Satellite

Outline Specifications

Outline

Mio is an octagonal spin-stabilized satellite designed to measure in-situ plasma and electromagnetic fields from the orbit of Mercury.

Murakami, G., Hayakawa, H., Ogawa, H. et al. Mio—First Comprehensive Exploration of Mercury’s Space Environment: Mission Overview. Space Sci Rev 216, 113 (2020). https://doi.org/10.1007/s11214-020-00733-3

Orbit

  • A highly elliptical polar orbit with initial periapsis and apoapsis heights of 590 and 11,649 km, respectively.
  • The initial periapsis and apoapsis: close to the equatorial plane of Mercury and rotate slowly because of the gravitational coefficient.
  • The orbital plane of Mio is along the Sun-Mercury line at perihelion (true anomaly angle (TAA) = 0°) and aphelion (TAA = 180°), and is perpendicular to the Sun-Mercury line at TAA = 90° or 270°.
  • Mio stays in the upstream region of the solar wind most of the time and passes the nightside region close to the Mercury at TAA = 0° , therefore a small TAA would have been suitable to investigate upstream solar wind.
  • While at TAA = 180° , Mio stays close to the magnetopause or in the magnetotail, giving a unique opportunity to investigate solar wind-magnetosphere interaction.
  • Mio passes the duskside magnetosphere close to Mercury at TAA = 90°. Hence, Mio observes the magnetosphere close to Mercury as the planet revolves. Combining observations at TAA = 0° and 180° gives the distance dependence in the magnetosphere.

Schematic view of the Mio spacecraft identifying the science instruments. The location of each instrument and sensor is indicated from top view [Murakami et al., 2020].

[Murakami et al., 2020].

Specifications of the Mio

Shape Octagonal shape within a 1.8 m diameter circle with two 5 m extendable mast and four 15 m (from tip to root) electric field antenna
Height 1.52 m (launch configuration)
2.66 m (observational configuration)
Mass 255 kg (including 3.7 kg N2 gas) excluding 20 kg separation mechanism which remains on MMO sunshield interface (MOSIF)
Power (spin averaged) ≧271 W (periapsis at aphelion)
≧368 W (average at aphelion)
≧530 W (average at perihelion)
Designed mission life One Earth year observation at the Mercury orbit and an extension of one Earth year (or more)
Thruster 6 × 0.4 N N2 cold gas jet
spin rate 15 rpm (4 s/spin)