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 Earth Independant Mars Pioneering Architecture Mars Colonization Initiative Final Report Alfredo Iturralde Jacob Harper David Blyton Richard Zang Casey Leavens Philip Burt 1 Table of Contents: Nomenclature
2 Executive Summary
2 Introduction
10 Mission Architecture
11 Subsystems
13 Structure
13 Launch Vehicle
15 Propulsion
16 Ground Control
17 Communication
18 C&DH
19 GNC
22 Power
23 Thermal
25 ECLSS
27 Payloads
30 Conclusion
31 References
31 Appendix I
32 Appendix II
33 Appendix III
34 2 Nomenclature: HAB
­Habitation module SD
­Supply Drop GH
­Greenhouse SLS
­Space Launch System MDAV ­Mars Descent/Ascent Vehicle LEO
­Low Earth Orbit MCC
­Mission Control Center POCC
­Payload Operations Control Center SOCC
­Spacecraft Operations Control Center EDL
­Entry Descent and Landing ISS
­International Space System C&DH
­Command and Data Handling GNC
­Guidance Navigation and Control R­DET
­Regulated Direct Energy Transfer PPT
­Peak Power Transfer Executive Summary: Intro: The Mars Colonization Initiative’s goal is to create a permanent, self­sufficient colony on the surface of Mars that can support 24 people with a rotation of 4 colonists every 2.2 years. The Martian base must be able to support 24 people indefinitely by the end of the 40 years, with the ability to expand as needed. The base must be able to gather the necessary resources from the local environment and process them to produce water, oxygen and construction materials. The goal of settling Mars requires successfully building up the colony’s ability to be self­reliant in as many ways as possible, as quickly a possible. This ultimately means using today’s technology to give the colonists the ability to make for themselves what would otherwise have to come from Earth. Shown below in Fig Exec Sum­1 is a schematic of the colony showing the final base design once construction is finished. Each structure connects to two other structures for redundancy purposes, to ensure that one route closure will not jeopardize the whole colony. The exception to this is the industrial HAB which only has one connection to the base, and also has an airlock to the Martian surface. As it will likely prove advantageous to keep this area unpressurized, redundancy in the form of an 3 air­tight connection is unimportant. In order to construct the base pictured a robust and flexible timeline was developed to allow the construction and completion of the base. Shown in Figure Exec Sum­2 is the timeline of approximate launch dates for all equipment and vehicles that will be needed to achieve the mission goal. Figure Exec Sum­1 MCI Base Figure Exec Sum­2 4 Shown below in Table Exec Sum­1 are the overall mass, power and cost requirements of the entire 40 year mission. These numbers are estimates based on previous missions and cost estimation for the mission. Table Exec Sum­1 Figure Exec Sum­3 below shows the mission scenario cartoon of the mission and a rough rendering of the Cycler, and how the goal will be accomplished. Figure Exec Sum­3 Structure: Each supply drop performed for the future colonists have a different purpose, but share many similar features. Each supply drop will deliver approximately 20 metric tons of supplies to the surface of Mars, of varying composition. Once on the surface it is the responsibility of the colonists to unpack and put the supplies to the purpose they were intended. Some drops will contain important emergency supplies, while others will contain advanced equipment from Earth to improve the quality of life on Mars. 5 All cycler vehicles will be built to a similar standard, focused on their deep space mission of providing crew transfer capability. The superstructure of cyclers will be largely adapted from the Deep Space Habitat 60­day configuration, currently being developed by NASA. To modify the cyclers’ ability to carry consumables, the main structure will be mated to a modified Bigelow Aerospace Inflatable Module. The final structural element will be a self­contained propulsion and attitude control module that holds the attitude thrusters, main engine and propellant tanks. The base envisioned by MCI is designed to maximize space and capability, while minimizing cost and resources necessary. The base consists of 7 underground structures, 3 for living areas and 4 for other industrial and life support purposes. Additionally 5 greenhouses for food production, 2 HAB’s for the initial landing, an industrial HAB and a mining HAB. The industrial HAB is for working on industrial processes, such as brick production. The mining HAB is designed to move freely and gather Martian resources to use on site. The 5 greenhouses will produce all food for the colonists in addition to producing the necessary oxygen. Launch Vehicle: The Launch Vehicle will be the Space Launch System. This is the only vehicle currently in development that is capable of meeting our launch mass needs. The vehicle is being developed in different stages.The SLS block 1 can send 70 metric tons to LEO, where vehicles will need a separate propulsion system to get to Mars. The SLS block 2 is capable of sending 130 metric tons to LEO, or around 30 metric tons directly to Mars. Propulsion: Interplanetary vehicles will make use of hydrazine propulsion systems. More specifically, all unmanned vehicles will make use of hydrazine monopropellant attitude control thrusters and engines. The cycler craft will make use of hydrazine/ nitrogen tetroxide control thrusters and engines. These systems offer reliable use over long duration missions. Ground Control: Throughout the extent of the MCI Campaign, an entire array of ground control will be required as has been in any large manned space related effort. The Mission Control Center for MCI will be located at Houston, Texas and will be contained within its own facility separate from the ISS MCC. It will operate similarly to the way in which the former Apollo Program’s MCC operated and is estimated to have approximately 100 flight controller personnel. The Spacecraft Operations Control Center will also be 6 located in the same building, but a different room and will have approximately 35 flight controllers to monitor all of the unmanned and manned subsystems. The Payload Operations Control Center will be located at Marshall Space Flight Center in Huntsville, Alabama and will share the current facilities that are there possibly occupying another room if needed. It will consist of approximately 35 flight controllers as well. At all facilities, the flight controllers will be split over 3 shifts so that their respective roles are manned 24 