The CAESAR spacecraft is being designed to collect and return to Earth a sample from the surface of a comet.

The long journey and small target body call for solar electric propulsion similar to what was used on the Dawn spacecraft. Use of this type of propulsion means that with a months-long launch window, as opposed to a few weeks like other missions, the spacecraft could still target Comet 67P and arrive back on Earth at a specific date and time.

Caesar flight spacecraft

CAESAR plans to be the farthest-reaching spacecraft to use solar power, flying well beyond Jupiter’s orbit, and this means designing some of the largest solar arrays ever used on a planetary mission. Prototypes for these panels are flexible so that they can be stowed to fit inside the launch vehicle and “rolled out” after launch.



Once a sampling site has been selected, the CAESAR spacecraft would fire conventional hydrazine rockets to slow down, drop out of orbit around Comet 67P, and begin its decent to the surface. Continued periodic firings of these rockets are planned in order to match the spacecraft’s motion to the comet’s motion, allowing for a delicate vertical touchdown.



Camera Suite

The camera suite is being designed for selecting the site for sample collection, navigating the spacecraft down to that site, and documenting the site in detail before, during and after collection. These cameras would also provide insight into how the surface of Comet 67P has changed in the years since the Rosetta mission. Camera prototypes currently being assembled and tested are very similar in design to those used on previous missions.

Sampling System

The robotic arm with the sampling device would deploy during the spacecraft’s final decent to the comet’s surface in preparation for the touch-and-go maneuver planned for collecting the sample.

CAESAR spacecraft tag arm

Upon gently touching down on the surface, the design of the arm includes an internal spring to allow compression during the brief surface contact and sample collection. A moment later the rockets would fire to back the spacecraft away from the surface. After the spacecraft has left the comet’s surface, a gentle swinging motion of the arm is planned in order to measure the centripetal force and determine how much material was collected. If the collection is determined to be successful, the arm would then deliver the sample to the containment system.

Rocks in a sample collection device at NASA


Read more detailed information

From the 2018 Lunar Planetary Science Conference.