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s Parameter Value Initial Mach number 2 Initial altitude 10 km Final velocity 100 m/s Final altitude (above surface) 2 km HMM Assessment Study Report: CDF-20(A) February 2004 page 360 of 422 Table 4-45: Descent Requirements The size (area) of each parachute is limited by the restrictions of manufacturing, packing and deployment. Using present technology, a parachute area of around 1000 m 2 (diameter of about 36 m) is considered to be a reasonable upper limit. 4.4.7.2 Assumptions and trade-offs For this application disk-gap-band type parachutes are used. Of the options available, they provide the best area to mass ratio and have a sufficiently high Mach number application. Also, this type of parachute was used for the Mars Viking Lander so the Mars landing application has been successfully demonstrated (although not at the scale required here). Initially it was intended to have a drogue chute in addition to the main parachute(s). However, it was found that with the relatively small deceleration achieved with the drogue chute, the vehicle would continue to descend at a rate that would put it at too low an altitude for main parachute deployment. Therefore, the use of a drogue was rejected. It is assumed the MEV heat shield is jettisoned before the initiation of the parachute descent phase. 4.4.7.3 Baseline design Given the initial and final altitude and velocity constraints and the properties of the disk-gapband parachute, sizes and masses for the parachute system can be obtained. The total nominal parachute area required to obtain the necessary deceleration is 4384 m 2 . This is divided among four parachutes to be closer to the maximum area per parachute constraint. The total design therefore consists of 4 main parachutes, each with a nominal area of 1096 m 2 and a nominal diameter of 37.4 m. An additional, backup parachute of the same design as the main parachutes is also included in the design. This parachute will be deployed in the event that one of the main parachutes fails. The descent of the vehicle from parachute opening to rocket firing is reshown in the following figures that show the altitude and velocity versus time. The terminal velocity of 100 m/s is not quite reached at the altitude of 2 km, but it is sufficiently close to be acceptable for the rocket system.
s velocity (m/sec) altitude (km) 500 400 300 200 100 PCHUT5: Descent Body Velocity & Position Vs Time (ODE23 l i ) 0 0 5 10 15 20 25 30 35 40 45 50 10 8 6 4 2 0 0 5 10 15 20 25 time (sec) 30 35 40 45 50 Figure 4-100: Velocity and altitude of MEV from parachute opening to landing rocket firing 4.4.7.4 Budgets HMM Assessment Study Report: CDF-20(A) February 2004 page 361 of 422 The mass of each parachute can be estimated taking into account the canopy, lines, deployment equipment, swivel, bridle, and pilot chute. The masses are based on previous built parachutes and components for applications that differ significantly from the present one, so there is a great deal of uncertainty in the mass estimate. The mass for each parachute is estimated to be about 103 kg, giving a total system mass of 515 kg. The maximum system mass margin of 20% is used to account for uncertainties. 4.4.7.5 Options Within the framework of the current design, one option is to have fewer, larger parachutes. This would be preferable from the point of view of reducing the complexity and number of potential failure points in the system. However, further work would be required to determine if larger parachutes are feasible. To reduce (or possibly even eliminate) the deceleration requirements for the parachutes, the heat shield of the MEV could also be used for braking from 10 km to 2 km, rather than jettisoning it as is presently done. However, having both options available as now is beneficial from the point of view of redundancy.
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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 4-52: Regenerative Fuel Ce
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s Figure 4-54: Solar irradiance on
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Page 373 and 374: s Inclination (deg) 47.5 47 46.5 46
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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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