The commercial LEO Passenger Travel market is becoming real and is beginning to exert a "pull" for products to supply LEO passenger transportation and infrastructure services. The number of companies demanding transportation and infrastructure services is steadily growing. Early passenger loads can be expected to be a mix of business travelers, adventure travelers, as well as crew traveling to the space station. Review of the technical requirements for commercial LEO Passenger Travel have found them to be partially or wholly within the domain of NASA's crew access to space station technical requirements, though often business and operational requirements may conflict. This paper will summarize some of the key requirements which need to be addressed to enable safe, commercial, reliable, affordable passenger access to LEO. The paper will touch on the regulatory and economic factors associated with achieving those requirements. A customer driven Future Space Transportation Architecture (FSTAR) derived from the requirements is presented.

Andrews Space and Technology, under contract to NASA, recently investigated systems engineering transportation requirements for selected future commercial market segments: semiconductor production, tissue engineering, manufacture of recombinant drugs, and LEO passenger travel. The study was undertaken to determine systems engineering transportation requirements, such as orbital destination, mission mass, flight rate, payload parameters, etc. Requirements of each market segment were then reviewed against other market segments to determine where the requirements might intersect and differ. Instances in which the requirements align strengthens the need to implement a particular requirement. Where they differ, the cost of designing to the extra requirements must be weighed against risk and potential return. In the market segments reviewed for this study many of the requirements have been found to be partially or wholly within the domain of NASA's access to space station technical requirements, though often business and operational requirements may conflict.

LEO Passenger Market Characterization Our study found that the commercial LEO Passenger Travel market is real and exhibiting a growing demand for LEO passenger services. Unlike many other opportunities, this market is exerting a "pull" for products to supply LEO Passenger transportation and infrastructure services. During 2000, MirCorp, BrainPool, and NBC's "Destination Mir" television program announced intentions to fly tourists to orbital destinations, many as part of entertainment endeavors. BrainPool, a German television production company, announced that it had signed a contract with Astrium, a subsidiary of EADS (European Aeronautic, Defense and Space Co.) to provide the training, as well as transportation to a space station, for seven contestants on separate missions between 2002 and 2008. Since Dennis Tito's groundbreaking flight to the International Space Station ( ISS) in April 2001, additional interest in tourism spaceflights has emerged. Mark Shuttleworth, a South African computer entrepreneur, has begun training for a flight, while negotiating terms. A Russian rock band, Na-Na, recently announced that it is in discussions to fly two members of their group into space. A Danish and an Australian television production company have each announced interest in entertainment/tourism projects. In September, MirCorp revealed plans to develop and launch a small "space hotel," called Mini Station 1, in 2004. MirCorp has signed an agreement with RSC Energiya to conduct a preliminary feasibility study. Rosviakosmos has given Energiya the go-ahead to conduct the study and report back at the end of the year with its conclusions about the possibility of finding investors and potential clients.

Given that the current market can support demand at US$20 million a ticket (for Dennis Tito), market growth potential is significant. Kelly Space & Technology, as part of their NASA NRA8-27 effort, conducted a survey and placed the demand at 10,000 tourists a year at a ticket price of US$400,000, which would yield annual revenues of US$4 billion at that price point. World wide, the tourism industry has US$1 trillion in annual revenues, with US $200 billion of those coming from adventure travel related activities

Our study was focused on interviews with the airline industry, gauging their interest in the space travel market, and using the interviews to derive market specific space transportation vehicle design requirements. Current US airlines are very aware of the space tourism market, and have been analyzing possible scenarios, should a legitimate launch system be offered. This has not happened to date for a number of different reasons, most of which are related to technical risk and the poor financial showing by the first generation reusable launch vehicle providers.

Figure 1: RLV System Requirements are derived from Market Needs.

