A Scout-D orbital rocket with cutaway sections showing the motor in the fourth stage and the payload in the payload nosecone.

The Scout was a class of rocket developed jointly by NASA and the U.S. Air Force to get small satellites into orbit. Scout is actually an acronym; it stands for "Solid Controlled Orbital Utility Test system". Because NASA wanted to get satellites into orbit immediately, the first Scourt rocket used off-the-shelf hardware. It was designed in 1957 at the Langley space center. Because solid fuel was easier to deal with, each stage of the Scout was a solid fuel rocket. There were four stages. The "Algol" first stage used an Aerojet General motor previously used in the Polaris missile. The "Castor" second stage was developed using the U.S. Army's Sergeant surface-to-surface missile, and used a Thiokol motor. The "Antares" third stage used an Allegany Ballistics Laboratory motor originally used in a Vanguard rocket. The "Altair" fourth stage also used an Allegany Ballistics motor.

The rocket's guidance system was gyroscopically based, and and used four fins on the first stage for stability in the atmosphere.

The Scout D was first built in 1972. It used an Algol III rocket motor, which greatly improved performance and thrust.