hours a day, 7 days a week. Communications: The communications subsystem’s focus is divided into two main components: the system aboard the ferry, and the system on base itself. Both systems will communicate with the Earth through the Deep Space Network. If availability becomes a problem, new facilities may be created to support the base, with a design very similar to the Deep Space Network. The system aboard the ferry will be constrained by the available power, the maximum diameter of the dish, and the difficulty in accurate pointing. The ferry will not be able to reposition itself due to the need to minimize the stress on the inflated sections, so the transmitter will need to move independent of the rest of the spacecraft. As the ferry gets further from Earth, communication will become significantly more difficult, so the system has to be designed to function at the maximum distance. of its orbit, which has been assumed to be the same as the maximum distance as Mars. The communications from the base will be provided by ground station located on the perimeter of the base. The ground station will only be able to communicate with the Earth for 30% of a day, but given the long delay associated with communications, any time critical crisis will probably need to be solved by the base itself with limited input from the Earth. A ground station provides opportunities for repair and maintenance that are not present in a satellite communications system. C&DH: On any spacecraft a means of Command and Data Handling is required. It has been decided that for the MCI Campaign all manned interplanetary spacecraft and/or transfer vehicles to and from Mars will utilize the same C&DH system manufactured by Honeywell that NASA has selected for the Orion spacecraft. The reasoning behind this decision is to ensure that the setups for C&DH are consistent across both the Orion spacecraft and the Interplanetary Cycler vehicle. This will allow the possibility for both systems to be temporarily integrated to minimize power usage during the manned 7 transfer phases of the campaign. Both craft will possess similar architectures if not the same architectures. As for the base, all of the life­critical vehicles and HABs will use centralized architectures with independent on­board processing and the data­intensive vehicles will possess multiple processors utilizing a distributed data bus to ensure that the C&DH system does not get overloaded during use. This is also to accommodate any intensive programs that the C&DH system may need to run. The non­life­critical unmanned craft at the base will use a simple ring topology and a single processor in each of them to simplify bus architecture and reduce overall cost. GNC: For all unmanned launches a Hohmann transfer will be used. However with all manned missions we will be utilizing an Aldrin Cycler orbit. The cycler system will perpetually cycle orbits between Earth and Mars by using the relative gravitational forces of these two planets to maintain the orbit. This method reduces fuel usage while also providing a reusable and sustainable method for sending humans to the base. The transfer from Earth to Mars will take five months, much faster than the Hohmann transfer time of over 8 ½ months. Power: The interplanetary vehicles will make use of solar cells and various batteries in their journey from Earth to Mars. The unmanned vehicles will have enough solar cells to provide 100 watts of power near Mars. The cycler will need much more power to be able to keep its human crew alive and comfortable, approximately 54 KW of power. One advantage to the crew vehicle is that it will be able to make use of fuel cells while there are human onboard to help power life support systems, which would otherwise be dormant. Table Exec Sum­2 below shows the power distribution for the Cycler. 8 Table Exec Sum­2 The Mars colony will be initially powered by four fission reactors designed and built as part of NASA’s Surface Fission Power program. These reactors will supply the colony with an initial power budget of 160 kilowatts of electrical power. As the colony grows and becomes increasingly self­reliant, solar arrays will be built up until they are the primary power source. Given that these arrays would be located on a planet, they can be as large as is necessary to meet and then exceed the reactors’ initial 160 kilowatts of power. Table Exec Sum­3 below shows the power distribution of the base. Table Exec Sum­3 9 Thermal: Several methods will be used to control the temperature within the ferry to keep it within human safe levels. While the ferry approaches Earth it will need cooling capabilities, as the ferry approaches near Mars it will require slight heating. The ferry will use multiple layer insulation to minimize heat loss. While the ferry is near Earth cooling loops will be activated to prevent overheating. The Martian base will require a significant amount of thermal protection to guard against the extremely cold temperatures of Mars. Since much of our base is underground the thermal requirements of the living quarters will remain constant, coupled with high quality insulation to minimize power draw. ECLSS: Once on the surface of Mars the base will need to have the ability to provide all of the life support systems necessary for the colonists to survive. MCI plans on using the greenhouses as the main system to produce oxygen, via photosynthesis of the plants. This oxygen rich air will be circulated through the base, excess oxygen will be vented into the atmosphere within the greenhouses. This system allows the base to produce the necessary oxygen without using much power. Water is also an important aspect of the colony. The main method to gather water involves the colonists leaving desiccants exposed to the atmosphere, which will collect ambient water. The cycler used by MCI will serve as a reusable transport for the colonists on their way to and from Mars. The cycler will need to provide enough oxygen, water and food for the colonists on their 6 month journey to or from Mars. The main portion of the ferry will serve as the platform for the ECLSS machines. An inflatable habitat module will attach to the ferry, which will provide the needed food and water for the colonists. Payload: Several different payloads will be launched and landed on to the surface of mars for the survival of the Mars Colonization Initiative’s 40 year program. These payloads vary widely in functionality and size. The payloads can be broken into the following categories: HABs, construction supplies, reactors, sustenance supplies, living payloads, rovers, and satellites. The payloads will vary in quantity during the progression of the program. Since the goal of the MCI is to have a self­sustaining colony by year 40, the only payload by the end of the program will be living payloads or humans for crew rotations. Table Exec Sum­4 below shows the mass breakdown of each unmanned mission. 