13 december 2019

On the Rosetta and Philae mission to comet 67P/Churyumov-Gerasimenko

Hieronder is een blog te lezen van Matt Taylor, die als ‘project-scientist’ nauw betrokken is bij het wetenschappelijk onderzoek van de Europese Rosetta sonde en de Philae lander aan de komeet 67P/Churyumov-Gerasimenko. In februari j.l. spraken wij Matt en we spraken toen af dat hij voor de Astroblogs een blog zou schrijven en dat heeft hij gedaan – nog wel tijdens zijn vakantie, waar hij een belabberde 3G verbinding heeft! Wij zijn héél blij met zijn bijdrage voor de Astroblogs en wensen hem nog een fijne vakantie toe én heel veel succes met het onderzoek aan 67P.

Dear Astroblogs

In February this year I had the chance to meet with Astroblogs people Arie Nouwen, Jan Brandt and Daniela de Paulis to talk about Rosetta. Arie asked me if I would be interested in writing something for Astroblogs. I said yes, but asked that he remind me, as things are rather hectic this year. Arie kindly did remind me in May and did again this week! His persistence paid off and I have managed to get in front of my laptop to write something, I hope its worth while !


Since last speaking to Arie, a lot of things have gone on with Rosetta. Early this year we had moved from a “gravitationally bound” or circular orbit at around 30 km, to more extended fly by legs, including a number of close fly bys.  We carried out a close fly by on 14th February that was specifically designed to investigate zero phase with respect to the comet, such that the spacecraft would fly with the sun directly behind it, to investigate the interaction of solar radiation and illumination on the surface features from that view point. We managed to capture some very good data, including OSIRIS images of the shadow of the spacecraft itself! In fact, there was an issue with data handling (memory) on OSIRIS such that just after the zero phase, we didn’t get any more images. As with all things on spacecraft, you are sometimes lucky. If that glitch had occurred 8 minutes earlier we wouldn’t have got the zero phase data (and the great image of the shadow of Rosetta on the surface of the comet). The 14th Feburary flyby was the closest we have gotten to C67P so far in the mission, around 6 kilometres from the surface, flying above the “belly” of the duck, know as the Imhotep region using the naming convention we have (as indicated in the Science paper by Thomas et al., 2015) which was recently further described in the nice A&A paper by El-Maary et al. and featured in an ESA Rosetta Blog (blogs.esa.int/rosetta/2015/07/15/getting-to-know-rosettas-comet-boundary-conditions/). I know some of you will very much like that blog , as it has a number of OSIRIS images in it!.  Talking of images, you can look at many of the cool NAVCAM images,included those taken from closest distances – http://blogs.esa.int/rosetta/2015/04/29/major-release-of-navcam-images-800-to-30-km/.

Close ups van 67P (Credits: ESA/Rosetta/NAVCAM – CC BY-SA IGO 3.0).

Back to the fly by in February. During the fly by, we had encountered some issues with the star trackers (STRs), which we need to accurately point the spacecraft. These navigation devices are located on the -X face of the spacecraft (where Philae used to be). For reference, a majority of the instruments are on the +z side of the spacecraft. The STRs were finding it difficult to distinguish stars from the dust around the spacecraft in the cometary coma. To try to avoid this issue, in the next fly by, the ESOC team took the STRs out of the loop, to allow the spacecraft to drift without using the STRs. The logic was that we would avoid the region where the STRs were getting confused and only use them outside that window. However, what happened in March was that the region we expected the STRs to be “blinded” was actually much bigger. In the end the STRs could not successfully lock onto stars for nearly a day and as such the required accurate pointing was not possible and we started to lose pointing , which meant beginning to lose contact of the High gain antenna with the Earth! Luckily this did not happen (it would have put the spacecraft in a mode we wish to avoid – survival mode!). Part of the issues during this fly by put us in a safe mode and we ended up moving away from the comet. Since that time we have had to change the way we operate the spacecraft, reacting every few days to the comet environment. We began flying triangular legs on the dayside of the comet (similar to the way we approached the comet last year in September-October using pyramid arcs) and then moved into the terminator plane.  We found that the terminator plane allows us to get the closest to the comet, which was around 150 km a few weeks ago. We are now moving further way, due to increased dust in the environment. Ultimately however, we are flying trajectories with the high level science goals of getting as close as possible as soon as possible.  So we “ride” the edge of what is possible with the spacecraft WITHOUT putting the spacecraft at risk.

Philae wakes up from hibernation on june 13th.

On 13 June I was watching Defiance” on Netflix. I got a whatsapp message from Armelle at ESOC – “Its Back!” “What is back ?” I replied. “Its got 3 legs!!! Sylvain has texted you!!!” she messaged back. I checked another web page and my work phone. The lander had made contact!!!. This was very exciting. We had expected it, but I had expected it more in July.http://blogs.esa.int/rosetta/2015/06/14/rosettas-lander-philae-wakes-up-from-hibernation/Since that first contact, we have had a number of other contacts, but have not been able to secure a stable link with the lander. All data we are getting is house keeping data, no science. We need a stable link to command science. We are currently in the process of looking to try how we can command the science instruments with only small communication windows. The lander looks in reasonable good shape, but the lack of stability of link, coupled with lack of predictability of secure link mean that the lander team are examining all possibilities on the lander to try to improve the situation. Since June, the revival of the lander has meant that the orbiter has kept in a certain location with respect to the comet (in the northern hemisphere). This has reduced the amount of science we have been doing, in particular looking at the southern part of the comet which has only recently (since May) come into sunlight. In the next weeks, we are looking to swing past southern latitudes, possibly being at those latitudes during perihelion. A blog update on the lander situation should be out in the next days (probably already out by the time you read this text!).

