Technical Papers

  • Simplifying the Structural Verification Process to Accommodate Responsive Launch

    The time it takes to develop a spacecraft and prepare it for launch is often driven by integration with the launch vehicle: meetings, analyses, and tests that together ensure compatibility. Structural verification (ensuring the spacecraft can withstand launch environments) is particularly time consuming and must be greatly simplified before responsive launch will become a reality. Objectives are to eliminate the need for mission-specific coupled loads analysis (CLA), simplify and standardize the structural test program, minimize dependence on analysis, and reduce technical and schedule risk. The envisioned solution for small spacecraft is to combine three strategies: (1) tighter constraints on the physical characteristics of the spacecraft, (2) variational CLA to assess that range of characteristics, and (3) vibration isolation.

  • Designing Effective Static Tests for Spacecraft Structures

    This paper describes and demonstrates a process for designing effective static tests for spacecraft structures. The emphasis is on devising load cases that effectively simulate the extreme dynamic loads experienced during launch and screen the structure for potential failures. The process entails devising preliminary load cases that deform the structure in its key excited mode shapes and then adjusting the cases to achieve target stresses and margins of safety. Although the discussion centers on bus (body) structures, the described techniques apply to smaller structural assemblies and launch vehicles as well.

  • Eliminating the Need for Payload-specific Coupled Loads Analysis

    Through a project recently completed for Operationally Responsive Space (ORS), we have demonstrated the feasibility of a more efficient structural verification process for small satellites. This new process eliminates the need for payload-specific coupled loads analysis (CLA) and simplifies structural testing while not increasing mission risk.

  • Roles of Testing in Design and Verification of the FalconSat-2 Structure

    FalconSat-2 (FS2) is a micro-sat being developed at the United States Air Force Academy (USAFA), to be launched as a Hitchhiker payload on the Space Shuttle. The program adopted the philosophy of testing early and often, recognizing budget constraints and limited analysis capabilities of the staff, which consists mostly of cadets. The objective of this program is mainly to teach, and testing, combined with theory, is a great way to learn. Early development testing on a shaker table of a crude but representative structure provided useful information for designing the flight structure and also for improving the accuracy of a simple finite-element model. Analysis is being used selectively to provide the most value. Low-cost testing will be the final verification of most structural requirements. The test program is not complete as of the date of this paper, but we hope to demonstrate structural integrity to the Space Shuttle Safety Panel without a single color stress plot!

  • Improving the Loads-cycle Process

    • Assessing Launch Loads with the Traditional
    • Loads-cycle Process
    • Ways to Improve the Loads-cycle Process
    • Managing the Math Models
    • Integrating Stress Analysis with Loads Analysis
    • Eliminating the Need for Mission-specific Coupled Loads Analysis when Launching Small Payloads
    • Taking Advantage of a More Efficient Process for Large Payloads
  • Testing as Part of a Sound Engineering Approach

    This paper is a reminder of the roles of testing in a sound and cost-effective process for developing spacemission products. Topics include development testing, qualification testing, acceptance testing, and analysisvalidation testing. Emphasis is on why these tests are done, related to both mission success and cost-effectiveness. The purpose of this paper is to help refocus organizations and people in a time when many perceive tests as requirements (and thus do not do them when not "required") rather than tools for product development.

  • Variational Coupled Loads Analyses: Reducing Risk in Development of Space-Flight Hardware

    Before space hardware can be launched, positive structural margins of safety must be demonstrated relative to the booster-supplied math model and forcing functions. To identify appropriate structural loads on which to base such margins, several iterations of coupled loads analyses are typically performed during hardware development. Such analyses are traditionally done with a single payload dynamic math model, derived fromfinite element models, which are combined to form a booster/payload system-level model. Uncertainty in such analyses, relative to both the hardware's final configuration and its modes of vibration, is most often addressed with uncertainty factors selected without any insight into actual loads sensitivity. With recent advances, the analysis process has been accelerated, allowing for variational coupled loads analyses. Such an analysis can account for possible variations in the final hardware configuration: for example, frequency, weight, presence of comanifested payloads, damping, etc. The results of such a variational analysis are presented. The results demonstrate that the use of uncertainty factors can greatly penalize much of the structure with overly conservative load criterion, while at the same time being unconservative for those structural elements most sensitive to the variations. The conclusion is that the utilization of variational coupled loads analyses can result in both reduced risk and more efficient structural designs.