10 Table Exec Sum­4 Introduction: The Mars Colonization Initiative’s goal is to create a permanent, self­sufficient colony on the surface of Mars that can support 24 people with a rotation of 4 colonists every 2.2 years. The Martian base must be able to support 24 people indefinitely by the end of the 40 years, with the ability to expand as needed. The base must be able to gather the necessary resources from the local environment and process them to produce water, oxygen and construction materials. The goal of settling Mars requires successfully building up the colony’s ability to be self­reliant in as many ways as possible, as quickly as possible. This ultimately means using today’s technology to give the colonists the ability to make for themselves what would otherwise have to come from Earth.This report’s design level is to lay out the final version of MCI’s plan, including several specific values on at least a first order basis. 11 Mission Architecture: Figure MA­1 The plan put forward by MCI to construct a permanent self­sufficient colony on Mars focuses on the sending of capabilities to Mars for the colonists. A timeline was created to maximize the chances of success, while minimizing risk. Figure MA­1 shows a graphical representation of this timeline, highlighting several of the key milestones to the colony’s construction and progress. Between July 2022 and March 2031 the only things sent to Mars are unmanned payloads, each designed to improve the colonist’s quality of life and chances of survival. The first manned launch using the cycler system occurs in March 2031. Once the colonists arrive on Mars they immediately begin construction of the first greenhouse and underground facilities. As the colony grows and expands more advanced technology is sent to the colony to enable performance of specialized functions. By September 2050 the colony should be self­sufficient, but two more supply drops are scheduled to be sent to cover any problems or delays that may arise as the colony grows. The full timeline may be found in Appendix I. 12 Figure MA­3 The colony itself has been designed to provide the maximum amount of living space and safety, while minimizing the work involved. Figure MA­3 shows the floor plan of the Martian colony with several reference measurements. The “D”­shaped underground portion was chosen to ensure safety. If a single portion of the base collapses, or becomes dangerous, the colonists still have access to the rest of the base. By placing a large portion of the base underground the colonists will have a steady climate and strong protection from radiation. This also maximizes the use of local materials, driving down the amount of materials that need to be delivered from Earth. Table MA­1 Table MA­2 13 Shown in Table MA­1 is the cost estimation for the base and all of its aspects, in FY 2014. The QuickCost model developed by NASA was used to calculate the initial price of the supply drops. Table MA­2 shows the specific values used for the QuickCost model. Since there are many repetitive missions a cost improvement model with a 95% learning curve was used to reflect the lessons learned in each new mission. Subsystems: Structure: Figure Structure­1 The Martian base is comprised of 3 main types of structure: HABs, greenhouses and underground facilities. An example of the underground facilities, shown in Figure Structure­1, are designed to maximize the living area, while minimizing the work and materials to construct them. There is a total of 7 underground facilities, each with a width of 7 meters, height of 3 meters and a length of 30 meters. The roof is built with a layer of aluminum to withstand the compressive forces of the three feet of Martian regolith above. Another aspect of the Martian base are the pre made HAB’s, these are built on Earth and shipped to the Martian colony. The purpose of these structures is to provide a safe place for the colonists to live on Mars early in the campaign. The estimated size of the HABs’ are a height and diameter of 6 meters. Only 2 living HABs will be sent, however a third will also be sent as an early industrial center. These HABs will be able to provide all the thermal, life support and storage needs of the colonists until they 14 expand the base further. Later in the mission they can be repurposed into surface­side workshops or laboratories. Figure Structure­2 The last type of structure in the colony are the 5 greenhouses, which will provide all the necessary food for the colonists to survive. The greenhouses are domes, which measure 11.3 meters radius and approximately 3 meters tall. To contain an atmosphere within the greenhouse a smaller dome is placed underneath the ground and connected to the top portion. This allows the greenhouses to withstand the pressure of the internal atmosphere. Figure Structure­2 shows a 3D rendering of the top portion of a greenhouse. Figure Structure­3: Diagram modified from ​
Mission to Mars 15 The structure of the cycler will closely follow the design provided by Buzz Aldrin. It will contain a Deep Space Habitat for the crew, a propulsion system to maintain orbit, and a Bigalow module for storage of supplies. These modules are designed to be easy to replace between crewed trips of the cycler in order to ensure that the cycler contains the necessary supplies. The cycler will also contain a large communications array to keep in contact with Earth and Mars, as seen in Figure Structure­3. Launch Vehicle: To complete MCI’s mission, it is necessary to begin by getting resources, crew and vehicles off of the ground. This can be accomplished by using two launch vehicles, the SLS Block 1 and the SLS Block 2. These two vehicles will be used in a way that optimizes the launch schedule with payloads and, perhaps more importantly, as they come into operation. The SLS Block 1 is slated to be operational by 2018, and as such will be flying the bulk of the early mission assets. The SLS Block 2 should be operational by 2030, and as such will launch later payloads to Mars. The SLS Block 1 will have the ability to launch 70 metric tons into LEO (Space Launch System). When used in conjunction with an entry, descent and landing (EDL) system, as is being developed currently by NASA and RASC­AL teams, this leaves 20 metric tons for