Polaris Project: Tall Lunar Tower (TLT)

Enabling Capabilities Special Project Series:
Polaris Project, small flight experiments or risk reduction projects to fulfill high-priority capabilities gaps.

Project Description & Objectives:
The Tall Lanar Tower (TLT) In-Space Assembly (ISA) team’s purpose is to design, analyze, fabricate, autonomously assemble a TLT assembly engineering development unit (EDU). The effort is intended to raise the technology readiness level (TRL) of robotic assembly of vertical structures on the lunar surface, such as towers and shelters. The system includes a tall lunar tower EDU and a robotic tower assembly system EDU. Development advances cross-cutting robotic truss assembly technology to enable construction of infrastructure in the lunar environment. 

In the coming decades, it is anticipated that the lunar economy will require robust surface infrastructure. The National Aeronautics and Space Administration (NASA) Moon to Mars Objectives include demonstrating autonomous construction capabilities and developing a lunar surface of power and communication network. Current state of the art lunar surface power and communications technology is small scale and short range. State of the art lunar solar collection systems are deployable and limited to shorter ~16-meter-tall-deployed columns. Early Artemis Communications will likely utilize legacy voice and Wi-Fi video systems with ranges on the order of 1.0 km and 100 m, respectively. However, missions in the 2026-2028 timeframe (Artemis V+) will require 10 km+ coverage and higher data rates. Preliminary results from a 3GPP range analysis study indicate that the range and data rate requirements can be met using 4G LTE or 5G type systems that are positioned at a height of ~30 m above the surface of the moon.

Power architecture building blocks are currently planned to start with 10-50 kW, likely scaling over time to 100-200 kW. Early ISRU pilot plant demos and construction demos in the 2028-2032 timeframe will require power on the order of 100’s of kW continuous. Full-scale industrial ISRU, Manufacturing, and Construction along with habitat and mobility systems will require power on the order of 1s-10s of MW depending on the process or surface system. Thus, flexibility and scalability of the power architecture building blocks is required. It is anticipated that a combination of smaller deployable vertical solar arrays (e.g., VSAT) and larger permanent power systems (solar and FSP) will be needed. One of the key challenges is that solar power generation at many of the proposed Artemis landing locations will have to contend with shadowing and extended periods of darkness due to the low light incidence angle and the lunar surface topology. However, at a height of 30 m, there are expansive areas that receive illumination 99% of the year. Thus, elevation of the solar panels above 30 m would be required to maximize the illumination and power generation potential at these sites, with similar benefit from elevating the solar panels at other sites.

Project Objectives:

The Tall Lunar Tower project is the first NASA project addressing the trade space for very tall towers on the lunar surface (30 m or greater) to meet these needs. The activity raises the technology readiness level (TRL) of various lunar surface tower assembly technologies to TRL 4 with a laboratory demonstration. The path to achieving the laboratory demonstration requires the following objectives:

1. Determine requirements and evaluate environment for tall lunar tower assembly.
2. Trade technology options for assembling a tall lunar tower.
3. Develop a design process to characterize the dimensional & structural stability of tall (50 – 100 m) lunar towers to support a variety of user defined payloads.
4. Design and test an autonomous robotic tower assembly engineering development unit.
5. Design and test a lunar tower engineering development unit.
6. Demonstrate autonomous assembly of a tall lunar tower in a laboratory environment.

Project Deliverables:

1. A lunar tower sizing and design software tool (Software)
2. A robotic assembly process for tall lunar towers (Concept of Operations)
3. Truss assembly robotics with supervised autonomous control software (Hardware and Software)
4. A design for dust-tolerant, robotically assemble-able, and ISRU compatible truss joints (Hardware)
5. Realistic lunar lighting simulation and machine learning vision system implementation (Software)
6. A full-scale demonstration of the assembly process and EDU fabrication (Laboratory Test)
7. An investigation of ISRU truss component implementation (Study)

Major Milestones:

• Project Year 1
  • (12/31/21) Complete trade studies for robotic tall lunar tower assembly approach    
  • (02/28/22) Developed Tower Configuration Utility (TCU) Software        
  • (03/31/22) Fabricate prototype components for Tower EDU         
  • (06/30/22) Fabricate prototype for Assembly Robotics EDU          
  • (08/17/22) Preliminary Design Review     
• Project Year 2
  • (12/16/22) Prototype level assembly demonstration         
  • (02/28/23) Autonomous Control Software Prototype         
  • (02/28/23) Robotic Assembly Process Developed 
  • (03/31/23) Dust Tolerant and Robotically Assemble-able finalized truss joint    
  • (07/17/23) Critical Design Review (CDR) 
  • (09/18/23) Test Readiness Review (TRR) 
  • (09/27/23) Laboratory Assembly Demonstration           

Project Status:
A demonstration of the TLT EDUs was completed in September 2023. The project successfully demonstrated assembly and raising of a 3.5-meter-tall tower (five 0.75-meter cubic bays) with two fixed base robotic manipulators and a synchronized tower lifting system.

The tower assembly system, referred to as the construction robot system (CRS) performs jigging, lifting, and inspection tasks to allow robotic manipulators, called the assembly robot systems (ARSs). The robotic manipulators are each equipped with a specialized end effector allowing truss strut placement, joining, and visual feedback. Behavior trees are used to automate the assembly process and allow the coordinated placement of parts and synchronized tower lifting. After a bay is assembled within the jig, the tower is lifted upwards. When the tower reaches the desired height, the tower is then connected to the foundation that the CRS and ARS are attached to. Payloads, such as communication equipment, can be installed on top at the beginning of the assembly or added to the sides during assembly.

