The friction exerted during atmospheric re-entry is enough to turn spacecraft into glowing scoria comets if not properly attenuated – but otherwise. The Space Shuttle, when still in service, was designed to strike the farthest edges of Earth’s atmosphere while traveling (~17,000 MPH) and then ride a wave of superheated plasma – generated because the forces of friction are so great that they literally tear the surrounding air apart at the molecular level – down into the atmosphere until the aerodynamic surfaces regain their effectiveness.
“Using atmospheric drag is the most mass-efficient method of slowing down a spacecraft”, . To survive those intense 3000 degrees F temperatures, the shuttle that would melt and break apart, taking with it extra heat, but for the reusable spacecraft of tomorrow, NASA has something better in mind.
NASA has scheduled a launch window beginning Nov. 9 for the LOFTID mission. It will fly alongside a new NOAA “polar weather satellite”. Once the satellite separates from the upper stage of the Atlas rocket, the LOFTID will deploy and inflate into low Earth orbit before re-entry.
“One of the biggest differences is before we do suborbital testing, coming in at around 5,600 miles per hour or 2.5 kilometers per second, which is already difficult,” Steve Hughes, LOFTID aeroshell manager at NASA’s Langley Research Center. “But with LOFTID, we’ll get to almost 18,000 miles per hour, or 8 kilometers per second. That’s about three times faster, but it means nine times more energy.
The LOFTID heat shield provides four layers of protection against all that energy. The outermost layer is made of ceramic and silicon carbide yarns woven into fabric on the same types of industrial weavers that make denim. The second and third layers are two types of insulation, they are there to protect the fourth layer – the actual inflatable pieces. Everything is stacked in a series of concentric rings – themselves constructed from a woven polymer ten times stronger than steel by weight – which will help guide the expansion of the shield.
NASA has been developing Hypersonic Inflatable Aerodynamic Decelerator (HIAD) technology for over a decade. LOFTID (Low-Earth Orbit Flight Test of an Inflatable Decelerator) is the latest iteration of this technology, a new type of heat shield that potentially avoids many of the problems NASA encounters with the current generation of rigid aeroshells. These hard shields have a strict size limit, dictated by the diameter of the rocket fairing. Soft aeroshells do not face this limitation and can be extended well beyond the edge of the fairing, allowing NASA to protect larger and heavier payloads as they enter the atmosphere.
This is especially important for our future plans for exploring the solar system, because the other problem with current heat shields is that they only work in Earth’s atmosphere. You’re trying to place something the size of the space shuttle on the surface of Mars, and this exercise is going to end with your spacecraft on a very long drag across the Red Planet – or a very short crater if you’re particularly unlucky. Mars’ atmosphere is simply not thick enough to generate enough friction against modern-sized heat shields to safely slow the shuttle’s descent. So, NASA is testing an inflatable that is.
When it begins its descent, LOFTID will be moving at more than 25 times the speed of sound. NASA hopes that in the end, LOFTID will crawl at a relatively low speed of 609 MPH. Throughout its flight, the test shield’s onboard data logger will transmit the most relevant sensor and video data while storing as much as possible on board in an ejectable recorder. If all goes as planned, the LOFTID shield will slow enough to deploy a landing chute before touching down in the Pacific Ocean before being picked up by the ULA.
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