Chapter3 - Space Environment & Its Effects

1
Chapter 3: Space Environment &

Its Effects to Orbit
Chapter outline
 Space Radiation
 Atmospheric Drag
 Third-Body Perturbations
 Non Spherical Earth
Space Environment
2
Charged particles
Atmosphere Radiation
Non spherical earth

Magnetic field
Debris
Vacuum
Effects to Orbital Movement
3
• Space Radiation
– Radiation from the Sun, produce radiation pressure
• Atmospheric Drag
– Drag from the atmosphere Earth
• Third-Body Perturbation
– Effects of Sun and Moon
• Non Spherical Earth
– perturbation
4
Space Radiation
Nuclear Fusion
5
• Nuclear fusion processes occur in the center of the

Sun at a temperature of , generates a energy of 26.3
MeV and neutron.
Solar Physics
6
Radius
Mass
Particles within plasma 91% H, 8% He, 1% others
Mass density on average
Mass density at center
Luminosity
Effective radiation 5780 K
temperature
Solar constant 1.371 KW/m^2 0.3%
Distance to Earth on average
Distance to Earth at perihelion
Distance to Earth at aphelion
Sidereal rotation period at the 24.8 days
equator
Solar Wind
7
• Properties of solar wind:

Chemical composition 96% protons, 4% &
electrons
Density 6 per/cm^3
Temperature 3500-500000K
Free path length 10^8 km
Velocity 200-400 km/s (slow)
600-2000 km/s (fast)
• The solar wind changes the shape of the magnetosphere

and also generates a strong magnetic field.
• The strong magnetic from the solar wind affects
operation of electrical devices in its area.
Momentum of Radiation
8
• Waves not only carry energy but also momentum. The effect is very
small (we don’t ordinarily feel pressure from light).
Radiation Pressure
9
• Want to relate the pressure felt by the paper to the

intensity of light
 For 100% absorption of light
 100% reflection of light

Example: Radiation Pressure
10
Problem1: How much is the radiation pressure 1.5

m away from a 500 Watt light bulb?
Problem2: Calculate the radiation pressure of the
Sun to the Earth? (Distance from the Sun to Earth
is about 150 million Km, of the Sun)
Radiation Pressure Effect to Satellite
11
• Radiation pressure force from the Sun
 For 100% absorption of light
 100% reflection of light
-
-
• Satellite above 800km altitude, acceleration from solar radiation
pressure is greater.
Example: Radiation Pressure
12
• Example: A satellite has mass of 50kg and area

of . Calculate changes of velocity and distance
in 1 day. (assuming that it is 100% absorption of
light).
13
Atmospheric Drag
General Information
14
• Drag acts opposite the direction of the velocity

vector, thus slowing the satellite and removing
energy from the orbit.
• Satellite altitude:
- 120 to 160 km of the Earth’s surface, atmospheric
drag will bring it down in a few days.
- Final disintegration occurring at an altitude of
about 80 km.
- Above 600 km, drag is so weak that orbits usually
last more than 10 years – beyond a satellite’s
operational lifetime.
Satellite Decay
15
• Explain: satellite decay due

to atmospheric drag from an
• The figure shows dropping apogee
eliptical orbit to a circular of a orbit
orbit.
Effects of Atmospheric Drag
16
• Acceleration due to atmospheric drag:
- : drag coefficient (depend on the shape of

spacecraft 2.2 (averaged for typical spacecraft))
- : mass density of atmosphere (kg/m^3)
- : velocity of spacecraft (m/s)
- : area cross of spacecraft (m^2) (perpendicular to velocity
vector)
- : mass of spacecraft (kg)
17
• For a circular orbit, we can approximate the changes in

semi-major axis, period, and velocity per revolution using
the following equations:
- : ballistic coefficient
- : orbital radius
• , , for a cycle.
Example1:
18
• Calculate orbit decay/orbital & cycle/day?

For:
Height (km)
100 5.6*10^-7
200 2.5*10^-10
300 1.9*10^-11
500 5.2*10^-13
Example2:
19
• A satellite is in a circular Earth orbit at an altitude of 400 km.

