SSPI Satellite Network Design & Operations 3 — Questions and Answers
Question 1: In a VSAT star topology, what is the function of the hub earth station?
- It provides direct peer-to-peer communication between remote sites
- It acts as the central gateway that routes traffic between remote terminals and the terrestrial network (Correct answer)
- It only monitors satellite health telemetry
- It assigns orbital slots to VSAT remotes
Correct answer: It acts as the central gateway that routes traffic between remote terminals and the terrestrial network
In a star topology, all remote VSAT terminals communicate through the central hub, which manages routing, protocol conversion, and network access.
Question 2: What distinguishes a regenerative (processing) satellite payload from a bent-pipe transponder?
- A regenerative payload demodulates, processes, and re-modulates the signal onboard rather than simply amplifying and retransmitting (Correct answer)
- A bent-pipe transponder uses digital switching while regenerative uses analog amplification
- A regenerative payload only operates at Ka-band frequencies
- A bent-pipe transponder requires no ground infrastructure
Correct answer: A regenerative payload demodulates, processes, and re-modulates the signal onboard rather than simply amplifying and retransmitting
Regenerative payloads perform onboard signal processing, enabling separate uplink and downlink optimization and reducing end-to-end latency.
Question 3: What is the primary purpose of a satellite's apogee kick motor (AKM)?
- To maintain station-keeping in the geostationary arc
- To circularize the orbit at geostationary altitude after launch vehicle injection (Correct answer)
- To de-orbit the satellite at end of life
- To adjust the satellite's transponder power levels
Correct answer: To circularize the orbit at geostationary altitude after launch vehicle injection
The AKM fires at apogee of the transfer orbit to raise perigee and circularize the satellite into geostationary orbit.
Question 4: Which multiple access technique assigns dedicated time slots to each earth station transmitting through a shared transponder?
- FDMA
- TDMA (Correct answer)
- CDMA
- SDMA
Correct answer: TDMA
TDMA divides the transponder's time into sequential slots, with each station transmitting burst traffic during its assigned slot.
Question 5: Rain fade is most severe at which frequency bands used for satellite communications?
- L-band (1-2 GHz)
- C-band (4-8 GHz)
- Ka-band (26.5-40 GHz) (Correct answer)
- UHF (300 MHz-3 GHz)
Correct answer: Ka-band (26.5-40 GHz)
Rainfall attenuation increases significantly with frequency, making Ka-band systems most susceptible to rain fade.
Question 6: What is the purpose of a satellite network's Frequency and Polarization Plan?
- To define how spectrum is allocated among beams and transponders to maximize capacity while minimizing interference (Correct answer)
- To schedule satellite launches within the geostationary arc
- To specify the modulation coding rate for each user terminal
- To assign IP addresses to VSAT terminals
Correct answer: To define how spectrum is allocated among beams and transponders to maximize capacity while minimizing interference
The frequency and polarization plan organizes spectrum reuse across beams and transponders to optimize capacity and isolation.
Question 7: In satellite telemetry, tracking, and command (TT&C), what is the primary function of the command subsystem?
- To transmit payload data to earth stations
- To send control instructions from the ground to the satellite to adjust its configuration or operations (Correct answer)
- To measure satellite attitude using star trackers
- To relay voice communications between ground stations
Correct answer: To send control instructions from the ground to the satellite to adjust its configuration or operations
The command subsystem receives and executes ground-originated instructions to control satellite functions such as transponder switching and attitude maneuvers.
SSPI Satellite Network Design & Operations 3
In a VSAT star topology, what is the function of the hub earth station?