More than five months since it streaked back to Earth at more than 20,000 mph (32,000 km/h), the Orion spacecraft from last December’s Exploration Flight Test (EFT)-1 mission will subject elements of its 16.5-foot-diameter (5-meter) heat shield to minute analysis by a team of NASA engineers at the Marshall Space Flight Center in Huntsville, Ala. In total, around 180 small squares of Avcoat, the outermost coating of the heat shield—which protected the conical Crew Module from re-entry temperatures as high as 2,200 degrees Celsius (4,000 degrees Fahrenheit), about 80 percent as hot as would be experienced during a return from lunar distance—will be removed from Orion’s Crew Module for inspection and detailed analysis. This will be followed, in June, by delivery of the spacecraft to the Langley Research Center in Hampton, Va., for water impact testing and eventual use on the Ascent Abort-2 test of the Launch Abort System (LAS) in 2018.
As described in an AmericaSpace history series of articles, published in November 2014, Orion arose from the ashes of tragedy, following the loss of shuttle Columbia and her STS-107 crew in February 2003. A year after the disaster, President George W. Bush proposed the Vision for Space Exploration (VSE), which called for the retirement of the inherently flawed shuttle fleet by 2010 and the development of an entirely new space vehicle, capable of delivering astronauts Beyond Low Earth Orbit (BLEO) for the first time since the end of the Apollo era. Originally known as the Crew Exploration Vehicle (CEV), the spacecraft gained the name “Orion” in August 2006 and, under the guidance of NASA and prime contractor Lockheed Martin, steadily grew from the drawing board into design, development and fabrication. As part of the program, it was anticipated that Orion would stage a piloted mission in 2015 and return humans to the Moon by 2020.
However, inadequate funding and a distinctly lukewarm response from President Barack Obama—who entered the White House in January 2009—led to a bitterly disputed cancellation of the program. Nevertheless, work on Orion continued and, in May 2011, it was unveiled in the incarnation of the Multi-Purpose Crew Vehicle (MPCV), targeted to explore myriad BLEO objects, including Near-Earth Asteroids (NEAs). In November of that year, NASA announced plans for the unpiloted EFT-1 mission, to fly atop a Delta IV Heavy, which currently provides the greatest heavy-lift capability of any booster in the United States’ inventory. Originally planned for March 2014, and then September, EFT-1 eventually settled on an early December target.
The history of Orion’s heat shield is a fascinating lesson of modern technology, juxtaposed with a harkening back to the glories of yesteryear and the Apollo era. In September 2006, only weeks after Lockheed Martin was announced as prime contractor, Boeing was selected to design a heat shield capable of providing the spacecraft with re-entry protection at lunar-return velocities in excess of 20,000 mph (32,000 km/h). Early options centered upon Phenolic Impregnated Carbon Ablator (PICA) and a raft of alternate technologies explored in subsequent contracts.
For more than three years, NASA’s Orion Thermal Protection System Advanced Development Project worked on eight candidate materials, before finally narrowing them down to the previously flight-proven PICA and Avcoat, the latter of which had been utilized previously as a heat shield component for the Apollo Command Module (CM). At length, in April 2009, NASA selected Avcoat—a material composed of silica fibers with an epoxy-novalic resin, filled in a fiberglass-phenolic honeycomb and manufactured directly onto Orion’s heat shield substructure and installed as a complete unit onto the Crew Module—which was described as “the more robust, reliable and mature system”.
“The biggest challenge with Avcoat has been reviving the technology to manufacture the material such that its performance is similar to what was demonstrated during the Apollo missions,” said John Kowal, manager of Orion’s Thermal Protection System (TPS) at the Johnson Space Center (JSC) in Houston, Texas, speaking in 2009. “Once that had been accomplished, the system evaluations clearly indicated that Avcoat was the preferred system.”
