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Glossary

This is an alphabetized glossary of common term definitions used throughout the Aerie ecosystem and related domains.

A​

  1. Activity Directive - A record in an activity plan that describes start time and arguments for an activity type. An activity directive is an input for simulation, that instantiates an object with the specified arguments and executes at the specified time.

  2. Activity Plan (Plan) - A collection of activity directives within a time span bounded with plan start and plan end time.

  3. Activity Type - A Java class in the mission model that is the archetype of a unit operation an activity simulation. Activity types are units for modeling and planning for ground operations, and are not recognized by the flight system. An activity type in Aerie describes:

    • Parameters that define the range of execution for each instance of the activity
    • Computed attributes that define values that will be computed
    • An effect model that can query or modify modeled resources
    • A start time and arguments for children activities that are called or spawned during the execution of the activity. Note that the latter is referred to as decomposition in our user interface and docs.

  4. Argument - A value given to an activity or simulation configuration parameter.

C​

  1. Call - A function in the Merlin simulation modeling API. Call() executes a provided task and blocks until that task has completed. Typically Call() is used by a mission modeler who wants to execute an activity and wait for its completion before continuing execution of their modeling code. Call() has a few function signatures so that it can be used to call an activity type and arguments or a Java lambda/Runnable.

  2. Cell - Allows a mission model to express time-dependent state in a way that can be tracked and managed by the host system.

  3. Command Expansion - A mechanism to generate commands per simulated activity.

  4. Command Expansion Logic - A logic snippet that applies to all simulated instances of an activity type, returning a collection of commands. Generally it maps activity arguments to command arguments. Potentially can return different commands for different instances.

  5. (Command) Expansion Set - A collection of expansion logic which will be input for an expansion request. An expansion set can contain only one expansion logic per activity type. Expansion set can have logic for all activity types or for a subset.

  6. Common Access Manager (CAM) - A NASA AMMOS utility which provides application layer access control capabilities, including single sign-on (SSO), federation, authorization management, authorization checking & enforcement, identity data retrieval, and associated logging.

  7. Constraint Checking - A downstream analysis of a simulation dataset that evaluates a set of constraints and returns time windows of violation.

  8. Constraint - An expression built up with the Aerie constraints eDSL, which evaluates to a set of windows during which the condition(s) defined by the expression is true or false. Aerie supports various constraint types such as safe ranges for resources or necessary pre-conditions for safe execution of activities. Aerie constraints is a mechanism to represent and check many flight rule types.

D​

  1. Decomposition - A method for modeling the behavior of an activity (root activity) by composing a set of activities. Each composed activity describes some smaller aspect of behavior. The root activity orchestrates the execution of each child activity by interleaving function calls to spawn(), delay(), and call(). The goal of decomposition is to allow mission modelers to modularize their activity modeling code and to provide greater visibility into the simulated behavior of an activity. For example, consider an activity which models taking an observation with a particular spacecraft instrument. The process of taking an observation may include the distinct phases of instrument startup, take observation, and instrument shutdown. The mission modeler can decide to modularize their modeling and use decomposition to model each of the three phases separately and then compose them with a root activity called "observation" which orchestrates the execution of each of the three activities.

  2. Delay - A function in the Merlin simulation modeling API. A modeler can delay (pause) an activity’s execution during simulation effectively modeling some passage of simulated time, before resuming further modeling.

  3. Deployment - We refer to a particular configuration of the Aerie system as an "Aerie Deployment", in the context of a broader ground data system (GDS) deployment.

  4. Docker - A set of platform as a service (PaaS) products that use OS-level virtualization to deliver software in packages called containers.

G​

  1. GraphQL - An open-source data query and manipulation language for APIs, and a runtime for fulfilling queries with existing data.

H​

  1. Hasura - A GraphQL schema compiler and GraphQL API server. As a compiler, Hasura parses a PostgresDB schema and generates a GraphQL schema defining a data graph of Queries, Mutation, and Subscriptions. Aerie utilizes a Hasura component to expose select database tables as the Aerie GraphQL API.

