morehead state university morehead, ky prof. bob twiggs [email protected] understanding orbits...
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Morehead State UniversityMorehead, KY
Prof. Bob [email protected]
Understanding OrbitsAssessment Questions
11-10-25
1
SSE-120
Understanding Orbits
Sun – Earth System
Eclipse
Sun’s rays
Earth’s rotation axis
Equator
Orbiting Spacecraft
Spacecraft orbit plane
1. Why are the suns rays assumed parallel when reaching the earth?Sun is far away and large that the rays can be assumed parallel.
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
2. How much is the earth tilted on it’s axis? 23.5 degrees
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
3. Does the earth have the axis tilted all year long?
Yes
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
4. What is the nadir point of a spacecraft?
The point directly below the SC toward the center of gravity.
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
5. How is the inclination of a LEO spacecraft orbit defined?Angle between equator and orbit plane for an ascending node.
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
6. Why is inclination defined only for an ascending node (nadir point crossing the equator?
Need to have a unique reference. Ascending node make it unique.
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
What is the approx. inclination of the orbit shown?30 degrees
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
7. If a spacecraft could change directions of flight by 180 degrees, how would that change the inclination?
Inclination would now be 180 degrees minus original inclination = 150 degrees.
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
8. Will the inclination change with increase in altitude?
No no no no.
SSE-120
Understanding Orbits
Earth System
q
Orbit inclination
r
Earth radius
h
Orbit altitude
Orbit plane
Ascending node crossing the equator
9. Will the inclination change if the orbit were elliptical?
No
SummerWinter
Equinox
Equinox
SSE-120
Understanding Orbits
Earth’s rotation around the sun
10. If there are no perturbations to the orbit, can you draw a terminator orbit for each season?
Super bunch!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
SummerWinter
Equinox
Equinox
SSE-120
Understanding Orbits
Earth’s rotation around the sun
11. Does the eclipse of the earth change with seasons?
Changes directions, but not shape or size.
SSE-120
Understanding Orbits
All orbits go thru the center of the earth
12. Why must all earth orbits rotate around the earth’s center of gravity?Forces of gravity make it that way.That is just the way it is. Nature is in control.
SummerWinter
Equinox
Equinox
SSE-120
Understanding Orbits
Earth’s rotation around the sun
13. Does the terminator or noon-midnight orbit differ for each season?
Both change if no perturbations.
SSE-120
Understanding Orbits
Spacecraft enters eclipse
Noon – Midnight Orbit
Spacecraft Leaves eclipse
14. Will the eclipse time of the spacecraft change with an increase in altitude? Why?
Because the time in eclipse is almost constant, but orbit time will increases.
SSE-120
Understanding Orbits
Noon – Midnight Orbit
15. What would be the percentage of eclipse time if a spacecraft could orbit at zero altitude?
Half the period or 50%.
SSE-120
Understanding Orbits
q
q
r + h
r h
= Q cos-1 [r/(r+h)]
Eclipse time = [(2* )/360] * f orbit time
Calculating eclipse time for a noon-midnight orbit
Solution
f = 90 - Q
f
f
16. What is the eclipse time for an altitude of 750 km for the noon-midnight orbit? Make a Excel (spread sheet) chart for eclipse time from 300 km to 800 km by steps of 50 km.
SSE-120
Understanding Orbits
q
q
r + h
r h
= Q cos-1 [r/(r+h)]
Eclipse time = [(2* )/360] * f orbit time
Calculating eclipse time for a noon-midnight orbit
Solution
f = 180 - Q
f
f
17. What would be the maximum eclipse time for a 750 km altitude orbit if the inclination was 90 degrees? Do you need more information?
Need orbit orientation toward sun --- noon-midnight, terminator, or in between?
SSE-120
Understanding Orbits
C
T
BA
N-M
Changing orbit inclination. Change of eclipse time.
18. How does the eclipse vary with inclination?
From a terminator orbit, decrease in inclination will increase eclipse time after entering the eclipse.
SSE-120
Understanding Orbits
Earth’s rotation around the sun for a GEO stationary spacecraft.
Winter
Equinox
Summer
Equinox
19. Does an eclipse occur with a GEO stationary spacecraft? Yes, during equinoxes.
SSE-120
Understanding Orbits
Earth’s rotation around the sun for a GEO stationary spacecraft.
Winter
Equinox
Summer
Equinox
20. How often during the year will there be an eclipse of a GEO stationary spacecraft?
Twice – each equinox.
Equinox
SSE-120
Understanding Orbits
GEO stationary spacecraft.
What is the max eclipse time?
21. How would you calculate the maximum time of the GEO eclipse?
Same way as for the LEO spacecraft. Only altitude of GEO is larger.
Start here Thursday for Menifee
Equinox
SSE-120
Understanding Orbits
GEO stationary spacecraft.
22. How long would be the period that the GEO would continue to have some eclipse twice a year?
Find when time between entrance to eclipse to exit from eclipse. (days)
Before EquinoxAfter Equinox
http://www.satellite-calculations.com/Satellite/satellite_suneclipse_info.htm
SSE-120
Understanding Orbits
Done