Rosetta comet chaser completes "big burn"

JupiterKid · 29-09-2015 2:21am

_Tombstone_ wrote: »

Rosetta confirmed as two Comets mashed together.

Fascinating. The Rosetta mission is really proving its worth. We are learning a lot more about comets as this mission continues.

_Tombstone_ · 09-10-2015 10:03pm

Meet Claudia Alexander, NASA Badass Who Never Got Her Due

Comet 67P/Churyumov—Gerasimenko is a tiny world of ice and rock, just 5 kilometers long. The comet is shaped vaguely like a rubber duck, with steep cliffs and other prominent features that stand much taller in relation to the size of the world. One of remarkable features is a twin set of sharp “horns” on the head of the rubber duck, known now as C. Alexander Gate.

Claudia Alexander served as project scientist for the Rosetta mission, which is orbiting Comet 67P. Until her death in July, she helped lead the United States side of the project, coordinating the various scientific and engineering aspects of the mission. Last week, her colleagues named the C. Alexander Gate in her honor and memory, with her European Space Agency counterpart Matt Taylor making the announcement.

_Tombstone_ · 29-10-2015 8:51pm

Oxygen has been found on Rosetta, they can't explain how it can exist there and it throws alot of theoretical models of how the Solar System was formed in the Bin.

http://qz.com/536393/the-discovery-of-oxygen-on-a-comet-could-change-everything-we-know-about-the-solar-system/

MeteoritesEire · 06-11-2015 12:12am

http://www.nature.com/news/historic-rosetta-mission-to-end-with-crash-into-comet-1.18713

Historic Rosetta mission to end with crash into comet

There were other options, but super close-up shots on descent will provide
science bonanza.

Elizabeth Gibney
nature.com
04 November 2015

A year since a probe called Philae made history by touching down on a
comet, the team that pulled off the feat is plotting a different kind
of landing. Next September, the European Space Agency will crash Philae's
mothership Rosetta into the icy dust ball, but as gently as possible.

The dramatic act will bring the mission to an abrupt end - and give Rosetta's
wealth of sensors and instruments their closest view of the comet yet.
"The crash landing gives us the best scientific end-of-mission that we
can hope for," says Rosetta project scientist Matt Taylor.

The collision will be emotional for the scientists, some of whom have
worked on the mission since its inception in 1993. "There will be a lot
of tears," says Taylor.

Launched in 2004, the Rosetta orbiter caught up with the comet
67P/Churyumov-Gerasimenko
ten years later as the rock was travelling from deep in space towards
the Sun - and dropped Philae onto the surface a few months later, on 12
November. Scientists have not heard from Philae since July, and don't
know if they will do so again, but Rosetta's operations to survey the
comet from orbit are in full swing. However, the orbiter can't keep up
this work indefinitely. Funding for the mission runs out in September
2016 - and by that time 67P/Churyumov-Gerasimenko will be well on its
way back out into deep space, where the solar-powered orbiter will receive
too little sunlight to function.

Discussions about what to do with Rosetta when that happens have continued
for more than a year. Rosetta flight director Andrea Accomazzo says that,
ideally, Rosetta would hibernate while the comet remains in deep space,
then be resurrected when 67P again approaches the Sun in 4 or 5 years'
time. But the cold of deep space would probably damage the craft, Accomazzo
says; others fear that fuel and other resources would run out. Moreover,
many of the mission's principal investigators (PIs) began their work more
than 20 years ago and "there's no point putting an old experiment with
old PIs into hibernation", jokes Kathrin Altwegg, a planetary scientist
at the University of Bern.

Crash-landing Rosetta emerged as the preferred option last year, but only
now are orbiter navigators and operators working out how to go about it.
Rosetta's closest encounter with the comet so far was from 8 kilometres
above the surface, when it dispatched Philae. The current thinking sees
Rosetta spiral down to a similar distance next August before creeping
ever closer in elliptical orbits and crashing in September, says mission
manager Patrick Martin - but that could still change.

