Final preparations are being made for the end of the 12-year old Rosetta mission. The Rosetta spacecraft, currently orbiting the comet 67P/Churyumov-Gerasimenko will complete its mission in a controlled descent and crash to its final resting place on the surface of the comet during the early morning hours of Friday, Sep 30. In doing so, it will join its companion, the stranded robot probe Philae, in eternal sleep.
After two years of orbiting the comet, sending back an unprecedented wealth of information, Rosetta and the comet are now heading out beyond the orbit of Jupiter again. In principle, Rosetta can be left in orbit around 67P and it will reappear a few years later, but the aging spacecraft is unlikely to survive the journey to the cold outer regions of the comet’s orbit, just beyond Jupiter’s orbit. Hence, ESA decided to perform a controlled descent (slow crash) of Rosetta into 67P and gather additional scientific data in the process.
See diary at www.dailykos.com/... for an earlier photo diary about the mission.
See www.esa.int/… for media events on Rosetta’s final chapter. Live streaming of the impact event will begin at 06:30 EDT via rosetta.esa.int.
Artist’s conception of Rosetta at moment of impact
Rosetta’s Planned Trajectory
Since 9 August, Rosetta has been flying elliptical orbits that bring it progressively closer to the comet – on its closest flyby, it came within 1 km of the surface. On September 2, Rosetta located the Philae lander for the first time after its failed landing on Nov 12, 2014, finding it wedged against a large overhang.
The final flyover will be completed on September 24. Then a short series of manoeuvres needed to line Rosetta up with the target impact site will be executed over the following days; the collision manoeuvre will take place in the evening of September 29, around 16:40 EDT, to a spot at an altitude of about 20 km. Rosetta will then free-fall slowly for about 14 hours, towards the comet, making observations and measurements and transmitting them back to earth in real-time.
Impact is expected to occur on September 30 at 06:40 EDT.
Rosetta’s final trajectory
Impact Site
The impact site in a region known as Ma’at, lies on the smaller of the two lobes of Comet 67P/Churyumov–Gerasimenko. It is home to several active pits more than 100 m in diameter and 50–60 m in depth – where a number of the comet’s dust jets originate. The walls of the pits also exhibit intriguing meter-sized lumpy structures called ‘goosebumps’, which scientists believe could be the signatures of early ‘cometesimals’ that assembled to create the comet in the early phases of Solar System formation. Researchers argue that these pits arise when cavities beneath the surface cave in.
The spacecraft will target a point adjacent to a 130 m-wide, well-defined pit that the mission team has informally named Deir el-Medina, after a structure with a similar appearance in an ancient Egyptian town of the same name.
Rosetta planned crash landing site
Rosetta will target the smooth region between the pits labelled Ma’at 02 and 03.
Pit Ma’at 02 has been named by the mission team as Deir el-Medina, after a pit in an ancient Egyptian town of the same name.
Rosetta will not be able to see the Philae lander during its descent. Rosetta’s planned touchdown site is on the small comet lobe, but on the opposite side from where Philae has been located at Abydos. Due to a combination of orbital dynamics and illumination reasons, the current trajectory plan does not see Rosetta pass over Philae during the descent.
Final Impact
Rosetta will do a slow free-fall descend to the surface of Comet 67P/C-G for about 14 hours. During this descent, Rosetta will capture close-up images, along with information on the dust, gas, and plasma environment very close to such pits, which will help scientists understand their connection to the comet’s observed activity, and as well to learn more about how they relate to the formation and evolution of the comet..
In the final seconds before impact, Rosetta will bid final adieu as its main systems will be turned off, including the attitude and control systems and the main transmitter, the latter in order to meet regulations aimed at avoiding interference on deep space network communications channels.
The impact velocity will be around 90 cm/s, around walking pace. Signal from the spacecraft, ~720 million km away, will take 40 minutes to reach Earth.
Rosetta was not designed as a lander, and some of its appendages including the 32m-wide solar panels will be damaged by the impact. This energy dissipation will very likely ensure that Rosetta will not bounce back into orbit.
Instruments
Many of the science instruments are expected to be operational and stream back their data until the last few seconds.
The Rosetta orbiter instruments combine remote sensing techniques, such as cameras and radio science measurements, with direct sensing systems such as dust and particle analysers. sci.esa.int/...
The Swan Song
For obvious reasons, all scientific data collected during the descent must be relayed back to Earth in quasi real-time, and will not accumulate in the on-board mass memory storage for subsequent downlink as is usually the case.
The bit rate for the Madrid Deep Space Network ground station during the descent is 45,760 bps and the expected data downlinked between the end of the collision manoeuvre on 29 September and impact on 30 September, over about 14 hours, is 1558 Mbits (195 MBytes).
The break-down per instrument is expected as follows:
ALICE: 37 Mbits
GIADA: 3 Mbits
MIRO: 6 Mbits
NAVCAM: 64 Mbits
OSIRIS: 1177 Mbits
ROSINA: 49 Mbits
RPC: 128 Mbits
Instrument House Keeping: 93 Mbits
Here is a video visualizing Rosetta’s final moments.
Epilogue
After 12 years, 6 months and 28 days in space, after travelling 7.9 billion km, after 21,000 science observations, after one last gift to humanity, Rosetta will join the abode of heavenly bodies, the source of its creation.
Perhaps, some future civilization will find and read Rosetta’s and humanity’s story on the Rosetta disk, the micro-etched nickel alloy disk inscribed with 13,000 pages of text in 1,200 languages.
Final Update
Rosetta completed its final mission and crash-landed on comet 67P at 06:19 EDT, Sep 30, 2016.
Rosetta's last image of Comet 67P/Churyumov-Gerasimenko, taken shortly before impact, an estimated 51 m above the surface. The image is blurry since the camera was not designed to focus at such short distances.
References
- Photo diary about the Rosetta mission www.dailykos.com/…
- Rosetta page at ESA — www.esa.int/…
- Hi-res images of Comet 67P/Churyumov-Gerasimenko - twitter.com/…
- Archive of thousands of images of the mission — imagearchives.esac.esa.int/...
- Asteroids and Planetary Defense — www.dailykos.com/…
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All images attributed to ESA.
