Two Russian cosmonauts and a U.S. astronaut launched toward the international space station (ISS) aboard a Russian rocket April 2 amid heightened security.

The three spaceflyers lifted off from Kazakhstan’s Baikonur Cosmodrome aboard a Soyuz TMA-18 spacecraft four days after Chechen suicide bombers killed 40 people on two Moscow subway trains.

The Russian government increased security measures at the remote launch site, deploying sniffer dogs and helicopter surveillance, according to Russian wire reports.

NASA astronaut Tracy Caldwell Dyson and Russian cosmonauts Alexander Skvortsov and Mikhail Kornienko were due to dock at the space station April 4 to take up long-term residence as Expedition 23 flight engineers, bringing the station’s crew complement to its maximum of six. They will join current ISS commander Oleg Kotov of Russia, as well as Japanese astronaut Soichi Noguchi and T.J. Creamer of NASA.