[Spice_discussion] Converting MPC elements to SPICE ephemerides
Boris Semenov
Boris.Semenov at jpl.nasa.gov
Tue May 24 15:47:38 PDT 2011
Hi Bill --
Your understanding of the cause of the error is correct: Type 17
(Equinoctial Elements) is intended for elliptical orbits and will not
work for hyperbolic orbits.
The right SPK type for the elements that you have is Type 5 (two body
propagation).
With the following modified setup using Type 5, correct NAIF ID for
comet Elenin (1003113), and corrected reference frame for the elements
(ECLIPJ2000 instead of J2000 because the orbital inclination in MPC is
relative the ecliptic plane):
\begindata
INPUT_DATA_TYPE = 'ELEMENTS'
OUTPUT_SPK_TYPE = 5
OBJECT_ID = 1003113
CENTER_ID = 10
REF_FRAME_NAME = 'ECLIPJ2000'
PRODUCER_ID = 'W. Thompson, NASA/GSFC, USA'
DATA_ORDER = 'EPOCH RP E INC NOD PER MEAN'
INPUT_DATA_UNITS = ('ANGLES=DEGREES' 'DISTANCES=AU')
START_TIME = '2011 MAY 01'
STOP_TIME = '2012 MAY 01'
DATA_DELIMITER = 'EOL'
LEAPSECONDS_FILE = 'naif0009.tls'
PCK_FILE = ('pck00008.tpc', 'gravity.tpc' )
SEGMENT_ID = 'SPK_ELEMENTS_5'
\begintext
and with the input without the D*/DT terms:
2011-09-10T17:22:33.600
0.482462
1.000024
1.8391
323.2242
343.8085
0.0
I was able to make an SPK file that showed agreement with a Elenin SPK
made using Horizons Web interface
http://ssd.jpl.nasa.gov/x/spk.html
to better than 5,000 km for a few month period in 2011 (see attached plot).
Regards,
Boris.
William Thompson wrote:
> I would like to generate a SPICE ephemeris for Comet Elenin. The IAU
> Minor Planet Center gives these elements for this comet:
>
>> The following orbital elements are taken from MPC 75009:
>>
>> C/2010 X1 (Elenin)
>> Epoch 2011 Aug. 27.0 TT = JDT 2455800.5
>> T 2011 Sept. 10.7240 TT MPC
>> q 0.482462 (2000.0) P Q
>> z -0.000049 Peri. 343.8085 +0.6023572 +0.7979954
>> +/-0.000004 Node 323.2242 -0.7287529 +0.5399501
>> e 1.000024 Incl. 1.8391 -0.3257069 +0.2676887
>> From 1621 observations 2010 Dec. 10-2011 May 10, mean residual 0".5.
>
> (from
> http://scully.cfa.harvard.edu/cgi-bin/returnprepeph.cgi?d=c&o=CK10X010)
>
> I tried making an SPK file out of this with the following setup file
>
> \begindata
> INPUT_DATA_TYPE = 'ELEMENTS'
> OUTPUT_SPK_TYPE = 17
> OBJECT_ID = -900
> OBJECT_NAME = 'ELENIN'
> CENTER_ID = 10
> CENTER_NAME = 'SUN'
> REF_FRAME_NAME = 'J2000'
> PRODUCER_ID = 'W. Thompson, NASA/GSFC, USA'
> DATA_ORDER = 'EPOCH RP E INC NOD PER MEAN DPER/DT DMPN/DT DNOD/DT'
> INPUT_DATA_UNITS = ('ANGLES=DEGREES' 'DISTANCES=AU')
> START_TIME = '2011 MAY 01'
> STOP_TIME = '2012 MAY 01'
> DATA_DELIMITER = 'EOL'
> LEAPSECONDS_FILE = '/solarsoft/stereo/gen/data/spice/gen/naif0009.tls'
> PCK_FILE = ('pck00008.tpc' 'gravity.tpc')
> SEGMENT_ID = 'SPK_ELEMENTS_17'
> \begintext
>
> and the following data file
>
> 2011-09-10T17:22:33.600
> 0.482462
> 1.000024
> 1.8391
> 323.2242
> 343.8085
> 0.00
> 0.00
> 0.00
> 0.00
>
> However, when I try to run mkspk, I get the following error message:
>
> > mkspk -setup elenin.setup -input elenin.dat -output elenin.bsp
>
> MKSPK Program; Ver. 4.3.0, 20-DEC-2004; Toolkit Ver. N0060
>
> Loading setup file ...
>
> Processing setup file keyword values ...
>
> Writing comments to the output SPK file ...
>
> Started processing input data ...
>
> Writing next SPK segment ...
>
> ================================================================================
>
>
> Toolkit version: N0060
>
> SPICE(BADSEMIAXIS)
>
> The semimajor axis supplied to the SPK type 17 evaluator was
> non-positive. This
> value must be positive. The value supplied was -3.0073036604979E+12.
>
> A traceback follows. The name of the highest level module is first.
> MKSPK --> SPKW17
>
> ================================================================================
>
>
> I think this error is caused by the fact that the eccentricity is
> slightly above 1, i.e. the orbit is hyperbolic. Is this my problem, or
> have I misunderstood the input parameters to mkspk?
>
> Bill Thompson
>
>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: elenin_horizon_vs_elements.png
Type: image/png
Size: 6480 bytes
Desc: not available
Url : http://naif.jpl.nasa.gov/pipermail/spice_discussion/attachments/20110524/04c4de4c/elenin_horizon_vs_elements.png
More information about the Spice_discussion
mailing list