Rosetta Data Released

ESA has released the first block of data from Rosetta to the general public.  This data covers the period from the 8 months of approach to orbit, and includes datasets from the four main instruments on Rosetta. (The navigation camera visible light imagery has been dribbling out continuously.)

Why now? The science team had a six month period to clean up and analyze the data and to publish the initial papers (quite a few papers!). At the end of that period, the data was delivered to ESA for archiving and public release.

As the ESA blog notes, it was necessary to check and cross check the data and to debug the processing systems. “These complex checks and interactions have taken quite some time”.

So what can you get? Well, unlike Hollywood, it takes quite a bit of work to get the data. Setting aside the clunky interface (based on the pre-WWW pioneering Plantetary Data System from NASA JPL), even understanding the data is serious work, let alone making scientific sense of it.

Set mode = nerd.

Let’s glance at one instrument, Rosina (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis). The datasets are described in a dozen documents, such as this one. This is way cool, because they tell us everything. (It’s call science.) These docuemtns tell us how the data was collected, how the instrument works, and exactly what each number means.

The datasets themselves are here.  (My browser had trouble following the links from the blog.  The link I give here is where the data is.)

There are many files, each with many numbers. There are many different kinds of datasets, with different measurements, and measurements are taken repeatedly.. The files each have metadata to tell us what each file is.

For example, one file I picked at random is CE_20140425_092001649_M0160.TAB, which is a table (in PDS3 format) of data collected in April 2014 (specifically, from 2014-04-25T09:21:07.202 to 2014-04-25T09:21:29.202). The file contains 95 lines of header, and another 200 plus lines of metadata about the status of the instrument and spacecraft and then 22 lines of data! The latter are readings from the mass spectrometer, which you need to look up to interpret.

(A PDF rendition of this file is here.)

For example, the one line of the data reads:

1,         38,         16, 2.181175E+001, 1.182010E+000,

The PDS Metadata tells us how to interpret these five numbers:


——————————————                     OBJECT                                   =     COLUMN
NAME                                  =     STEP
DESCRIPTION               =     “CEM Step Number. The values are in the
range from 1 to 150 and ascending.”
UNIT                                    =    “STEP_NUMBER”
DATA_TYPE                     =     ASCII_INTEGER
START_BYTE                   =     1
BYTES                                  =     3                                       END_OBJECT                     =     COLUMN                                 OBJECT                                 =     COLUMN
NAME                                 =     COUNTS
DESCRIPTION                =     “Digital counts of the channeltron.”
UNIT                         =     “COUNTS”
DATA_TYPE                     =     ASCII_INTEGER
START_BYTE                   =     5
BYTES                         =     12                                     END_OBJECT                      =     COLUMN                                 OBJECT                           =     COLUMN
NAME                         =     GAIN
DESCRIPTION                   =   “Gain which was used. Default is 16.”
UNIT                         =     “GAIN_NUMBER”
DATA_TYPE                     =     ASCII_INTEGER
START_BYTE                   =     18
BYTES                         =     12                                     END_OBJECT                       =     COLUMN                                 OBJECT                           =     COLUMN
NAME                         =     ANALOG_HG
DESCRIPTION                   =     “Analog signal with high-gain.”
UNIT                         =     “COUNTS”
DATA_TYPE                    =     ASCII_REAL
START_BYTE                   =     31
BYTES                         =     15                                     END_OBJECT                       =    COLUMN                                 OBJECT                           =     COLUMN
NAME                         =     ANALOG_LG
DESCRIPTION                   =     “Analog signal with low-gain.”
UNIT                         =     “COUNTS”
DATA_TYPE                     =     ASCII_REAL
START_BYTE                   =     47
BYTES                         =     15                                     END_OBJECT                       =     COLUMN
OBJECT                           =     COLUMN
NAME                        =     “SPARE”
DESCRIPTION                   =     “Blank padding to fixed record length”
DATA_TYPE                     =     “CHARACTER”
START_BYTE                   =     63
BYTES                         =     16                                     END_OBJECT                       =     COLUMN                                 — EOF

Do I know what this means? No, of course not. Could I figure it out? Eventually. Because everything is published and documented.

(A list of science publications to date can be found here or here.  These will have actual results, and references to explain how the data was interpreted.)

And so on. Thousands of files.

How would I do science with this data? With some serious software, which took ESA years and millions of Euros to create. (This is part of why the science team gets first crack at the data—they earned it.) Other scientists have their own software that can use these files.

It is important to bear in mind just how obsessively detailed the software must be: the meaning of these numbers depends on understanding where they came from, which means you have to understand the spacecraft as well as the physics of the orbits and so on. Phew!

The basic point is: ESA has released the data, but it is real science and engineering data. You can’t expect to just click on it and see pretty pictures.

But sometimes it is good to get nerdy and just dig in to the data to see what is there.


Space Saturday

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