Final Proposal:
Lunar Exploration Transportation System
(LETS)
Spring 2008 Integrated Product Team (IPT)
Submitted By:
April 28, 2008
Submitted To:
Dr. Robert A. Frederick, Jr.
Associate Professor
Technology Hall N231
Department of Mechanical and Aerospace Engineering
University of Alabama in Huntsville
Huntsville, AL35899
Contributors
Executive Summary
English
The desire to establish a long-term base on the moon has led NASA to search for a rover that can examine the Shackleton Crater on the South Pole of the Moon. International Space Works’ (ISW) Byrd Explorer is capable of performing this mission. The Byrd Explorer is a semi-autonomous rover capable of sampling the Shackleton Crater for extractable water-ice. The rover uses a rocker-bogie drive system powered by a radioisotope thermoelectric generator (RTG), which allows the rover to explore the crater for extended periods of time. The simplistic design of the rover keeps the safety of the rover extremely high while also allows for easy integration into NASA’s mission plan. ISW believes in using nothing but the best components, allowing its products to be lightweight, accurate, and dependable.
French
DaedalusCompliance Matrix
Specification / CDD Location / Proposal LocationAtlas V-401 EPF shroud configuration with a total landed mass of 997.4 kg / 2.1 / 1.3.1
64.6 kg of the total landed mass is devoted to the propulsion system dry mass / 2.1.1
Propellant shall be housed in two spherical propellant tanks, each 0.55 m in diameter / 2.1.2
Helium shall be housed in 2 spherical tanks, each 0.4 m in diameter / 2.1.2
Two (2) MR-80B monopropellant liquid rocket engines / 2.1.3
Twelve (12) MR-106 monopropellant thrusters / 2.1.4
First mission to be at a polar location / 2.2
Capability to land at other lunar locations / 2.3
Launch to the moon NLT September 30, 2012 / 2.5
Capability to move on the surface / 2.6
Survive for one year on the surface of the moon / 2.7
Meet both the Science Mission Directorate (SMD) and the Exploration Systems Mission Directorate (ESMD) objectives / 2.9
Landing at a slope of 12 degrees (slope between highest elevated leg of landing gear and lowest elevated leg) / 2.11
G-loads during lunar landing not to exceed the worst case design loads for any other phase of the mission (launch to terminal descent) / 2.12
Table of Contents
List of Figures
List of Tables
Common Terms and Acronyms
IPT 2: Final Report Feasibility of Lunar Exploration Transportation System
2.01.0 Final Report: Lander on Wheels Concept
1.1 Overview
1.2 The Need
1.3 The Requirements
1.4 The Solution
1.4.1 Concept Overview
1.4.2 Dimensional Properties
1.4.3 Operations Scenario
1.5 The Performance
1.5.1 LETS Figures of Merit
1.5.2 LOW FOM
1.5.3 LOW Attributes
1.6 The Implementation
1.6.1 Design and Research Phase
1.6.2 Testing Phase
1.6.3 Implementation
3.02.0 Technical Description of Methods Used
2.1 Overview
2.2 Project Office
2.3 Systems Engineering
2.4 Power
2.5 Guidance, Navigation, and Control
2.5.1: System Overview
2.5.2: Terminal Descent Phase
2.5.3: Excursion Phase
2.6 Thermal
Figure 5: Effect of Temperature on Emissivity
2.7 Structures
2.8 Payload
2.9 Communication
2.10 Concept of Operations
2.11 Systems Interactions
3.0 Implementation Issues
3.1 Schedule
3.2 Hardware Development
4.0 Team Capabilities
4.1 Team Overview
4.2 Personnel Description
5.0 Summary and Conclusions
6.0 Recommendations
Appendices
Appendix A - Concept Description Document
Appendix B - Project Office
Appendix C - Systems Engineering
Appendix D – Power
Appendix E - Guidance, Navigation, and Control
Appendix F - Thermal
Appendix G - Structure
Appendix H - Payload
Appendix I - Communication
Appendix J - Concept of Operations
Appendix K -Level II Requirements
List of Figures
List of Tables
Common Terms and Acronyms
Word or symbol / CommentsIPT Spring 2008 Report: Feasibility of Daedalus
1.0 Final Report: Daedalus
1.1 Overview
1.2 The Need
The new national Vision for Space Exploration calls for a permanent human presence on the Moon. The Shackleton Crater Rover is one of several missions designed to help sustain a permanent lunar base.The presence of water-ice is of particular interest and will be a key factor in establishing a permanent lunar base because, if found in extractable quantities, water-ice provides potable water, breathable oxygen, fuel cell reactants, and rocket propellants. Water is also an excellent working fluid and stores easily at room temperature. Hence, the availability of water is critical to sustaining a human presence on the Moon.
