1 Winter Launch Block Modeling and Results MMS Flight Dynamics Team MIWG 8 Feb. 20, 2014

2 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

3 CONSTRAINT RELAXATION

4 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 page ecl Sun

5 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: 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)

6 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 entry 12:25 06:00 00:00 18:00 12:00 Spring-like launch Launch 03:20 Phase 1 start 20:00 10-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

7 Constraint Relaxation Constraint (in order of most often changed) Current Requirement RelaxationImplication Phase 1a GSE Start Time 17:00 – 19:001.15:00 – 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 costs 2.Very, very slight reliability concern on paper? Early eclipse durationNo eclipses > 2 hours in first week ramping linearly up to 3 hours during second week (turned off afterward) 1.Turn off 2.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 hours1.Increase durationSystems has approved an increase to 4.5 hours Fuel usageAngle between spin-axis and orbit-normal at the mid-point of the apogee raising campaign <= 20 degrees 1.Increase allowed angle deg requires an increase in kg (some seasonal dependence) 2.Jeopardizes extended mission Phase 1a GSE latitude |  | <= 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

8 OPEN QUESTIONS

9 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

10 Details on Launch Opportunity Types, 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

11 Details on Launch Opportunity Types, Late Winter (Mar. 15) Spring-like Fall-like B

12 PERIGEE ALTITUDE

13 Fall-Like A Launch Opportunity and Nominal Mission Min Perigees

14 Spring-Like Launch Opportunity and Nominal Mission Min Perigees

15 Fall-Like A Launch Opportunity and Extended Mission Min Perigees

16 Spring-Like Launch Opportunity and Extended Mission Min Perigees

17 CENTAUR LIFETIME

18 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)

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

20 Spring-Like Launch Opportunity and Centaur 5-Year Minimum Perigee

21 EXTENDED MISSION - ECLIPSE DURATIONS

22 Early Winter Launch Opportunities and Extended Mission Eclipses

23 Late Winter Launch Opportunities and Extended Mission Eclipses

24 PUTTING ALL THE CONSTRAINTS AND CRITERIA TOGETHER

25 Factors in Selection of Target for Fall-Like A Launch Opportunity Phase 2b eclipse margin Long extended mission eclipses GSE start time margin Neutral sheet dwell time margin Better perigee evolution

26 Factors in Selection of Target for Spring-Like Launch Opportunity Phase 2b eclipse margin Much better perigee evolution

27 FEEDBACK ON OPEN QUESTIONS

28 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.