Sputnik 1 enters Earth orbit

A Signal Above the Earth

On October 4, 1957, the Soviet Union launched Sputnik 1 into Earth orbit. The satellite was a polished metal sphere fitted with four antennas. It was small enough that pictures of it are sometimes surprising beside the political reaction it produced. Its radio transmitters sent signals that listeners could receive on suitable equipment. The sound offered evidence of a body moving overhead even for people with no access to official Soviet tracking stations. The result was a worldwide event because the object's motion and transmission could be independently observed far from the place where the rocket had lifted off.

What It Took to Stay Up

The launch vehicle was derived from the Soviet R-7 rocket. To enter orbit, the satellite needed sufficient sideways speed as well as altitude. Instead of rising and coming directly back down, it kept falling toward Earth while moving far enough around the curved planet to continue its path. Sputnik did not have to fire an engine continuously to stay there. Drag gradually changed the orbit, and the satellite reentered in January 1958. Its radio batteries stopped operating earlier. The period during which people could hear it and the period during which it remained in orbit were therefore different.

Why a Small Payload Was Enough

Sputnik 1 did not carry the range of instruments later associated with research satellites. A transmitter and a known orbit could already tell scientists something about propagation through the upper atmosphere, while changes in the orbit offered information about drag. More important to the public, the first spacecraft had been placed into orbit by a system powerful enough to deliver it there. That ability attracted attention in a Cold War context where rocket technology had military implications. It also gave research institutions a reason to reconsider which observations might become possible if instruments could regularly operate above the atmosphere.

The Responses on the Ground

The American reaction included renewed attention to space research, technical education and missile development. The United States put Explorer 1 in orbit early in 1958, and NASA began operations later that year. Those events did not come from a standing start; American and Soviet teams had been developing launch and satellite programs before October 1957. Sputnik changed their public urgency and the evidence against which plans could be judged. The orbit demonstrated that spaceflight had become a practical activity, while the repeated radio signal gave people a memorable way to experience what had happened without seeing the satellite itself. Observers also saw the larger discarded rocket stage, so a bright moving object reported as Sputnik was not necessarily the small transmitting sphere.