Podcaster: Ken Brandt
Title: Perseverance & The Exploration of Mars – Part 1
Organization: Robeson Planetarium/JPL Solar System Ambassador
Link: https://www.robeson.k12.nc.us/o/robeson/page/robeson-planetarium
Description:
Perseverance lands on Mars February 18. Here the overview of the process of entry, descent, and landing for this Martian explorer.
Bio: Ken Directs the Robeson Planetarium in rural North Carolina. He is also a volunteer in NASA/JPL’s Solar System Ambassador program, which is a national network of passionate volunteers who explain and educate about space exploration for their audiences.
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Transcript:
On the 18th of this month, Perseverance lands on Mars. The landing, conveniently enough, should occur shortly after 7:50 PM UT. This series will explore some of the facets of this complex and ambitious mission to further our knowledge about Mars.
Perseverance lands seven minutes after entering Mars’ thin atmosphere. The Jet Propulsion Lab (JPL), who manages and built this robot, calls this time the seven minutes of terror. Part of the terrific nature of this landing has to do with the speed of light. Right now, it takes light (and radio waves) about 10 minutes to travel from Mars to earth. So, for example, when the robot signals JPL that the parachute has opened properly, the rover has already landed or crashed on Mars.
Then there is the matter of timing and precision. JPL isn’t just trying to land on a random spot on Mars, they’re landing Perseverance inside a crater barely 30 miles wide-and in a small portion of that, to boot! The landing ellipse is roughly 4 miles long and 3 miles wide. JPL has some serious Math skills, skills necessary to time a landing on a spinning planet with such awesome precision. This is one reason why we know exactly when Perseverance is touching down: they’ve done the math.
The first thing that must go right is insertion into the Martian atmosphere. It is this phase of the landing that is most dangerous: come in at too steep an angle, and you overwhelm the heat shield and burn up. Come in too shallow, and you go skipping off into space. Friction with the atmosphere results in two things; heating of the shield to over 2,500 degrees Fahrenheit, and reducing speed, from more than 12,000 miles an hour, to about 1,000.
After about four minutes of this, the parachute deploys. This further reduces the speed to less than 300 miles an hour. About 20 seconds later, the heat shield is jettisoned. Now things get really precise, as the rover’s radar and descent cameras get busy, trying to determine where they are over Mars.
At roughly 4.5 miles from the surface, the radar locks onto its target-the floor of Jezero crater. At the same time, descent imaging sends images of the ground to Perseverance’s onboard computer, which compares the images taken by the rover to a library of surface images taken by orbiter, such as the Mars Reconnaissance Orbiter. The rover uses Terrain Relative Navigation to steer itself to a smooth landing spot.
At approximately 1.3 miles above Mars, the landing system of jetpack and rover descends toward the ground. Four rockets on the jetpack fire in a coordinated pattern to slow the rover down further, and guide it to an ideal landing site, all the while snapping more images, and comparing terrains with orbiter images.
The “skycrane maneuver” begins at about 70 feet above Jezero crater’s lakebed. Perseverance is now travelling at 17 MPH, slowly being lowered by three tethers about 20 feet below its jetpack. The jets are angled so that the exhaust doesn’t kick up a lot of dust. Slowly Perseverance descends, gradually reducing speed to less than 1 MPH. The wheels touch the lakebed, and the tethers are cut, releasing the rover, while the jetpack flys far away, to crash-land elsewhere on Mars. If you watch the live stream on the 18th, it’s at this point when you’ll see a bunch of excited engineers and scientists at JPL celebrating a job well done.
These celebrations involve dry roasted peanuts. “According to NASA: Good-luck peanuts made their first appearance in 1964 during the Ranger 7 mission. JPL had six failures prior to this effort. The Ranger 7 launch day arrived and with it came the peanuts. The mission performed flawlessly, as did its peanut-powered successors, Ranger’s 8 and 9. Up until the Voyager mission, peanuts showed up only at launch. Nowadays, they are often seen in mission control facilities during critical mission stages such as orbit insertions, flybys and landings, or any other event of high anxiety or risk.” Who says that science-types aren’t superstitious.
The Robeson Planetarium is teaming up with the NC Museum of Natural Sciences, JPL, and NASA to bring live landing day coverage to you. To register, go to https://naturalsciences.org/calendar/event/perseverance-landing-event/ and sign up. I will be doing a presentation about Jezero crater, and fossil hunting. Coincidentally, this is also the topic of the next article in this series, coming up next Saturday.
End of podcast:
365 Days of Astronomy
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