On-Orbit Assembly Strategies for Next-Generation Space Exploration
- Paper number
IAC-06-D3.3.03
- Author
Ms. Erica Gralla, Massachussets Institute of Technology (MIT), United States
- Coauthor
Dr. Olivier de Weck, Massachussets Institute of Technology (MIT), United States
- Year
2006
- Abstract
As the world looks ahead to the next generation of space exploration programs, we must focus on designing architectures for both sustainability and affordability. By viewing exploration programs as a “system-of-systems,” we can focus on reducing costs through the use of flexible, reusable infrastructures to support various aspects of manned and unmanned spaceflight. One of the most difficult pieces of the system-of-systems is the issue of access to space. It is clear that human lunar or Mars exploration will require spacecraft much larger than any current or planned launch vehicle can lift, but very little attention has been given to the resultant problem of assembling separately launched components on-orbit. This paper addresses this deficiency by examining the combined launch and assembly tradespace, with the goal of understanding how various on-orbit assembly strategies can enhance the sustainability and affordability of space exploration.
In a previous paper [1], we discussed a preliminary study to evaluate assembly strategies for manned spaceflight, concluding that space tugs had promise as a cost-effective, reusable assembly strategy. This paper explores the concept in greater detail, comparing more varied assembly strategies and investigating more complex aspects such as on-orbit refueling and docking mechanisms. The vehicles are modeled in greater detail and results are computed for specific case studies, including NASA’s human lunar and Mars exploration architectures.
We examine three basic strategies for on-orbit assembly:
- Self-assembly: Each module performs its own rendezvous and docking operations.
- Space tug: Dedicated tug module waiting in orbit assembles the modules.
- On-orbit refueling: Tug or modules can be fueled in orbit from a waiting propellant depot.
The main advantage of the tug case is that each separate module does not require its own propulsion and guidance/control capabilities, reducing the module mass and complexity.
A model is developed to compare these assembly strategies for various launch scenarios (launch vehicle size, reliability, schedule) and vehicle scenarios (number of modules, mass, propulsion systems, docking mechanisms). Based on several sample operations concepts (including NASA’s lunar architecture), we compute the time and propellant required to assemble all components in each case. By comparing these metrics across all launch and vehicle scenarios, we can understand how various assembly strategies impact launch scheduling and mass requirements. Finally, sensitivity analysis is performed in order to determine the driving factors (e.g. number or size of modules) for choosing one assembly strategy over another, and to understand the impact of parameters such as launch dispersion and propulsion type.
Results indicate that space tugs reduce launch mass in certain scenarios, while on-orbit refueling (of tugs or modules) is nearly always advantageous. More generally, we show that assembly strategy has a significant impact on overall launch mass and launch scheduling. Therefore, the design of a sustainable human space exploration system-of-systems should take into account the assembly requirements as a key component of the launch infrastructure. When combined with modular spacecraft design, investment in a reusable tug-based assembly infrastructure could enable new mission concepts and enhance the sustainability and affordability of human spaceflight programs.
References
[1] E. Gralla and O. de Weck, "On-Orbit Assembly Strategies for Human Space Exploration." 56th International Astronautical Congress, Fukuoka Japan, Oct 2005.
- Abstract document
- Manuscript document
IAC-06-D3.3.03.pdf (🔒 authorized access only).
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