Rosetta Blog

Mystery remains: Rosetta fails to observe swingby anomaly

danielscuka — Mon, 23 Nov 2009 17:26:12 +0100

We reported earlier on the two-decade-old Earth Swingby Anomaly:

Since 1990, scientists and mission controllers at ESA and NASA have noticed that their spacecraft sometimes experience a strange variation in the amount of orbital energy they exchange with Earth during planetary swingbys. The unexplained variation is noticed as a tiny difference in speed gained or lost during the swingby when comparing that predicted by fundamental physics and that actually measured after the event.

Last week, after analysing the radiometric data gathered by ESA and NASA ground stations that tracked Rosetta during her successful 13 November swingby, ESA's Trevor Morley, the lead flight dynamics specialist on Rosetta, sent us a brief mail update. His report?

"For Rosetta's third and final Earth swingby, there was no anomaly."

(Access more details under 'Full story' below) -- Daniel

First, some background details taken from our earlier web report (see full report in the ESA website here):

ESA's Rosetta has made two Earth swingbys, in 2005 and 2007. It too, experienced the strange anomaly. Frustratingly, Rosetta sped up by an unexplained 1.8 mm/s during the first passage, but experienced no slowing or speeding in 2007. No one knows what will happen on 13 November 2009 for Rosetta's third and last Earth swingby: scientists are stumped.

"It's a mystery as to what is happening with these gravity events. Some studies have looked for answers in new interpretations of current physics. If this proves correct, it would be absolutely ground-breaking news," says Trevor Morley, lead flight dynamics specialist working on Rosetta at ESOC, ESA's European Space Operations Centre, Darmstadt, Germany.

Together with ESA colleague and orbital mechanics specialist Frank Budnik, Morley co-authored a scientific report in 2006 that studied the Rosetta anomaly during the 2005 swingby and listed possible causes.

These range from tidal effects peculiar to the near-Earth environment, atmospheric drag, or the pressure of radiation emitted or reflected by the Earth, to much more extreme possibilities, such as dark matter, dark energy or previously unseen variations in General Relativity, one of the most fundamental and well-tested theories of modern physics.

One American research team, led by ex-NASA scientist John Anderson, is even looking at the possibility that Earth's rotation may be distorting space-time - the fundamental fabric of our Universe - more than expected, thus affecting nearby spacecraft. But there is as yet no explanation how this could happen.

At ESOC on 13 November, the mission control and flight dynamics teams will be watching closely as ESA's 35m New Norcia station in Australia tracks Rosetta during the closest approach, expected at 08:45:40.0 CET, followed - after a visibility gap of 20 minutes - by ESA's 15m Maspalomas station.

The tracking activity will generate highly precise data that will record whether the spacecraft speeds up or slows down more or less than expected. Deep space ground stations operated by NASA, at Canberra, Australia, and Goldstone, California, will also observe the spacecraft before and after closest approach.

ESA/NASA Cassini-Huygens swings by Earth 1999, slowing unexpectedly
"We are using as many ground stations as are available to maximise the amount of swingby data we record. The more data we get, the better the chance that we may eventually come up with an answer," says Morley.

The data is keenly awaited by scientists on a number of continents, who are hoping to see whether the anomaly is present and whether an explanation is finally possible.

"As it stands now, no one knows what's behind this - it really is a mystery. And your prediction as to whether Rosetta will experience any swingby speed anomaly at all on 13 November is as good as anyone's," says Morley.

Now, here is the full text of Trevor's email report from last Friday:

For the Earth swingbys where the anomaly has been detected, the main manifestation has been the inability to get anything like a reasonable fit of an orbit to an arc of radiometric data that encompasses both the pre- and post-perigee intervals. This is not the case for Rosetta's Earth swingby one week ago. For those cases when an anomaly has been seen, the determination of the outgoing asymptotic velocity has been very slightly different from the expected value based on processing the pre-perigee data.

In every case, a reasonable data fit could be established only by inserting an artificial velocity change along the direction of the orbital velocity in the vicinity of perigee. In the case of Rosetta's first Earth swingby, this artificial delta-V had a magnitude of 0.67 mm/s, equivalent to an increase in the asymptotic velocity of 1.82 mm/s.

For last week's swingby, one of the additional orbit determination runs made allowed the software to estimate an impulsive manoeuvre at perigee, aligned along the orbital velocity. The <i>a priori</i> value for the manoeuvre magnitude was zero. The resulting estimate was a magnitude of 4 microns/s (retrograde) with a 1-sigma uncertainty of 44 microns/s. The difference in the quality of the data fit was absolutely negligible. For Rosetta's third and final Earth swingby, there was no anomaly.

That's it! The mystery continues, arguably deeper now that we've seen another swingby without an unexplained increase or decrease in velocity.

Anyone have any ideas?

Rosetta image chosen as NASA APOD

danielscuka — Mon, 23 Nov 2009 10:43:09 +0100

Today, NASA's popular "Astronomy Picture of the Day" website features a cool image acquired by none other than our favourite comet chaser, Rosetta!

