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Rosetta flyby of Asteroid Steins, 5th September 2008
peter59
post Jun 19 2008, 06:53 AM
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Only 78 days to Stein encounter ! I can't believe I forgot about this event.


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dmuller
post Jun 19 2008, 09:00 AM
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Indeed, almost there ... 78 days and 121 million km to fly. Currently 61 million km away from Steins: Rosetta Real-Time Simulation

Does anybody have more details on the flyby trajectory? I currently have it nailed down to minute precision with closest approach being on 05 Sep 2008 18:35 spacecraft event time at a distance of 712 km


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ugordan
post Jun 19 2008, 09:05 AM
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QUOTE (peter59 @ Jun 19 2008, 08:53 AM) *
Only 78 days to Stein encounter !

Anyone wanna bet if the previous flyby data (Earth, Mars) will hit the Planetary Science Archive before or after this flyby? rolleyes.gif


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peter59
post Jun 19 2008, 10:01 AM
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QUOTE (ugordan @ Jun 19 2008, 09:05 AM) *
Anyone wanna bet if the previous flyby data (Earth, Mars) will hit the Planetary Science Archive before or after this flyby? rolleyes.gif


PSA announcements:
First release of Rosetta data - early 2008 ??
First release of Venus Express data - July 2008 !?

Planetary Science Archive


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jasedm
post Jun 19 2008, 10:11 AM
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Perhaps it's time for a dedicated 'Steins' thread...
A few details on the rock:

Main belt asteroid
Discovered: November 4th 1969
Spectral type: E
Diameter 4.6km
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ugordan
post Jun 19 2008, 10:47 AM
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QUOTE (peter59 @ Jun 19 2008, 12:01 PM) *
PSA announcements:

That's just what they are: announcements.


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djellison
post Jun 19 2008, 10:58 AM
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They had previously been announced ( both of them, iiirc ) as being earlier. I would essentially ignore the announcement dates and just wait for stuff to actually arrive.

Alice data is already available upto and including the most recent Earth flyby. No other instrument has provided anything to date.

Doug
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Paolo
post Jun 21 2008, 09:23 AM
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Some details about Steins that I collected for the third volume of my book "robotic exploration of the solar system"

Steins is a small body less than 10 km across, discovered on 4 November 1969 by Soviet astronomer N. Chernykh at the Nauchnyj Observatory in Crimea and named after Karlis Steins, former director of the Latvian University Astronomical Observatory. While the properties of Lutetia, the second asteroid target are relatively well known, being a largish and bright object discovered more than a century ago, almost nothing was known about Steins, and observational campaigns were started in 2004 to characterize it. Steins was observed by the largest astronomical observatory on Earth, including the European Very Large Telescope (VLT) in Chile, JPL's Table Mountain Observatory, the Spitzer infrared astronomy satellite and Rosetta itself.
The Rosetta orbiter observed continuously Steins (1.06 AU away) for 24 hours with its science camera on 11 March 2006 in order to collect a “light curve” at phase angles larger than ever achievable from Earth, due to observational geometry constrains and for a longer time span, uninterrupted by day and night cycles. A total of 238 images were taken, covering four rotations.
Although researchers initially catalogued Steins in the S class (like most previously-visited bodies), the observational campaigns found that its spectral and polarimetric properties placed it in the E taxonomic class of reddish bodies with high albedo believed to be thermally evolved and of igneous origin, which underwent at least a partial melting and differentiation early in their history. E asteroid spectra probably makes them related to some rare enstatite chondrite or aubrite meteorites and therefore these bodies are believed to have a surface consisting of iron-free or iron-poor silicates. Observations pinpointed Steins' rotation period at about 6.05 hours, while the measured diameter could vary between 2 and 5 km, depending on its albedo. Asymmetries in the light curve confirmed that the small body has an irregular shape, with a ratio between the main axes of about 1.3. Other researchers pointed out that some of the characteristics of Steins could hint at a young and very rough surface at most a few million years old.
While fewer than 30 members of the E class of asteroids were known, including (44) Nysa, the largest, and two near-Earth objects, (3103) Eger and (4660) Nereus (a recurrent space mission target), little is known about the evolutionary history of the type. Steins was initially placed in the same family as (64) Angelina, but other studies showed that it shared most of the same spectral characteristics as Eger, both bodies being believed to be members of an old eroded family which formed in the inner asteroid belt close to the present position of Steins, which appears to be the largest member of the family. The presence of Eger in an Earth-intersecting orbit of course provides a path for enstatite and aubrite meteorites to hit our planet.
The encounter on 5 September 2008 will be at a distance of 1745 km and a relative speed of 8.6 km/s


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IM4
post Jun 21 2008, 10:04 AM
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Even more details for Rosetta fans !!!

