San Marco 1

San Marco 1: Italy’s First Satellite and Atmospheric Research Mission

Mission Overview

• NSSDCA/COSPAR ID: 1964-084A

• Launch Date: December 15, 1964

• Reentry Date: September 14, 1965

• Launch Site: Wallops Island, Virginia

• Launch Vehicle: NASA-provided Scout Booster

• Crew: Fully Italian launch team

Mission Objectives

San Marco 1 was Italy’s first satellite, designed to collect data on atmospheric density and ionospheric characteristics. This mission marked a significant milestone in Italy’s entry into space exploration, with NASA supplying the launch vehicle while an Italian crew managed the launch operations.

Spacecraft Design & Systems

• Structure: A heavy cylindrical inner core encased within a lightweight aluminum sphere measuring 66 cm in diameter.

• Mass: 115.2 kg

• Stabilization: Spin-stabilized at 3 rpm

• Thermal Control: Alternating black and white longitudinal paint sections on the surface.

• Power Supply: A 12-watt mercury battery (Mallory RM-42R cells) capable of providing 200 working hours of power.

• Antenna System: Four equatorial antennas extended from the spacecraft for communication and data transmission.

Communications & Tracking

• Primary Transmission: A 0.25-watt crystal-controlled transmitter operating at 136.53 MHz, using a PAM/FM/PM telemetry system.

• Data Channels:

  • Four continuous channels for the atmospheric drag experiment.

  • One sub-commutated channel for housekeeping data and ionospheric measurements.

• Beacon Signal: A 50-milliwatt transmitter at 136.74 MHz, used for tracking via vector-sum modulation of three balance channels.

• Command System: Operated via a 140-150 MHz radio frequency link, consisting of a command receiver, tone decoder, and command decoder.

Scientific Experiments

1. Air Drag Experiment

   • Utilized three orthogonal displacement transducers connecting the inner and outer spheres to measure atmospheric density at perigee.

2. Ionospheric Experiment

   • Employed a 670-milliwatt transmitter at 20.005 MHz with a 4-meter dipole antenna to study ionospheric properties.

Mission Challenges & Outcomes

• Initial difficulties in receiving commands due to limited communication range were resolved by sending signals when the satellite was near a ground station.

• A suspected open diode in the battery cells led to unexpected power drain, limiting operational lifespan.

• To conserve power, all long-term transmissions were halted.

• The air-drag experiment functioned until December 30, 1964, when data transmission ceased to prioritize the ionospheric experiment, which operated successfully for two weeks before battery depletion.

• The spacecraft reentered Earth’s atmosphere on September 14, 1965, with remnants of the fourth-stage igniter reportedly discovered in Thailand.

The Scout Booster

The Scout Booster (S-137) was a four-stage solid-fueled rocket consisting of:

1. First Stage: Algol IIB

2. Second Stage: Castor I

3. Third Stage: Antares II (ABLX-259)

4. Fourth Stage: Altair (ABLX-258), which included a fairing and heat shield to protect and deploy the satellite into orbit.

Significance of San Marco 1

San Marco 1 was a landmark mission for Italy, making it the fourth nation to launch a satellite into space after the Soviet Union, the United States, and the United Kingdom. The data collected contributed to atmospheric and ionospheric research, improving understanding of satellite drag and radio wave propagation. The mission also laid the foundation for Italy’s future San Marco satellite series, further advancing the country's role in space exploration.