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ACS327 Space Systems > All topics > Flashcards

All topics Flashcards

slide 1 space weather

1
Q

What purposes to satellite’s fulfil [4]

A
  • Weather
    -Navigation
    -Space Physics
  • Communication
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2
Q

What do planetary Explorers do? [4]

A
  • Fly-bys
    -Probes
    -Landers
    -Rovers
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3
Q

What do Manned Spacecraft do? [3]

A

-Probes
-Lunar Landers
Stations

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4
Q

Force Equation of two planets

A

F=MmG/r^2

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5
Q

Spacecraft Angular Momentum

A

h=r*v=const (both vectors)

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6
Q

Velocity of circular orbit

A

v=sqrt(mew/r)

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7
Q

period of circular orbit

A

P=2pi*sqrt(r^3/mew)

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8
Q

Escape velocity

A

v=sqrt(2mew/r)

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9
Q

Specific energy(kinetic plus temp specific)

A

e=-mew/2a

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10
Q

velocity for all orbits

A

sqrt(2mew/r -mew/a)

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11
Q

a for parabolic and hyperbolic

A

a=infinity a<0

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12
Q

eccentricity [2]

A

sqrt(1-h^2/(mew*a)) c/a (c is foci and middle)

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13
Q

co planer equation

A

change in v= 2vi*sin(a/2)

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14
Q

What is the vernal equinox vector?

A

The vector from the centre of earth to the sun on the spring equinox day. Its a reference system.

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15
Q

Equation for launch site on earth

A

cos(i)=cos(latitude)sin(azimuth)

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16
Q

What does equation for launch site assume?

A

Earth doesn’t rotate

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17
Q

Draw out space craft horizon thing find sw,ah,Dh

A

check in ipad

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18
Q

What is a sidereal day?

A

a full earth rotation- not counted as an actual day.

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19
Q

What is a solar day?

A

An actual day, when you’ve turned around enough to face the sun again

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20
Q

What is rotation of Apsides?

A

Earths pivot point changing each day

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21
Q

What is regression of nodes?

A

Nodes of an orbit decreasing due to drag

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22
Q

What is a patched conic orbit

A

A way of getting from one planet to another by orbiting the sun and using hyperbolic orbits

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23
Q

What is C3 in regards to patched conic orbit?

A

Vhe^2 used to asses energy required for launch of planetary mission

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24
Q

How does Photon propulsion work?

A

Powerful laser beam directed to provide momentum.

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25
Q

How does Solar sail propulsion work?

A

Large sheet of film, highly reflective use energy of solar radiation particles

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26
Q

What do Space rockets need that Aircraft engines don’t

A

oxygen to carry with them

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27
Q

Rocket Equation

A

v=v0+ vr*ln(m/m-f)

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28
Q

Rocket Equation w/ Impulse

A

v=v0+Ispgln(m/m-f)

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29
Q

What is Cold Gas propulsion?

A

Letting pressurised gas out of a nozzle

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30
Q

Why would you use Cold Gas over over propulsion?

A

Simple

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31
Q

What is Thermal-Solar rockets?

A

Uses solar energy to increase heat of something

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32
Q

Why would you pick a liquid rocket? [3]

A

Controllability, Throttling, Restart avalible

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33
Q

What is Throttling?

A

Changing the Thrust

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34
Q

Why would you pick a solid rocket? [3]

A

Simple, reliable, quick launch time

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35
Q

What is a hybrid rocket?

A

solid fuel, liquid oxidiser

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36
Q

What can liquid rocket systems be subdivided into?

A

Monopropellant and bipropellant

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37
Q

What is monopropellant?

A

Catalytic decomposition of a single propellant

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38
Q

What is bi propellant

A

Chemical reaction between fuel and oxidiser

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39
Q

How does Electric thermal work

A

heat up propellant by passing over a heating element and means it expands and go out fast.

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40
Q

Electrostatic thrusters what they do?

A

Accelerate positively charged particles in static electric field

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41
Q

Lorentz and Hall what do they do?

A

Use there own force to move particles to create propulsion

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42
Q

What does nuclear propulsion do?

A

Some kind of nuclear reaction created heat and therefore pressure

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43
Q

What is Albedo radiation?

A

Planets reflecting sun radidation

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44
Q

What is predicted temperature range?

A

results of thermal modelling of the system

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45
Q

What is design operating range?

A

extremes of predicted temperature range

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46
Q

What is Acceptance temperature range

A

Limits for operating and non operating modes of a unit

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47
Q

What is a black body?

