Plagued for years by scandals and setbacks, Russia's new Vostochny cosmodrome is set to hold its inaugural launch Wednesday as the country strives to boost its space programme despite economic woes.

The new spaceport, located in the far eastern Amur region, will launch a Soyuz 2.1a rocket carrying three satellites at 0201 GMT after having been delayed by several months over construction mishaps.

Hailed by President Vladimir Putin as the country's biggest current building project with a budget estimated between 300 and 400 billion rubles ($4.5 to $6 billion, four to 5.3 billion euros), the construction of the new cosmodrome began in 2012.

Some 10,000 workers have since toiled to build 115 kilometres (71 miles) of roads in the immense but sparsely populated region, as well as 125 kilometres of railways and a town with housing for 25,000 people.

The Kremlin's goal is to ease Russia's dependence on space launches in Baikonur, Kazakhstan, a launchpad Moscow has been forced to rent at a cost of $115 million a year since the collapse of the Soviet Union.

Russia is also home to the Plesetsk cosmodrome in the far north, which is used for satellite launches and missile testing.

Vostochny, like Baikonur, is closer to the equator, making launches more energy-efficient and cheaper.

Covering an area of 1,000 square kilometres (386 square miles), the new cosmodrome now has one launchpad for the Soyuz, the only rocket currently being used for manned space flights.

A second construction phase will begin next year to build a reinforced launchpad for the new Angara rocket, which is currently being tested to replace the ageing Proton workhorse rockets.

- String of scandals -

Construction on the Vostochny cosmodrome has been marred by a string of labour disputes, corruption scandals and delays.

In January, the pro-Kremlin Izvestia daily reported that some 1.4 billion rubles from the federal budget had been embezzled during construction, which was managed by the state Spetsstroy agency.

Spetsstroy said that month that it had filed 31 corruption complaints for a total of four billion rubles.

Construction workers who had gone unpaid for months have also protested their employment conditions, appealing for intervention by Putin himself.

The first satellite launch had been scheduled for late 2015, but setbacks forced authorities to reconsider the timetable.

Putin demanded that deputy prime minister Dmitry Rogozin, who oversees the space and defence industries, ensure the cosmodrome be completed by the spring of 2016.

"Some construction work is still under way at the site, but it won't affect the launch," said Igor Marinin, the editor-in-chief of Russia's Space News magazine.

International news organisations, including AFP, have been barred from attending the inaugural launch and foreign press access to the cosmodrome has yet to be scheduled.

- Debate over use -

Russia already uses three cosmodromes -- Baikonur, Plesetsk and one in Kourou, French Guiana -- equipped with Soyuz launchpads.

This has raised concerns that Russian federal space agency Roscosmos will have trouble justifying launches from Vostochny.

Facing an economic crisis, the Russian government is also pressed to make budget cuts and its space programme has slipped down its list of priorities.

Despite being in financial limbo, Roscosmos announced its programme for the next decade in January. The plan has not yet been confirmed.

Roscomos chief Igor Komarov admitted earlier this year that Russia "does not have financial capabilities for advanced space projects."

"In theory there could be a launch everyday," Marinin said. "But where are you going to find all the necessary rockets?"

Wednesday's inauguration will be Vostochny's only launch this year, and only one launch is scheduled for 2017.

Russian authorities have meanwhile insisted that the Vostochny cosmodrome will not put other facilities out of use.

Rogozin said earlier this month that the Baikonur cosmodrome will be used for manned flights until 2023.

"The second construction phase (on Vostochny) needs to begin as quickly as possible so that Angara launchers can be used," Marinin said, adding that authorities had hurried to build a facility ill-adapted to the latest rocket technology.

Vostochny's first launches using Angara -- the first rocket Russia has developed since the collapse of the Soviet Union -- will not happen before 2021, Roscosmos has said.