# Internet of Spacecraft for Multi-Planetary Defense and Prosperity
## 2 Extra-Terrestrialization: Make Life Multi-Planetary
### Foundation on Another Celestial Body  
Founding a human base or even a self-sustaining city on another celestial body is challenging in light of the current technological level [35]. Building the first colony for humankind on another celestial body with or without a thin atmosphere, with more severe damage from cosmic rays, solar radiation, or even asteroid impact, will have a challenging kickoff. Specifically, constructing reliable shelters either on the ground or underground is a huge mission requiring significant workforces and resources that depend on transportation at the very beginning. Take Mars, for example, 1 million people is a threshold required to maintain a civilization, which translates to at least 10,000 trips and 1000 ships [26]. Another challenge is the Earth-Mars rendezvous timing is roughly 26 months when the distance between two celestial bodies becomes periodically minimum, which means a huge number of preparation sand launches will occur in a very narrow time window, and the Mars fleet will have to depart en masse [26]. Compared to any other celestial body in the solar system, Mars is the most habitable telluric planet due to the suitable distance from the Sun and similar day length, land mass, and a bit less gravity (about 38% of Earth). The average Mars atmospheric pressure is about 600 Pa, or 0.5921% of Earth's standard atmosphere (ATM). Moreover, the Mars atmosphere is mainly composed of 95.32% CO\({}_{2}\), 2.7% N\({}_{2}\), 1.6% Ar, 0.13% O\({}_{2}\), etc. Moreover, billions of years ago, when Mars was warmer and the atmosphere was denser, channel-like valleys and riverbeds were highly likely to have emerged on the surface with flowing water [36; 37; 38]. However, due to the low temperature and atmospheric pressure today, liquid water cannot exist on the surface, although some water vapor is held in the atmosphere and some other liquid water might be released occasionally by the volcanic activity and asteroid impact. Most of the water on Mars is locked in the polar caps of which the larger one is the northern cap, Planum Boreum, with a dimension of 1000 km across and 1.2 km thick. Furthermore, the northern cap is composed of 90% of water ice and carbon dioxide (CO\({}_{2}\)) ice that has a seasonal change observed by the Hubble space telescope [39]. The southern  
Figure 7: Illustration of Mars transit system architecture and flowchart, based on concept in [26]. cap (Planum Australe) has a thick base of water ice topped with an 8-m layer of (CO\({}_{2}\)) ice. The southern cap is the only place where CO\({}_{2}\) ice persists on Mars' surface year-around. The rich content of CO\({}_{2}\) and water ice on Mars can facilitate local mass production of propellant based on the Sabatier reaction process as shown in Figure 7. For oxygen and methane production, the Sabatier catalytic reactor (SR) and co-production/electrolysis are shown as follows [40, 41]:  
\[\text{CO}_{2}+4\,\text{H}_{2}\longrightarrow\text{CH}_{4}+2\,\text{H}_{2}\text{O (g)}\ \ -164\ \text{kJ mol}^{-1}\ \text{(at 298\ K)}, \tag{1}\]  
where ruthenium (Ru) is used as the catalyst under the temperature of 200-300 \({}^{\circ}\)C.  
\[2\,\text{H}_{2}\text{O}_{\text{(I)}}\xrightarrow{\text{electrolysis}}2\, \text{H}_{2(g)}+\text{O}_{2(g)}. \tag{2}\]  
According to [40], every 1 kg of propellant made on the Moon or Mars saves 7.4 to 11.3 kg in the LEO. The Mars ISRU can significantly take advantage of atmospheric and soil resources and thus facilitate future Moon and Mars missions or even missions to other celestial bodies. On the other hand, the minerals contained in the Mars soil such as iron, aluminium, magnesium, silicon, titanium, etc., can be used for building self-sustaining cities and spacecraft. However, there are challenges such as how to operate the construction and mass production in extreme environments with extreme temperature, pressure, dust, cosmic rays radiation, low gravity, and micro-gravity.