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space systems > orbit concepts > Flashcards

orbit concepts Flashcards

1
Q

what do kepler’s laws provide?

A

reasonable approximation of the dynamics of a small body orbiting about a much larger body

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2
Q

what is kepler’s first law?

A

path of a planet is an ellipse whose radius vector is measured from the sun which is fixed at one focus

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3
Q

what is kepler’s second law?

A

time taken by a planet to reach a particular position is represented by the area swept out by the radius vector drawn from the fixed sun

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4
Q

true or false: the velocity of the spacecraft is constantly changing around the orbit

A

true

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5
Q

what is kepler’s third law?

A

the square of the period of any planet is proportional to the cube of the semi-major axis of the planet

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6
Q

circle, ellipse, parabola, hyperbola

provide the eccentricity and semi-major axis ranges for different conic sections

A
  • circle: e = 0, a = r
  • ellipse: 0 < e < 1, 0 < a < inf
  • parabola: e = 1, a -> inf
  • hyperbola: e > 1, a < 0
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7
Q

define lagrange points

A

points where the gravitational pull of two large masses equals the centripetal force required for a small object to move with them

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8
Q

true or false: forces are the strongest when they are together and the weakest when they are apart from each other

A

true

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9
Q

assuming that there are no other forces acting on the body, what can be said about gravitational and kinetic energies?

A

the sum of KE and PE remains constant throughout the orbit

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10
Q

what is the role of the vis-visa equation?

A

relates an orbiting body’s speed to its distance from the body it is orbiting

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11
Q

what assumptions does the 2 body problem consider?

A
  • masses m and M are the only two bodies involved
  • mass M&raquo_space; mass m
  • mass M spherically symmetrical
  • gravity only force acting
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12
Q

define closed orbit

A

orbit where object in orbit is permanently associated with body being orbited and decribes a closed conic section such as circle or ellipse

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13
Q

what is the total energy of a closed orbit?

A

negative

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14
Q

can an object orbiting a body in a closed orbit escape?

A

no

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15
Q

define open orbit

A

orbit where the object is not permanently associated with the body being orbited and describes an open conic section, such as parabola or hyperbola

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16
Q

what is the total energy of a parabolic orbit?

A

0

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17
Q

what is the total energy of a hyperbolic orbit?

A

positive

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18
Q

in what plane does the earth orbit the sun?

A

ecliptic

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19
Q

what angle does the earth spin on its axis?

A

23.45º

20
Q

what causes seasons?

A

earth’s spin angle of 23.45º

21
Q

where are the tropics of cancer and capricorn located?

A

23.45º north and south

22
Q

define vernal equinox

A

where equatorial and ecliptic planes intersect

23
Q

define apparent solar day

A

time interval between two successive solar transits across a local meridian

24
Q

what is responsible for the duration of the apparent solar day?

A
  • rotation of earth around its axis
  • earth’s revolution around the sun
25
Q

define the mean solar day and its duration

A
  • time taken for the sun to appear in the same position in the sky
  • 24h per day
  • 365.25 days a year
26
Q

define sidereal time and its duration

A
  • time required to rotate earth on its own axis with respect to fixed stars or inertial space
  • 23h, 56m, 4s
27
Q

define universal time

A

index mark for 24 time zones of 15º longitude each

28
Q

list the keplerian orbit elements and what they determine

A
  • semi major axis (SMA) = orbit size
  • eccentricity (ECC) = orbit shape
  • true anomaly (TA) = satellite position on orbit
  • inclination (INC) = orbital plane orientation
  • ascending node / right ascension (RAAN) = orbital plane orientation
  • argument of perigee (AOP) = orbital plane orientation
29
Q

define orbital inclination

A

orientation of orbit with respect to earth’s equatorial plane

30
Q

define prograde and retrograde, and define their angles

A
  • prograde = with the spin of the earth (if i = 0º-90º)
  • retrograde = against the spin of the earth (if i = 90º-180º)
31
Q

define the ascending node

A

defines the location of the line of nodes which are given by the intersection between the orbit plane and the equatorial plane

32
Q

define the argument of perigee

A

defines an angle in the plane between the line of nodes and the periapsis

33
Q

define the true anomaly

A

position of the satellite in the orbit, given as angle between the direction of periapsis and current position of body

34
Q

define periapsis

A

point in orbit where orbiting object is closest to body it orbits

35
Q

list the types of earth orbits

A
  • low earth orbit (LEO)
  • medium earth orbit (MEO)
  • high earth orbit (HEO)
  • geosynchronous orbit (GSO)
  • geostationary orbit (GEO)
  • highly elliptical orbit (MOLNIYA)
  • sunsynchronous orbit (SSO)
36
Q

altitude, velocity, orbit period, used for?, advantages, disadvantages

list the features of an LEO

A
  • altitude = between 100 - 2000km
  • velocity = between 7 and 7.8km/s
  • orbit periods = between 90 and 130min
  • used for detailed observation of earth’s surface and atmospheric measurements
  • adv = high res imaging, low energy req, low comms power
  • disadv = limited coverage, short periods of coverage, high atmospheric density, costly to re-position
37
Q

altitude, velocity, orbit period, used for?, advantages, disadvantages

list the features of an MEO

A
  • altitude = between 2000 - 35786km
  • velocity = between 3.3 and 7km/s
  • orbit periods = between 2 and 20h
  • used for navigational systems, galileo at 20000km altitude
  • adv = great coverage, more time on station, cheaper to change orbit
  • disadv = high radiation and charged particle level
38
Q

list the altitude of a high earth orbit HEO

A

35786km < altitude < 929000km

39
Q

list the features of a gysynchronous orbit (GSO)

A
  • altitude: between 2000 and 35786km
  • period: 23h, 56m, 4s
  • used for missions that require continuous coverage such as comms satellites
40
Q

list the features of a geostationary earth orbit (GEO)

A
  • orbit plane is in line with the equator such that the inclination and eccentricity are 0
  • used for communication satellite missions, but do not have coverage over the poles
41
Q

list the features of molniya orbits

A
  • altitude: low perigee altitude (< 1000km) and high apogee altitude (< 35800km)
  • adv: long dwell time over region below apogee, potential for no eclipse period during mission ops
  • disadv: potential traverse through van allen belts, for continous coverage need more than one satellite, wide variation in range, range rate and coverage region
42
Q

list the features of sun synchronous orbits (SSO)

A
  • altitude: between 600-800km
  • period: between 96 and 100min
  • inclination: ~98º
  • used for earth observation where similar lighting conditions are required, change in RAAN is same as Earth’s and solar angle is the same
43
Q

define ground tracks

A

traces of the sub satellite point, on the surface of the earth that a satellite generates in one orbit about the earth

44
Q

how can the inclination of an orbit be determined from ground tracks?

A

max latitude of orbit ground trace

45
Q

when calculating the orbit period using ground tracks, we can assume the angular velocity of the earth to be?

A

0.25º/min

46
Q
A

space systems (8 decks)

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