A trio of astronauts from the United States, Russia and Italy are headed for the International Space Station, a step toward boosting U.S. research projects aboard the orbiting laboratory.

The Russian Soyuz rocket carrying the three spaceflight veterans blasted off at 11:41 a.m. ET from the Baikonur Cosmodrome in Kazakhstan, a NASA TV broadcast showed.

.<a href="https://twitter.com/AstroKomrade">@AstroKomrade</a>, <a href="https://twitter.com/astro_paolo">@Astro_Paolo</a> & <a href="https://twitter.com/Ryazanskiy_ISS">@Ryazanskiy_ISS</a> are safely in orbit after an 11:41am ET launch, set to arrive at <a href="https://twitter.com/Space_Station">@Space_Station</a> at 6pm ET <a href="https://t.co/ii2wtEPoK8">pic.twitter.com/ii2wtEPoK8</a> —@NASA

The three astronauts are:

Randy Bresnik with the U.S. National Aeronautics and Space Administration.

Sergey Ryazanskiy with the Russian space agency Roscosmos.

Paolo Nespoli with the European Space Agency.

The men were slated to reach the station at 6 p.m. ET, where they will join three crew members already aboard the station, a $100-billion US lab that flies about 400 kilometres above Earth.

Doubling research

Their arrival will mean NASA, for the first time, has four crew members instead of three available for medical experiments, technology demonstrations and other research aboard the station, the U.S. space agency said.

The extra astronaut will effectively double the amount of time for research, program manager Kirk Shireman said at a station conference last week.

NASA does not oversee the Russian staff, which was reduced to two in April until a long-delayed research module joins the station next year.

Previously, Russia flew three cosmonauts, with the remaining three positions filled by a combination of European, Japanese, Canadian and U.S. astronauts.

By the end of next year, NASA intends to begin flying astronauts aboard space taxis under development by SpaceX and Boeing. Both spaceships have room for a fourth seat, bumping the station's overall crew size to seven once Russia returns to full staffing.

Prepping for Mars, lunar missions

NASA is using the station to prepare for human missions to the moon and Mars and to stimulate commercial space transportation, pharmaceutical research, manufacturing and other businesses.

The agency also conducts physics, astronomy and Earth science investigations aboard the outpost, which has been staffed by rotating crews of astronauts and cosmonauts since 2000.

The trio of astronauts wave to onlookers after donning their space suits, shortly before their launch. (Shamil Zhumatov/Reuters)

Bresnik, 49, last flew on the space shuttle in 2009 during a space station assembly mission. Ryazanskiy, 42, spent five-and-a-half months aboard the station in 2013-2014. Nespoli, 60, is making his third space flight, having previously served on both space shuttle and space station crews.

The men are slated to return to Earth in December.