Spacecraft & Martian Habitat Life Support System

Spacecraft & Martian Habitat Life Support System:

Space Transit & Surface Operations on Mars

“An analysis and integration of current life support systems

for a Mission to Mars”

Prepared for

ASEN 5116 - Spacecraft Life Support Systems

University of Colorado - Boulder

By

Red Midnight

Contact Person: Ritch Shidemantle

December 16, 2002

TABLE OF CONTENTS

1 Introduction 2

1.1 Objective 2

1.2 Class Specific Scope 2

1.3 Mars Design Reference Mission (DRM) 3

2 Requirements 3

2.1 DRM Requirements 3

2.2 Environment Issues 5

2.3 High Level Assumptions 7

3 System Design Philosophy 7

4 Atmosphere Subsystem 8

4.1 Requirements 8

4.2 Design Approach 9

4.3 Results 9

4.4 Operations 15

4.5 Summary 16

5 Water Subsystem 16

5.1 Requirements 16

5.2 Design Approach 17

5.3 Results 17

5.4 Operations 19

5.5 Summary 20

6 Waste Subsystem 20

6.1 Requirements 20

6.2 Design Approach 21

6.3 Results 21

6.4 Operations 22

6.5 Summary 22

7 Food Subsystem 23

7.1 Requirements 23

7.2 Design Approach 24

7.3 Results 25

7.4 Operations 27

7.5 Summary 27

8 Integrated System 27

8.1 Integration Process 27

8.2 Integration Results 28

9 Conclusions 31

9.1 Limitations 32

9.2 Suggestions 32

10 Bibliography 32

Appendices are available on attached CD-ROM.

1  Introduction

With the completion of the International Space Station slated for the 2007 to 2009 timeframe, NASA and the International Space Community are going to be looking to shift focus to Mars. Throughout space flight’s short history, humans traveling into space at great risk have fascinated people and although robotic missions serve a great need to the science community and sometimes to commercial entities, the public needs its heroes to capture its attention and inspire young imaginations. Without a significant human flight program the public will lose interest in NASA programs and continue to ask if their money is being spent the way they want it to be. Without public interest, NASA’s funding will continue to get cut more and more.

A human mission to Mars will rejuvenate the public’s interest and excitement in NASA and space flight in general. If NASA begins designing for a human Mars mission after completion of the ISS, it will have approximately a decade to develop a program that will act much the same as the Apollo program. Picture it’s 2010, the president of the United States comes on television and addresses the world stating that a human will step foot on Mars by the end of the decade. Nine years later in 2019, Fifty years after the Moon landing, a human steps foot on Mars for the first time. Many people have forgotten what it meant for mankind to step foot on the Moon. Maybe a human stepping foot on Mars is what is needed to help bring back that meaning and inspire a world community to come together for a common goal.

1.1  Objective

With NASA’s focus expected to shift to a human Mars mission in the near future, it is necessary to develop a new Life Support System (LSS) to satisfy new issues that arise with a mission to Mars. Some of these issues include the inability to quickly return home, living in a range of gravity conditions, and the psychological factors that will arise from a long duration, high-risk mission. In order to meet the system and mission requirements, available life support technologies will be analyzed and integrated. The Mars Design Reference Mission (DRM) document will be used as the baseline mission and an approach will be developed to provide a comprehensive life support system that will optimally satisfy the needs of the Mars DRM.

1.2  Class Specific Scope

The scope of this project is to research relevant technologies and determine an integrated system that will successfully accomplish the above-mentioned objective. The project was completed over the course of the Fall 2002 semester for 3 credit hours. The Appendix CD-ROM contains the schedules and theoretical budget for the semester. The semester budget was calculated assuming all group members to be Graduate Research Assistants and was determined to be $73,173. Meetings were held twice a week to facilitate subsystem interaction discussions and basic management issues.

