Team:Stanford-Brown-RISD/MissionArchitecture
Designing the space mission is an extremely important, yet complicated part of a NASA proposal. The term "Mission Architecture" refers to the overall structure of the mission - beginning with on-Earth preparations, and concluding after setup of our habitats at the destination planet. In this section, we'll go over these considerations chronologically, and emphasize how the different subprojects (glues, filters, etc.) fit into the overall mission plan.
I. Habitat Design
Beginning on Earth, the first task involves manufacturing the plastic shell for our habitats. Our habitat is designed as a three-layered plastic dome.
The outer layer is designed to hold H2O, which can provide some measure of temperature insulation (high specific heat) and radiation protection (due to the high hydrogen-composition, which interacts with harmful primary radiation, while producing less secondary radiation than compounds composed of heavier elements)1,2,3. The supply for the H2O layer will be drawn via melted subsurface ice water at the landing site.
The middle layer is designed to hold cyanobacteria, which can fix compressed CO2 and molecular nitrogen to produce oxygen for our main biomass (the mycelia), as well as for our astronauts to breathe. In addition, these diazotrophic cyanobacteria can produce organic carbon and fixed (biologically usable) nitrogen. In some of our experiments, we show that additional nutrients for cyanobacteria growth can be provided by Martian regolith and small quantities of fertilizer brought from earth. The light for photosynthesis passes through the topmost layer to reach the cyanobacterial layer.
The final layer is designed to hold the mycelia, which provide the structural integrity and additional radiation protection for the habitat. This mycelia can also be functionalized for several other purposes, which you will see in other sections: primarily MycoGlue (to assemble smaller objects), and Filtration (to provide clean water for astronauts).
Note that, between each layer are one-way valves allowing water to flow into the cyanobacteria layer, and cyanobacteria to flow into the mycelial layer (keeping each organism alive).
Figure 1: Habitat Design
Figure 2: Cyanobacteria growing on Martian & Lunar Regolith (special thanks to SSERVI for supplying us with the regolith!)
II. Launch, Travel, and Landing
Once the habitat is designed, built and loaded with mycelial starter filaments and dried cyanobacteria or spores (akinetes), we need a way to get the structures from Earth to another destination (e.g., the Moon or Mars). There are a few rockets we can choose from: the Falcon Heavy6 from SpaceX, and the newly developed Space Launch System from NASA are potential options. The launch site will likely be Cape Canaveral in Florida.
In talking to Prof. Rick Fleeter from Brown University (an industry-veteran and consultant to the Italian Space Agency), he suggested allocating at maximum 80% of the actual rocket payload to the weight of our structures - providing us with a ballpark estimate of how much material we can carry. As other infrastructure is needed for a human settlement, we aimed to be substantially lower.
Once in space, estimated travel time to Mars is approximately 6-7 months, in the closest approach between Earth and Mars (which occurs no less than ~1.5 years apart)2.
Numerous factors need to be considered when choosing a Martian landing site. These include equatorial proximity (to reduce temperature fluctuations on the order of hundreds of degrees between day/night), low altitude (thicker atmosphere allows for easier rocket deceleration, and meaningful quantities of useful gases), and availability of sub-surface water (for use by astronauts).
We first spoke to Dr. Lisa Pratt, NASA's Planetary Protection Officer, to better understand the regulations regarding which types of landing sites are off-limits, or may require additional precautions. Then, based on consideration of these factors, and in talking to Professor Jim Head (an interplanetary mission expert focusing on Mars) from Brown University, we chose as our landing site Deuteronilus Mensae; which in particular, is thought to have ice/water deposits under the surface.
Figure 2: "MOLA shaded relief map of the Deuteronilus Mensae area, with the groundtracks of SHARAD observations shown as yellow lines." Red indicates potential ice detections4.
At destination, our habitats will assemble with the help of robots (the mycelial growth is effectively rate-limited by access to feedstock) on the order of weeks, and will hopefully provide a safe living environment for our astronauts or to enable human colonies on other planets.
III. Cyanobacteria Oxygen-Production Validation
Cyanobacteria play an important role in our structure: serving as feedstock for the mycelia, and producing oxygen for use by astronauts. We wanted to quantify the ability of cyanobacteria to provide sufficient oxygen to sustain a habitat. We chose the strain Anabaena 7120 mainly because it is diazotrophic and photosynthetic, in addition to other favorable qualities for use on other planets5.
Figure 3: Differential Interference Contrast Microscopy Image of Anabaena 7120. Credit: Lynn Rothschild.
Using 425 ml of Anabaena in liquid culture, we used wireless oxygen and carbon dioxide sensors (Vernier Go Direct Series) in an airtight environment to quantify the production of these gases on a short time-scale. We used BD Anaerobic Sachets to achieve a <0.5% oxygen environment, and a 1627 mL Nasco Whirl-Pak airtight bag to maintain a suitable environment.
Given the empirically observed rate of oxygen production from our liquid culture, we reason that it will take ~92 hours (4 days) to achieve 20% oxygen, almost mimicking Earth's atmosphere. This time-frame is certainly reasonable in the context of our mission architecture. (For more details, please refer to the Results page.)
Figure 4: Setup to quantify oxygen production. Credit: Santosh Murugan.
In a separate experiment, we also attempted to grow Ganoderma lucidum (a strain of fungus) directly on Arthrospira platensis (a strain of cyanobacteria). A separate flask of Anabaena provided the oxygen supply. Unfortunately, we have thus far not been successful in showing measurable Ganoderma growth. We believe the Arthrospira culture which was being used as feedstock for the Ganoderma may have had too much water, and the Anabaena culture may also have been too dilute. Future experimentation will hopefully yield more optimal results (one of our mentors, Chris, was indeed successful in growing mycelia on Arthrospira.)
Figure 5: Phase contrast microscopy image of the cyanobacterium Arthrospira. Credit: Lynn Rothschild.
Sources:
[1] USGS. Heat Capacity of Water, www.water.usgs.gov/edu/heat-capacity.html.
[2] Mars Architecture Steering Group. Human Exploration of Mars Design Reference Architecture 5.0 Addendum. NASA, July 2009, www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf.
[3] Space Faring: The Radiation Challenge. NASA, www.nasa.gov/pdf/284275main_Radiation_HS_Mod3.pdf.
[4] Plaut, J J, et al. “THICK ICE DEPOSITS IN DEUTERONILUS MENSAE, MARS: REGIONAL DISTRIBUTION FROM RADAR SOUNDING.” 41st Lunar and Planetary Science Conference (2010), Mar. 2010.
[5] 2011 Stanford-Brown iGEM Team. “Cyanobacteria.” Brown-Stanford IGEM Wiki, Oct. 2011, 2011.igem.org/Team:Brown-Stanford/PowerCell/Cyanobacteria.
[6] “Falcon Heavy.” SpaceX, SpaceX, 16 Nov. 2012, www.spacex.com/falcon-heavy.