An inflatable heat shield was successfully tested on Monday, demonstrating for the first time that these light, flexible devices could be used to protect spacecraft on their way through planets' atmospheres.
Other spacecraft use solid heat shields that either drop away as the spacecraft near the surface, as happened with the Mars rovers, or gradually erode in the atmosphere.
But these solid shields are heavy, and their weight limits the mass of the spacecraft they are designed to protect, since both must launch on the same rocket. Their physical size is also limiting, since the shields must be small enough to fit inside a launch rocket.
Balloon-like shields can in theory sidestep these issues, since they are lightweight and can inflate to relatively large sizes after being folded up during launch. These weight and size savings allow for heavier spacecraft payloads.
The new shield, called the Inflatable Re-entry Vehicle Experiment (IRVE), launched aboard a small rocket on Monday morning from NASA's Wallops Flight Facility on Wallops Island, Virginia. It was the first successful test of an inflatable heat shield.
"We're totally thrilled with the data results we've received," says project manager Mary-Beth Wusk of NASA's Langley Research Center in Hampton, Virginia.
Inflatable mushroom
The launch rocket shot up 218 kilometres in about four minutes before detaching from the 40-kilogram shield. The shield was packed into a 40-centimetre-wide shroud for takeoff, but puffed out to a mushroom-shaped pillow that spanned 3 metres when filled with pressurised nitrogen.
After it parted from the rocket, IRVE and its payload, which included navigation and data-collecting electronics, plunged back into the Earth's atmosphere at hypersonic speeds. Engineers expected it to reach Mach 5, about 1.7 kilometres per second, though they won't be certain of its actual speed until they finish analysing the data.
How hot the shield was when it splashed down in the Atlantic is also uncertain, although Wusk estimates it was over 140° Celsius. The shield is made of several layers of heat-resistant fabric woven from thin strands of ceramics. This covers an inner pouch of silicon-coated Kevlar, which holds the balloon-like shape.
Greater drag
The design resembles a device known as a "ballute", a cross between a balloon and a parachute. Ballutes sport inflatable pouches, like IRVE, but not its flexible outer layer. Several companies and government agencies have worked on ballute and other inflatable shield designs for years, including the firm Andrews Space in Seattle, Washington.
"The NASA test is significant in that it's the most advanced test yet of an inflatable heat shield for re-entry applications," says Jason Andrews, president of Andrews Space.
The temperature the shield can withstand depends on how wide it is, says chief engineer Robert Dillman of Langley. A wider shield slows the craft down more and spreads the heat over a greater surface area.
"It's like if you're swinging a ping-pong paddle through the air edge-on, and then you turn it sideways," he told New Scientist. "That is spreading your energy across more area. The whole item, whether it's a ping-pong paddle or an inflatable, is all exposed to the air."
Heavier payloads
Since inflatable shields can be wider than the rockets used to launch them, they can support more weight than traditional heat shields. Their own low mass also allows spacecraft to carry more or heavier payloads.
"Right now the rigid ones are at the weight limit of what we're trying to send to Mars," Dillman says. "If you want to take larger payloads to Mars, they'll have to either do something quite creative or switch to an inflatable."
Dillman says the IRVE could be used for missions to Mars or Titan, or to bring things back to Earth from the International Space Station. "It'll work anywhere with an atmosphere," he says.
But to get there, IRVE will have to face yet more heat. "This was just a demo flight – it didn't have the whole heating you'd get smacking into the atmosphere at interplanetary speed," Dillman says. "We need to do some more development to test larger versions, scale up to something that you could actually use for a payload at Mars."
The team hopes to subject the shield to higher temperatures during the next flight test – which would occur from a higher altitude – in early 2012, says principal investigator Neil Cheatwood of Langley.
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Other spacecraft use solid heat shields that either drop away as the spacecraft near the surface, as happened with the Mars rovers, or gradually erode in the atmosphere.
But these solid shields are heavy, and their weight limits the mass of the spacecraft they are designed to protect, since both must launch on the same rocket. Their physical size is also limiting, since the shields must be small enough to fit inside a launch rocket.
Balloon-like shields can in theory sidestep these issues, since they are lightweight and can inflate to relatively large sizes after being folded up during launch. These weight and size savings allow for heavier spacecraft payloads.
The new shield, called the Inflatable Re-entry Vehicle Experiment (IRVE), launched aboard a small rocket on Monday morning from NASA's Wallops Flight Facility on Wallops Island, Virginia. It was the first successful test of an inflatable heat shield.
"We're totally thrilled with the data results we've received," says project manager Mary-Beth Wusk of NASA's Langley Research Center in Hampton, Virginia.
Inflatable mushroom
The launch rocket shot up 218 kilometres in about four minutes before detaching from the 40-kilogram shield. The shield was packed into a 40-centimetre-wide shroud for takeoff, but puffed out to a mushroom-shaped pillow that spanned 3 metres when filled with pressurised nitrogen.
After it parted from the rocket, IRVE and its payload, which included navigation and data-collecting electronics, plunged back into the Earth's atmosphere at hypersonic speeds. Engineers expected it to reach Mach 5, about 1.7 kilometres per second, though they won't be certain of its actual speed until they finish analysing the data.
How hot the shield was when it splashed down in the Atlantic is also uncertain, although Wusk estimates it was over 140° Celsius. The shield is made of several layers of heat-resistant fabric woven from thin strands of ceramics. This covers an inner pouch of silicon-coated Kevlar, which holds the balloon-like shape.
Greater drag
The design resembles a device known as a "ballute", a cross between a balloon and a parachute. Ballutes sport inflatable pouches, like IRVE, but not its flexible outer layer. Several companies and government agencies have worked on ballute and other inflatable shield designs for years, including the firm Andrews Space in Seattle, Washington.
"The NASA test is significant in that it's the most advanced test yet of an inflatable heat shield for re-entry applications," says Jason Andrews, president of Andrews Space.
The Inflatable Re-entry Vehicle Experiment (IRVE) successfully protected its payload as it fell to Earth from an altitude of more than 200 km this week (Image: NASA/Sean Smith)
The temperature the shield can withstand depends on how wide it is, says chief engineer Robert Dillman of Langley. A wider shield slows the craft down more and spreads the heat over a greater surface area.
"It's like if you're swinging a ping-pong paddle through the air edge-on, and then you turn it sideways," he told New Scientist. "That is spreading your energy across more area. The whole item, whether it's a ping-pong paddle or an inflatable, is all exposed to the air."
Heavier payloads
Since inflatable shields can be wider than the rockets used to launch them, they can support more weight than traditional heat shields. Their own low mass also allows spacecraft to carry more or heavier payloads.
"Right now the rigid ones are at the weight limit of what we're trying to send to Mars," Dillman says. "If you want to take larger payloads to Mars, they'll have to either do something quite creative or switch to an inflatable."
Dillman says the IRVE could be used for missions to Mars or Titan, or to bring things back to Earth from the International Space Station. "It'll work anywhere with an atmosphere," he says.
But to get there, IRVE will have to face yet more heat. "This was just a demo flight – it didn't have the whole heating you'd get smacking into the atmosphere at interplanetary speed," Dillman says. "We need to do some more development to test larger versions, scale up to something that you could actually use for a payload at Mars."
The team hopes to subject the shield to higher temperatures during the next flight test – which would occur from a higher altitude – in early 2012, says principal investigator Neil Cheatwood of Langley.
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