Rockets are typically launched from stationary pads on solid ground or, in rare cases, from planes. Even rarer still, rockets can launch from offshore barges, as the San Marco satellites did, and they are the subject of This Week in Rocket History.

In the 1960s, Italy wanted a satellite of its own but did not have the experience in making or launching orbital rockets. So, they worked with NASA to build a launch pad on a barge for an American rocket, the Scout, which would launch Italian satellites. San Marco 1 was launched from Wallops in Virginia, but starting with San Marco 2, the launches would be conducted from the barge, which was located roughly on the equator in the Indian Ocean just off the coast of Kenya.

San Marco 2 was launched by Italy on a Scout B rocket on April 26, 1967. San Marco 2 did not have solar panels to generate electricity, instead relying entirely on batteries. The satellite did have four solar cells but only as a means of measuring satellite attitude, not to generate electricity.

Compared to San Marco 1, San Marco 2 had several upgrades, including adding a radio beacon and a redesigned battery and command transmitter, which failed on San Marco 1. The satellite weighed 129.3 kilograms and was a simple sphere with five antennae, and controlled its orientation by spinning. This shape was to make its primary mission – analysis of the atmosphere – easier by providing a constant cross-section as it moved forward in its orbit, which was the main reason why it lacked solar panels.

On August 14, 1967, the satellite ran out of power and reentered the atmosphere on October 14, 1967.

Between 1967 and 1988, the Italian Space Agency launched San Marco 3, 4, and 5 to continue the missions of 1 and 2, namely measuring the atmosphere at 200-kilometer altitude.

San Marco 3 introduced a new satellite design. The basic shape was the same, but the internal structure was different. To accurately measure atmospheric drag, the spherical spacecraft was hollow with another sphere on the inside that connected to the outside shell. The spacecraft measured the force using several arms connecting the spheres to determine atmospheric drag. San Marco 3 also had several instruments to directly measure the drag, including a mass spectrometer, and other instruments to measure the density of different atmospheric components.

San Marco 3 also improved on the basic design of the spacecraft by adding an attitude and spin control system. Spinning swept the different instruments through the space around the satellite to collect data, and the new control mechanism made this easier and more consistent, resulting in better data.

San Marco 3 was launched in 1971 and continued the monitoring of the Earth’s atmosphere.

Launched in 1974, San Marco 4 was similar to 3 but added two additional instruments to further its atmospheric mission. San Marco 3 and 4 were also the first in the series to have solar panels.

The last San Marco mission, San Marco 5, was launched fourteen years after 3, in 1988. It was the largest of the San Marco satellites and had the most complicated mission. Its goal was to “explore the relationship between solar activity and thermosphere-ionosphere phenomena.” It did this with the same Drag Balance System as its predecessors and added a Wind and Temperature Spectrometer, Airglow Solar Spectrometer, and Electric Field Meter. The spacecraft used magnetic torque to control its spin rate and Sun and horizon sensors to control attitude.

San Marco 5’s mission ended on December 6, 1988, when it reentered the atmosphere.

More Information

San Marco 1 info page (NASA)

San Marco 2 info page (NASA)

San Marco 3 info page (NASA)

San Marco 4 info page (NASA)

San Marco-D/L info page (NASA)