When I use Horizons values, the initial elliptical orbit and the corresponding xyz trajectory values match almost perfectly up until the flyby, as they should. Note that I'm only using the xyz trajectory coordinates and not the velocity component. I haven't taken the time to figure out the correct message to have velocity included, so the set of commands shown below returns only the asteroid's xyz positions, once per day.
These elliptical orbit coordinates were obtained by using Horizon's telnet interface.
Code: Select all
#*******************************************************************************
#JPL/HORIZONS (2012 DA14) 2012-Oct-03 11:54:37
#Rec #:745306 (+COV) Soln.date: 2012-May-13_02:50:12 # obs: 188 (79 days)
#
#FK5/J2000.0 helio. ecliptic osc. elements (AU, DAYS, DEG, period=Julian yrs):
#
#EPOCH= 2456007.5 ! 2012-Mar-21.00 (CT) Residual RMS= .28422
#EC= .1082356434519823 QR= .8933003245207058 TP= 2455895.355491354
#OM= 147.2896474597286 W= 271.0806938513611 IN= 10.33969989795044
#A= 1.001722392200821 MA= 110.2455360245707 ADIST= 1.110144459880936
#PER= 1.0026 N= .9830667360000001 ANGMOM= .017115762
#DAN= .98797 DDN= .9920099999999999 L= 58.3881762
#B= -10.3378405 TP= 2011-Nov-29.8554914
#
"2012_da14_00" "Sol"
{
Class "planet"
Radius 100
Color [1 0.3 0]
Texture "asteroid.jpg"
BlendTexture true
EllipticalOrbit {
Epoch 2456007.5 # 2012-Mar-21.00 (CT) Residual RMS= .28422
SemiMajorAxis 1.001722392200821
Eccentricity 0.1082356434519823
Inclination 10.33969989795044
Period 1.0026
AscendingNode 147.2896474597286
ArgOfPericenter 271.0806938513611
MeanAnomaly 110.2455360245707
}
Albedo 0.2
}
To obtain the xyz trajectory coordinates, I used the Horizons email interface and an appropriately modified version of the xyz request template that I created some years ago. The template (which includes brief instructions not quoted below) is available at
http://www.lepp.cornell.edu/celestia/ho ... mplate.txtCode: Select all
!$$SOF (ssd) JPL/Horizons Execution Control VARLIST
EMAIL_ADDR = 'seb1@cornell.edu'
COMMAND = '2012 DA14'
OBJ_DATA = 'NO'
MAKE_EPHEM = 'YES'
TABLE_TYPE = 'VECTORS'
CENTER = '@10'
REF_PLANE = 'ECLIPTIC'
SITE_COORD = '0,0,0'
START_TIME = '2012-Oct-01 00:00'
STOP_TIME = '2013-JUL-01 00:00'
STEP_SIZE = '1d'
REF_SYSTEM = 'J2000'
OUT_UNITS = 'KM-D'
VECT_TABLE = '1'
VECT_CORR = 'NONE'
TIME_DIGITS = 'MIN'
CSV_FORMAT = 'NO'
VEC_LABELS = 'NO'
ELM_LABELS = 'NO'
R_T_S_ONLY = 'NO'
CA_TABLE_TYPE= 'EXTENDED'
CALIM_SB= '0.1'
CALIM_PL= '.1, .1, .1, .1, 1.0, 1.0, 1.0, 1.0, .1, .003'
!$$EOF++++++++++++++++++++++++++++++++++++++++++++++++++++++
The first few lines of the response, with 1 day sampling intervals, were
Code: Select all
Automated mail xmit by MAIL_REQUEST, PID= 31231 Wed Oct 3 12:07:37 2012
++++++++++++++++++++++++++++++++ (part 1 of 1) +++++++++++++++++++++++++++++++
*******************************************************************************
Ephemeris / MAIL_REQUEST Wed Oct 3 12:07:37 2012 Pasadena, USA / Horizons
*******************************************************************************
Target body name: (2012 DA14) {source: JPL#35}
Center body name: Sun (10) {source: DE405}
Center-site name: BODY CENTER
*******************************************************************************
Start time : A.D. 2012-Oct-01 00:00:00.0000 CT
Stop time : A.D. 2013-Jul-01 00:00:00.0000 CT
Step-size : 1440 minutes