Although Philae sent back some data during its descent, Rosetta has more
powerful - and more varied - sensors and instruments. The orbiter will
also descend much more slowly than Philae did, allowing it to gather more
data and better pictures. Once it gets to 4 kilometres, for example, Rosetta
should be able to distinguish between the gases emerging from each of
the duck-shaped comet's two lobes to determine whether the regions vary
in composition, says Altwegg, who leads the team behind ROSINA (the Rosetta
Orbiter Spectrometer for Ion and Neutral Analysis). That could shed light
on the environments in which each was formed.

Rosetta's cameras will get their best-resolution shots of the comet's
surface yet - less than 1 centimetre per pixel once the craft is within
500 metres of the surface, adds Holger Sierks, PI for Rosetta's OSIRIS
(Optical, Spectroscopic, and Infrared Remote Imaging System). This will
allow researchers to look at surface properties and link these to comet
activity that Rosetta has observed from orbit.

Over and out

How far into the descent Rosetta will be able to send data back to mission
control will depend on whether engineers can design the final trajectory
such that the craft crashes on the side of the comet that faces Earth.
Navigating while close to the comet will be difficult because the body's
gravitational field is uneven, but spacecraft-operations manager Sylvain
Lodiot hopes that the orbiter will transmit until the very end.

The crash will definitely be a hard stop to the mission, he says, however
gentle the landing. Designed to manoeuvre in orbit, once Rosetta is on
the comet's surface it will no longer be able to point its antenna to
communicate with Earth. Similarly, it will not be able to angle its solar
array, so it will lose power, says Lodiot. "Once we touch, hit or crash,
whatever you want to call it, it's game over."

Before then, though, the mission still has much to accomplish. As the
comet approached the Sun, it heated up, with vaporizing ice causing more
and more gas and dust to stream from its surface. Rosetta had to retreat
into a wider orbit to stop the dust from confusing its navigation system.
But now that the comet is speeding away from the Sun, mission scientists
are relishing the opportunity to steer Rosetta back in. Priorities will
then be to get images that would enable comparisons of the comet before
and after its swing around the Sun, as well as a close-up of the southern
hemisphere, which was largely in darkness until May and will disappear
back out of view in March.

Rosetta will also resume listening out for Philae. Given the huge public
interest in anything to do with the lander, Rosetta's finale will make
for a fitting end to the story, adds Altwegg. "This way Rosetta gets to
live happily ever after on the comet with Philae."

Nature 527, 16–17 (05 November 2015)

shedweller · 06-11-2015 2:31am

I vote for a flyby of the expected philae landing site. All other science can feck right off till we have pics of the little fella!!

_Tombstone_ · 23-12-2015 12:24am

They've given up trying to find the poor little thing, they're hoping it'll get back in touch in May/June.

http://www.onemk.co.uk/PHILAE-European-Space-Agency-announced-longer/story-25950212-detail/story.html

_Tombstone_ · 13-01-2016 2:24am

One of the final attempts by the European Space Agency to communicate with the Philae comet lander has most likely failed. The agency sent a command to the spacecraft yesterday in a last-ditch attempt to trigger some kind of response and potentially move the lander, but the vehicle remained silent; it's essentially the same state Philae has been in since 2014, when it first landed on Comet 67P/Churyumov-Gerasimenko. Now it's looking more and more likely that the spacecraft will stay silent until it ends operations sometime at the end of January.

http://www.theverge.com/2016/1/12/10754190/philae-comet-lander-communication-failure-january-2016

_Tombstone_ · 05-02-2016 2:53am

Inside Rosetta

No big caverns, just water and dust that make low density "fluffy" aggregate.

How they know that and the gravity effect is interesting though

Pätzold’s team made their discovery by using the Radio Science Experiment (RSI) to study the way the Rosetta orbiter is pulled by the gravity of the comet, which is generated by its mass.

The effect of the gravity on the movement of Rosetta is measured by changes in the frequency of the spacecraft’s signals when they are received at Earth. It is a manifestation of the Doppler effect, produced whenever there is movement between a source and an observer, and is the same effect that causes emergency vehicle sirens to change pitch as they pass by.

