The Hopter project

is being developed by the Space Research Centre of the Polish Academy of Sciences, the WROONA project, Astronika Sp. z o. o., and the Angström Space Technology Centre., and the Finnish Geospatial Research Institute.

See the presentation at the 11th Low-Cost Planetary Missions conference in Berlin (June 9-11, 2015).

The Hopter is an innovative locomotion system designed to investigate in situ planetary mountains and ultra-low gravity Solar System bodies.

Planetary exploration: problems with the current mobile exploration platforms

Exploration of ultra-low Solar System bodies: lessons from the Philae platform

Lessons from the Moon

HOPTER: the Highland Terrain Hopper

Mopters, Phobters and Kbopters

Hopter features

Current development stage

The Hopter compared to previous space hoppers

Planetary exploration: problems with the current mobile exploration platforms

All the known solid bodies of the Solar System have gravity lower than the Earth. The platforms currently used for the exploration of these bodies include rovers and landers. Landers consist of an immobile platform from which analysis of the ground and environment is performed; their strength is therefore, in addition to accurate in situ observations, the ability to monitor events at that site, for instance weather patterns. The strength of rovers lies in the possibility of exploring many kilometres; however two severe restrictions apply: (1) related to landing and trafficability (both place dramatic constraints on slopes and terrain roughness throughout the 10s of km wide landing ellipse; e.g. [1]); (2) related to the surface gravity: roving relies on adherence of wheels to the ground, so that on ultra-low gravity bodies such as Phobos and Deimos, asteroids, cometary nuclei or Kuiper Belt Objects (KBOs), roving is not possible.

The landing and trafficability issues cause major problems for geology. Most of the knowledge of field geologists is learnt from highland terrains indeed, whether on land or in the sea, because mountains give a three-dimensional view of the geological processes. Roaming around provides information on their geographic extent as well as on their evolution through time (Figure 1). Escaping the landing ellipse takes a lot of time: although the dimensions of the landing ellipse for the MSL/Curiosity rover was smallest ever (20 x 25 km), it took the rover 692 Earth days to cross its landing ellipse border [2], meaning that:

(1) due to the nearly flat terrain constraints on planetary landing and roving, the view that rovers give us can be compared to the view that geologists would have of the Earth if only kilometres of regions such as the Sahara and the Mississippi delta were explored;

(2) the instruments and the main system are already 2 years old once the 'Sahara reg landing constraints' is released; the observed damages on the Curiosity wheels testifies to this concern (Figure 2).


      The Hopter project is developped by a
       team lead by:

      Jerzy Grygorczuk, Chief Engineer
       Daniel Mège, Chief Scientist

       Core team members are:
      Joanna Gurgurewicz, researcher
       Łukasz Wiśniewski, engineer
       Marek Banaszkiewicz, researcher
       Hans Rickman, researcher

Downloads and links

Figure 1. One of the most astounding achievements of field geology: west-east geological profile across the Alps, an excerpt of an evolution scenario of the Alps, one of the most complex terrestrial orogens, proposed by Swiss geologist Emile Argand in 1916. The modern geological and geophysical works have remarkably confirmed this interpretation. It is especially consistent with plate tectonics, which was theorised 51 years later.

Figure 2. Damaged Curiosity wheel in August 2014, after roving on flat terrains during 2 terrestrial years.

The lifetime estimate of the Curiosity wheels on the terrains it was investigating in 2014 corresponds to 8-14 km, which motivated revision of the planned route to Mount Sharp, its destination [3]. The question of accessing interesting terrains beyond the landing ellipse has been recognized critical [4]. Surfaces of loose materials such as debris slopes of crater walls also prevent from accessing overlying crater wall outcrops.

The adherence issue for ultra-low gravity objects limits exploration of these objects to landers, i.e. to a study of a single site at the surface, chosen as a function of the landing constraints (slopes, rock abundance, spacecraft motion relative to the studied object…) and instrument requirements (communication with the orbiting spacecraft or the Earth, sunlight…), not significantly of the intrinsic scientific interest of the landing site compared to other potential sites.

Mandatory is to access planetary mountains in order to gain 3-dimensional views of the surfaces, as well as having mobility within these mountains. On Mars, such mountains are, for instance, Valles Marineris, Cerberus Rupes, Olympus Mons basal scarps and slopes. On the Moon, steep rille walls display crustal outcrops, and impact basin rims and central peaks open a window to the materials that compose the deep lunar crust.

Exploration of ultra-low bodies: lessons from the Philae platform

After release from the Rosetta spacecraft, the Philae lander bounced twice before being ar-rested against a rock, in spite of a sophisticated mechanism that should have kept it at the site of first touchdown. The MUPUS instrument on Philae, designed and built at the Space Research Centre (SRC) PAS in Warsaw (under contract with DLR), worked perfectly well and returned scientific data that are currently being analysed.

Figure 3. Philae release from Rosetta (credit: ESA/Rosetta/Navcam) and modelling of Philae orientation after its final rebound. Philae is blocked by the surrounding topography (credit: ESA/Rosetta/Philae/CIVA).

This calls for the following remarks:

1. Predicting a final landing site on a very low gravity body such as a cometary nucleus or an asteroid is extremely difficult (and expensive);

2. Why not take advantage of bouncing instead of attempt to avoid it? The Philae jumps illustrate that jumping on low gravity bodies is easier and more efficient than any other locomotion system and allows, with a very small quantity of energy, to investigate large portions, or the whole surface of the studied bodies in detail. Jump analysis is also able to provide information on the subsurface structure ot the studied body.

3. With MUPUS, SRC PAS has demonstrated skills to develop original, complex and efficient low gravity space systems. This offers a huge potential for future space exploration. The importance of landing in low gravity conditions is critical to space exploration today indeed, for scientific research and investigation of resources, as most solid bodies in the Solar System have a gravity field which is lower than the Earth's.

Lessons from the Moon and other neighbours

Video 1. Apollo 17 astronaut Eugene Cernan jumping and discussing with Harrison Schmitt: jumping is the best way of moving on low-gravity bodies.

167:09:45 Cernan: (Doing long, two-footed hops) This is the best way for me to travel. Uphill or downhill.
167:09:48 Schmitt: What's that?
167:09:50 Cernan: Like this. Two-legged hop.
167:09:53 Schmitt: There seems...Yeah.
167:09:54 Cernan: And on level ground, I can skip. I don't like that loping thing.
167:09:59 Schmitt: Oh, the loping's the only way to go.
167:10:01 Cernan: Well...See, when I'm on level ground, I can skip. But this two-legged thing is great! Man, I can cover ground like a kangaroo!

 Transcript is © 1995 by Eric M. Jones.

The Apollo movies of the Moon (like in Video 1) emphasize that the astronauts had realized that jumping is more efficient and saves more energy than walking on low-gravity bodies because of the low adherence to the ground and the resulting low friction, which makes difficult displacement parallel to the planetary surface. On Mars and the Moon, jumping is an efficient way of moving; on even lower gravity bodies such as asteroids, jumping is the only way. Therefore, a platform that is to replace a field geologist on low-gravity and ultra-low gravity bodies needs to combine the ability of climbing (and climbing down) scarps by following the most appropriate path, and recovering in case of fall or slip, as a geologist would do in mountains, but also jump.

Jumping is also the main locomotion system for a number of animal species. Galagoes (Video 2) are among these, and the Highland Terrain Hopper has been nicknamed Galago.