useful payload on the surface of Mars. This is ideal for landing the unmanned payloads in the early portion of the mission. These payloads include building materials, a digging robot, and prefabricated structures to begin the building processes on the surface. This capability is also enough to begin assembly of the cycler craft which will transfer crew to Mars, or the Mars Transfer Cycler. The SLS Block 2 will have ability to throw 130 metric tons into LEO (Space Launch System). This makes it ideal to launch the components of the second cycler, which would function as the Earth Return Cycler. The Exploration Upper Stage can also be used to help begin pushing the cyclers into their cyclical orbits. This would in turn reduce the required size and strength of the cyclers’ propulsion systems, which are primarily to be used for orbit corrections rather than boosting the cyclers into orbit. This results in overall, smaller and less complex cyclers, which is highly preferable as they will already be extremely complex. This upper stage will find more regular use in getting the Orion Capsule and service materials up to speed, around 6 km/sec, to rendezvous with the cycler (Aldrin). 16 Propulsion: MCI has three classes of vehicles which require propulsion schemes. The first of these is the supply drop, which for the purposes of propulsion includes HABs, and robots, ground vehicles, reactors or any other vehicle delivering an unmanned payload to the surface. These vehicles will make use of the EDL system being designed, or some adaptation there of, referenced in the Launch Vehicle section and its component propulsion system. This leaves two unique systems for MCI to designate, the cyclers’ and the MDAV propulsion system. Propulsion Figure 1: Adapted from SMAD; all numbers shown refer to vacuum The cycler must be able to perform orbit corrections, store its fuel for long durations, and have minimal impact on its power systems. These constraints clearly define the need for a hypergolic propulsion system, using hydrazine and nitrogen tetroxide as its bipropellant combination. Among the better rocket engines that use this propellant mix is Aerojet’s Orbital Maneuvering System with a nominal thrust of 26.7 kN (Wertz). An adaptation of this system would be ideal for use as the cyclers’ main drive system. Additionally, using hydrazine makes this system an excellent candidate to run in a dual­mode, where the hydrazine would be used a monopropellant to drive attitude control thrusters. A sound choice would be Aerojet’s MR­107N monopropellant engine. Both engines are described in some detail in Propulsion Figure 1. Allowing for the fact that the Orbital Maneuvering System was a unique system integrated into the Shuttle, this system could be combined with MR­107’s to drive down structural and plumbing mass and cost. The MDAV will be the first of its kind. As such much of its systems and design remains unknown. That said there is one certainty, it must be able to be refueled at Mars prior to being used to ascend back into space. That means that its propellant must be locally available. The only current viable option would therefore be an engine that uses liquid oxygen and liquid methane, as both of these chemicals are readily 17 synthesizable on Mars. This in turn would require the use or adaptation of an engine being designed by SpaceX to do just that, the Raptor. The Raptor is reported to be able to generate 4,500 kN of thrust, which would allow it to lift the MDAV back into space (​
Belluscio​
). Ground control: Throughout the MCI campaign, the usual array of ground control facilities will be required, as it has been in all large manned space missions. There will be three facilities charged to handle the entirety of the mission. The MCC will be the the facility through which all communications with the crew will take place and will work very closely with the other branches of ground control. The POCC will monitor the status of any unmanned missions carrying payloads to Mars. The final facility will be the SOCC, which will monitor most of the operations and subsystems of the MDAV, Orion spacecraft, and cycler. The locations and human resources of the ground facilities have been modeled after those used for the International Space Station and the Apollo Program. As a note, the flight controller numbers, later reported, compose the whole staff. The flight controllers will be split over three shifts such all roles are manned 24 hours a day, 7 days a week. The MCC will be located in Houston, Texas and will be contained within its own facility separate from the current ISS MCC. It will operate similarly to the way the former Apollo Program’s MCC was operated. It is estimated to require approximately 100 flight controller personnel. Houston was selected as the location for the MCC since traditionally MCCs have been housed there. This means that the required skills, infrastructure, and experience needed can be found in the area already. The POCC will be located at Marshall Space Flight Center in Huntsville, Alabama and will share the facilities that are currently there, possibly occupying another room if needed. It will consist of approximately 35 flight controllers. This location was decided because it is where the current POCC operations are held for the ISS and formerly the space shuttle. Since payload operations are not nearly as personnel­demanding, or life­critical, as manned operations are, there is no need to construct an entirely new facility. Finally, the SOCC will be located in the same building as the MCI MCC but will have its own room or floor within that building. It will also have approximately 35 flight controllers. It was decided that the SOCC would be best to be located at the same location as the MCC to allow the two facilities to work closely together, given that many 18 of their objectives overlap. The campaign cannot be achieved without active monitoring of the subsystems aboard the various craft and effective mission planning. Communication: The communication subsystem was divided into three main categories: the system on the cycler, the system on the Martian base, and the system on Earth. Each category came with its own unique design challenges, and therefore needed to be designed separately with independent assumptions. Link budgets were created for each of them in order to ensure that they could meet any required need. The cycler needed to be able to receive commands from both the Martian surface and Earth. It needed to always be able to receive commands from Earth regardless of the distance; however, the cycler only needed to receive