ECE 514E - Molniya & Tundra Satellites Quiz

Test your knowledge of highly elliptical orbit satellite systems. Select the best answer for each question.

1. What is the primary orbital period of a Molniya satellite?
2. The critical inclination of 63.4° is essential for Molniya and Tundra orbits because it:
3. What is the key difference between Molniya and Tundra orbits?
4. Which of the following is a major challenge in designing communication systems for HEO satellites like Molniya?
5. How many Molniya satellites are typically needed in a constellation to provide near-continuous coverage?
6. The primary advantage of HEO systems like Molniya and Tundra over GEO satellites is:
7. What is the approximate apogee altitude of a Molniya orbit?
8. Which real-world satellite system uses a Tundra-like orbit for its operations?
9. For electrical engineers designing ground stations for HEO satellites, which of the following is a critical requirement?
10. The "quasi-stationary" behavior of HEO satellites refers to:

Answers and Explanations

Question 1: What is the primary orbital period of a Molniya satellite?
Correct Answer: b) 12 hours
Molniya orbits have a 12-hour period, which is exactly half a sidereal day. This allows a constellation of 2-3 satellites to provide continuous coverage, with one satellite always near apogee over the service area.
Question 2: The critical inclination of 63.4° is essential for Molniya and Tundra orbits because it:
Correct Answer: b) Prevents the argument of perigee from drifting due to Earth's oblateness
At 63.4°, the perturbation caused by Earth's equatorial bulge (J2 effect) results in zero rate of change of the argument of perigee. This keeps the apogee fixed at the desired high latitude, which is crucial for maintaining consistent coverage.
Question 3: What is the key difference between Molniya and Tundra orbits?
Correct Answer: c) Tundra has a 24-hour period while Molniya has a 12-hour period
The fundamental difference is orbital period: Molniya orbits have a 12-hour period, while Tundra orbits are geosynchronous with a 24-hour period. This gives Tundra satellites a longer dwell time at apogee.
Question 4: Which of the following is a major challenge in designing communication systems for HEO satellites like Molniya?
Correct Answer: b) Large variation in path loss due to changing satellite distance
The distance from ground station to satellite varies dramatically - from about 1,000 km at perigee to 40,000 km at apogee. This creates a path loss variation of approximately 32 dB, requiring sophisticated power control and receiver AGC systems.
Question 5: How many Molniya satellites are typically needed in a constellation to provide near-continuous coverage?
Correct Answer: b) 2-3
A constellation of 2-3 Molniya satellites is sufficient for near-continuous coverage. With a 12-hour orbit, each satellite spends about 8 hours near apogee, so properly phased satellites can ensure one is always in the useful part of its orbit.
Question 6: The primary advantage of HEO systems like Molniya and Tundra over GEO satellites is:
Correct Answer: b) Better coverage of polar regions
GEO satellites are ineffective for high-latitude regions (above ~55-60°) as they appear very low on the horizon or below it. HEO satellites with apogee over polar regions solve this problem, making them ideal for serving countries like Russia, Canada, and Scandinavian nations.
Question 7: What is the approximate apogee altitude of a Molniya orbit?
Correct Answer: d) 40,000 km
Molniya orbits have an apogee altitude of approximately 39,300 km, which is similar to GEO altitude (~36,000 km). The perigee is much lower, typically around 500-1,000 km.
Question 8: Which real-world satellite system uses a Tundra-like orbit for its operations?
Correct Answer: c) SiriusXM satellite radio
SiriusXM uses satellites in inclined geosynchronous orbits (similar to Tundra orbits) to provide satellite radio coverage across North America, with extended dwell time over the continent.
Question 9: For electrical engineers designing ground stations for HEO satellites, which of the following is a critical requirement?
Correct Answer: b) Steerable antennas to track the satellite
Unlike GEO satellites that appear stationary, HEO satellites move significantly across the sky, especially during their useful apogee phase. Ground stations require steerable antennas to maintain communication links.
Question 10: The "quasi-stationary" behavior of HEO satellites refers to:
Correct Answer: b) Their slow movement at apogee, appearing to hover over a region
Due to Kepler's second law, satellites move slowest at apogee. For HEO satellites with apogee over a region of interest, this creates the illusion of "hovering" for several hours, similar to but not as perfect as GEO satellites.