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s 4.4.6 Mechanisms HMM Assessment Study Report: CDF-20(A) February 2004 page 356 of 422 4.4.6.1 Requirements and design drivers The HMM science requirements do not state any specific requirements applicable to the DM mechanisms. As a result of the DM’s configuration, the following necessary mechanisms and their requirements can be derived: • Vehicle Stage Separation System o Release & Separation of De-orbit Propulsion Module. • Separation System o Heat Shield Jettison System. • Deployable Landing Leg System 4.4.6.2 Assumptions and trade-offs The requirement for a deployable landing leg system is dependent upon the dynamics of the Landing Vehicle. The Footprint dimension is sized to prevent the vehicle from toppling when contact with the ground happens and there is a residual horizontal velocity component acting on the system. Essentially, this can de (simplistically) analysed by looking at the situation when the horizontal and vertical force moment components are in equilibrium i.e. the point of initiating the topple moment when the horizontal moment component is greater than the vertical moment component. Figure 4-98 shows the principle force or moment balance system: Figure 4-98: Momentum balance system Hv = Height at which the engine thrust is cut-off. • Max. Height for ‘Thrust’ cut-off = 2 m max. Vv = The residual Vertical Velocity at the moment of engine thrust cut-off • Final Vertical Velocity= 0→2 m/s, g=3.8 m/s2)
s HMM Assessment Study Report: CDF-20(A) February 2004 page 357 of 422 Hv = The maximum residual horizontal velocity at contact with the surface. • Max. Horizontal Velocity 1 m/s Additional Data: • Lander Mass = 42000 Kg. • Vehicle CoG Height about 6 m. • Mars Gravity constant = 3.8 m/s2. Additional assumptions: • Assume deceleration time the same for both velocity components= 0.5 secs. • A margin or 2.5° added to α. • This approach excludes any Lander attitude errors or surface terrain effects. • Damping in the leg system is not taken in to account other than applying the deceleration time. Stability or no toppling is assumed when α is chosen such that FMV=FMH i.e induced moments are equal. The following remarks can be made regarding this analysis approach: • The problem is handled as a quasi-static problem. • As formulated above, the analysis excludes the changing velocity vector due to the rotation over or about the foot or feet. • Any induced rotation will be experienced as ‘damping’ for the toppling motion due to the Gravity vector- this can be treated as a (small) ‘margin’ The analysis has been performed according to the following steps: 1. Calculate the velocity at surface impact at minimum and maximum residual velocities using v2= u2+ 2.a.s where ‘u’ is the residual velocity, ‘’is the Martian gravitational constant and ‘s’ is the height at which the engine thrust is cut. 2. Calculate the Vertical Force component (Fv) due to the deceleration [mass * (Fv/0.5 secs)]. 3. Calculate the Horizontal Force component (Fh) for 3 horizontal velocities (Hv = 0.5 m/s, 1 m/s & 1.5 m/s) [mass * (Hv/0.5)]. 4. Calculate the angle α where Fmv = Fmh [α = atan(Hv/Fh) + 2.5° margin] for minimum and maximum vertical velocities. 5. Calculate the minimum footprint area required based upon the estimated CoG height. 6. Compare the required minimum footprint dimension against the available envelope dimension. The above model has been reshown in an ‘excel’ spreadsheet. The following graph represents the output from the analysis.
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s HMM Assessment Study Report: CDF-
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s STUDY TEAM HMM Assessment Study R
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s T A B L E O F C O N T E N T S HMM
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s L I S T O F F I G U R E S HMM Ass
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s L I S T O F T A B L E S HMM Asses
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s 1 INTRODUCTION 1.1 Background HMM
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s 2 GENERAL ARCHITECTURE 2.1 Study
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s 2.2.4.2 Accelerations HMM Assessm
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s 2.2.4.4 Temperature and relative
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s Figure 2-10: Trajectory Overview
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s 2.4.3.5 TEI and planetary protect
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s Mars Excursion Vehicle Transfer H
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s 2.7.5.1 Mission elements dry mass
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s 2.7.5.8 MEV release The MEV is re
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s Total mission time (days) 1200 10
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s stack 9 Propellant mass of the ne
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s The core supporting structure has
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s 2.7.7.1.3 Mars excursion module S
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s 2.7.7.1.4 Earth return capsule HM
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s Mission Phase Description Event s
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s Mission Phase Description Event s
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s 2.7.10 Mission performance Table
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s Days on Martian surface 450 400 3
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s Maximum manoeuvre duration 6 mont
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s % of loss from baseline 20 18 16
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s 2.7.15 Sensitivity analysis HMM A
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s 2.7.15.4 Influence of the mass of
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s Parameters used: • No Shuttle
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s 2.8.3.3 Launch 3- Front node Figu
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s 2.10.1.4 Communications HMM Asses
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s 2.10.2.2.2 LEO assembly HMM Asses
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s Basic RF link Four 70-m Ka-band s
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s 3 TRANSFER VEHICLE 3.1 Systems…
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s Operational Requirements It shall
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s Trans Mars Injection Module Mars
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s Figure 3-2: Parallel configuratio
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s Figure 3-6: Global dimensions com
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s Front Node 3.2.3.1.3 EVA systems
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s Trans Mars Injection (three stage
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s Figure 3-16: Recommendations for
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s Factors to be considered Impacts
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s Figure 3-24: Baseline design back
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s Figure 3-26: Baseline design priv
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s Module part 3............= 0 m 3
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s 3.3.2.1 Requirements and design d
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s 3.3.3.1 Requirements and design d
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s flux [W/m2] 250 200 150 100 50 0
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s Figure 3-38: Power required to ma
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s 3.3.4.3 Assumptions and trade-off
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s 3.3.4.3.3 Power conditioning and
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s 3.3.5 AOCS HMM Assessment Study R
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s Configuration Length (m) Total ma
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s 3.3.5.5 ACS for TMI 1 st HMM Asse
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s 3.3.6.2 Baseline design HMM Asses
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s 5 Reduce 2dB pointing precision t
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s 70-m antenna 70-m antenna 3.3.7.5
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s Angular separation SEM > 10º SEM
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s Figure 3-63: Communications MEV/M
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s Element 1: Transfer Habitation Mo
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s Radiation Shielding Shielding Req
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s The propulsion system and its cha
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s Item Nr. Mass [kg] Margin [%] Mas
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s 3.4.4 Mechanisms HMM Assessment S
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s 4 MARS EXCURSION VEHICLE 4.1 Syst
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s Figure 4-2: Option 2: Vertical co
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s 4.3 Surface habitation module Fig
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s Figure 4-11: Section through the
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s 4.3.1.5.3 Top level Figure 4-20:
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s Schedule in hours for the most ac
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s 4.3.3.6 Waste production HMM Asse
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s Figure 4-26: Total pressure vs. O
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s ECLS system mass: Figure 4-27: Ma
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s Figure 4-28: Mars albedo (L), ars
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s sun flux (W/m2) 450 400 350 300 2
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s Insulation structure (external) F
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s cryocooler heat lift [W] cryocool
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s • a duty cycle value (duration
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s Figure 4-48: MAV Power Inputs HMM
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s 4.3.5.4.2 Power storage HMM Asses
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s Figure 6-1: Example of buried rea
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s 7 APPENDIX B - REFERENCES [RD1] C
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s [RD26] IES2, Phase A0: Final Repo
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s [RD85] Mars Transportation Enviro
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s 8 APPENDIX C - ACRONYMS AAA Avion
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s MLI Multi-Layer Insulation MMH Mo
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