Comments and blank lines may be added freely. (Anything beginning with a space is a comment.) If a line is uncommented, it's probably controlled via the user interface. The default version of this file is stored in 'environ.def'. Once you've run Find_Orb or 'fo' (Find_Orb's non-interactive sibling), new settings are written to 'environ.dat'. If you decide at some point that you'd like to reset to factory defaults, just delete 'environ.dat'. Windows Find_Orb ignores the following 'CONSOLE_OPTS' line. For the console flavor of Find_Orb, this line gives the default MPC code for ephems, which items are shown on-screen, residual display format, and whether all, some, or only one MPC code(s) are displayed. CONSOLE_OPTS=500 15 3 1 The 'settings' give the comet magnitude type used (defaults to 'N', or 'nuclear'); the format used for orbital elements; the precision used in orbital elements (defaults to five places for angular elements); the ephemeris output options, in a complicated form; the maximum residual filtered, in arcseconds (defaults to 2); and the Gaussian "noise" added, in sigmas, when running Monte Carlo orbits. SETTINGS=N,4,5,66560,2.000000,1.000000 DEFAULTS=N4 EPHEM_START=+0 EPHEM_STEPS=100 1 REFERENCE=Find_Orb EPHEM_LON=W 69.900 EPHEM_LAT=N 44.010 EPHEM_MPC_CODE=1 500 'filtering' gives the assumed probability that an observation is a blunder (defaults to 2%); the over-observing time span (defaults to one day); the "ceiling" on over-observing (defaults to five observations); and a number which is 1 if "filtering" uses blunder management, or 0 if we are doing traditional rejection based on an observation having residuals greater than N sigmas, with N specified in 'settings' (see above). By default, blunder management is used (see the Find_Orb Web page for a description of blunder management and over-observing parameters). FILTERING=2.000 1.000000 5 1 Observations sent via e-mail frequently end up with spaces added or removed. Find_Orb will (usually) parse such observations anyway. Remove or comment out the following line, and Find_Orb will switch to being "strict" about lines being exactly 80 characters long, etc. FIX_OBSERVATIONS=1 By default, ephemerides can cover the range -1000 to +3000. If you want to go beyond that, alter the following line. TIME_RANGE=-1000,3000 MPC has requested that NEOCP data not be redistributed. So in pseudo-MPECs, NEOCP observations are "redacted" (blacked out and the data replaced with garbage). The following observers have kindly given permission for their NEOCP observations to be redistributed in "unredacted" form. (Contact me if you're willing to be added to this list.) GREENLIT=033 568 703 970 C95 G58 G96 H01 H41 H43 H45 I41 I52 I93 J95 V03 V06 We default to assuming that no object will have an observed arc greater than 200 years, and that if it _is_ longer than that, it's a mistake. This is a pretty good assumption, though some comets and four asteroids do have longer observed arcs than this, possibly requiring you to adjust the following line. MAX_OBSERVATION_SPAN=200 For radar stations, power (in watts), temp in K, gain, altitude limit in degrees, and an arbitrary "radar constant" are needed. So far, the only radar stations for which I have those data are (251) Arecibo and (253) Goldstone. [Correction: at least most of these data are provided in Table 1 of https://arxiv.org/pdf/1604.01080v1.pdf. And Table 2 provides 'relative sensitivities', based on DSS-14 Goldstone (253) = 1, including for bistatic modes. One could, and I probably eventually will, copy the (253) line for use with other stations; compute ephemerides that way; replace the power, temperature, etc. values with the ones that actually apply for that telescope; then scale up/down the "radar constant" to get SNRs that are the appropriate multiple of (253) Goldstone.] RADAR_251=900000,25,10,70.5,1.5e-11 RADAR_253=430000,17,.94,20,1e-11 The Parkes radio telescope in Australia lacks an official MPC code. But it has an unofficial MPC code in 'rovers.txt' (q.v.). RADAR_d43=430000,17,.94,20,7e-14 'Settings2' gives five parameters. The first is 1 if observation weighting is used and 0 if it is not. Next, the 'faint limit' on ephemerides (by default, ephemerides are not listed if the object is fainter than mag 22). The third value defaults to zero; if it's non-zero, the positional sigmas for observations are shown in the (normally blank) columns 57-65 of MPC reports. The fourth number indicates a central object for orbital elements, if one isn't allowing