the deep space network scheduling problem brad clement, mark johnston artificial intelligence group...
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The Deep Space Network Scheduling Problem
The Deep Space Network Scheduling Problem
Brad Clement, Mark Johnston
Artificial Intelligence Group
Jet Propulsion Laboratory
California Institute of Technology{bclement, mdj}@aig.jpl.nasa.gov
http://ai.jpl.nasa.gov/
Brad Clement, Mark Johnston
Artificial Intelligence Group
Jet Propulsion Laboratory
California Institute of Technology{bclement, mdj}@aig.jpl.nasa.gov
http://ai.jpl.nasa.gov/
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Space Networks
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Deep Space Network (DSN)
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Activities, Tracks, & Viewperiods
• A track is an allocation of an antenna to a mission over some time interval
• A viewperiod is the time interval when a spacecraft is visible to an antenna
• An activity is a track wrapped with setup and teardown time
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Deep Space Network Scheduling
• 56 missions
• 12 antennas– different capabilities
– shared equipment
– geometric constraints
– human operator constraints
• some schedule as long as 10 years into future
• ~370 tracks & ~1650 viewperiods per week
• ~2000 tracks & ~80000 viewperiods per year
• some require schedule freeze 6 months out
• complicated requirements originally from agreement with NASA with flexibility in antennas, timing, numbers of tracks, gaps, etc.
• ~30 people employed full time to schedule for multiple missions
• schedule centrally generated, meetings and horse trading to resolve conflicts
• similar to coordination operations across missions
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Other Space Scheduling Problems
• comm. scheduling TDRSS and AFSCN
• Mars relay scheduling
• antenna command generation
• science planning
• measurement scheduling
• command sequence generation (ground and onboard)
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Constraints• No two spacecraft can use
antenna at same time– except MSPA where antenna
points to both (2 at most) and uplinks to at most one
• Spacecraft must be in view of antenna
• At Goldstone, no track/activity can be scheduled where two other tracks/activities start within 15 minutes– except the four Cluster s/c
• At other complexes, no two may start within 5 minutes of each other
U/LD/L
D/L U/L
D/L
MEXMERA
NAV
0
5
2 3 2 232
30
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Requirements
– abstraction of requirements as an AND/OR tree→use HTN planning
– optional and/or multiple resource usage – start time and duration ranges– temporal constraints (STN)– all activity/track start times and
durations must be evenly divisible by 5 minutes (except for Cluster)
– locks on resource and timing→ remove resource choices (OR branches)→add/shrink temporal constraints
to current time allocation→ASPEN has scheduling permissions
– override / blockout
[3hr, 8hr]
0
∞
0
∞
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Requirements (cont’d)
periodic tracks – ranges specifiedfor some of:
• initial start time• overall end of period• number of tracks• total duration of tracks• duration of individual
tracks• time gap/overlap
gap[min,max]
d1 d2
consumptionequal toduration
cons
umab
lere
sour
ce min total duration(added at end)max total
duration must scheduledi to not overfillor exhaust
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Scheduling in ASPEN
Start (if conflicts exist and user time-limit not exceeded)
...Select a conflict
Select a repair method...
move
...
...
Select an activity
Select a start time
Perform theaction, collectthe new conflicts,and repeat
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Scheduling Performance
• Generates schedule of 1861 tracks from ~3 weeks of requests in 39 minutes (resolving 2305 initial view period/antenna conflicts)
• Reschedules to accommodate individual emergency tracks in 0.2 seconds and emergency antenna downtime in 0.2 seconds
• Handles doubling of one mission’s track requests over one week (to 42 total) in 2.7 seconds
• Initial performance acceptable for interactive conflict resolution, possibly for initial schedule generation
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Systematic Search Algorithms• Local search in ASPEN can handle large schedules (for
long-term requirements) but gives no guarantees of optimality or that an existing solution will be found
• Systematic search can give these guarantees for small problems (conflict resolution)– BT1: depth-first backtracking, all times/resources permitted
(provided there are viewperiods available)• most constrained first track selection• smallest from original time/antenna assignment
– BT2: same as BT1 but limited to original antenna– A*: optimal graph search, objective is to minimize changes from
original schedule (in both both antenna and time)– Assumptions made for these algorithms and experiments:
• track durations are fixed in these experiments• tracks that span day boundaries are considered locked in place• tracks without viewperiods are considered locked in place
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M. Johnston
Resolving conflicts forSchedule after Conflict Negotiation Meeting
Finds solution (or proves no solution) to each within a few hundredths of a second
Found optimal solutions to most within a few minutes
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M. Johnston
Finds solution to each within a few hundredths of a second
Found optimal solutions to most within a few minutes
Resolving conflicts Schedule Before Conflict
Negotiation Meeting
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User-Interface Design
• Met repeatedly with users (MDAPT, RAPSO, DSN, and mission operations staff) to understand requirements and obtain feedback on application design.
• Collaboration with NASA Ames’ Human Computer Interaction group (Alonzo Vera, Mike McCurdy & Chris Connors), who (with us and user feedback) have designed user-interfaces.
– designed interface forediting of requirements
– designed interface forrefining requirements withaid of automated scheduler
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Requirements Editor Dialog
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Visualization
• Gantt chart design• Mouse over details in
tabular view• simultaneous schedule +
metric visibility w/user-specifiable gradient
• visualization of differences between two schedule versions
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Applications – DSN Arrays
• NASA may build 3600 10m weather-sensitive antennas
• 1200 at each complex in groups of 100 spread over wide area
• High automation requested—one operator for 100 or 1200 antennas
• Spacecraft may use any number of antennas for varying QoS, and may need link carried across complexes
• Only some subsets of antenna signals can be combined
– depends on design of wiring/switching to combiners
– combiners may be limited
• Local response time should be minimized
DSCC
Array Signal Proc
Other DSN Systems
Array Sites
Sig ProcSig Proc
Sig Proc
Sig Proc
Sig Proc
Sig Proc
Sig Proc
Sig Proc