1955 in spaceflight

In 1955, both the United States and the Soviet Union (USSR) announced plans for launching the world's first satellites during the International Geophysical Year (IGY) of 1957–58. Project Vanguard, proposed by the US Navy, won out over the US Army's Project Orbiter as the satellite and rocket design to be flown in the IGY. Development of Intercontinental Ballistic Missiles, the Atlas by the US and the R-7 by the USSR, accelerated, entering the design and construction phase.

Both the US and USSR continued to launch a myriad of sounding rockets to probe the outer reaches of Earth's atmosphere and to take quick glimpses of the sun beyond the obscuring layers of air. The Aerobee Hi, first launched in April, promised a comparatively low cost alternative to other high altitude sounding rockets. The State University of Iowa meanwhile experimented with balloon-launched rockoons on its fourth expedition into the Atlantic Ocean.

The Aerobee family of rockets expanded considerably this year, both in variety and capability. Most significant was the introduction of the Aerobee-Hi, doubling the altitude range of the Aerobee sounding rocket from 125 km (78 mi) to 220 km (140 mi) and increasing the payload carried from 68 kg (150 lb) to 91 kg (201 lb). Able to probe the upper atmosphere, its $30,000 per flight price tag compared favorably to that of its high altitude contemporaries, the Viking and the Bumper; at least one 1955 Aerobee-Hi flight returned scientific data.^[a] Other, less capable, Aerobee rockets still lofted instruments beyond the 100-kilometer (62 mi) boundary of space (as defined by the World Air Sports Federation) returning spectra of the Sun in ultraviolet and investigating atmospheric airglow.

The Viking series of rockets wrapped up with the flight of Viking 12, launched 4 February 1955. Reaching an altitude of 143.5 mi (230.9 km), the rocket's K-25 camera snapped an infrared picture of the Southwestern United States, from the Pacific coast to Phoenix, just after reaching its apogee.

A number of sounding rockets based on the Nike booster (used as the first stage in various anti-aircraft missiles), were developed and launched. Just one, the 5 April Nike-Deacon flight, breached the limits of space. The Soviet Union launched three R-1E sounding rocket variants of its R-1 missile (a copy of the German V-2), all carrying dogs as biological payloads.^[b]

^a (the mission date has not yet been determined) ^b (see table below for details and citations)

Members of the State University of Iowa (SUI) physics department embarked September 1955 on their fourth naval expedition into the Atlantic Ocean to survey the distribution of cosmic rays and auroral radiation by latitude using balloon-launched rockets (rockoons). The team leader was Frank B. McDonald, formerly of the University of Minnesota. Their vessel was the USS Ashland, a World War 2 era Dock landing ship originally used to transport and launch landing craft and amphibious vehicles. Two research teams with the Naval Research Laboratory also sailed on the Ashland. In addition to the Deacon-equipped rockoons that had been used on the prior expeditions, the SUI team experimented with Loki I rockets launched from balloons. The new vehicle worked perfectly, the first being launched 23 September.

This set the stage for the most ambitious missions of the cruise: the launchings of two two-stage Loki I/Deacon rockoons. The first was a failure, the smaller Loki second stage failing to separate from the Deacon. On the second attempt, both stages fired properly. However, two and a half seconds after second stage ignition, telemetry from the rocket abruptly stopped. Professor James Van Allen, head of the SUI physics department, determined that the thin aluminum nosecone on the rocket had melted due to the incredible friction encountered at its speed of more than 8,000 km (5,000 mi) per hour. Had it reached its target altitude, Van Allen later stated, it might well have discovered the Van Allen Belts two and a half years before the missions of Explorer 1 and Explorer 3. As it turned out, no more Loki/Deacon missions were attempted.