System installation and integration of a test umbilical arm recently was completed at NASA's Kennedy Space Center in Florida. Components of this arm eventually will be mounted on the new mobile launcher tower to support vital functions on the space agency's Space Launch System, or SLS, an advanced heavy-lift rocket that will provide the capability for human exploration beyond low Earth orbit.
A key element of NASA's plan for future exploration, SLS will boost the Orion spacecraft designed for crews of up to four astronauts traveling on deep space missions to asteroids and eventually Mars.
The test umbilical arm will support cryogenic, or super-cold, propellant loading for the new rocket's propulsion systems. It recently was mounted to the mobile launcher tower simulator at Kennedy's Launch Equipment Test Facility, or LETF, for further checkouts and simulations.
The results and lessons learned from the testing will be used to develop the next round of umbilical hardware. When testing is complete, some of the hardware will be re-used as part of the Orion service module umbilical on the mobile launcher.
The Orion spacecraft consists of two main parts: a conical crew module and a cylindrical service module holding the spacecraft's propulsion system and expendable supplies. The service module umbilical arm supports the primary power and environmental control systems of the spacecraft.
"Design work on the umbilical arm began in the 2008," said Steve Larsen, lead design engineer for liquid oxygen systems in NASA's Engineering and Technology Directorate. "The umbilical was originally developed as part of the Constellation program to provide propellant, pneumatic services, power and data connections to the Ares I launch vehicle. After this test we are planning to reconfigure the arm to provide the same for SLS."
After cancelation of the Constellation program, Kennedy's Ground Systems Development and Operations Program office funded fabrication of one umbilical system for testing in the LETF and potential use supporting future NASA launch vehicles.
In the summer of 2011, EMF Corp. of Merritt Island, Fla., received a contract to fabricate the umbilical arm. The company specializes in manufacturing and designing custom parts and assemblies for a variety of uses.
"After EMF delivered the arm to Kennedy, LETF technicians assembled the arm to its flight-like configuration and installed it for test activities," said Jeff Crisafulli, manager of NASA's Launch Equipment Test Facility.
With the umbilical arm attached to a simulated portion of the launch umbilical tower at the LETF, a complex series of simulations will follow.
"The primary objective of the tests will be to validate engineering analysis models involving the dynamics of the umbilical arm's retraction, stress and thermal conditions at the ground-to-flight interface," Larsen said. "We'll use the vehicle motion simulator in the LETF to simulate on-pad vehicle sway and lift-off."
Some secondary objectives include evaluating a new fault-tolerant quick disconnect, measuring the performance of a new type of insulation for environmental control system pipes, and assessing the viability of the technology for use on the Space Launch System.
"Since one of the major roles of the umbilical is to load cryogenic propellants for the launch vehicle's propulsion system, we'll perform tests at both ambient and cryogenic temperatures," Crisafulli said. "For this testing we plan to use liquid nitrogen which costs less, is readily available and far less hazardous than liquid hydrogen."
Liquid nitrogen is 321 degrees below zero Fahrenheit, compared to liquid oxygen at 368 degrees below zero and liquid hydrogen at 423 degrees below zero. These commodities bring challenges to hardware due to the extreme cold temperatures involved.
Crisafulli noted that an important focus is on the mechanical and electrical disconnects. "With safety and reliability among our primary concerns we want to be sure the system is 'fault tolerant,'" he said. "Altogether we plan to run more than 800 different tests with the vehicle motion simulator."
By engineering and designing the hardware to be "fault tolerant," it ensures the system will still work if one component fails.
"The way the umbilical arm is designed, it retracts away from the SLS rocket by tilting up rather than moving to the side or dropping down," Larsen said. "This allows the umbilical arm to track the vehicle as it is moving up if the primary release mechanism fails. The secondary release mechanism is passively engaged when the vehicle reaches a predetermined height."
While there is still much to do, Crisafulli believes their systems will be ready to support Orion and SLS when they are ready to fly.
"LETF testing is on the critical path for mobile launcher operational readiness," he said. "There are currently nine different umbilicals scheduled for qualification testing at the LETF. Once we complete all the needed simulations, we'll be ready to have the hardware installed on the mobile launcher tower. We'll be ready when Orion and SLS are ready to go."
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