Dream Chaser Integrated Spacecraft and Pressure Suit Design

45th International Conference on Environmental Systems ICES-2015-117 12-16 July 2015, Bellevue, Washington

Dream Chaser® Integrated Spacecraft and Pressure Suit Design

Kenneth J. Stroud1 Sierra Nevada Corporation, Louisville, CO, 80027

Shane E. Jacobs2 David Clark Company Incorporated, Worcester, MA, 01604

The new era of commercial human spaceflight offers the opportunity to develop new technologies while applying lessons learned from the past. The Dream Chaser spacecraft and the full pressure suit proposed for use by its crew members tie the past to the present in both spacecraft and pressure suit design, in order to maximize crew safety. Sierra Nevada Corporation’s (SNC) Dream Chaser spacecraft is a state-of-the-art reusable lifting-body vehicle that traces its heritage to NASA’s HL-20 lifting body spacecraft design. Due to its design, SNC’s Dream Chaser operates similar to the space shuttle, including the ability for crewmembers to bailout of the spacecraft if an atmospheric contingency is experienced. To protect against rapid cabin depressurization during ascent and entry, as well as the low atmospheric pressure during bailout, each Dream Chaser crewmember will wear a full pressure suit, along with other integrated crew survival equipment. The suit, designed by David Clark Company Incorporated, is a light-weight pressure suit specifically designed for Dream Chaser operations, with heritage in the Contingency Hypobaric Astronaut Protective Suit (CHAPS) and the S1034 pressure suit design that is currently flown by U-2 pilots. As part of maximizing crew safety, several lessons learned from the Space Shuttle Columbia accident and subsequent Columbia Accident Investigation Board (CAIB) report are incorporated into both the Dream Chaser spacecraft and pressure suit designs. These lessons learned include considerations for optimal integration of the suit, seat, survival equipment and cockpit, accommodations for extended visors-down time, and use of a conformal helmet providing significantly improved head protection. In addition, the Dream Chaser spacecraft design requires a vertical climb between the ingress hatch and the cockpit in the launch configuration, which is facilitated by pressure suit design features. Together, the integrated design and development of the Dream Chaser spacecraft and the pressure suit provide next generation human spaceflight capability and safety.

Nomenclature AGL = above ground level +Gz = acceleration in the upward direction; “eyeballs down” in-lb = inch pounds MSL = mean sea level ppO2 = partial pressure of oxygen psia = pounds per square inch absolute psid = pounds per square inch differential

I. Introduction N July 11, 2011, the Space Shuttle Atlantis landed at Kennedy Space Center, and the United States O relinquished its capability to fly astronauts into space. The U.S. currently has to rely on the Russian Soyuz space capsule to transport NASA astronauts to the International Space Station (ISS), at a cost of over $70 million per seat - more than triple the cost the Russians charged NASA before the end of the Space Shuttle Program in 2006. In order to reduce cost and end U.S. reliance on Russia for transporting American astronauts to space, NASA

1 Crew Systems IPT Lead, Dream Chaser Program, 315 CTC Blvd, Louisville, CO 80027 2 Softgoods Design Manager, Research and Development, 360 Franklin St. Worcester, MA 01604

© 2015 Sierra Nevada Corporation created the Commercial Crew Program (CCP) in 2010 with the goal of transporting crews aboard U.S. spacecraft to the ISS by 2017. At the same time, several corporate and privately-funded space programs have been in development, ranging from air-launched suborbital spacecraft to balloon systems and specialized pressure suits. As part of CCP, Sierra Nevada Corporation (SNC) developed the Dream Chaser spacecraft to transport astronauts and cargo to the ISS. Dream Chaser is a reusable, optionally piloted, lifting body spacecraft that launches vertically on an Atlas V rocket and lands horizontally on a conventional runway. The winged design and vehicle operations of Dream Chaser are reminiscent of the space shuttle, from which several lessons have been learned and applied. To protect against a myriad of hazards, including a cabin depressurization during the mission, Dream Chaser crewmembers will wear full pressure suits, developed by David Clark Company Incorporated (DCCI). DCCI, a pioneer in aerospace crew protective equipment and the designer and manufacturer of the Model S1035 Advanced Crew Escape Suit (ACES)[1] (and precursor Model S1032 Launch Entry Suit and Model

