👩🏼‍🚀Intro to Aerospace Engineering Unit 9 – Spacecraft Systems: Propulsion & Life Support

Key Concepts and Terminology

• Propulsion generates thrust to move a spacecraft by expelling matter or energy in the opposite direction
• Life support systems maintain a habitable environment for the crew, including air, water, food, and waste management
• Delta-v ($\Delta v$) represents the change in velocity required for a spacecraft to perform a maneuver or reach a destination
• Specific impulse ($I_{sp}$) measures the efficiency of a propulsion system, expressed as the thrust per unit of propellant consumed per second
  • Higher $I_{sp}$ indicates better fuel efficiency and longer mission durations
• Environmental control and life support system (ECLSS) regulates temperature, humidity, pressure, and air composition
• Closed-loop systems aim to minimize resupply by recycling resources (water, air) while open-loop systems rely on stored consumables
• Trade-offs between system mass, complexity, reliability, and cost are crucial in spacecraft design
• Redundancy incorporates backup components to ensure system reliability and crew safety in case of failures

Propulsion System Basics

• Propulsion systems convert energy into thrust to overcome gravity and atmospheric drag
• Chemical propulsion relies on exothermic chemical reactions to generate high-temperature, high-pressure gases expelled through a nozzle
  • Liquid propellants (hydrogen, oxygen) offer high performance but require complex storage and handling
  • Solid propellants (aluminum, ammonium perchlorate) are simpler and more reliable but less efficient and controllable
• Electric propulsion uses electromagnetic fields to accelerate ionized propellants (xenon) to high velocities
  • Offers high $I_{sp}$ but low thrust, suitable for long-duration missions and station-keeping
• Propellant storage and management systems ensure reliable delivery of propellants to the engines
• Nozzle design affects propulsion efficiency by optimizing the expansion and acceleration of exhaust gases
• Thrust vectoring controls the direction of thrust to steer the spacecraft and perform maneuvers

Types of Spacecraft Propulsion

• Chemical rockets are the most common propulsion system, using liquid or solid propellants
  • Liquid bi-propellant engines (Space Shuttle Main Engine) mix fuel and oxidizer for combustion
  • Solid rocket boosters (Shuttle SRBs) provide high thrust for launch vehicles
• Electric propulsion systems include ion engines, Hall thrusters, and magnetoplasmadynamic (MPD) thrusters
  • Ion engines (Deep Space 1) use electrostatic fields to accelerate ionized propellant
  • Hall thrusters (Starlink satellites) employ magnetic fields to confine electrons and ionize propellant
• Nuclear thermal propulsion heats a propellant (hydrogen) using a nuclear reactor, offering high $I_{sp}$ and thrust
• Solar sails use radiation pressure from sunlight to propel a spacecraft, requiring large, lightweight reflective surfaces
• Tether propulsion systems use the Earth's magnetic field and a conductive tether to generate thrust
• Advanced concepts include fusion propulsion, antimatter propulsion, and beamed energy propulsion

Life Support System Fundamentals

• Life support systems maintain a safe and comfortable environment for the crew during space missions
• Atmosphere control regulates pressure, composition (oxygen, nitrogen), and removes contaminants (carbon dioxide, trace gases)
  • Oxygen is supplied by stored tanks, chemical generators (candles), or water electrolysis
  • Carbon dioxide is removed by lithium hydroxide canisters or regenerative systems (molecular sieves)
• Thermal control maintains a stable temperature range for crew and equipment
  • Passive methods include insulation, surface coatings, and heat pipes
  • Active methods use heaters, coolers, and radiators to regulate heat transfer
• Radiation protection shields the crew from harmful cosmic rays and solar particle events
  • Passive shielding uses high-density materials (aluminum, polyethylene) to absorb radiation
  • Active shielding employs electromagnetic fields to deflect charged particles
• Food and water supply provide essential nutrients and hydration for the crew
  • Stored food includes dehydrated, thermostabilized, and irradiated meals
  • Water is recycled from humidity, urine, and hygiene activities

Environmental Control and Air Recycling

• Environmental control and life support system (ECLSS) maintains a habitable atmosphere inside the spacecraft
• Air revitalization system (ARS) removes contaminants, controls humidity, and maintains oxygen and carbon dioxide levels
  • Trace contaminant control system (TCCS) filters harmful gases and particulates
  • Carbon dioxide removal assembly (CDRA) uses adsorption beds to remove CO2 from the air
• Oxygen generation system (OGS) produces oxygen through water electrolysis
  • Sabatier reaction combines hydrogen from electrolysis with CO2 to produce water and methane
• Humidity control removes excess moisture from the air to prevent condensation and maintain crew comfort
  • Condensing heat exchangers cool the air below its dew point to remove water vapor
• Ventilation system circulates air throughout the spacecraft to maintain a uniform atmosphere
• Fire detection and suppression systems protect the crew and equipment from fire hazards
  • Smoke detectors and fire extinguishers are strategically placed throughout the spacecraft

