Introduction to Spaceflight > Satellite Engineering > Flashcards

Satellite Engineering Flashcards

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1
Q

How many satellites are approximately currently in orbit?

A

9900

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2
Q

What are some (6) types of satellite subsystems?

A
  • Command and data
  • Power supply
  • Pointing control
  • Mission payload
  • Communications
  • Thermal control
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3
Q

What are the definitions of Payload (1) and Subject (2)?

A
  1. The combination of hardware and software that interacts with the subject
  2. The portion of the outside world that the spacecraft is looking at
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4
Q

What are some (2 each) payloads for Communications (1), Remote Sensing (2), Navigation (3), Weapons (4) and In Situ Science (5)?

A
  1. Transceiver, Transmitter
  2. Imagers and Cameras, Radiometers
  3. Clock and Transmitter, Transceiver
  4. Warhead, High-energy weapon
  5. Physical and life sciences, Sample collection/return
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5
Q

What are 3 types of information that can be collected and which sensors can detect them?

A
  • Spatial information (Imagers, Altimeters, Sounders, Imaging Spectrometers, Imaging Radiometers)
  • Intensity information (Radiometers, Polarimeters, Scatterometers, Imaging Radiometers, Spectro-Radiometers)
  • Spectral Information (Spectrometers, Spectro-Radiometers, Imaging Spectrometers)
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6
Q

What is the dual nature of light?

A

It behaves as a particle and wave

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7
Q

What lies in increasing wavelength (1) and what in decreasing (2)?

A
  1. Infra-red, microwaves, radiofrequency waves
  2. Ultraviolet, X-rays, gamma rays
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8
Q

What does all matter do for temperatures above 0K?

A

It emits electromagnetic radiation

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9
Q

What is total energy emission of a perfect blackbody dependent on?

A

Temperature

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10
Q

What does energy emission of actual matter depend on except temperature?

A

Surface properties

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11
Q

How is Stefan-Boltzmann’s law defined?

A

Wb = sigma * T^4
- Wb: total radiant emmitance
- Sigma: Stefan-Boltzmann constant
- T: Absolute temperature

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12
Q

How is Wien’s Displacement Law for peak spectral radiance defined?

A

max wavelength = 2.898/T

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13
Q

What does an object’s spectral radiance (brightness) depend on?

A

Its equivalent blackbody temperature

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14
Q

What do visual systems looking at Earth’s surface take advantage of?

A

The Sun’s reflected energy (6000K)

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15
Q

What do IR and microwave radiometry measure scenes against?

A

Earth’s thermal radiation background (300K)

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16
Q

What are some (9) sources of radiation for a sensor looking at Earth?

A
  • Sunlight scattered by atmosphere into the sensor
  • Sunlight reflected off the Earth and then scattered by the atmosphere into the sensor
  • Sunlight reflected off the Earth’s surface
  • Sunlight scattered by the atmosphere then reflected off the Earth’s
    surface into the sensor
  • Ground emission
  • Ground emission scattered by the atmosphere into the sensor
  • Atmospheric emission
  • Atmospheric emission reflected by the Earth’s surface into the sensor
  • Atmospheric emission scattered by the atmosphere into the sensor
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17
Q

What parts of the EM spectrum provide a challenge for Earth observation (1) and what can they be utilized for (2)?

A
  1. The atmosphere’s opaque EM spectrum bands, which need to be avoided when trying to observe the ground
  2. Sounding the atmosphere, measuring cloud properties
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18
Q

What is the focal length needed to record a scene of radius R defined as?

A

Focal length is the distance of the focal point from the lens, determined by instrument field of view and size of image plane

f/h = rd/R = magnification
- f= focal length
- h = height of aperture above object
- rd = image plane radius
- R = object plane radius

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19
Q

What are the 3 primary aperture types and an example where each is used?

A
  • Monolithic (e.g. Hubble Space Telescope)
  • Segmented (e.g. James Webb Space Telescope)
  • Sparse (e.g. Terrestrial Planet Finder-Interferometer)
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20
Q

What is of importance for Earth observing systems (1) and what is a limitation we face (2)?

A
  1. Ground Sampling Distance, the ability to resolve fine detail on the surface
  2. Diffraction, the bending of light that occurs at the edge if the optical system
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21
Q

What effect does diffraction have on resolution?

A

The image of a distant point source does not appear as a point, but as a series of concentric circles (Diffraction disk)

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22
Q

What is the angular distance from the center of an image to the first dark interference ring called?

A

Rayleigh limit

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23
Q

What are 4 observation payload types?

A
  • Visible systems (UV 0.3 to visible 0.75 micrometers, high spatial resolution due to short wavelength, can only operate in daylight)
  • Infrared systems (1 to 100 micrometers, subject to atmospheric transmission windows, can operate at day and night)
  • Microwave radiometers (millimeter wavelengths, low resolution but large area coverage)
  • Radar systems (cm to mm wavelengths, require their own illumination, penetrate most atmospheric disturbances)
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24
Q

What are the 8 steps to design a power system?

