AIR FORCE RESEARCH LABORATORY
A Feasible Approach
for
Implementing Greater Levels
of
Satellite Autonomy
March 3, 1998
Paul Zetocha
Air Force Research Laboratory
Space Vehicles Directorate
Outline
•Background
• Impediments to achieving new levels of autonomy
• Requirements that address the impediments to
autonomy
•A feasible approach
•Conclusion
Background
Current Environment
• Very little automation on-board
• Manpower intensive ground operations
- Information overload textual displays
- Very little in the way of automated fault detection, isolation
and resolution
-- Some limit checking
• Commanding is a manual process
- Human command validation and verification
• Majority of satellite tasks are time driven
• Payload data processing is almost entirely done on ground
• Satellite resource scheduling is largely a manual process done on ground
• Attitude control automated on-board
- Reason is largely because it has to be
Background
Future Environment
• More on-board fault detection, isolation, and resolution
- On-board limit checking
- Top level analysis and correction
- Ground involvement for complex or critical problems
• Routine satellite maintenance functionality automated on-board
- i.e., Battery reconditioning, orbital maneuvers (partly), etc
• Increased on-board mission data processing
• Information downlinked to the ground versus data dumps
• Enhanced on-board automated planning and scheduling
Impediments to Enhancing Autonomy
No.
1
2
3
4
5
6
7
8
9
Description
It’s too risky to let an orbiting satellite make its own complex decisions
Operators/engineers fear an inability to control the actions of an autonomous satellite
Autonomous software development seems too costly when compared to ops personnel
Autonomous flight software is difficult to verify and validate
Satellite manufacturers are reluctant to release proprietary info to AI software developers
Ground automation is evaluated by operations personnel who feel their positions will be
rendered obsolete
Ground facility supervisors derive their prestige from the number of people, rather than the
number of computers, in an operations center
A quantitative analysis of the benefits of autonomy has never been performed
Operational satellites will receive minimal benefit from autonomous ground software
Impediments to Enhancing Autonomy
• To risky to let an orbiting satellite make its own complex decisions
- Bad connotation of artificial intelligence
- Problem similar to that which automation faces in many domains but
more severe due to resource cost and criticality
- Many satellite functions which need to be on-board are already
automated (i.e., attitude control)
Autonomous software need not be risky
• Fear an inability to control actions of an autonomous satellite
- Belief that control is implemented in a way such that user oversight
and intervention is not possible
- Autonomy need not be all or nothing
-- Implement piecewise with more and more functionality
automated as comfort level grows
Impediments to Enhancing Autonomy
• Autonomous software development is costly when compared to
the cost of operations personnel
- Up front autonomous software development cost vs. cost of
additional personnel required to operate a satellite
- Development cost need not be as expensive as in the past
-- Availability of Commercial-Off-The-Shelf (COTS) tools will
reduce cost
• Autonomous software is difficult to verify and validate
- Generally true for most complex software development
- Techniques exist to test conventional software. Many of these
techniques are directly applicable
- High fidelity simulators will help
-- Generally expensive and imperfect
Strive for software certification
Impediments to Enhancing Autonomy
• Quantitative analysis of benefits of autonomy needs to be performed
- What are the resulting cost savings from implementing autonomy?
- What functionality should be made autonomous?
- What functionality should be automated on-orbit, automated on the
ground, or remain under operator control?
• Current operational satellites will receive minimal benefit from satellite
autonomy
- Much enhancement to on-board flight software may not be feasible
-- Hardware limitations (i.e., CPU, RAM)
- Cost of Changing existing ground software must be weighed against
against future cost savings
Impediments to Enhancing Autonomy
• Satellite manufacturers are reluctant to release proprietary info
to AI software developers
• Operators may feel that satellite autonomy may mean job losses or
that their job will become less prestigious
• Ground operations supervisors may feel that their job importance is
reduced with less personnel to supervise
The above arguments are largely political and psychological
and can be overcome
4
3
4
3
3
3
3
4
4
3
3
4
4
3
Neural Networks
Agent-Based
4
4
4
4
4
3
4
Case-Based
3
3
4
3
4
4
4
Model-Based
Description
Fully deterministic computing results
Time-driven and event-driven control
Well leant to functional migration
Facilitates long-term trending
Supported by COTS products/vendors
Proven track record for satellite control
Requires minimal software expertise
Finite State-Based
No.