1.3  Mars Design Reference Mission (DRM)

The Mars Design Reference Mission (DRM) was used as a baseline mission in the design of the Life Support System for this project. The DRM is part of an ongoing project by NASA that summarizes studies done on Mars exploration. It outlines a basic mission approach to provide a baseline for further studies. As new technologies emerge and robotic missions provide a better understanding of the Mars environment the DRM is periodically updated. The most recent updates to the DRM are outlined in Reference Mission 3.0 (Drake 1998), which was used in conjunction with the more complete DRM 1.0 (Hoffman 1997) as the reference for this project.

The Reference Mission 3.0 document provides a more detailed description of launch sequence options and mission vehicles. Two unmanned launches start the mission sequence. The first launch will insert the Earth Return Vehicle (ERV) into Mars orbit. This vehicle will remain in orbit until the crew is ready to return home. It is also equipped with the systems necessary to support the crew for approximately 700 days in the case that the surface phase of the mission must be aborted. The crew will be able to use the ERV as a habitat until the next Mars to Earth transit opportunity. The second unmanned launch will land the Mars Ascent Vehicle (MAV) as well as the In-Situ Resource Utilization (ISRU) unit and nuclear power supply. The ISRU will produce the fuel (methane and LOX) from the Mars atmosphere to be used to launch MAV from the surface into orbit to rendezvous with the ERV. MAV fuel production will be completed, and the integrity of the ERV and the surface modules will be verified before the first piloted mission leaves Earth. In addition to providing fuel the ISRU will provide back up caches of oxygen and water that is available to the LSS during the surface mission phase. The piloted transit mission will take from 130 to 180 days. The TransHab module will aerocapture Mars orbit and then perform a circularization burn prior to final descent controlled by parachutes. This same method is also used for the unmanned modules that land on the Mars surface. Approximately 2 months after the crew lands a second ERV will arrive in Mars orbit, and a second ISRU and MAV module will arrive on the surface. The second MAV and ERV provide the crew with redundant systems to reach Mars orbit and return to Earth. After a surface stay of approximately 619 days the crew will launch into Mars orbit via the MAV. The Earth to Mars / Surface habitat will be left on the surface to be utilized by the next crew in addition to their own habitat. Once in orbit the crew will transfer into the ERV and complete insertion into trajectory to Earth. Upon arrival at Earth the crew will land using a re-entry capsule similar to those used for the Apollo missions.

2  Requirements

Requirements for this project have been obtained in three ways, those that are stated by the DRM, those that are derived from the environment interactions, and the gathered assumptions.

2.1  DRM Requirements

Reference Mission 3.0 describes several options for the systems used for different mission stages. The mission not yet being completely defined results in some ambiguity in the requirements derived from the DRM. Where applicable, assumptions made for each requirement are provided. Specific references are also included.

Crew Size: A crew size of six was used for this LSS design, as stated in DRM 1.0 Section 3.3 - Flight Crew.

Mission Duration: The duration of the transit mission phase to and from Mars is stated as a maximum of 180 days and a minimum of 120 days in DRM 1.0 Section 3.5.3.1 – Trajectory Type. Minimum transit duration for the piloted modules is desirable; as it reduces the amount of time the crew is exposed to the space radiation environment. A transit time to and from Mars of 130 days and a surface stay of 619 days were used for this LSS design, based on the mission described in (Drysdale 1999), Table 3.9.2.

Mass: DRM 1.0 Table 3-13 provides a mass breakdown of the Mars Transit/Surface Habitat Element. A total mass of 6,000 kg is allotted to the LSS, including a consumable mass of 3000 kg and a dry mass of 3,000 kg. A total mass of 22,500 kg was allotted to “Crew Accommodations”, including a consumable mass of 17,500 kg and a dry mass of 5000 kg. Table A4-4 of DRM 3.0 compares the total mass of each subsystem for the new TransHab design with the original DRM 1.0 figures. The total mass allotted to the LSS for the TransHab option is 4661 kg, and the total mass for “Crew Accommodations” is 12,058 kg. The ratio of these mass reductions was used to scale the mass breakdowns for consumable mass and dry mass provided in DRM 1.0. This resulted in an approximate crew accommodations consumable mass of 9,378 kg for the TransHab option. The total system mass requirement for our design includes the 4,661 kg allotted to the LSS in DRM 3.0, as well as 90% of the crew accommodations consumable mass described above. This resulted in a total mass of 13,100 kg dedicated to the LSS and consumables for the Mars Transit/Surface Habitat. As 90% of the crew accommodations consumable mass was used, the design is required to include things like clothing and disposable wipes in mass estimates.