S1030A Ejection Escape Suit worn by shuttle crewmembers throughout the Figure 1. Model S1034 Pilots program) has been developing pressure suits for a number of commercial Protective Assembly space applications, including Red Bull Stratos[2]. DCCI has also developed the lightweight Contingency Hypobaric Astronaut Protective Suit (CHAPS) to address the specific and unique requirements of the commercial space market. The Dream Chaser Pressure Suit (DCPS) is based largely on lessons learned from the CHAPS, the ACES, the Red Bull Stratos suits, and the S1034 pressure suit design that is currently flown by U-2 pilots (Figure 1). Unique features from each of these suit systems have been identified and optimized for Dream Chaser applications. The DCPS represents the culmination of design lessons learned from high-altitude full pressure suits with bailout capability. Additionally, a strong focus has been placed on the integrated design of the DCPS with the Dream Chaser spacecraft, such that the suit is an integral component of the vehicle’s many subsystems to which the suit interfaces, including the seats, the life support system, displays and controls, and ingress and egress paths. This paper describes the overall process of developing and integrating the designs of the Dream Chaser spacecraft and pressure suit. To this point, this effort has included the definition of a spacecraft-suit architecture that includes lessons learned from other space flight and aircraft programs, and ingress and egress testing to validate the architecture and provide inputs into the detailed design for both spacecraft and suit. Detailed design has not been completed, and is currently on hold.

II. Dream Chaser Operations The diverse crew activities onboard Dream Chaser, from pre-launch to post-flight as well as emergency scenarios, drive the need for a robust system to support the astronauts performing those tasks. Dream Chaser crew operations begin during ingress of the vehicle while it sits in the vertical position on the launch pad, where crewmembers must ingress a hatch on the dorsal side of the vehicle, and climb up into their seats while wearing pressure suits. Astronauts must also be able to exit on their own in an emergency.

Dream Chaser ascent operations are automated, with astronauts monitoring vehicle trajectory and systems. Atmospheric entry operations are also Figure 2. Dream Chaser launch automated, with the optional ability for the pilot to manually land the vehicle in case of an anomaly. Similar to the space shuttle, Dream Chaser astronauts also have the ability to bail out of the aft hatch while wearing a parachute to land safety on the ground or into the ocean in an emergency. To protect against a loss of cabin pressure during ascent, astronauts wear pressure suits.

On orbit operations for Dream Chaser vary greatly depending on the mission. For a mission to transport crew to a space station, Dream Chaser operations would primarily be focused on rendezvous and docking, which would likely occur within one or two days of launch. Other missions could include free flight, where Dream Chaser operations are focused on scientific experiments or other mission tasks (robotics, servicing, observation, etc.) and may include different numbers of crewmembers on orbit for different durations. If a depressurization were to occur during a free flight orbital phase where crew are unsuited, astronauts would don their suits while preparing for deorbit and landing. Before return to Earth, astronauts again don pressure suits to protect against a potential loss of cabin pressure. Although the g-forces during entry in Dream Chaser are minimal (about +1.5 Gz), long-duration crewmembers could lose consciousness during the return to Earth without countermeasures because of their weakened cardiovascular system after living in microgravity for several months. To protect against loss of consciousness during entry, long-duration astronauts must be able to sufficiently recline or be recumbent during entry to ensure that the heart can adequately pump blood to the brain. The time from deorbit burn to landing is approximately 70 minutes, during which the Pilot monitors trajectory and subsystems, able to take over manually during an emergency. Upon nominal landing, astronauts “safe” the vehicle so ground personnel can approach and ingress the vehicle to assist the astronauts out of their seats and the vehicle. In the event of an emergency landing where astronauts must exit the vehicle quickly, they must do so unassisted which requires opening the hatch and jumping down approximately four feet to the ground. Alternatively, they may exit the dorsal hatch on top of the vehicle, and jump to the ground near one of the wing’s leading edges about five feet above the ground.

III. Spacecraft and Pressure Suit Integrated Design Due to its similarity to the space shuttle in many respects, including the ability to land on a runway, Dream Chaser is the benefactor of several lessons learned from the Space Shuttle Program. However, Dream Chaser also has some important inherent differences.