automatic selection of elements. By default, the central object is 3, i.e., the earth. The final number is 1 if FCCT14 astrometric debiasing is applied, and 0 if it is not. FCCT14 removes (most of) the star catalog position/proper motion biases, using tables from Farnocchia, Chesley, Chamberlin, Tholen, _Icarus_ 245 (2015) 94-111, http://adsabs.harvard.edu/abs/2015Icar..245...94F . See https://www.projectpluto.com/bias.htm for more information. SETTINGS2=1 22.00 0 3 0 Note the comments in the above paragraph about FCCT14 debiasing. By default, Find_Orb looks for the 'bias.dat' file to be in the same directory as Find_Orb itself. However, you can set the file name with the following line. FCCT14_FILE= Most JPL filenames can be automatically detected via the list in 'jpl_eph.txt'. But if it's in a different folder or an odd name, you can add the path to one of the following, depending on whether you're on Windows or Linux. (LINUX_JPL_FILENAME is also used for OS/X and *BSD.) LINUX_JPL_FILENAME= JPL_FILENAME= When Find_Orb loads up a short arc, it uses "statistical ranging" (SR), and defaults to trying 100 possible orbits at a mix of distances and radial velocities to characterize the possible orbits for the object. You can raise or lower that number here. MAX_SR_ORBITS=100 By default, if asteroid perturbers are turned on, Pallas is included if it is within 10 AU of our target object. This 'asteroid threshhold' is scaled by the square root of the perturbing asteroid's mass; for example, an asteroid with a quarter the mass of Pallas would only be included if it were within 5 AU. This helps to assure that the tiny contributions of most of the 300 asteroids do not have to be computed. If you think you have a case where they _do_ matter, increase the following setting. If you think you're unnecessarily including asteroid perturbations that cannot possibly matter, decrease it. ASTEROID_THRESH=10 By default, we consider all 300 asteroids listed in BC-405. You can get a good speed-up by cutting this down, at the risk of maybe ignoring some tiny rock that just happens to pull your target around more than you expected. BC405_ASTEROIDS=300 By default, geoocentric elements are referred to the J2000 _equator_. Everything else (heliocentric and other non-earth-centric) is referred to the J2000 _ecliptic_. Set the following to be 1 to force all elements to be J2000 ecliptic (including geocentric ones), or 2 to force all elements to be J2000 equatorial. Set it to be 3 to force all elements to be body-centric. Note that for geocentric elements, this will result in elements that are slightly different from those you'd get by default, due to precession and nutation since 2000; the angles should be passably close to those seen in TLEs. ELEMENTS_FRAME=0 Find_Orb will apply geopotential terms (spherical harmonics) for objects close to the earth. It has a bit of logic to determine how many should be computed, as a function of distance (only J2 for most cases, but many terms as one gets close to the earth). The following GEO_TERMS quantity can be raised to include more terms, or lowered to get better speed for artsats. However, through experimentation, I've found that setting it to the default value of 6 gets good results; increasing it doesn't change orbits much, lowering it causes them to start showing errors. GEO_TERMS=6 Find_Orb can use either the method of Encke (do a two-body solution relative to the 'best fitting' body, integrating perturbations to that orbit). By default, it instead uses the method of Cowell (the 'direct' method, in which you just integrate the accelerations from all bodies). I'm still experimenting with both methods. But you will probably be best off leaving this value at zero, meaning Cowell is used. ENCKE=1 By default, the DRAG_SHUTOFF=1 tells Find_Orb not to include the effects of atmospheric drag. Set it to zero if you want objects entering the earth's atmosphere to be affected by drag. DRAG_SHUTOFF=1 By default, Find_Orb will look for an orbit covering, at most, 20 years (7300 days) of observations. This is simply for speed reasons, and you can toggle additional observations once the object is loaded and extend the orbit. You can adjust the initial parameter here. AUTO_ARC_LEN=7300 VECTOR_OPTS gives three values controlling state vector and Cartesian coordinate ephemerides. The first value can be zero (the default) for equatorial J2000 vectors, or one for ecliptic J2000. (I may add mean and/or apparent coordinates at some point, and perhaps