A

A material that absorbs all incident radiation

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47
Q

Qualification temperature limit

A

Flight hardware should be able to operated within these limits to be accepted as part of the satellite (biggest temp limit)

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48
Q

Absorptivity

A

percentage of incoming radiation that is absorbed by a material

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49
Q

Emissivity

A

Proportion of radiation emitted by surface compared to a black body at the same temp

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50
Q

Equilibrium Temperature eq

A

G a A cos(theta) = A omega Eir T^4

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51
Q

Scaling G

A

G1 * D1^2=G2*D2^2 (unchecked)

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52
Q

What is surface irradiation?

A

G- total amount of radiation incident upon the surface per unit time and area

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53
Q

What is surface Radiosity?

A

Total amount of radiation leaving the surface per unit time

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54
Q

What do you assume when doing thermal analysis on real

A

uniform Temp, constant J, G,a,e across surface.

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55
Q

Equation for net thermal energy leaving a surface

A

q=(E-J)/(1-e)/eA

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56
Q

Sum of view factors are

A

unity

57
Q

Two parts of Oppenheim network for each surface

A

Node with temp, node with J
Node with temp connected to J with eA/(1-e)
Node with G connected to everything else with AF

58
Q

Oppenheim Thermal network: Deep space what changes?

A

Temperature of 0 so Js=0 now thermal branch

59
Q

Oppenheim Thermal network: Insulated walls what changes

A

j=sigmaT^4

60
Q

How do you include conduction in the network?

A

Make new radiation constant with different temperatures i guess

61
Q

What’s the difference between thermal active and passive control systems?

A

Active is active pumping shit and passive just like let heat out

62
Q

What is a heat pipe?

A

Way of getting rid of heat by vaporising wick and then it flows to the outside and then condenses again.

63
Q

What is an Optical Solar Reflector?

A

Reflective surface with low absorptivity

64
Q

Downsides of Optical Solar Reflector

A

High cost and fragile

65
Q

What is like an Optical Solar Reflector but more durable?

A

Silver coated teflon

66
Q

What is a Phase Change Device

A

Absorbs heat from sources that use high power over a short period

67
Q

What are Cryogenic systems

A

Used to cool IR detectors

68
Q

Is it easier to cool for a long time or a short time?

A

Short time

69
Q

Active refrigeration Systems, how long, pros and cons

A

Long duration, problems with vibration, operating life

70
Q

Expendable cooling systems, how long, how does it do it

A

short duration mission, fluid absorbs heat and then is yeeted into space

71
Q

What are moving hardware torques?

A

deployment of solar panels, antennas, cameras

72
Q

What are two types of mass expulsion torques

A

unintentional, intentional

73
Q

What are some examples of unintentional mass expulsion torque?[2]

A

leakage of fuel, accidental thrust firing or in the wrong direction

74
Q

What are some examples of intentional mass expulsion torque?

A

Dumping of propellant, payload separation

75
Q

What is Propellant slosh?

A

The torque caused by fluid in a partly filled tank

76
Q

How can you mitigate propellant slosh?

A

Small tanks and tanks with baffles- type of vane

77
Q

What is the problem with Crew motion?

A

Can cause disturbances and change attitude

78
Q

Why does gravity gradient torque disturbances occur?

A

Because of the variation in the Earths magnetic field

79
Q

What Shape of spacecraft is most affected by gravity?

A

Long ones

80
Q

What is Solar Radiation Torque caused by?

A

Radiation incident on spacecrafts surface

81
Q

Solar Radiation Torque depends on? [4]

A

Intensity, surface geometry and optical properties, direction of the sun

82
Q

What is the Aerodynamic force disturbance?

A

Due to atmosphere effects

83
Q

Equation linking torque force and, S distance between cog and cop

A

T=F*S

84
Q

What causes Magnetic Torque disturbances?

A

The interaction between the spacecrafts magnetic field and the planets magnetic field

85
Q

What parts of the Spacecraft cause a magnetic field?

A

Current loops and metallic components residual magnetism

86
Q

What is a spin stabilised system?

A

a spacecraft that it made to spin in one direction that makes it resistance to disturbance torques

87
Q

Pros of spin stabilised systems [4]

A

Simple to stabilise, good pointing accuracy, don’t need sensors sometimes, natural scanning motion

88
Q

Cons of spin stabilised systems [3]

A

Bad at manoeuvring, need redundant solar arrays, some equipment such as antenna not possible

89
Q

What are dual spin systems

A

Most of it spinning apart from one bit on top

90
Q

What makes dual spin system better then spin stabilised? [2]

A

Allows body pointing sensors and higher pointing accuracy

91
Q

What makes dual spin system worse then spin stabilised? [2]

A

Expensive, break easily

92
Q

What is a three axis stabilised system?

A

Maintains alignment, using sensors, thrusters and reaction wheels.