commands from Mars when it is near the planet. The diameter of the communication system needed to be as small as possible in order to minimize the required mass, but still large enough to satisfy the communication needs. The cycler settled on a deployable communications array with a diameter of 15 meters. The mass on this system will be reduced with inflatable components. The power of the cycler is a finite number, and 13.44 kW were allocated to the communications system. Communications from Mars will be performed with a large ground based facility. This ground facility is superior to orbital satellites primarily due to the issue of maintenance. If the facility has a problem, a colonist can rather easily walk over to it and repair the issue. If a satellite requires maintenance, an entire mission must be launched for this task. The colony requires constant access to communication to Earth in order to function, and the ground facility is a more reliable way to perform this communication. The low gravity on Mars allows for the creation of large structures with few materials, resulting in the creation of a 35 meter communication disk. Although the base contains a significantly larger power generation capability than the cycler, it also has far more demands on its supply, resulting in only 12.1 kW available for communication. Earth communications are vital to the success of the mission. Instead of attempting to take over the existing Deep Space Network infrastructure, the Mars Colonization Initiative will fund new facilities in the same locations as the existing DSN locations (California, Madrid, and Australia). These facilities will have the same specifications as the larges DSN dishes (70 meter diameter) and be able to provide 1 MW of power for transmissions. When the facilities are not needed to communicate with 19 a cycler or Mars, their time will be rented out to other groups who desire this communications capability. Two frequencies for the communications were selected based on the recommendations of the Space Frequency Coordination Group. Transmissions from Mars or the cycler will be at 8.4 GHz, and transmissions from Earth will be at 7.1 GHz. This small difference in position did not significantly affect the link budget, but reduce the possibility that different communications will cancel each other. The data transfer rate was established at 40,000,000 bps to allow colonists, on Mars or the Cycler, the ability to send low resolution video messages back to Earth. A higher data transfer rate will occur on Earth, at 230,000,000 bps, in order allow the Earth to transmit high definition video. The colonists will greatly appreciate this source of entertainment on the isolated planet. The calculation for the link budget is shown in the section entitled Link Budget. All the link budgets are well within the desired link margin. Some systems, such as Earth to Mars, are significantly higher than necessary, but also provide a comfortable factor of safety. C&DH: Each vehicle in the MCI campaign has a command and data handling design that follows a general pattern to promote cost effectiveness and safety. There are three main bus architectures that have been designed for the different vehicles. The larger components of MCI, such as the HABs and the base use the most complex bus architectures which incorporate many fail­safe features and backup systems. The MDAV and cycler being used follow another design that is similar to that of the base, but are simpler in certain aspects. The simplest bus architecture is for the supply drop vehicles which require minimal C&DH and are not life­critical. 20 Figure C&DH­1 Figure C&DH­1 shows the bus architecture for the base . Each room or living space associated with the base has its own set of subsystems. It is set up this way so that if there is a failure of one area the entire base is not compromised. Since an entire set of subsystems for each room involves a large number of sensors and various components, each room contains its own bus. The entire base has a main array of central processors and each processor is connected to one of the busses. The array is then connected to a control console which can be controlled from generally any room of the base. This bus architecture allows simultaneous monitoring of the entire base as a whole and micromanagement of all the systems in each section. It follows a centralized topology approach for each room so that if a single component in a room fails, the entire room does not lose all of its subsystems. Also, the processors are all connected together on a bus which allows control for one room to be transferred from one processor to another. Overall it becomes a very versatile bus design. 21 Figure C&DH­2 Figure C&DH­2 shows the bus architecture for the cycler and MDAV. As the cycler and MDAV do not involve multiple independent structures like the base, the bus architecture for these two craft is different. Though it is slightly simpler, it still contains the safety aspects of the base’s architecture. Like the base structures, the cycler and MDAV both utilize a distributed bus architecture comprised of many processors. There are enough processors to provide one or more to each subsystem. Each subsystem is comprised of its components such as sensors, valve controls for propulsion, thermometers, etcetera. All of these components are tied into the main data bus which is connected directly to the processors. The processors can then handle and distribute the data and load requirements as necessary. This system is inherently safe for the cycler’s and MDAV’s life­critical missions because it also permits a centralized topology to be implemented. Figure C&DH­3 Finally, Figure C&DH­3 shows the simplest bus architecture being used on MCI missions. This architecture uses a federated bus with a single processor and can be either fitted to centralized or ring topology depending on the particular needs of the supply drop craft using this architecture. This architecture has minimal materials and is 22 thus cost effective for the mission at the cost of some safety. If the processor should fail for any reason, the entire craft is compromised. GNC: The guidance, navigation, and control subsystem is responsible for monitoring and adjusting the trajectory of all of the spacecraft included in this mission. Starting in 2020 we will be launching an SLS Block II twice every 2.2 years. It is vital that we be able to track all of the spacecraft being sent accurately. This will ensure all of the spacecraft land at the planned landing site, as well as cut down on the fuel needed to make