Final Project

Korki M.

Legislator:  David Farabee, Representative

 

Landing of the Mars Pathfinder

On July 4, 1997, the Mars Pathfinder landed on the Martian surface.  It was the first spacecraft to return to the surface since the Viking landers twenty years ago.  It used a new innovation to arrive on the surface of Mars, and was one of the cheapest departures into space yet. 

The Pathfinder’s mission was to deploy a microrover onto the planet’s surface to scout out the terrain and to make atmospheric and meteorological observations during descent and to function as a weather station. 

The Pathfinder launched December of 1996 off of a Delta II rocket from the Kennedy Space Center in Florida.  It received its final boost to break away form the Earth’s orbit.  The Mars Pathfinder uses an Earth-Mars transfer orbit.  Regardless of the launch date, the Pathfinder is scheduled to arrive on Mars on July 4, 1997.  The total flight time between Earth and Mars is 6 to 7 months.  During the seven-month cruise to Mars, various subsystems of the spacecraft keep the lander and rover in top efficiency.  Systems to be checked on were the solar array and battery, thermal control, attitude determination and control, and the communication subsystems.  The rover is checked on fifteen days after launch.  The rover will be checked again thirty days before arriving on Mars.   During the final day of approach, the navigation team is producing orbit solutions on a regular basis, and adjustments are made to determine when the parachute should be deployed. 

The landing site chosen was Ares Vallis.  This is approximately the same site where the Viking 1 landed.  Ares Vallis is an ancient flood plain.  Years ago, water flourished in this area.  Today, there only exists a rocky plain.  NASA chose this site for its variety of rock and soil samples present at the mouth of the channel, 19.5N, 32.8W.

The Pathfinder would aerobrake in the upper Martian atmosphere using an aeroshell and a parachute.  Just before impact with the surface of the planet, airbags would inflate to cushion the landing.  The microrover would roll out to examine the soil nearby.  NASA planned the arrival of the Pathfinder on Mars to be in July because the spacecraft is solar-powered, and Mars will be receiving maximum sunlight during this time. 

The landing was a success!  The parachute deployed, the spacecraft hung in the air for a while, and the airbags inflated and compressed to cushion the impact against the surface of the Martian planet.  The compressed air bounced back, and the spacecraft bounced, but the bounces became less and less as the lander came to a halt.  ILC Dover designed the airbags.  They use the art and science of inflatable design and advanced materials development together in robust, engineered shapes for aerospace applications.  For the airbags, they used technological advances including the application of advanced materials in multiplayer fabric construction.  Once the Pathfinder had settled on the surface, pyrotechnic devices in the lander petal latched are blown to allow the petals to be opened.  The latches are necessary because of the pulling forces exerted on the lander by the deployed airbag system.  As the petal latch releases, a retraction system slowly begins dragging the airbags toward the lander.  It takes about sixty-four minutes to fully retract the bags.  The petals open up after about three hours, and the rover continues on with the mission.  The Mars Pathfinder returned 2.3 billion bits of information, including 16,500 images from the lander and 550 images from the rover, as well as more then fifteen chemical analyses of rocks and soil and extensive data on winds and other weather factors.  Both the rover and the lander outlived its primary design life. 

Many questions followed the Mars Pathfinder Mission.  How was the Mars Pathfinder airbag system activated?  How were the airbags retrieved after landing? 

Robert Manning said, “Software sets off initiators which fire three gas generators that inflate the bags in less that 0.25 seconds.  These “gg”s are really (Thiokol) rocket motors whose exhaust is catalytically.  The bags were mechanically retracted toward the closed lander petals (see web pages) before the petals were opened (mostly).  Each of the four bags on each of the four petals of the lander tetrahedron had its own retraction motor (winch) that drew in Kevlar retract cords that were strategically placed inside the bags.  This causes them to bunch up on each of the petals initially before the petals are opened, thereby giving room for the rover to egress.  These actuators used the Swiss Maxon motors.”

Manning went on to talk about the strategies used to test the airbags.  At first, the team has made a full scale of the vessel and experimented in the Sandia National Lab in New Mexico.  When realizing that the atmosphere on Earth is extremely different to that on Mars, the results were scraped.  The pressure on Earth is about 14.7 pounds per square inch, but Mars’ pressure is about 1% that of the pressure on Earth.  The airbags used on the Pathfinder depended a lot on the amount of air on the inside of the bags as well as the amount of air on the outside.  The airbags on earth need a lot of air in them to keep inflated, but not on Mars.  The next testing area tried was NASA Lewis Research in Sandusky, Ohio.  There, they have an enormous vacuum.  After adding a couple of jagged rocks, the team had created the perfect Martian environment.  After several tests and adjustments, the airbags were ready for the mission. 

It was very hard to envision this shape of the Pathfinder and to grasp the understanding of the airbags, so tests and models were created to further my understanding.  After extensive research on the Pathfinder and the landing of the spacecraft, I came across a blueprint of a mini-Pathfinder.  After some assembly, I recreated the shape of the Pathfinder, the minirover, and the electronics box.  With some imagination, I gathered the concept of how the lander opened, and how the rover was able to roll out of the lander.

The airbags were a different story.  It’s hard to imagine a vessel with some velocity at one moment stopping in mid-air and then landing safely.  Why was it so important to have airbags?  During the research, I came across an Egg Drop Lab.  It was designed to help people like me get the idea of the picture.  The instructions were simple- make a tetrahedron and tape bubble wrap, balloons, and marshmallows to the outside of it.  On the inside, secure a raw egg.  Close the tetrahedron (which somewhat resembled the Pathfinder) and drop the vessel from a high place.  The egg did not break.  I was really expecting yellow yoke everywhere.  I took a look at the vessel I made.  It was surrounded in bubble wrap and had three deflated balloons on its sides.  Then it hit me.  When playing basketball, people always wanted the balls that were inflated to get a higher bounce.  NASA wanted a ball that was deflated to lose the higher bounce.  When bouncing an inflated ball, it returns quickly and powerfully.  If you try bouncing a deflated ball, it rests on the ground for some time after the first bounce, bounces a little bit, and rolls off.  That was the goal of the Pathfinder’s airbags- to stay close to the ground and cushion the blow upon impact.  The idea is actually quite ingenious.   Perhaps for more successful missions to Mars, NASA will still include the airbag theory to ensure a safe arrival on the foreign planet.

Sources included:

www.ilcdover.com/default.htm, aerospacescholars.org/scholars/earthmars/unit3/Index.htm (one of the Click here links in the Liftoff), mars.jpl.nasa.gov/MPF/mpfwwwimages/education/lander_cutout_small.gif.  Other sources with origin unknown are included in the package.

Last Updated: 09/07/01