ESA’s Comet Interceptor: A Dance with Cosmic Destiny

The launch of the Comet Interceptor mission, intended for the study of long-period comets, was originally planned on the Ariane 6 rocket alongside the Ariel telescope mission, which will explore exoplanet atmospheres. The launch was scheduled for the second half of 2029, despite the Comet Interceptor itself being ready by 2028. However, a recent review of Ariel’s schedule postponed its readiness for launch to the second half of 2031, potentially delaying Comet Interceptor by about three years.

This would necessitate storing Comet Interceptor for three years with all the associated costs,” explained ESA project scientist Michael Küppers. “Moreover, it’s extremely difficult to maintain team efficiency for three years when virtually nothing is happening.”

As a result, the mission team began considering alternative launch options. The preferred option is a launch on an Ariane 64 rocket as a secondary payload along with a commercial communication satellite to be placed in geostationary orbit. After detaching the commercial payload, the Ariane’s upper stage will direct Comet Interceptor to the Earth-Sun Lagrange point L1, from where the spacecraft will then move to point L2.

The new launch plan was approved by the ESA’s Science Program Committee back in December. Currently, the agency, along with Arianespace, is exploring the possibility of a launch window from August 2028 to July 2029.

Mission Feature and Potential Targets

A distinctive feature of the Comet Interceptor is that the mission target can only be determined after launch. The spacecraft will stay at the Earth-Sun L2 point for several years, awaiting the appearance of a suitable comet. The primary mission target remains a flyby of a long-period comet arriving from the outer Solar System. Besides the main spacecraft, Comet Interceptor will deploy two smaller probes provided by the Japan Aerospace Exploration Agency (JAXA). These probes will allow observations during the flyby at relative speeds of up to 70 kilometers per second (44 mph).

As an alternative, an interstellar object like 3I/ATLAS is being considered, although the probability of finding such an object within the mission’s lifetime remains “relatively low,” according to experts.

If no suitable long-period comet is found, the spacecraft will target a short-period comet that has repeatedly passed through the inner Solar System.

The Technical Advantage of the Alternative Launch

The alternative launch option also has a significant technical advantage. The available delta-v for Comet Interceptor to intercept a comet will increase from approximately 600 to 1000 meters per second (2236 mph). This is due to the greater allowable mass of the spacecraft in the new launch configuration, allowing it to carry more fuel. This, in turn, significantly increases the chances of a successful encounter with a long-period comet.

Küppers estimates the probability of not finding a suitable target within the six-year mission reduces from about 20% to less than 10%.