Cruise
Image of a spacecraft during the cruise stage

InSight is on its way to Mars, moving away from Earth at a speed of 6,200 miles per hour (10,000 kilometers per hour). Mission navigators have been tracking the spacecraft almost continuously since launch. The team adjusts InSight's flight path several times during cruise to make sure that it is flying at the right speed and direction. Six such adjustments are planned during the almost seven-month trip to Mars, as are two back-ups. The first adjustment to InSight’s flight path was completed on May 22, 2018, just 17 days after launch.

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

The Trip to Mars

Cruise starts soon after the spacecraft separates from the launch vehicle and ends 205 days later, about three hours before entry into the Martian atmosphere. During cruise, the lander is tucked inside its protective aeroshell, with the aeroshell attached to the cruise stage. The trip to Mars takes almost seven months. Some of the key activities during the cruise phase include:

  • 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 ensure that everything is working just as it should. They get the spacecraft ready for landing and prepare 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 help guide its path. Full image and caption ›

InSight's Navigation Tools

The spacecraft has several tools that help guide its path:

  • A star tracker tracks InSight's position against the stars in the night sky. This tells navigators how the spacecraft is oriented.
  • An inertial measurement unit with a gyroscope provides information on which way it is moving and how fast.
  • Sun-sensors help the spacecraft know the direction of the sun.

InSight Turns its Steering Wheel

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

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

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

InSight has eight thrusters, four big and four small. These thrusters can 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 help InSight turn and travel in the correct direction. The four smaller ones are 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 is planned to minimize its travel time. After its launch in May 2018, InSight travels less than halfway around the sun before it reaches Mars. In late July 2018, while InSight is on its way, Mars is at the point in its orbit where it is 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 points away from Mars; this is known as the "trajectory bias." Once the spacecraft separates from its launch vehicle, it must turn and point towards Mars. Only the spacecraft heads towards Mars, while the launch vehicle upper stage never comes close.

After launch, navigators fine-tune the spacecraft orbit to make sure it arrives at the correct point above the Martian atmosphere and lands in the right place. Trajectory correction maneuvers help point the spacecraft towards Mars and fine-tune its orbit. The back-up maneuvers are used in case a planned maneuver cannot be performed on time, or if the spacecraft’s flight path needs final adjustments just before it enters the atmosphere.

Date (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 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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