The satellite has a cylindrical shape 2 m in diameter by 4 m
long and has a mass of 1,000 kg. The satellite is traveling
with its long axis perpendicular to the velocity vector and it's
drag coefficient is 2.67. Calculate the perturbations due to
atmospheric drag.
20
Third-Body Perturbation
Effects of the Sun and Moon
21
• The gravitational forces of the Sun and Moon cause the change of
longitude of the ascending node and argument of perigee.
• Equations describe these effects:
- Longitude of the ascending node:
(degree/day)
- Argument of perigee:
(degree/day)
Example: Effects of the Sun and Moon
22
• Calculate the perturbations in longitude of the ascending

node and argument of perigee caused by the Moon and
Sun for the International Space Station orbiting at an
altitude of 400 km, an inclination of 51.6 degrees, and
with an orbital period of 92.6 minutes.
23
Non Spherical Earth

Gravitational Potential
24
• GEO (Geographic coordinate system): Equation of

gravitational potential at :
- : latitude of object
- : equatorial radius (=6378.142 km)
- : Lagrange function
Effect of J2
25
only consider
• The change of longitude of the ascending node:
• The change of argument of perigee:
- ,
Example: Effect of J2
26
• A satellite is in an orbit with a semi-major axis of 7,500

km, an inclination of 28.5 degrees, and an eccentricity of
0.1. Calculate the J2 perturbations in longitude of the
ascending node and argument of perigee.
Effect of J2
27
Effect of J2
28
Perturbations
29
Orbit design (Earth Orbiting)
30
• Factors should be considered:

– Recurrent orbit
– No perturbation
– Usage of perturbation
– Constellation design
Recurrent orbit
31
• The satellite periodically flies over the

earth surface after a whole number of
obits.
Earth rotation Perturbation

Satellite ground tracks
32
Semi-concurrent orbit
33
• If swath is small -> more detail of

observation
• Swath is small -> observation is
overlapped.
• Swath is big -> observation gap is
Swath
occurred.
Swath depends on altitude and field of view

No perturbation
34
1) .
2)
3)
Usage of a certain perturbation
35
• Sun-synchronous orbit (SSO): orbital plane should rotate about .
 It’ s useful because:
• Sun-shining angle would be almost constant (good for
Earth observation).
• Good for thermal design
-> SSO is the best for Earth observation.

Analytical Orbit Models
36
• Variation of the elements
• where R(a, e, i. w, Q, M) is the disturbing potential and n is the mean

motion.
Orbit Determination
37
• SGP4 model “Simplified General Perturbation Model No.4”

developed by North American Aerospace Defense Command
(NORAD).
• NORAD orbital elements are published in a two-line data format,
nickname “two-line elements”.
• https://www.celestrak.com/NORAD/documentation/tle-fmt.php
Two-line Element
38
Two-line Element
39
Two-line Element
40
• https://www.n2yo.com/satellite/?s=25544
41

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1

Chapter 3: Space Environment &

Non spherical earth

• Nuclear fusion processes occur in the center of the

• Properties of solar wind:

• The solar wind changes the shape of the magnetosphere

• Want to relate the pressure felt by the paper to the

 For 100% absorption of light

 100% reflection of light

Problem1: How much is the radiation pressure 1.5

• Radiation pressure force from the Sun

 For 100% absorption of light

 100% reflection of light

• Example: A satellite has mass of 50kg and area

• Drag acts opposite the direction of the velocity

• Explain: satellite decay due

• Acceleration due to atmospheric drag:

- : drag coefficient (depend on the shape of

• For a circular orbit, we can approximate the changes in

• Calculate orbit decay/orbital & cycle/day?

• A satellite is in a circular Earth orbit at an altitude of 400 km.

• Calculate the perturbations in longitude of the ascending

Non Spherical Earth

• GEO (Geographic coordinate system): Equation of

• The change of longitude of the ascending node:

• The change of argument of perigee:

• A satellite is in an orbit with a semi-major axis of 7,500

• Factors should be considered:

• The satellite periodically flies over the

Earth rotation Perturbation

• If swath is small -> more detail of

Swath depends on altitude and field of view

• Sun-synchronous orbit (SSO): orbital plane should rotate about .

 It’ s useful because:

• Sun-shining angle would be almost constant (good for

• Good for thermal design

-> SSO is the best for Earth observation.

• Variation of the elements

• where R(a, e, i. w, Q, M) is the disturbing potential and n is the mean

• SGP4 model “Simplified General Perturbation Model No.4”

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