Robot Technology for the Cometary Landing Mission Rosetta

R. Mugnuolo

Italian Space Agency (ASI)

E. Pozzi, M. Fenzi

Tecnospazio (I)

Résumé
Rosetta est une mission pierre angulaire de l'Agence, qui sera consacrée à l'étude de l'environnement des noyaux cométaires et de leur évolution au voisinage du Soleil. La mission met en oeuvre un module orbital et une sonde autonome, qui se posera à la surface d'une comète pour y effectuer des analyses. L'un des éléments-clés du module d'atterrissage est son sous-système de sondage, de forage et de distribution, outil robotisé capable de prélever des échantillons de la surface cométaire et de les distribuer aux instruments de bord pour analyse.

Contractors:
Tecnospazio (I), Tecnomare (I), Rodio (I) and Dallara (I).

Funding:
Italian national programme

Introduction

Rosetta is an ESA cornerstone science mission to study, in situ, the environment of cometary nuclei and their evolution in the inner solar system. The main scientific objectives of the mission are to investigate the origin of the solar system by studying the origins of comets and to study the relationship between cometary and interstellar material. To enhance the scientific capabilities of the mission, the orbiter spacecraft will carry one probe, a lander which will land on the comet surface of the comet and perform investigations in situ.

The Rosetta orbiter spacecraft will be launched in 2003 and, after a 9-year cruise, will begin the cometary close observation phase. By 2012 the in situ investigations will be complete. The lander (Figure 1) is being developed by combined effort in Germany, Italy, France,
the United Kingdom, Hungary, Finland and Austria.

Figure 1. An artist's impression of the Rosetta cometary lander.

Sampling, drilling and distribution subsystem

The sampling, drilling and distribution (SD2) subsystem will provide microscopes and advanced gas analysers with samples collected at different depths below the surface of the comet. Specifically SD2 can bore up to 250 mm into the surface of the comet and collect samples of material at predetermined and/or known depths. It then transports each sample to a carousel which feeds samples to different instrument stations: a spectrometer, a volume check plug, ovens for high and medium temperatures and a cleaning station. SD2 will be accommodated on the flat ground-plate of the Rosetta, where it will be exposed to the cometary environment
(Figure 2).

Figure 2. The sample, drilling and distribution subsystem of Rosetta.

The main performance requirements of SD2, which must operate in microgravity, are:

• high level of autonomy due to long communication time delay between Earth and the lander;

• simple and reliable operation with a vast range of materials ranging from fluffy snow to rock (tuff) at temperatures as low as
  -200°C;

• introduction of little or no contamination to samples;

• minimisation of sample material loss during sampling operations;

• a total mass less than 3.1 kg (including electronics) and power consumption of less than 5 W;

• capability to reuse the micro containers for several experiments;

• production of images of the bore-hole;

Subsystem design

SD2 has three main components: a tool box, a carousel and a local control unit. The tool box houses the drill and the sampler in a protective structural shell (made of composite material) which ensures that no external contamination can reach the tools and the four actuators located inside.

The tool box can rotate about an axis which is vertical to the flat ground plate. The drill has two degrees of freedom: it can move laterally to approach and penetrate the comet surface and it can rotate around its own axis. After the drilling operation is complete, the drill bit is removed from the bore-hole and the sampler is inserted to collect specimens. The sampler also delivers the specimen to the ovens. Since the choice of drilling parameters and the characteristics of the cometary material must be determined automatically, the drilling head is fitted with a compact force and torque sensor.

The carousel (Figure 3) is a thin platform which is mounted on the flat ground plate and which has several micro-containers (ovens) to hold the material samples. A rotational actuator enables the carousel to mate a given micro-container with the cleaning and measurement stations. A cleaning station is needed because some of the containers will be reused.

Figure 3. The carousel used for collection and analysis of samples.

The local control unit autonomously interprets and executes commands and tasks, provides an electrical interface for exchanging data with the Rosetta lander and for motor control. To meet constraints of low mass and power, a new three-dimensional electronics packaging technology is under evaluation.

Conclusions and future development

The work briefly described in this article faces a great challenge in both mechanical and electronics technology. It is a consistent step towards the use of automatic systems in space, and shows once again the importance of robotics for scientific purposes in space. The know-how gained will be useful for investigating possible applications to other missions, for example the exploration of Mars or the Moon.