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Winter Launch Block Modeling and Results

MMS Flight Dynamics Team MIWG 8

Feb. 20, 2014

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Outline of Slides• Goal: obtain launch opportunities for all dates in the Winter Block (defined

as Dec. 29, 2014-Apr. 14, 2015, inclusive)

• Method: Determine what requirements (scientific and engineering) must be relaxed in order to launch on this range of dates?

• Open Questions: There is still ambiguity in determining the LV Targets• In the case of launch dates for which more than one type of launch

opportunity exists, which type should be selected?• Once a launch opportunity has been selected, how is a specific launch

target within this lozenge to be selected?

• Flight Dynamics has picked a set of criteria to determine answers to the open questions but wants feedback on the process before publishing a new update to the LV Target Spec

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CONSTRAINT RELAXATION

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Reminder of the GSE Frame

• GSE +X-axis is defined as the vector from the center of the Earth to the sun, GSE +Z-axis is defined as the ecliptic normal vector, and GSE +Y-axis completes the right hand coordinate system.

06:00

00:00

18:00

12:00

GSE Frame

z out of pageecl

Sun

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Types of Launch Opportunities(nominal mission in yellow)

120-day commissioning

17:00

~02:00

06:00

00:00

18:00

12:00

Fall-like launch (red)

~00:00

15:00

120-day commissioning

17:00

~02:00

06:00

00:00

18:00

12:00

Spring-like launch (green)

~05:00

21:00

For comparison: Nov 26, 2014 LRD

For comparison: May 11, 2015 (Spring launch block)

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Changing GSE Start Time

• All cases assume 120-day commissioning

• Green & blue cases (spring-like) add padding between the end of commissioning and resize campaign so that 160-km scale starts as in the nominal mission

06:00

00:00

18:00

12:00

Fall-like launch

Launch 22:20

Phase 1 start 15:00

10-km scale entry12:25

06:00

00:00

18:00

12:00

Spring-like launch Launch

03:20

Phase 1 start

20:0010-scale

entry 15:25

06:00

00:00

18:00

12:00

Spring-like launch

Launch 07:20

Phase 1 start

24:00

10-scale entry 15:25

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Constraint Relaxation

Constraint (in order of most often

changed)

Current Requirement

Relaxation Implication

Phase 1a GSE Start Time

17:00 – 19:00 1. 15:00 – 16:00 (Fall-like)

2. 18:00 – 24:00 (Spring-like)

1. Jeopardizes resize campaign timing?2. Increases mission length

1. Modest increase in ops costs2. Very, very slight reliability

concern on paper?

Early eclipse duration No eclipses > 2 hours in first week ramping linearly up to 3 hours during second week (turned off afterward)

1. Turn off2. Change 2 hours -> 2.5

or 3 hours

Systems has approved the change from 2.5 to 3 hours

Phase 2b max eclipse duration

No eclipse > 3.85 hours 1. Increase duration Systems has approved an increase to 4.5 hours

Fuel usage Angle between spin-axis and orbit-normal at the mid-point of the apogee raising campaign <= 20 degrees

1. Increase allowed angle

1. 25-27 deg requires an increase in 5-15 kg (some seasonal dependence)

2. Jeopardizes extended mission

Phase 1a GSE latitude |f| <= 20 degrees Just live with what results – sometimes as high as 30 degrees

Science to supply

One size does not fit all: mixing-and matching of constraint relaxation is the only way to open the entire Winter block up

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OPEN QUESTIONS

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Additional Criteria

• Since there is ambiguity in the Winter Block (more detail to follow), Flight Dynamics has chosen the following criteria to aid in selecting LV targets

– Perigee altitude behavior of the MMS spacecraft over the life of the mission• Determines fuel usage – perigee maintenance maneuvers relatively expensive• A by-product of this analysis is that Flight Dynamics also can estimate the Centaur

lifetime across each daily window (i.e. as a function of RAAN & AOP for each day)

– Duration of eclipses in the Phase 2b orbit (period of approximately 2.85 days)• Currently working with a relaxation of 4.5 hours of eclipse but due to power and

thermal concerns there is a direction from the project to avoid going over 4 hours where possible

– Possibility of an extended mission• Generally there is enough fuel (ignoring the perigee maintenance question for

now) to fly in formation for about one more year• Extended mission can’t be used if the shadow durations are so long that they ‘kill’

the spacecraft

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Details on Launch OpportunityTypes, Early Winter (Jan. 15)

Fall-like A

Fall-like B

Spring-like

• Jan. 15 case presents 3 possible set of launch opportunities (called a lozenge)

• Perigee altitude & shadow durations for each lozenge differ substantially

• For example Fall-like A has better perigee altitude behavior than Spring-like

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Details on Launch OpportunityTypes, Late Winter (Mar. 15)

Spring-like

Fall-like B

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PERIGEE ALTITUDE

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Fall-Like A Launch Opportunityand Nominal Mission Min Perigees

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Spring-Like Launch Opportunityand Nominal Mission Min Perigees

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Fall-Like A Launch Opportunityand Extended Mission Min Perigees

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Spring-Like Launch Opportunityand Extended Mission Min Perigees

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CENTAUR LIFETIME

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Centaur Lifetime

• The target perigee altitude at separation is still an open question– 510 km assumed for Fall launch block– 460 km assumed for Spring launch block– Winter block is a hybrid between the two – what to choose?

• To answer this question, Flight Dynamics supplied LSP with 107 different RAAN and AOP pairs for a survey of Centaur lifetimes as a function of perigee altitude

• Flight Dynamics is going to tweak the RAAN and AOP pairs based on discussions at the MIWG but the conclusions LSP reached should still be valid– Most tweaks are on the order of a few degrees in RAAN and AOP– Largest tweak was a change of 8 degrees in RAAN to open a daily window– Centaur behavior varies slightly across the width of a lozenge (see next two

slides)

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Fall-Like A Launch Opportunity and Centaur 5-Year Minimum Perigee

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Spring-Like Launch Opportunity andCentaur 5-Year Minimum Perigee

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EXTENDED MISSION - ECLIPSE DURATIONS

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Early Winter Launch Opportunitiesand Extended Mission Eclipses

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Late Winter Launch Opportunitiesand Extended Mission Eclipses

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PUTTING ALL THE CONSTRAINTS AND CRITERIA TOGETHER

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Factors in Selection of Target forFall-Like A Launch Opportunity

Phase 2b eclipse margin

Long extended mission eclipses

GSE start time margin

Neutral sheet dwell time margin

Better perigee evolution

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Factors in Selection of Target forSpring-Like Launch Opportunity

Phase 2b eclipse margin

Much better perigee evolution

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FEEDBACK ON OPEN QUESTIONS

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Flight Dynamics Request Feedback

• Flight Dynamics needs/wants feedback on– The process by which the lozenges and targets within are chosen– The estimates on Centaur lifetime– The rules for when RAAN-steering will be employed

• The amount and type of feedback, especially on RAAN-steering, will determine when work for the next version of the LV Target Spec will be complete.