Past studies: SIMONE

More detailed information on the SIMONE mission is available on the Executive Summary

Mission Concept

SIMONE (Smallsat Intercept Mission to Objects Near Earth) is a unique interplanetary mission concept comprising a fleet of low-cost microsatellites that will individually rendezvous with a different Near Earth Object (NEO), each of a distinct spectral and/or physical type. In-situ science measurements taken by instruments on-board each spacecraft enable the wide diversity in the physical and compositional properties of the NEO population to be characterised in a highly cost-effective manner. Analysis of the in-situ measurement data from the SIMONE rendezvous missions will provide:

  • Valuable scientific knowledge on the nature, origin and processing of NEOs;

  • Critical physical/compositional information needed for the accurate prediction of impact risk (particularly damage potential) posed by NEOs;

  • Critical physical/compositional information needed for the development of effective NEO risk mitigation strategies that are specifically tailored for each NEO type.

The SIMONE mission study team is led by QinetiQ (UK) in partnership with the Planetary and Space Sciences Research Institute (PSSRI) of the Open University (UK), SciSys (UK), Politecnico di Milano (Italy) and Telespazio (Italy).

Mission overview

SIMONE can be realised by the use of microsatellite technology - this would be a world-first for an interplanetary mission. Conducting multiple NEO rendezvous missions with large conventional spacecraft would be prohibitively expensive. It is planned to deploy 5 of the SIMONE microsatellites to their intended rendezvous targets within the budget envelope of an ESA Flexi-mission. In order to achieve this target, a low-cost approach is needed and this is only attainable by using microsatellite technology.

The SIMONE microsatellites are based around a single spacecraft system design, configuration and payload, and a single ground segment, thereby significantly lowering recurring costs. "Piggyback" launch opportunities on the Ariane Structure for Auxiliary Payloads (ASAP) on Ariane-5 will be exploited in order to obtain low launch costs. Traditionally, launch costs are a significant cost driver for interplanetary missions because a dedicated deep space launch is usually required for direct injection onto an interplanetary trajectory. Instead, these launches will place each SIMONE spacecraft into a Geostationary Transfer Orbit (GTO).

From GTO, on-board propulsion is required to achieve an Earth escape trajectory, adjust the interplanetary trajectory and eventually rendezvous with the target NEO. This places high delta-velocity requirements on a spacecraft that has a tightly constrained mass budget. As a piggyback payload on an Ariane 5 launch, the mass of each spacecraft is limited to 120kg. Mission feasibility is assured by the use of efficient low-thrust solar electric propulsion in order to achieve the demanding rendezvous mission objectives with a low propellant mass consumption. The ion propulsion system is driven by lightweight, high power solar arrays that can be efficiently stowed within the limited launch volume.

Science objectives

The primary mission objectives of the SIMONE mission at each different NEO are to determine (in priority order):

  • Bulk density: requiring both the mass and volume (size, shape) to be measured. For the particular spectral/physical class, it then allows predictions of the mass (and thus impact energy) to be made for other objects that are determined to be of the same class from ground observations. Bulk density can also be an indication of porosity.

  • Gravity field: spherical/elliptical harmonics of the gravity field, together with a shape model, allow the derivation of large-scale internal density variations using a mass distribution model. These variations may have a bearing on the dynamical behaviour of a similar object on Earth approach, entry and impact, as well as providing extra evidence as to the internal structure for aiding mitigation strategy development.

  • Surface topography/morphology: the high-resolution surface information, in conjunction with compositional information, can be interpreted to give indications as to the object's internal structure. Surface features to examine include craters, grooves, fracture lines, regolith and boulders. From surface measurements, a detailed shape model will be constructed to improve mass and hence bulk density determination accuracy.

  • Composition: provides spatial information to allow macroporosity to be estimated. Precise elemental/mineralogical composition can only be determined by a spacecraft encounter such as with SIMONE. Variations in composition across the surface will be correlated with topographic/morphological features, adding to the information available for assessment of the object's sub-surface properties/structure.
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