In this case, Rosetta was being pulled by the gravity of the comet, which changed the frequency of the radio link to Earth. ESA’s 35-metre antenna at the New Norcia ground station in Australia is used to communicate with Rosetta during routine operations. The variations in the signals it received were analysed to give a picture of the gravity field across the comet. Large internal caverns would have been noticeable by a tell-tale drop in acceleration.

ESA’s Rosetta mission is the first to perform this difficult measurement for a comet.

“Newton’s law of gravity tells us that the Rosetta spacecraft is basically pulled by everything,” says Martin Pätzold, the principal investigator of the RSI experiment.

“In practical terms, this means that we had to remove the influence of the Sun, all the planets – from giant Jupiter to the dwarf planets – as well as large asteroids in the inner asteroid belt, on Rosetta’s motion, to leave just the influence of the comet. Thankfully, these effects are well understood and this is a standard procedure nowadays for spacecraft operations.”

Next, the pressure of the solar radiation and the comet’s escaping gas tail has to be subtracted. Both of these ‘blow’ the spacecraft off course. In this case, Rosetta’s ROSINA instrument is extremely helpful as it measures the gas that is streaming past the spacecraft. This allowed Pätzold and his colleagues to calculate and remove those effects too.

Whatever motion is left is due to the comet’s mass. For Comet 67P/Churyumov-Gerasimenko, this gives a mass slightly less than 10 billion tonnes. Images from the OSIRIS camera have been used to develop models of the comet’s shape and these give the volume as around 18.7 km3, meaning that the density is 533 kg/m3.

_Tombstone_ · 17-02-2016 4:06am

They're not sending anymore Commands to Philae but will keep the listening channel on just incase.

ROSETTA’S PHILAE LANDER IN PERMANENT SLEEP

Scientist regrets Philae was not yellow and pink

Screen-Shot-2016-02-15-at-6.40.18-PM-1024x563.jpg

Screen-Shot-2016-02-15-at-6.40.18-PM-1024x563.jpg

(How sad is this??)

FROM ONE COMET LANDING TO ANOTHER: PLANNING ROSETTA’S GRAND FINALE

_Tombstone_ · 20-02-2016 2:18pm

Art of Science: Chasing a Comet From Lab to Studio

http://thefinchandpea.com/2016/02/03/art-of-science-chasing-a-comet-from-lab-to-studio/

_Tombstone_ · 05-09-2016 4:58pm

And they've finally found Philae.

shanew · 05-09-2016 5:20pm

link to the ESA article with photo

Skyknight · 05-09-2016 9:32pm

Here's a video (showing location):

_Tombstone_ · 16-09-2016 3:47am

Going in for controlled impact on the 30th but not before it finds Complex Organic Molecules

josip · 30-09-2016 10:21am

Touchdown in about an hour, confirmation 40 minutes after.
By the time we receive the signal it will have gone to sleep for ever.