More than three years later, in the summer of 2012, the EFT-1 Orion spacecraft arrived at the Operations & Checkout Building at the Kennedy Space Center (KSC) in Florida for final processing. The titanium “skeleton” of the heat shield was attached with more than 3,000 bolts onto Orion’s carbon-fiber skin in January 2013 at Lockheed Martin’s Waterton Facility in Denver, Colo. It was then shipped to Textron Defense Systems, near Boston, Mass., in March, for installation of a fiberglass-phenolic honeycomb structure, whose 320,000 “cells” were hand-filled with the Avcoat ablator. During re-entry, the latter would provide insulation and consume heat energy by chemical decomposition and gas release. After installation, the entire skeleton was then X-rayed and sanded to meet NASA’s design specifications.
Meanwhile, the 16.5-foot-diameter (5-meter) heat shield itself arrived in Florida in December 2013, aboard NASA’s Super Guppy aircraft, and was installed onto the titanium skeleton in May 2014. Embedded within the heat shield were 200 sensors, designed to acquire data on thermal, acceleration and other loads during Orion’s hypersonic entry into Earth’s sensible atmosphere. Having launched from Cape Canaveral Air Force Station, Fla., atop the Delta IV Heavy booster, on 5 December 2014, the EFT-1 vehicle achieved a peak apogee of 3,600 miles (5,800 km) during a 4.5-hour flight and endured a blistering return to Earth at over 20,000 mph (32,000 km/h)—significantly more severe than even the 17,500 mph (28,800 km/h) entry profiles of the now-retired shuttle orbiters—with temperatures on its flight surfaces peaking at 2,200 degrees Celsius (4,000 degrees Fahrenheit).
Following its return from EFT-1, Orion was initially shipped by the USS Anchorage from the waters of the Pacific Ocean, about 600 miles (965 km) off the west coast of Baja California, to U.S. Naval Base San Diego, and was then transported overland by truck back to the Kennedy Space Center (KSC) in Florida, where it returned to its launch site a few days before Christmas. Over the following weeks, the first analyses were undertaken, revealing that about 20 percent of the Avcoat ablated from the shell of Orion during re-entry, thereby spotlighting the virtually flawless performance of the system which will someday protect humans coming home from deep space.
At length, on 9 March 2015, the heat shield arrived at the Marshall Space Flight Center and was ensconced in the facility’s state-of-the-art, seven-axis milling machine in Building 4705. This device employs precision, computer-aided tools to fluidly maneuver in a variety of ways to manufacture parts and cut large metal or composite materials. Built for NASA by Lockheed Martin, the milling machine is the largest of its kind in the world, with the exception of its twin, which is currently employed at NASA’s Michoud Assembly Facility in New Orleans, La., to fabricate components for the Space Launch System (SLS) booster, due to undertake its maiden voyage in late 2018.
With Marshall engineers leading the machining effort, their colleagues from NASA’s Ames Research Center in Moffett Field, Calif., and from the Johnson Space Center (JSC) in Houston, Texas, will work together to inspect the 5,000-pound (2,270 kg) heat shield and remove samples from its ablated surface. For the remainder of May, the team will remove the Avcoat squares, and the sophisticated re-entry environment and thermal protection performance sensors embedded within them, by hand, after which the milling machine will smooth the 320,000 honeycomb-like cells of its denuded surface to leave a uniform layer about a tenth of an inch (0.2 cm) above the shield’s composite inner surface.
Once removed, the Avcoat squares, the sensors and other materials will be shipped to research teams across NASA, for close inspection of their thermal performance. This is part of an overall effort to refine computer models and develop safer and more cost-effective methods of designing and building the critical thermal protection systems for spacecraft which NASA aims to deliver humans beyond low-Earth orbit for the first time in more than five decades.
In the nearer term, in June, the spacecraft will be delivered to the Langley Research Center in Hampton, Va., for water impact testing, ahead of full water landing certification, and will also be refurbished and utilized for the Ascent Abort-2 (AA-2) test of the Orion Launch Abort System (LAS) in 2018. The latter event will see Orion, mounted atop a converted Peacekeeper missile and outfitted with a fully functional LAS, whose three solid-propellant motors—an abort motor, an attitude-control motor and a jettison motor—will be employed to demonstrate their ability to safely pluck the spacecraft away from a failed booster in flight.