Aerospace Engineering - Special Topics

Flashcards covering the key concepts of Atmospheric Entry, Spacecraft Power Systems, and Telecommunications for Aerospace Engineering students.

Entry Flight Mechanics

Studies the physics of spacecraft reentry into a planetary atmosphere, addressing deceleration, heating, and trajectory control.

Entry Velocity (Uentry)

The spacecraft's velocity upon atmospheric interface; significantly affects aerodynamic heating and deceleration forces.

Entry Angle (γentry)

Flight path angle at atmospheric entry; determines how deeply the spacecraft penetrates before deceleration.

Atmospheric Density ρ(h)

Affects both drag and heating rates and varies with altitude; often modeled using an exponential scale height equation.

Ballistic Coefficient (β)

Measure of how a body responds to atmospheric drag; a high value means deeper penetration before slowing down.

Ballistic Entry

Entry trajectory with no lift, follows a simple descent path, and experiences high G-forces and heating.

Lifted Entry

Entry trajectory that generates lift using aerodynamic control, reducing G-loads and providing maneuverability.

Skip Entry

Entry trajectory that uses lift to exit and re-enter the atmosphere multiple times, extending range and reducing heating.

Hypersonic Entry

Dominated by aerodynamic heating and shock wave interactions at extremely high speeds (Mach > 20).

Deceleration and Peak Heating

Phase where maximum aerodynamic forces are experienced, and thermal protection systems are essential.

Subsonic Descent and Terminal Guidance

Phase where parachutes or retropropulsion may be deployed, and precision landing mechanisms are activated.

Convective Heating

Heat transfer due to direct interaction between hot gases and the spacecraft surface.

Radiative Heating

Emission of electromagnetic radiation from the hot gas surrounding the spacecraft.

Stagnation Point Heating

Experiences the highest heating due to the direct impact of airflow; use of blunt bodies to spread heat.

Ablative TPS

Material burns away, carrying heat with it (e.g., Apollo heat shield).

Reusable TPS

Withstands heating without significant degradation (e.g., Space Shuttle tiles).

Active Cooling TPS

Uses circulating coolant to dissipate heat (rare in atmospheric reentry).

Laminar Flow Regime

Smooth and predictable flow over the spacecraft; lower heat transfer rates compared to turbulent flow.

Turbulent Flow Regime

Chaotic, high-energy motion increasing heat transfer; can be mitigated using surface roughness control.

Transition Region

Shift from laminar to turbulent flow; must be carefully analyzed for accurate heat load predictions.

Radiative Heating Dominance

Occurs when radiative heating becomes the primary concern because speeds becomes very high

The sum of convective and radiative heating over time

Total Heat Load (Qtotal)

Blunt-Body Concept

A spacecraft experiences in reentry; achieved by slowing airflow to create a detached shockwave, to reduce heat transfer.

Blunt-Body Concept

Slows down airflow to create a detached shockwave, reducing heat transfer.

Ablative TPS

Material burns away, carrying heat with it

Reusable TPS

TPS withstands heating without significant degradation

SpaceX Starship's

Stainless steel body for durability.

Dream Chaser:

Hybrid lifting body design for soft landings.

Aeroassisted Orbit Transfer (AOT)

Use of atmospheric drag and aerodynamic forces to alter a spacecraft's trajectory, minimizing propellant usage.

Aerobraking

Gradual orbit reduction using repeated atmospheric passes.

Aerocapture

A single atmospheric pass that captures the spacecraft into orbit.

Aerogravity Assist

Uses atmospheric drag and lift to change trajectory and increase or decrease inclination for interplanetary missions.

Constraints on Spacecraft Power:

• Major limitations on space vehicle design since the beginning of the space age.

Development of RTGs:

• Convert heat from radioisotope decay into electricity via thermoelectric effect.

Orbital Parameters:

influence onboard energy storage requirements.

Major Element - Primary Power Source:

Includes Solar arrays, RTGs, nuclear reactors, fuel cells

Energy Storage:

Consists of Batteries, capacitors, flywheels

Variety of Options:

Substantial variety of options exist within each power system element.

Direct Current Switching

Place switches or relays in the positive line to an element. * * Direct connection to "ground" on the negative side.

Location of Arc Suppression Devices:

Place devices close to the source of the arc.

Modular Construction

Simplifies testing and replacement of failed units.

Batteries

Primary means of electrical energy storage onboard spacecraft.

Silver-Zinc (Ag-Zn):

Excellent energy density, still widely used.

Characteristics Primary Batteries:

Often dry before activation, activated by allowing electrolyte to enter from a reservoir.

Battery Function:

Converts chemical energy directly to electrical energy.

BatteriesCategory: Primary Batteries

Higher energy and power densities, not rechargeable

Secondary Batteries:

Rechargeable, lower energy density, limited depth of discharge.

