Digging machine

Digging Machines are used to dig holes into the ground and to move large amounts of material. On Mars specialized digging machines are required to

• gather regolith as raw material for a variety of substances
• fetch water ice from deeper layers
• shape caves for further usage

Types of machines

Excavators

Mechanical shovels, or the smaller backhoes, are used for general digging work in surface operations. These can be used on Mars with modifications to take the extreme cold and lower gravity into consideration.

Tunnel boring machines

Tunnel boring machines are used to dig circular tunnels in rock of various quality. Their size varies from 1m in diameter to about 17m. Tunnel boring machines could be used to build entire habitats in a single pass, providing radiation protection through underground construction and, if the rock is of good enough quality, structure for the habitat.

• Many tunnels require lining, which increases the cost significantly. Most tunnel boring machines include a liner installation system, as well as rock bolt installations and grouting for gaps between the liners and the excavated tunnels. the liners can be precast elements, fabricated off site and assembled with post tensioned wires.
• Tunnel boring machines use less energy than drill and blast techniques, that would require a continuous supply of explosives, that would need to be manufactured and include the synthesis of the combustibles composing the explosives.

Road-headers

Road-headers have rotary heads on the end of booms. They are used in mining and for non circular tunnels and underground railway or subway stations.

Adaptation to Mars

Existing digging machines would need to be adapted to function on Mars:

• The extreme night and winter cold temperatures affect rubber and flexible materials. Most reach the Glass Transition Phase and become brittle making them impossible to use on Mars. The development of tires, in particular, is difficult.
• The lower gravity reduces the pressure that can be exerted in digging. Production rates might be lower.
• Any operator cabin would need to be pressurized.
• Seals for hydraulics might leak during cold periods. Shock absorbers might have similar problems.
• Water ice can get very hard at cold temperatures. This may make moving soil and surface deposits more difficult. Water at freezing temperature has a hardness of about 1.5 Mohs. This puts it between talc and gypsum, so relatively soft. However, ice gets harder as it gets colder. At -70C its hardness on the Mohs is about 6, or just below the hardness of quartz. See the Water_Infrastructure topic.

Some of these problems might be reduced by keeping the equipment inside heated garages during the Martian night, or adding local heat tracing on cold sensitive parts.