Is a subscription needed to receive telemetry? / How does commanding-in-the-blind work?

This is foreseen using hardcoded aggregations, as written in the M&C book, page 2-11:

In many situations it is expected that basic summary or overview information about the state of a system or spacecraft be published without an initial consumer request. For example, for safety reasons it is normal for a spacecraft to broadcast basic status information when in recovery/safe mode to help diagnose any communication issues that might exist.

Whilst no operations for this situation have been explicitly defined it should be noted that it is completely valid for a service provider to publish these aggregation updates without having received a subscription request from a consumer. In this situation the registration request from the consumer is hardcoded into the provider application, the MO publish/subscribe concept is not modified but in effect parts of it have been hardcoded into the deployment.

How does Parameter time-stamping work in the Aggregation Service?

The Aggregation Service allows the monitoring of multiple Parameters simultaneously. Inside an Aggregation, Parameters are grouped into Parameter Sets. Therefore an Aggregation is a list of Parameter Sets. Each Parameter Set has two Time related values, deltaTime and intervalTime.

  • deltaTime is the time between a Parameter Set and it’s previous. If the Parameter Set is the first, then deltaTime is relative to the aggregation’s report timestamp (i.e. the MAL message delivering the aggregation).
  • intervalTime is the time between each Parameter in a Parameter Set.

Note that both deltaTime and intervalTime are optional fields, the default value is 0.

What accuracy can be supported for aggregations?

Timestamp intervals in the Aggregations are defined using the Duration field type as defined in the Message Abstraction Layer.

The Duration structure (…) represents a length of time in seconds. It may contain a fractional component.

The accuracy of the duration field is then defined per deployment via what is named a Mapping Configuration Parameters.

For example the Space Packet Transport Binding and Binary Encoding states that the Duration field is configured using: P-Field of the CUC Time Code Format.