. Safe Haven Configurations for Deep Space Transit Habitats
Note about Videos: Atthe right, here's a little introduction to the Kalpana One space settlement, followed by a rotation and fly-past.
1955 Von Braun Space Station
Additional Findings: Every time a new study is done with internal layouts there are additional findings and inputs that warrant consideration in both the requirements and in future design iterations. Here are some of the findings from this study that are noteworthy
1) External viewing: Based on the ISS experien ce there is a preference that windows be provided for external viewing from the habitat as well as cameras for external views of the habitat and approaching vehicles. The EMC Mars transit habitats represented by configurations 1 through 3 include view ports in each of thedocking port hatches, or 5 windows when counting the forward hatch, three radial hatches, and a standard Window Observational Unit in the 4th radial port position. The remaining views were planned to be covered by high definition cameras and internal screens. Configurations 4 and 5 did not include radial ports, so one Window Observational Unit was provided in a radial position and a forward and aft view port in each docking
hatch were included. It is not clear if these provisions are sufficient for the mission duration planned, and so further consideration is recommended.
2) Propulsion systems: Habitat configurations 1 through 3 were pre-integrated with a large hybrid propulsion system for the initial transfer to cis-lunar space. The hybrid system includes a large solar electric propulsion (SEP) system,6 so some avionics and most of the power systems are on the propulsion element. Once in cislunar space the habitat is loaded with logistics and the hybrid propulsion system is re-fueled in preparation for the crew’s journey to Mars. The greater length of configurations 4 and 5 precluded the pre-integration of the hybrid system so an alternative chemical system was utilized. It includes a small integrated propulsion system for the initial transfer from Trans-Lunar Injection (TLI) to cis-lunar space where it is then loaded with logistics and berthed to chemical propulsion stages for the transfer to Mars. In Mars orbit the habitat berths with another set of propulsion stages that have been pre-deployed for the return trip. All avionics and power systems are integrated as part of the habitat element.
3) Power systems: The power requirements for all configurations were about the same since they all had similar requirements to support 4 crew for 1100 days. Habitat configurations 1 through 3 draw power from the solar arrays provided by the SEP system on the hybrid propulsion stage, whereas configurations 4 and 5 utilize a set of deployable solar arrays sized for the habitat power requirements in Mars orbit.
4) Thermal systems: The thermal requirements for all configurations were also about the same since they had similar thermal loads. Each utilized both passive and active systems with body mounted radiators. The possible exception of note is configuration 4 where the diameter of the larger module is the same as the core stage. Several options were discussed including the use of body mounted radiators with an aero shell for protection during launch, enclosure in a 10 m diameter payload fairing, or deployable radiators located inside the fairing on the smaller safe haven module.
5) Waste management: A noted benefit for the full duration safe haven is that a second waste management compartment is also included.
6) Stowage systems: Long-term stowage of food is a concern in the radiation environment of space and may require greater utilization of refrigeration and freezer units than currently planned. In addition, the impact on food packaging and life support consumables if exposed to vacuum is not fully understood. Duplicate stowage was not considered in the mass estimates for these safe haven configurations and so additional research is needed to confirm that packaging and food stores can survive the potential for explosive decompression and cold when going to vacuum. All configurations were found to have limited packaging volume except configuration 4. Configurations 1 through 3 and 5 required a higher packaging density than currently used on ISS. Acceptable packaging densities need to be confirmed.
7) Research systems: All configurations used a reduced mass and only one research station in the layout for
research systems. Concern over the reduction of research equipment and associated volume along with the packaging density concerns for stowage are among the reasons for exploring the larger volumes shown in
configurations 4 and 5.
8) Concept of operations: A detailed concept of operations for safe havens is needed to examine a variety of scenarios where their use might be required to prevent loss of mission and/or loss of life. Going through the concept of operations analysis should help generate better requirements that can be applied to more detailed design solutions.9) Interior layouts: Configuration 1 uses a vertical layout on two deck levels with open circulation between levels similar to the way Skylab was designed. Large crew quarters are provided in a horizontal orientation for the bunk area with the intent of applying this design towards surface habitats and artificial-g configurations. Configurations 2 and 3 are the same, but the open space is restricted by the addition of a bulkhead/dome and an IVA airlock. Configurations 4 and 5 use a horizontal layout on three deck levels with vertical circulation through each end dome. The layout is intended for in-space use only so the crew quarters
are in a vertical orientation with sleeping bags on the walls as done in the ISS crew quarters. In general, the
vertical layout appears to provide more open public space for the small volume provided, whereas the
horizontal layouts appear to provide more private spaces and improved packaging efficiency. The packaging efficiency improvements include opportunities for additional workstations, easier access to stowage along the outside walls, and a separate utility room as opposed to packaging utilities under the floor in the end domes. In addition, the vertical layouts locate the crew quarters around the perimeter whereas the horizontal layouts locate the crew quarters in the center of the module providing the possibility for maximizing radiation protection using stowage and habitation systems.
