The day when humans are on Mars is not far away. It was only 500 years ago that Columbus "discovered" the Americas. Who could have imagined then that we would be able to fly abroad, as we do today? Not only public sector such as NASA in the United States and JAXA in Japan, but also the private sector would expand to Mars in the not-too-distant future. In order to do so, it is essential to know exactly what kind of place Mars is. We are developing TEREX (TERahertz EXplorer), the world's first micro terahertz explorer to Mars. It will precisely measure the amount of water molecules and oxygen molecules, and search for water resources and the possibility of life on Mars. Our goal is to make a system to send cheap, light, small explorers to Mars on a regular basis. We are currently developing two explorers. TEREX-1 is a lander-type explorer that lands on Mars. TEREX-2 is a satellite-type explorer to make observations from orbit around Mars.
TEREX-1 is a extra-small landing-type explorer. It is about the same height, width, and torso as a Sumo Wrestler Yokozuna Hakuho (192 cm, 151 kg) with his arms outstretched. It weighs less than he does! The body is like an oil drum and has solar-power wings. The body is kept as simple as possible so that many scientists can carry their own equipment
Challenges in Development:Landing
Numerous projects around the world have attempted to explore Mars, but about half of them have failed. One of the most challenging aspects of planetary exploration is the EDL: Entering a planet, Descending, and Landing. The EDL on Mars has been called the "Seven Minutes of Terror".
For successful EDL, we must overcome several problems. Firstly, the approach speed must be reduced by more than 99% in the thin atmosphere of Mars. The explorer uses aerodynamic drag to reduce the speed. The thin air makes it harder to brake. Secondly, the body of explorer will be very hot before landing, so it must be extreme heat resistant. Finally, on landing, the explorer should be slowed down as much as possible to reduce the impact of the fall.
TEREX-1’s landing gear consists of an aeroshell and an airbag (Under consideration). Both are made of a thin film of ZYLON®, an extremely light and heat-resistant material. The aeroshells are made of the lightest material and are designed to have a large surface area. It allows for a significant deceleration in the upper atmosphere and avoids the generation of large amounts of heat near the surface. The airbag is designed to absorb as much of the impact as possible by releasing gas from the inside when it is impacted.
TEREX-2 Observing from the orbit of Mars as an artificial satellite
TEREX-2 is a microsatellite. It weighs 100 kg. It will orbit at a height of about 400 km from the ground in 5 hours and 20 minutes. It will measure temperature, wind speed, magnetic field, and four types of atmospheric molecular concentrations: Oxygen O2, ozone O3, water H2O, hydrogen peroxide H2O2. It will provide us with the most accurate information in history about where and how much oxygen and water exist on Mars.
There are two observation methods: from directly above (nadir observation) or from the side (limb observation). The limb observation has advantages such as high sensitive detection of atmospheric constituents and high vertical resolution. The nadir observation has advantages such as measuring surface emission which is the key parameter of surface temperature and component.
The figure below is a prediction of the results based on known facts. The shape of the graphs tell us where and how much of substances essential for life, such as oxygen and water. If the actual observation result is as this, it’s ok. If they are not, yes, it’s a great discovery!
Simulated signal for the TEREX-2 sensor [refer from Figure 4 in R.Larsson et al., 2018]. Panel (a) shows the simulated limb-scanning geometry for several tangent altitudes. The legend contains the tangent altitudes. Panel (b) shows the simulated nadir-staring mode signal.
Challenges in Development:Accuracy
The climate on Mars is more severe than the Sahara. Because there is less water vapor in the air, the temperature is very variable in a day. Dust storms often occur, and the atmosphere is covered with dust. In addition, on Mars there are four seasons like on the Earth. The temperature and pressure changes dramatically throughout the year.
This is why we need to make many observations to learn about the Martian climate. Even if we observe at the same place in the same season, we will have very different results depending on the solar activity and dusts in the air at that time.
And the accuracy of the observations is very important. Before the explorer is launched, we use computer simulations to determine the instrumental accuracy and atmospheric circulation model. Based on the data, we are verifying how much of an error we can observe. As a result, we have confirmed that it has sufficiently accuracy.
