Adieu, Rosetta !


Well, it’s an emotional moment, I have to admit. Knowing that Rosetta will reach the surface of the comet 67P/Churyumov-Gerasimenko in a controlled impact in several hours from now, is quite hard to imagine. But this is the reality, however. Launched in 2004, Rosetta arrived at her comet in August 2014 after more than 10 years of space travel and has been accompanying this amazing bi-lobed space rock for more than 2 years to day. In a nutshell, during this time Rosetta could vividly investigate the comet and successfully land its Philae lander, amassing a treasure trove of scientific data, that was only in the imagination earlier. Various instruments on-board Rosetta and Philae sent back to Earth copious amounts of data which have already let to fabulous discoveries about comets and early solar system. The goal today in this post is not to talk about all these science, but to extend my gratitude to the entire space mission Rosetta and all the eminent people behind it, for Rosetta had a direct positive impact in my life.

2 years ago, this day I was back in Hanoi, Vietnam starting my second year of Master at USTH (University of Science and Technology of Hanoi). I would start the first semester of my the academic year and during one of the courses, I had the opportunity to meet a lecturer who works with the Rosetta mission. It was just before the Philae landing in 12th November 2014 and he would share some information about the mission. By this time Rosetta had already made some buzz since its wake-up from the deep-space hibernation in January 2014 and I had been closely following the mission updates. Therefore it was quite interesting meet a scientist who worked with the mission and even get to know some first-hand information. This encounter was sort of a spark and I got myself glued to the mission and rejoiced at the successful landing event as I watched that famous live broadcast from Damstadt, Germany. Few weeks later, it was the time to apply for the Master 2 internship which would last for an entire semester (6 months). It was the end of December 2014 and I applied for an internship at LESIA (Laboratoire d’Etudes Spatiales et d’Instrumentation en Astrophysique) of Paris Observatory. LESIA is one of the prestigious and renown labs of Paris Observatory, and is specialised in space studies and astrophysics instrumentation. The biggest highlight, coincidentally, was that the internship would involve the very Rosetta mission. It was about spectrophotometry of the comet 67P using images from OSIRIS imaging instrument on-board Rosetta…..

After an examination of my candidacy, I got the green light and I found myself in Paris, which would consequently end up my home for a while. Thus I started in March 2015, the internship, learning basics about comets and trying to understand the photometric behaviour and morphology of this duck-shaped space rock. Later on I managed to secure a scholarship from the Parisian doctoral school of astronomy and astrophysics (Ecole Doctorale 127) to start a PhD thesis on small bodies of the solar system, still at LESIA ! The thesis in fact was an extension of the study I had been working on during my internship and this meant that I could continue working with OSIRIS data. That being said, I officially started my PhD on 1st of October 2015 and today 30th of September 2016 marks the end of the 1st year of thesis, as does the end of the Rosetta space mission.

I guess that reflects some of my memories with Rosetta, the mission that brought me to France. What an audacious mission, with unprecedented achievements, the fruit of a lot of hard-working individuals quite simply put. I spent countless mornings checking the OSIRIS image archive for the latest images transmitted to Earth previous day or the other day. Sometimes it was necessary to wait longer for the calibration processes to finish. The simple feeling that there will be no more new images after tomorrow, is difficult to believe and accept. But thank you again Rosetta for what you have done, and what you leave us with. I’m sure your legacy will be cherished for years to come, while we wrestle with the data you sent back and will be sending back later today before you take your final rest next to Ma’at pits on the small lobe of 67P.

Well, the following is for those who want to get a bit technical about the Rosetta’s touch down, tomorrow, with respect to the OSIRIS imaging instrument.

We know that Rosetta will be operating most of its instruments during the descent and will be sending the data as soon as she collects them. The latest data will probably be corresponding to a distance of about 100 m from the surface. We know that OSIRIS instrument has 2 scientific cameras, namely NAC (Narrow Angle Camera) and WAC (Wide Angle Camera) with different fields-of-view and different spatial resolutions and OSIRIS will be functional to the very end. One could juggle with numbers and find the following for the expected spatial resolutions of the images at different stages at the descent.

At ~ 20 km altitude (collision manoeuvre) : NAC ~ 37 cm/pixel & WAC 200 ~ cm/pixel
At ~ 1 km altitude (final images of NAC as it becomes out of focus) : NAC ~ 1.86 cm/ pixel & WAC ~ 10 cm/pixel
From this altitude onwards only the WAC will be used.
At ~ 200 m altitude (WAC starts to be out of focus) : WAC ~ 2 cm/pixel
From this altitude onwards WAC images will be blurred.

Equipped with these numbers, let’s wait what the tomorrow brings (A glance at my laptop clock reminds me that it’s already tomorrow)! It’s the time I got some sleep before the dawn.

Rosetta blog reports that the collision manoeuvre has now been made and all is set for the controlled impact. Here you go ROSETTA !

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