# Internet of Spacecraft for Multi-Planetary Defense and Prosperity
## 4 Planetary Defense: State-of-the-Art
### State of the Art Space Objects Detection
#### 4.3.3 On-Ground Observatories  
One of the possible and feasible strategies is to deploy more survey stations dedicated to discovering more asteroids/comets, which are not only categorized as NEOs but also are located in more distant regions. When reviewing the current near-Earth asteroid discoveries by survey, as illustrated in Figure 16, a majority of NEA discoveries have been made by Arizona-based Catalina and Hawaii-based Pan-STARRS since 2011. The Catalina Sky Survey uses three telescopes: a 1.5 m f/1.6 Cassegrain reflector telescope on the summit of Mount Lemmon (around 2791 m), a 68 cm f/ 1.7 Schmidt telescope near Mount Bigelow, and a 1-m f/2.6 follow-up telescope also on Mount Lemmon. Furthermore, the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS) is located at Haleakala Observatory, Hawaii, US, and consists of two 1.8 m Ritchey-Chretien telescopes on the summit of Haleakala (also known as East Maui Volcano) which has an elevation of 3055 m. The construction of both telescopes was funded by the U.S. Air Force and the NASA Near-Earth Object Observation Program. Both locations offer ideal observation conditions; for example, the air pollution and light pollution are minimal, the air density is significantly lower, the annual precipitation is extremely low, and the temperature fluctuation through the year is also very small. Furthermore, in astronomy, seeing refers to the degradation of the image of an astronomical object due to turbulent airflows in the atmosphere of Earth, and it may cause the blurring, twinkling, or variable distortion of the image. The Haleakala observatory can also provide the best condition in terms of seeing. Another place providing such conditions is Roque de los Muchachos Observatory, located on the island of La Palma in the Canary Islands, Spain. Therefore, finding ideal locations for ground observatories is challenging since many unique conditions need to be fulfilled. Moreover, when looking at the bigger picture, the ground observatories in the northern hemisphere or the southern hemisphere can only observe some portion of the entire sky. Joint efforts should be synchronized to thoroughly survey the entire sky in order not to miss any suspicious near-Earth object. In fact, the ideal place for founding observatories in the southern hemisphere is in the Atacama Desert, which is a desert plateau in northern Chile, covering a 1600 km strip of land on the Pacific coast, west of the Andes Mountains. The Atacama Desert has a high elevation and is the driest nonpolar desert globally, receiving less precipitation than the polar deserts. Due to its unique geological and weather conditions, some of its regions have been used for astronomical observatories and experimentation sites on Earth for Mars expedition simulations. The European Southern Observatory (ESO) operates three major observatories in the Atacama, which are known as, the La Silla Observatory, the Paranal Observatory, and the Llano de Chajnantor Observatory, and the ESO is currently building a fourth one, the Cerro Armazones Observatory, site of the future Extremely Large Telescope (ELT). The Llano de Chajnantor Observatory includes the famous Atacama Large Millimeter/submillimeter Array (ALMA), which is an astronomical interferometer of 66 radio telescopes and observes electromagnetic radiation at millimeter and submillimeter wavelengths. The array was constructed at the 5000 m elevation, which is crucial to reducing noise and decreasing signal attenuation due to Earth's atmosphere. However, these telescopes are not mainly dedicated to the NEO survey. On the other hand, on-ground telescopes for the NEO survey mainly use radio frequencies and visible light. Only a few of them are infrared-based, such as the NASA Infrared Telescope Facility (NASA IRTF). Infrared telescopes hold some advantages, one of which is, for example, when observing in the near-infrared, the dust is transparent to it.