A Spacecraft design for mars water survey

To probe the possibility of water sources on Mars and research the surface environment of Mars, a Martian spacecraft was designed in detail in this study. Camera PIXL was selected as the payload. The service platform includes an orbit control system, communication system, thermal control system, main computer, energy system, and structure system, which was designed to support the operation of the spacecraft to complete required space missions. The consequence of this research furnishes some guidance for the design of the Martian spacecraft, which discovers water sources on Mars.


Introduction
Following the expeditious development of deep space exploration, the detection range of the spacecraft is expanded, and space mission requirements become more complicated [1] .With the increasing demand for deep space research results, low-earth orbit satellites do not suit the higher demands of space research.Hence, to research planets such as Mars effectively, a spacecraft to research Mars should be designed [2] .Compared with Earth orbit satellite, Mars as an Earth-like planet has already become an active research for a lot of researchers, and the study contents mostly concentrate on functional rovers (the Curiosity and Perseverance rovers [3] ), orbiters spacecraft (Mars Express, Mars Reconnaissance Orbiter, and the Tianwen-1 [4] ), and Mars sample return missions [5] .Moreover, life might arise on Mars because of evidence of water.
Water is the indispensable substance for the emergence and evolution of life.During the 21st century, ESA and NASA have some programs to follow the water, providing some scientific data about the distribution and abundance of water on Mars.The 2001 Mars Odyssey discovered proof of water on Mars based on pictures [6] .Mars Reconnaissance Orbiter (MRO) suggests that Mars has had an abundant history of the progression of water according to some photographs taken.Mars Phoenix lander affirmed the presence of massive water ice in the northern area of Mars.Mars Express used radar equipment and mapped the surface of Mars to search for verification of underground water.Mars Exploration Rovers (MERs) discovered a lot of proof about foregone water on Mars [7] .
These research outcomes obtained that some liquid water may be present on Mars.According to the research results of domestic and foreign scholars, this paper designed a spacecraft flight five years around Mars to take pictures.These pictures provided certain guidance for researching water on Mars.

Spacecraft design
According to the goal of a space mission, a spacecraft that should find water on Mars must include two parts.The first part is the payload.This paper selects a camera that takes pictures on Mars.These pictures provided evidence that found possible existing water.The second part is the service platform, which includes a propulsion system, orientation and stabilization system, communication system, control system, energy system, main computer, thermal control system, and structure.Some details of these eight systems will be described later.

Payload
Payloads and missions for spacecraft are diverse.This paper chooses camera PIXL as an implement referred to as an X-ray spectrometer, as shown in Table 1.This camera can take very clear photographs of soil textures and rocks and observe super-small characteristics like a grain of salt.In short, this information can help researchers to seek some evidence of water on Mars.We divide the entire orbit into earth-centered escape orbit, heliocentric-earth-fire transfer orbit, and Mars capture orbit.In the heliocentric orbit segment, the transfer from the Earth to Mars is from the inner planet to the outer planet.At this stage, there are four schemes: Hohmann transfer orbit, great ellipse, parabola, and Venus leverage.According to the literature review, the characteristics of these kinds of orbits are shown in Table 2.It can obtain the consequence that the duration of the Hohmann transfer orbit is better and the fuel is the best.Therefore, this paper chooses the Hohmann orbit for simulation analysis and designs the spacecraft flight orbit.The three main flight trajectories will be calculated and simulated in detail below, including earthcentered escape orbit, Hohmann earth-mars transfer orbit, and Mars Capture Orbit.
During the earth-centered escape orbit (Figure 1), the spacecraft tracks at an altitude of 300 km and escapes the earth's gravitational field at a speed v ∞ .During the Homann transfer orbit (Figure 2), spacecraft flights from Earth to Mars.For Mars capture orbit (Figure 3), this paper chooses a parking orbit of 300 km from the surface of Mars.In this parking orbit, the Mars rover will operate for 5 years.During these 5 years, the surface of Mars photographs was continuously taken and sent back to the earth.Researchers will use these photos to conduct related research, for example, whether there is water and life on Mars, and whether it is suitable for human habitation.

