EDL Challenges with India’s Mangalyaan-2 Mission – Part II
By Dr. Gary Deel, Ph.D., J.D.
Faculty Director, School of Business, American Military University
This is the second article in a two-part series discussing the India Space Research Organization’s (ISRO’s) Mangalyaan-2 mission. Read part I here.
The NASA Spirit and Opportunity rovers landed on Mars in 2004. They used a unique entry, descent, and landing (EDL) sequence that allowed for safe landing on the red planet. First, the rovers were encapsulated by heat shields that protected them from the heat of aerodynamic drag in the initial entry into the Martian atmosphere.
Get started on your Space Studies Degree at American Military University.
Once the spacecraft had been significantly slowed by the aero drag, they jettisoned their heat shields and deployed huge parachutes that continued to slow their descents. Then, the lander carriages dropped out of the spacecraft backshells on tethers and instantly inflated huge airbags forming a protective, pyramid-shaped, inflatable cocoon around the rovers.
When the rovers neared the surface, the spacecraft backshells — still attached to the parachutes and dangling the protected rovers beneath them — fired a set of retrorockets that momentarily stopped their downward movement. The tethers connecting the rovers to the backshells were then cut, allowing the rovers to fall to the surface.
When the rovers touched down, their airbag cocoons bounced repeatedly until they eventually rolled to a rest. Only then were the airbags deflated and the protective carriages opened. That allowed the rovers to power up and drive away.
This EDL method on Mars permitted a safe landing by using heat shields, parachutes, retrorockets, and inflatable cocoons to bring the speed from thousands of miles per hour at the top of the atmosphere to zero, without any damage to the rovers. The inflatable airbag cocoons also had the ancillary effect of insulating the rovers from any dust that might have been kicked up during their landing process
Another example from which ISRO could take cues is the NASA Curiosity Rover, which landed on Mars in 2012. Curiosity’s EDL process was similar to that of Opportunity and Spirit, but with some key distinctions.
First, Curiosity entered the Martian atmosphere with a heat shield just like its predecessors. Once it had lost all the speed it could manage to lose from aerodynamic drag, it jettisoned its heat shield and deployed a massive parachute that continued to slow its descent. The parachute was the lightest and strongest supersonic parachute ever built at the time; it weighed only about 100 pounds but could withstand more than 65,000 pounds of force.
Once the parachute had done its job, the spacecraft was still descending at close to 200 mph. At this point, rather than lower the rover carriage out of the backshell on a tether like the Opportunity and Spirit missions, the carriage was actually ejected free from the backshell altogether. It then immediately fired a set of retrorockets to slow its descent. However, because the parachute and backshell were still directly above the rover carriage, it also needed to perform an extreme horizontal evasive maneuver to avoid a collision.
Once the rover carriage had restabilized its descent, it dropped to an altitude of about 66 feet above the Martian surface. However, it paused there because, if the rover had descended all the way to the surface on rocket power, the exhaust plumes from the rockets would have kicked up a huge dust cloud that would have landed back down on the rover and caused the problems discussed earlier in this article series. So NASA’s solution was what they called the sky crane.
Hovering above the surface, the sky crane lowered the rover down from the carriage frame on cables until it gently touched down on the surface. At that point, the cables were immediately released from the rover. The carriage was still hovering directly above the rover, however, so the last step was for the rockets to jettison the carriage up and away so that it could crash land on the surface at a safe distance, to avoid any risk of damage to the rover.
So Curiosity was able to achieve a safe landing on the surface and avoid any significant contamination from dust. The EDL was as successful as those of the Opportunity and Spirit rovers, just using a slightly different approach.
Obviously, these examples are not the only methods that ISRO might use for making a safe landing on Mars. For example, NASA’s Mars InSight Lander, which successfully touched down in 2018, utilized an EDL method very similar to that of Curiosity, except that it forewent the skycrane maneuver. Instead, it used retrorockets to take the InSight Lander all the way down to the surface. The viability of this approach depends on many factors, including the weight of the lander and the sensitivity of electronic components or science instruments to damage by Martian dust.
Another approach would be to use retrorockets and a displacement bag for a cushioned landing. Russia’s Mars 2 and Mars 3 landers both attempted this approach. Mars 2 was unsuccessful, and while Mars 3 did make it to the surface and report back, it immediately lost contact with Earth and was never recovered. So while this EDL method might be viable, it obviously doesn’t have the best track record.
A final means of landing on Mars would be by penetration, which involves deploying small, robust landers to hit the surface at high speed and bury themselves deep under the surface. This method was attempted by both Russia with its Mars 96 mission and the United States with the Mars Polar Lander (MPL) mission. Unfortunately, neither mission succeeded. Again, the laws of physics suggest that, if ISRO’s mission is compatible with a penetrating lander, the method is theoretically workable. But history has shown that it is not easy to achieve in practice.
Assuming that ISRO is successful with landing a Mangalyaan-2 lander or rover on Mars, it will still face a number of other challenges. For example, different parts of Mars regularly experience dust storms. So depending on the landing location, a lander or rover might be exposed to forces of nature on Mars that could threaten mission longevity. However, their biggest obstacle by far will be getting safely to the surface in the first place.
The good news is that they have plenty of examples from successful Mars missions launched by other national space agencies that they can look to for design choices and innovation. If ISRO follows these cues, there is every reason to believe that its Mangalyaan-2 mission will be just as successful as its predecessor, in principle, and in execution.
About the Author
Dr. Gary Deel is a Faculty Director with the School of Business at American Military University. He holds a J.D. in Law and a Ph.D. in Hospitality/Business Management. Gary teaches human resources and employment law classes for American Military University, the University of Central Florida, Colorado State University and others.