NASA furthers its trailblazing research in space exploration by simulating the stresses that vehicles experience in flight.
By David Absher
NASA’s New Vibro-Acoustic Test Capability (VTC) facility is a one-of-a-kind testing center designed to replicate the intense shaking and extreme sound associated with launch, emergency abort and re-entry of the vehicles that will one day carry America’s astronauts and equipment to the International Space Station and beyond. Built by Science Applications International Corp. (SAIC), the VTC is actually two separate testing facilities: the Mechanical Vibration Facility (MVF), which tests the vibration resistance of objects weighing up to 75,000 pounds, and the Reverberant Acoustic Test Facility (RATF), which measures resistance to acoustic and high-impulse vibration up to 163 decibels (dB).
The facility is unlike any other in the known universe. It supports initiatives including the development of the Multi-Purpose Crew Vehicle (MPCV) that’s slated to replace the Space Shuttle. The VTC complements and expands upon the existing research and testing capabilities of NASA’s Glenn Research Center in Sandusky, Ohio, which simulate thermal, atmospheric and electromagnetic effects on spacecrafts and other equipment. A major component of the Glenn Center’s Space Environmental Test (SET) facilities, the VTC will support future manned and unmanned NASA missions, as well as private research and testing.
The initial contract defined project delivery as a design-build “turnkey,” based on requirements stipulated in the contract’s statement of work. Soon after SAIC won the project, however, the requirements evolved and the project as it existed could no longer satisfy NASA’s needs. The method offered minimal client engineering reviews and interaction and changing customer requirements represented a risk and obstacle to the schedule and rework. SAIC’s project team collaborated with NASA scientists and engineers to better identify the agency’s requirements and realize the concept.
SAIC’s architects, engineers and constructors realigned their internal processes to give NASA engineers more insight into the details of the project design and construction. NASA was involved in the calculations performed to guide selection of materials and methods; every calculation was submitted, reviewed, corrected if necessary, and reviewed again for final approval before ordering, construction and installation. One of the project’s biggest achievements was successfully integrating the system engineering processes into a design-build paradigm that met NASA’s technical and economic requirements.
As with many projects, end-item specifications (EIS) changed to meet the needs of the user. NASA notified the project team that the VTC’s EIS were changing substantially in March 2009. Working closely with its NASA counterparts, the SAIC engineering team developed a revised program that would meet and exceed the new EIS in technical capabilities and performance, project scheduling and budget in just eight weeks. The program “reset” culminated in a series of meetings that took place at SAIC’s office in August 2009, in which each and every new EIS was jointly evaluated and approved.
The changes resulted in a contractual modification prepared using the Alpha contracting process. The Alpha process requires concurrent participation by the contractor and the government in the preparation of contractual documents, including a detailed statement of the work and EIS, as well as preparation of the responding proposal and basis-of-estimate document. The resulting modifications sped the contract’s schedule and increased its value.
Spaceship in a Bottle
In addition to its other stringent technical specifications, the VTC facility needed to be built within an existing operating facility, requiring coordination to avoid impairment or interruption of ongoing operations. Similar to constructing a ship in a bottle, the VTC was built in an existing room, with all materials, equipment and personnel entering and exiting through a 14-foot-by-18-foot overhead door. The materials entering through this portal included 11 million pounds of concrete; 60-inch diameter, high-density polyethylene (HDPE) ductwork; and acoustical doors that measure 58 feet by 26 feet.
In addition to constructing the VTC inside an existing facility, its long-term operation — designed for a minimum of 30 years — had to have no effect on the existing facility. SAIC performed extensive transmissibility analyses to verify this aspect of the completed design.
The Sound and the Fury
The Reverberant Acoustic Test Facility simulates the varying conditions of liftoff, descent and mission abort that the newest generation of space-exploration vehicles will be required to endure. The RATF was designed to produce an overall sound-pressure level of 163 dB, which has never been previously achieved in a man-made setting, and the entire structure including walls, floors and ceilings is designed to handle a future acoustic level of 166 dB. As a point of reference, every 3 dB doubles effective sound levels, which means 163 dB is 128 times louder than a jet engine. The RATF generates the most acoustic energy for its size in the world.
The project team designed and installed 36 horns and noise sources in one wall of the chamber. The noise-generation system emulates eight different spectra of sound (25, 35, 50, 80, 100, 160 and 250 hertz), each of which mimics a specific period of launch and/or re-entry. Multiple horns were required for each type of noise. All were custom-designed and custom-built of half-inch stainless steel with the exception of the 250-hertz horns, which were pre-manufactured using fiberglass.
The MVF includes a depressed “pit” area that required the installation of more than 100 rock bolts that function like expansion anchors. The design and location of each rock bolt was completed within exacting tolerances. The normal tolerances specified for installation are a maximum of 3° over the length of the anchor; on this project, rock bolts were within a tolerance of 1°.
The vibration systems and the vibration table to which test items will be attached surpassed the capabilities of all existing mechanical-vibration systems in the world today. EIS for the MVF indicated a one-piece, all-aluminum, 18-foot vibration table that can hold 75,000 pounds of dead weight and test an article up to 75 feet tall. Because vibration tests occur in vertical (X) and lateral (Y and Z) axes, the team designed the system so the test article could be tested on any axis without repositioning. SAIC connected 16 vertical actuators, four horizontal actuators and 16 spherical couplings to the vibration table, powering the system components with an 800-gpm, 3,160-psi hydraulic power system.
The project team also designed and fabricated a Construction Integration Fixture (CIF) to support integration, testing and verification of the MVF. The CIF was instrumental in tuning and validating performance of the MVF and maintaining the schedule. Another main feature of the VTC is a 1,024-channel digital data-acquisition system that reads the facility’s strain gauges, microphones, force, acceleration and displacement instruments at 256 KB per second.
The VTC project was officially completed on Sept. 20, 2011. Since then, NASA engineers have developed scenarios to test various pieces of space-exploration equipment and components; official testing was set to start at press time. With the VTC, NASA and private firms alike can test equipment to safely go where few have gone before.
Bill “David” Absher is a Registered Architect and served as the Chief Engineer and Director for Design for the NASA VTC project. Based in SAIC’s Oklahoma City office, Absher has almost 40 years of experience in the design and construction industry.
Project: Vibro-Acoustic Test Capability Facility
Location: Plumbrook Station, Sandusky, Ohio
Owner: NASA Glenn Research Center
Design-Builder: SAIC Constructors, LLC
Architect and Engineer: SAIC Energy, Environment & Infrastructure, LLC
Specialty Consultants: TEAM, Aiolos and Zin Technologies
Specialty Contractors: Commercial Contracting Corp., Triangle Electric and John E. Green