Planetary Defense Ground Zero: MASCOT's View on the Rocks - an Update between First Images and Sample Return

At 01:57:20 UTC on October 3rd, 2018, after 3½ years of cruise aboard the JAXA spacecraft HAYABUSA2 and about 3 months in the vicinity of its target, the MASCOT lander was separated successfully by from an altitude of 41 m. After a free-fall of only ~5m51s MASCOT made first contact with C-type near-Earth and potentially hazardous asteroid (162173) Ryugu, by hitting a big boulder. MASCOT then bounced for ~11m3s, in the process already gathering valuable information on mechanical properties of the surface before it came to rest. It was able to perform science measurements at 3 different locations on the surface of Ryugu and took many images of its spectacular pitch-black landscape. MASCOT’s payload suite was designed to investigate the fine-scale structure, multispectral reflectance, thermal characteristics and magnetic properties of the surface. Somewhat unexpectedly, MASCOT encountered very rugged terrain littered with large surface boulders. Observing in-situ, it confirmed the absence of fine particles and dust as already implied by the remote sensing instruments aboard the HAYABUSA2 spacecraft. After some 17h of operations, MASCOT‘s mission ended with the last communication contact as it followed Ryugu’s rotation beyond the horizon as seen from HAYABUSA2. Soon after, its primary battery was depleted. We present a broad overview of the recent scientific results of the MASCOT mission from separation through descent, landing and in-situ investigations on Ryugu until the end of its operation and relate them to the needs of planetary defense interactions with asteroids. We also recall the agile, responsive and sometimes serendipitous creation of MASCOT, the two-year rush of building and delivering it to JAXA’s HAYABUSA2 spacecraft in time for launch, and the four years of in-flight operations and on-ground testing to make the most of the brief on-surface mission

The Application of a Thermal Mathematical Model during Lander Operations on the surfaces of Small bodies

Landing on small bodies like asteroids and comets is an extreme challenging operation. The unknown thermal and physical properties of the surface after a multi-annual journey in deep space require a high degree of flexibility for operations planning and execution during the landing and consecutive on-surface mission phases. The presentation describes the planning and analysis loop used to establish and execute the operations for two of these landers, the comet lander Philae on 67P/Churyumov–Gerasimenko and the asteroid lander Mascot on Ryugu, by the DLR Lander Control Centre in Cologne in collaboration with the other mission partners. This planning and analysis loop, focusing on power and thermal aspects, is mainly built by the Thermal Mathematical Model (TMM) of the respective lander interacting with an Operations Planning Tool, which e.g. translates the planned operation in dissipation profiles for all relevant nodes of the TMM. Moreover as one of the reason for thermal analysis during operation is the life extension of the batteries, the TMM is prepared with a detailed electrical and thermal model for the batteries and their management and, in case of Philae, it is also interacting with a Solar Array Illumination and Power Prediction tool. In addition, to plan long-term surface operations, the TMM needs to include a dedicated and flexibly adaptable comet or asteroid surface model because, as especially seen during the post-landing operations of Philae, the impact factor of the real environmental conditions found after landing is considerable. On the other hand the TMM needs to support its alternating application between moving and resting on-surface configurations as required by Mascot, the Mobile Asteroid Surface Scout. The presentation shows details of the necessary TMM preparation in order to optimize its application during real-time operation

Thermal Analysis and Constraints for the MASCOT Landing Site Selection on the Asteroid Ryugu

In June 2018, after 4 years of cruise, the Japanese space probe Hayabusa2 [1-Watanabe S. et al.: Hayabusa2 Mission Overview. (2017)] reached the Near-Earth Asteroid (162173) Ryugu. Hayabusa2 carried a small Lander named MASCOT (Mobile Asteroid Surface Scout) [2-Ho T. M. et al.: MASCOT-The Mobile Asteroid Surface Scout on-board the Hayabusa2 mission. (2017)], jointly developed by the German Aerospace Center (DLR) and the French Space Agency (CNES), to investigate Ryugu's surface structure, composition and physical properties including its thermal behaviour and magnetization in-situ. The Microgravity User Support Centre (DLR-MUSC) in Cologne was in charge of providing all thermal conditions and constraints necessary for the selection of the final landing site and for the final operations of the Lander MASCOT on the surface of the asteroid Ryugu. This article provides a comprehensive assessment of these thermal conditions and constraints, based on pre dictions performed with the Thermal Mathematical Model (TMM) of MASCOT using different asteroid surface thermal models, ephemeris data for approach as well as descent and hopping trajectories, the related operation sequences and scenarios and the possible environmental conditions driven by the Hayabusa2 spacecraft. A comparison with the real telemetry data confirms the analysis and provides further information about the asteroid characteristics

Operational comet surface thermal models: lessons learnt from Rosetta/Philae

Abstract: For the landing site selection and operations of Philae, operational CSTMs (comet surface thermal models) had to be calculated in a frenzy: Between August 2014 (orbit insertion) to September (final selection). Input relied on two Rosetta Orbiter instruments, VIRTIS (IR) and MIRO (microwave, subsurface) to estimate thermal inertia. Comet 67P/Churyumov-Gerasimenko was then, r> 3AU, rather inactive; so sublimation was not considered for the predictive models. We explain the model parameters, give some examples and report on the numerous unexpected difficulities to get a CSTM right on a small body with a complex shape

