HARPOON mission concept: Hydration And Regolith Penetration Observatory On Mars

Understanding the present-day behaviour of water on Mars —including its exchange between the atmosphere and subsurface, potential for transient liquid phases, and stability of shallow ice deposits— remains a central question in planetary science. A critical scientific challenge is to determine where, when, and for how long thermodynamic conditions —in the near-surface atmosphere and the shallow subsurface— are favourable for brine formation.

In this work we will present the overall concept of HARPOON (Hydration And Regolith Penetration Observatory On Mars), a mission aimed at investigating how does water actively exchange between the Martian atmosphere and subsurface and to what extent may this lead to the formation of transient liquid phases. HARPOON is based on a reduced network of micro-probes landed at three different sites on Mars. These probes are based on the MarsConnect concept, consisting of small penetrators with a very simplified Entry, Descent and Landing (EDL) architecture [1].

 

Scientific Objectives

HARPOON objectives are: (A) Determine the number of hours and sols with favourable temperature and humidity conditions for brine formation, detect their presence, and estimate their formation kinetics; (B) Quantify the influence of atmospheric conditions on water exchange with the subsurface over diurnal and seasonal timescales; and (C) Determine the regolith insulation capacity for subsurface ice stability under modern Martian climatic conditions.

These investigations will be carried out through a combination of atmospheric and subsurface sensors.

Preselected landing sites include 3 different latitudes from 10 to 40 degrees North in vast regions of Mars where the probability of detecting transient brines is considered higher [2].

Fig.  1. Maps of Mars showing the percentage of year that a Calcium Perchlorate brine formed by deliquescence can exist on the Martian surface (from Rivera-Valentin et al., 2020). Preselected landing areas marked in red.

 

Mission Approach

The mission consists of three penetrating micro-probes. These penetrators enter the Martian atmosphere inside a rigid aeroshell that provides the necessary thermal protection and is ejected before impact. The mission is proposed as a piggy-back of a bigger one, being ESA’s Ligthship propulsive tug the baseline [3]. The de-orbit from Lightship orbit (at 5720 km) to the surface is done individually by each probe thanks to a spin-stabilized Transfer Stage. Different options entailing diverse delta-V values have been considered for each target landing site.

Fig.  2. Conceptual view of one probe with its Transfer Stage (left). Two possible types of descent trajectories (right).

Approaching the atmosphere, the Transfer Stage releases the probe. It enters the atmosphere at about 140 km height and starts an uncontrolled descent through it. Once the peak heat load altitude has passed, still at supersonic regime, the probe aeroshell is ejected and the penetrator drops alone. To increase braking and reduce impact speed —that will happen at 80 to 120 m/s depending mainly on the atmospheric density— the penetrator deploys a semi-rigid drag-skirt.

The penetrator can survive and operate on Mars for one Martian year in latitudes up to 30 degrees, and all year but local winter at 40 degrees.

Details on the scientific objectives, mission approach, technical implementation, scientific sensors and technology development needs will be presented.

 

REFERENCES:

[1] Ignacio Arruego et al., “Mars environmental networks through the MarsConnect microprobes”, EPSC Abstracts, Vol. 17, EPSC2014-92.

[2] Edgard G. Rivera-Valentín et al., “Distribution and habitability of (meta)stable brines on present-day Mars”, Nature Astronomy, 4, 756-761, 2020.

[3] Mars Exploration Study Team, ESA, “Lightship 1 – Mission Description Document”, ESA-E3P-LS1-TN-001, 2024, unclassified.