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Due to the growing international recognition of the academic activities on space tourism by the Japanese Rocket Society ( JRS) with the vehicle's name of Kankoh-maru, the Transportation Research Committee has decided to study safety standard for designing space tour vehicles as a third phase research program. The reason is clear why the establishment of the safety standard is necessary. There must be clear promises to space line companies that this kind of commercial transportation system is fundamentally safe in design for passengers. Thus the "spaceworthiness" is to be provided now.
The Japanese aviation regulations have been established by the Civil Aircraft Bureau of the Ministry of Transportation in 1952. The third phase study has begun to review the airworthiness that are specified for the airplane category type T and the rotorcraft category type TA/TB. Then the applicability to space tour vehicles has been assessed. Since the space tour vehicles are operated beyond the regimes in speed and altitudes of subsonic and supersonic aircraft, the certification regulations are to be tailored, modified and added with new issues of environmental conditions during exo-atmospheric and reentry flight.
Concerning safety, there is a fundamental difference in design between conventional rockets and space tour vehicles. Since the expendable rockets are designed based on the piling of the reliability of onboard components, the launch success is expected by the figure of probability. If an accident occurred, the rocket will be destroyed by the command from ground for the safety of residents. On the other hand, deterministic safety is required for the space tour vehicles not only by the reliability approach of redundant system but also by the abort operation for the unexpected subsystem failure. The space tour vehicles primary consider the safety of passengers and will never be destroyed.
The Transportation Research Committee has employed an idea of "integrated certification process" that the space tour vehicles are to be designed with "built-in" safety margins based on the existing commercial aircraft's fail-safe design rule. It must be the shortest way of realizing commercial space tour to inherit the property of the aircraft's safety philosophy.
A Study Conference on Space Tourism was first held on April 14 1993, as a part of the JRS Annual Meeting in Tokyo. At the suggestion by Professor Nagatomo of ISAS (the Institute of Space and Astronautical Science), the theme "Space Tourism" was then selected as an academic research program of the JRS.  Soon the Transportation Research Committee was established to prepare a conceptual design of a vehicle suitable for space tour, which has been led by Kawasaki Heavy Industries. The committee includes members from Japanese major aerospace industries, such as Mitsubishi Heavy Industries, Fuji Heavy Industries, Nissan Motor Company, All Nippon Airways, Teisan. The ISAS, the National Development Agency (NASDA) and Japan Aircraft Development Agency (JADC) have also been participated in the meeting of the committee as observers.
The Transportation Research Committee has already seven years in its history of Space Tourism study. Now the activity has got into the third phase.
A reference model of the space tour vehicle was studied in the first phase of the study program from 1993 to 1994 in order to study passenger service, medical aspects and business development (Fig. 1). The model capable of carrying 50 passengers resulted in a takeoff weight of 550 tons and a body length of 22m (Fig. 2). 
In the next study program phase, the Transportation Research Committee prepared a detail development schedule in detail including the total development and manufacturing cost. 
The cost estimation result was then transferred to the Business Research Committee, who studied the issues of vehicle operations. The cost study, which was based on a large extent on the development cost of the Japanese H2 rocket and on the experience of aircraft development in the past, has been first evaluated using a cost engineering model by Koelle. 
Due to the growing international recognition of JRS Space Tourism study program with the vehicle's name of Kankoh-maru, it was decided to continue it in the third phase. In order to deliver such kind of space tour vehicles into commercial based market and into passenger transportation services, it has been gradually recognized that the establishment of a regulation is necessary for certifying their safeties. The selected main subject by the Transportation Research Committee was to give considerations on the safety standard for the space tour vehicles, which will be operated for future commercial manned space transportation, in contrast with the existing airworthiness of Japanese aviation regulations. 
THIRD PHASE STUDY PLAN
The purpose of the third phase study is to propose "a draft of the safety standard that will be applied to future commercial manned space vehicles". The Transportation Research Committee has begun to review the existing Japanese aviation regulations that specify the airworthiness of airplanes and helicopters, which have been established by the Civil Aircraft Bureau of the Ministry of Transportation.
It is obvious that the safety standard adopted for the transportation airplane or helicopter, such as FAR (Federal Aviation Regulations), is the most reliable and completed in the present knowledge of science and technology. It is also an international standard based on many actual lessons learned and accidents in the past. Therefore the Transportation Research Committee has employed an idea of "integrated certification process" that the space tour vehicles are to be designed with "built-in" safety margins based on the existing commercial aircraft's fail-safe design rule. It must be the shortest way of realizing public space tour to inherit the property of the aircraft's safety philosophy.
The lessons learned by reviewing the airworthiness of aircraft gave us an amount of considerations what are going to be needed for certifying space tour vehicles with the same reliability and safety level as the current commercial aircraft is required.
Since the space tour vehicles operate beyond the regimes in speed and altitudes of subsonic and supersonic aircraft, the certification regulations are to be tailored, modified and added with new issues of environmental conditions during exo-atmospheric and reentry flight. The issues of safety standard that are unique for space transportation have been discussed and listed.