Follow at
http://rosetta.esa.int/

Badly formatted cut and pastes from press pack below

On the night of 29 September, at 20:50 UTC, one last manoeuvre will be executed in
which the spacecraft will fire its thrusters, for about 3 minutes. It will then begin a
leisurely 14-hour drop to the comet’s surface. In those hours it will cover a distance
of 20 km.
Initially its speed will be just 30 cm/s (about 1 km/h). This will gradually increase
due to the gravity of the comet. At about 55 minutes before touchdown, at a
distance of 2 km above the surface, Rosetta will be travelling at 60 cm/s.
Calculations show that the final impact speed will be about 90 cm/s. This is roughly
walking pace and is about the same speed as Philae hit the surface back in
November 2014.
12
Data and images will be transmitted for as long as possible in the run-up to the
touchdown. Being that close to the comet, the spacecraft may be buffeted by dust
and gas that continue to escape the weak gravitational field.
To prevent the spacecraft from entering a ‘safe mode' and losing contact before
impact, spacecraft operators have reprogrammed some of its tolerance to errors. For
example, some star tracker checks have been disabled for some weeks now. The star
trackers are small telescopes that recognise the pattern of the stars and tell the
spacecraft how it is oriented is space. Dust from the comet can blind these devices,
and, in the past, this has led the spacecraft into ‘safe mode’ several times.
The flight team have also solved a unique problem: how to turn the spacecraft off
upon touchdown. Spacecraft are designed to be almost constantly in communication
with their operators on Earth and to function autonomously when out of contact. And
that means no one really builds them with an 'off switch’. If Rosetta survived the
touchdown, the main transmitter could randomly transmit signals that might affect
the ability of other spacecraft to communicate with Earth.
But how do you turn off a spacecraft that was never designed to be turned off? It
proved a challenge for the flight control team to force the spacecraft to enter a
special mode that was used during testing of the spacecraft on Earth more than a
decade ago. But eventually they found a way, and have written and uploaded a
software patch for this. When the spacecraft touches the surface, some of the
checks that are still enabled will trigger, leading the spacecraft to that mode. This is
called ‘passivation of the spacecraft’.
Like Philae before it, Rosetta may tumble on the surface before coming to rest.
Unlike Philae, there will be no way to know exactly where it comes to rest because
no communication will be possible and no telescope could possibly resolve anything
on the comet's surface.

Collecting science until the very end
Rosetta will continue to collect science data until the very end of its descent to the
comet. The opportunity to study a comet at such close proximity makes the descent
phase one of the most exciting of the entire mission.
Not all instruments will be working during the descent. Rosetta is so far from the
Sun now that it cannot generate enough power from its solar panels to keep
everything running.
As a result, careful consideration had to be given to which instruments would make
measurements during the descent to the surface. Taking into account science
operations constraints – some instruments require quite some time to obtain their
measurements – and the potential science return, the timeline prepared by the
science operations team with the Rosetta science working team, sees MIDAS,
COSIMA and VIRTIS turned off. The other instruments will be working right up until
the end of the mission.
Getting the data obtained close to the surface back from Rosetta is going to be a
challenge because the main antenna will be switched off as soon as the spacecraft
touches down. Even if it wasn’t, Rosetta will almost certainly tilt or tumble in the
comet’s weak gravity and this will break the communication connection with Earth.
To know exactly when the impact is likely to take place, the NavCam navigation
camera will take 5 images during the early part of the descent, shortly after the
spacecraft has been set on a collision course for the comet. These images will be
downloaded to Earth in the early hours of 30 September and will be used by the
flight team to predict the impact time to within a four-minute window.
This is vital information because it is no use taking exquisitely detailed data but
losing it because it takes too long to beam back.
During the descent, the OSIRIS cameras (narrow-angle and wide-angle) will image
the regions of the large lobe that it passes over. As the spacecraft approaches the
small lobe the cameras will image the walls of the Ma’at pits. The very high
resolution data of these features will provide important information for our
understanding of how activity is driven on the comet and maybe how the comet was
formed in the first place. For the final hour of descent, OSIRIS will acquire images at
a high cadence. The intention is to capture one last image about 15 m from the
surface with a resolution of 3 mm per pixel.
15
Other instruments, such as GIADA, ROSINA, RPC and MIRO will be collecting and
transmitting data and it is expected that the last observations to be transmitted will
give data from between 20 m to five m above the surface.
ROSINA will collect unique data on the density of gas around the comet and its
composition. It is expected to provide readings down to the Knudsen Layer, where
the evaporation of the gases actually happens.
MIRO will complement OSIRIS and ROSINA measurements by measuring the surface
temperature.
GIADA will measure the dust’s density and the way the dust grains are accelerated
away from the comet.
The RPC instrument suite will monitor the plasma environment, and also the
smallest dust particles. This will give a unique close-up look at the interaction
between the solar wind and the surface of the comet, and it will sample levitating
charged grains.
Alice will get its highest resolution ultraviolet spectra of the surface of the whole
mission and provide complementary measurements to some of the RPC data.
RSI will get the most accurate measurements of the gravity field during descent.