space environment

Question 1

define the space boundary

Answer 1

line where aerodynamic and gravitational forces balance at approximately 100km

Question 2

define the von Karman criterion

Answer 2

aerodynamic and gravitational forces are balanced

Question 3

describe the construction of the earth’s atmosphere, including altitude, temperature, and density

Answer 3

troposphere: 0 - 15km -> T = 288 - 217K -> density = 100 - 7% sea level
stratosphere: 15 - 50km -> T = 217 - 271K -> density <= 7% sea level
mesosphere: 50 - 80km -> T = 271 - 181K -> density = 1 millionth sea level
thermosphere: 80 - 600km -> T = 81 - 1508K -> density = extremely low
exosphere: 600 - 10000km -> T = 1000 - 2500K -> density = extremely low

Question 4

describe the ionosphere

Answer 4

region from 60-1000km, residual gases are ionised by solar radiation

Question 5

when do drag forces stop acting on spacecraft and why?

Answer 5

above ~600km. because the prevalence of residual gases is low enough that there is no appreciable force exerted

Question 6

describe the hostile natural conditions

Answer 6

high vacuum, high EM radiation, particle radiation, collision, chemical effects

Question 7

describe the kind natural conditions

Answer 7

zero effective gravity, no wind, no water vapour, clean environment

Question 8

define astronomical unit

Answer 8

distance from the earth

Question 9

what are PHAs and at what distance are they considered?

Answer 9

potentially hazardous asteroids - below 0.05AU

Question 10

list and describe the near-earth objects

Answer 10

asteroid = small body orbiting sun ranging from 10-100km in size
meteoroid = small body of matter in solar system ranging from 100micron - 10m in size.
micrometeoroid = small meteoroid, known as interplanetary dust
meteor - small body of matter from outer space that enters earth atmosphere
meteorite = meteor that survives its passage into earth’s atmosphere and strikes the ground
comet = small solar system body orbiting the sun, loose collection of ice, dust and small particles

Question 11

what is the solar cycle?

Answer 11

11 years -> 4 year rise and 7 year fall in solar activity

Question 12

how does the solar cycle exist?

Answer 12

due to the build up in magnetic field distortions in the sun

Question 13

how can we predict solar activity and the effects of it?

Answer 13

using the periodicity of the solar cycle

Question 14

define the van Allen belt

Answer 14

earth’s magnetic field region

Question 15

how are charged particles formed in space?

Answer 15

sun is prone to flares and ejections resulting in hot plasma ejected which contain charged particles (electrons, protons, heavier ions i.e. solar wind), these charged particles are then trapped in van Allen belt

Question 16

define the altitude range of the van Allen belts, and state the peak intensity altitude

Answer 16

inner belt: 2000 - 10,000km
outer belt: 10,000 - 60,000km
peak intensity @ 35,800km

Question 17

define the south atlantic anomaly

Answer 17

region where the van Allen belt altitude is at 200km

Question 18

how does spacecraft charging occur?

Answer 18

• spacecraft in LEO have negative floating potential compared to space as their orbital velocity is much higher than thermal velocity of ions
• fast moving electrons collected by spacecraft and thus plasma sheath forms around spacecraft surfaces

Question 19

describe local charging (differential charging)

Answer 19

caused by characteristics of the surfaces’ materials leading to potentially dangerous electrostatic discharges

Question 20

list the effects of radiation exposure

Answer 20

• disruptions in semiconductor’s crystal structure
• cause electric charge to build up on insulators

Question 21

define the Total Ionising Dosage

Answer 21

max radiation that a circuit can withstand

Question 22

list and describe the categories of effects of radiation exposure

Answer 22

• single event upset (SEU) = change of data state induced by energetic particle (TEMPORARY)
• single event latch-up (SEL) = condition which causes loss of device functionality (PERMANENT)
• single event burnout (SEB) = condition which can cause device destruction due to high current state in a power transistor

Question 23

which category of radiation exposure is most likely at the south atlantic anomaly?

Answer 23

single event upset (SEU)

Question 24

describe the induced environment during the pre-launch phase

Answer 24

• covers the manufacture, assembly, integration and testing of the satellite prior to launch
• characterised by precise control of cleanliness and humidity throughout the processes involved

Question 25

which is the most severe mechanical environment for a spacecraft?

Answer 25

the launch phase induced environment

Question 26

which two categories of loading exist in the launch phase?

Answer 26

static loading, dynamic accelerations

Question 27

describe static loading

Answer 27

longitudinal loads - due to launch vehicle thrust and drag profiles
lateral loads - dependent on wind gusts, engine shut down, gimballing

Question 28

describe dynamic accelerations

Answer 28

noise field source - ground reflection
random vibrations - structural excitation, small thrust fluctuations, fuel turbo pumps

Question 29

how are vibrations typically transmitted?

Answer 29

by the launch vehicle to the payload via the launch vehicle mechanical interfaces

Question 30

describe the induced environmental effects during the in-orbit phase

Answer 30

• static accelerations (orbit transfer burns, station keeping, pointing manoeuvres)
• thermal loading
• surface contamination of arrays & optics (out gassing of materials or thruster exhaust plumes)
• impact from man made space debris