Nozomi (PLANET-B)

1. Historical Context and Detailed Objectives

The scientific void that the Nozomi mission intended to fill comprised the exhaustive study of atmospheric escape mechanisms on Mars and the dynamic interaction between its upper gaseous envelope and the particle flow of the solar wind. The primary objectives focused on:

Scientific:

• Investigate the interaction between the Martian upper atmosphere and the solar wind.
• Observe the planet's intrinsic magnetic field and the structure of its ionosphere.
• Quantitatively analyze the escape of atmospheric gases into interplanetary space.
• Perform optical remote sensing of the Martian surface and its natural satellites.

Engineering:

• Validate the Japanese interplanetary platform based on a spin-stabilized bus with controlled pointing.
• Test advanced X-band and S-band telecommunication systems at prolonged interplanetary distances.

2. Vehicle Architecture and Main Subsystems

The Nozomi spacecraft featured a launch mass of 540 kg, with an estimated dry mass between 258 kg and 225 kg, housing approximately 282 kg of chemical propellant for transfer and braking maneuvers. Structurally, the main body adopted the geometry of a truncated octagonal prism 1.6 m wide by 1.6 m long and 0.58 m high. Electric power supply depended on silicon solar panels arranged in two deployable wings, responsible for feeding the onboard subsystems and the nickel-metal hydride (Ni-MH) batteries. Downlink and uplink communications operated through dedicated transponders in X-band (8410.93 MHz) and S-band (2293.89 MHz), connected to a main dish antenna on the top surface and complemented by masts and wire antennas with a span of up to 50 meters tip to tip.

3. Payload and Scientific Instrumentation

To fulfill the geophysical and aeronomic missions, the payload consisted of 14 specialized instruments:

• MIC (Mars Imaging Camera): Camera for obtaining optical images of the Martian surface and satellites.
• MGF (Magnetic Field Measurement): Magnetometer intended for measuring planetary and interplanetary magnetic fields.
• PET (Probe for Electron Temperature): Instrumental probe to record the temperature of ionospheric electrons.
• ESA (Electron Spectrum Analyzer): Electron spectrum analyzer in the plasma environment.
• ISA (Ion Spectrum Analyzer): Ion spectrum analyzer to characterize the local solar wind.
• IMI (Ion Mass Imager): Ion mass imager to study ion composition.
• EIS (Electron and Ion Spectrometer): Combined spectrometer of energetic electrons and ions.
• TPA (Thermal Plasma Analyzer): Low-energy thermal plasma analyzer.
• PWS (Plasma Wave and Sounder): Plasma wave and ionospheric sounding instrument.
• LFA (Low Frequency Plasma Wave Analyzer): Low-frequency plasma wave analyzer.
• NMS (Neutral Mass Spectrometer): Mass spectrometer for the characterization of neutral gases.
• MDC (Mars Dust Counter): Dust counter intended for recording interplanetary and Martian particle impacts.
• XUV (Extra Ultraviolet Scanner): Extreme ultraviolet optical scanner.
• UVS (Ultraviolet Imaging Spectrometer): Ultraviolet imaging spectrometer for atmospheric profiling.

4. Chronology and Mission Phases

The launch was executed on July 3, 1998, using an M-V rocket from Uchinoura. Following a series of lunar and Earth gravity assists in December 1998, the spacecraft suffered a critical propellant overconsumption that forced a replanning of the trajectory toward a heliocentric orbit with arrival at Mars rescheduled for December 2003. During this prolonged cruise, intense solar flares and storms affected the electrical systems and caused the freezing of fuel lines. On December 9, 2003, the technical impossibility of executing the orbit insertion maneuver was confirmed, definitively ruling out Martian capture after a distant flyby on December 14, 2003. The mission was formally concluded after the final shutdown performed on December 31, 2003.

5. Results and Discoveries

Despite not reaching Martian orbit nor gathering data on the planet's atmosphere or surface, the prolonged interplanetary transit allowed the MDC instrument to successfully record 96 dust particle impacts in the interplanetary and terrestrial medium. Likewise, the plasma sensors and magnetometers operational during the cruise provided valuable records on the solar wind and the energetic particle environment in deep space.

6. Legacy and Importance

Nozomi represented Japan's first foray into interplanetary exploration and Martian orbiter design. Although propulsion failures and damage accumulated from space weather prevented fulfilling the objectives in Mars orbit, the engineering experience acquired laid the methodological foundations for future deep space missions by the JAXA agency.