DORA: Deployable Optics for Remote sensing Applications

The technological developments that led to the miniaturization of satellites, bringing to the market mini (<500kg), micro (<100kg) and nano (<10kg) satellites, impose that an analogue technological step forward is carried out as far as payload is concerned.

Small platforms allow reducing costs of development and management of single missions but also ease the possibility of using distributed systems in space making use of more satellites flying in formation or as a constellation. Furthermore, mini, micro and nano satellites are optimal candidate as platforms for the test and validation in space of innovative technologies with a lower level of maturity and thus not directly usable onboard “standard” sized satellites.

The new generation of mini, micro and nano satellites can be proficiently used for the exploration and commercial utilization of small bodies of the Solar System (NEA, NEO, MBC, Asteroids); the characterisation of those bodies, in terms of composition, dimensions and interior structure, is of fundamental importance for the study of the evolution of our Solar System but also for the exploitation of extraterrestrial natural resources.

There is a considerable advantage in using deployable systems onboard small satellites as these have considerable limitations in some of the resources, mainly mass and volume. The identification of payloads capable of minimising resources usage at launch, still guaranteeing in flight performances analogues to those of more “expensive”, in terms of resources, instruments is an extremely valuable benefit.

The capability of using deployable telescopes allows to access scientific objectives and applications otherwise difficult to reach. In fact, remote sensing payload in the VIS/IR is strongly handicapped by the limited resources available onboard a mini-satellite which limits the size of the primary mirror and/or the length of the telescope assembly, thus resulting in reduced performances in terms of spatial resolution and signal to noise ratio. Precision-deployable, stable, optical telescopes that fit inside smaller, lower cost launch vehicles and small platform are a prime example of a technology that will yield breakthrough benefits for future scientific as well as more commercially-oriented applications.

The DORA (Deployable Optics for Remote sensing Applications) project has been funded by the Italian Ministry of Research in the framework of the Italian National Research Plan 2015-2020 with a 30 months contract in a partnership between private companies (led by SITAEL the largest Italian privately-owned Company operating in the Space Sector), INAF (IAPS-Rome and Astronomical Observatory of Padua) the Parthenope University in Naples and Politecnico of Milan. Objective of the project is the design, realisation and test of a prototype of deployable optical system for Remote Sensing applications in the VIS and IR spectral ranges; a deployable telescope and straylight shield will be interfaced to a focal plane instrument (e.g. camera, imaging spectrometer, Fourier spectrometer). The telescope shall be stored in a closed configuration during launch to minimize volume and will be fully deployed in operative configuration once in flight by means of actuators. Similar deployable systems can be used to extend antennas used in microwave instrumentations (e.g., radiometers).  

The range of applications of such optomechanical technologies, in a space environment and onboard small satellites, are potentially very wide extending from Earth Observation satellites, used for environmental monitoring and for risk management, to Solar System exploration missions.  

In the framework of the DORA study the deployable optical system will be interfaced to an infrared Fourier spectrometer. We are taking advantage of the availability of the prototype of a miniaturised Fourier Spectrometer named MIMA (Mars Infrared MApper) [1] originally designed and built for the ExoMars 2020 mission but finally not among the selected payload; MIMA will be interfaced as a focal plane instrument to the Deployable telescope.

MIMA is a double pendulum interferometer providing spectra in the 2 – 25 μm wavelength domain with a resolving power of 1000 at 2 μm and 80 at 25 μm. The radiometric performances are SNR >40 in the near infrared and a NEDe = 0.002 in the thermal region. The instrument design is very compact, with a total mass of 1 kg and an average power consumption of 5 W. The prototype has been tested and reached a Technology Readiness Level (TRL) of 5 level of development.

The original FOV of the MIMA instrument was 3.2° which, although adequate for the in-situ analysis of the Martian soil, it is not sufficient to guarantee challenging results for typical Remote Sensing applications; thus MIMA will be matched to a 30 cm diameter, f/#=16, Cassegrain deployable telescope to reduce the FOV to ≤0.3°. The large sized primary mirror will guarantee the increase in collecting area needed to compensate for the considerable reduction of the FOV of the instrument.

Such a combined instrument can be used proficiently for the study of small bodies of the Solar System. These bodies are remnants of original planetesimals from which the planets were formed. Differently from planets, which have experienced alterations during their evolution, the majority of small-sized asteroids underwent much less internal heating, resulting in a better preservation of their pristine composition. Since small bodies were the impactors of the primordial Earth, they may have been the principal carriers of water and organic material, the building blocks necessary to create life.

A MWIR spectrometer like MIMA onboard a small mission will improve our understanding of the primordial cosmochemistry from small bodies remote sensing observations, providing unique data related to surface properties, mineralogy and thermal inertia. The scientific objectives can be summarised as:

• Analyse the thermophysical properties of the surface by measuring the temperature changes occurring during the diurnal cycle;
• Provide information on surface mineralogical composition and physical properties (grain size distribution, roughness);
• Search for thermal anomalies associated to the presence of surface rocks;
• Measure the thermal inertia of the surface

 

The presentation will describe the development status of the DORA project providing detailed information on its expected performances.

Acknowledgments. This study is funded by Ministry of Research PNR 2015-2020, specialisation area “aerospace” project n.ARS01_00653

References: [1] G. Bellucci et al., (2007). Proc. SPIE 6744, Sensors, Systems, and Next-Generation Satellites XI, 67441R, doi: 10.1117/12.737912