AIM is expected to contribute to the scientific understanding of the formation of binary asteroid systems, as well as show the capability to characterise the dynamical state and the physical properties of an asteroid along with a change of these parameters following a high-velocity collision with an external object. The following payload instruments have accordingly been selected for their ability to provide the required measurements or as demonstrators for enabling technologies:
Visual Imaging System (VIS)
The Visual Imaging System on AIM would be used both for guidance, navigation and control functions and to perform scientific measurements. In its scientific role it will be imaging the target asteroid system from multiple fixed positions and from various distances during the course of the AIM asteroid observation phases.
The purpose of the measurements is to provide information on the binary asteroid dynamics and – especially for the smaller Didymoon, DART´s target – its physical characteristics.
The VIS would be used to accurately determine Didymoon’s shape and size, as well as its dynamical state (period, orbital pole, spin rate) both before and after impact. It would also be able to image the bulk surface features, search for dust presence and perform real-time ejecta observations. After impact the VIS would be used to determine the crater density and compare the geomorphology of both Didymain and Didymoon.
Thermal InfraRed Imager (TIRI)
The thermal imager's (TIRI) primary goal is to discriminate between different possible surface properties of Didymoon, such as bare rock versus granular or dusty surfaces. Its secondary goal is to measure the thermal properties of the asteroid surface that are relevant to the characterisation of the soil structure and cohesion, and those that contribute to the thermal effects, in particular 'Yarkovsky/YORP' rotational changes.
The scale of interest for the AIM mission is given by the likely size of a crater generated by a DART-like impact. Numerical simulations of the DART impact indicate that a resolution of at least 20 m will be required.
TIRI would also be used to study the ejecta plume to determine the temperature of the expelled dust plume and the rate of change, which may give information on dominant grain size, the thermal inertia of the dust and the crystallinity and mineralogical composition of the dust.
AIM would also be the first mission to demonstrate use of an IR instrument to support the asteroid rendez-vous phase by acquiring complementary data for flight dynamics analyses.
High-Frequency Radar (HFR)
The main objective of AIM’s monostatic High-Frequency Radar (HFR) is to obtain information on the structure of the asteroid´s outermost surface and sub-surface layers, up to a depth of 10 m with a resolution of maximum 1 m (goal would be 0.2 m). Scanning Didymoon with an HFR instrument would enable the scientists to study the layering of the sub-surface and the 2D distribution of “rocks” on the surface.
Moreover, the HFR might be used to estimate the dielectric permittivity of the sub-surface material to gain insight into the surface composition and the content of volatile compounds. It may also provide valuable data on dust particles around Didymoon (before and after impact) and may be used to support the visual data on Didymoon’s mass and shape.
Low-Frequency Radar (LFR)
The AIM bistatic Low-Frequency Radar (LFR) main goal is to obtain data on the asteroid internal structure, with a typical resolution of 30 meters. Both the main AIM spacecraft and the lander will carry an emitter and receiver of the LFR so that signals can be sent through Didymoon during full asteroid rotations. During these measurements the geometry will change from the lander facing the main spacecraft to the lander and the main spacecraft being on opposite sides of the asteroid.
These full asteroid rotation measurements will enable a full characterisation of the homogeneity of Didymoon and extensive study of the mineralogy and porosity of the internal structure. Variations in density and a complete mapping of Didymoon’s 3D structure (and deep layering) will also become apparent.
Optical laser terminal (Optel-D)
The Optel-D optical downlink system will be an In-Orbit-Demonstration of the capability to transmit data over large distances. The copious amounts of data gathered from Didymoon’s surface and subsurface mapping will be returned via laser beam to ESA’s optical ground station in Tenerife, thereby accomplishing high-bandwidth optical communications from deep space.
The optical communication system will for the first time demonstrate deep-space communication between the main spacecraft and Earth.
As an altimeter the optical laser terminal will have a vertical and horizontal surface resolution of 1 m or better to accurately position the AIM spacecraft around Didymoon. This will allow a more precise release of the MASCOT-2 lander, so the risk of bouncing off the asteroid can be further reduced.
The optical system will also provide accurate measurements of the 3D shape of Didymoon, as well as of the asteroid’s surface topography with a precision of 20 cm. By measuring the wobble of Didymain before and after impact it will be possible to determine the amount of mass loss on Didymoon caused by the impact.