9.6 Data Budget and Profiling

A data budget assists the CDH specialist in choosing components that satisfy the mission. The payload and other subsystem components must generally have their memory, throughput, update rate/frequency, connector, and communication protocols. The task now is if you put all of these components together, what would the spacecraft need in the way of processing power, memory, timing accuracy, data bus connections, and protocols? Just like the power budget and profiling exercise, we will step through the process step by step to analyze the accumulation of data, the necessary computation or throughput, and the timing accuracy in each mission operational mode. In the power budget, we’ve already defined time in each mission operation phase and components that are on/off in each mode, so we will start the data budget process by:

1. Defining the subsystem components’ throughput, CPU utilization, non-volatile memory, volatile memory, update frequency, and required timing synchronization.

2. Summarize the computer characteristics for each mode by summing the individual characteristics of each component in each mode and determine which mode will drive the computer design. Typically, science operations and communications drive the computer component characteristics

3. Derive the data generation and downlink profile over time of an orbit using your payload throughput, compression estimate, communication downlink rate, and ground pass characteristics. An analogy to the power generation profile is that your mass storage is like your battery: you want to pay attention to the total capacity of your mass storage and make sure you are downlinking at about an equal rate as you are generating payload or housekeeping data.

From this analysis, we see that the non-volatile memory capacity over the orbit returns back to empty, verifying that the mission is sufficiently supported by the mass storage system. If the mass storage slowly fills up every orbit,

• the CDH specialist must find a larger mass storage system, or
• the systems engineer must modify the mission operations timeline to spend longer periods in downlink mode or make more frequent passes overground stations, or
• the communications specialist must find a radio that is more capable of downlinking data.

If the data budget reveals a large surplus of mass storage that’s just sitting there, the systems engineer may decide to utilize that mass storage by modifying the mission operations to downlink less, save on the power consumption to conduct more science.

Artemis Kit Specific