BEIJING - Two navigation satellites launched by China on Saturday mark another solid step towards building a homegrown positioning system with global coverage, a lead scientist said Sunday.

Scientists put two satellites for the Beidou Navigation Satellite System (BDS), an indigenous alternative to US - operated GPS, into orbit Saturday at midnight.

According to Xie Jun, chief engineer of the Beidou project, the "twin sats" are designed to be "trail blazers" as the BDS expands its coverage globally.

Named after the Chinese term for the plough or the Big Dipper constellation, the Beidou project was formally launched in 1994, some 20 years after the inception of GPS. It was not till 2000 when the first Beidou satellite was launched.

Nonetheless, by 2012, a regional network had already taken shape, and the BDS is already providing positioning, navigation, timing and short message services in China and several other Asian countries.

Beidou is currently one of the four dominating navigation systems in the world, along with the US GPS, Russia's GLONASS, and the European Union's Galileo.

The plan is to set up a complete "constellation" of 35 navigation satellites and expand their coverage to the entire globe by 2020.

Saturday's launch of the "twin sats" - the 18th and 19th of the whole Beidou project and the third this year - and their mission to test navigation signaling and inter-satellite links, are a big part of that plan, said Xie.

"We have deployed a new type of signal format for the 'twin sats', which enable us to double the data exchanged between satellites within the same period of time," he said, "That means faster and better service for BDS clients."

Xie said scientists will examine the satellites' distance measurement and anti-jamming capabilities. They will also join the duo with the 17th Beidou satellite, launched in late March, in the mission of testing inter-satellite connectivity.

The inter-satellite links will also allow Beidou satellites to connect with their GPS and GLONASS counterparts.

"The compatibility edge allows BDS clients to use GPS data for corrections in positioning in order to improve service accuracy and convenience," Xie said.

"Though we started late, the BDS now could almost rival any foreign counterparts in terms of general performance. In fact, we might even have a little edge in the fields of regional enhanced services, positioning reports, and short message services," he said.

Home made

Xie said 98 percent of the "twin sats" components were domestically made.

"When we first started the Beidou project, China was not at the time technologically equipped to manufacture much-needed items of technical sophistication, so we have to buy them from other countries," he said.

Technology embargoes made it hard, and often the purchased items malfunctioned.

Scientists managed to break that barrier, gradually substituting foreign-made satellite parts with domestic ones, Xie said.

These include the rubidium atomic clocks. Dubbed the "heart" of the navigation satellites, the atomic clocks are the workhorses which send synchronized signals so sat-nav receivers can triangulate their position on Earth.

Xie said high-precision rubidium atomic clocks carried by the "twin sats" could provide more accurate positioning for BDS.

A new-generation engine, measuring only 600 grams in weight, also helps the satellites move more precisely in space and can last up to 15 years, almost doubling the life expectancy of its predecessors.