Figure 1 illustrates the requirements derivation process. The various attribute/requirement pairs considered in this study were chosen to reflect the needs of the market that is to be served, while maintaining the minimum number of limitations imposed on the transportation system designer. All of the collected attributes were sorted into six major categories, each with a number of subcategories:

1. Scheduling
   • Payload Schedule
   • Operations Schedule

2. Operations
   • Reliability
   • Safety

3. Performance
   • Payload Mass
   • Payload Manifest

4. Interfaces
   • External Infrastructure
   • Payload Accommodations

5. Business
   • Economics
   • Regulatory Agencies

6. Provider Specific
   • Scheduling
   • Operations
   • Interfaces
   • Business

   Requirement values were derived for each individual market segment and the most limiting values distilled based on the investigated markets. Based on the three markets analyzed, the Space Travel market has the most limiting requirements (Figure 2). The current uncertainty of these numbers is significant, but the accuracy of the model will further increase with the collection of additional data.

   
   Figure 2: Market Constraints on Requirements
   LEO Passenger Travel Systems Requirements

   The following requirements reflect information provided by our interviews with two airlines.

   Additional interviews and further analysis are expected to change and refine this data.

   1-1-1 Payload Processing Time
   Time from payload delivery to the carrier to payload being fully integrated into the vehicle.
   LEO Travel Market	6 hours maximum
   1-1-2 Pre-Departure
   Idle Time Time from sealing the vehicle to departure
   LEO Travel Market	6 hours maximum
   1-1-3 Transit Time
   Time from departure to arrival (min/max). This requirement may address the need for loiter times, shelf-live restrictions of components (e.g. batteries), or passenger comfort in addition to product cycle-times or other economical considerations.
   LEO Travel Market	2 h desired, 6 h maximum, 1 week emergency
   1-1-4 Post Arrival Idle Time
   Time from vehicle arrival until the payload is made available to the customer.
   LEO Travel Market	0.5 h desired, 2 h maximum
   1-2-1 Advanced Booking Time
   Maximum and minimum lead time acceptable to the customer when booking a payload manifest.
   LEO Travel Market	Less than 1 week desired, 3 months maximum
   1-2-2 Launch Window
   Maximum delay the system can absorb and still launch successfully.
   LEO Travel Market	2 hours (Next orbit)
   2-1-1 Successful Delivery
   Probability of the vehicle delivering the customer payload successfully and as scheduled.
   LEO Travel Market	98%
   2-1-2 Service Availability
   Probability of a flight being available when requested by a customer (assuming minimum lead-time is observed).
   LEO Travel Market	95% availability
   2-1-3 On-Time Delivery
   Probability of the customer payload departing and arriving on time. Note that this includes the activities of pre and post payload processing, and is thus the probability of the entire system.
   LEO Travel Market	50%, same day delivery
   2-2-1 Emergency Egress
   Any required emergency Egress capabilities for crew, cargo or passengers.
   LEO Travel Market	Demonstrated egress after takeoff failure
   2-2-2 Abort Capabilities
   Any required vehicle, landing site, and operations capabilities for abort scenarios.
   LEO Travel Market	1/10,000 chance of abort failure
   2-2-3 Catastrophic Failure
   Maximum probability of catastrophic system fault (loss of payload) acceptable to the payload customer.
   LEO Travel Market	< 1/10,000
   3-1-1 Payload Mass
   Maximum and/or minimum mass for any single payload to be transported.
   LEO Travel Market	Up to 50,000 lbs to LEO/ ISS (up/down)
   3-1-2 Payload Rate
   Anticipated rate of payload mass transported per year of customer / provider relations.
   LEO Travel Market	Up to 9.3 million pounds per year (up/down)
   3-2-1 Multiple Destinations
   Minimum and maximum number of destinations for a single mission flight.
   LEO Travel Market	1 minimum, possibly 2.
   3-2-2 Multiple Payloads
   Number of payloads and distinct payload types for a single flight.
   LEO Travel Market	Assortment of non-standardized luggage / passengers
   4-1-1 Facility Location
   Desired locations of transit departure and arrival. This is not necessarily identical to the location of payload processing (see 4-1-3).
   LEO Travel Market	Commercial airport type operations
   4-1-2 Infrastructure Attributes
   Types of infrastructure the vehicle is required to be compatible with during nominal operations (commercial airport, spaceport, specific launch ranges, national or geographic locations, ISS, Mir, etc.).
   LEO Travel Market	Airport / on-orbit infrastructure compatibility
   4-1-3 Payload Processing
   Limitations on facility type / location / capabilities (cleanroom specifications, security, passenger amenities, etc.) where the payload is handed to the service provider.
   LEO Travel Market	Luxurious airport accommodations
   4-2-1 Payload Volume
   Range of three-dimensional volume the payload may occupy. Note that a maximum as well as a minimum is of interest, since very small, yet massive and/or fragile payloads are conceivable (high value small crystals, super dense exotic materials, etc) and may require specific accommodations.
   LEO Travel Market	Up to 3,200 cubic feet
   4-2-2 Acceleration Loads
   Level, direction and duration of maximum acceleration sustainable by the payload.
   LEO Travel Market	Max 1.5g (nominal) downmass; Max 3.0g upmass FAR 25.561(3) emergency
   4-2-3 Processing Orientation
