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Commercial Space Tourism and Space Weather

2007; American Geophysical Union; Volume: 5; Issue: 8 Linguagem: Inglês

10.1029/2007sw000333

1542-7390

Ronald E. Turner,

Space Science and Extraterrestrial Life

Space tourism, a concept that even a few years ago was perceived as science fantasy, is now a credible industry. Five individuals have paid up to $25 million each to spend more than a week on the International Space Station. Bigelow Aerospace, a company hoping to build the first commercial space station, has launched a prototype, subscale version of an orbital, inflatable module, a precursor to a full-scale habitable orbital module that may be launched in the 2010–2012 time frame. Other space tourist contenders are also making progress toward first launch. For example, Rocketplane Kistler is developing and building a fully reusable, two-stage orbital launch vehicle capable of serving multiple markets, and is providing expertise toward a reusable vehicle for the suborbital tourist market. Virgin Galactic, building on the success of Burt Rutan's X-Prize-winning SpaceShipOne, is on the verge of launching suborbital flights and has already sold tickets at $200,000 each for their first flights. Space tourism is expected to be a booming industry. In a talk at this year's Space Weather Week in Boulder, Colo., Virgin Galactic estimates they will have flown over 8000 customers into space by the year 2020. Futron Corporation, a market analysis firm that specializes in space commerce, recently released a report suggesting that the worldwide market for suborbital flight would exceed 10,000 people by 2020 [Futron Corporation, 2006]. In light of this, the Federal Aviation Administration's Office of Commercial Space Transportation (AST) released regulations in December 2006 authorizing the transportation of commercial passengers for the first time [Federal Aviation Administration (FAA), 2006]. The emergence of space tourism now presents new opportunities and new responsibilities for the commercial space weather community, as the space tourism operators will rely on accurate and timely space weather forecasts. Adverse space weather can interfere with communications, damage sensitive electronics, and affect orbit lifetime. With adequate consideration, preparation, and appropriate caution, none of these impacts needs to be severe. General techniques for commercial missions designed to ensure communications, minimize hardware failure, and maintain optimal orbit can be drawn from the extensive experience of the aerospace community. Further, a description of space weather monitoring activities needed to support space tourism, as well as U.S. exploration of space, can be found in a recent National Research Council report, “Space radiation hazards and the vision for space exploration” [National Research Council Space Studies Board, 2006]. Though damages to spacecraft from adverse space weather can be costly, protecting tourists and crew from harmful radiation is of paramount concern to those overseeing space tourism. This article focuses on potential radiation-induced human health risks inherent in space tourism and suggests appropriate countermeasures to mitigate these risks. Operational space weather monitoring support to human space flight is the domain of government entities such as the NOAA Space Environment Center and the NASA Space Radiation Analysis Group, with help from a wide range of other government and industry resources. These groups watch for three distinct natural sources of space radiation that will affect the crew and passengers of commercial space missions: trapped radiation in the Earth's magnetosphere, high-energy, low-flux galactic cosmic radiation (GCR), and periodic, lower-energy, extremely high flux solar particle events. Particles within the trapped radiation belt peak in density at altitudes significantly above the normal altitude for human space flight. Nonetheless, trapped radiation from the South Atlantic Anomaly (SAA), a low-altitude region of enhanced radiation density, may still affect tourists and crew. Each orbital mission will have four to six transits of the SAA per day, contributing to about half of the background radiation exposure expected for orbital space tourists. GCR are energetic but very low flux particles that originate outside our solar system. While GCR are attenuated by the Earth's magnetic field at low orbital altitudes, this radiation will contribute the remaining half of the background radiation exposure. Further, the Earth's magnetic field tends to shield low-Earth-orbiting spacecraft from the impact of solar particle events. However, the poles are accessible to incoming energetic solar particles. High-inclination orbits would expose the crew and passengers to these particles during polar cap transits. For more information about space weather impacts on space flight, see National Research Council Space Studies Board [1999, 2006]. The cumulative effect of exposure to ionizing radiation is a function of total dose, location and distribution of the dose within the body, rate of accumulation of the dose, and types of ionizing radiation that produce the dose. A high dose over a short period can lead to acute effects such as headaches, nausea, and skin “burns.” In extreme cases, the effects of high dose rates can be severe, either directly through radiation sickness or indirectly, as from vomiting in a space suit. A lower dose over a prolonged period can have long-term impact, including increased risk of cancer, effects on genetics or fertility, development of cataracts, and cumulative damage to tissue (particularly the central nervous system, digestive system, cardiovascular system, and immunological system). For further discussion of the radiation hazards, see National Research Council Space Studies Board [1999, 2006], National Research Council [1996, 2002], and National Council on Radiation Protection and Measurements [1989, 1993, 2000, 2006]. While there is no doubt that exposure to significant levels of radiation will increase the probability of cancer, there is substantial uncertainty in quantifying the details, largely in the biological effects of radiation [Cucinotta et al., 2002]. Sources of uncertainty include but are not limited to a lack of understanding of the causative chain of events from exposure to cancer; the difference between the space environment and terrestrial exposure experience; and a lack of directly relevant data (most case histories are based on weakly ionizing radiation, as opposed to the highly destructive ionizing particles in the space environment). Until very recently, conventional wisdom has held that 20 cSv (equivalent dose) exposure increases the probability of a fatal cancer by 1 percent [National Council on Radiation Protection and Measurements, 1989, 1993, 2000]. NASA has moved away from this paradigm to a confidence interval approach incorporating uncertainties [Cucinotta et al., 2002]. However, a 20 cSv per percent