Heyd, Tiffany L.

Tracewell, David A.

NASA Technical Reports Server

Mission Operations Working Group
June 2 – 4, 2015
1
International Earth Science Constellation 
Mission Operations Working Group
June 2-4, 2015
Terra Future Maneuver Plans
Tiffany L. Heyd & David A. Tracewell
EOS FDS, esmo-eos-fds@lists.nasa.gov, +1.301.416.5050
https://ntrs.nasa.gov/search.jsp?R=20150011481 2019-08-31T07:27:22+00:00Z
Mission Operations Working Group
June 2 – 4, 2015
• Fuel Usage Based on Multiple Estimation Strategies
• Terra Requirements Overview
• 19 km vs. 4 km
• Analysis Assumptions
• Maneuver Plans Through 2017
• Maneuver Plans Beyond 2017
– Option A 
– Option B
Agenda
2
Mission Operations Working Group
June 2 – 4, 2015
Fuel Usage Based on Multiple
Estimation Strategies 
3
10-15 kg span
using varying 
estimation 
types
**All analyses 
based on 
“worst case” 
fuel levels**
Mission Operations Working Group
June 2 – 4, 2015
• Mean Local Time at the Descending Node
– 10:15 to 10:45 AM
• Mean Semi-Major Axis Height
– 705 km
• Altitude Range
– 694 to 711 km
• Repeat Ground Track
– 16 day cycle
Note: Verification of requirements in progress, slide still in work
Terra Requirements Overview 
Level 1 Mission Requirements
4
Mission Operations Working Group
June 2 – 4, 2015
• Based on the 2010 definition from the Afternoon Constellation 
Operations Coordination Plan:
– “The apogee of a spacecraft that has exited the constellation 
must be at least 2 kilometers below the minimum perigee of all 
current constellation members.”
– To effectively exit the Constellation, exited spacecraft’s maximum 
apogee must be lowered below 692 km, which is 19 km below 
constellation members’ maximum apogee
• Based on the 2014 Constellation Coordination Plan just signed 
by all member missions:
– Safe constellation exit is defined by being completely outside the 
constellation “envelope”
– To effectively exit the Constellation, exited spacecraft’s maximum 
apogee will be at least 4 km below constellation members’ 
maximum apogee
19 km vs. 4 km Origin
5
Mission Operations Working Group
June 2 – 4, 2015
• Terra will perform 320-second retrograde constellation exit 
maneuvers centered at apogee or perigee
– The maneuver burn durations are restricted to 320 seconds due to 
attitude disturbances on burn durations longer than 320 seconds
• Maneuvers will be executed in pairs (1 apogee, 1 perigee)
– ~300 minute settling time in between burns
– Maneuver pairs on Tuesdays & Thursdays
• 5 kg of propellant is assumed unusable in the analysis
– Spacecraft manufacturer estimates 1.5 kg - 3.9 kg of fuel will remain in 
propulsion lines
– The remaining 1.1 - 3.5 kg will be conserved for possible RMMs prior to 
passivation
• One RMM is ~0.1kg of fuel, leaving roughly 11-35 RMMs in reserve
• Only 8 RMMs performed on Terra since launch (15+ years)
– All plans use the most conservative estimate for the initial fuel level and the 
most conservative prediction method for future maneuvers
Analysis Assumptions
6
Mission Operations Working Group
June 2 – 4, 2015
• The table below summarizes the results of the Terra lifetime 
maneuver simulation:
•
Maneuver Plans Through 2017
7
Mission Operations Working Group
June 2 – 4, 2015
• Option A
– Formerly “Baseline Plan”
– Lowers Terra at least 19 km below the constellation
• Option B
– Formerly “Proposed Plan”
– Lowers Terra at least 4 km below constellation
Maneuver Plans Beyond 2017
8
Mission Operations Working Group
June 2 – 4, 2015