2.2.2
Communication system There are three main mechanisms in the communication system.One of these mechanisms needs the high-gain antenna to travel directly to direct at the Earth, and two of these mechanisms are necessary for the solar arrays to travel directly to the Sun.We refer to these three mechanisms as high-gain antenna and low-gain antenna.During the flight of spacecraft in orbit, the high-gain antenna plays a major role.Therefore, this paper mainly analyzes and studies the high-gain antenna.
When the spacecraft flies around Mars, these gimbals can make high-gain antennae to direct at Earth.At the same time, both of the two solar arrays are directly at the Sun.Data transfer speed is calculated in Equation (1).
Where n 1 are number of photos taken by the camera during one circular; S PIXL is the size of one photo; t 21 is the data transfer time during one circular.
A high-gain antenna was found, which meets the requirements of transmission rate, transmission frequency, working power, and other parameters, as shown in Table 3.
Table 3 -55~125 To meet the requirements of the thermal parameters of the spacecraft, this paper chooses radiator Alpha to change the temperature of the spacecraft.Spacecraft temperatures are determined by how much heat is absorbed, stored, or dissipated by the spacecraft (as Figure 4) [8] .
Where solar is solar heating; q albedo is solar heating reflected by the planet; q planetshine is IR heating from the planet; Q gen is heat generated by the spacecraft; Q stored is heat stored by the spacecraft; Q out,rad is the heat emitted via radiation.The equation can be balanced by adjusting the value of Q out,rad , which depends on the surface area of the radiator A sph .Based on Equation ( 2) and some heating data of Curiosity, Q out,rad can be calculated in Equation (3) According to Stefan-Boltzmann law: Where ε rov is the emissivity of the rover, σ is the Stefan-Boltzmann constant, and T rov is the rover's equilibrium temperature.Based on Equation ( 4) and some data from references, the surface area of the radiator will be calculated in Equation ( 5).

2.2.4
Main computer When flying around Mars at an altitude of 300 km, this spacecraft takes a photo every 100 km.During the 5 years, number of photos taken by spacecraft was calculated in Equation ( 6).
5 360 24 60 60 5302420 29.33 Where t total is five years of flying time and Δt is the time interval required to take a picture every 100 km, whose value can be calculated in Equation (7).Therefore, the size of the flash memory of the main computer is shown in Equation (8).
Where S PIXL is the size of one photo; n is the number of photos taken by the camera during five years, which can be calculated in Equation (9): 5 360 24 60 60 5302420 29.33 Where t all is five years; the value of Δt is the same as Equation (6).According to the above calculation data, this paper chose a computer shown in Table 5, which can store such a huge number of pictures.Energy system At present, the energy used by spacecraft mainly includes solar energy, nuclear energy, and high-pressure gas stored in pressure vessels during launch.Almost all satellites use solar energy as the main energy source.According to the data, we can get the energy transmitted by the sun to Mars, and the surface area of the solar panels (14.6 m 2 ) can roughly be estimated.
During Mars parking orbit, the spacecraft cannot use solar panels sometimes because of sunlight shadow (as shown in Figure 5).(11) Where s 12 is the distance of shadow; the value of v 0 is the same as Equation ( 7); t is one circle time; t 12 is the time of shadow.
During the shadow of Mars period, the spacecraft cannot get power from the sun.To maintain the normal operation of various equipment of the spacecraft, the spacecraft began to use batteries (shown in Table 6).According to the flight time of this spacecraft, this paper chooses a Lithium-sulfur dioxide battery as the primary battery.Based on the data in Table 7 and experimental testing, this spacecraft's 3D model can be created in Solidworks, as shown in Figure 6.

Conclusion
According to the goal of the spaceflight mission to find water on Mars, this paper chooses a suitable payload, which is a PIXL camera.Then, each subsystem of the spacecraft is designed in detail.All instruments are designed to ensure spacecraft flight to orbit around Mars and life for five years in orbit.In these five years, the PIXL camera will take enough photos to help researchers find water on Mars.

Figure 4 .
Figure 4. Heating simplified overview.The balancing energy of spacecraft thermal control is shown in Equation (2).
v 0 is the speed of the spacecraft in a circular orbit; μ Mars is Mars gravity parameters; r p is the radius of perigee.

Figure 5 .
Figure 5. Shadow of spacecraft.Shadow of time and sunshine of time were calculated in Equation (10) and Equation (11).

Table 1 .
Camera on spacecraft.According to the MATLAB program, the launch window is July 27, 2024.After 230 days of flight, the spacecraft will arrive on Mars on March 14, 2025.

Table 4 .
Some instrument temperature requirements of this spacecraft are sorted out in Table4.Temperature requirements. .

Table 6 .
Primary battery.According to the above research, some data on spacecraft is shown in Table7.