Marco Polo: A Sample Return Mission to a Primitive NEO
MetadataShow full item record
Marco Polo is a Near-Earth Object (NEO) sample return mission currently studied by the European Space Agency (ESA). The intention is to perform this mission in collaboration with the Japanese Aerospace Exploration Agency (JAXA). It has been selected as a medium-class mission candidate for a one-year competitive assessment study within the Cosmic Vision 2015-2025 programme of ESA. At the end of 2009 a further down-selection will occur and the retained missions will enter into definition phase. Eventually the final M-class mission will be selected in 2011 to enter into implementation phase. The primary goal of Marco Polo is to return to Earth samples of surface material from a primitive NEO (e.g. D or C-type). At this early stage many design options are being assessed, including the NEO target which is one of the primary mission drivers. A number of them have been identified based on their scientific interest and analyses are ongoing to determine which ones are most compatible with the technical, cost and programmatic requirements. A launch in 2017 onboard a Soyuz-Fregat 2-1b from Kourou is currently envisaged. Various launch and orbit insertion strategies are possible such as direct launch to escape trajectory to meet the Vinf requirement or launch to an intermediate HEO orbit and later burn sequence to achieve the required Vinf via the spacecraft propulsion module. In addition the interplanetary outbound and inbound transfer strategy, i.e. propulsion (impulsive vs low-thrust) and gravity assist, will be traded against scientific return, mass, transfer duration and cost criteria. Upon encounter with the NEO, the spacecraft is inserted within its vicinity, either out of its sphere of influence at a so-called "home" position or on a closer self-stabilizing orbit. During this phase a scientific payload suite characterizes the global physical and mineralogical properties of the NEO as well as identifies all surface hazards. Orbiting is currently preferred as it yields higher resolution data. Some instruments will also be used as navigation sensors so as to optimize onboard resources. Following this, up to five sampling sites are locally characterized at very high resolution and one of them is selected based on its scientific value and the risk it yields on the sampling operations. Due to the highly perturbed NEO gravity environment and the long communication times the spacecraft then autonomously descends towards the selected site, collects 10-100 g of material from the top surface layer, retrieves context information and verifies that a scientifically valuable sample has been acquired. The exact descent and sampling sequence is to be defined in the early stage of the study and will be based on one of the following approaches: hover and go, touch and go or soft landing. The possibility of sampling at more than one site is envisaged. The collected material is then transferred to the Earth Re-entry Capsule (ERC) which is carried back to Earth by the return vehicle and released shortly before arrival. Before landing the ERC undertakes a challenging high-speed re-entry through the Earth atmosphere at a velocity between 12 and 14 km.s-1, depending on the finally selected target. The current baseline is a fully passive ERC (i.e. no parachutes). Eventually the sample is transported to a dedicated curation facility. Due to the stringent mission cost and programmatic requirements simple and robust technologies with a high technology readiness level will be favoured throughout the assessment study. This paper will present the study status and an overview of the mission scenario with a focus on the key enabling technology areas involved in the NEO landing and Earth re-entry phases. These can efficiently build upon the expertise of ESA acquired in sample return mission studies (e.g. Mars Sample Return) and JAXA who has tremendous development and flight experience from the ongoing Hayabusa mission.