A
  1. Estimate power requirement
  2. Identify design criteria
  3. Identify environment
  4. Select prime power source
  5. Select storage system
  6. Identify system interfaces and requirements
  7. Select PMAD (Power Management and Distribution)
  8. Safety and fault analysis
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25
What should be the outputs of a power system design?
- Power system mass - Power system area - Power system volume - Spacecraft constraints - Thermal requirements
26
What is power usage divided into?
- Baseline power (continuously required) - Peaking power (required for shorter periods) - Dormant power (power required to keep the system alive) - Burst or Transient power (power needed for momentary surges)
27
What are 3 power sources and how do they compare?
- Chemical (like batteries, fuel cells): short time, low power - Solar arrays: long time, lower power - Nuclear reactors: long time, high power
28
What is the specific power of solar arrays (1), what is a requirement for some operations (2) and what are they particularly useful for (3)?
1. 25 to 300 W/kg 2. Require storage (batteries) for operations in eclipse 3. Near Earth operations
29
What are 3 solar cell technologies?
- Silicon (old, cheap and not that efficient) - Gallium Arsenide (more efficient) - Multibandgap (highest efficiency)
30
What are key requirements for solar array systems?
- Average electrical power for payload - Peak electrical power for payload - Mission life - Orbital parameters - Spacecraft configuration
31
What are 3 solar array designs?
- Body fixed - Spinner - Gimbaled
32
What are 3 uses of a power storage system?
- Powers spacecraft in eclipse - Allows primary power system to provide average power - Buffers transient power spikes
33
What is a primary (1) and secondary (2) battery cell?
1. Used once and discarded, usually higher capacity 2. Can be recharged and used repeatedly
34
What is a cell (1) and a battery (2)?
1. A single electro-chemical energy storage unit 2. Many electrically connected cells (Series connection increases voltage, parallel connection increases capacity)
35
What is the relation between battery charge and discharge cycles and mission duration?
The number of times the battery cycles through charge and discharge is the mission duration divided by day/night period
36
What is the battery life dependent on?
DOD, depth of discharge: The fraction of the battery's total capacity that is used
37
What is the purpose of thermal control?
Control operating temperature of spacecraft systems (systems, propellant, humans can fail or be damaged)
38
What are the 3 functions of thermal management?
- Heat rejection (minimize thermal input, maximize thermal radiation) - Heat conservation (maximize thermal input, minimize thermal radiation) - Transient amelieration (make sure spacecraft doesn't overheat/freeze during transient high/low thermal load)
39
How is thermal equilibrium defined for a spacecraft?
Balance between: - Solar radiation - Albedo radiation - Planetary radiation - Internally generated heat And: - Radiation to space
40
What is convection (1) and what 2 types are there (2)?
1. Heat transfer via liquid or gas flow 2. - Free convection (not a factor in space) - Forces convection (pumped fluid flow)
41
What is Conduction (1) and Radiation (2)?
1. Heat transfer through solids (heat flow is proportional to area of conducting path) 2. Heat transfer via infrared radiation (primary method of heat flow in vacuum)
42
What do absorptivity and emissivity depend on?
Wavelength
43
What is the relationship between absorptivity, emissivity and reflectance for a non-transparent material?
absorptivity = emissivity = 1 - reflectance
44
What is the view factor?
What fraction of the solid angle of the sky, viewed from an area A1, is obscured by another area, A2?
45
What does the energy absorbed by a solar array in Earth orbit consist of?
- From Sun on top surface - Earth IR - Sunlight reflected from Earth
46
What are some (4) materials and coatings used for thermal control?
- Selective surfaces (Absorptivity is not equal to emissivity) - Paints, mirrors, silvered plastics - Optical Solar Reflectors (Second surface mirror under a transparent cover) - Silver coated Teflon
47
What is the purpose of multi-layer insulation (1) and what is it made of (2)?
1. Minimizes radiative heat transfer to and from a spacecraft 2. Made of alternate layers of aluminized Mylar of Kapton with thin net of material between
48
How can thermal properties degrade?
- UV radiation darkening increases solar absorptivity over time - Outgassing, contamination and material instability
49
What are ways to control transient heat?
- Thermal mass - Heat spreaders - Phase change material
50
What are 9 thermal control components?
- Electric heaters - Space radiators - Cold plates - Doublers (passive aluminum plates that increase heat exchange surface area) - Heat pipes - Louvers (shield radiator surfaces to moderate heat flow to space) - Temperature sensors (Thermistors: Semiconductors whose resistance varies with temperature, Platinum Resistance thermometers: Resistance changes with temperature) - Thermal isolators - Thermoelectric coolers
51
What do heat pipes contain?
A wick running the length of the sealed pipe, partially filled with a fluid such as ammonia (leads to high heat transfer rates)
52
What is an uplink (1), downlink (2) and crosslink (3)?
1. Communication link from ground to satellite 2. Communication link from satellite to ground 3. Communication link between two satellites
53
What are relays?
Intermediate satellites receiving signals from one satellite and retransmitting them to another satellite or ground station
54
What is TT&C?
- Telemetry: Collecting and transmitting data - Tracking: Determine and monitor satellite's position and trajectory - Command: Sending instructions from ground to satellite
55
What funcionalities are required for systems and satellites?
- TT&C - Data Collection - Data Relay - Onboard processing - Autonomous satellite control - Network management
56
What are some (7) factors to consider in design of satellite communication?
- Orbit - RF spectrum - Data rate - Duty factor - Link availability - Link access time - Threat
57
What are some (6) factors influencing frequency selection?
- Spectrum availability and FCC allocation - Relay/Ground Station frequency - Antenna size - Atmospheric/Rain attenuation - Noise temperature - Modulation and coding
58
What are some (4) measures to reduce data rate?
- Increase duty cycle - Collect only above-threshold data - Record amplitude changes only - Data compression
59
What are the 3 steps to design a link?
1. Define requirements for each link 2. Design each link (frequency, modulation and coding, antenna size) 3. Size the payload (payload antenna, estimate transmitter mass and power, estimate payload mass and power)
60
What are sources of external noise to an antenna?
- Galactic noise - Clouds, rain in path - Solar noise - Earth - Man-made noise - Nearby objects - Satellite structure
61
What is modulation (1) and what are 4 parts of it (2)?
1. Modifies an RF carrier signal so that it contains input signal information 2. - Amplitude - Frequency - Phase - Polarization
62
What are 5 modulation techniques?
- BPSK (Binary Phase Shift Keying) - QPSK (Quadriphased Phase Shift Keying) - FSK (Frequency Shift Keying) - MFSK (Multiple FSK) - DPSK (Differential Shift Keying)
63
How is the bit error rate (BER) defined?
- Primary figure of merit for digital link performance - Energy/Bit to Noise spectral density ratio
64
What are some advantages of BPSK, DPSK, QPSK, FSK and 8FSK?
- BPSK: Good BER performance, good use of spectrum - DPSK: Not suspectible to phase disturbances - QPSK: Excellent use of spectrum - FSK: Not suspectible to phase disturbances - 8FSK: Good BER performance, not suspectible to phase disturbances
65
What are some disadvantages of BPSK, DPSK, QPSK, FSK and 8FSK?
- BPSK: Suspectible to phase disturbances - DPSK: Higher Energy/Bit to Noise spectral density ratio required - QPSK: More suspectible to phase disturbances - FSK: Higher Energy/Bit to Noise spectral density ratio required, poor use of spectrum - 8FSK: Poor use of spectrum
66
What is Forward Error Correction (1) and what are some advantages of it (2)?
1. Sends additional data to help detect and correct errors 2. - Reduces Energy/Bit to Noise spectral density ratio requirement - Reduces required transmitter power - Reduces antenna size - Increases margin - Increases data rate and bandwidth
67
What provides attenuation for satellites?
- Atmosphere absorbs some frequencies
68
What is the worst elevation angles in context of attenuation?
<20°
69
What are some forms of communication payload antennas?
- Parabolic - Helix - Horn - Phased Arrays (Multiple beams, Hopping beams)
70
What is the purpose of compressing data?
- If more data than bandwidth accommodates needs to be send (especially large: image files) - Bandwidth is limited by link equation and international regulation
71
What are 2 forms of data compression algorithms?
- Lossless compression (used for data which can not tolerate mistakes like executable code or numeric data) - Lossy compression (used for still images, video, audio which contains more information than human can perceive)
72
What does the ground segment of a satellite support?
- Tracking - Mission data acquisition - Commanding
73
In what mission phases does the ground segment of a satellite help?
- Support launch and early operations - Support regular operations - Solve contingencies - Support decommissioning
74
What are the 3 facilities of the ground segment and how do they interact?
1. Spacecraft Operations Control Center (SOCC) - Monitors and commands spacecraft - Schedules commands for MCC 2. Mission Control Center (MCC) - Plans and schedules operations for the entire mission - Computes spacecraft positions, ground passes - Schedules operations and contact information for POCC 3. Payload Operations Center (POCC) - Analyzes telemetry data from instruments - Command requests from SOCC
75
What 7 parameters have to be considered when choosing the ground station site?
- Location in relation to orbit - Political implications - Distance to control centers - Weather - Ground properties and seismic activity (pointing stability) - Obstacles (buildings, trees, mountains) - Interference with other RF sites (airport)
76
What will dimension the system of a ground station?
The link budget of the space-ground communications
77
What are 7 forms of data handling?
- Multiplex/Demultiplex - Encryption/Decryption - Encoding/Decoding - Data compression - Time tagging - Data storage - Data quality monitoring
78
What is ranging (1) and how can it be performed (2)?
1. Needed to estimate spacecraft position and update orbital propagation computations 2. RF or laser observations
79
Where does the radio spectrum lie?
1kHZ to 100GHZ
80
What is the difference between an isotropic and a directive antenna?
- Isotropic: Radiates in all directions uniformly - Directive: Concentrates power in one direction
81
What do we send when transmitting signals and how does modulation come into play?
A carrier signal, which is modulated by the data signal
82
What is the bandwidth?
How much of the electromagnetic spectrum our signal occupies
83
For which signals does the atmosphere become an obstacle?
Signals above 10 GHz
84
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