Morehead State University Morehead, KY Prof. Bob Twiggs Understanding Orbits Assessment Questions

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  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  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  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  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  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  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  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  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  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

Summer Winter 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!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Summer Winter 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.

Summer Winter 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   r + h r h  cos -1 [r/(r+h)] Eclipse time = [(2*  orbit time Calculating eclipse time for a noon-midnight orbit Solution     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   r + h r h  cos -1 [r/(r+h)] Eclipse time = [(2*  orbit time Calculating eclipse time for a noon-midnight orbit Solution     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 B A 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 Equinox After Equinox

SSE-120 Understanding Orbits Done