Keywords

Metal bellows, shock absorber, hopper, damper, impact absorber

Abstract

Numerous spacecraft designs exist for exploring the surfaces of planetary bodies and each have their own advantages and disadvantages. All successful landings have been made by stationary landers or wheeled rovers that rely on one-time use mechanisms, such as crushable aluminum honeycomb shock absorbers or inflatable airbags, to reduce shock loading to the spacecraft during landing. The stationary lander is the simplest type of lander, but can only take data from one location. Wheeled rovers add complexity in exchange for mobility to explore different locations. Rovers are limited by the terrain they can traverse; rovers becoming stuck have ended missions. In contrast to rovers and stationary landers, hoppers explore by making multiple launch and landing hops. They have the advantage of being able to avoid terrain that would cause a rover to become stuck. A hopper may require a landing shock absorber that can reliably operate multiple times in harsh environments. Most terrestrial shock absorbers use hydraulic fluid, allowing for compact and inexpensive devices. Hydraulics have been used in space applications, but require thermal controls to maintain the proper fluid viscosity. They also require dynamic seals which, in the case of a leak, can degrade performance, shorten mission life, and contaminate sensitive science equipment. Leakage is also a concern in pressurized systems in space because missions can take decades from when a system is installed to when it actually is used. To address these issues, a pressurized metal bellows shock absorber is proposed. This shock absorber could operate at nearly any expected spacecraft environment. Metal bellows are designed to operate from cryogenic temperatures to several hundred degrees Celsius. A hermetically sealed system eliminates the risks of a system with seals. Metal bellows are in common use for terrestrial harsh environments and vacuum applications. Small metal bellows are used as dampers for pressure control systems with small displacements. Models for the dynamics of this device are developed and presented here. Starting from the ideal gas law, polytropic compression, and compressible flow through an orifice, differential equations of motion and pressure are derived. These equations are nonlinear for the displacements under consideration and are nondimensionalized to help provide insight. Equations for static equilibrium, maximum initial displacement bounds, and estimated natural frequency are presented. Metal bellows can operate as a passive damper with a simple orifice between the control volumes. Optimization is performed for the nondimensional model of a passive damper. Because the response is highly nonlinear, a method is developed to estimate a damping coefficient that is used as the objective function for this optimization. Feasibility of this concept is investigated through an example design problem using data from a metal bellows manufacturer as constraints. An optimal mass configuration is found that meets the design constraints. Performance can be improved over the passive system by adding control. The first control strategy involves a check valve, such that the effective orifice size varies between compression and extension. The next control strategy replaces the orifice with a control valve. Varying the valve opening and closing timing can achieve optimal performance. Finally, using the metal bellows as an actuator to help launch the hopper is investigated. While the valve is closed, the gas in the second volume is compressed. Then the valve is opened the hopper is launched. The results of this research show that a metal bellows device holds promise as a landing shock absorber and launch actuator to extend the range of hopper spacecraft.

Notes

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Graduation Date

2015

Semester

Fall

Advisor

Kauffman, Jeffrey L.

Degree

Master of Science in Mechanical Engineering (M.S.M.E.)

College

College of Engineering and Computer Science

Department

Mechanical and Aerospace Engineering

Degree Program

Mechanical Engineering; Mechanical Systems

Format

application/pdf

Identifier

CFE0006015

URL

http://purl.fcla.edu/fcla/etd/CFE0006015

Language

English

Release Date

December 2015

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Subjects

Dissertations, Academic -- Engineering and Computer Science; Engineering and Computer Science -- Dissertations, Academic

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