Rosetta Lander: Philae on comet 67P/Churyumov-Gerasimenko

Rosetta is a Cornerstone Mission of the ESA Horizon 2000 programme. In August 2014 it reached comet 67P/ Churyumov-Gerasimenko after a 10 year cruise. Both its nucleus and coma have been studied with its orbiter payload of eleven PI instruments, allowing the selection of a landing site for Philae. The landing on the comet nucleus successfully took place on November 12th, 2014. Philae touched the comet surface seven hours after ejection from the orbiter. After several bounces it came to rest and continued to send scientific data to Earth. All ten instruments of its payload have been operated at least once. Due to the fact that the Lander could not be anchored, the originally planned first scientific sequence had to be modified. Philae went into hibernation on November 15th, after its batteries ran out of energy. Re-activation of the Lander was expected for May/June 2015, when CG would be closer to the sun and, indeed, radio contact with the Lander was re-established on June 13th and for (so far) seven more occasions. Rosetta is an ESA mission with contributions from its member states and NASA. Rosetta's Philae lander is provided by a consortium le al contributions from Hungary,UK, Finland, Ireland and Austri

Rosetta Lander - Landing and operations on comet 67P/Churyumov-Gerasimenko

The Rosetta Lander Philae is part of the ESA Rosetta Mission which reached comet 67P/Churyumov–Gerasimenko after a 10 year cruise in August 2014. Since then, Rosetta has been studying both its nucleus and coma with instruments aboard the Orbiter. On November 12th, 2014 the Lander, Philae, was successfully delivered to the surface of the comet and operated for approximately 64 h after separation from the mother spacecraft. Since the active cold gas system aboard the Lander as well as the anchoring harpoons did not work, Philae bounced after the first touch-down at the planned landing site “Agilkia”. At the final landing site, “Abydos”, a modified First Scientific Sequence was performed. Due to the unexpectedly low illumination conditions and a lack of anchoring the sequence had to be adapted in order to minimize risk and maximize the scientific output. All ten instruments could be activated at least once, before Philae went into hibernation. In June 2015, the Lander contacted Rosetta again having survived successfully a long hibernation phase. This paper describes the Lander operations around separation, during descent and on the surface of the comet. We also address the partly successful attempts to re-establish contact with the Lander in June/July, when the internal temperature & power received were sufficient for Philae to become active again

Thermophysical modeling of Didymos' moon for the Asteroid Impact Mission

Although typically less resolved through observations, the secondary in a binary system of asteroids is an interesting target for space missions such as the Asteroid Impact Mission. Estimates of the surface temperature distribution are important for mission design. Based on known, assumed and derived physical properties, a thermophysical model of the smaller body in the 65803 Didymos system is established. Because of the unknown thermal inertia, a parameter study has been carried out for a thermal inertia range of 50 -1000 J m-2 K-1 s-1/2. Results are presented for the minimum and maximum values of this range and a likely value of 500 J m-2 K-1 s-1/2. The parameter study extends from the unshadowed to the eclipsed case where shadowing through the primary is simulated in a simplified manner assuming that the orbit of the moon lies in the equatorial plane of the primary with its z-axis normal to this plane. Results from this study are used to investigate performance for instruments foreseen for the Asteroid Impact Mission. Preliminary results are obtained for the signal-to-noise ratio of a proposed thermal infrared imager. Furthermore, MASCOT-2 Lander thermal survivability has been investigated for several possible landing sites and specific settings

Rosetta Lander Batteries Experience During All Operation Phases

Rosetta is an ambitious ESA mission, launched in March 2004 from Kourou and which performed a rendezvous with comet 67/P Churyumov-Gerasimenko. Its lander, Philae, achieved landing on comet soil on the 12th November 2014 and performed 64 hours of science activities on its batteries before going into hibernation due to lack of solar energy. Philae is operated by the Lander Control Centre (LCC) at DLR Cologne Germany and the Science Operations and Navigation Centre (SONC) at CNES Toulouse France. The Lander system was provided by a European consortium (Germany, France, Italy, Hungary, Finland, UK, Ireland, Switzerland and Austria) and supports a scientific payload of 10 instruments. The Philae battery system was provided by CNES, it is composed of a Saft primary battery (1518Wh) and an ABSL secondary battery (151Wh). The primary is made of non-rechargeable LSH20 (LiSOCl2) Saft cells and the secondary of rechargeable ABSL Li-ion 18650HC. For the Philae mission, the energetic constraint was very important. Indeed, before launch, the operations had to be planned considering variability of several parameters (descent duration, communication slots, comet temperature, solar power availability, etc.). Since Rosetta launch, cells and batteries have been stored and specific ground test plans have been identified in order to follow the battery ageing and to validate the final Philae operation schedule. From ground test results, an electrical model of the batteries was developed to help the operations scheduling. During cruise, the operations consisted of secondary batteries monitoring and tests and primary battery conditioning. During separation and on-comet operations, the behaviour of the batteries system was checked and electric simulations helped with activities scheduling. Firstly, this paper will describe the Philae mission. In a second part, the batteries system will be presented. The ground strategy will be detailed. Finally, the operations of Philae batteries system will be described