2014 Comet Siding- Spring came so close to Mars that the Mars orbiters were evicted to remove possible harmful debris. Picture credits: NASA / JPL-Caltech – http://photojournal.jpl.nasa.gov/figures/PIA18611_fig1.jpg, Public Domain, https://commons.wikimedia.org/w/index.php?curid=36018137  Once the ESA scientists have identified and selected a long-running comet, Space Interceptor will launch its propulsion system and set off for a rendezvous. The Interceptor actually consists of three spacecraft in one, and each of the three is loaded with complementary scientific instruments. When the spaceship approaches the comet, it is divided into three parts.
Each of the three will offer different perspectives of the cometary nucleus and its gas, dust and plasma environment. By measuring the comet from three points, scientists get the detailed 3D information they need to understand the dynamics of an untouched comet as it is exposed to the ever-changing solar wind environment.
But the target of the comet interceptor may not be a comet at all. The spaceship may be aimed at another interstellar object similar to Oumuamua. Oumuamua visited our solar system in 2017 and it is the only interstellar object we have discovered through our system. There was a lot of funny speculation (and some pretty wild speculation) about the nature of the object, but in any case we'll never see it again. However, scientists say that interstellar objects are not rare and that there is likely to be an object moving through our solar system at some point in time.
Artistic representation of the first interstellar asteroid / comet "Oumuamua". This unique object was discovered on 19 October 2017 from the Pan-STARRS 1 Telescope in Hawaii. Picture credits: ESO / M. Kornmesser
Regardless of whether the comet interceptor is to investigate a comet or another object, this is a first for science. In fact, the overall ability to perform this mission is fairly new.
We now have instruments that can scan the sky deeper and more effectively than ever before. These instruments, such as Pan-STARRS and the upcoming Large Synoptic Survey Telescope, automatically scan the sky and alert us early that objects are approaching. This gives scientists the advantage of being very selective in their approach and choosing carefully and patiently.
The Comet Interceptor is a mission of the "F-Class" or the fast class. This title refers to how long it took to select the project from among the 23 pitches it has received from companies since it was announced last July. It also refers to how fast the craft can be developed. Only eight years elapse between the selection of the mission and the start. That's pretty fast for a complex space mission.
An artistic representation of the Planet Hunt spacecraft ARIEL of the ESA. The comet interceptor will be launched in 2028 on the same rocket as ARIEL. Source: ESA / ARIEL consortium.
The comet interceptor will launch in 2028, probably in the same rocket as ESA's planetary hunt, ARIEL (Atmospheric Remote Sensing Infrared Spacecraft Exoplanet Large-survey), which is also destined for LaGrange Point 2. It will take about a month to reach L2. Then the wait begins and no one can say how long it will take for a desired destination to approach.
But once a target is selected and the comet interceptor reaches the comet or other interstellar object, the resulting science is worth the wait.