Power: DRM 1.0 Table 3-15 gives an “Estimated Power Profile for Outbound and Return Transits.” The power allocated to the LSS for the transit phase is 12 kWe for nominal operations. On the surface, a nuclear power plant provides power for the In-Situ Resource Utilization unit (ISRU), as well as the surface habitat. It is assumed that at least 12 kWe will be available to the LSS on the surface, so a maximum power of 12 kWe was used for this design.

Volume: DRM 3.0 pg. 6 states a pressurized volume requirement of 90 m3 per crewmember, resulting in a total pressurized volume of 540 m3. The TransHab option includes an inflatable area of the habitat that will increase the pressurized volume during transit and surface mission phases. Our design uses a pressurized volume of 250 m3 for the TransHab module in unexpanded configuration. The inflatable structure adds 330 m3 of additional livable volume, resulting in a total livable volume of 580 m3. Figure 2.1 illustrates this concept.

Redundancy: DRM 1.0 section 3.2.4 – Risk Mitigation Strategy states that “life-critical systems will have two backup levels of functional redundancy.” Multiple levels of redundancy are built into the mission architecture, as outlined in DRM 3.0 section A2.2.2 – Redundancy

Considerations: The ISRU unit will have produced “enough water and oxygen for the entire surface mission to run open loop.” A second ISRU unit will be landing a couple of months after the crew, and could also be used to provide water and oxygen. If the crew must abandon the surface phase of the mission the ERV will be equipped to support the crew for the duration of the surface stay until the next transit opportunity back to Earth. Finally, a second ERV unit will arrive in Mars orbit a several months after the crew lands on Mars, which could also be used by the crew. During the transit phases the LSS must provide the two backup levels of functional redundancy, as the resources described above will not be immediately available.

2.2  Environment Issues

After the crew makes the six-month transit to Mars, a whole new set of challenges will be awaiting them on the Martian surface. To be sure that the base provides the necessary attributes to support human life, it is important to understand the environment of Mars and the in-situ resources that are available. The transit vehicle’s life support system must be designed using vacuum as the driving design parameter for transit, however, special attention is being paid to analyzing the interactions of the Martian environment since this part of the mission will involve an environment that has not been previously explored by humans.

Physical Parameters of the Martian and Habitat Environments:

With an atmosphere composed mainly of carbon dioxide, temperatures ranging from 170-268 K and surface pressure on the order of only 7.4 to 10 mbars, designing a life support system will be an engineering challenge. Table 2.1 shows surface values for the physical parameters of Martian atmosphere and environment. The physical parameters that are desired for the transit vehicle and habitat are in Table 2.2.

Table 2.1: Physical Parameters of the Martian Atmosphere (Larson 1999)

Table 2.2: Physical Parameters of the Transit Vehicle and Habitat (Larson 1999)

Radiation Concerns:

Although radiation concerns are not addressed in the design of the LSS, they are a major issue that cannot be ignored. Only the sources of radiation and basic exposure limits will be discussed here. Means of protecting the crew is outside the scope of this project and will have to be developed at a later time.

Solar Flares are energized alpha and beta particles that can be blocked with a few centimeters of shielding. A ‘storm shelter’, or elevator sized safe haven padded with food and water stores is sufficient to block this radiation.

Galactic Cosmic Rays cause more of a concern than solar flares. Cosmic rays come from every direction and are constantly present. The heavy, slow-moving atomic nuclei cause much more damage than the alpha and beta particles and are very difficult to block. The penetrating radiation is especially damaging to fast regenerating cells such as DNA, cells and tissues. Several meters of shielding are required to block this radiation.