A. Ingress and Egress While the habitable volume where astronauts live and work is comparable between the two vehicles, the space shuttle crew cabin was short and wide with two decks, and Dream Chaser is long and narrow with a single deck (Figure 3). This makes packaging of hardware, including life support equipment, crew seats and cargo, and crew ingress and egress challenging. With no discernible aisle between crew seats and life support equipment and cargo, the only path between the hatch and the cockpit is over folded seats. To reach the cockpit seat while the vehicle is in the vertical position on the launch pad, the Pilot must climb approximately 12 feet over folded seats while wearing a pressure suit, without a helmet. Astronauts use handholds and footholds to climb from the hatch to their seats and, to prevent falling greater than a few feet

Figure 3. Full scale Dream Chaser crew cabin mockup. The while climbing in the vertical launch orientation, forward portion separates and rotates to vertical for launch they can be tethered to hard points in the vehicle pad scenarios ingress path. In a launch pad emergency, astronauts would have their helmets and gloves on, and would likely not have time to attach and detach tethers during their climb down to the hatch and will instead rely solely on footholds and handholds. Suited space shuttle astronauts did not have to climb up or down while ingressing the spacecraft, and unpressurized suit mobility was sufficient for the limited movement that was required. However, with the need to climb within a limited ingress and egress path in Dream Chaser, unpressurized suit mobility is much more important. To ensure that crewmembers can perform these tasks, the DCPS is designed to be as low bulk and lightweight as possible, to enable unpressurized mobility comparable to that of shirtsleeves. A lightweight liquid cooling vest and a slim, mechanical counter pressure orthostatic intolerance garment eliminate much of the bulk associated with the anti-g suit and liquid cooling garment used with the shuttle ACES.

Softgoods-based mobility joints designed into the elbows and knees of the suit provide excellent pressurized mobility, and ensure the necessary easements for the crewmembers to climb over and around seats and cargo when pressurized or unpressurized. Joint torque data for the DCPS Tucked Fabric elbows is shown in Figure 4. EMU data from Dionne [3] is shown for reference. The data shows that the DCPS elbows can be bent at 4.3 psid through the full range with less than 40 in-lbs of torque, and can be bent to 90 degrees with less than 20 in-lb. Straightening the elbow requires Figure 4. Elbow flexion torque for the DCPS Tucked Fabric elbows only 11 in-lb. Both DCPS and EMU data sets were obtained with the elbows pressurized at 4.3 psid, for comparison purposes. The integrated design of the DCPS, parachute harness, seat and seat restraints also eliminates a set of connections that would otherwise need to be disconnected in the event of an emergency egress. Additional lessons learned from other programs [4] were leveraged for the design of the DCPS, to optimize ingress and egress operations. The DCPS employs a conformal helmet that attaches to the suit at a suit-to-helmet disconnect, which employs a bearing (Figure). The visor of the conformal helmet is designed to provide the crewmember with the entire fixed- head field of view. One significant benefit of the conformal helmet in this application is that the helmet moves with the crewmember’s head while turning the neck. Since the visor provides the entire fixed-head field of view, and the visor is fixed relative to the head as it moves, the helmet does not limit the crewmember’s field of view in any direction, enabling the best possible visibility as the crewmember climbs out of the vehicle during an emergency egress. For cockpit operations, the design includes a torso posture adjustment zipper to keep the head properly positioned relative to the torso while seated and pressurized. This zipper is an alternative to the standard helmet hold-down system, which includes webbings that present a snag hazard. A conformal helmet also offers greater head protection from falls, sudden accelerations and projectiles, as compared to a non-conformal helmet where the head would contact the internal helmet surface, leading to injury. The helmet is designed to accomodate head sizes up to the 95th percentile male. Smaller head sizes are accommodated through the use of five different insert sizes for optimal fit. One potential drawback of the conformal helmet is the inability to include a Figure 5. Baseline conformal helmet Valsalva device to aid crewmembers in clearing their ears during pressure changes. However, many existing and historical programs that use a conformal helmet, including the U-2 and SR-71, rely on other techniques for ear clearing, which can be trained. The gloves for the DCPS are also designed to enable climbing and smooth ingress and egress (Figure 6). Twelve sizes of gloves ensure a near-optimal fit for each crewmember, while embedded silicone in the palms and finger pads ensures the necessary tactility and grip. Most critically, the gloves present minimal bulk and enable the crewmember to grab hand holds and other egress aids. The wrist disconnects are extremely lightweight (~8 ounces for the pair) ensuring that the crewmember is not burdened by bulky weights at the ends of the arms. A new feature

