Vela 2B (also known Vela 4, Vela Hotel 4 and OPS 3674) was a U.S. reconnaissance satellite for detecting explosions and nuclear tests on land and in space, the first of the second pair of Vela series satellites, taken together with Vela 2A and satellites. The secondary task of the ship was space research (X-rays, gamma rays, neutrons, magnetic field and charged particles). The ship remains in orbit around Earth.