SSPI Orbital Mechanics & Spacecraft Operations 1 — Questions and Answers
Question 1: What is the orbital period of a geostationary satellite?
- 12 hours
- 24 hours
- 23 hours 56 minutes (Correct answer)
- 48 hours
Correct answer: 23 hours 56 minutes
A geostationary satellite has a sidereal period of approximately 23 hours 56 minutes (one sidereal day), which keeps it fixed over a point on the equator.
Question 2: At what altitude do geostationary Earth orbit (GEO) satellites operate?
- 2,000 km
- 20,200 km
- 35,786 km (Correct answer)
- 100,000 km
Correct answer: 35,786 km
GEO satellites orbit at approximately 35,786 km above the equator, where their orbital period matches Earth's rotation.
Question 3: Which orbital parameter describes the shape of a satellite's orbit?
- Inclination
- Right ascension of ascending node
- Eccentricity (Correct answer)
- Argument of perigee
Correct answer: Eccentricity
Eccentricity defines the shape of the orbit, with 0 being a perfect circle and values approaching 1 representing increasingly elongated ellipses.
Question 4: What is the purpose of a Hohmann transfer orbit?
- To maintain station-keeping at GEO
- To efficiently move a satellite between two circular orbits (Correct answer)
- To deorbit a satellite at end of life
- To correct inclination drift
Correct answer: To efficiently move a satellite between two circular orbits
A Hohmann transfer orbit uses two engine burns to move a spacecraft between two circular orbits using an intermediate elliptical path, minimizing propellant use.
Question 5: Which Keplerian element defines the tilt of a satellite's orbital plane relative to the equator?
- Eccentricity
- Inclination (Correct answer)
- Semi-major axis
- True anomaly
Correct answer: Inclination
Inclination is the angle between the orbital plane and Earth's equatorial plane, ranging from 0° (equatorial) to 90° (polar) and beyond.
Question 6: What causes a satellite in low Earth orbit to gradually lose altitude over time?
- Solar radiation pressure
- Magnetic field interaction
- Atmospheric drag (Correct answer)
- Gravitational perturbations from the Moon
Correct answer: Atmospheric drag
Residual atmospheric drag in LEO continuously removes orbital energy, causing the satellite to spiral inward and eventually re-enter the atmosphere.
Question 7: What is the semi-major axis of an orbit?
- The radius at apogee
- Half the longest diameter of the elliptical orbit (Correct answer)
- The distance from perigee to the center of Earth
- The altitude of the satellite above the surface
Correct answer: Half the longest diameter of the elliptical orbit
The semi-major axis is half of the longest dimension (major axis) of the ellipse and is directly related to the orbital period via Kepler's third law.
SSPI Orbital Mechanics & Spacecraft Operations 1
What is the orbital period of a geostationary satellite?