   Any limitations on the orientation in which the payload can be loaded onto the vehicle (horizontal vs. vertical).
   LEO Travel Market Horizontal loading / unloading highly desirable
   4-2-4 Data Interface
   Requirements on the type, rate, direction, and interface of data transfers required by the payload while in the supervision of the carrier. Also, specifications for any particular mission segment during which the data transfer is required (if applicable).
   LEO Travel Market	Comparable to current commercial carriers
   4-2-5 Deployment Parameters
   Attitude, rotation rates, and relative velocity requirements (with associated accuracy) imposed by the payload customer for the payload if deployed in flight. (This requirement has no value if the payload is loaded/unloaded at external infrastructures.)
   LEO Travel Market	Comparable to existing launchers
   4-2-6 Shock Environment
   Level and direction of maximum shock loads the payload may be subjected to.
   LEO Travel Market	Comparable to existing launchers
   4-2-7 Vibration Environment
   Level, mode and spectrum of maximum vibration loads acceptable to the payload. This includes the first fundamental resonant frequency for cargo items.
   LEO Travel Market	Comparable to existing launchers
   4-2-8 Acoustic Environment
   Level and spectrum of maximum acoustic loads acceptable to the payload.
   LEO Travel Market	TBD decibels (equal or better than existing launchers)
   4-2-9 Temperature Environment
   Range of temperature and maximum rate of change acceptable to the payload customer. Note that this does not include heat rejection and absorption requirements, which are covered under 4-2-11 "Payload Consumables".
   LEO Travel Market	FAR Part 25 Subpart D Sec 25.831
   4-2-10 Pressure Environment
   Range of pressure and maximum rate of change acceptable to the payload customer.
   LEO Travel Market	FAR Part 25 Subpart D Sec 25.841
   4-2-11 Payload Consumables
   Type, amount and rate of consumables required/rejected by the payload. Including heat, electrical power, fluids (N2, O2, water, etc.) and solids (e.g. food, refuse, etc.).
   LEO Travel Market	H2O, Food & Refreshments
   4-2-12 Structure Interface
   Type and restrictions of the structure interface required by the payload (e.g. Marmon Clamp, Passenger Seat, etc.).
   LEO Travel Market	FAR Part 25 Subpart D Sec 23.783, 23.807
   4-2-13 Atmosphere Composition
   Composition of the atmosphere (if any) that the payload is exposed to during transit.
   LEO Travel Market	FAR Part 25 Subpart D Sec 25.831
   4-2-14 Impact Prevention
   Maximum probability of penetrating debris impact acceptable to the payload customer.
   LEO Travel Market	1/10,000 probability of penetration
   4-2-15 Radiation Protection
   Type and intensity of radiation levels acceptable to the payload customer.
   LEO Travel Market	AEC requirements; NASA requirements
   4-2-16 Illumination
   Level and spectrum of illumination(s) required inside the payload compartment during all mission phases. May include specifications such as "window seats".
   LEO Travel Market	Passenger illumination required, "windows" desirable
   5-1-1 Standardization
   Any customer imposed requirement with the goal of encouraging open standardization as to avoid captivecustomer scenarios
   LEO Travel Market	TBD
   5-1-2 Price Stability
   The maximum percent fluctuation the specific payload price may exhibit over time without disabling the customer business case or product market.
   LEO Travel Market	TBD
   5-1-3 Specific Payload
   Price The price per unit mass of payload delivered to its destination charged by the service provider to the payload customer.
   LEO Travel Market	$500-US$1000 / lb passengers,US$1,750-US$3,000 / lb cargo
   5-1-4 Evolvability
   Requirements on the systems ability to adapt to changing requirements.
   LEO Travel Market	Must be able to meet projected traffic growth
   5-2-1 Regulation
   Required regulatory standards for customer payload accommodation.
   LEO Travel Market	Meet applicable FAA regulations
   5-2-2 Service Globalization
   Any requirements on the international availability of services required by the payload customer.
   LEO Travel Market International destinations and customers
   6-1-1 Turn Around Time
   The total time from the vehicle's arrival to the next scheduled departure. Note that this is not identical with vehicle turn around time, since the requirement states only the limitations on the time-interval between flights, and not how many vehicles are utilized in the entire fleet to accomplish compliance.
   LEO Travel Market	10 days minimum, 56 hours desired
   6-1-2 LRU Replacement
   The time needed to replace any Line Replaceable Unit (LRU) of the system.
   LEO Travel Market	Less than vehicle turnaround time.
   6-2-1 Operations Reliability
   The percentage of the transportation systems intended lifetime during which it is required to operate fault free and with nominal performance within the design envelope.
   LEO Travel Market	Asset utilization 50% or higher
   6-3-1 Support Equipment
   Possible limitations on support equipment interfaces to accommodate legacy infrastructure or COTS availability of system components.
   LEO Travel Market	Maximum utilization of existing infrastructure
   6-4-1 Specific Payload Cost
   Cost to the service provider per unit mass of payload delivered to the designated destination.
   LEO Travel Market	40% below price or less
   6-4-2 Technology Globalization
   Requirements on international accessibility of LRU's and other support equipment (e.g. ITAR or national security restrictions).
   LEO Travel Market	No Data