that was added to the DCPS gloves allows interaction with capacitive touch screens, which may be used with procedures. Finally, the boots of the DCPS are designed to enable simple and timely vehicle ingress and egress. In other similar programs, a standard aviator flight boot has been used. These boots are heavy, bulky, and not optimized for this application. Climbing through tight areas and over seats and cargo is extremely difficult with heavy, bulky footwear. The DCPS boots are much lighter weight while still providing the necessary foot and ankle protection and integrating to the pressure suit. The sole of the boots provides a tactile surface for the crewmember to accurately sense their foot position while climbing through the vehicle. Ingress and egress testing was performed in the full-scale Dream Chaser crew cabin mockup with participants wearing S1034 pressure suits (Figure 7). Although heavier than the DCPS, the S1034 was used based on its similarity to the DCPS design and its availability for use in testing. The purpose of the tests was to evaluate the integrated Dream Chaser cabin and Figure 6. Baseline DCPS gloves DCPS design in relation to the performance of time critical and volume driving tasks. In particular, the type and location of ingress and egress aids, and how they integrated with the DCPS, was evaluated. Twenty participants, representing a wide range of critical anthropometric measurements, including stature and shoulder breadth, performed five different ingress and egress scenarios. These scenarios included assisted launch pad ingress, unassisted launch pad egress, bailout, unassisted landing egress after launch abort and unassisted landing egress with a deconditioned crew configuration (reclined/recumbent seats). The bailout scenario required participants to egress the mockup while wearing a parachute harness with a life preserver and a shuttle Personal Parachute Assembly (PPA). To perform launch pad scenarios, the front portion of the mockup rotates to the vertical position and crewmembers ingress and egress through a hatch on the dorsal side. Because these initial mockup evaluations were performed to evaluate vehicle and DCPS design and ensure the safety of participants, versus testing against requirements, the participants were instructed to perform their tasks slowly and carefully. Despite being performed more slowly than would be expected in an actual event, all scenarios were able to be safely performed by participants, often within or close to their required times. For example, unassisted pre-launch Figure 7. Egress testing in Dream Chaser crew and post-landing egress for the entire crew was required to be cabin mockup with the S1034 pressure suit accomplished within 90 seconds. During testing, unassisted post-landing egress with a deconditioned crew configuration was accomplished within 52 seconds, and unassisted launch pad egress within two minutes and five seconds, each after a single familiarization run. This integrated testing validated that the DCPS and Dream Chaser design were compatible for ingress and egress and informed potential modifications to both designs for enhanced safety and efficiency of operations.

B. Cockpit Operations Unlike the Space Shuttle cockpit that seats both a commander and a pilot, Dream Chaser’s minimal number of controls and high degree of automation allow for a single, centered pilot seat design. During ascent, the pilot monitors trajectory and systems, and during atmospheric entry may also need external views for the landing phase. While the Dream Chaser can perform an automated entry and landing, the ability for the pilot to take over manually in the event of an emergency is provided. Space shuttle pilot seats included inertial reels that would allow the commander and pilot to lean forward and sideways when in the unlocked position, but would restrain the crew upon exposure to rapid acceleration, similar to automobile seat belts. The CAIB report cited the failure of these inertial reels to restrain the crew upon exposure to slow-onset acceleration that led to severe injuries on Space Shuttle Columbia on flight STS-107. While inertial reels were required on the space shuttle to allow the commander and pilot to reach all of the cockpit switches while

