*Question E1D02:
[97.211(b)] Which of the following may transmit encrypted messages?*  

*Correct Answer is  B: Telecommand signals from a space telecommand station*  

### AI Response: (may contain errors)  

To understand why "Telecommand signals from a space telecommand station" is the correct answer for the question about transmitting encrypted messages, let's break down each option:

### Correct Answer: 
**B: Telecommand signals from a space telecommand station**

- **Explanation**: The FCC regulations allow encrypted messages for telecommand signals sent to space stations. This is necessary for security and to prevent unauthorized access to the control of space equipment. The encryption ensures that only authorized personnel can control or communicate with the spacecraft.

### Incorrect Answers:
**A: Telecommand signals to terrestrial repeaters**  
- **Explanation**: Telecommand signals to terrestrial repeaters must be unencrypted. The purpose of these signals is to relay communications, and encryption would hinder the ability of operators to monitor and ensure proper operation of the repeaters.

**C: Auxiliary relay links carrying repeater audio**  
- **Explanation**: Similar to terrestrial repeaters, auxiliary relay links that carry audio must remain unencrypted. This is to ensure that all operators can access and monitor the audio being relayed, which is essential for emergency communications and coordination.

**D: Mesh network backbone nodes**  
- **Explanation**: Mesh network backbone nodes are typically used for local communications and must also remain unencrypted. This allows for open access and monitoring by all users within the network, which is crucial for maintaining network integrity and functionality.

### Summary:
- Only telecommand signals from space telecommand stations are permitted to be encrypted under FCC regulations, primarily for security reasons.
- All other options involve communications that must remain open and accessible for monitoring and operational integrity.

### Useful Rule of Thumb:
- **Encryption in Amateur Radio**: Generally, encryption is not allowed in amateur radio communications except for specific cases like space telecommand signals. Always check the specific regulations for the type of communication you are involved in.