Protocol CR91 dictates that when a base is presumed to be lost to an enemy incursion, a lethal neurotoxin will be released from orbit, allowing Stargate Command to later mount a salvage operation. When the carnivorous alien insect known as R75 breached containment and took over the Gamma Site, Landry initiated Protocol CR91, and Odyssey was sent to launch a payload of the toxin into the atmosphere. Because the planet's unique radioactive ionosphere interfered with communications and the signal from subcutaneous transmitters, SG-1 was unable to alert the Odyssey that they and the members of the IOA had survived the insects and the destruction of the facility. However, they were able to make their way to the planet's research station, and Carter was able to boost the power and adjust the communication array to reach into planetary orbit and allow the Odyssey to triangulate their position. They were beamed aboard the Odyssey before the neurotoxin was released.
Cross Reference: Gamma Site, Odyssey, R75
Episode Reference: The Scourge