm Seraphim Space said only the most cost-efficient of the few dozen nano-satellite operators would likely make it.

While larger operators such as Elon Musk's Starlink are focusing on providing high-speed Internet connection on the ground from a network of thousands of satellites, startups are setting up smaller networks, dubbed constellations, to extend the reach of the "Internet of things", or IoT.

Sateliot is aiming at connecting small devices, such as monitoring equipment on refrigerator containers shipped by sea, with satellites. Potential customers include logistics companies, farmers, oil platforms, or environmental applications, Sanpera said.

Luigi Scatteia, space adviser at PwC said the ability to operate and maintain the whole system seamlessly, including robust, low-power, autonomous equipment at the user end, complete with advanced software, is another key challenge, possibly more complex than deploying the satellites.

Sateliot, in which defence contractor Indra, telecoms infrastructure operator Cellnex and the Spanish government hold stakes of 10.5%, 3.5% and 4.69%, respectively, plans to deploy the 100 satellites by 2028 and hit 1 billion euros in revenue by 2030.

($1 = 0.9196 euros) (Reporting by Inti Landauro and Miguel Vidal, editing by Andrei Khalip and Tomasz Janowski)