course corrections. Therefore, the trajectory of each of the launches will be tracked using a Sun and Star sensing method. This method is quite accurate and has been used on previous missions to Mars. Multiple large supply drops will be needed in order to provide the astronauts with all the various equipment, materials, and food. The transfer time of supply drops is less vital to the mission than that of manned launches. This is why a Hohmann transfer will be used for all unmanned payloads. This will minimize the ΔV required and cut down on cost. A Hohmann transfer from Earth to Mars takes 259 days and requires a total ΔV of 5.6 km/sec. All manned missions will be sent using the Aldrin Cycler system. The cycler system will continuously cycle orbits between Earth and Mars by using the relative gravitational forces of these two planets to maintain the orbit. This method reduces fuel usage while also providing a reusable and sustainable method for sending humans to and from the base. The Orion spacecraft will carry and attach the astronauts to the cycler. The Mars lander will also attach to the cycler. During the transfer to Mars the astronauts will be able to utilize the space inside an inflatable space hab that will be part of the cycler. The transfer from Earth to Mars will take 146 days, much faster than the Hohmann transfer time. When the cycler arrives at Mars the astronauts will descend to the surface using the Mars lander. Some years there will be crews returning using the cycler and refueled Mars lander. The cycler will also include a momentum wheel and hydrazine monopropellant attitude control clusters. This will ensure the cycler stays on course and will continue to assist in all manned transfers to Mars throughout the mission. Each launch using the Aldrin cycler will require a total ΔV of roughly 8 km/sec. 23 Power: The MCI campaign is very large in nature and thus requires a complex system to provide enough power to meet the rigorous demands. The requirements between the cyclers’ and base’s systems vary greatly. The main components of the overall power system are solar panels and rechargeable batteries. Selection of these panels and batteries involved a process that took into account cost effectiveness, longevity, and many other variables. There were also several reasonable assumptions made when determining how many panels and batteries were required to meet the needs of the mission based on the uniqueness of the MCI campaign. On a typical day, the base needs approximately 222 kW of power. This value is based on the base needing an estimated 200 kW of power during the day and a margin of safety. 81% of this power, or 162 kW, is used to supply the major needs of the base which comprise of the thermal subsystems, ECLSS subsystems, and industrial sections. 12.1%, or 24.8kW, is reserved for the remaining subsystems, communications and C&DH. The remaining 6.9%, or 13.8kW, is left to take into account general power losses. To preserve power during the night hours at the base, only thermal, ECLSS, and C&DH will be powered. The C&DH will run at 25% of its normal power since it will not be running as many systems during that time. This results in a nighttime need of only 118.825 kW. These numbers describe the behavior of the end goal base, to be completed near 2050. The early base will have much lower requirements and will be powered by four imported, small fission reactors, each generating a constant 40 kW of power day and night (Martin). It was decided that the base will use silicon solar panels, in the long term, for since they are the least expensive and the basic materials for them are present on Mars. Since the power demands at night will be less, as described before, not as many solar panels will be required as would be if all the systems were running constantly. Using an assumption that the base will use 131.895 kW, with a built in margin, at night, the required area of solar panels needed to fulfill this demand equates to approximately 23233.4 square meters. This area approximates to roughly 4.34 football fields. Taking into consideration that the International Space Station currently is the size of a single football field as a whole, this estimate seems reasonable for an entire Mars base. To provide extra assurance that the base will indeed have enough power, it was decided to standardize the area to 26765.1 square meters or 5 football field areas. This will provide an additional 93.6 kW of power per day which can be stored for use in emergencies or in the event of future expansion. 24 It is worth noting that to make these estimates the model in SMAD was used which traditionally accounts for spacecraft in orbit, rather than stationary panels on the ground. To account for this, an eclipse duration of 924.8 minutes was assumed, using the shortest day of the year on Earth, since Mars’ rotational rate is similar to that of the Earth, and subtracting this value from a standard Martian sol. Lastly, a sun angle of 0 degrees was assumed, even though it should be around 90 degrees. This is because a 90 degree sun angle would yield an unrealistic value for beginning of life power for the solar panels. For the power storage needs of the base, nickel hydrogen batteries will be used. These batteries were selected because they have been widely used in the space industry. Additionally, they have been demonstrated to survive a large number of charging cycles at high rates. These are the same type of batteries used on the ISS. It was found that the base will require 33.49 metric tons of nickel hydrogen cells to meet the power needs of the base during the eclipse hours. This value was calculated using a typical space rated nickel hydrogen specific power value of 60.7 wh/kg. 10 metric tons of these batteries will be sent to Mars from Earth during the early campaign. The remaining 23.49 metric tons will be manufactured at Mars. The other major component of MCI are the cyclers which are needed to transfer the crew to and from Mars. A cycler uses considerably less power than the base and is more in scale with the current ISS in terms of its consumption rates. The cycler will nominally have a maximum power rating of 56 kW but will generate a total of 61.6 kW for a 10% margin of safety. 