# 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
Therefore, this explains why an optical telescope would be unable to see a star hidden in dust, whereas one working in the near-infrared would be able to detect its emission. Another advantage is that relatively cold objects invisible to optical telescopes become visible in the infrared. Interstellar gas, dust discs, asteroids, and brown dwarfs are all examples of objects that are too cold to shine in visible wavelengths but become conspicuous when viewed in the infrared [145]. Consequently, an infrared facilitated survey is beneficial for detecting asteroids/comets, which are usually cold and hard to discover. However, most infrared telescopes such as the Herschel, the NEOWISE, and the JWST, are placed in space to completely eliminate the interference from the Earth's atmosphere. Furthermore, cryogenic technology will be needed with spaceborne infrared detection since the low temperature can effectively suppress the detection of dark currents and background noise [146]. Figure 16: Plot of the number of NEA discoveries per year, by survey [139]. Moreover, from the radio astronomy perspective, powerful ground-based radio telescopes can effectively detect NEOs. For example, the California-based Goldstone Deep Space Communications Complex (GDSCC) made a historic observation of the 1000 th near-Earth asteroid [147] on 22 August 2021 on its Deep Space Station (DSS) 14: \"Mars\" where an enormous Cassegrain antenna of 70-m diameter is installed. When created by the JPL to support the Pioneer program of deep space exploration probes, the location of the Goldstone complex was chosen to be in the Mojave Desert, distant from radio interference. The GDSCC was mainly intended for the vital two-way communications link that tracks and controls interplanetary spacecraft. However, it can also be used as high-sensitivity radio telescopes for astronomical research, such as radar mapping planets, asteroids, and comets. Furthermore, the advances in astronomical spectroscopy also provide better measurement of the spectrum of electromagnetic radiation from celestial bodies. Scientists could detect molecules of interesting materials on celestial bodies and better understand the solar system's evolution. For example, a semiconfocal cavity coupled pulse echo spectrometer system designed in 65-nm CMOS is able to detect Nitros Oxide (N\({}_{2}\)O) that re-emits at 100.4917 GHz [148]. Furthermore, a 180-GHz pulsed CMOS transmitter with a high output power of 0.6 mW is presented for emission-based molecular detection [149]. It is predicted by Dr. [PERSON] that the emission spectroscopy will play a crucial role in analyzing a plume or gas emission of a celestial body and be used in radio-astronomy looking at distant stellar objects. Therefore, emission spectroscopy can also be utilized to conduct precise spectroscopic analysis of the asteroids that are currently classified into three major types according to their spectra. In the former Tholen classification, the C-types are made of carbonaceous material, S-types consist mainly of silicates, and X-types are metallic. Then in 2002, the Tholen classification was upgraded into the SMASS classification, expanding the number of categories from 14 to 26 [150].