The adventure continues: ESA today confirmed that its Rosetta mission will be extended until the end of September 2016, at which point the spacecraft will most likely be landed on the surface of Comet 67P/Churyumov-Gerasimenko.

In June we also found out that our proposal to extend the mission (which I was working on in Jan-February) was accepted.http://blogs.esa.int/rosetta/2015/06/23/rosetta-mission-extended/We will now continue the mission until September 2016 , with the end of mission seeing us slowly spiral Rosetta closer towards the comet, until we “touchdown” although I think this should really be considered a crash-landing. We will get some excellent high resolution measurements during that spiral, in particular allowing us to investigate the near comet coma, the characteristics of the dust and gas.By August you should have heard more about the first lander results. Already we had an early publication from a collection of lander results, which was two “firsts” the first lander results AND the first combined Lander – Orbiter science. This was a paper examining the magnetic field of the comet and its surroundings using the lander ROMAP instrument and the RPC MAG on the orbtiter. This is the stuff I like, as I am a plama physicist. Arie and Jan and Daniela were amazed that I wasn’t as interested in the OSIRIS images, but that’s as I am interested in the invisible stuff, the electric and magnetic fields, the electrons and ions. J.  This ROMAP and RPC results demonstrated that that comet did not appear to have an intrinsic magnetic field (at least to the scale of > 1 metre) . This result was only possible BECAUSE of the multiple landings we had with Philae, we got a nice multipoint measure of the surface of the comet. This result is important when considering the environment of the early solar system and how important magnetic fields were in aiding aggregation of planetessimals (and cometessimals).

Comet 67P/C-G on 22 May taken with the VLT/FORS2 instrument. It is a combination of 2 x 30s R-band exposures, aligned on the comet. The comet moved against the background stars between the two images, leading to double stars in this combination. Credits: Colin Snodgrass / Alan Fitzsimmons / ESO.

The comet is now beginning to be observable from the ground, and we have begun to see spectacular images (I believe we can also now start to get an idea of the gas in the coma from the ground as well!).http://blogs.esa.int/rosetta/2015/06/12/cometwatch-from-earth-22-may/To close, please keep an eye on the Rosetta blog, the blog is where the best, most up to date information is. We have a number of papers being accepted and reported (many form part of the A&A special issue that should come out later this year, but we are repoting the results as soon as they are accepted). We are looking to update everyone on the latest news on perihelion day – http://blogs.esa.int/rosetta/2015/07/13/preparing-for-perihelion/ so stay tuned.Of course, you should also follow the Rosetta twitter feed, maybe even follow me, but its not as scientifically interesting (especially my interactions with @iamcomet67p)CheersMattPS just to note – the Rosetta communications team won an award!!! I think they deserve it as they have helped spread the story of Rosetta far and wide! http://blogs.esa.int/rosetta/2015/07/17/rosettaphilae-outreach-team-win-sir-arthur-clarke-award/

The Sir Arthur Clarke Award for Space Achievement – Education and Outreach, 2015.

Matt Taylor Over Matt Taylor

Dr. Matt Taylor (ESA/ESTeC) studeerde natuurkunde aan de universiteit van Liverpool. Hij promoveerde bij het Imperial College in Londen en deed voornamelijk onderzoek op het gebied van in-situ metingen aan plasma's in de ruimte. Hij werkte onder andere in Europa en de USA aan de ESA Cluster en als projectwetenschapper aan het Double Star project - een samenwerking tussen ESA en China. In 2013 werd hij benoemd als projectwetenschapper bij de Rosetta-missie. Als zodanig is hij betrokken bij de wetenschappelijke verrichtingen van zowel de Rosetta sonde als de Philae lander, die beiden onderzoek doen aan de komeet 67P/Churyumov-gerasimenko. Hij werkt voornamelijk bij ESTeC in Noordwijk.

Comments

  1. Matt, what an honour to have you here on the Astroblogs with this wonderful article on Rosetta, Philae and the comet they are observing, 67P. Thanx for writing this article, especially during your vacation. Succes with all your research (in particular with making a stable connection to Philae) and enjoy the rest of your vacation!

  2. Olaf van Kooten Olaf van Kooten zegt

    Thank you Matt, it’s a great article 🙂

    off-topic: according to your twitter, you’re a real metalhead! that’s very nice to hear, although Cannibal Corpse is not my cup of tea 😉

  3. Jan Brandt zegt

    Greetings to thee, “Rosetta Matt”

    So you were hoping that your (first ever…my sincere congratulations with this true milestone in your scientific carreer, mate..hihi!!!) Astroblog was worth while reading material?? Well,….now there is one hell of a big fat juicy interplanetary understatement!! To me It reads like a script for a wildly exiting Startrek-episode…That is, if you are, yep…I plead guilty…like me, a devout Trekkie!!
    Anyway, thanx for the effort, happy “hols”…and..ah…if possible, more where that came from, please!!!

  4. Monique zegt

    Hi Matt, welcome to Astroblogs as a guest writer. We’ll keep an eye open for the upcoming up to date information.

    [Off topic] Well, the tattoos on your body look almost like art, tho. Personally I don’t like tattoos on my body.
    Good taste of music, Matt!
    Smiley
    Btw, can you play guitar?
    Keep up the good work.

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