Lithium-Based Secondary Batteries:

Excellent energy density, some chemistries require reconditioning.

Nicad Reconditioning:

Required to obtain maximum life from a Ni-cd battery.

Preliminary Concept Design:

• Substantial overlap between regimes.

Solar Arrays

Made up of many individual cells on a substrate

Flexible Roll-Up Arrays:

Thin cells and substrates enable roll-up and fold-up designs.

Radioisotope Thermoelectric Generators

Convert heat from radioisotope decay into cool.WO volts

Fuel Cells

Direct conversion of chemical energy into electricity

Dynamic Isotope Systems

Obtain more electrical power from isotope heat source used in RTGs.

Advantages: Dynamic Isotope Systems

Heat working fluid of Brayton, Rankine, or Stirling cycle engine to drive alternator.

AMTEC

Alkali metal thermal-to-electric conversion.

Solar Dynamic Systems

Machines driving electrical generator using sun as energy source. * Conversion efficiency five to seven times that of solar photovoltaic arrays.

Droplet Radiators

High performance, liquid-to-solid phase change.

Membrane Radiators

Fluid flows inside rotating membrane, enhanced by gas-to- liquid phase change.

Rotating Band Radiators

Continuous loop of high-temperature metal moving between heated rollers.

Telecommunications: (Key Differences from Earthbound)

Long Range: Ranges from a few hundred to several billion kilometers.

Role of Telecommunications System Earthbound Link:

critical for accepting commands and returning data.

Relay Commands:

• Function like switch closures (on/off functions or complex sequences).

RelayCommands:

Function like switch closures (on/off functions or complex sequences).

Soft Errors:

Temporary errors from energetic particles, corrected by reloading commands.

Simple Parallel Systems

Uses two completely separate parallel systems.

Subsystem-Level Redundancy:

Employs cross-strapping, allowing subassemblies to be used in either string.

Cross-Strapping:

Ensures a working command system can be assembled by selectively cross- strapping between strings.

Increasing Autonomy

Driven by advancements in computer capability and complex missions.

Modern Spacecraft Element D. Command Processor:

*Interprets commands, checks for validity, and sends signals to appropriate destinations.

Modern Spacecraft ELement D Command Processor

*Functional block of code in a multipurpose processor.

D. Command Processor E Telemetry Subsystem:

Prepares engineering or scientific data for transmission to the ground.

Nyquist Rate: E. Telemetry Subsystem

Minimum sampling rate is twice the maximum frequency of the signal.

Frequency-Division Multiplexing (FDM):

Subdivides frequency bandwidth and allocates data streams to separate portions.

Time-Division Multiplexing (TDM):

Assigns different sets of bits within a data frame to different users.

D. Command Processor F. Onboard Processors:

Essential SubsystemControls nearly all aspects of spacecraft behavior.

Evolution *Evolution: F Onboard Processors Element

*Early onboard computers were simple timers with modest logic circuitry.

G. Onboard Storage:H. Modulation Methods:

Spacequalilied GPS receiver capability Paramclcrs Performance.

D. Command Processor H. Modulation Methods:

*Encodes a baseband information-bearing signal onto an RF carrier.

Radio Frequency A. Antennas and Gain:

Types of Antennas *Omni directional (Omni): Radiates energy equally in all directions.

Radio Frequency Antenna Gain Radio Frequency

Power on the bore sight axis to an ideal isotropic radiator (0 dB gain). A Radio Frequency

Radio Frequency Beamwidth Radio Frequency

Antenna between the -3 dB (half-power) points relative to the power on the bore sight axis RadiioFrequency

Radio Frequency *Multipath Loss

Signals that arrive at the receiving antenna after being reflected off other objects. B Loss Mechanisms

Radio Frequency B Loss Mechanisms *Includes Thermal Noise and Noise

Noise power approximated by PN=kTB where k is Boltzmann constant, Tis temperature, and B is bandwidth - Any received power that interferes with the desired signal.

Radio Frequency Theorem: ShannonD Comms

Error-free channel capacity whereC=Blog2(1+SNR) . D. Noise Figure:

Radio FrequencyG

Link Analysis: Distills communication link performance into a comprehensive analysis

Spacecraft Tracking Groun-Based Tracking Stations

Receiving spacecraft telemetry and routing it to the control center.

Spacrecraft Tracking

Tracks and Data Relay Satellite System Replaced extensive network of ground stations

Spacrecraft Tracking Accuracy Role of TrackingStations

Supply position and velocity data for orbit determination algorithms

Spacecraft Tracklng Optical Navigation

Vehicle determines its navigation state and relays it to the ground GPS no applicable

Spacecraf Tracking

Observes angles between fixed stars and nearby planetary bodies Spacecraft Tracking *Autonomous Optical Navigation