10:15
10:29
10:45
10:31
Final IAM
October 2020
Mission Requirement
Operational Range
MLT < 10:29
December 2020
MLT < 10:15
& Constellation Exit
August 2022***
*After Jan 2020 Option A partially level 1 compliant
**After Mar 2022 Option A not Level 1 compliant
Final IAM
Oct 2017
Constellation Exit
January 2020*
MLT < 10:15
March 2022**
MLT < 10:29
March 2018
Option A
Option B
9
Maneuver Plans Beyond 2017
Mean Local Time
***After Aug 2022 Option B not Level 1 compliant
RMM fuel available after 
exit in both options
Mission Operations Working Group
June 2 – 4, 2015
• The table below summarizes the results of the Terra lifetime 
maneuver simulation:
• ~45 kg of fuel are needed for constellation exit
– Includes the 5 kg of unusable fuel
– 10 maneuvers to exit constellation
• Note:  This is only a representative maneuver scenario given the current 
mission requirements and solar flux predictions.
Maneuver Plans Beyond 2017
Option A
10
Mission Year
(--)
Inclination Maneuvers 
(--)
Delta Inclination
(Deg)
DMU Maneuvers
(--)
Fuel Used
(kg)
Fuel Remaining
(kg)
2014 2 Spring, 1 Fall 0.011495 8 12.983 81.852
2015 2 Spring, 1 Fall 0.033871 4 12.140 69.712
2016 1 Spring, 2 Fall 0.033114 2 11.304 58.408
2017 2 Spring, 1.75 Fall 0.040625 1 13.616 44.792
2018 0 Spring, 0 Fall 0 2 0.214 44.578
2019 0 Spring, 0 Fall 0 2 0.160 44.418
Mission Year
(--)
Inclination Maneuvers 
(--)
Delta Inclination
(Deg)
DMU Maneuvers
(--)
Fuel Used
(kg)
Fuel Remaining
(kg)
2014 2 Spring, 1 Fall 0.011495 8 12.983 81.852
2015 2 Spring, 1 Fall 0.033871 4 12.140 69.712
2016 1 Spri g, 2 Fall 0.033114 2 11.304 58.408
2017 2 Spring, 1.75 Fall 0.040625 1 13.616 44.792
8 0 0 0 2 0.214 44 578
9 0 0 0 2 0.160 44 4 8
Mission Operations Working Group
June 2 – 4, 2015
Maneuver Plans Beyond 2017 - Option A
Apogee and Perigee Height - 2020
Apogee
Perigee
Partial Orbit 
lowering Burn
692 km Constellation Exit Altitude
Constellation 
Exit Burns
Constellation Orbit
11
Mission Operations Working Group
June 2 – 4, 2015
Maneuver Plans Beyond 2017 - Option A
Lifetime Fuel Estimates
Definitive
PredictiveFuel to Exit Constellation
“Unusable” Fuel
Constellation 
Exit
End of IAMs
12
Mission Operations Working Group
June 2 – 4, 2015
• The table below summarizes the results of the Terra lifetime 
maneuver simulation:
• ~12 kg of fuel are needed for constellation exit
– Includes the 5 kg of unusable fuel
– 2 maneuvers to exit constellation
• Note:  This is only a representative maneuver scenario given the current 
mission requirements and solar flux predictions.
Maneuver Plans Beyond 2017
Option B
13
Mission Operations Working Group
June 2 – 4, 2015
Maneuver Plans Beyond 2017 - Option B
Apogee and Perigee Height - 2022
Apogee
Perigee
Constellation 
Exit Burns
Lowering orbit by ~5 km (~1km more than the min Envelope requirement)
14
Mission Operations Working Group
June 2 – 4, 2015
Constellation 
Exit
End of IAMs
Definitive
Predictive
Fuel to Exit Constellation
“Unusable” Fuel
Maneuver Plans Beyond 2017 - Option B
Lifetime Fuel Estimates
15
Mission Operations Working Group
June 2 – 4, 2015
Maneuver Plans Beyond 2017 - Option B
Long Term Terra Orbit After Constellation Exit
676
678
680
682
684
686
688
690
692
694
696
698
700
702
704
706
708
710
712
714
0 45 90 135 180 225 270 315 360
A
ve
ra
ge
 H
e
ig
h
t 
(k
m
)
Argument of Latitude (deg)
• Over eight years the orbit eccentricity remains fairly consistent, 
which can be seen on the plot due to the apogee and perigee 