© 2015 Sierra Nevada Corporation seated, the Dream Chaser cockpit design includes a much smaller number of switches and other controls, which are all placed such that crewmembers of all sizes can reach them in a fully restrained position, thus eliminating the need for inertial reels. In addition, the views out the window for a piloted entry and landing are provided in the restrained position. In addition to optimized cockpit layout, the design of the DCPS maximizes crew reach. To ensure that seated and restrained crewmembers can reach and actuate all required controls in the cockpit, the DCPS provides crewmembers with adequate mobility of the arms, legs and fingers in both the pressurized and unpressurized states. The integrated design of the DCPS, parachute harness and seat further ensures optimal reach and seated position for cockpit operations. Given the different visual tasks in the cockpit, the pressure suit helmet must provide adequate field of view. As noted above, the DCPS includes a conformal helmet that fixes the visor relative to the astronaut’s face, which improves field of view as compared to a non-conformal helmet. The space shuttle’s ACES helmet was non- conformal, meaning that the crewmember could turn their head within the helmet, resulting in them looking into the opaque side of the helmet. Crewmembers could use their hands to grab the helmet and rotate it with their head, but clearly this is non-optimal for this application. The conformal helmet allows the helmet to rotate with the crewmembers head, keeping their hands free for other activities. The compatibility of the DCPS gloves with capacitive touch screens enables crewmembers to use tablets and other touch screen devices within the cockpit, which may be used to minimize the bulk typically associated with manuals, procedures and checklists.

C. Cabin Depressurization Loss of cabin pressure can lead to injury including decompression sickness (DCS), trauma to the ears, lungs and other air-filled cavities, hypoxia and even death. The greatest risk of depressurization is during ascent and entry, and therefore crewmembers wear full pressure suits to mitigate consequences. To protect against a cabin depressurization in an orbital emergency scenario, Dream Chaser carries additional breathing gas that would be released into the cabin to “feed the leak”, in order to delay depressurization, or reduce the depressurization rate caused by a small hole until the vehicle can deorbit and enter the atmosphere. To reduce the Figure 8. Dream Chaser on orbit risk of barotrauma, the rate of depressurization must be minimized, which is largely accomplished with the vehicle’s “feed the leak” capability. To reduce the risk of DCS, the final pressure must be maximized, which is accomplished by a combination of vehicle and DCPS pressurization. To reduce the risk of hypoxia, a minimal partial pressure of oxygen must be maintained, which is accomplished with a combination of vehicle and DCPS pressure, and breathing gas makeup. The DCPS is designed to provide crewmembers hypobaric protection in the event of any cabin depressurization, rapid or otherwise. The current design pressure for the DCPS is 3.5 psia, although this pressure is being evaluated. This provides the required partial pressure of oxygen (when breathing 100% oxygen), while minimizing suit delta pressure to maximize pressurized suited mobility. As ascent and entry present the greatest risk of cabin depressurization, it is imperative that crewmembers be sealed in their suits, visors-down, during these most dynamic and dangerous flight segments. To enable a longer period (~30 minutes during entry) of visors-down capabilities within the vehicle, the systems design choice was made to supply the crewmembers with Nitrox (30% oxygen, 70% nitrogen) during these mission phases, as opposed to 100% oxygen, as was used in the Space Shuttle Program. Prolonged visors down operations in the shuttle with the open loop ACES breathing system could result in dangerously high ppO2 (partial pressure of oxygen) levels in the shuttle cabin. This potential forced space shuttle astronauts to raise their visors within two minutes after launch and terminate the flow of O2 into the suit. It also greatly limited visors-down time during entry to prevent cabin oxygen levels from exceeding fire hazard limits. While the DCPS is also an open-loop system, the use of Nitrox instead of 100% oxygen ensures that cabin oxygen levels remain below acceptable limits for a longer duration, keeping the crewmembers in the visors-down configuration that will protect them from a cabin depressurization with minimal crew actions. Alternatively, a closed-loop pressure suit architecture would prevent expired gases from