Besides water-ice, the rover will also directly measure the type, form, and distribution of subsurface volatiles. The Shackleton Crater being investigated is 80% in shadow, an important factor because the Sun could not have evaporated volatiles close to the lunar surface. Other volatiles might have uses in establishing other parts of the atmosphere the astronauts would breathe the availability of fuel, oxygen, or water on the lunar surface will allow for fewer supply missions to the Moon and greatly reduce the amount of fuel required on spacecraft headed to the Moon that will make a return trip. Other volatiles could yield reactants for propellants or fuel cells. The determination of volatiles available on the lunar surface is critical to establishing a permanent lunar base on the Moon.
1.3 The Requirements
1.3.1Customer Requirements. The following requirements were given by the customer as Level 1 Requirements.
1.3.1.1The LETS shall have a landed mass of 1450 kg ± 100 kg
1.3.1.2The LETS shall be design for its first mission to be at a polar location
1.3.1.3The LETS shall be designed with the capability to land at other lunar locations
1.3.1.4The LETS shall minimize cost across the design
1.3.1.5The LETS shall launch to the moon no later than September 30, 2012
1.3.1.6The LETS shall have the capability to move on the surface
1.3.1.7The LETS shall be designed to survive for one year on the surface of the moon
1.3.1.8The LETS shall survive the proposed concept of operations
1.3.1.9The LETS shall be capable of meeting both the Science Mission Directorate (SMD) and the Exploration Systems Mission Directorate (ESMD) objectives
1.3.1.10The LETS shall land to a precision of ± 100m 3 sigma of the predicted location
1.3.1.11The LETS shall be capable of landing at a slope of 12 degrees (slope between highest elevated leg of landing gear and lowest elevated leg)
1.3.1.12The LETS shall be designed for g-loads during lunar landing not to exceed the worst case design loads for any other phase of the mission (launch to terminal descent)
1.3.2Concept Design Constraints. The following constraints are placed on the LETS design
1.3.2.1The LETS shall be designed to interface with the Atlas V-431 Launch Vehicle per the Atlas Launch System Mission Planner's Guide, Rev 10a, January 2007, CLSB-0409-1109. The shroud configuration for the LETS shall be determined by each individual team
1.3.2.2The LETS shall be designed to survive the lunar cruise environment for up to 28 days per XXX
1.3.2.3The LETS shall be designed to survive the lunar surface environment at both the polar and equatorial regions
1.3.2.4The LETS shall maximize the use of off-the-shelf technology. Off-the-shelf technology shall have a technology readiness level of 9
1.3.2.5The LETS shall be designed to operate for one year
1.3.2.6The LETS shall be designed to accomplish the maximum surface objectives outlined below
1.3.3Figures of Merit. The following Figures of Merit (FOM) will be used to evaluate the LETS design concepts
1.3.3.1Number of surface objectives accomplished (as outlined below)
1.3.3.2Percentage of mass allocated to payload
1.3.3.3Ratio of objectives (SMD to ESMD) validation
1.3.3.4Efficiency of getting data in stakeholders hands vs. capability of mission
1.3.3.5Percentage of mass allocated to power system
1.3.3.6Ratio of off-the-shelf to new Development
1.3.4Surface Objectives. The following surface objectives were provided by the customer
1.3.4.1Single Site Goals – Geologic Context
1.3.4.1.1Determine lighting conditions every 2 hours over the course of one year
1.3.4.1.2Determine micrometeorite flux
1.3.4.1.3Assess electrostatic dust levitation and its correlation with lighting conditions
1.3.4.2Mobility Goals
1.3.4.2.1Independent measurement of 15 samples in permanent dark and 5 samples in lighted terrain
1.3.4.2.2Each sampling site must be separated by at least 500 m from every other site
1.3.4.2.3Minimum: determine the composition, geotechnical properties and volatile content of the regolith
1.3.4.2.4Value added: collect geologic context information for all or selected site
