The successful launch of the USSR's Sputnik 1 sent the United States into a panic. It was October 1957 and the two countries were in the midst of the Cold War that developed following the end of WWII. The Space Race became an outgrowth of this war as both governments aimed to display their technological superiority through space exploration. The launch of the satellites Sputnik 1 in 1957 and Sputnik 2, just a month later, meant that the USSR took the lead and it was not until the following year, 1958, that the Americans began to catch up, launching the satellite Explorer I. A working mock-up of Explorer I comes to Bonhams Online Air & Space Sale between July 12-21. It has an estimate of $40,000-60,000.

Bonhams Head of Sale, Adam Stackhouse, said: "Explorer I's success was not just proof that the US could launch a satellite into orbit, but it led to the discovery of the Van Allen radiation belt and inspired an entire generation to pursue the stars. It's an exciting prospect for us to handle this c.1957 mock-up that was used in the testing and integration phase of Explorer I. This makes its existence all-the-more historically intriguing."

This working mock-up comes from the collaboration between the Army Ballistic Missile Agency (ABMA) and the Jet Propulsion Laboratory (JPL) in Pasadena. Following the USSR's successful launches of Sputnik 1 and Sputnik 2 there was immense pressure on the US to reach space, which grew even greater when the first US attempt, Project Vanguard, suffered a major setback when the rocket carrying the TV-3 satellite exploded on the launch pad. The Explorer program, which had been put on hold in favour of Project Vanguard, was hastily salvaged to redeem American honour.

University of Iowa physicist James Van Allen was enlisted to provide some of the satellite's payload instrumentation. He and his team later sifted through miles of recorded tape of transmitted data from the Explorer I satellite and made the first discovery of the space age - the Earth's radiation belts, named in the physicist's honor the Van Allen Belt. The mock-up, which includes the payload carrier, nose cone weighted antennae and original wooden carrying case, shows clear signs that it was used during the testing and development phase possibly for integration with ABMA's Jupiter C rocket.

Other highlights include:

• Apollo 16 Mission Control-Used Lunar Surface Relief Map. The 3-dimensional map was used at Mission Control in Houston during the 3 Lunar EVA's (when an astronaut leaves a spacecraft and enters the vacuum of space) of astronauts John Young and Charlie Duke. The map helped to assess the time each astronaut had before they had to return to the Lunar Module. Each EVA is marked in tape and pen with pins placed at stopping points. Estimate: $6,000-8,000

• High Altitude Helmet and Flight Suit Cover Assembly, 1971. The A/P22S-6 High Altitude Flight Suit and HGK-19 Helmet were used in high altitude aircraft such as the North American X-15 and the Lockheed U-2. They share a lineage with the suits used in the space program. Estimate: $8,000-12,000

• Space Shuttle Concept Model. This large, nearly 3-feet tall, circa 1972 model produced at Marshall Space Flight Center is McDonnell Douglas's sleek take on a space shuttle and appears to be a progression of Maxime "Max" Faget's "DC-3" shuttle design. Estimate: $3,000-5,000

• A rare contractor-issued album of 4 original 8 x 8-inch color photographs from the Apollo 11 mission. The images include Michael Collins' Earth View, two Neil Armstrong photographs of Buzz Aldrin on the Lunar surface, and Buzz Aldrin's photograph of the Lunar Module. It was issued by Schlegel Mechanical Contractors in 1969. Estimate: $1,500-2,500