The Melting Probe

The exploration of the ocean worlds in the outer solar system is of particular interest for the search for extraterrestrial life. Under a kilometer-thick ice-shell, the global oceans are well hidden and not easily accessible, posing extreme challenges to the TRIPLE melting probe. Therefore, ice drilling and state-of-the-art technologies need to be developed to meet the requirements.

With regard to future missions to icy moons, an analogous terrestrial demonstration is planned for the Dome-C region in Antarctica. This is considered the hardest test site on Earth, where none of the existing technologies is suitable for withstanding the resulting environmental conditions. The Dome-C mission demands a retrievable melting probe to get through a 4 kilometers-thick ice-layer. For the mission it is of great importance for the melting probe to be capable of detecting and avoiding obstacles on its trajectories, anchoring at the ice-water boundary to release and support the nanoAUV.

The TRIPLE melting probe concept for the demonstration in Antarctica alongside a snowcat and a 40 ft. container serving as transport container, surface station and launch pad.
(© GSI GmbH)

One of the many challenges for the melting probe is the required high melting speed to execute the mission within one Antarctic summer season. Taking the distance of 4 kilometers into account, a minimum speed of 10 m/h is needed. To reach this high speed a high power transmission with as little loss as possible over the large cable length is required. As the most critical component, the cable must also bear the weight of the probe.

In 2014, the very first successful application of a melting probe to collect contamination-free subglacial water samples was demonstrated by the melting probe “Ice-Mole” on the Antarctic Taylor glacier. The Ice-Mole was developed within the Enceladus Explorer (EnEx) project mounted by the German Space Agency at DLR. To get to the scientific object of desire, a crevasse in the Taylor glacier, the Ice-Mole had made its way through an ice layer of about 16 m with a melting speed of one meter per hour [2].

As a first demonstrator towards the TRIPLE-melting probe, a modular melting probe is under construction within the project TRIPLE-IceCraft [1]. This project is a collaboration between the GSI GmbH and the RWTH Aachen University. The development aims for a fully functional and retrievable melting probe that provides standardized cargo area for arbitrary scientific payloads and a drill depth of several hundred meters. It is designed for a maximum speed of up to 5 m/h. One of the key challenges is the full retrievability of the system and therefore the need for a dedicated cable management system. This is constructed as a combination of internal storage and an electric-motor-powered winch for uncoiling and recoiling the cable. 

In order to prove the performance of the system, a field test on the Langenferner glacier in Italy is planned for 2022. The final demonstration will be performed at the Ekström shelf ice in Antarctica at the end of the project early 2023.

Scheme of the TRIPLE-IceCraft structure and submodules 
(© GSI GmbH)

The development of the forefield reconnaissance system for the melting probe is running in parallel within the project TRIPLE-FRS. A combination of radar and sonar techniques is chosen to benefit from both sensor principles inside ice. To account for the respective propagation speed of electromagnetic waves, an in-situ permittivity sensor will also be included. By integrating the radar antennas together with a specialized pulse amplifier as well as a piezoelectric acoustic transducer into the melting head, obstacles as well as the ice-water interface can be detected. 

Section through the FRS melting probe demonstrator. The different color indicate a simplified division of the installation space between the FRS-subsystems (© FRS)

In July 2021, the first FRS-field test was carried out on the Langenferner glacier in Italy delivering promising results. Several field tests on alpine glaciers will follow up in 2022 and 2023.

Foto of the FRS melting probe demonstration on the Langenferner glacier in Italy – July 2021 (© FRS)


[1]  D. Heinen, J. Audehm, F. Becker, G. Boeck, C. Espe, M. Feldmann, G. Francke, P. Friend, N. Haberberger, K. Helbing, C. T. Nghe, M. Stelzig, M. Vossiek, C. Wiebusch & S. Zierke, „The TRIPLE Melting Probe – an Electro-Thermal Drill with a Forefield Reconnaissance System to Access Subglacial Lakes and Oceans“, OCEANS 2021: San Diego – Porto, 2021, pp. 1-7, doi: 10.23919/OCEANS44145.2021.9705999.

[2] J. Kowalski et. al., “Navigation technology for exploration of glacier ice with maneuverable melting probes”, Cold Regions Science and Technology, Volume 123, 2016, Pages 53-70, ISSN 0165-232X, doi: 10.1016/j.coldregions.2015.11.006