Water and Waste Management

• Water recovery system (WRS) collects, processes, and recycles wastewater to minimize resupply needs
  • Urine processor assembly (UPA) uses distillation and filtration to recover water from urine
  • Water processor assembly (WPA) treats and purifies water from humidity condensate and hygiene activities
• Waste management system collects and stores solid waste for disposal or resource recovery
  • Fecal collection system uses air flow and storage containers to isolate waste
  • Trash compactor reduces the volume of solid waste for storage
• Hygiene facilities include sinks, showers, and toilets adapted for microgravity
  • Vacuum toilets use air flow to collect and store waste
  • Waterless hygiene products (wipes, rinseless shampoo) minimize water usage
• Water quality monitoring ensures the safety and purity of recycled water
  • Sensors detect contaminants (bacteria, chemicals) and verify treatment effectiveness

Power Generation and Distribution

• Spacecraft require reliable and efficient power systems to support propulsion, life support, and mission operations
• Solar arrays convert sunlight into electricity using photovoltaic cells
  • Gallium arsenide (GaAs) cells offer high efficiency and radiation resistance
  • Sun-tracking mechanisms optimize power generation by orienting arrays towards the sun
• Batteries store excess solar energy for use during eclipse periods or peak demand
  • Lithium-ion batteries provide high energy density and long cycle life
• Fuel cells generate electricity through the chemical reaction of hydrogen and oxygen, producing water as a byproduct
• Nuclear power systems, such as radioisotope thermoelectric generators (RTGs), provide long-lasting power for deep space missions
• Power conditioning and distribution systems regulate voltage, control power flow, and protect against faults
  • DC-DC converters adjust voltage levels for different subsystems
  • Power management and distribution (PMAD) architecture optimizes power allocation and minimizes losses

System Integration and Trade-offs

• Spacecraft design involves complex interactions and trade-offs between propulsion, life support, and other subsystems
• Mass and volume constraints limit the size and capacity of life support systems
  • Regenerative systems (water recovery, CO2 removal) reduce consumables but increase complexity and power requirements
  • Open-loop systems are simpler but require more storage space and resupply
• Reliability and redundancy are critical for crew safety and mission success
  • Fault-tolerant designs incorporate backup components and multiple failure modes
  • Maintenance and repair capabilities enable in-flight servicing and extend system lifetimes
• Integration challenges include ensuring compatibility, minimizing interference, and optimizing performance across subsystems
  • Thermal management must balance heat generation from propulsion, power, and life support systems
  • Vibration and acoustic isolation protect sensitive components from engine noise and structural loads
• Cost and schedule constraints drive technology selection and risk management decisions
  • Heritage components with flight-proven performance reduce development costs and risks
  • Advanced technologies offer improved capabilities but require more extensive testing and validation

Future Trends and Innovations

• Regenerative life support systems aim to close the loop on air, water, and waste recycling
  • Bioregenerative systems use plants to produce oxygen, remove CO2, and provide food
  • 3D printing of spare parts and tools reduces inventory requirements and enables on-demand manufacturing
• Electric propulsion advancements focus on increasing power, efficiency, and lifetime
  • Nested Hall thrusters offer scalable power and improved plume characteristics
  • Field emission electric propulsion (FEEP) uses liquid metal propellants for high $I_{sp}$ and precision control
• Nuclear propulsion research explores high-performance options for deep space exploration
  • Nuclear thermal propulsion (NTP) offers high thrust and $I_{sp}$ for rapid interplanetary transit
  • Nuclear electric propulsion (NEP) combines a nuclear reactor with electric thrusters for efficient, long-duration missions
• In-situ resource utilization (ISRU) technologies extract and process resources from planetary surfaces
  • Oxygen and propellant production from Martian atmosphere and soil reduces launch mass and enables refueling
  • Water extraction from lunar regolith and asteroid materials supports sustainable exploration and habitation
• Artificial gravity systems mitigate the physiological effects of long-duration microgravity exposure
  • Centrifugal habitats create artificial gravity through rotation
  • Tethered spacecraft concepts use tether tension to generate linear acceleration