1.3.4.2.5Value added: determine the vertical variation in volatile content at one or more sites
1.3.4.2.6Assume each sample site takes 1 earth day to acquire minimal data and generates 300 MB of data
1.3.4.3Instrument package baselines
1.3.4.3.1Minimal volatile composition and geotechnical properties package, suitable for a penetrometer, surface-only, or down-bore package: 3 kg
1.3.4.3.2Enhanced volatile species and elemental composition (e.g. GC-MS): add 5 kg
1.3.4.3.3Enhanced geologic characterization (multispectral imager + remote sensing instrument such as Mini-TES or Raman): add 5 kg
1.4 The Solution
1.4.1 Concept Overview
1.4.2 Dimensional Properties
1.4.3 Operations Scenario
1.5 The Performance
1.6 The Implementation
1.6.1 Design and Research Phase
1.6.2 Testing Phase
1.6.3 Implementation
2.0 Technical Description of Methods Used
2.1 Overview
2.2 Project Office
The project office creates a plan for how each phase will be approached. These plans include setting deadlines and specifying what is expected from the subsystem engineers. The project office is also the liaison between LunaTech and the customer. Furthermore, the project office runs the design team meetings and ensures work is progressing and the various subsystems are working as specified per the systems engineer.
Deadlines are set to allow a margin ofat least two days before something must be presented to the customer and the review panelin order to have all of the editing finished. Generally, there are several deadlines set to ensure there is more than two days in order to submit the best possible finished product. The deadlines are also set to allow editing time before drafts are submitted for review to make sure that steady progress is made throughout the planned period and the project office can take a more hands off role and reduce the amount of micro-managing taking place.
The expectations for each subsystem dictated by the project office are set extremely high, almost to the point where some goals are unobtainable. This is done to ensure each engineer puts in the best effort possible so the team as a whole will submit the best possible product to meet the customer’s need. The project office also works closely with the systems engineer to set expectations based on what the systems engineer observed in the area of team communication and subsystem compatibility.
Team meetings are set up such that each subsystem gives an update to the group as a whole before moving on to individual work and questions. This allows other team members who may have some expertise in other areas to comment on different ideas. Approaching meetings in this manner keeps everyone accountable to each other and helps the work to progress on its own.
2.3 Systems Engineering
2.4 Power
2.4.1 Methods and Assumptions
The main goal throughout the design of the power system is to survive a one year mission on the moon. This is just one of the critical requirements that affected the design of the power system. Another driving factor of the design is to land at a polar location. Due to the polar location, 14 days of light and 14 days of darkness is assumed. However, certain landing locations on the southern pole may allow for the Daedalus to receive 70% sunlight per month. The Daedalus is to be launched no later than September 30, 2012; therefore time is critical for acquiring all components.
There were many considerations reviewed for generating power. The first option assumed was solar cells with batteries. This would utilize the available source of light to generate power and charge batteries during the daylight, while the batteries would be active during the dark periods. Many batteries were reviewed and Lithium batteries were considered to be the most appropriate due to the high specific energy and storage capacity. Lithium-Sulfur Dioxide batteries and Lithium-Ion batteries were the two choices for the power system. However, Lithium-Sulfur Dioxide batteries were eliminated due to the voltage drop after initial power surge. The voltage drops well below operating voltage for a period of time, such as seconds or minutes.