   LEO Passenger Travel Requirements Discussion

   The system requirements necessary to capture a significant space tourism market are daunting. Chief among these are a very small probability of loss-of-vehicle over its lifetime, on-time launch availability, and a very rapid rendezvous and dock capability. We will take these requirements one at a time and show how they impact the system design.

   Low probability of loss of vehicle - Launch system safety is driven by rocket engine catastrophic failure characteristics. Rocket engines are very highly loaded mechanical/thermodynamic systems confining combustion gases almost as hot as the surface of the sun. Occasional failures are to be expected and significant portions of these failures are catastrophic (i.e. result in an explosion which damages nearby engines and systems). We believe catastrophic rocket engine failures are unavoidable in the foreseeable future and have embraced the aircraft design philosophy of designing the vehicle system to withstand catastrophic failures. This involves discarding vertical launch and taking off horizontally from a runway using wings (This is an easy conclusion, i.e. how many successful vertical takeoff airplanes are there?). One can show that having fault tolerance with respect to engine catastrophic failure instantly reduces the probability of loss of vehicle to 1/20,000 or less which means there is 1/7 chance of loosing a vehicle during its 3000 flight lifetime.

   On-time Launch Availability - Business requires timely delivery of goods and services. This is especially true of the adventure travel market where executive travelers operate on very tight schedules. The airlines view a launch availability of 98% as crucial to capturing and maintaining market share. Current US launch systems don't come close. The Russian systems do, but they are very robust and operate out of a desert environment where hurricanes and heavy rain are not an issue. The solution is robustness and system flexibility. If your launch system can operate out of several sites and move the launch point up range or downrange to avoid weather, then availability is much greater. This is why air-launch has such appeal.