The Transportation Research Committee is now working on arranging the draft of the safety standards, which will be expected to become a regulation model of "spaceworthiness". The final report of the research is going to be summarized soon at the end of the year 1999 (Fig. 3)
JAPANESE AVIATION REGURATIONS
The Japanese aviation regulations were first established in 1952, which cover all the types of aircraft for piloted airplanes, rotorcrafts, gliders and air-ships.
The original model of the regulations was completed based on the FAR containing flight, structure, design/construction, power plant, equipment and operating limitations/information. The aviation regulation applied to the category of airplane is equivalent to the FAR Part 25, and that of rotorcraft corresponds to the FAR 29.
TECHNOLOGICAL CULTURE GAP BETWEEN ROCKET AND AIRPLANE
Frontier Spirit and Commercialization
As the committee meeting proceeds, members become aware that there are plenty of different way of thinking in design between rocket and aircraft. It could be called a "culture gap" of technology.
Rocket engineers used to develop expendable and unmanned vehicles for National programs, which contribute Japanese science and technologies. The frontier of science and technology runs always risks. It is sometimes emphasized that the space development is one of the noblest activities, as more dangerous it becomes.
On the other hand, the aircraft engineers are familiar with the development of commercial product. Risks that lessen the safety must be avoided using already proven and reliable technologies. The Civil Aircraft Bureau of the Ministry of Transportation does not allow those aircraft, which is suspected unsafe, to fly. The manufacturers are accused of accidental homicides in injury or death for criminal liability. They can be also charged with defect production or design failure for civil action. The product liability is severe.
One has to make it clear that the activity of manufacturing manned space tour vehicles for commercial use is completely different from that of noble academic space exploration aimed at science and technology development.
It is impossible for those who are ambitious of space tourism commercialization to go against the times back to the early age of acrobat show with airplane, or the transatlantic adventure flight of Lindbergh. The customers desire as more reliable and safe space tour vehicles as the modern aircraft promises.
Reliability and Safety
The mission success of rocket launch can be estimated merely by the reliability calculation. Thus the loss probability of the rocket is directly the figure of failure rate or the reciprocal number of reliability. This means that the rocket is launched by "probabilistic operation" for launch success (Fig. 4).
The airplane design consists of three issues of quality engineering (Fig. 5). The first one is safety engineering, the next one is reliability engineering and the last one is maintenance engineering.
The purpose of maintenance engineering is to improve the rate of operation by taking accessibility and easier exchange of failure part into account. The reliability engineering aims at cost effectiveness considering how optimal MTBF (Mean Time between Failure) should be for the total life cycle. The safety engineering is the most important design issue not to cause human injured for both the passengers and residents.
Even though the safety engineering is based on the reliability engineering, the rate of hardware failure critical for vehicle loss is extremely improbable by redundancy design.
The airworthiness basically requires safe operation even for the case that the subsystems or components of airplane get out of order. Thus the aircraft generally does not get into dangerous condition in case of subsystem failure and must withstand structural defect until the next inspection or overhaul time. It can be said that aircraft aims at "deterministic operation" for safe fligh (Fig. 6).
TYPICAL SAFETY STANDARD ISSUES FOR SPACE TOUR VEHICLES
Although the existing aviation regulations do not cover all the issues of space flight design, production, test and evaluation, and operations, the new regulations for the space tour vehicles should first start with the basis of what is required for the commercial aircraft concerning fail safe design and maintenance. The aircraft has been succeeded in the business of commercial passenger transportation with adequate reliability and safety.
The authors agree with Gaubatz's idea on the "integrated certification process" that the space tour vehicles should be designed with "built-in" safety margins using existing commercial aircraft fail-safe design rules and method. 
The Space Transportation Committee has conducted to assess the applicability of the Japanese aviation regulations specified for the airplane category type T and the rotorcraft category type TA/TB to space tour vehicles. The study focuses on the vertical takeoff and vertical landing type, such as "Delta Clipper" of former McDonnell Douglas and Kankoh-maru of JRS (Fig. 7). The summary of the assessment study shown in Table 1 is that for the airplane category type T.
General description of regulation
New vehicle types must be first defined according to launch and landing configurations. There are three candidates of space tour vehicles now. The first one is a vertical takeoff and vertical landing type ( VTVL). The next one is the vertical takeoff and horizontal landing type ( VTHL) like "Venture Star". The last one performs horizontal takeoff and horizontal landing ( HTHL) as future aerospace plane aims at.
The design standard for space tour vehicles should specify environmental conditions especially critical for space flight. Unique issues are vacuum environment, space radiation, space debris and meteoroid, which must be taken into account for long duration of space flight.
The airplane is required safe takeoff including accelerate-stop and landing in case of one-engine inoperative condition. In order to specify the performance, critical speeds such as V1, VR, V2 and runway length must be determined (Fig. 8).
