Start from what the mission needs, not from a favorite technology.
Mission Needs Come First
- “Use Ka-band” is an implementation choice
- “Use a relay” is an architecture choice
- Start with what information must reach whom, how much, how quickly, and how dependably
- Then compare ways to make that happen (see Communications Architectures)
Start With Eight Questions
- Where is the information produced?
- Where must it ultimately go?
- How much must be delivered?
- How soon must it arrive?
- How complete and reliable must delivery be?
- Are some data more important than others?
- What security is required?
- What resources and constraints limit the design?
Start With Source and Destination
- Geometry sets range, visibility, and propagation time (see Link Geometry)
- Interfaces identify the systems and organizations involved
- The final destination may be far beyond the ground antenna
- Different sources may need different paths and services
Different Data Need Different Services
| Data product | Volume | Latency | Other needs |
|---|---|---|---|
| Science imagery | High | Hours | Very high completeness |
| Event alert | Tiny | 10 minutes | Urgent |
| Housekeeping | Moderate | — | Priority changes with spacecraft state |
| Command | Tiny | Mission-dependent | Must be authorized and correct |
The smallest data product may drive the most expensive design choice
- E.g. the tiny event alert with a 10-minute deadline can’t wait for a twice-daily contact, while the huge science volume can (example not on slide) (see adding a latency need)