Enter, descend, land — persevere

Wednesday, February 17, 2021
A test version of the rover Perseverance was used ahead ofd sending the actual rover to Mars, which is set to land on the Red Planet on Thursday. Contributed photo

Wheaton grad plays role in landing Mars rover Thursday

While human exploration on Mars may be many years in the future, a rover named Perseverance will land on Mars on Thursday, paving the way for future missions and possibility.

Erisa (Hines) Stilley, a 1998 Wheaton graduate and entry-descent-landing (EDL) systems engineer with Jet Propulsion Laboratory (JPL), worked as part of the cruise operations team which landed the rover Curiosity on Mars in 2012.

Erisa (Hines) Stilley, a 1998 Wheaton graduate and entry-descent-landing (EDL) systems engineer with Jet Propulsion Laboratory (JPL), worked as part of the cruise operations team which landed the rover Curiosity on Mars in 2012 and is part of the team that is landing Perseverance on Mars Thursday. Contributed photo

JPL is a federally funded research and development center and NASA field center in California that does contract work for NASA, so it is essentially part of the NASA family.

Stilley has an everyday title as an EDL systems engineer, and on her latest mission with the rover Perseverance, she is one of three of the EDL operations leads. Her team’s task is to physically land the rover Perseverance on Mars.

Stilley said while it is the shortest phase of the mission, it is the only part that is completely autonomous and is the most dangerous in terms of what can kill the mission.

“Our job doesn’t start until a few days before the mission, so a few days ago,” she said. “We do work before and after the landing, preparing and collecting data after the land to help us reconstruct the event of future use.”

Aside from preparation and data retrieval, the biggest and hardest part of an EDL engineers job is called the “seven minutes of terror.”

EDL engineers have seven minutes to get from the top of the atmosphere to the surface of Mars, and there is zero margin for error.

From thousands of miles per hour to a cold stop, even a small boulder can affect a rover’s landing.

“Risk factors, in terms of EDL, can be thought of as a series of events — one event is triggered by another and so on,” she said. “From the moment we enter the Martian atmosphere and begin to slow down, every step matters.”

EDL engineers use entry guidance, which is similar to flying an airplane.

“This help us to better steer towards our target,” Stilley said. “These triggers sense velocity, altitude and deceleration, but also timers, which are an on board software. If any one of these things hiccups or fails to complete, it will keep the entire sequence from continuing.”

In addition, there are single-point failures, which can be the event like deploying the parachute failing or the parachute ripping.

“These failures will not allow the rover to land correctly,” she said. “We can do testing on Earth, but because the physics of Earth and Mars are different, we can’t recreate the event at 100 percent.”

The moment the rover Perseverance lands on the surface of Mars will be the first real test in the environment it is built for.

“We are trying to land in Jezero Crater,” Stilley said. “It is a beautiful river delta that once spilled into a lake. There is preserved sediment from 3.5 billion years ago.”

The main mission the rover Perseverance is to collect those soil samples, which will later be retrieved.

“It is challenging to land there,” Stilley said. “There are two things that will help on this mission. One is the range trigger. The range trigger helps us to reduce the area we are landing in by 30 percent.”

The other is the Terrain Relative Navigation (TRN).

“The TRN is a more technical development that has been in the works for a long time and has finally made its way into its first mission,” she said. “TRN gives us the ability during flight to take photos and compare them to onboard maps. This allows us to localize and reduce our landing within tens of meters, while searching for the safest place to land.”

The maps have been previously loaded and coded in accordance to the safest landing they can estimate, but the real time photo comparison will a slow the rover to make a quick detour allowing for safe landing if the original spot has been deemed unsafe.

Even small boulders can make the landing unsafe for the rover, and while the EDL engineers have an idea of the surface, they won’t know exactly what is there until the landing occurs.

“One interesting thing to remember when thinking about the seven minutes of terror in which we have to land the rover, is that the communication between Earth and Mars is 11 minutes — one direction,” she said. “So, while it feels real time and looks real time, it will actually be delayed by 11 minutes and 22 seconds.”

The EDL engineers won’t even know if the rover has successfully landed or not until more than five minutes after it is done.

“However, we have engineers calling out events as they are happening,” she said. “This allows us to get data during the landing and still have time to react.”

As soon as the rover Perseverance lands successfully, the surface engineers are waiting to be handed over the vehicle and the information gathered.

“We are going to this ancient river delta to for the main mission of looking for signs of ancient life,” Stilley said. “We will be taking core samples using a drills and storing the samples in tubes. A future mission will retrieve the samples.”

NASA only has a rough timeline on sample retrieval, in the early 2030s.

The photos from the TRN technology will only be received if the landing is successful.

“Hopefully we will see those photos coming in within days of landing so we can share them with the public,” she said. “These are some interesting first-time things that are happening on this mission that will set the stage for future missions.”

In addition to the new technology, the Ingenuity will be making its first ever appearance on Martian land — or sky.

Ingenuity is a Mars helicopter that will be the first powered flight ever on Mars.

“It is bolted to the rover,” Stilley said. “This is the first time we have sent a vehicle to Mars that can fly. The vehicle is meant to last 30 sols (Mars days) and will be controlled from command through the rover.”

This means there will be no direct contact from command to the helicopter itself.

The Mars 2020 rover Perseverance will also hold the Mars Oxygen ISUR Experiment (MOXIE).

“This instrument can turn pure carbon dioxide into oxygen,” Stilley said. “This is a precursor to sending humans to Mars. The Perseverance has lofty explorations.”

Stilley said it is easy to get lost in the day to day of life, but she believes the missions she works on serve a greater purpose.

“Not all missions are huge to the public, but this is a big deal,” she said. “Every time we do it, especially with the success we have had, I think it makes it more and more exciting for people.

“In reality, it is nice to have something that pulls us out of the day to day and shows us that our world is bigger than we think.”

Stilley said this is all paid for by the taxpayers, so it is really all for the public.

“Moments like this inspire the next generation,” she said. “For some, it was Apollo; for me, it was the Challenger that made an impact; and for this generation, it may be this mission right now.

“Our students can be inspired to be problem solvers by seeing this moment.”

Perseverance’s touchdown is scheduled for approximately 2:55 p.m. Thursday.

Live coverage and landing commentary from NASA’s Jet Propulsion Laboratory in Southern California will begin at 1:15 p.m. on the NASA TV Public Channel and the agency’s website, as well as the NASA App, YouTube, Twitter, Facebook, LinkedIn, Twitch, Daily Motion, and THETA.TV.

Respond to this story

Posting a comment requires free registration: