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Spaceflight > I2S - Lecture 6-8 (Satellite Design) > Flashcards

I2S - Lecture 6-8 (Satellite Design) Flashcards

1
Q

How many satellites are in orbit today?

A

9.900 active satellites as of May 2024

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2
Q

What are the definitions of payload and subject?

A
  • Payload = combination of hardware and software that interacts with the subject
  • Subject = the portion of the outside world that the s/c is looking at / interacting with
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3
Q

Name some types of s/c missions

A
  • Communications
  • Remote Sensing
  • Navigation
  • Weapons
  • In-situ science
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4
Q

What are transmission characteristics of the Earth’s atmosphere?

A

EM spectrum has many bands for which Earth’s atmosphere is opaque (needs to be avoided)

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5
Q

What is the ground sampling distance (GSD)?

A

Ability to resolve fine detail on the surface of Earth observing systems

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6
Q

State observation payload types

A
  • Visible Systems - high spatial resolution, operates only in daylight
  • Infrared sytems - subject to atmospheric transmission windows, operates both day and night
  • Microwave Radiometers - low resolution, but collect information over large areas
  • Radar systems - require own illumination, penetrate most atmospheric disturbances
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7
Q

Name systems that require electrical power

A
  • Payload
  • Computer
  • Communications
  • Guidance, Navigation, attitude control
  • Sensors
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8
Q

What is PMAD?

A

Power Management and Distribution

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9
Q

Power usage is divided into …?

A
  • Baseline power (required continuously)
  • Peaking power (required for shorter period)
  • Dormant power (req. to keep the system alive)
  • Burst or Transient power (needed for momentary surges)
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10
Q

Compare different power source comparison

A
  • Chemical (batteries, fuel cells): short time, low power
  • Solar arrays: long time, lower power
  • Nuclear reactors: long time, high power
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11
Q

Name characteristics of solar arrays

A
  • High specific power (25 - 300 W/kg)
  • Require storage (batteries) during eclipse
  • Good option for near Earth operation
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12
Q

Compare solar cell technologies

A
  • Silicon - cheap but not terribly efficient
  • Gallium Arsenide - more efficient, lower temp coefficient
  • Multibandgap - even more efficient with several semiconductor layers
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13
Q

What are the key system requirements for solar arrays?

A
  • Avg electrical power for payload
  • Peak elect. power for payload
  • Mission life
  • Orbital parameters
  • Spacecraft configuration
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14
Q

What is the difference between cells and batteries (terminology)?

A
  • A primary cell is used once and discarded
  • Secondary cell and can be recharged and used repeatedly
  • Batteries consists of many cells
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15
Q

What is the battery lifetime?

A

The number of times the battery is cycled through charge and discharge equals the mission duration divided by the day/night period

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16
Q

What is the DOD?

A

Depth of discharge, fraction of the battery’s total capacity that is used.
Since the numbers of battery cycles descreases as the depth of discharge increases

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17
Q

What is the purpose of thermal control?

A

To control the operating temperature of spacecraft systems

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18
Q

Thermal management includes…

A
  • Heat rejection, minimize thermal input and maximize thermal radiation
  • Heat conservation, maximize thermal input and minimize thermal radiation
  • Transient amerlieration, components dont overheat during transient high thermal load, or dont freeze during low thermal load
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19
Q

What are thermal inputs for a s/c?

A
  • Solar radiation
  • Albedo radiation
  • Planetary radiation (infrared)
  • Internally generated heat
20
Q

Heat transfer mechanisms in space?

A
  • Internal: Convection (liquid/gas), Conduction (solid), Radiation
  • External: Radiation (infrared)
21
Q

Name thermal control components and purpose

A
  • Materials and coatings (paints, mirrors, optical solar reflectors)
  • Multilayer insulation
  • Electric heaters
  • Space radiators (waste heat into space)
  • Cold plates (mount for electronic equipment) (fluids)
  • Doublers (passive heat exchange surface) (aluminum)
  • Heat pipes (fluid based transfer)
  • Sensors, isolators, coolers,….

Minimizes radiative heat transfer from/to a s/c component

22
Q

What is TT&C?

A

Tracking, Telemetry and Control

23
Q

Why do satellites communicate with Earth?

A
  • Transmit telemetry
  • transmit payload data
  • receive commands
24
Q

What is the advantage of crosslink?

A

Satellites communitcate with each other, therefore they dont need to be in contact with gound station all the time

25
Q

Factors to consider in design…

A
  • Orbit
  • RF Spectrum (frequencies are limited)
  • Data rate
  • duty factor
  • link availability and access time
  • threat
26
Q

What are the frequency selection drivers?

A
  • Spectrum availability and FCC allocation
  • Relay/Ground station frequency
  • Antenna size
  • Atmospheric attenuation
  • Noise temperature
  • Modulation and coding
27
Q

How reduce the data rate?

A
  • Increase duty cycle
  • collect only above-threshold data
  • record amplitude changes only
  • data compression
28
Q

What is the Link Design Process?

A
  1. Define requirements for each link
  2. design each link
  3. size the payload
29
Q

Name some external noise sources

A
  • Galactic noise
  • Clouds, rain in path
  • Solar noise
  • Earth (290k)
  • Man-made noise
  • Nearby objects
  • satellite structure
30
Q

What is modulation?

A

Modulation modifies an RF carrier signal so that it contains input signal information

31
Q

What is the BER?

A

The bit error ratio (also BER) is the number of bit errors divided by the total number of transferred bits during a studied time interval.

32
Q

Name two compression algorithms

A
  1. Lossless compression - ensures data is exactly the same (heavy data)
  2. Lossy compression - does not promise that received data is the same as data sent, better compression ratios
33
Q

Why compress data?

A

Need to send more data than bandwidth accommodates, since it is limited by the link equation and international regulation

34
Q

Name some antenna types

A
  1. Parabolic reflector
  2. Helix
  3. Horn
  4. Biconical Horn
35
Q

How expensive is the ground segment?

A

Represents approx. 25% of total cost

36
Q

Name communications bands with frequency

A
  1. S Band - 2-3 GHz
  2. C - 3-6 GHz
  3. X - 7-8 GHz
    …
37
Q

What are factors for the Ground Station?

A
  • Location in relation to s/c orbit
  • Geopolitical
  • Distance to control centers
  • Weather
  • Seismic activities
  • Obstacles
38
Q

What is the ranging function of a ground station?

A

A ground station can measure range and position of a s/c to update the orbital propagation computations, vie RF or laser observations

39
Q

What is the ADCS?

A

Attitude Determination and Control Subsystem

40
Q

What is the attitude error?

A

Low frequency s/c misalignment

41
Q
A
42
Q

What are the dominant disturbances to s/c attitude?

A
  • Solar Radiation pressure
  • Atmospheric drag
  • Magnetic field (interaction with earth magnetic field)
  • Gravity-Gradient (difference in gravitational acceleration between different points of the s/c)
43
Q

Name s/c control methods

A
  • PASSIVE CONTROL
    Gravity Gradient control, momentum bias wheel, passive magnetic control
  • SPIN CONTROL TECHNIQUES
    Spin stabilization, dual-spin stabilization, 3-axis control techniques
44
Q

What contains the 3-axis control technique?

A

Combination of momentum wheels, reaction wheels, control moment gyros, thrusters, solar or aerodynamic control surfaces, magnetic torquers

45
Q

What is SWaP?

A

Size, Weight and Power
three key budgets to keep track of during s/c design

Spaceflight (8 decks)

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