1
2
3
4
5
6
7
Addresses
Impediments
1, 5, 4
1, 2
2, 3, 4, 9
1
2, 3, 4, 9
1, 8
2, 3
Rule-Based
Requirements that Address Impediments
3
3
4
3
Requirements that Address Impediments
• Fully deterministic computing results
- To reduce perceived risk software should not be allowed to learn
and at most be minimally stochastically based
- Strong candidates:
-- Finite state based system:
--- Known states and transitions
--- Upon encountering unknown state hand off to operator
-- Model based reasoning (MBR) system:
--- Given that models are representative of actual satellite similar
inputs will generate the same outputs
--- A comprehensive MBR system is probably not feasible
- Weaker candidates
-- Rule-based expert system
--- Generally deterministic, rule firings can have time component
which will make them nondeterministic
-- Cased based reasoning (CBR)
--- Case retrieval based on feature weighting
Requirements that Address Impediments
• Autonomous software should be capable of both time and event
driven control
- Allows flexibility to carry out operations within operational
constraints
- Time driven: Tasks which have fixed start and stop times and/or
are sequentially based
- Event driven: Tasks that should be handled immediately
(i.e., responding to an anomaly, surveillance action, attitude correction)
- Stronger candidates
-- Finite State space system:
--- Can be either
-- Rule based system:
--- Inherently event-driven but can be given time-driven control
-- Agent based system
--- Implementation dependent but conceptionally event-driven
- Weaker candidates
-- MBR and neural networks have applicability but along a more
narrow scope
Requirements that Address Impediments
• Well meant to functional migration
- Allow for gradual implementation of autonomy
- Most systems that have modular knowledge bases are capable of
satisfying this requirement
- Potential candidates:
-- All
In all cases software must be implemented correctly to have this capability
• Facilitation of long-term trending
- Although not a necessity this is a desirable trait
- Candidates
-- Rule-based expert system
-- State-space system
-- Neural networks
-- Agent based system
Requirements that Address Impediments
• Technology should be supported by COTS products/vendors
- Advantages include:
-- Lower cost
-- Higher degree of up front testing (i.e., validation and verification)
- Strong candidates:
-- Rule-based expert system
-- State-space system
-- CBR system
- Weaker candidates:
-- MBR system
-- Agent-based system
-- Neural networks
Note: Classification boundary between COTS and non-COTS is fuzzy
Requirements that Address Impediments
• Proven track record for satellite control
- In using any technique the bulk of work is spent up front during the
knowledge engineering phase
- Stronger candidates:
-- Rule-based system:
--- Proven on ground though not entirely accepted by all
--- Limited implementation on-board
-- State-space system:
--- The number of ground implementations is increasing
- Weaker candidates:
-- MBR and CBR systems:
--- Limited prototypes have been developed
•Implementation should require minimal software expertise
- Stronger candidates:
-- Rule-based and state space systems:
--- Fairly easy to implement
- Weaker candidates:
-- CBR system: Potentially easy if right tools are used
A Feasible Approach to Implementing Autonomy
• Impediments must be sufficiently addressed
• Autonomy should be implemented incrementally
- Path to autonomy:
-- Autonomy software on ground acting as advisor
-- Automation on ground
-- Autonomy software on-board acting as advisor
-- On-board autonomy
- Ideal framework is one that supports a knowledge base both on-board
and on the ground and which can incrementally be added to
• Flight experiments are needed to get satellite community to buy into
autonomy
- Government test satellites
- End of life experiments with on-orbit satellites
Conclusion
• Current environment dictates a need for increased satellite autonomy
• Most of the technologies needed to implement autonomous satellites
already exist
• Ideal solution is a heterogeneous combination of technologies
• If autonomy is to be successfully implemented must have strong
backing from designers, operators, and management
• Majority of impediments to satellite autonomy have political and
psychological aspects to them
• Flight experiments are needed to demonstrate and validate the
benefits of autonomy