Since I prefer life the way it is presented through a telescope rather than a television screen, I’ve spent an inordinate amount of time on aerology (especially the study of Mars) this past year. I figure I’d better get my looks in now because the red planet won’t be this close for another 50,000 years or so, and I might have something more pressing on my schedule then.
Mars and transport packaging came into conjunction for me (in a convoluted manner) at this year’s Pack Expo Las Vegas. The economic, as well as technical, advantages of using air as an ingredient in dunnage was a hot topic with several folks on the crowded show floor. It seems getting the air part correct is easy. Finding the proper material to encapsulate the air is another matter. Of course, Sealed Air figured it out long ago and gave us Bubble Wrap. The company was demonstrating ways to save space in the truck and warehouse by shipping its encapsulating material without shipping the air. You can now use your own air — hot or cold — to fill the bubbles. Marketing managers would probably call that adding value.
So where’s the astronomy hook? Earlier this year, NASA’s Jet Propulsion Laboratory launched two Mars exploration rovers (Spirit and Opportunity), set for delivery on the fourth rock from the sun in January 2004. How do you package a product weighing 286 pounds, traveling 34.9 million miles (closer than the 248.5 million miles when the planet is at its farthest point from Earth), to a place with a mass equal to one-tenth of Earth’s and touching down at Interstate highway speed? Receipt of delivery will be electronic. (Actually, 36 10-second radio tones will be transmitted during the descent through the Mars atmosphere, which will take about six minutes, to let us Earthlings know all is well.)
The answer to this challenge is airbag technology. In transport packaging, weight and space are always at a premium. Using air to protect the product often makes the most sense.
Added to the complexity of a Mars landing, and protecting the goods, is the fact that the airbags can only be inflated seconds before the rover touches down, and must be deflated once delivery is assured.
Landing at high speed is one thing; the rough texture of Mars is something else again. The bags have to be made of material capable of sustaining inevitable puncture from rocks, to say nothing of the kinds of weapons those little green men might be using.
As with all good packaging challenges, the folks at NASA and ILC Dover, designer and maker of the airbags, did a lot of testing. The encapsulating fabric used is called Vectran, a synthetic material with twice the strength of Kevlar. There are six 100-denier layers (denier is the term used to measure the diameter of thread in a product) protecting one or two inner bladders of the same material in 200-denier strength.
Each rover uses four airbags with six lobes each, all of which are connected. This connection is important because it helps abate some of the landing forces by keeping the bag system flexible and responsive to ground pressure. If you’re having trouble picturing this, imagine really big Bubble Wrap, or a glob of salmon eggs floating in a stream.
The fabric of the airbags is not attached directly to the rover. Ropes crisscross the bags and hold the fabric to the vehicle. The ropes give the bags shape, which makes inflation easier. While in flight, the bags are stowed, along with three gas generators used for inflation. We’re still not certain about the air quality out there, so the scientists at NASA are sending some of our own.
And, since we’re unsure if our Martian brethren will even be there to unwrap these electronic gifts, the airbags will automatically deflate and retract. Then four petals of the landing module pop open and the rover egress aids (that’s governmentspeak for ramps) are deployed. Solar array panels on the rover deploy and the show begins!
I guess tooting the horn when the rover pulls up to the door would be asking a bit too much.
Clyde E. Witt, executive editor