10.3 Spacecraft design and instrumentation for planetary science

Spacecraft design for planetary science is a complex balancing act. Engineers must create robust systems that can survive harsh space environments while carrying out scientific missions. From power generation to data transmission, every component plays a crucial role in exploring distant worlds.

Instruments are the heart of planetary missions, gathering data to unlock cosmic secrets. Cameras capture stunning vistas, spectrometers analyze chemical compositions, and radar peers beneath alien surfaces. These tools, along with careful mission planning, help scientists unravel the mysteries of our solar system.

Spacecraft Components and Subsystems

Essential Subsystems

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• Power system generates, stores, and distributes electrical energy to all other subsystems
  • Includes solar panels (for generating power), batteries (for storing power), and power distribution units
• Propulsion system provides thrust for orbital maneuvers, trajectory corrections, and attitude control
  • Can include chemical thrusters, electric propulsion (ion engines), or a combination of both
• Communication system enables the spacecraft to send and receive data to and from Earth or other spacecraft
  • Consists of antennas, transmitters, receivers, and associated electronics
• Thermal control system maintains the spacecraft and its components within acceptable temperature ranges
  • Employs insulation, heaters, radiators, and heat pipes to regulate heat transfer
• Attitude determination and control system (ADCS) determines and controls the spacecraft's orientation in space
  • Uses sensors like star trackers and sun sensors to determine attitude
  • Uses actuators like reaction wheels and thrusters to maintain the desired attitude
• Command and data handling (C&DH) system manages the spacecraft's operations, data processing, and storage
  • Includes the onboard computer, memory, and software that control the spacecraft's functions and handle scientific data

Payload and Scientific Instruments

• Payload, which includes scientific instruments, is a critical component of a planetary exploration spacecraft
• Payload is designed to gather data and perform experiments to achieve the mission's scientific objectives
• Examples of payload instruments include cameras, spectrometers, radar systems, and in situ sampling devices

Planetary Mission Instruments

Cameras and Imaging Systems

• Used to capture visual data of planetary surfaces, atmospheres, and phenomena
• Operate in various wavelengths like visible, infrared, and ultraviolet light
• Provide valuable information about the morphology, composition, and dynamics of planetary bodies
• Examples include high-resolution cameras for surface imaging and wide-angle cameras for global mapping

Spectrometers

• Analyze the wavelengths of electromagnetic radiation emitted, absorbed, or reflected by planetary surfaces or atmospheres
• Help determine the chemical composition, mineralogy, and physical properties of the target body
• Examples include gamma-ray and neutron spectrometers (for subsurface composition), infrared spectrometers (for surface mineralogy), and mass spectrometers (for atmospheric composition)

Radar and Radio Science Instruments

• Study the surface and subsurface properties of planetary bodies
• Can penetrate through obscuring layers like clouds and regolith
• Provide information about the topography, roughness, and electrical properties of the target
• Examples include ground-penetrating radar and bistatic radar experiments

Magnetometers and Plasma Instruments

• Investigate the magnetic fields and charged particles around planetary bodies
• Help understand the interactions between the solar wind and planetary magnetospheres
• Study the internal structure and dynamics of the target body
• Examples include fluxgate magnetometers and plasma spectrometers

In Situ Instruments

• Designed to directly sample and analyze planetary environments
• Include seismometers (for studying internal structure), thermal probes (for measuring heat flow), and chemical analyzers (for determining composition of soils, rocks, or atmospheric gases)
• Examples include the Alpha Particle X-ray Spectrometer (APXS) on Mars rovers and the Gas Chromatograph Mass Spectrometer (GCMS) on the Huygens probe

Design for Mission Objectives

Influence of Mission Objectives on Spacecraft Design

• Mission objectives dictate the scientific goals and requirements of the spacecraft
• Scientific goals and requirements influence the design of the spacecraft and its subsystems
• Target body's characteristics (distance from Earth, surface conditions, atmosphere) affect spacecraft design
  • Impacts power system, propulsion, thermal control, and communication capabilities

Payload Selection and Design

• Desired scientific measurements and experiments determine the selection and design of payload instruments
• Instruments' requirements (power, data rate, pointing accuracy) impact the spacecraft's subsystems and overall design
• Example: High-resolution imaging requires precise attitude control and high-bandwidth communication

Mission Duration and Trajectory Considerations

• Mission duration and trajectory influence the spacecraft's power and propulsion systems
• Long-duration missions may require advanced power technologies like radioisotope thermoelectric generators (RTGs)
• Long-duration missions may benefit from efficient propulsion methods like electric propulsion
• Example: New Horizons mission to Pluto used an RTG and a gravity assist trajectory to reach its distant target

Operational Constraints

• Spacecraft design must consider the mission's operational constraints
• Data storage and transmission limitations affect the design of communication and data handling systems
• Example: Voyager missions used tape recorders for data storage and high-gain antennas for long-distance communication

Design Trade-offs and Constraints

Mass and Volume Constraints

• Spacecraft and instruments must be designed to fit within the launch vehicle's payload capacity
• Limitation requires careful optimization of the spacecraft's size, mass, and payload allocation
• Example: CubeSats are small satellites designed to fit within standardized launcher configurations

Power Constraints

• Available power from solar panels or other sources limits the number and type of instruments that can be operated simultaneously
• Instruments with high power demands may require duty cycling or dedicated power systems
• Example: Mars rovers often use radioisotope heater units (RHUs) to keep critical components warm during the cold Martian nights

Data Rate and Storage Constraints

• Amount of data that can be collected, processed, and transmitted back to Earth is limited by onboard storage capacity and communication bandwidth
• Data compression and selective downlinking are often necessary to manage these constraints
• Example: Mars Reconnaissance Orbiter uses a large high-gain antenna and a solid-state recorder to manage its high-resolution imaging data

Thermal and Radiation Constraints

• Instruments and spacecraft components must be designed to withstand harsh thermal and radiation environments in space and at the target body
• May require specialized shielding, insulation, and active thermal control systems
• Example: Parker Solar Probe uses a heat shield and active cooling to survive close approaches to the Sun

Reliability and Redundancy

• Spacecraft and instruments for planetary exploration must be highly reliable and able to operate autonomously for extended periods
• Redundant systems and fault-tolerant designs are often employed to mitigate the risk of component failures
• Example: Juno spacecraft at Jupiter has redundant avionics and a radiation vault to protect sensitive electronics

Cost Constraints

• Development, launch, and operation of planetary exploration missions are expensive endeavors
• Cost constraints affect the selection of instruments, spacecraft components, and mission scope
• Trade-offs between scientific return and cost must be carefully evaluated
• Example: Discovery-class missions like Dawn and InSight have cost caps that limit their scope and complexity

Planetary Protection

• Spacecraft and instruments must be designed to minimize the risk of forward and backward contamination between Earth and the target body
• Requires strict sterilization and contamination control measures, which can impact the design and integration of the spacecraft and its payload
• Example: Mars 2020 Perseverance rover underwent extensive sterilization to prevent contamination of the Martian environment