# Survey on Unmanned Aerial Vehicle for Mars Exploration: Deployment Use Case
## 3 Preliminary Studies
### Previous Major Devastating Failed Missions in Space Exploration  
The main objective of a vehicle sent for space exploration is to explore the terrain appropriately, map over the wide region of the planetary body, and get information that is better in both quantity and quality. This section provides prior failure in space exploration through various techniques used. However, many works have attempted to cover the application of UAVs in space to achieve QoS, such as throughput, low latency, uniform coverage, reduced overhead, and connectivity backhaul [48; 49; 50; 51; 52; 53; 54; 55; 56; 57; 58; 59]. Furthermore, UAVs have been proposed to extend and improve the capabilities of rovers and landers for planetary exploration. Various approaches used earlier for planetary exploration have many limitations. Landers are limited to the landing site's surrounding area and can only explore appropriate terrain. For example, the range reported by the JPL for the MER is a total distance of 1 Km, whereas a Mars UAV can potentially explore 500 Km [26]. Since landers may have minimal (or no) freedom to walk around freely, they have only had a single, one-time body experience. In sterile conditions, certain landers, such as Huygens on Titan or Mars landers, must be designed to prevent Earth contamination [60]. Rovers have some benefits over stationary landers, as they examine more territory and lead to exciting features. However, the greater likelihood of loss, owing to landing and other threats, is the downside of rovers relative to orbiters and that they are limited to a restricted area around a landing site that is only roughly expected. Moreover, owing to the contact time delay between Earth and other planetary bodies, travelling safely from rock to rock or position to location is a big challenge. The rover drivers on the spatial body cannot immediately see what is happening to a rover at any given moment, unlike a remote-controlled vehicle, and they could not send fast instructions to prevent the rover from crashing into a rock or falling down a cliff [61]. From the Yutu (from 2013-2016) and the Opportunity (2004-2018), the rovers have just been able to drive up-to-the-distance of 0.1 and 45.16 km, respectively [62]. Table 3 discusses some of the major previously failed missions for planetary exploration. Compared to landers and rovers, an orbiter can gather a lot more data, which helps get more accurate information about the planetary body it is researching. Orbiters are capable of spatial mapping over wide regions, but the resolution of the orbiter is limited to a few meters. Furthermore, the danger from meteoroids and atmospheric debris to the space shuttle orbiter can be broken down into two elements: the possibility that the space shuttle orbiter or crew will be hit (susceptibility) and the likelihood that the mission will be disrupted by an impact [63]. Another very popular approach for investigating the planetary body is sending a human crew to that spatial body. However, sending human crew for space missions is too complex, too expensive, and it seemed to be unnecessary [64]. Furthermore, sending astronauts on a space mission causes severe health issues. As discussed earlier, these health issues can have both short-term and long-term effects. An example of human life at risk is, at NASA, a total of 17 astronauts lost lives in the Space Shuttles Challenger and Columbia tragedies and the Apollo launch pad fire in 1967 [65]. Furthermore, sending human pilots on the spatial body will reduce the station timings. When landers, orbiters, rovers, and human crew are limited, UAVs may be used to accomplish many mission objectives. Exploring the spatial body through UAVs will clearly give more station time, cover the more significant part of the body, and thus, provide huge information [61]. The use of UAVs would balance the analysis, risk of execution, and expense in the field of space exploration. Unlike orbiters, UAVs are nearer to the celestial body's surface; therefore, the information will be comparatively more accurate.