Entry, Descent, and Landing

Entry, Descent, and Landing Technologies

The Mars 2020 rover mission has major new technologies that improve entry, descent, and landing: Range Trigger, Terrain-Relative Navigation, MEDLI2, and its EDL cameras and microphone.

Range Trigger

The Range Trigger technique shrinks the Mars 2020 rovers landing ellipse significantly, landing the rover closer to the target area of scientific interest. This example shows Mars 2020's ellipse in relationship to Mars rover Curiosity's landing ellipse. Mars 2020 will be landing in a different location. Credit: NASA/JPL-Caltech

A Major Improvement in Landing Accuracy

It's hard to land on Mars, and even harder to land a rover close to its prime scientific target. Previous rovers have landed in the general vicinity of areas targeted for study, but precious weeks and months can be used up just traveling to a prime target. The Mars 2020 mission team is working on a strategy to put the rover on the ground closer to its prime target than was ever before possible. The Range Trigger technology reduces the size of the landing ellipse (an oval-shaped landing area target) by more than 50%. The smaller ellipse size allows the mission team to land at some sites where a larger ellipse would be too risky given they would include more hazards on the surface. That gives scientists access to more high priority sites with environments that could have supported past microbial life.

Range Trigger - It's All About Timing

The key to the new precision landing technique is choosing the right moment to pull the "trigger" that releases the spacecraft's parachute. "Range Trigger" is the name of the technique that Mars 2020 uses to time the parachute's deployment. Earlier missions deployed their parachutes as early as possible after the spacecraft reached a desired velocity. Instead of deploying as early as possible, Mars 2020's Range Trigger deploys the parachute based on the spacecraft's position relative to the desired landing target. That means the parachute could be deployed early or later depending on how close it is to its desired target. If the spacecraft were going to overshoot the landing target, the parachute would be deployed earlier. If it were going to fall short of the target, the parachute would be deployed later, after the spacecraft flew a little closer to its target.

Shaving Time Off the Commute

The Range Trigger strategy could deliver the Mars 2020 rover a few miles closer to the exact spot in the landing area that scientists most want to study. It could shave off as much as a year from the rover's commute to its prime work site.

Another potential advantage of testing the Range Trigger is that it would reduce the risk of any future Mars Sample Return mission, because it would help that mission land closer to samples cached on the surface.

Terrain-Relative Navigation

Terrain-Relative Navigation is an innovative entry, descent, and landing technology that allows the rover to detect tricky terrain and divert itself to a safer landing area. Credit: NASA/JPL-Caltech

Terrain-Relative Navigation helps us land safely on Mars - especially when the land below is full of hazards like steep slopes and large rocks!

How Terrain-Relative Navigation Works

  • Orbiters create a map of the landing site, including known hazards.
  • The rover stores this map in its computer "brain."
  • Descending on its parachute, the rover takes pictures of the fast approaching surface.
  • To figure out where it's headed, the rover quickly compares the landmarks it "sees" in the images to its onboard map.
  • If it's heading toward dangerous ground up to about 985 feet (300 meters) in diameter (about the size of two professional baseball fields side by side), the rover can change direction and divert itself toward safer ground.

Why Terrain-Relative Navigation is Important

Terrain-Relative Navigation is critical for Mars exploration. Some of the most interesting places to explore lie in tricky terrain. These places have special rocks and soils that might preserve signs of past microbial life on Mars!

Until now, many of these potential landing sites have been off-limits. The risks of landing in challenging terrain were much too great. For past Mars missions, 99% of the potential landing area (the landing ellipse) had to be free of hazardous slopes and rocks to help ensure a safe landing. Using terrain relative navigation, the Mars 2020 rover can land in more - and more interesting! - landing sites with far less risk.

How Terrain-Relative Navigation Improves Entry, Descent, & Landing

Terrain-Relative Navigation significantly improves estimates of the rover's position relative to the ground. Improvements in accuracy have a lot to do with when the estimates are made.

In prior missions, the spacecraft carrying the rover estimated its location relative to the ground before entering the Martian atmosphere, as well as during entry, based on an initial guess from radiometric data provided through the Deep Space Network. That technique had an estimation error prior to EDL of about 0.6 - 1.2 miles (about 1-2 kilometers), which grows to about (2 - 3 kilometers) during entry.

Using Terrain-Relative Navigation, the Mars 2020 rover will estimates its location while descending through the Martian atmosphere on its parachute. That allows the rover to determine its position relative to the ground with an accuracy of about 200 feet (60 meters) or less.

It takes two things to reduce the risks of entry, descent, and landing: accurately knowing where the rover is headed and an ability to divert to a safer place when headed toward tricky terrain.


Improving Models of the Martian Atmosphere for Robotic and Future Human Missions to Mars.

MEDLI2 is a next-generation sensor suite for entry, descent, and landing (EDL). MEDLI2 collects temperature and pressure measurements on the heat shield and afterbody during EDL.

MEDLI2 is based on an instrument flown on NASA's Mars Science Laboratory (MSL) mission. MEDLI stands for "MSL Entry, Descent, and Landing Instrumentation." The original only collected data from the heat shield. MEDLI2 can collect data from the heat shield and from the afterbody as well.

This data helps engineers validate their models for designing future entry, descent, and landing systems. Entry, descent, and landing is one of the most challenging times in any landed Mars mission. Atmospheric data from MEDLI2 and MEDA, the rover's surface weather station, can help scientists and engineers understand atmospheric density and winds. The studies are critical for reducing risks to both robotic and future human missions to Mars.

Entry, Descent, and Landing (EDL) Cameras and Microphone

Unprecedented Visibility into Mars Landings

Mars 2020 has a suite of cameras that can help engineers understand what is happening during one of the riskiest parts of the mission: entry, descent, and landing. The Mars 2020 rover is based heavily on Curiosity's successful mission design, but Mars 2020 adds multiple descent cameras to the spacecraft design.

The camera suite includes: parachute "up look" cameras, a descent-stage "down look" camera, a rover "up look" camera, and a rover "down look" camera. The Mars 2020 EDL system also includes a microphone to capture sounds during EDL, such as the firing of descent engines.

A First-Person View of Landing on Mars

In addition to providing engineering data, the cameras and microphone can be considered "public engagement payloads." They are likely to give people on Earth a good and dramatic sense of the ride down to the surface! Memorable videos depicting EDL's "Seven Minutes of Terror for the 2012 landing of NASA's Curiosity Mars rover went viral online, but used computer-generated animations. No one has ever seen a parachute opening in the Martian atmosphere, the rover being lowered down to the surface of Mars on a tether from its descent stage, the bridle between the two being cut, and the descent stage flying away after rover touchdown!