Mariner 10: First to Mercury

Artist's Illustration of Mariner 10. Credit: NASA

• Launch Date: November 3, 1973
• Launch Site: Space Launch Complex 36B, Cape Canaveral Florida, United States
• Launch Vehicle: Atlas Centaur (AC-34/Atlas 3D no. 5014D/Centaur D-1A)
• Mission Type: Flyby
• Targets: Venus & Mercury
• Dimensions: N/A
• Mass: 502.9 Kilograms

You can build your own Mariner 10 spacecraft out of LEGO here.

Mariner 10 was the first spacecraft to fly by Mercury, the closest planet to the Sun. Due to orbital mechanics, this is really difficult to achieve. No other spacecraft explored Mercury for 30 years afterword.

The Mission

Mariner 10 launched on an Atlas Centaur booster on November 3, 1973. This spacecraft was first to visit two planets: Venus and Mercury. It was also the first mission to use gravity assists. Flybys of Venus helped the spacecraft to lower its orbital velocity, so it could intercept Mercury. Unlike MESSENGER and BepiColombo, Mariner 10 never entered orbit around Mercury.

Artist's Illustration of Mariner 10's gravity assist maneuver. Credit: NASA

Mariner 10 tested it's camera's by taking pictures of Earth and Moon as it departed, but it soon had many technical difficulties. The maneuvering system and high-gain antenna were fraught with malfunctions, which lead to limited data return from the long period comet C/1973 E1 Khoutek.

Closest flyby with Venus during Mariner 10's gravity assist was on February 5, 1974. After a mid course correction on March 16, Mariner 10 was ready for its first Mercury flyby. During the flyby, on March 29, 1974, Mariner 20 discovered that Mercury possessed a weak magnetic field.

On September 21, 1974, Mariner 10 performed its second Mercury flyby. The spacecraft was able to gather images of Mercury's south polar region during this flyby.

Due to problems with the maneuvering system, Mariner 10's controllers had to use solar pressure from sunlight to keep the spacecraft stable. This would prove the feasiblilty of future solar-sail spacecraft like Japan's IKAROS.

On March 16, 1975, Mariner 10 performed its third, and final, Mercury flyby. Less data was able to be obtained during this flyby, due to a tape recorder failure and data restrictions. Last contact with the spacecraft was on March 24, 1975.

The Targets

Original and enhanced views of Venus from Mariner 10. Credit: NASA/JPL-Caltech

• Date Discovered: Known To The Ancients
• Radius: 6051.8 Kilometres
• Surface Pressure: 90.82 Atmospheres
• Atmospheric Composition: Carbon Dioxide, Suphuric Acid, and Hydrogen Sulfide
• Mass: 4.8673x10^24 Kilograms
• Density: 15.243 g/cm^3
• Rotational Period: -243.018 Days*
• Orbital Period: 224.7 Days

*Negative number indicates retrograde (clockwise) rotation

Image of Mercury from NASA's MESSENGER spacecraft. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie

• Date Discovered: Known To The Ancients
• Radius: 2439.7 Kilometres
• Mass: 3.301x10^23 Kilograms
• Density: 5.43 g/cm^3
• Rotational Period: 58.65 Days
• Orbital Period: 87.97 Days