If you see a flying saucer in the sky tomorrow over Hawaii, don’t panic — it’s just NASA. At 12:30PM ET on June 2nd, NASA’s low-density supersonic decelerator (LDSD) will be tested at the US Navy’s Pacific Missile Range Facility in Kauai, Hawaii. That test brings the technology a little closer to its ultimate destination: Mars.
Humans have explored the Red Planet for four decades using robotic probes. In 1976, the twin Viking landers successfully touched down on the Martian surface — the first Mars landing. In 2012, NASA’s Curiosity rover survived the “seven minutes of terror” known as entry, descent, and landing to successfully touch down on the Martian surface with the help of that same Viking-era parachute. That system, though reliable, is limited: it can’t support a payload of more than a ton.
The technology to launch crews is currently in development, but what happens when we arrive?
NASA is planning increasingly ambitious robotic missions to Mars, gearing up to a human mission in the 2030s. In preparation, the agency is constructing its next big rocket — the Space Launch System (SLS), capable of propelling its Orion spacecraft further into space than ever before. The technology to launch crews is currently in development, but what happens when we arrive?
The engineering challenges are significant. Landing on Mars isn’t the same as landing on Earth, or even on the Moon. Our atmosphere is very dense; the Moon has no atmosphere at all. The Martian atmosphere is somewhere in between. That thin atmosphere means any spacecraft would need more than a parachute to land. And Mars has just enough atmosphere to rule out landing via rocket motors alone, as is done on the Moon.
In order to support an eventual human mission, NASA needs technologies capable of landing between 20 to 30 metric tons on the Martian surface. The LDSD is a step in that direction: it supports payloads of two to three tons, doubling the current capabilities.
NASA is betting on atmospheric drag, better known as air resistance, as a solution. Using drag for deceleration saves engines and fuel. NASA’s future Mars missions require heavy-duty planetary landers capable of delivering larger payloads and maneuvering to higher elevations. Current technology coupled with the thin Martian atmosphere make mountaintops and the high-altitude southern plains inaccessible, limiting what areas of the Red Planet we can explore.
The LDSD features three different devices meant to address these problems. Two massive, donut-shaped airbags constructed out of kevlar — dubbed supersonic inflatable aerodynamic decelerators (SIADs) — will inflate around the vehicle. By increasing the surface area of a vehicle such as Orion, the amount of air resistance will also increase, decelerating the spacecraft. To design the technology needed for this task, NASA turned their attention to the Hawaiian pufferfish. When frightened, the puffer fish inflates itself, intimidating potential predators. Engineers thought this same technique could be used as a means of deceleration. Rapidly inflating the SIAD would increase the surface area of any spacecraft bound for the Red Planet, and dramatically reduce its speed.
These SIADs come in two different versions: the SIAD-R, which is meant for robotic missions and is 6 meters in diameter when deployed; and the larger SIAD-E, meant for human missions, which expands to 8 meters in diameter once inflated. The SIAD-E is designed to slow surface-bound vehicles, like Orion, from upwards of 2,600 mph — about three and a half time the speed of sound — to 1,400 mph in under three minutes.
It’s not practical to test these new technologies on Mars
The final part of the LDSD system is a parachute that’s 30.5 meters in diameter — twice the size of the Viking-era parachute. Once the SIAD deploys and slows the payload to roughly 1,400 mph (Mach 2), the parachute takes over. It’s tasked with slowing the vehicle to subsonic speeds. All three devices will be the largest of their kind ever flown at supersonic speeds.
Since it’s not practical to test these new technologies on Mars, researchers use the next best thing: the thin layer of Earth’s upper atmosphere known as the stratosphere. The LDSD will be tested over the Pacific Ocean, since that’s where the atmosphere most closely resembles Mars. By simulating the supersonic entry and descent speeds Orion and other vehicles will experience on Mars, engineers will have an idea of how well the LDSD technology will perform on Mars.
During the test, a high-altitude helium balloon will carry the test vehicle to an altitude of 120,000 feet above the Earth’s surface. The test vehicle will then be released from the balloon, dropping a few thousand feet. Four small rocket motors will ignite, stabilizing the test vehicle through a controlled spin, before an OrbitalATK Star 48 solid rocket motor ignites, propelling the craft to an altitude of 180,000 feet and speeds of 2,880 mph. The eight meter SIAD will deploy, decelerating the spacecraft to about 1,400 mph before the parachute takes over, slowing the spacecraft to a safe speed for a water landing.
In the last test, the parachute failed
The first full-scale test of the LDSD system at supersonic speeds was conducted at the PMRF in Hawaii in June 2014 and featured the 6-meter SIAD-R together with the massive parachute. The parachute failed. Tomorrow’s test will feature an improved parachute design.
Will the new design hold up to the initial rush of supersonic wind? Or will the team recover another shredded chute? Regardless of the results, we can expect some amazing views from the onboard cameras.
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