The effort has resulted in two papers presented at AIAA SciTech 2022, five papers presented at AIAA ASCEND 2023, and two Master’s Thesis topics.

1. K. Song, M. Martin, M. Mahlin, J. Taylor, “Sizing and Design Tool for Tall Lunar Tower,” AIAA, SciTech 2023.
2. W. Doggett, J. Heppler, M. Mahlin, J. Teter Jr, R. Pappa, K. Song, B. White, I. Wong, and  M. Mikulas, “Towers:  Critical Initial Infrastructure for the Moon, Such as a Power Module Support,” AIAA, SciTech 2023.
3. B. Notosubagyo, M. Mahlin, and J. Cassady, “Unreal Engine Testbed for Computer Vision of Tall Lunar Tower Assembly”, Ascend Conference, October 2023.
4. J. Merila, M. Mahlin, and J. Neubert, “Scaling Climbing Collaborative Mobile Manipulators for Outfitting a Tall Lunar Tower and Truss Structures”, Ascend Conference, October 2023
5. J. Cassady, M. Mahlin, E. Kravets, M. Vaughan, and M. Rodgers “Software Design for the Supervised Autonomous Assembly of a Tall Lunar Tower”, Ascend Conference, October 2023
6. K. Song, R. Amundsen, A. Stark, M. Mikulas, M. Mahlin, and J. Cassady, “Sizing, Buckling, and Thermal-Structural Analysis of Tall Lunar Tower”, Ascend Conference, October 2023
7. D. Tiffin and M. Mahlin, “Tall Lunar Towers: Systems Analysis of a Lunar-Surface-Assembled Power, Communication, and Navigation Grid”, Ascend Conference, October 2023

Active project work includes facilitating small business research into robotic tall tower assembly, flight-capable joining systems such as laser welding (in collaboration with Marshall Space Flight Center), testing with flight-like robotics, versatile joint development, In-Situ Resource Utilization (ISRU) derived aluminum struts, functional outfitting, assembly physics simulation, and a deployable light-weight tower assembly system. To prepare for a technology demonstration flight on a lunar lander, the next iteration of the TLT development will focus on subsystem testing in relevant environments and designing a demonstrator that can provide useful power generation and communication capability. Future work also includes autonomous truss retrieval, placement, and assembly evaluation.

• Our funding for FY 24 and FY 25 are for transition efforts. I’ll try to lay out our activities as quarterly milestones, and some sub-bullets for status:
  • FY24 Q1 ECI proposal development
    • Not selected by Langley
      • Selected by MSFC and became the LASAR project that two TLT personnel are supporting laser welded tower joint design 
    • FY24 Q2 GCD Proposal development (For which a call never came and is no longer expected).
      • We collaborated with ARC to develop an NOI, requirements, and planned studies
      • Collaborated with STMD Principal technologists to submitted proposals for studies
    • FY24 Q3 SBIR Phase 1 Tall Lunar Tower assembly and outfitting subtopic
      • Funded three proposals
    • FY24 Q4 Hardware iteration (LaRC provided 100k in procurement)
      • Lightweight tower lifting mechanism design and fabrication
      • Fabrication for structural mockup of tower iteration and payload
    • FY25 Q1 Hardware design and demonstration AIAA SciTech paper 
      • Submitted to STRIVES for review
    • FY25 Q1 M2M X-Hab project Reviews
      • Initiated with University of Alaska – Fairbanks, completed System Requirements Review
    • FY25 Q2 Manual assembly of structural mockup
    • FY25 Q3 Testing of lightweight tower lifting mechanism
    • FY25 Q4 Complete Autonomous Lunar Surface Assembly concept of operations study

A tall power and communications tower is seen as an important near-term infrastructure element that can provide continuous power and long-range surface communications needed for Artemis missions to the south pole. The assembly and outfitting technologies developed are expected to be scalable to support the construction of an expanded communications and power grid (M2M Objectives LI-1 and LI-2) and will also be extensible to the creation of other infrastructure such as towers/booms for offloading of payloads from medium to large landers, blast containment shields for landing pads, radiation and thermal shields/walls, shelters, and habitats (see M2M Objectives LI-4 and LI-8). In addition, it is expected that future structural assemblies will be achieved by using ISRU-based structural elements, thus leading to truly sustainable lunar construction paradigm. Demonstrating the assembly and outfitting of a communication and power tower is a valuable first step in providing early and useful infrastructure while simultaneously proving out robotic assembly and outfitting technologies, capable of constructing infrastructure in the future.

Contributions from the TLT Project

• Tall towers enable direct collection of solar energy at the lunar south pole enabling generation of 50 kW or more.
• Tall towers enable reflection and concentration of solar energy to a solar farm on the surface.
• Assembly technologies compatible with the lunar environment
• Truss structures that enable high load capability and dynamic stability
• Robotic surface truss assembly enabling a variety of structures
• Utility installation for functionalized structures
• Maintainable, upgradeable, and evolvable lunar surface structures
• Scalable truss-based infrastructure

Technology Infusion Potential

• Launch plume deflectors
• Environmental shields
• Radiator support structures
• Surface cargo transportation systems
• Lunar Safe Haven shelters for permanent habitation
• Lunar material excavation and processing structures for ISRU
• Orbital truss assembly

The technology development goal is to enable robotic assembly of tall truss structures on the lunar surface. Truss structures are very mass efficient for their load capacity and can take a variety of forms. Truss structures can be used for energy collection, communication, environmental shields, safe havens for astronauts, and manufacturing buildings for ISRU operations.