   Rapid Rendezvous and Dock - Space Adventure Travelers who have put up more than US$100,000, are not going to spend 36 hours in a small transfer cabin while plane-change maneuvers take place, nor should they. Airlaunch can make launch windows obsolete and direct ascent trajectories practical. As can be seen, meeting the safety and operations requirements drives an RLV to horizontal takeoff where catastrophic engine failures can be withstood.

   If the business case analysis determines that a particular market should be addressed, the requirements would be folded into the overall vehicle requirements. Figure 3 shows how Future Commercial Market Design Requirements flow down to arrive at a Future Space Transportation Architecture (FSTAR) RLV Solution. Starting with the design requirements gathered from meeting with candidate customers design attributes are derived which enable design requirements to be developed. A series of design trades are completed to arrive at design solutions.

   
   Figure 3: Requirements Flow Down to an Architecture Solution Set

   Air Collection and Enrichment System Andrews Space and Technology, along with a team of subcontractors, have been investigating a variant on an Air Collection and Enrichment

   System (ACES), where air is collected during subsonic cruise using bleed from turbofan engines. We call this variant Alchemist, and data developed so far suggests that it may offer less risk than other airbreathing-to-orbit options, while providing more design flexibility. Without Alchemist ACES, all near-term RLV design options are excessively heavy and large, and therefore more difficult to design, develop and operate. Alchemist ACES may provide the key to improve system margins to increase safety and operability.

   FSTAR RLV Description

   Our research suggests that any pr oposed Future Space Transportation Architecture (FSTAR) should address the commercial LEO Passenger Travel market, and therefore must meet a high flight rate with low cost, having adequate safety and reliability. The high safety and flight rate requirements drive the solution toward a system with airplane type operating modes, redundancy and infrastructure.

   Unlike currently proposed systems, a FSTAR RLV should use an airbreathing / rocket combined cycle propulsion system where the airbreathing and the rocket components operate largely independently. This RLV would be a Horizontal Takeoff, Horizontal Landing ( HTHL) two-stage-to-orbit ( TSTO). Both stages would use LOX / LH2 for rocket powered flight. The second stage, would consist of either an orbiter or an expended cargo carrier, which would ride "piggyback" on the first stage. The combined RLV system would takes off and climb using conventional turbofan engines. Since it does not have LOX on-board, it can meet all airport noise and safety standards. At altitude, the RLV would begin LOX generation and switch the turbofan from JP-8 to gaseous hydrogen fuel, which is a byproduct from the Alchemist system.

   During this process, the combined vehicles can cruise up to 2000 nautical miles, so the system can be based in the southern United States or Europe, and launch over the equator. Once LOX tanking is finished the RLV would take the proper heading, all rocket engines fire, and the combined vehicles began a rapid climb. The turbofan engines are shutdown about Mach 1.3 and the inlets covered. At approximately Mach 6, the propellant cross-feeds disconnect, the first stage throttles back to match the acceleration of the second stage, and the vehicles separate. The first stage then shuts down its engines, and using RCS rotates to high angle of attack (~ 65 degrees) for reentry. With the large planform area and thick wing skins on the first stage it may be possible to design a heat sink Thermal Protection System (TPS) for at least the aerodynamic surfaces. The second stage proceeds to LEO and begins payload operations as required. The second stage is not impacted by Alchemist and is very similar to parallel-burn RLV second stages proposed before.

   Conclusion

   The commercial LEO Passenger Travel market is real and beginning to exhibit a demand for LEO passenger services. Meetings with candidate customers has led to the collection of early transportation vehicle requirements. Preliminary analysis of those requirements, coupled with a revolutionary Air Collection and Enrichment System propulsion approach, suggest that it may be possible to develop a low risk future space transportation architecture which can meet LEO Passenger Travel market requirements.

   References
   1. Federal Aviation Administration, "FAR Part 25 Subpart D - Airworthiness Standards: Transport Category Airplanes - Design and Construction"
   2. Andrews Space & Technology, January 2001, "Future Space Transportation Study" (FSTS), Phase 1: Final Report
   3. Kelly Space & Technology, January 2001, "Space Transportation Market Demand, 2010 - 2030", NRA 8-27 Final Report