The aim of this thesis is to determine the requirements for deflecting hazardous asteroids and comets, commonly known as Near-Earth Objects, or NEOs, that are on a collision path with the Earth. Since currently NEO that is predicted for Earth impact does not exist, the analysis is conducted by devising two hypothetical impact scenarios, one for an asteroid encounter, and another for comet encounter, using fictitious NEOs. Choice of the parameters assigned for the hypothetical scenario is justified through investigation of literature about NEO physical and orbital properties and detection systems, allowing realistic and reasonably accurate analysis to be conducted. This executive summary outlines the findings.
♦ NEO is categorised into two main groups; Near-Earth Asteroid (NEA) and Near-Earth Comet (NEC). NEA is further grouped into Aten, Apollo, Amor and Inner Earth Object (IEO), and NEC is categorised as short-period comet (orbital period of less than 200 years), and longperiod comet (orbital period of greater than 200 years)
♦ Through use of statistical models and past impact data, population of NEA is estimated to be several million for 500 m-class, 1000 to 2000 for 1 km-class, and less than hundred for diameter greater than 1 km. Currently, approximately 75% of 1 km-class NEA have been discovered and characterized. NEC population has not been well-characterized due to their approach to inner solar system being very rare, and their orbital properties making them difficult to detect. However, it is estimated that total NEC population is approximately 1% of the population of NEA.
♦ NEA impact probability is estimated to be once every 70,000 years for 500 m-class, 1 million years for 1 km-class and 100 million years for 10 km-class. As NEC population has not been well understood, impact probability for NEC has not been accurately defined, however, it is suggested that it is 1% of the NEA impact probability.
♦ Investigation of appropriate literature about NEO observation and physical properties, typical value of its density is between 2 to 5 g/cm3, and orbital semi-major axis of 1 to 1 AU, and eccentricities between 0.2 and 0.6. For NEC, based on the observation data of general, nonhazardous comet population, density is estimated to be between 0.2 to 0.8 g/cm3, and typical orbital semi-major axis of 4 AU and eccentricity of 0.8 for short-period comets, and 40 AU and eccentricity of 0.98 for long-period comets.
♦ Current detection systems are capable of predicting the NEO’s orbit trajectories to several centuries into future once detected. Reasonable information about its physical properties can be obtained with current optical and radar observation equipment. Therefore, since NEA population is well understood, and it is easier to detect and characterize, 15 years warning time is set for hypothetical NEA encounter. Of this lead time, 5 years allocated for mitigation mission planning and development of required equipment, and 10 years for actually applying the deflection action. However, for NEC case, where they are only detected typically at 1 AU from the Earth, only 2 years warning time is assigned, allowing 1 year for preparation and another year for applying the deflection action.
♦ Based on the above findings, the velocity change required to deflect 500 m, 1 km and 10 km NEAs by 2 Earth radiuses in 10 years action time is found to be 1.5 cm/s. For NEC of same diameters, this value is approximately 8 cm/s, where time allowed for deflection is only 1 year.
♦ The analysis considered both short-term impulsive and long-term slow-push option for deflecting the incoming NEO. The methods include; nuclear detonation and kinetic impactor for impulsive approach, mass driver, focused solar ablation, focused laser ablation, gravity tractor, attached thrusters, and utilization of enhanced Yarkovsky effect. The analysis found that stand-off nuclear detonation is the most effective and practical option considering the system requirements, mass, and the amount of NEO characterization needed. The amount of nuclear explosive yield needed for NEA deflection is 23 Kt TNT, 190 Kt TNT and 190 Mt TNT for diameters 500 m, 1 km and 10 km respectively. For NEC case, the values are 126 Kt TNT, 1 Mt TNT and 1 Gt TNT for diameters 500 m, 1 km and 10 km respectively.
♦ The mitigation mission would be carried in 2 stages; first transport the equipment to the lowearth orbit using a launch vehicle, and then using the on-board electric propulsion system, perform a Hohmann orbital transfer to reach the target NEO.
♦ The total payload mass range, which includes the mass of the nuclear devic, propulsion system, propellant and other support equipment, is 3,000 to 3,600 kg for 500 m and 1 km diameter NEAs, 3,200 to 7.500 kg for 500 m and 1 km diameter NECs, 43,000 to 60,000 kg for 10 km diameter NEA, and 210,000 to 500,000 kg. These payload masses are within the current launching capabilities except for 10 km NEC case, where further advancement is required.