1. Sputnik 1:

- Launched by the Soviet Union on October 4, 1957.

- Weighed 83.6 kilograms (184.3 pounds).

- Transmitted beep-beep-beep radio signals allowing scientist to track it while in orbit.

- Orbited the Earth every 96.2 minutes at a maximum velocity of 29,000 km/hour (18,000 mph)

2. Explorer 1:

- Launched by the United States on January 31, 1958.

- Weighed 30 pounds (13.6 kilograms).

- Discovered the Van Allen radiation belts encompassing the Earth.

3. Vanguard 1:

- Launched by the United States on March 17, 1958.

- Weighed 1.54 pounds (0.7 kilograms).

- Designed to last for 2000 years in space.