Question E2A12:
What is the purpose of digital store-and-forward functions on an amateur radio satellite?  

Choices:  
A: To upload operational software for the transponder  
B: To delay download of telemetry between satellites  
C: To hold digital messages in the satellite for later download  
D: To relay messages between satellites    

Correct Answer is  C: To hold digital messages in the satellite for later download  

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Digital store-and-forward on an amateur satellite is essentially an onboard mailbox. Users upload messages/files when the satellite is in view; the satellite stores them and later downlinks them to other ground stations when it passes over those stations.

Correct answer (C): To hold digital messages in the satellite for later download  
- This is exactly what “store-and-forward” means: the satellite stores user data and forwards it later. Historically seen in “PACSAT”-type satellites that acted like a space-based BBS/PBBS.

Why the other choices are incorrect:
- A: To upload operational software for the transponder  
  - Software uploads are a command-and-control function handled by the satellite’s control team, not a user-facing store-and-forward service.
- B: To delay download of telemetry between satellites  
  - Amateur satellites rarely interlink with each other, and telemetry is typically downlinked directly to Earth in real time or buffered by the satellite’s own housekeeping, not via a user store-and-forward system.
- D: To relay messages between satellites  
  - That would be inter-satellite cross-linking/real-time relay. Store-and-forward is about delayed delivery from the same satellite, not inter-satellite relaying.

Useful rules of thumb:
- LEO satellites are only in view for short windows (about 5–15 minutes per pass), with an orbital period roughly $T \approx 90$ minutes. Store-and-forward lets stations that are never simultaneously in view exchange messages asynchronously.
- Terminology: a “digipeater” is real-time forwarding; a “store-and-forward” system is a mailbox/BBS function.