Stephan Ulamec

The landing(s) of Philae and inferences about comet surface mechanical properties

The Philae lander, part of the Rosetta mission to investigate comet 67P/Churyumov-Gerasimenko, was delivered to the cometary surface in November 2014. Here we report the precise circumstances of the multiple landings of Philae, including the bouncing trajectory and rebound parameters, based on engineering data in conjunction with operational instrument data. These data also provide information on the mechanical properties (strength and layering) of the comet surface. The first touchdown site, Agilkia, appears to have a granular soft surface (with a compressive strength of 1 kilopascal) at least ~20 cm thick, possibly on top of a more rigid layer. The final landing site, Abydos, has a hard surface.

Organic compounds on comet 67P/Churyumov-Gerasimenko revealed by COSAC mass spectrometry

Comets harbor the most pristine material in our solar system in the form of ice, dust, silicates, and refractory organic material with some interstellar heritage. The evolved gas analyzer Cometary Sampling and Composition (COSAC) experiment aboard Rosetta’s Philae lander was designed for in situ analysis of organic molecules on comet 67P/Churyumov-Gerasimenko. Twenty-five minutes after Philae’s initial comet touchdown, the COSAC mass spectrometer took a spectrum in sniffing mode, which displayed a suite of 16 organic compounds, including many nitrogen-bearing species but no sulfur-bearing species, and four compounds—methyl isocyanate, acetone, propionaldehyde, and acetamide—that had not previously been reported in comets.

The COSAC experiment on the lander of the ROSETTA mission

Abstract The COSAC experiment on the Lander of the ESA mission ROSETTA is aimed at the in situ investigation of matter of a cometary nucleus (P/Wirtanen) with respect to its chemical and isotopic composition. Special emphasis is put on the identification of complex organic molecules including their chirality. The instrument, presently under development, will employ for analysis a multi-column gas-chromatograph and a high-resolution TOF mass spectrometer. These instruments can be controlled from ground and used either separately or in the GC/MS coupling mode. They are suited for analysis of the natural cometary atmosphere or pyrolytically generated gas from surface or near-surface samples.

Rosetta lander in situ characterization of a comet nucleus

Abstract Rosetta is one of the cornerstone missions within the science program “Horizon 2000” of the European Space Agency (ESA). Its objective is the characterization of comet Wirtanen, which will be reached after 9 years of cruise in the year 2012. As comets are believed to be the most primitive bodies in our planetary system, having preserved material from the early stages of its formation, the Rosetta mission shall result in a better understanding of the formation of the solar system. The Rosetta Lander, part of the Rosetta payload, is contributed to the mission by an international consortium of research institutes. It will perform in situ measurements on the surface of the comet nucleus. The science objectives of the Rosetta Lander can be comprised by: • • determination of the composition of cometary near surface matter: bulk elemental abundances, isotopes, minerals, ices, carbonaceous compounds, organics volatiles -in dependance on time and insolation. • • measurement of physical parameters — mechanical strength, density, sound speed, electrical permittivity, heat conductivity and temperature. • • investigation of topology, surface structure including colour and albedo, near surface structure (strategraphy) and internal structure. • • the comets interaction with solar wind. The payload of the Rosetta Lander consists of nine instruments with a total mass of about 20kg. The Rosetta Lander system with an overall mass of about 85kg consists of a light weight structure of carbonfibre material, solar cells to provide power, a thermal control system securing operation without the use of radiactive heaters, a telecommunications system, using the orbiter as relay to Earth and a central computer, serving all subsystems and the payload. The lander will be ejected from the main spacecraft after selection of an adequate landing area from an orbit, about 1–5km above the surface of the nucleus. The actual descent strategy is highly depending on the (yet unknown) physical parameters of P/Wirtanen (like mass, shape and rotation period). Thus, a flexible landing concept, which allows the setting of the landing parameters interactively during the mission is required. Landing will take place on a tripod that includes a device that dissipates most of the impact energy and allows rotation of the main structure. At impact, a hold-down thruster and the shot of an anchoring harpoon will avoid rebound from the surface.

Experimental Investigations of the Comet Lander Philae Touchdown Dynamics

The comet lander Philae (as part of Europe’s Rosetta mission) is en route to its target, 67/P Churyumov-Gerasimenko. With landing operations coming up at the end of 2014, a partial retesting of the Philae lander’s touchdown system was carried out in spring of 2013. Intensive testing was performed as part of Philae’s design and verification program approximately 10 years ago. However, the new test series specifically addresses touchdown conditions that have been out of capability of the pendulum test facility used at those times. Thus, the follow-up tests focus on touchdown conditions such as asymmetric loads, effects from terrain undulation, and the effect of granular soil mechanics, which could not be studied sufficiently in the original tests. This paper provides insight into the touchdown system of the Philae lander, the characteristics of the used test facility, its weight offloading operating mode, and the specific application to a small-body landing test. The results of the study are presented and d...

Current status and scientific capabilities of the ROSETTA Lander payload

Abstract ESAs cornerstone mission “ROSETTA” to comet 46P/Wirtanen will bring a 100 kg Lander (provided by an international European consortium) with a scientific payload of about 27 kg to the surface of the comets nucleus. After a first scientific sequence it will operate for a considerable fraction of the cometary orbit around the sun (between 3 AU and 2 AU). The Lander is an autonomous spacecraft, powered with solar cells and using the ROSETTA Orbiter as a telemetry relais to Earth. The main scientific objectives are the in-situ investigation of the chemical, elemental, isotopic and mineralogical composition of the comet, study of the physical properties of the surface material, analyze the internal structure of the nucleus, observe temporal variations (day/night cycle, approach to sun), study the relationship between the comet and the interplanetary matter and provide ground reference data for Orbiter instruments. Ten experiments with a number of sub-experiments are foreseen to fulfil these objectives. In this paper we present the current status of the instrumental development and the scientific capabilities of each of the experiments.

