PARAMETERS & ASSUMPTIONSSOLID MODELBACKGROUND

TRENCHING AND LAYING CABLE ON THE LUNAR SURFACE

MEHRDAD HOOSHMAND, CITY COLLEGE OF NEW YORK

POWER REQUIREMENTS

NASA’s future in space exploration is focused on expanding and building upon the achievements of the past 60 years, including return missions to the moon and expanded plans to visit Mars. Efforts to return to the moon are to be coupled with the potential construction of self-contained lunar colonies, which will allow scientists to study the geology, astronomy, and physics of extended stays in space, providing the data and confidence necessary to develop missions to destinations such as Mars and beyond.

Extended missions on the surface of the moon require a power source for both humans and autonomous robots. Historically, astronauts conducting missions on the moon have not had the means to generate electricity in sufficient quantities, thereby limiting the duration of surface missions. In addition, autonomous vehicles, such as lunar rovers, are equipped with solar panels, which are limited in their power-generating capacities due to small size and minimal efficiency. Thus, power generation is a major concern during the development of extended lunar missions.

Currently, solar panels are the most accessible form of power generation on the lunar surface. However, other methods have been proposed, including the utilization of lunar regolith that is excavated and processed to extract oxygen and various other elements that may be used in power generation. The challenge then becomes: the development of means by which power can be routed from power stations to the proper location, including lunar outputs, rover charging stations, and various other power-consuming destinations.

OBJECTIVES

The routing of power on the lunar surface necessitates the routing of power cables from one station to another. However, several factors must be considered:

• Surface temperature extremes: temperatures can range from 122°C in the daytime to -158°C nighttime

• Radiation: the lack of an atmosphere exposes surface materials to electromagnetic, particle, and ionized radiation

• Micrometeoroids: meteoroids that are typically less than 1mm in diameter; these can cause sufficient damage due to high speed impacts in the range of 10-20 km/sec

Thus, a trenching and cable laying rover on the lunar surface must be designed to ensure the protection of power cables:

1. Trench to proper depth (typically 50-60cm)2. Lay cable of various sizes in trench3. Utilize excavated regolith to backfill the trench4. Minimize power requirements5. Allow for modular excavation and cable size

Cable SpoolCan be modified to

fit various sized cable spools

GuideStationary,

angled interior guides

regolith from excavator to

conveyor

Spool GuideCable is routed from

the spool to the spool guide, which

includes an actuator to ‘press’ the cable on trench bottom

Bucket Wheel (front)10 excavating buckets with

teeth, and conic interior which allows for regolith redirection. Guide prevents regolith from dumping prior to designated

area

Bucket Wheel (back)

Conic interior reduces materials used; central shaft

placement

Excavator AssemblyRegolith is excavated and dumped onto the

large conveyor; as excavator traverses a pre-defined path, the spool assembly dispenses and lays cable at the bottom of trench. The trench is then backfilled by the regolith via

the secondary conveyor belt assembly

Taking into account the parameters and assumptions (right), in addition to the dynamic and static stresses on the components, approximate power requirements can be calculated:

Excavator Dynamic Impact

In order to calculate forces and power requirements of the design, several parameters must be defined, and various assumptions made:

Parameters• Lunar gravitational acceleration: 1.63 m/s2

• Regolith penetration force at 10-15cm: 100 kN/m2 (Apollo 15)

• Average density of regolith (γ): 1680 kg/m• Regolith cohesion range (c): 0.44 – 3.8 kPa• Regolith friction angle range (ϕ): 41° – 55°

Assumptions• Lunar base is 1 square mile ≈ 2.6 km2

• Longest trench is approximately 900 m• Average speed of excavating rover: 2 cm/sec• Average RPM of excavator at given speed: 6.5 RPM• Bucket wheel excavator has 10 buckets

• ½ of buckets (5) excavating at any given time• Each bucket is 60% full upon exiting regolith• Max depth of each bucket: 15cm• Base of bucket teeth: 3cm x 30cm

•Overall design efficiency (η): 80%•Safety factor: 3 (4 for components subject to vibration)

Since the base of each excavating bucket teeth is 0.009m2, we can calculate the force on each bucket during initial soil penetration: Power as a function of tool speed and soil

resistive forces

Along with the values calculated above, the assumptions and parameters provided, and the graph to the right, we can calculate the peak power consumption of the excavator:

Digging Forces (Swick & Perumpral Model)

F, d, and n are given parameters, while P and ω can be calculated, accounting for the independent variables along with soil properties

Digging force as a function of bucket tooth depth and tool speed

In order to calculate operating power usage, the Swick & Perumpral Model predicts an approximately 470 N force during the regolith pushing and digging process:

Sponsors:National Aeronautics and Space Administration (NASA)NASA Goddard Space Flight Center (GSFC)NASA Goddard Institute for Space Studies (GISS)NASA New York City Research Initiative (NYCRI)Stevens Institute of Technology (SIT)

Contributors:Dr. Siva Thangam, PIProf. Joseph Miles, PIMehrdad Hooshmand, UG

FUTURE WORKFurther analysis is necessary to determine the complete power requirements of the conceptual design presented. In addition to the excavator, the regolith transport subassembly and the cable laying guide require electrical power considerations. Further work can be focused on material selection, power source analysis (solar, nuclear, etc.), and rover mounting method.

The trenching and cable-laying assembly may be mounted on a rover utilizing the rocker-bogie drive mechanism (Curiosity, left) or on a hex-limbed rover capable of a larger range of motion (ATHLETE, right).