93
Q

Pros of 3 axis stabilised? [2]

A

Unlimited pointing accuracy, All solar arrays are used all the time.

94
Q

Cons of 3 axis stabilised? [3]

A

ACS hardware complex, expensive, too many points of failure

95
Q

What is gravity gradient stabilisation?

A

Only for long objects gravity will keep them facing the same way.

96
Q

Advantages of Gravity Gradient stabilisation? [2]

A

Long life time, simple

97
Q

Disadvantages of Gravity gradient stabilisation [2]

A

Only good for low orbits, modest pointing accuracy

98
Q

Attitude determination for spin stabilised system

A

If you know spin axis and spin rate of your space craft. Use earth and sun sensors and measure angle and rate of them. Direction matching of one will be stable.

99
Q

Attitude determination for 3 axis stabilised systems

A

use distance to the sun and distance to some other star and use that to find the coordinate system and therefore where it is

100
Q

What are sensors?

A

They provide information about the position of spacecraft to known quantities

101
Q

Inertial sensors what?

A

Measure position of sun, earth, bright stars

102
Q

Rate sensors what

A

Detect spacecraft rotations in inertial space

103
Q

Earth Horizon Telescope what?

A

a telescope with a narrow field of view, sends a pulse when starts seeing and stops seeing earth.

104
Q

What does an analogue sensor output?

A

Continuous function of sun angle

105
Q

What does sun presence sensor output?

A

Constant output when sun is in FOV

106
Q

What does digital sun sensor output?

A

digital encoded output as a function of the suns angle

107
Q

What is a analogue sun sensor?

A

Normally a solar sensor, measure current use cos to work out angle

108
Q

How can you improve an analogue sun sensor?

A

Use multiple in different angle or just a bar or masks

109
Q

what is a sun presence sensor?

A

like a photo cell in a slit

110
Q

What is a digital sensor?

A

Strips of photocells

111
Q

How accurate are star sensors?

A

Very

112
Q

Can star sensors operate when they are close to facing the sun

A

no

113
Q

What does a magnetometer sense?

A

Senses planets magnetic field

114
Q

Pros of magnetometer? [3]

A

Reliable, lightweight, low power requirements

115
Q

Cons of magnetometer? [2]

A

Only work close ish to planet
Solar winds can disturb them

116
Q

What is a gyroscope?

A

Uses a rapidly spinning mass to sense and respond to changes in inertial orientation.

117
Q

What is an actuator?

A

Used to change satellite attitude

118
Q

What can be used as a actuator? [4]

A

Thruster, magnetic torque rods, movable appendages, momentum wheels

119
Q

What is a momentum wheel

A

store angular momentum
or make manoeuvres happen

120
Q

What is a magnetic torque rods?

A

Torque rods are surrounded by a coil each tried to control it

121
Q

Downside of magnetic torque rods?[2]

A

interferes with reading of magnetic field, and can only be done close to a planet

122
Q

What is proportional control equation

A

t=-K* theta

123
Q

What is position plus rate control?

A

T=-Ktheta rate -K2theta

124
Q

What is bang-bang control? (where theta is error)

A

T=-a/aTmax

125
Q

What is the geospace?

A

The area with size 200 Re around earth

126
Q

What are ground induced currents caused by

A

Space weather leads to earths magnetic field changing which induces the currents

127
Q

What do ground induced currents effect? [2]

A

PowerGrid’s
Pipelines

128
Q

What is reconnection?

A

The coming together of antiparralel magnetic fields which produce space weather

129
Q

What effects to solar flares cause? [3]

A

-Radio Blackouts
Degradation of solar panels
Increased drag as X-rays are absorbed heating up atmosphere

130
Q

What are coronal mass ejections?

A

Magnetic fields interacting lead to energised particles being released from the sun

131
Q

What are galactic cosmic waves?

A

High energy particles from supernova events from different suns

132
Q

Equation decay or orbit radius

A

CdrhoA/msqrt(mewr)

133
Q

Equation decay of orbit period

A

-3piCdrhoA/mr

134
Q

Source of Energetic Particles in Space [3]

A

Cosmic Rays, the sun, radiation belts

135
Q

What is deep dielectric charging

A

Build up of energetic particles lead to charge on internal electronic components

136
Q

What is Displacement damage?

A

Energetic particle knocks nuclei from regular position

137
Q

What is total ionising dose?

A

Ionisation slowly degrading efficiency of solar arrays

138
Q

First stage comes off first or last

A

1st

139
Q

Difference between space craft horizon and swath width.

A

Spacecraft horizon is circle that spacecraft can see and swath width is the diameter of the circle

ACS327 Space Systems (1 decks)

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