Structures: The internal bulk shown in Configuration 2 was found to be nearly three times more massive than a standard end dome due to the requirement for supporting pressure loads from either side which places the dome in a possible tension or compression load. As a result, it was found that there is little mass difference between a pressure vessel with an internal bulkhead and two separate pressure vessels. The bulkhead design provided a more compact solution but requires an additional airlock for EVA access outside the habitat. The dual pressure vessel solution offers simpler manufacturing, possible use of the IVA airlock for EVA access too, but is much longer and less compact. In total, the additional structures mass was found to be around 1700 kg for both bulkhead and dual pressure vessel options.
Avionics: Most of the internal avionics, consisting primarily of communications and data handling equipment, was duplicated to provide a complete system inside each pressure vessel. It was noted that the highest risk for pressure loss would be from collision during docking operations when communications, data handling, and vehicle controls would be critical. In total, the additional avionics mass was found to be around 742 kg.
Findings and Recommendations
The primary mass drivers for the safe haven were found to be in structures, avionics, and the life support system, which totaled about 3000 kg for a 30-day safe haven and about 5000 kg to 6000 kg for a full duration safe haven.
Safe Haven Configurations for Deep Space Transit Habitats
Smoke, fire on board, as well as pressure loss or a collision with another spacecraft during docking or undocking operations could provide For Mars missions, ground operations will be limited, quick return impossible.
So, the risk of a collision during deep space missions could yield disastrous results, such a loss of mission and a loss of crew for transit habitat designs without safe haven capabilities.
The safe haven concept was inspired to help to resolve these issues by determining the mass impact for providing a second pressure vessel that the crew could move into to give them time to recover from a mishap, and designed in a configuration that could be launched efficiently on the Space Launch systems (SLS).
Configurations considered included a single pressure vessel with an internal bulkhead, dual pressure vessels of the same size, and a primary pressure vessel with a second smaller unit for the safe haven.
Life support options included duplicate closed loop life support systems for full duration in either volume, and a single closed loop life support system in the primary volume with an open loop life support for 30-day duration in a smaller secondary volume.
The concept study start with the Mars Transit Habitat base-lined in the Advanced Exploration Systems, the Evolvable Mars Campaign.
The Configuration A (CA) is the standard single volume monolithic habitat planned for Mars missions in the 2030s, which includes an advanced closed loop life support system designed to support 4 crew for 1100 days. In the Configuration B, it is an upgraded version of CA, which required a little more volume for stowage, uses structures and end domes based on current SLS manufacturing standards, and uses current life support systems from the International Space Station (ISS).
The interior layout for the monolithic design is arranged in a vertical orientation on two deck levels. The lower deck includes all of the crew systems for research, vehicle controls, galley, exercise, and waste management. The life support systems are located below the floor in the lower end dome. Translation from the lower deck to the upper deck is through a large opening in the center of the module providing a more open layout approach. The upper deck includes the four crew quarters with stowage packed in between and around the quarters to further enhance radiation protection for the crew.
Configuration 2, shown in Fig. 2, has the same exterior appearance as configuration 1b but creates a safe haven by installation of an internal bulkhead between the upper and lower decks with an intra-vehicular activity (IVA) airlock, and a duplicate closed loop life support system that provides for full duration capability in either volume. The crew systems are split between the two deck levels to minimize loss if evacuation from one side is required. Each level includes two crew quarters and about half the stowage, a split in the crew systems functions, and a complete life support systems packaged in the decks over the dome and bulkhead for each level.
In the event of pressure loss in one side, duplicate life support and avionics are provided on each side to sustain life for the full duration and provide communications and vehicle control systems on each side. In concept, the IVA airlock provides passage through the bulkhead for transfer of stowage and equipment needed for the duration of the flight. Conveniences like research equipment, hygiene, and exercise, might be lost or downgraded in one side or the other, but with access to the unpressurized volume it is believed that operational workarounds can be found to resolve life sustaining issues.
Internal and external repairs might be possible so the habitat is designed for both internal and external access to the pressure vessel walls. The interior uses a modular pallet system that can tilt up from the floors above the domes and away from the walls. An external inflatable airlock is also available at one of the radial hatches (not shown), to provide EVA crew access to the entire pressure shell for repair operations.
When configurations 1b and 2 are compared the basic increase in mass for a full duration safe haven can be found. It came to 5,969 kg, which included 1700 kg for the additional structure required for the internal bulkhead and airlock, 742 kg for the duplicate avionics required for each volume, and 3,527 kg for the duplicate life support system. So, for around 6,000 kg it seems reasonable to assume that a full duration safe haven can be provided in most Mars transit habitat designs that will protect the crew from smoke, fire, and pressure loss for the duration of their mission. The advanced life support system planned for the 2030s included in the EMCs Configuration 1a is about 1000 kg lower in mass, which would bring the total impact of the safe haven mass down to only 5,000 kg.
These estimates do not include duplicate food stowage systems. It is assumed that the crew will be able to pass through the internal airlock to collect the supplies they need. Which, also assumes that the stowed provisions are not permanently damaged by exposure to smoke, fire, or vacuum. These operational details and concerns are part of the recommendations for further analysis of safe haven concepts.
Configuration 3 shown in Fig. 3 is the same as configuration 2, but uses two pressure vessels of equal volume. When configuration 3 is compared to configuration 2 it was found to be about 300 kg more massive, all attributable to the additional structures mass. This comparison indicates that manufacturing simplifications for configuration 3 may be worth further investigation for the dual pressure vessel option.