Rocket

Black Mesa and the Resistance used two rockets to close dimensional rifts.

Half-Life
During the Black Mesa Incident aliens from the borderworld Xen were attacking in full force, and the scientists at the facility eventually resorted to using a Satellite Delivery Rocket Black Mesa had to shoot up a satellite into space to close the increasing dimensional rift. HECU personnel intervened and killed the team that was attempting the launch. Gordon Freeman eventually is tasked to launch the rocket no matter what, as at the time it is believed that sealing the rift is the only way to stop the Xenian invasion. Later on, after reaching the fabled Lambda Complex, he was told that the rocket failed in its job due to the rift still being held open by the powerful Nihilanth.

Half-Life 2: Episode Two
After Gordon and Alyx's escape from City 17 and the Citadel's collapse, Alyx attempts to make contact with White Forest to tell them about the codes they had received in the Citadel and the situation of the Superportal. Dr. Magnusson orders them to get to White Forest Base as soon as they can, believing that the codes Alyx is carrying can be used to close the Superportal via a rocket the base had been preparing for some time. Upon arrival to the base, Alyx and Gordon are put to work preparing the rocket for launch, and even defending the base from the weakened Combine's feeble attempts to stop the launch. When all is safe, and the rocket is fully prepared, Gordon receives the honor of launching the rocket and finally closing the Superportal and the last remaining link to the Combine Overworld. However, the rocket itself can be reached and surprisingly enough has collision enabled, allowing the player to in fact ride on top of it. It may also be noted that Dr. Kleiner reported before launch that the rocket had an anomaly payload of 8 lbs. Earlier in the silo chamber Lamarr can be seen crawling into the hatch on the rocket. The player has the opportunity to close the hatch with Lamarr inside. It can be assumed that Lamarr has in fact died.

Behind the scenes
According to Matt Wright, the team designed Magnusson's rocket around blueprints from the Titan family of missiles instead of just making up something that fit their fantasies of a rocket. He adds that grounding the details of their world in reality, making them as precise as possible, makes the invented, fantastic elements seem that much more believable.

List of appearances

 * Half-Life
 * Half-Life: Decay
 * Half-Life 2: Episode Two