Since the VTVL space tour vehicle has no wings, the operation will be significantly different from that of the airplane. The particular airworthiness with respect to the issues for takeoff and landing must be modified or newly defined (Fig. 9).
It is also an important issue to specify abort operation unique for orbit injection, such as RTLS (Return to Launch Site), TAL (Transoceanic Abort Landing), AOA (Abort One Around) and ATO (Abort to Orbit).
Space tour vehicles will be operated with highly autonomous flight control and management system. Thus the requirements for hybrid controllability by both the aerodynamic surface and engine control including engagement of pilot must be carefully discussed.
In addition to the aerodynamic loads, static and dynamic loads originated from propulsion, such as static acceleration, sine wave vibration, random vibration and pogo pulsation, have to be introduced. The heat load suffered during reentry flight, and low temperature condition of orbital flight and cryogenic propellant must be also taken into account.
Structure test using full scale airframe is usually conducted to prove strength and fatigue requirement of aircraft. Since space tour vehicles will be larger compared with that of aircraft, the compliance with the structure requirement using the full scale vehicle must be carefully assessed.
One of the critical design requirement for Kanko-maru would be the attitude to protect occupant under emergency landing on land or water (Fig. 10). Another airworthiness that the maximum seating capacity can be evacuated from the vehicle within 90 seconds might be also a severe requirement for Kankoh-maru with the passenger deck on the top.
Since the life of space tour vehicles is considered short compared with that of aircraft, the rocket engineer has to go into detail discussion on the applicability of damage-tolerance design and fatigue design to space tour vehicles (Fig. 11).
Design and Construction
In addition to the issues of materials, various design factors, flutter and bird strike required for airplane, critical design environments for space flight must be supplemented. Out gas in vacuum environment, material deterioration by space radiation and protection of space debris/meteoroid must be considered.
Requirement of emergency provisions for orbital flight, landing on ground and water could be one of the critical design issues. The cabin must be designed so as to make the occupant easier to escape.
The airworthiness requires that the powerplant of airplane, which includes engines and all the necessary propulsive units, must satisfy, engine isolation, fuel system independence, restart capability and fuel jettisoning for safe go-around.
Generally airplane has independent tank for each engine onboard, but can make cross-feed of propellant from another tank to other engines in case of tank failure. If the necessity of propellant tank independence for each engine is required for space tour vehicles, the realization of tank structure will be a most critical design issue. This requirement would certainly leads to a certain amount of weight penalty (Fig. 12).
Since the VTVL type space tour vehicle has completely different flight profile, many requirements of equipment installation will be reconsidered. Navigation equipment for space flight and initialization instrument in orbit are the new requirements. Rearrangement of light must be also reviewed. Fasten equipment is necessary onboard for microgravity operation.
In order to establish crew and passenger safety for emergency, additional safety equipment must be requested. In case of accident in orbit, airlock, rescue capsule or life boat, and space suits will be required.
Operating Limitations and Information
As discussed, operation limitations are completely different from those of airplane. Thus the flight manual will be newly furnished. And marking and placards must be designed for additional space flight equipment.
GUIDELINE OF SPACEWORTHINESS
As a provisional result of the third phase study, the spaceworthiness content is listed in Table 2 for the vertical takeoff and vertical landing type vehicle.
Part I - Vertical Take-off and Vertical Landing Vehicles
Section 1. General
Section 2. Flight
Section 3. Stricture
Section 4. Design and Construction
Section 5. Powerplant
Section 6. Equipment
Section 7. Operating Limitations and Information
Part II - Propulsion
Part III - Reaction Control System
The regulation is divided into three parts, the first of which specifies the safety design issues of the vehicle design, the second part deals with the propulsion and the third with the reaction control system. 
It is believed that the present study program by the Transportation Research Committee of JRS on the safety standard of space tour vehicle is one of the important steps to realize the commercialization of space transportation. 
The members of the research committee become aware that there is a deep culture gap between rocket and aircraft design. If we want realize true space tour vehicle, it is unnecessary to run risk for adventure. We have to understand that manufacturing manned space vehicles is completely different from that of noble activities such as academic space exploration for science and technology development.
The airworthiness, which is one of the most scientific and reliable design standard for today's commercial transportation, teaches how different the deterministic safe flight of airplane is from the probabilistic launch operation of rocket.
We believe that the safety standard required for the certification of space tour vehicles does not restrict their design, but changes the fundamental operation process from probabilistic launch to deterministic takeoff and landing with enough reliability and safety like aircraft. Thus it is increasingly recognized that the existing legal/regulatory environment needs also to be reformed for promoting the commercial passenger flights to and from space. 9
The authors are grateful to the persons concerned with the Space Tourism study of the Transportation Research Committee ; especially Professor M. Nagatomo (ISAS), Associate Professor Y. Inatani (ISAS), Mr. Y. Naruo (ISAS), Mr. A. Watanabe (NASDA) and Dr. P. Collins (NASDA) for their kind advises and useful discussions.