Our NASA colleagues wrote:

"Goodbye Earth. Earlier this month, ESA's interplanetary Rosetta spacecraft zoomed past the Earth on its way back across the Solar System. Pictured above, Earth showed a bright crescent phase featuring the South Pole to the passing rocket ship. Launched from Earth in 2004, Rosetta used the gravity of the Earth to help propel it out past Mars and toward a 2014 rendezvous with Comet Churyumov-Gerasimenko. Last year, the robot spacecraft passed asteroid 2867 Steins, and next year it is scheduled to pass enigmatic asteroid 21 Lutetia. If all goes well, Rosetta will release a probe that will land on the 15-km diameter comet in 2014."

On behalf of the entire team working on Rosetta, 'Thanks guys!' -- Daniel

(Click on the image above to view the original version in ESA website.)

Rosetta's OSIRIS team responds to blog comment

amehta — Fri, 20 Nov 2009 12:59:15 +0100

Stubbe Hviid, OSIRIS Operations Manager, has sent us a response to a comment made on this post:

"In the last pic, I'm wondering what the tiny dots are (multiple white and one black) : due to Osiris?, to data processing?, to objects above clouds? (X,Y) for the black at (760pxl/2048, 456pxl/1083) and for one white at (753/2048, 172/1083). At least the block dot is also present on the first pic."

Stubbe says that the white dots are caused by cosmic ray events. When the images were taken, the spacecraft was in open space (of course). This means that the spacecraft experiences the full effect of the solar wind and high energy particles. These high energy particles are detected by the CCD as light flashes. On the surface of the Earth, we normally do not see these cosmic ray events because the atmosphere shields us.

The white dots due to the cosmic ray events are completely normal. For example, the coronagraph of ESA's SOHO satellite regularly experiences a bakeout. With respect to SOHO bakeout, Stubbe added:

It is the same effect but a different kind of detector. OSIRIS also has the capability to 'bake out' the CCD (also called annealing). As a rather extreme example of this, here's an image we took of Comet Machholz back in 2005, during which Rosetta was caught in a Coronal Mass Ejection solar flare with a radiation level about 100 000 times higher than normal.

Views of Rosetta from Earth: Quick thanks

danielscuka — Tue, 17 Nov 2009 11:52:34 +0100

Note a comment left by J.M. Mondelo, who observed Rosetta on 12 November 2009 (thanks for the link and great pictures!). -- Daniel

Rosetta receding

amehta — Tue, 17 Nov 2009 11:46:15 +0100

Kristin wrote to us early on Saturday morning, 14 November.

During the night of 13/14 November, the team at ESA's Optical Ground Station, Tenerife, imaged Rosetta receding from Earth. The spacecraft's brightness was very low as they were looking at the non-illuminated side of the solar arrays; in contrast, during approach, sunlight was reflected from the solar arrays toward us (this explains the long exposure time and bad image quality compared with the approach observations done on 11/12 and 12/13 November).

This movie was recorded between 04:51 and 05:20 UTC on 14 Nov. It consists of 10 images with an exposure time of 2 min and a separation of 3 min. The field is located in Leo and has a size of 5 x 5 arcmin; North is up and East is left. The telescope was tracking the stars so that Rosetta appears as a stripe while the stars appear as dots. Rosetta moves roughly from East to West. The bright star at the bottom of the image has magnitude 12.5, and the bright star at the top has magnitude 13.4.

This image was taken at 05:39 UTC on 14 Nov with an exposure time of 5 min. The field is located in Leo and has a size of 5 x 5 arcmin, North is up and East is left. The telescope was tracking the stars so that Rosetta appears as a stripe a little above centre-right of the image. The spacecraft moves less than 1 arcmin during the 5 min exposure, roughly from East to West. The brightest star at the bottom of the image has magnitude 12.6. Note that the vertical bright line that crosses Rosetta is a camera artefact. Kristin Wirth wrote:

"I will leave the Teide Observatory and Tenerife now, and head for the airport. I really enjoyed my time at the Optical Ground Station, together with a great team and at a special location - opposite the Teide mountain, with the clouds below us. I would like to thank everybody for their support, in particular Lilian Dominguez Palmero who operated the telescope for me." -- Kristin

And we're going to take this opportunity to thank Kristin for all her great help and input for the Rosetta Blog over the past week!

Finally, a 'farewell' (for now) from us both and a sincere 'thank you' to every one who visited the Rosetta Blog - it has been a lot of fun and we have especially enjoyed seeing the many comments left by visitors.

We plan to be back again in 2010 as Rosetta continues on her fascinating journey to the outer Solar System - including preparations for deep-space hibernation and the encounter with asteroid Lutetia on 10 July 2010 (from a distance of just 3000 km!). --Amruta & Daniel

Swirling clouds over the South Pacific

amehta — Mon, 16 Nov 2009 14:00:13 +0100

New images from the OSIRIS team received over the weekend!

