Slowing for Mars

Contributed by
Aug 8, 2014
<?xml encoding="utf-8" ?>

Over the summer, NASA and JPL tested hardware that they’re hoping will give humanity far better access to Mars.

That’s a hard trip. Mars isn’t exactly next door—well, on a solar system scale, it is, but it’s still a six-month journey of hundreds of million of kilometers—so the technical problems just with getting there are legion. If you overcome them, you still have a payload moving at multiple kilometers per second relative to the planet. How do you slow it down for a soft landing? If you don’t, all you’ve accomplished is making a new and very expensive Martian crater.

Enter the LDSD: the Low-Density Supersonic Decelerator. This is a lightweight (hence the LD) saucer-shaped device that will test various technologies to slow down (hence Declerator) a Mars probe from its initial rapid speed (hence Supersonic) to something that can be handled by more conventional ways of slowing down (like small parachutes and rockets).

Mars has an atmosphere, but it’s thin. That makes it hard to use a parachute; you need something quite large to catch enough air to slow down, but that can also withstand the huge forces involved at these very high speeds. The idea behind this particular LDSD test flight was to use two main ways to slow down: an inflatable doughnut-shaped ring (called a SIAD, for  Supersonic Inflatable Aerodynamic Decelerator) to use air drag, then deploying a parachute designed for use at supersonic speeds.

NASA tested these ideas and created a video explaining them.

A balloon lifted the test vehicle to over 36 kilometers (22 miles) in altitude, then a rocket motor sent it up to 55 km (34 miles), accelerating it to four times the speed of sound. At that height, the Earth’s atmosphere has about the same conditions a spacecraft will meet when going through the atmosphere of Mars.

The SIAD was deployed first, and worked very well, even exceeding expectations. It inflated rapidly, smoothly, and without disturbing the platform. Once it was done, the parachute was deployed … to somewhat lesser success. It shredded immediately; at those high speeds and pressures even small tears grow rapidly. While you might think of this as a failure, engineers tend to think of it as a learning experience. This isn’t just phrasing; it’s rare to create something that works flawlessly in its first real-world test. What they learn from this will help them eventually design a ‘chute that can withstand the forces necessary.

Which is just what they plan to do. New test vehicles have already been delivered to JPL, and they’ll begin the work to launch them again next summer. As we’ve seen with Mars rovers, getting bigger machines to Mars scales up the sort of science you can do there. To do what we want to do—explore the Red Planet, look at its history, its chemistry, determine if life ever existed there, and eventually put down humanity’s roots there as well—the LDSD program may be what allows us to land there safely.