Another option of power considered was nuclear power. A Radioisotope Thermoelectric Generator (RTG) and a Stirling Radioisotope Generator (SRG) were reviewed. Both of the nuclear power options were eliminated. The SRG has a low Test Readiness Level (TRL) compared to the RTG. Therefore, it was eliminated. Cost for the Daedalus is to be as minimal as possible. RTGs come at a very high cost. Another reason for elimination is due to the assumption that time and availability would be an issue. The acquirement of nuclear power may affect the launch date previously mentioned.
The final option of power was solar cells in combination with fuel cells. Regenerative fuel cells and Hydrogen fuel cells were the two reviewed choices. The fuel cells are very effective, yet they contain a large amount of mass. And, since the Daedalus would be testing samples, the fuel cells were eliminated due to the by-product of water. This water may have an adverse effect on the sample testing.
The power that needs to be obtained to maintain all systems running off of power is 700 Watts. This budget is derived from the initial power budget table that can be found in Table X. The estimated mass of the power system is 158.6 kilograms. This budget is derived from the initial mass budget that can be found in Table Y.
2.4.2 Results and Discussion
All of the methods and assumptions have contributed to the power combination of solar arrays and Lithium-Ion batteries. The solar power system allows Daedalus to power itself during light periods and recharge the Lithium-Ion batteries for use in the dark periods.The maximum output power of this arrangement is 902 Watts. This is over the initial power budget. LunaTech designed the power system to generate excess power to charge the batteries, make up any lost power in case of damaged parts, and/or to extend the mission past its required lifetime. The total mass of the solar cells, Lithium-Ion batteries, and support system is 182.3 kilograms. This is over the initial power budget. The mass is based upon calculations that can be found in Appendix D. The design of this system is based upon the Venus Express spacecraft which launched in 2005.
Since there is the available light source from the sun, the Daedalus design utilized solar cells. The total solar array area for the Daedalus is 5.98 square meters. This is due to the reason that there are 2 and 1/5 panels. The extra 1/5 panel is to provide the extra amount of energy generation needed for this design. The panels are covered with Optical Surface Reflectors (OSRs) to minimize the effect of extreme temperatures. Each panel is 1.78 meters in length and 0.8 meters in width. Each panel weighs 20.25 kilograms with an output power of 410 Watts. The total power acquired from these panels is 902 Watts with a total weight of 44.55 kilograms.
It is important for the design to include batteries that have a high specific energy and a long cycle life. The Daedalus will run off of batteries during the dark periods that occur on the lunar surface as well as during an eclipse. The design will use Sony 18650HC Lithium-Ion batteries. Lithium-Ion batteries were chosen due to the notion that they have a high specific energy, high output power to weight ratio, and the availability for space applications. The specific energy is 114.6 W-hr/kg. Each battery has an energy rate of 9 Ampere-hours. The batteries have a charge time of 12 hours.
The number of batteries needed to provide adequate power to the Daedalus is 15. This results in a total calculated mass of 70.4 kilograms and a total volume of 2.2 cubic feet. The mass of batteries were estimated upon how much each subsystem would be running during the dark periods. The dark period consists of 14 days, which is 336 hours. The systems that will be running 10% of the time are power and thermal. The batteries have an operating temperature of -10 degrees Celsius to 40 degrees Celsius. When generating, these batteries generate a lot of heat, therefore the thermal system does not have to be on 100% of the time. Payload, communication, and guidance, navigation, and control will only be running 1% of the time during the dark periods. This results in a total energy-rate output of 7.64 kW-hrs. Review Appendix D for calculations.
With the solar cells and Lithium-Ion batteries, a power management and control is needed due to the reason that the solar cells will be operating during sunlight and the batteries will be operating in the darkness. The batteries must be fully charged from the solar cells once daylight has ended. The average charge time of the batteries is 12 hours. The mass of the power control unit is 18 kilograms, while the regulator/converter unit is 40.6 kilograms, and the mass of the wiring is 2% of the estimated dry mass which is 19 kilograms. This comes to an overall mass of the power support system to be 67.3 kilograms. Refer to Appendix D for calculations. The way the system operates is based upon the subsystem set up that can be shown in Figure A.