Flyby in a nutshell:
  1. Closest approach on 5 Sept. 2008 18:33:57 ± 30 sec
  2. Heliocentric distance 2.14 AU, geocentric distance 2.41 AU
  3. Low phase angle during approach, high phase angle after closest approach, coverage 0-140°
  4. Minimum flyby distance of 800 km
  5. Zero phase angle will be reached at a distance of 1280 km
  6. One way light travel time will be 20 min

Flyby strategy
  1. Default pointing
  2. Spacecraft flip (T-40 min -> T-20 min)
  3. Inverted pointing (> T-20 min)
  4. +Z axis points at Steins at all times

Flyby Science:
  1. Alice: point at Steins to obtain FUV spectra search for exosphere/coma around Steins
  2. COSIMA: execute normal dust collection cycle
  3. GIADA: Impact sensor operational, but cover closed
  4. MIRO: Steins observations during approach and recession. Special asteroid mode sequence at closest approach (CA)
  5. ROSINA: Pressure monitoring, single mass measurement sequence
  6. RPC: Measurements of plasma environment
  7. RSI: Attempt for mass determination (probably not feasible)
  8. OSIRIS: Light curve for 2 weeks before CA for shape reconstruction. At CA: spectrophotometry, mapping and surface properties, satellite/dust search
  9. VIRTIS: Steins light curve determination starting 7 hours before CA. At CA: mineralogy mapping

Expected data volume:
  1. 600 MiB before closest approach
  2. 2400 MiB after closest approach
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tasp
post Jun 21 2008, 11:35 AM
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Do we have any radar data indicating binary/satellite existence for any asteroid in this size range ?

Just wondering what the odds are for 'nother Dactyl type discovery. Would 200+ images for albedo study yield enough light curve data to rule out a satellite? Particularly one that was in an orbit inclined enough so that the satellite was never eclipsed or transited the primary.

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gpurcell
post Jun 21 2008, 03:31 PM
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These sort of encounters always fascinate me...this is likely to be the only close approach data humanity collects on this particular hunk of rock for hundreds of years. Some time in the distant future an asteroid miner will pull up these old images on his way to this asteroid and wonder at the folks who sent a barbaric robot out to it....
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centsworth_II
post Jun 21 2008, 04:16 PM
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QUOTE (gpurcell @ Jun 21 2008, 11:31 AM) *
Some time in the distant future an asteroid miner...

I'm assuming this will be an AI robotic miner. laugh.gif
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nprev
post Jun 21 2008, 05:00 PM
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QUOTE (tasp @ Jun 21 2008, 03:35 AM) *
Do we have any radar data indicating binary/satellite existence for any asteroid in this size range ?


Wasn't there an NEO radar-imaged by Aricebo that was a small binary object? It's certainly possible that Steins is binary or has a small satellite, but if so I suspect it would have to have been the product of a weak, recent impact event. There's not a lot of gravitation exerted by a 4.6 km body.


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tedstryk
post Jun 21 2008, 08:39 PM
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QUOTE (nprev @ Jun 21 2008, 05:00 PM) *
Wasn't there an NEO radar-imaged by Aricebo that was a small binary object? It's certainly possible that Steins is binary or has a small satellite, but if so I suspect it would have to have been the product of a weak, recent impact event. There's not a lot of gravitation exerted by a 4.6 km body.


There has been a multitude of such objects. Castalia was the first one. Arecibo and Goldstone will be observing the upcoming flyby of 2008 BT18 (July 6 and 7 for Arecibo, July 11 for Goldstone]. It will pass about 2.3 million kilometers away and is 700 to 800 meters across, so we should get some nice images and, with some luck, maybe another binary.


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jasedm
post Jun 25 2008, 04:21 PM
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QUOTE (tasp @ Jun 21 2008, 12:35 PM) *
Do we have any radar data indicating binary/satellite existence for any asteroid in this size range ?

I couldn't find any relevant radar data, but it appears see here that a moon has been likely ruled out for Steins.
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