# Space Habitat Data Centers--For Future Computing
## 2 Background
The use of air free cooling and heat pipe back rack approach is recognized to have low power consumption; while the use of rotating wheel heat exchanger and water free cooling approach has high power consumption. The required use of pump in the case of water free cooling approach contributes to the high costs. However, the discussion in [PERSON] et al. [11] aims to identify free cooling technologies suitable for reducing data centre operational costs. Nevertheless, it is important to note that the use of water free cooling technologies is suitable for situations with a high cooling load. However, additional and required evaluation of the environmental effects of using water as a free cooling medium for data centres does not receive consideration. The evaluated and examined literature focuses on the design of different free cooling strategies with a focus on terrestrial data centres. However, data centres can also benefit from free cooling in other locations such as the stratosphere [13] and in underwater environments [13,14]. In addition, data centres are not used in isolation but constitute important entities in cloud radio access networks as seen by Perioda [13]. Therefore, it is important that data centres are sited close to subscribers to achieve low latency content access. However, previous focus has been on enhancing the PUE and reducing the WUE. Preferential locations for siting data centres are naturally cold-climate locations such as Scandinavia, North America, and Europe. This is because countries in these locations have a natural low environmental temperature. However, this is not so for subscribers in locations such as the African continent. Therefore, subscribers in Africa seeking to access content from data centres located in distant European locations experience high content access latency. The use of underwater data centres is recognized in references [13,15] to be capable of reducing the latency for content access with regard to coastal subscribers. The siting of data centres in the ocean is different from that of using terrestrial data centres. The use of underwater data centres poses long-term questions and concerns such as scalability and long-term environment friendliness and sustainability. For example, the suitability of the ocean will attract several data centre operators. This increases the competition for the use of suitable ocean zones and locations. Therefore, it is important to design suitable mechanisms enabling an equitable sharing of the ocean's resources for several potential data centre operators in the future. The concern of long-term environment friendliness and sustainability arises because of the increase in ocean temperature due to the presence of multiple underwater data centres. This increase in ocean temperature poses an existential threat to life under the ocean. These challenges constitute a limitation on the large-scale use of underwater data centres for future computing and networking applications. In addition, the discussion has not considered the processing of the increasing amount of data arising from deployed in-orbit satellites. This is considered in [PERSON] et al. [19], who propose a space edge computing paradigm comprising multiple satellites. The satellites can acquire, store, process and forward data from end user stations. Examples of considered end user stations are vehicles, airplanes, ships, buoys and sensors. The satellites can virtualize on-board resources to form a resource pool. The motivation for using the proposed space edge computing system is to improve the quality of service for a space-based internet of things system. This results in lower latency and improved coverage of terrestrial-satellite communications. The satellites in the proposed edge computing mechanism are reconfigurable and software defined satellites. A challenge that is not considered in [PERSON] et al. [19] arises with the sufficiency of computing resources aboard intelligent satellites that are nodes in the space edge computing network.