Click to download the hi-res version

False-colour composite of cloud structures in an anticyclone over the South Pacific. It depicts a portion of the scene below with five times the resolution. The image was taken with the narrow-angle camera on 13 November at 06:48 CET, using orange, green and blue optical filters

Click to download the hi-res version

Taken three minutes before the image above with the wide-angle camera, this image is shown in a logarithmic scale to bring out details in the varying light intensity. As a result the scene looks roughly the same as it would appear to the human eye.

Click to download the hi-res version

The same area in the South Pacific imaged with the orange filter of the narrow-angle camera in a logarithmic intensity scale.

--Amruta

New animation shows Earth approaching

danielscuka — Sat, 14 Nov 2009 09:45:06 +0100

As a reader commented, the images clearly show Earth smiling back at Rosetta!

The OSIRIS team has composed this animation from a sequence of images taken once every 24 hours, beginning when Rosetta was at a distance of 50 000 km at 22:28 UTC last night. The resolution is 6.5 km/pixel. Access the animation in the main ESA web site. -- Amruta

Getting some help from Orville on the blog...

danielscuka — Fri, 13 Nov 2009 18:04:58 +0100

It's been a long day here on the Rosetta Blog - and we're finally getting some much-needed help from the Rosetta Flight Control Team's mascot, Orville - who, apparently, speaks French! :-) We'll log off for the the day now - thank you for visiting the Rosetta Blog -- Daniel

Earth seen by Rosetta's Navigation Camera

amehta — Fri, 13 Nov 2009 17:35:47 +0100

Rosetta's operations team just handed us a couple of breath-taking images taken by the spacecraft's navigation camera (navcam). The camera is actually designed for navigation purposes, so they aren't to be compared with the full-colour scientific capabilities of OSIRIS - but they are amazing views!

This image was captured at 14:23 UTC (15:23 CET), when Rosetta was at a distance of approximately 236 000 km from Earth's centre. It shows a cloud-covered North America in some detail. (Click on 'Full story' for a second cool pic!) -- Daniel

This image shows a cloud-covered North America, and was captured at 14:03 UTC (15:03 CET), when Rosetta was at a distance of approximately 224 000 km from Earth's centre. It is not quite as nice as the first, and shows a few smears from the CCD camera output.

The navcam is used for precise determination of the orbit and optical visualisation. The output of the camera tells you where the centre of the object that is in the centre of the field of view is - it also gives physical parameters of the object.

The photos were taken to test the camera's operation with a large physical object. Previously, Steins was also imaged, but it is rather small (about 5 km across). Next year, the camera will be used to view Lutetia, which is much larger (about 95 km across). In the camera field of view, Lutetia shoudl appear about as large as the Earth looks in these images.

Some cool tech stuff... RPC-LAP & SREM

danielscuka — Fri, 13 Nov 2009 16:52:07 +0100

We're received a couple of emails from several colleagues around ESA and at the science teams working on Rosetta from other institutes. They've kindly sent in some of the data they've seen during the swingby campaign, and herewith we'd like to publish a couple of cool 'techie' updates.

The first came in from Anders Eriksson, the PI (principle investigator) for Rosetta's RPC-LAP at the Swedish Institute of Space Physics, Uppsala, and the second from ESA's Petteri Nieminen, working on Rosetta's SREM instrument at ESA/ESTEC, the Netherlands. Click on 'Full story' for details. -- Daniel

This received from Anders (click image for high-res):

Nice blogging on the Rosetta ESB3! Perhaps you are interested in the attached plot (above): I confess it isn't as sexy as the Osiris images, but it is fun in that it shows the thruster firings on November 10 (night). When the thrusters are fired (for reaction wheel offloading, in this case), a portion of the gas released gets ionized by the solar UV radiation, creating a plasma cloud easily detected by the Langmuir probes of the RPC (Rosetta Plasma Consortium), turned on since Monday night. We knew the time slot for the wheel offloading, but not the exact timing: however, from the data we can say that they did three thruster firings within a few minutes, and we can quite accurately time them.

At each firing, we see a sudden jump in the probe potential, decaying at a slower rate as the cloud disperses. The scale at the left is really in volts, showing the potential of one of our probes with respect to the spacecraft. The three peaks reach different height, probably just because of a sampling effect (we only take one sample per second for the moment).

This came in from Petteri (click image for high-res version):

These diagrams show the SREM radiation measurements as Rosetta passed through the Earth's radiation belts during the fly-by.

The top two panels: The distance of Rosetta from the Earth is shown in Earth radii, together with count rates for three of the SREM channels. The TC3 channel is sensitive to electrons (>500 keV) and protons (>10 MeV), TC1 for electrons (>2 MeV) and protons (>27 MeV), and S34 for protons only (>11 MeV).

The bottom two panels show the Earth's magnetic field strength, and the derived electron fluxes in different energy ranges as a function of geomagnetic coordinates.

Credits: ESA/ Paul Buehler / PSI

Thanks guys!!