20 kW of this power will be generated by fuel cells. The remaining 41.6 kW will be generated using silicon solar panels. Assuming a typical eclipse duration of 30 seconds per day, since the cycler will not encounter darkness during most of its journey to Mars, and a lifetime of approximately 30 years, the estimated area of solar panels for the cycler is 2857.6 square meters. This is approximately equal to half a football field. Again, with respect to ISS, this area seems reasonable. Since the cycler will not encounter many periods of eclipse, the power drawn by all the subsystems throughout its flight will be relatively unchanging. With regards to storing power on the cyclers, the process is relatively simple. As stated before, the cycler will not experience many periods of eclipse and thus only needs to store enough power for emergencies. During a real emergency many of the subsystems would be able to be shut down to conserve power. Since the cycler typically uses 56 kW during normal operation, it was assumed that during an emergency it would use no more than 30 kW, likely less, at the maximum. Using this assumption and the fact that the longest eclipse period is likely to be no more than 90 minutes as it 25 traverses around Mars, the estimated mass of the nickel hydrogen batteries required is 494.2 kg. This would be enough battery cells to run the spacecraft at the 30 kW capacity for one hour or at 20 kW for 90 minutes. The base will use a R­DET scheme since the ground solar panels will be stationary and will not track the sun throughout the course of a Martian sol. The cyclers will make use of a PPT mechanism to maximize power gains from the solar array during its flight. This is to ensure that it receives the most amount of power possible so that it can minimize usage of its reserve power. This will also permit most of the subsystems to function at near full capacity should the fuel cells fail. The cyclers’ power distribution will operate at a standard 28 volts since it is small in size and the distance the power must travel is relatively small. It will use a centralized distribution scheme to keep the system simple and will use DC to eliminate the need for inverters. For fault protection, all of the subsystems and their various components will be isolated and wiring will be such that if there is a failure on a particular circuit it does not compromise the safety of the crew or vital subsystems. The base will operate at the Earthly standard of 120 volts since it is rather large in size and the power will travel much farther distances. The base will use decentralized distribution so that special loads such as those in the industrial area of the base can be accommodated without affecting the voltage on the main bus for the rest of the base. The base will operate using the AC standard on its main bus and multiple inverters so that motors and other various instruments requiring AC power can be easily accommodated. Every room of the base, and their respective subsystems, will be isolated so that a single circuit failure will not compromise the entire base. A table of power allocations for the various subsystems by percentage and wattage is provided in Appendix III. Thermal: There are two main areas that need thermal systems installed and functioning; the Cycler and the base. Since people will be in both areas the temperature should ideally be 70 degrees Fahrenheit, but have upper and lower limits of 80 and 60 degrees Fahrenheit respectively. On the surface of Mars, the base needs to protect against both radiative and conductive heat transfer, while the Cycler only needs to combat radiation based heat transfer. 26 The Martian base is comprised of 3 main aspects, greenhouses, HABS and the underground segments. Both the HABS and underground segments will be protected by a 0.1 m thick layer of Cryogel Z aerogel insulation(Aspen aerogels), manufactured by Aspen aerogels. This was chosen due to its specialty in dealing with cryogenic temperatures, its very low heat transfer, with a k of 0.017W/m*K. Cryogel Z is also a flexible blanket that can withstand compressive forces of 100 PSI. This makes it easy to install throughout the entire colony. While the Cryogel Z is able to resist heat loss through conduction, radiation is still a major concern, due to the large temperature differences between the inside and outside of the colony. To prevent losses through radiation, a material with an emissivity of approximately 0.05 will prevent most heat loss.The greenhouses are estimated to have heat losses similar to the underground portion of the colony. Table TCS­1 below shows the expected values of heating needs, not including the greenhouses. Table TCS­1 By using the Cryogel insulation and low emissivity material the total power requirements of the base are listed below in table TCS­2. The expected power needs are approximately 61.9 KW. This number is an approximation of the final base, which does not take into account any internal sources of heat such as, people, lighting or machines or processes. Table TCS­2 The next aspect of the thermal system is making sure the colonists are kept at a comfortable temperature on the Cycler system. Since there is a significant difference in solar energy the Cycler system will need to minimize as much energy gained or lost due to solar radiation. The Cycler will use MLI blankets to greatly reduce the emissivity of the craft. This will greatly reduce the energy needed to heat and cool the Cycler, however cooling will need to be provided to portions of the Cycler due to heat generated by internal processes. 27 ●
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ECLSS: The environmental control and life support systems control and manage all the aspects of the Martian base and ferry system that ensure the colonists are able to survive the dangers of space. The requirements of the life support subsystems are: Oxygen production and distribution for 24 people Food production for 24 people Water production and recycling for 24 people Humidity management Radiation protection or minimization Safe temperature range inside base ~ 60 to 80 degrees Fahrenheit Oxygen for crew en route to Mars Water for crew en route to Mars Must minimize possible psychological issues In order to produce oxygen for the colonists while on Mars the colonists will electrolyze water to break it up into hydrogen, which will be collected, and oxygen. The oxygen created will be dispersed throughout the base for the crew. The hydrogen will be collected to be used in the Sabatier process to produce more water and methane. The electrolysis reaction is shown below: 2 H​
O(l) → 2 H​
(g) + O​
(g); E​
= ­1.229 V 2​
2​
2​
0​
