TelemetryAnalysis.jl

This package defines an API to fetch and process telemetry packages from satellites.

Notice that this package does not provide a complete set of functionalities by itself. The user must add other packages that uses the API defined here to implement the required functions.

Application Programming Interface (API)

This section defines the API of TelemetryAnalysis.jl.

Sources

A source must fetch telemetry and encapsulate it in a Vector{TelemetryPacket}. It is defined using a structure with supertype TelemetrySource.

struct MyTelemetrySource <: TelemetrySource
    ...
end

It must implement two functions as follows.

function TelemetryAnalysis._api_init_telemetry_source(::Type{T}, vargs...; kwargs...)::T

This function initializes the source of type T. The arguments and keywords can be selected arbitrarily depending on the source's characteristic. The function must return an object of type T.

It is advisable to document the arguments and keywords by extending the documentation of the object init_telemetry_source.

function TelemetryAnalysis._api_get_telemetry(source::T, start_time::DateTime, end_time::DateTime)::Vector{TelemetryPacket}

This function must fetch the telemetry from the source between start_time and end_time. It must return encapsulate each packet in a TelemetryPacket and return a Vector{TelemetryPacket}.

Some sources may also implement the simplified version of _api_get_telemetry that fetches all the packets available:

function TelemetryAnalysis._api_get_telemetry(source::T)::Vector{TelemetryPacket}

Registering the source for interactive use

If the user calls the function init_telemetry_source(), the system will provide a list of registered sources for the user. However, this functionality requires that the source defines the API function:

function _api_init_telemetry_source(::Type{T})

without any other argument or keyword. Hence, it must obtain the information from the user interactively, or define it statically.

A source can be registered for interactive use by:

@register_interactive_source <Source structure>

Databases

A database must define three information:

1. How to get the timestamp from the telemetry packet;
2. How to unpack the telemetry packet into raw data; and
3. The variables inside the telemetry packet.

The database object is created by the function:

create_telemetry_database(label::String; kwargs...)

where label defined the database label. The available keywords are:

• get_telemetry_timestamp::Function: A function that must return the timestamp of a telemetry packet. The API is:

  get_telemetry_timestamp(tmpacket::TelemetryPacket)::DateTime

  (Default = _default_get_telemetry_timestamp)

• unpack_telemetry::Function: A function that must return a AbstractVector{UInt8} with the telemetry frame unpacked, which will be passed to the transfer functions. If the frame is not valid, it must return nothing. The function API must be:

  unpack_telemetry(tmpacket::TelemetryPacket)::AbstractVector{UInt8}

  (Default = _default_unpack_telemetry)

After creating the database, the variables can be added using the function:

add_variable!(database::TelemetryDatabase, label::Symbol, [position::Int, size::Int,] tf::Function; kwargs...)

• database::TelemetryDatabase: Database.
• label::Symbol: Variable label in the database.
• position::Int: Variable position in the telemetry database.
• size::Int: Size of the variable.
• btf::Function: Bit transfer function. For more information, see section Bit transfer function.
• tf::Function: Variable transfer function. For more information, see section Transfer function.

!!! note The position and size can be omitted if the variable is obtained only by the processed values of other variables. In this case, the keyword dependencies must not be Nothing.

This function allows the following keywords:

• alias::Union{Nothing, Symbol}: An alias of the variable. In this case, the function get_variable_description will also consider this alias when searching. (Default = nothing)
• default_view::Symbol: Select the default view for this variable during processing. For the list of available options, see process_telemetry_packets. (Default = :processed)
• dependencies::Union{Nothing, Vector{Symbol}}: A vector containing a list of dependencies required to obtain the processed value of this variable. If it is nothing, then the variable does not have dependencies. (Default = nothing)
• description::String: A description about the variable.
• endianess::Symbol: :littleendian or :bigendian to indicate the endianess of the variable. (Default = :littleendian)

Bit transfer function

The bit transfer function must have the following signature:

function btf(frame::AbstractVector{UInt8})::AbstractVector{UInt8}

Its purpose is to obtain the frame from the telemetry and process to the bits related to the current telemetry variable. The frame is a set of bytes obtained from the variable parameters position, size, and endianess.

Raw transfer function

The purpose of the raw transfer function is to obtain the telemetry byte_array created with the btf and process to a raw value. This value will be used in the transfer function to obtain the variable processed data.

The raw transfer function can have one of the following signatures:

function rtf(byte_array::AbstractVector{UInt8})

or

function rtf(byte_array::AbstractVector{UInt8}, processed_variables::Dict{Symbol, Any})

Transfer function

The variable transfer function can have one of the following signatures:

function tf(raw::Any)

Return the processed value of the variable given the raw information, obtained from the raw transfer function.

function tf(raw::Any, processed_variables::Dict{Symbol, Any})

Return the processed value of the variable given the raw information, obtained from the raw transfer function, and the set of processed variables in processed_variables. This signature must be used if the transfer function depends on others variables.