remaining at similar argument of latitude locations
Constellation 
Orbit
Terra orbit after 
constellation exit
• Monthly 
snapshots 
2022-2030 
(one orbit per 
month)
• Colors become 
lighter as time 
progresses
16
Mission Operations Working Group
June 2 – 4, 2015
Plan Name Analysis Year Last IAM 
Date
Date Crossing
10:29AM 
MLTDN
Constellation 
Exit Date
Date Crossing 
10:15AM 
MLTDN
Option A Fall 2014 Oct 2017 Mar 2018 Jan 2020 Mar 2022
Spring 2015 Mon 20YY Mon 20YY Mon 20YY Mon 20YY
Option B Fall 2014 Oct 2020 Dec 2020 August 2022 August 2022
Spring 2015 Mon 20YY Mon 20YY Mon 20YY Mon 20YY
Date of Interest Summary
17
Note: Items in red still to be updated
Mission Operations Working Group
June 2 – 4, 2015
QUESTIONS?
18
For any questions or comments in the future please contact:
ESMO-EOS-FDS@lists.nasa.gov
Mission Operations Working Group
June 2 – 4, 2015
Back-Up Slides
• Constellation Exit Equation
• Drag Models
19
Mission Operations Working Group
June 2 – 4, 2015
Maneuver Plans Beyond 2017 - Option B
Definition
• Based on being the constellation “envelope” and is 
represented by completely outside the following equation:
> Margin + Frozen Orbit Tolerance
Where:
- smaR = Mean semi-major axis
of the 705km
Reference Orbit
- eR = Mean eccentricity of the
705km Reference Orbit
- Margin value = 2.5 km
- Frozen Orbit Tolerance based
on a maximum eccentricity
deviation of 0.0002 (~1.5km)
- B subscript references the
satellite in question (e.g. Terra)
BMaxBRRBR esmaesmasmasma ** 
20
Mission Operations Working Group
June 2 – 4, 2015
2010 Constellation Exit Definition – Option A
Exited Spacecraft and the Constellations
Source: Jonathan Brown March 2013 MOWG
0 50 100 150 200 250 300 350
630
640
650
660
670
680
690
700
710
720
Argument of Latitude (deg)
H
e
ig
h
t 
(k
m
)
19 km at all latitudes
Constellation Orbit
Many Exited 
Spacecraft with 
varying 
eccentricities
(weekly snapshots)
21
Mission Operations Working Group
June 2 – 4, 2015
686
688
690
692
694
696
698
700
702
704
706
708
710
712
0 45 90 135 180 225 270 315 360
A
ve
ra
ge
 H
e
ig
h
t 
(k
m
)
Argument of Latitude (deg)
2014 Constellation Exit Definition – Option B
Any Exited Spacecraft and the Constellations
Constellation Orbit
Many Exited 
Spacecraft 
with varying 
eccentricities
(Weekly 
snapshots)
22
Mission Operations Working Group
June 2 – 4, 2015
Analysis
Year
Last IAM 
Date
Date Crossing
10:29AM 
MLTDN
Date Crossing 
10:15AM 
MLTDN
Constellation 
Exit Date
Date Crossing 
10:15AM 
MLTDN
Fall 2014 Oct 2017 Mar 2018 Jan 2020 Jan 2020 Mar 2022
Spring 
2015
Mon 20YY Mon 20YY Mon 20YY Mon 20YY Mon 20YY
Maneuver Plans Beyond 2017 - Option A
Comparison to Fall 2014 MOWG Plans
• Fall 2014 and Spring 2015 IAM performance
– Predicted delta-i: 0.035580 deg
– Achieved delta-i: 0.036490 deg
• Other contributing factors
– TBD, needs more updates from post-IAM analysis
23
Mission Operations Working Group
June 2 – 4, 2015
Analysis
Year
Last IAM 
Date
Date Crossing
10:29AM MLTDN
Date Crossing 
10:15AM MLTDN
Constellation Exit 
Date
Fall 2014 Oct 2020 Dec 2020 Aug 2022 Aug 2022
Spring 2015 Mon YYYY Mon YYYY Mon YYYY Mon YYYY
Maneuver Plans Beyond 2017 - Option B
Comparison to Fall 2014 MOWG Plans
• Fall 2014 and Spring 2015 IAM performance
– Predicted delta-i: 0.035580 deg
– Achieved delta-i: 0.036490 deg
• Other contributing factors
– TBD, needs more updates from post-IAM analysis
24


Terra Future Maneuver Plans

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