increase in cancer is still a useful rule of thumb if used with caution. According to the National Cancer Institute [National Cancer Institute, 2003], an average American's lifetime risk of dying from cancer is 23 percent for males and 20 percent for females. A detailed look at two candidate space tourists–a 50-year-old white male ("Bob”) and an average 30-year-old female race-averaged from the general population ("Alice”)–helps to illustrate these risks. Again referencing the National Cancer Institute [National Cancer Institute, 2005], Bob has a 7.4 percent chance of developing some cancer and a 2.1 percent chance of dying of cancer before his 60th birthday, while Alice has a 1.5 percent chance of developing some cancer and a 0.2 percent chance of dying of cancer before her 40th birthday. The typical U.S. population annual exposure to radiation is less than 0.5 cSv per year. Radiation worker limits are generally less than 5 cSv per year, and until recently, astronaut limits were 50 cSv per year. Figure 1 [Cucinotta et al., 2002] gives the cumulative experience of U.S. astronauts through 1999, and from the figure we see that measured total-mission exposure has ranged from 0.1 to 10 cSv. The exposure rate varies with altitude, inclination, solar cycle, solar activity, vehicle shielding, vehicle orientation, and location within the vehicle. Figure 2 shows that mission-averaged rates have ranged from 0.01 to 0.4 cSv per day [Cucinotta et al., 2003]. One can now make estimates of the space-flight-related excess cancer fatalities per 10,000 tourists. Assuming a 1-hour suborbital flight, at orbital exposure rates, the equivalent dose would be of the order of 0.002 cSv, leading to 0.01 lifetime fatal cancers among 10,000 tourists. Exposure after 1 week in orbit would range from 0.1 to 1 cSv, leading to 0.5 to 5 lifetime fatal cancers among 10,000 tourists. Compare these numbers with 740 incidences of cancer, 240 of them fatal, within 10 years for a pool of 10,000 Bobs; similar numbers for Alices are a bit better: 150 incidences of cancer, 20 of them fatal, for the same time period and sample size. The Federal Aviation Administration recently established requirements for human space flight as mandated by the Commercial Space Launch Amendments Act of 2004, including rules on crew qualifications and training, and informed consent for crew and space flight participants [FAA, 2006]. The requirements, effective 13 February 2007, provide an acceptable level of safety to the general public and ensure that individuals on board are aware of the risks associated with a launch or reentry. Section 460.45 of the rule requires an operator to inform each space flight participant in writing about the risks of the launch and reentry, including the safety record of the launch or reentry vehicle type. In addition, an operator must present this information in a manner that can be readily understood by a space flight participant with no specialized education or training, and must disclose in writing the following: (1) for each mission, each known hazard and risk that could result in a serious injury, death, disability, or total or partial loss of physical and mental function; (2) that there are hazards that are not known; and (3) that participation in space flight may result in death, serious injury, or total or partial loss of physical or mental function. Further, before flight, an operator must provide each space flight participant an opportunity to ask questions orally to acquire a better understanding of the hazards and risks of the mission, and each participant must then provide consent in writing that indicates that the participant understands the risk and that his or her presence on board the launch vehicle is voluntary. Note that these rules are specifically for launch and reentry, not the orbital phase, as it is not yet clear which regulatory organization is responsible for the time in orbit. The radiation environment of space is not explicitly handled in the FAA regulations. The closest reference is in a discussion of the Environmental Control and Life Support Systems (ECLSS). Among the factors that should be considered are severity of the hazards, likelihood for catastrophic or critical consequences of exposure, potential for rapid or large changes in conditions, and availability of practicable in-flight measurement techniques and devices. It appears the FAA believes it makes more sense to issue ECLSS guidelines and to refine them with industry input over time as operators gain experience. This approach may also be the practical approach to radiation exposure regulations. It is interesting to note that the FAA has much less stringent requirements for the crew. Section 460.9, “Informing crew of risk,” says only “an operator must inform in writing any individual serving as crew that the United States Government has not certified the launch vehicle and any reentry vehicle as safe for carrying flight crew or space flight participants.” Such forecasts could be accomplished by monitoring alerts and warnings from the NOAA Space Environment Center, along with a commercially provided space-weather interpretation specific to the launch operator. Characterizing nominal expected exposure prior to the mission and validating these estimates may be the most difficult tasks, as these require good environmental models and observations at difficult altitude and latitude ranges and a good transport code with adequate representation of the vehicle geometry. The model will need sufficient precision to represent the relatively small dose expected. There are a variety of detectors that could be used for the validation. There are several radiation monitoring devices that could be worn by the passengers and crew to meet the need for personal monitoring. To be most useful, these devices should provide more than an integrated dose, but rather should be able to produce a dose history, perhaps from the time the passenger initially arrives for preflight training through the final postflight processing. Clearly, a system to provide end-to-end space weather prediction and in situ radiation monitoring will be needed in the era of commercial orbital space flight when the exposure, while tractable, will far exceed terrestrial background levels. It will also be critical for suborbital flights, if only to follow through with due diligence and to be consistent with a policy of informed consent. Monitoring systems will also be a valuable resource for the operator should otherwise spurious lawsuits be filed claiming the radiation exposure during flight was the cause of a subsequent cancer or other adverse health impact. Space weather has long been recognized as relevant to society's many and varied terrestrial activities. As society itself expands into the frontiers of space, the space weather community must be prepared to welcome increasing roles and responsibilities to ensure the safety of these intrepid pioneers. Ronald Turner is a Fellow with Analytic Services, Inc. (ANSER), based in Arlington, Va.