The Close-Up Imager Onboard the ESA ExoMars Rover: Objectives, Description, Operations, and Science Validation Activities

Abstract The Close-Up Imager (CLUPI) onboard the ESA ExoMars Rover is a powerful high-resolution color camera specifically designed for close-up observations. Its accommodation on the movable drill allows multiple positioning. The science objectives of the instrument are geological characterization of rocks in terms of texture, structure, and color and the search for potential morphological biosignatures. We present the CLUPI science objectives, performance, and technical description, followed by a description of the instruments planned operations strategy during the mission on Mars. CLUPI will contribute to the rover mission by surveying the geological environment, acquiring close-up images of outcrops, observing the drilling area, inspecting the top portion of the drill borehole (and deposited fines), monitoring drilling operations, and imaging samples collected by the drill. A status of the current development and planned science validation activities is also given. Key Words: Mars—Biosignatures—Plane...The Close-Up Imager (CLUPI) onboard the ESA ExoMars Rover is a powerful high-resolution color camera specifically designed for close-up observations. Its accommodation on the movable drill allows multiple positioning. The science objectives of the instrument are geological characterization of rocks in terms of texture, structure, and color and the search for potential morphological biosignatures. We present the CLUPI science objectives, performance, and technical description, followed by a description of the instruments planned operations strategy during the mission on Mars. CLUPI will contribute to the rover mission by surveying the geological environment, acquiring close-up images of outcrops, observing the drilling area, inspecting the top portion of the drill borehole (and deposited fines), monitoring drilling operations, and imaging samples collected by the drill. A status of the current development and planned science validation activities is also given. Key Words: Mars-Biosignatures-Planetary Instrumentation. Astrobiology 17, 595-611.

Rosetta Lander: On-Comet Operations Preparation and Planning

The ESA Rosetta mission is a European cornerstone mission that will study the evolution of comet 67P/Churyumov-Gerasimenko on its trajectory around the Sun and will include the delivery of the Philae lander for in-situ investigation of the comet nucleus and sub-surface. Philae is funded and operated by a European consortium, and consists of an independent spacecraft platform including 10 scientific instruments. Philae operations are scheduled and implemented by the Science Navigation and Operations Center (SONC) at CNES/Toulouse and the Lander Control Center (LCC) at DLR/Cologne. Rosetta was launched in March 2004 and conducted a 7 year cruise phase, after which a 3 year long deep space hibernation phase followed, in order to cope with the large Sun distances around the trajectory aphelion. In January 2014 Rosetta was woken up and the comet rendezvous phase commenced. Landing is foreseen for November 2014 to a landing site which will be selected during the preceding three month landing site selection process. The final descent trajectory and postdelivery Rosetta trajectory, with associated Philae – Rosetta communication windows, will be computed 30 days prior lander delivery. The Philae operations team must ensure that the baseline descent and science timelines developed over the timeframe 2011 – 2013 are adaptable in order to cope with the intrinsic uncertainties. Furthermore, Philae will conduct a long term science phase during which various scientific measurements are performed in order to characterize the evaluation of the nucleus and subsurface as a function of the decreasing Sun distance. The operational process and procedure developed by the Philae operations team will allow for the rapid adaptation to landing site specific features such as the comet local landing epoch, day/night variations and communication window uncertainties.

Clean In Situ Subsurface Exploration of Icy Environments in the Solar System

To assess the habitability of the icy environments in the solar system, for example, on Mars, Europa, and Enceladus, the scientific analysis of material embedded in or underneath their ice layers is very important. We consider self-steering robotic ice melting probes to be the best method to cleanly access these environments, that is, in compliance with planetary protection standards. The required technologies are currently developed and tested.

Rosetta-Lander: On-Comet Operations Execution and Recovery after the Unexpected Landing

Philae’s landing on comet 67P/Churyumov–Gerasimenko on 12 November 2014 was one of the main milestones of the European Rosetta mission. The nature of Philae’s mission, to land, operate and survive on comet 67P, required a high degree in autonomy of the on-board software and of the operations scheduling and execution concept. Philae’s baseline operations timeline consisted of predefined and validated blocks of instrument deployments and scientific measurements. These were supported by subsystem activities such as rotation and lifting of the main body relative to the landing gear to allow for specific instrument deployment or in order to cope with the unknown attitude after landing. The nominal descent was followed by an unforeseen rebound at touchdown, lifting Philae again from the comet surface to enter a two-hour phase of uncontrolled flight over the comet surface. Philae’s unknown final landing site, unfavorable attitude with respect to the local surface, bad illumination and lack of anchoring required a complete rescheduling of the baseline timeline. The autonomy offered by the system and the predefined contingency operations were exploited by the operations team to maximize output despite this undesirable state. Implementation of the rescheduling to allow a maximum scientific output, despite the limitations due to unknown communication windows, unknown orientation with respect to the comet surface, the associated risks of any mechanisms activation, the lack of sufficient solar power and limited battery lifetime, is described and elaborated.