*******************************************************************************
Center geodetic : 0.00000000,0.00000000,0.0000000 {E-lon(deg),Lat(deg),Alt(km)}
Center cylindric: 0.00000000,0.00000000,0.0000000 {E-lon(deg),Dxy(km),Dz(km)}
Center radii : 696000.0 x 696000.0 x 696000.0 k{Equator, meridian, pole}
Small perturbers: Ceres, Pallas, Vesta {source: SB405-CPV-2}
Small body GMs : 6.32E+01, 1.43E+01, 1.78E+01 km^3/s^2
Output units : KM-D
Output format : 01
Reference frame : ICRF/J2000.0
Output type : GEOMETRIC cartesian states
Coordinate systm: Ecliptic and Mean Equinox of Reference Epoch
*******************************************************************************
Initial FK5/J2000.0 heliocentric ecliptic osculating elements (AU, DAYS, DEG):
EPOCH= 2456007.5 ! 2012-Mar-21.00 (CT) Residual RMS= .28422
EC= .1082356434519823 QR= .8933003245207058 TP= 2455895.355491354
OM= 147.2896474597286 W= 271.0806938513611 IN= 10.33969989795044
Asteroid physical parameters (KM, SEC, rotational period in hours):
GM= n.a. RAD= n.a. ROTPER= n.a.
H= 24.377 G= .150 B-V= n.a.
ALBEDO= n.a. STYP= n.a.
*******************************************************************************
JDCT
X Y Z
*******************************************************************************
$$SOE
2456201.500000000 = A.D. 2012-Oct-01 00:00:00.0000 (CT)
1.393482465976654E+08 -3.045100308179304E+07 -9.073242323681137E+06
2456202.500000000 = A.D. 2012-Oct-02 00:00:00.0000 (CT)
1.396038335849245E+08 -2.780262197650209E+07 -9.504777809338791E+06
2456203.500000000 = A.D. 2012-Oct-03 00:00:00.0000 (CT)
1.398117885504721E+08 -2.514475457408382E+07 -9.933069991457094E+06
2456204.500000000 = A.D. 2012-Oct-04 00:00:00.0000 (CT)
1.399717781680426E+08 -2.247826051757148E+07 -1.035795408850165E+07
2456205.500000000 = A.D. 2012-Oct-05 00:00:00.0000 (CT)
(plus many more lines)
I edited that response to create the xyz file
Code: Select all
2456201.500000000 1.393482465976654E+08 -3.045100308179304E+07 -9.073242323681137E+06
2456202.500000000 1.396038335849245E+08 -2.780262197650209E+07 -9.504777809338791E+06
2456203.500000000 1.398117885504721E+08 -2.514475457408382E+07 -9.933069991457094E+06
2456204.500000000 1.399717781680426E+08 -2.247826051757148E+07 -1.035795408850165E+07
2456205.500000000 1.400834849454027E+08 -1.980401241197275E+07 -1.077926489206265E+07
2456206.500000000 1.401466077334758E+08 -1.712289558444042E+07 -1.119683685387047E+07
2456207.500000000 1.401608622357275E+08 -1.443580782400091E+07 -1.161050417597367E+07
2456208.500000000 1.401259815169858E+08 -1.174365910042389E+07 -1.202010090406156E+07
(plus many more lines)
For the xyz trajectory, I used this SSC:
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"2012_da14_xyz" "Sol"
{
Class "planet"
Radius 100
Color [1 0.7 0]
SampledOrbit "2012_da14.xyz"
Albedo 0.2
}
Below are three screen grabs. The first two are with today's date, so the asteroid is far away.
This first picture shows the elliptical orbit path.
2012_da14_00.jpg
In the picture below, note that the trajectory and elliptical orbit are so close that part of the red trajectory path is overwritten by the blue path of the elliptical orbit.
2012_da14_xyz.jpg
Here's a closeup of the orbits on the day of the flyby. They look reasonably close to one another, I think. The path drawn for the xyz trajectory doesn't go through the asteroid's position because Celestia uses a simpler algorithm to draw a path than it uses to calculate an object's position.
2012_da14_flyby.jpg
i hope this helps a little.
