After a six-month voyage from Earth, NASA’s InSight Mars lander, streaking through space at at some 12,300 mph, will slam into the thin martian atmosphere Monday afternoon to begin a nail-biting six-and-a-half-minute descent to the surface, kicking off a billion-dollar mission to probe the red planet’s hidden interior.

“The goal of InSight is nothing less than to better understand the birth of the Earth, the birth of the planet we live on, and we’re going to do that by going to Mars,” said Principle Investigator Bruce Banerdt.

On Earth, plate tectonics and the constantly churning mantle have altered the planet’s deep interior, obscuring its history and evolution. But Mars is a smaller planet and much less active than Earth, retaining the “fingerprints” of those earlier processes.

“By mapping out these boundaries, these various different sections of the inside of the planet, we can then understand better how the planet formed and how our planet got to be the way it is where we can actually live and play and have a good time. … So, we’re going to go to Mars.”

A final correction maneuver was planned Sunday afternoon to slightly tweak InSight’s trajectory and ensure an on-target landing on a broad plain known as Elysium Planitia.

But as with all Mars landings, InSight’s fully automated descent 90 million miles away will take place far beyond any direct control — or help — from engineers on Earth. In fact, it will take radio signals 8.1 minutes to make their way to the Jet Propulsion Laboratory in Pasadena, Calif., where anxious scientists and engineers will be waiting to find out whether the spacecraft made it successfully to the surface.

“We’ve done everything we can, we’ve done everything we can think of to make sure we’re going to be successful,” said Tom Hoffman, the InSight project manager. “But you just never know what’s going to happen.”

Nestled inside a flying saucer-shaped “aeroshell” and protected by a state-of-the-art heat shield, InSight will begin its plunge at around 2:47 p.m. EST Monday, enduring braking forces up to 7.4 times the strength of Earth’s gravity as it rapidly slows down and heats up to around 2,700 degrees Fahrenheit.

Four minutes later, at an altitude of 7.5 miles and now moving at a still supersonic 928 mph, a 39-foot-wide parachute will unfurl, inflating with a force of 15,000 pounds per square foot to slow the craft to a much more manageable 295 mph or so.

The no-longer-needed heat shield then will be jettisoned, exposing the bottom of the lander to the environment, and 10 seconds after that, its three landing legs will unfold and lock in place.

A few seconds later, about one minute before touchdown, InSight’s downward-looking radar will be activated, measuring the spacecraft’s altitude and rate of descent and feeding those data to the lander’s flight computer.

Finally, less than a mile above the surface and descending at about 134 mph, InSight will be released from the aeroshell and parachute to fall freely on its own.

One second later, twelve small rocket motors will fire up, each one generating about 68 pounds of thrust as they pulse on and off 10 times per second, first moving the spacecraft to one side to avoid the falling parachute and aeroshell.

Nulling out its horizontal velocity and slowing to about 5 mph, InSight is expected to touch down on Elysium Planitia around 2:54 p.m., roughly 2 p.m. local time on Mars.
2018/11/26, 3:13:46 下午
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