# A Simulation of Contact Graph Routing for Mars-Earth Data Communication
## 1 Introduction  
The proximity of Mars to our Solar System makes it an obvious target for exploration, but there are numerous more reasons to investigate Mars. Searching for life, learning about the planet's surface and evolution, and preparing for future human exploration are the three main scientific justifications for exploring Mars [1] Mars, commonly referred to as the Red Planet, may have once been habitable because of evidence that suggests it was warmer, had a thicker atmosphere, and was covered with water. The history of water on Mars piques scientists' curiosity to know how life might have persisted. Aspects of Mars' past can be found in its volcanoes, meteoroid impact craters, atmospheric and photochemical effects, and geophysical processes. For future human exploration, we must know the risks before sending astronauts. Uncontained Martian material would inevitably be carried back to Earth by astronauts, either on their bodies or on their equipment. Planning and preparedness for these upcoming operations will be aided by the knowledge of any biohazards present in the dust and soil [1]. Since 1997, NASA has deployed several robotic rovers to Mars in order to investigate the planet's surface and its geology, and to look for evidence of current or former life. The most prominent rovers on Mars include Sojourner, Spirit, Opportunity, Curiosity, and Perseverance. Curiosity landed at Gale Crater in August 2012 and focuses on habitability studies, including learning more about Mars' long-term climate history and determining whether the aforementioned crater has ever had environmental conditions conducive to microbial life. On 18 February 2021, Perseverance, another rover, landed at the Jezero Crater. Its goals include looking for evidence of ancient microbial life on Mars, gathering soil and rock samples for a possible return to Earth in later missions, and researching the planet's climate, geology, and potential for supporting future human expeditions. NASA's dedicated Mars Exploration Program website [2] offers real-time updates on the rovers' activities. Both rovers send data from the exploration using UHF Ultra to contact the relay satellites; these data are then forwarded to station receivers in Madrid (Spain), Goldstone (United States), and Canberra (Australia). These form part of NASA's Deep Space Network (DSN), which is a global network of strong antennas used for communication with spacecraft in deep space or for missions that operate outside of the Moon's orbit. The DSN is essential for spacecraft navigation, scientific data collection, and communication with interplanetary missions. As shown in [3], stations on planetary surfaces, orbiters, and deep space relays make up interplanetary communication networks. Traditional Internet protocols like TCP/IP are unsuitable for deep space environments due to their reliance on continuous end-to-end connectivity and low latency. These networks must overcome major propagation delays, limited resources, and node mobility. The rovers ideally transmit as much research and exploration data as possible and as quickly as possible to Earth. The vast distance (143 million miles or 16 min of data transmission) to and from Mars is one of numerous restrictions, though. Additionally, each relay satellite has a unique orbit, resulting in varying communication windows [4; 5; 6]. The goal is for the rovers to transmit as much of the exploration and research data as they can to Earth as fast as possible. A unique type of computer network architecture known as Disruption/Delay-Tolerant Networking (DTN) addresses the limitations of the TCP/IP suite to satisfy deep space networking needs with sporadic end-to-end connectivity. The store-carry-forward method of data transmission in DTN involves the transfer of bundles (data) between relay nodes as custody. This offers more flexibility for erratic connectivity but calls for more intricate routing schemes, requiring more route calculations and network resource usage.