I​

  1. Initial Conditions (incons) - The initial value of resources before a simulation.

J​

  1. JUnit - A unit testing framework for the Java programming language.

M​

  1. Mission Model - The modeling code written in Java, packaged as a JAR that describes activity types and resource behavior models. Mission model is a required input for activity planning, simulation and scheduling performed by Aerie.

P​

  1. Parameter - A named variable (and data type) in a function description or Activity definition, utilized within the function/Activity definition.

  2. Planner - A person responsible for deciding how to concretely achieve a set of mission objectives over the course of a span of time, formalized as a plan, with the expectation that this plan will be executed by other mission elements, including (and especially) by a spacecraft’s onboard system. The planner’s concern is with achieving those objectives while balancing reward against risk. Planners iteratively perform scheduling and simulation in a feedback loop to refine their plans. Automated schedulers may themselves utilize simulation artifacts to inform their decisions.

  3. PostgreSQL - Also known as Postgres. A free and open-source relational database management system emphasizing extensibility and SQL compliance.

  4. Profile - The time-dependent behavior of a resource.

R​

  1. Register - A model of a resource which can have its value set and this value remains until it is set with a different value. The term register here is used to clearly indicate the semantics of this resource; the semantics of setting a memory register.

  2. Resource - Expresses the time-dependent evolution of quantities of interest to the mission.

  3. Resource Types - The schema describing the structure of data in a resource.

S​

  1. SPICE - NASA's Navigation and Ancillary Information Facility (NAIF) offers NASA flight projects and NASA funded researchers the “SPICE” observation geometry information system to assist scientists in planning and interpreting scientific observations from space-based instruments aboard robotic planetary spacecraft. In the Merlin context SPICE is most commonly incorporated to a mission model as a Java library. The library is configured with data files called “kernels” and then a mission model will query the library for an assortment of mission specific geometric data.

  2. Scheduling - A scheduling mechanism that automatically creates activity directives in a plan by serially executing scheduling goals given in a priority order.

  3. Scheduling Goal - A rule snippet describing conditions for windows to add an activity directive to the plan along with the desired arguments for the directive.

  4. Scheduling Specification - A set of scheduling goals in priority order input for a scheduling run.

  5. Sequence - A data record in seqJSON schema that contains commands, meta data and other inputs for downstream command simulation tools.

  6. Simulated Activity (Span) - A record for an activity instance created and executed during a simulation run. It lists start time, end time, all arguments that are used during the simulation as well as the values for computed attributes.

  7. Simulation - Simulation is the act of predicting the usage and behavior of mission resources, over time, under the influence of planned activities. Put differently, simulation is an analysis of the effects of activities in a plan upon modeled resources.

  8. Simulation Configuration - A Java class in the mission model that allows planners to tweak parameters for a simulation run and input source files necessary to use during this initialization. While simulation configuration is a highly flexible mechanism the main use cases for it are:

    • Setting initial values for resources
    • Tweaking modeling parameters such as computation fidelity

  9. Simulation Dataset (Results) - A data collection that stores the results of a simulation run including:

    • Start time, end time and arguments of all activities that are simulated. Includes both root activities that correspond to directives and activities that are result of a decomposition.
    • Profiles (values over time) for all modeled resources.

  10. State - The value of a resource at an instant in time (e.g. "The state of the radioMode resource is ON at time T1").

T​

  1. Task - Allows a mission model to describe time-dependent processes that affect mission state.

W​

  1. Window - The output of constraints checking. A boolean-type profile describing at what times a given constraint is violated. True means the state is nominal; false means the state is a violation.

  2. Worker - Aerie provides a multi-tenancy capability so that many users can run simulations concurrently. Simulation multi-tenancy is achieved by configuring Aerie to launch multiple simulation worker containers. Each simulation worker can execute a sand-boxed simulation run.