Cruise
Image of a spacecraft during the cruise stage

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    While it was on its way to Mars, InSight moved away from Earth at a speed of 6,200 miles per hour (10,000 kilometers per hour). Mission navigators tracked the spacecraft almost continuously after launch. The team adjusted InSight's flight path six times during cruise to make sure that it was flying at the right speed and direction. These were made in 2018--on May 15, June 26, July 28, Oct. 12, Nov. 18, and Nov. 25.

    InSight Trajectory
    InSight's Route to Mars: An illustration of the route InSight took to get to Mars. Full image and caption ›

    The Trip to Mars

    Cruise started soon after the spacecraft separated from the launch vehicle and ended 205 days later, about three hours before entry into the Martian atmosphere. During cruise, the lander was tucked inside its protective aeroshell, with the aeroshell attached to the cruise stage. The trip to Mars took almost seven months. Some of the key activities during the cruise phase included:

    • Health checks and maintenance of the spacecraft in its cruise configuration.
    • Monitoring and calibration of the spacecraft and subsystems.
    • Attitude correction turns (adjusts) to maintain the antenna pointing toward Earth for communications and to keep the solar panels pointed toward the Sun for power).
    • Navigation activities, including trajectory correction maneuvers, to keep track of InSight’s position and precisely control it prior to approach.
    • Preparation for entry, descent, and landing and surface operations, including communication tests used during entry, descent, and landing.

    These checks ensured that everything was working just as it should. They prepared the spacecraft for landing and also prepared the instruments for doing science.

    The spacecraft has several tools that help guide its path.
    InSight's Navigation Tools: The spacecraft has several tools that helped guide its path. Full image and caption ›

    InSight's Navigation Tools

    The spacecraft has several tools that helped guide its path:

    • A star tracker tracked InSight's position against the stars in the night sky. This told navigators how the spacecraft was oriented.
    • An inertial measurement unit with a gyroscope provided information on which way it was moving and how fast.
    • Sun-sensors helped the spacecraft know the direction of the Sun.

    Turning the Steering Wheel

    After InSight left the rocket's protective fairing, mission navigators used information from all of these tools to adjust its route. These adjustments are known as "trajectory correction maneuvers," or TCMs. They helped fine-tune the flight path so InSight hit just the right entry point at the top of the Martian atmosphere on landing day.

    insight gif
    InSight On Its Way to Mars: NASA's InSight spacecraft cruised to Mars. Full image and caption ›

    At times, InSight needed to make a large turn so it was pointed in the right direction. At other times, it needed to make smaller changes, like turning a car's steering wheel just slightly. Unlike some spacecraft, InSight did not spin around its axis. Instead, sensors attached to the spacecraft told it which way is up, down, left, right, forward and back. This is known as "3-axis stabilization."

    InSight had eight thrusters, four big and four small. These thrusters could be fired a little at a time to give a push to the spacecraft and help it turn and move in the right direction. The four large thrusters helped InSight turn and travel in the correct direction. The four smaller ones were used to keep the spacecraft stable and point it in the right direction.

    Fine-Tuning InSight's Flight Path

    This artist's impression shows InSight traveling to Mars.
    InSight Traveling to Mars: This artist's impression shows InSight traveling to Mars. Full image and caption ›

    InSight's flight path was planned to minimize its travel time. After its launch in May 2018, InSight traveled less than halfway around the Sun before it reached Mars. In late July 2018, while InSight was on its way, Mars was at the point in its orbit where it was closest to Earth. This happens roughly every 26 months and is also known as Mars Close Approach. This can sometimes be beneficial for Mars launches, and is one of the reasons why they are scheduled only every other year.

    At launch, the launch vehicle's upper stage pointed away from Mars; this is known as the "trajectory bias." Once the spacecraft separated from its launch vehicle, it turned to point towards Mars. In a Mars launch, only the spacecraft heads towards Mars, while the launch vehicle upper stage never comes close.

    After launch, navigators fine-tuned the spacecraft’s path to make sure it arrived at the correct point above the Martian atmosphere and landed in the right place. Trajectory correction maneuvers helped point the spacecraft towards Mars and fine-tuned its orbit. The back-up maneuvers were used in case a planned maneuver could not be performed on time, or if the spacecraft’s flight path needed final adjustments just before it enters the atmosphere.

    Originally Planned Dates (subject to change) Trajectory Correction Maneuvers Activity
    May 22, 2018
    17 days after launch
    TCM 1 To point InSight towards Mars and fine-tune its flight path after launch.
    July 28, 2018
    121 days before landing
    TCM 2 To point InSight towards Mars.
    Oct. 12, 2018
    45 days before landing
    TCM 3 To make sure InSight travels at the right speed and direction to arrive at the correct location at the top of the Martian atmosphere before its planned landing.
    Nov. 11, 2018
    15 days before landing
    TCM 4
    Nov. 18, 2018
    8 days before landing
    TCM 5
    Nov. 25, 2018
    22 hours before landing
    TCM 6

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