Space Operations as a Guide for a Real-World Scheduling

Competition

Eduardo Romero (eromero@conae.gov.ar)

Marcelo Oglietti (marcelo.oglietti@conae.gov.ar)

CONAE (Argentine Space Agency)

Scheduling a Scheduling Competition Workshop-ICAPS ´07-

Scheduling Competition

• One of the purposes of the scheduling competition should be bringing theory and applications closer.

• How?– Adding features of real-world problems to the

benchmark problems of the competition.

• What features?– We tackle this issue by describing three real-world

problems of satellite missions with different characteristics not present in classical scheduling problems.

Outline

• Satellite Mission Ground Segment– Ground Station Services– Mission Operation Center Services– User Ground Segment Services

• Characteristics of the problems

• Conclusions

Outline

• Satellite Mission Ground Segment– Ground Station Services– Mission Operation Center Services– User Ground Segment Services

• Characteristics of the problems

• Conclusions

CONAE Satellite Mission Ground Segment

(0) Tele Commands, Housekeeping Telemetry, Instruments Data.(1) Request and delivery of instruments raw data.(2) Tele Commands, Telemetry HK (RT & Stored), Scheduling, RT Monitor(3) Requests of science satellite data acquisitions. (4) Satellite Product Requests & Delivery.

Organization based on functionality and on responsibility scope.

Flight Segments

Ground Station Services(10 Antennas)

User Ground Segment Services

Mission Operation Center Services

Users

(0)

(1)

(2) (3) (4)

Outline

• Satellite Mission Ground Segment– Ground Station Services– Mission Operation Center Services– User Ground Segment Services

• Characteristics of the problems

• Conclusions

Ground Station Services

Antenna *

mass memory tlmy

RT tlmy

commands

Demodulator/

Bitsync *

Satellite

Demodulator/

Bitsync *Satellite M&C

System

Ingestion

System *

TCPN *

Satellite MOC

Ground StationSpace

ftpECLMatrix

RFMatrix

Science Data Download Services

Telemetry Tracking and Command Services (TT&CS)

• GSS receive requests of satellite contacts attendance.

• These are of several types, requiring the use of different sets of hardware and software units, during specific moments.

Antenna * RFMatrix

Demodulator/

Bitsync *Ingestion

System *ECL

Matrix

Satellite

* = multiple instances

Ground Station Services Scheduling Problem

• Given a set of ground services requested allocate the use of the units of the ground station in time lines (threads of execution). – Similar to the project-scheduling but with extra ingredients.

– Many of the units have to be instantiated with a set of parameters.

– Constraints between the use of the units depend on the

parameters.

SERVICES SAC-C X&S-Band

MACRO ID 108

ANTENNAS 7.3Ant & 13Ant.

DEMODULATORS DATRON-7m & ALCATEL-7m

INGESTION SYS. MEOS(Fep2,Ch1) & MEOS(Fep1,Ch1)

An example of a macro configuration (high level). All units have different variables that determine their mode of operation.

Outline

• Satellite Mission Ground Segment– Ground Station Services– Mission Operation Center Services– User Ground Segment Services

• Characteristics of the problems

• Conclusions

Mission Operation Center Services (MOCS)

• Satellites composition.– Subsystems: command and data handling, power,

attitude control, mass memory.– Payloads: radars, cameras, sensors.

• MOC receives requests for the use of the payloads and subsystems.

• Satellites are commanded through sets of basic commands, setting each payload and subsystem.

MOCS Scheduling Problem

MOCS Scheduling

Problem

Uploading Tele-

commands

Downloading Telemetry

Payloads and subsystems

usage

Resources conflicts (Power, Mass Memory,

atittud modes, etc)

Satellite health care

Visibility windows

On-board storage

Bandwidth

It consists in three linked scheduling problems with their associated constraints.

Payloads and Subsystems

The activities needed for the two parts of a camera (MMRS) acquisition (high level).

Outline

• Satellite Mission Ground Segment– Ground Station Services– Mission Operation Center Services– User Ground Segment Services

• Characteristics of the problems

• Conclusions

User Ground Segment Services

• Users request satellite products that have to be processed from raw science data.

• Production systems have multiple installations in several computers.

• Each product needs several production systems in order to be processed.

• Similar to classic job-shop scheduling problems, but priorities of the requests are considered.

Outline

• Satellite Mission Ground Segment– Ground Station Services– Mission Operation Center Services– User Ground Segment Services

• Characteristics of the problems

• Conclusions

Characteristics of the Problems

• Dynamic re-scheduling – When new services are requested.– In case of units failure an alternative schedule

has to be provided.– Has to be done minimizing the changes of

previous schedules (this could be used as a quality measure of the re-scheduling process).

• Distributed scheduling– The three problems and their sub problems are

linked but cannot be centrally solved because of the scope of responsibilities.

• Robust scheduling – Constant refresh with more exact parameters (e.g.,

TLE orbit data) demands robust schedules that tolerates minor changes preserving their consistency.

• Priorities and preferences of the requests arbitrarily imposed

Outline

• Satellite Mission Ground Segment– Ground Station Services– Mission Operation Center Services– User Ground Segment Services

• Characteristics of the problems

• Conclusions

Conclusion

• Add these features to the benchmark problems

• Use these as Benchmark Problems (?)– We propose to build a benchmark problem around these rich real-

life scheduling problems.

– It will cost time and effort, but it will help bring theory and applications closer.

– Data of the problems can be shared.

• We presented in the paper a modeling approach that has allowed us to capture many features of these domains