© 2015 Sierra Nevada Corporation entering the cabin, but create other hazards. Specifically, a leak in one crewmember’s suit in a closed-loop architecture, where all suits are connected to the life support system in parallel, would cause the pressure in the other crewmembers’ suits to also decrease. Locating and isolating such a leak would be difficult and time-consuming, during a period when time is critical. In the event of a cabin depressurization during ascent or entry, crewmembers would not need to take any actions at the suit to maintain pressure, as they would already be sealed in their suits, with gloves on and visors-down. The dual-suit controller, located on the right (as-worn) abdomen of the suit, automatically maintains the 3.5 psia pressure within the suit. However, the gas supplied to the suit would need to be switched from Nitrox to 100% oxygen, to prevent hypoxia. This could be done by the crew or be automated. While the use of Nitrox during nominal operations ensures that cabin oxygen concentration is minimized, it is not adequate for maintaining the required partial pressure of oxygen to the crew at lower absolute pressures. At absolute pressures below 2.7 psia, 100% oxygen is necessary to provide the required partial pressure of oxygen to prevent hypoxia, which can lead to performance decrements and loss of consciousness. If the crew were required to perform this function while breathing Nitrox in a 3.5 psia suit, they would have one to two minutes of useful consciousness to so do. While crewmembers could experience a drop in ambient pressure from 14.7 psia to 3.5 psia in a full cabin depressurization, the Dream Chaser “feed the leak” capability could keep the cabin pressure higher for up to several hours, depending on the size of the leak. Even with a full cabin depressurization, the risk of decompression sickness (DCS, or the “bends”) is reduced with the anticipated short duration that crewmembers would spend at 3.5 psia. In the event of a cabin depressurization, the vehicle would land as soon as possible. The duration crewmembers would have to spend at 3.5 psia depends on the phase of the mission that the cabin depressurization occurs. If the depressurization occurred during entry, the vehicle and crewmembers are already returning to the higher pressures of Earth’s atmosphere, and hence will only be at 3.5 psia until they can get below 35,000 feet MSL. If the event occurred during ascent, different abort modes are possible, each leading to different durations at 3.5 psia for the crewmembers. Return to launch site or transatlantic aborts would ensure very minimal durations for the crew to be at 3.5 psia. The worst case (longest duration) would be an abort once around (an abort to orbit is not an option with a compromised vehicle structure), which would lead to a partially depressurized cabin for up to 2 hours, though the time spent at 3.5 psia would be reduced as the cabin would be maintained at 8 psia for as long as possible, during which time the crewmembers would be breathing pure oxygen. If DCS were to occur, breathing 100% oxygen at full atmospheric pressure or greater (i.e. in a hyperbaric chamber) would likely be sufficient to treat the condition [5]. Additional protection against DCS, in the form of a pre-launch or pre-landing pre-breathe of 100% oxygen, similar to what is done before a spacewalk or a U-2 mission, was considered. However, this could take up to several hours of unbroken pre-breathe before launch and landing, and would raise cabin oxygen concentrations beyond safe levels given an open-loop pressure suit architecture. Further research is required to quantify DCS risk, but it is likely minimal given the probabilities associated with this scenario. A higher suit operating pressure, closer to 5psia, would provide additional protection against DCS but would slightly reduce pressurized mobility, and increase oxygen consumption. This trade is currently being evaluated.

D. Bailout In the highly unlikely event that Dream Chaser is unable to reach a runway after an ascent abort or during entry, the vehicle provides bailout capability through the aft hatch. To ensure a safe bailout, crewmembers must be protected against hypoxia at altitude and provided with parachutes and water survival gear for landing. While only supplemental oxygen is required for bailouts below 40,000 feet MSL, additional hypobaric and cold protection is required for higher altitude bailouts. Above ~63,000 feet MSL (Armstrong’s Line), a pressure suit is required to provide the necessary pressure on the body to prevent bodily fluids from boiling. Above 50,000 feet MSL, a pressure suit is required to provide the necessary partial pressure of oxygen to the lungs. Between 40,000 feet MSL and 50,000 feet MSL, pressure breathing is required to provide the necessary partial pressure of oxygen; however a pressure suit serves the same purpose without requiring the crewmember to pressure breathe. The pressure suit also protects the crewmember from the extreme temperatures found at these high altitudes. During the Red Bull Stratos program, Felix Baumgartner successfully demonstrated bailout from 127,852 feet AGL while wearing a DCCI pressure suit similar to the DCPS (Figure 9). Through the Red Bull Stratos test program and the final test flight, the technologies needed for this type of high altitude bailout were developed and proven out. The DCPS leverages these technologies, providing Dream Chaser crewmembers with the greatest protection possible in the event that they need to bailout.

