Visibility analysis of Phobos to support a science and exploration platform

The surfaces of the Martian moons, Phobos and Deimos may offer a stable environment for long-term operation of platforms. We present a broad assessment of potential scientific investigations, as well as strategic and operational opportunities offered by long-term operation of an instrumented lander. Studies using observations of Mars’ moons, and the detailed new findings expected from the JAXA Martian Moons eXploration (MMX) mission, International Mars Sample Return (MSR) Campaign and other upcoming Mars missions, provide a driver for feasibility and trade studies for follow-on missions that would build on the knowledge gain from those missions. We discuss the scientific questions and operational objectives that may be pertinent for landed platforms on the martian moons, including (1) monitoring and scientific investigations of Mars’ surface and atmosphere, (2) scientific investigations of the martian moons, (3) monitoring and scientific investigations of the space environment, (4) data relay for Mars surface assets or interplanetary missions and 5) use in a Mars navigation/positioning system. We present results from visibility calculations performed using the SPICE observation geometry system for space science missions, and a Phobos shape model. We compute as a function of location on Phobos, visibility quantities that are most relevant to science and operational objectives. These include visibility from Phobos of the Sun, Earth, Mars surface and atmosphere, Deimos, and Jupiter. We also consider occultation events by the Mars atmosphere of Earth and Deimos that may provide opportunities for radio science. Calculations are performed for a study period spanning one Mars year in a hypothetical future operational scenario (1 Jan 2030–18 Nov 2031). We combine visibility metrics to identify locations on Phobos most suitable for long-term operation of a platform. We find the Mars-facing side of Phobos, and limited areas on the leading and trailing sides, satisfy the most requirements defined for Mars and Phobos science, space environment monitoring, and data relay/navigation. We demonstrate that compliance with requirements related to visibility of Mars and its atmosphere are not mutually exclusive with those that are better satisfied on Phobos’ anti-Mars side, such as those aided by maximizing their cumulative view factor to the ecliptic plane (i.e. visibility to the Sun, Earth or outer solar system). Finally, our methodology allows to assess the extent to which combined visibility metrics can meet mission requirements. The process we describe can be used to support landing site identification and selection on planets, moons and small bodies. Graphical Abstract

Juventas Cubesat for the Hera mision

<p>The Juventas CubeSat, will be delivered to the Didymos binary asteroid system by ESA's Hera mission within the context of the Asteroid Impact and Deflection Assessment (AIDA) international collaboration. AIDA is a technology demonstration of the kinetic impactor concept to deflect a small asteroid and to characterize its physical properties. Due to launch in 2024, Hera would travel to the binary asteroid system Didymos. It will explore the binary asteroid and the crater formed by the kinetic impact the NASA’s Double Asteroid Redirection Test (DART). HERA will carry two 6U CubeSats, one of which is the Juventas CubeSat developed by GomSpace Luxembourg with the Royal Observatory of Belgium as principal investigator. The spacecraft will attempt to characterize the internal structure of Didymos’ secondary body, Dimorphos, over a period of roughly 2 months using a low-frequency radar, JuRa. During this period, Juventas will also perform radio science measurements using its Inter-Satellite-Link to characterize the mass and mass distribution of Dimorphos. Afterwards, Juventas will attempt to land on Dimorphos, during which the spacecraft is expected to perform several bounces. Once landed, Juventas will use its gravimeter GRASS to obtain measurements of the surface acceleration on Dimorphos for a nominal duration of two orbits. Through the monitoring of dynamics for landing and bouncing impacts as well as measurements from the GRASS gravimeter payload while on the surface, Juventas will determine surface mechanical properties and provide further information on subsurface structure and dynamical properties of Dimorphos.</p>

Sulfuric acid vapor and sulfur dioxide in the atmosphere of Venus as observed by the Venus Express Radio Science Experiment VeRa

<p>The main cloud deck within Venus' atmosphere, which covers the entire planet between approx. 50 and 70 km altitude, is believed to consist mostly of liquid sulfuric acid. The temperature below the main clouds is high enough to evaporate the H2SO4 droplets into gaseous sulfuric acid forming a haze layer which extends to altitudes as deep as 35 km. Gaseous sulfuric acid in Venus’ lower atmosphere is responsible for a strong absorption of radio waves as seen in Mariner, Pioneer Venus, Magellan and Venera radio science observations. Radio wave absorption measurements can be used to derive the amount of H2SO4 in Venus’ atmosphere. The radio science experiment VeRa onboard Venus Express probed the atmosphere of Venus between 2006 and 2014 with radio signals at 13 cm (S-band) and 3.6 cm (X-band) wavelengths. The orbit of the Venus Express spacecraft allowed to sound the atmosphere over a wide range of latitudes and local times providing a global picture of the sulfuric acid vapor distribution. We present the global H2SO4(g) distribution derived from the X-band radio signal attenuation for the time of the entire Venus Express mission. The observation is compared with results obtained from a 2-D transport model. The VeRa observations were additionally used to estimate the abundance of SO2 near the cloud bottom. The global distribution of SO2 at these altitudes is presented and compared with results obtained from other experiments. Eight years of VEX observation allow to study the long-term evolution of H2SO4 and SO2. The latter is presented for the northern polar region.</p>