body plane coordinates.) The second value is a multiplier for length. Lengths default to being in AU, with this multiplier being 1. Set it to 149597870.7 (the number of kilometers in one AU) to switch to kilometers, or to 23454.7800299146773197201 to switch the distance unit to Earth radii (this assumes the equatorial radius of 6378.140 km.) The final value gives the time unit: 1=days (default), 24=hours, 1440=minutes, 86400=seconds. For example, VECTOR_OPTS=1,149597870.7,86400 would get you ecliptic J2000 vectors in kilometers and km/s. VECTOR_OPTS=0,1,1 Comet non-gravitational forces in the "standard" Marsden-Sekanina model are assumed to be due to sublimating ice. As described at page 3 of http://www.lpi.usra.edu/books/CometsII/7009.pdf 'Cometary Orbit Determination and Nongravitational Forces', D. K. Yeomans, P. W. Chodas, G. Sitarski, S. Szutowicz, M. Krolikowska, "Comets II", this leads to a force whose magnitude is given by a function g(r), with parameters r0, m, n, and k. The following line gives those constants for non-gravs driven by sublimating water ice. Sekanina and Kracht have proposed different r0, m, n, and k for other sublimation processes. If you want to do that, change the line below. (Note that 'alpha' isn't given; it's a normalization quantity to ensure g(1) = 1. Find_Orb will compute it for you.) COMET_CONSTANTS=2.808,2.15,5.093,4.6142 Initial orbit determination (IOD) usually takes a couple of seconds. For longer arcs, it might take five or ten seconds. If it takes more than IOD_TIMEOUT seconds (defaults to 20), we stop looking for a better initial orbit and take whatever our best orbit thus far is. (Such cases usually come about because the observations are inconsistent and there isn't really a meaningful orbit that fits them.) IOD_TIMEOUT=20 Find_Orb defaults to looking for the BC405 ephemeris file (orbital elements at 40-day intervals for 300 asteroids used in the BC405 theory; see https://www.projectpluto.com/ast_pert.htm for details) in its configuration directory, then the local directory. But using the following line, you can move the 'asteroid_ephemeris.txt' file to a different directory, and/or rename it. # BC405_FILENAME=/home/phred/big/asteroid_ephemeris.txt I had a request (https://groups.yahoo.com/neo/groups/find_orb/conversations/messages/35) for an option to output planetary state vectors at the epoch of the orbital elements to 'elements.txt'. If you want to do that, set PLANET_STATES=1. By default, it's blank and planet states are not written out. PLANET_STATES= When looking for precoveries, one may want to list only images that haven't been measured yet, or only those that have been measured. (Note that the only way Find_Orb knows which images have been measured is by looking at the astrometry. That is to say, if the astrometry you've used to compute the orbit came from an image, Find_Orb will notice that fact. Otherwise, it'll assume that the image in question hasn't been measured.) A value of 1 means "show only measured images"; 2="show only unmeasured"; 0 or blank means "show all images". FIELD_INCLUSION=0 Set the following COMBINE_ALL parameter to any non-blank value, and all observations in a file will be loaded as if they were of a single object. This can be convenient when you're checking a linkage, for example; you can compute an orbit based on all the observations without having to change the designations to all be the same. COMBINE_ALL= In computing impact points on the earth, we're really mostly interested in the point where the object 'collides' with the upper atmosphere and is slowed down/explodes. Rob Matson tells me that for a 2-3 meter object, it should become visible at about 90 km and drop below 3 km/s by the time it gets down to 20-25 km. That's a bit of a range; let's go with 50 km. (The collision altitude is actually specified in meters, though.) COLLISION_ALTITUDE=50000 Current available language settings are e (English), f (French), i (Italian), d (German), r (Russian), s (Spanish). More could be added, and the current not-very-complete translations improved; please let me know if you're interested. LANGUAGE=e By default, ephems show RAs to 0.001 seconds and decs to 0.01 arcseconds. You can reset the following to be from -2 to 6, to get two fewer digits (RA to 0.1 seconds, dec to full arcseconds) to six extra digits. For the latter, the precision will be ten nanoarcseconds, which is essentially meaningless; the last few digits will be almost pure random numbers. ADDED_RA_DEC_PRECISION=0