GEM motors are manufactured with carbon-fibre-reinforced polymer casings and a fuel consisting of HTPB-bound ammonium perchlorate composite propellant.

Observations of the anomaly suggest the GEM 63XL's engine nozzle was either damaged or suffered a structural failure 35 seconds after ignition.

Vulcan Centaur Cert-2 continued into orbit successfully after burnout and separation of its two GEM 63XL boosters at approximately 2 minutes 10 seconds into flight.

[13] The GEM 40 was a 40.4-inch-diameter (1,030 mm) solid rocket motor developed for the 7000-series Delta II launch vehicle beginning in 1987 by Hercules.

[18] The GEM 46 was a 45.1-inch-diameter (1,150 mm) solid rocket motor originally developed for Delta III by Alliant Techsystems.

[20] On 27 August 1998, the GEM 46 boosters on the first Delta III, carrying the Galaxy 10 satellite, depleted their hydraulic fluid used to control the thrust-vectoring nozzle.

The nozzles were then stuck in a position that turned the rocket over, triggering the vehicle's self-destruct function 70 seconds after ignition.

[21][22] The GEM 60 was a 60-inch-diameter (1,500 mm) solid motor used on the Delta IV family of launch vehicles, used with and without thrust vector control.

[24] The added performance from the solid rocket motors allowed variants of the Delta IV Medium+ to accommodate a larger second stage.