By using this simple, yet scalable process the crew should be able to easily diagnose and fix any problems that arise without the need for external help. This process will also be used on the trip to Mars, albeit with a different machine to compensate for the lack of gravity. In order to survive, the colonists will need a steady and safe supply of water. To gather water on Mars, the colonists will allow desiccants to gather ambient water on the surface. Once the desiccants have gathered water, they will be heated to release water in the form of steam. After the steam has condensed the water will be used in a myriad of ways for the colonists. In addition to this system for gathering water, a water recycling system will be used to both recycle waste water and maintain humidity. Initial estimates show that up to 90% of water can be recycled and reused. While en route to Mars the colonists will need water to drink and electrolyse into oxygen. To accomplish this, water will simply be shipped from Earth, or gathered from the Martian surface. This method was chosen simply due to the fact there is no way to 28 gather water in space. Similar to the surface methods, a water regenerative system will be used to minimize the mass needed. One great problem to the potential colonists of Mars is the issue of radiation and its damaging effects on the human body. In order to minimize the doses of radiation experienced by the colonists on the surface of Mars, much of the base is located underground. With at least 3 meters of Martian regolith to shield the colonists the radiation doses experienced by the colonists are minimal. While the Martian regolith can protect the colonists on the surface, the ferry system needs methods to protect the colonists while in transit. To accomplish this, shielding is in place which will stop a significant portion of the radiation. In case of severe solar storms a safety room is in place, with an average density of approximately 35g/cm^3 (Zubrin) all but the worst of radiation will be minimized. In order for the colonists to survive the frigid days and even colder nights the temperature within the colony will need to be maintained between 60 and 80 degrees Fahrenheit, although ideally at 70 degrees Fahrenheit. To accomplish this a 0.1 meter thick layer of Cryogel insulation, which is a specific aerogel, and covering with a low emissivity will be installed throughout the entire colony. These levels provide a balance between maximum protection and minimizing mass. The next aspect of the ECLSS system is to manage the mental health of the colonists. Living in cramped conditions can have serious mental effects on a colonist. To minimize these serious effects the colony’s underground portion is split into 7 rooms to provide a different environment in each room. In addition the greenhouses are easily accessible and do not require special suits. The colonists will be able to enter the greenhouses to gather the helpful benefits of seeing green plants, similar to Earth. Finally, since their food is all grown in situ, the benefits of eating food grown by their hands will help deal with the problems of living on Mars. Modern humans, especially humans that live in developed countries, do not realize the how much of their food is fortified. Because of this, very few of them develop the symptoms and diseases caused by malnutrition. This is not the case in other countries and for most of history. Since the Martian base needs to be completely self­sufficient, the colonists would need to grow and/or raise all their food to meet their nutritional needs. The nutritional needs of healthy human can all (but one vitamin) be found from eating plants. The only essential need a human cannot get from plants is vitamin B12, which is only found in animal tissue. However, it takes 2 years before the symptoms of a vitamin B12 deficiency are seen. The simple solution is to have vitamin 29 B12 supplements sent to resupply the base every 2 years with the crew rotations. The plants that need to be grown on the base need be able to produce at an efficient rate as well as a high output per plant. In Table ECLSS­1 the vitamins, minerals and amino acids necessary to support human life is shown. Table ECLSS­2 shows the various plants that will be grown in the greenhouses, at a minimum, to sustain the colony (Whitney). Table ECLSS­1 Table ECLSS­2 30 Payloads: Several different payloads will be launched and landed on to the surface of mars for the survival of the Mars Colonization Initiative’s 40 year program. These payloads vary widely in functionality and size. The payloads can be broken into the following categories: HABs, construction supplies, reactors, sustenance supplies, living payloads, rovers, and satellites. The payloads will vary in quantity during the progression of the program. Since the goal of the MCI is to have a self­sustaining colony by year 40, the only payload by the end of the program will be living payloads or humans for crew rotations with minor resupply mass. Table Payload­1 31 Conclusion: Overall, the plan put forth by The Mars Colonization Initiative focuses on sending the colonists of Mars the abilities and resources to expand the base themselves. This method was chosen due to the high cost of sending resources to Mars, while the Martian surface provides all of the resources necessary resources to sustain and grow the colony. Most of the colony will be constructed from Martian resources, whose value is maximized from resources and technology sent from Earth. References: Aldrin, Buzz. Mission to Mars: My Vision for Space Exploration. Washington, D.C.:National Geographic Society, 2013. Print. Belluscio, Alejandro G. (2014­03­07). ​
"SpaceX advances drive for Mars rocket via Raptor power"​
. ​
NASAspaceflight.com​
. Retrieved 2014­03­07. "Cryogenic Insulation – Cryogel® Insulation For Cold Work." ​
Cryogenic Insulation – Cryogel® Insulation For Cold Work​
. N.p., n.d. Web. 19 Apr. 2015. Martin, Katherine K. | NASA. (2008, September 10). Retrieved from http://www.nasa.gov/home/hqnews/2008/sep/HQ_08­227_Moon_Power.html Wertz, James Richard., David F. Everett, and Jeffery John. Puschell. ​
Space Mission Engineering: The New SMAD​
. Hawthorne, CA: Microcosm, 2011. Print. Whitney, Eleanor Noss and Sharon Rady Rolfes, ​
“Understanding Nutrition”, 13th edition 2013. "Frequency Assignment Guidelines for Communications in the Mars Region." ​
Space Frequency Coordination Group (SFCG)​
. N.p., n.d. Web. 22 Apr. 2015. "Space Launch System." NASA Facts (2014): n. pag. NASA. Web. Zubrin, Robert, and Richard Wagner. ​
The Case for Mars: The Plan to Settle the Red Planet and Why We Must​
. New York: Free, 1996. Print. 32 Appendix I:​
Timeline 33 Appendix 2:​
Link Budgets 34 Appendix 3:​
Power Summaries Standard Power Allocations for the Base (based on 200 kW capacity) Standard Power Allocations for the Cycler (based on 56 kW capacity)