To enable a safe and successful bailout, the design and operation of Dream Chaser must also be considered. The location of the aft hatch at the back end of Dream Chaser makes bailout safer and a less complex operation than it was on the space shuttle, which required deployment of the escape pole out of the side hatch, and astronauts to attach to clips on it to ensure they would be safely dropped below the left orbiter wing. A clear path must exist between the seats and the aft hatch, which drives the location of items in the cabin, which is already narrow. In order to open the inward- opening hatch without pyrotechnics, the cabin pressure must first be equalized with the atmospheric pressure using equalization valves, which takes longer with higher altitude. Since the DCPS’s operating pressure is 3.5 psia, it will “feel” pressurized and limit mobility as the external (e.g. cabin, atmospheric) pressure drops

below 3.5 psia. To ensure the astronauts are able Figure 9. Felix Baumgartner demonstrates high-altitude to move easily through the small egress path in bailout in a pressure suit. Technologies developed during the pressure suits, it’s desired that the cabin pressure Red Bull Stratos program will be leveraged for Dream does not drop below 3.5 psia. Since the cabin Chaser must equalize with the external atmosphere before the hatch can be opened, this means that the hatch is opened at around an altitude of 35,000 feet MSL where atmospheric pressure is 3.5 psia. In case crewmembers need to begin egressing the vehicle before their suits are depressurized, mobility joints in the elbows and knees of the DCPS provide near shirtsleeves range of motion, even at 3.5 psid (refer to Figure 4 above). Additionally, the dual-suit controller, as described above, maintains a constant absolute pressure in the suit, not a constant differential pressure. As the ambient pressure increases, the suit differential pressure decreases, which comes with an associate increase in mobility. Therefore, at very high altitudes, the suit differential pressure will be near the absolute pressure of 3.5 psia, with near vacuum ambient conditions. However, as the Dream Chaser descends, the suit will automatically begin to depressurize, while maintaining the absolute pressure in the suit, hence the required partial pressure of oxygen. If, for unforeseen circumstances, crewmembers need to bailout at altitudes higher than 35,000 feet MSL, they will not be forced to move a pressurized suit at 3.5 psid, but at a lower pressure depending on their altitude. An additional benefit of this suit feature is that the crewmember does not need to think about depressurizing the suit once below 35,000 feet MSL, and will never have to contend with trying to land under parachute in a fully pressurized suit. To provide the required partial pressure of oxygen to maintain crewmember consciousness once they have bailed out, the DCPS provides 100% oxygen at its operating pressure of 3.5 psia using oxygen bottles that are integrated into the parachute harness. The DCPS helmet and oxygen delivery system are demand-based, which

limits consumable usage just to that which is Figure 10. Dream Chaser test vehicle at wheels stop required. This enables significantly longer duration bailout scenarios, for a given oxygen bottle size, as compared to a continuous flow system. The relatively low operating pressure also maximizes consumable consumption time. The DCPS must be integrated with several pieces of hardware for bailout, including a parachute, water survival equipment, radio and location aids. Given that the Dream Chaser ascent trajectory is largely over water, each crewmember must wear a life preserver unit and carry an individual life raft. Location aids include a beacon, which may be integrated with the radio, and other items including flares, sea dye marker, strobe lights, mirrors and chemlight sticks. To ensure that an unconscious crewmember is protected in a bailout, several functions are automated including parachute opening, water activated parachute release and life preserver unit inflation.

IV. Conclusion Human spaceflight is on the verge of becoming a commercial venture. With that comes the ability to capitalize on new technologies while including valuable lessons learned from previous space and related programs. The combination of spacecraft and pressure suit provide crewmembers their only protection from the hazards of spaceflight, which have to date largely been developed independent of each other. Where previous aircraft and spacecraft pressure suits have generally been integrated into vehicles after the vehicles have been designed and even operating, the parallel development of the Dream Chaser spacecraft and the Dream Chaser Pressure Suit provides the best opportunity to create integrated designs to enhance human spaceflight capabilities and safety. Continued research into lessons learned and state-of-the-art advancements will be integrated into both the vehicle and pressure suit to ensure the most safe and efficient design for all portions of Dream Chaser crew operations covering all mission scenarios.

Acknowledgments The authors would like to thank NASA for funding much of this work through the Commercial Crew Integrated Capability (CCiCap) Program. Specifically, we would like to thank Dustin Gohmert, Dick Watson and Rick Ybarra for their support during the ingress/egress testing. We would like to thank all of our colleagues at Sierra Nevada Corporation and David Clark Company Incorporated for their technical support.

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