- Level Two Menu
- Specifying attributes of, and executing operations on, the subject minor
planet
For several
operations (e.g., processing visual magnitude data, looking for known bodies
whose positions agree with the observations of the subject minor planet), it is
critical that CODES understand whether the subject minor planet is a comet or
an asteroid.
Thus, this
designation should be made immediately upon creating a new minor planet.
From the Level Two
Menu, simply click on "Designate"; on the resulting frame, select
whether the minor planet is a comet or asteroid, then click on
"Submit".
The designation
being made, CODES will save the data to disk and return to the Level Two Menu.
From the Level Two
Menu, simply click on "Add". From the resulting frame, the user can
then select from the following options:
Simply click on
"Optical". The user will then encounter up to three successive
frames:
The first frame
allows the user to specify the UTC date of the optical observation, the
astrometric right ascension and declination (with uncertainties), the visual
magnitude, and the fundamental catalog/epoch to which the observation refers.
Note: CODES supports observations and predictions for the
range 1800-2200.
The second frame
allows the user to specify either the MPC observatory code, or the geodetic
latitude, east longitude, and altitude, from which the observation was made.
Additionally, the user may check a box telling CODES to generate default Earth
Orientation Parameters; the third frame would then be skipped.
Note: For typical optical observations, where
uncertainties are on the order of 0.1 arc seconds or greater, the default
EOPs generated by CODES are sufficient.
The option to specify EOPs for optical observations will allow future
support of more precise astrometric techniques.
The third frame
allows the user to specify the Earth Orientation Parameters (EOPs) at the time
of the observation. EOPs allow calculation of the ultra-precise location of the
observer. These EOPs include the x and y coordinates of the Celestial Ephemeris
Pole, the values of UT1-UTC, and the Celestial Pole Offsets dPsi and dEpsilon.
(Note that these EOPs are required for four dates surrounding the observation;
Besselian interpolation is then used to approximate the values of the EOPs at
the precise observation time.) Additionally, the user must specify the number
of leap seconds and the Earth's angular velocity at the time of observation.
IMPORTANT: CODES now supports use of the International
Earth Rotational Service's "EOPC04" tables. Simply download the current "Series from 1962 to
the current week" file, and save it in the "codes"
folder as "eopc04.txt". If the
file is present, and the observation date falls within the table's span, CODES
will automatically read the relevant EOPs, and skip the third frame. If the file is not present, or if the
observation date is not covered by the table, CODES will either generate
default EOPs (if this option is checked), or proceed to the third frame for
manual entry of the EOPs.
IMPORTANT: Do not leave any data fields blank! This can cause a
run-time error.
IMPORTANT: From either of the three input frames, it is possible to cancel
the input function and return to the Level Two Menu; the new
(and incomplete) observation will be deleted.
When complete,
CODES will save the data to disk and return to the Level Two Menu.
Simply click on
"Radar". The user will then encounter three successive frames:
The first frame
allows the user to specify the UTC time of observation, whether this
observation is a delay or a doppler measurement, the measurement and its
uncertainty, and the transmitter frequency.
Note: CODES supports observations and predictions for the
range 1800-2200.
The second frame
allows the user to specify the location of both the transmitter site and the
receiver site. In each case, the user may either select one of several common
radar sites (in which case the lat/long/alt data fields may safely be left
blank), or select "other" and specify the geodetic latitude, east
longitude, and altitude of the transmitter/receiver.
The third frame
allows the user to specify the Earth Orientation Parameters (EOPs) at the time
of the observation. EOPs allow calculation of the ultra-precise location of the
observer. These EOPs include the x and y coordinates of the Celestial Ephemeris
Pole, the values of UT1-UTC, and the Celestial Pole Offsets dPsi and dEpsilon.
(Note that these EOPs are required for four dates surrounding the observation;
Besselian interpolation is then used to approximate the values of the EOPs at
the precise observation time.) Additionally, the user must specify the number
of leap seconds and the Earth's angular velocity at the time of observation.
IMPORTANT: CODES now supports use of the International
Earth Rotational Service's "EOPC04" tables. Simply download the current "Series from 1962 to
the current week" file, and save it in the "codes"
folder as "eopc04.txt". If the
file is present, and the observation date falls within the table's span, CODES
will automatically read the relevant EOPs, and skip the third frame. If the file is not present, or if the
observation date is not covered by the table, CODES will proceed to the third
frame for manual entry of the EOPs.
Note: For radar data, accuracies of 0.1 microsecond or 30
meters are typical. My sensitivity analyses indicate that 1 meter accuracy
could be supported without interpolating the published EOPs. However, the
state-of-the-art is advancing so rapidly that I feel it prudent to accommodate
future radar technology (up to 0.1 meter accuracy); thus, second-order
interpolation of the EOPs is used.
IMPORTANT: Unless otherwise noted, do not leave any data fields
blank! This can cause a run-time error.
IMPORTANT: From either of the three input frames, it is possible to cancel
the input function and return to the Level Two Menu; the new
(and incomplete) observation will be deleted.
When complete,
CODES will save the data to disk and return to the Level Two Menu.
The Minor Planet
Center (MPC) provides free web-based electronic circulars
containing formatted tables of new observations of recently discovered and
high-interest minor planets. The MPC also provides an Extended Computer Service
called MPCOBS which enables users to extract files containing all observations
of a specific minor planet.
With some help from
the user, CODES can batch-process the entire set of observations contained in
each of these files, thus avoiding the need for manual input.
Simply click on
"MPC". The next frame will ask the user to save the MPEC or MPCOBS
file (from the web browser or text editor) as ''mpec.txt'' in the ''codes''
folder, using file-type "text file" or ''text-only".
IMPORTANT: Some MPECs include observations of many minor
planets. In such cases, the user should edit out the observations of other
minor planets, leaving only the observations of the desired minor planet.
Note: Users will often want to refine computed orbits (and
collision analyses) using additional observations as they become available.
However, MPECs and MPC files list all observations of the subject minor
planet, including those which CODES has (presumably) previously processed. To
avoid the creation of duplicate entries, CODES checks each observation as it is
being processed; if an observation with the same date, observation location,
and measurement already exists, CODES will ignore this observation and skip to
the next.
When ready, simply
click on "Process".
The MPC format
allows CODES to extract the following data for each observation:
- UTC time of observation (receive-time for
radar observations)
- observational measurement plus uncertainty
(right ascension, declination, and visual magnitude for optical
observations, delay and/or doppler for radar observations)
- Observer location (including MPC observatory
code for fixed optical observations, lat/long/alt for roving observers,
x/y/z for satellite observations, and both transmitter and receiver MPC
observatory codes for radar observations)
CODES then either
reads or generates default Earth Orientation Parameters and processes the
observation.
IMPORTANT: CODES now supports use of the International
Earth Rotational Service's "EOPC04" tables. Simply download the current "Series from 1962 to
the current week" file, and save it in the "codes"
folder as "eopc04.txt". If the
file is present, and the observation date falls within the table's span, CODES
will automatically read the relevant EOPs and use them in determining the
observer's position. If the file is not
present, or if the observation date is not covered by the table, CODES will
generate default EOPs.
IMPORTANT: At present, the default EOPs determine observer
position to within about 1 km. While this accuracy is sufficient for current
optical observations whose precision average about 0.1 arc seconds (and
irrelevant for satellite observations, whose observer positions are read
directly from the observation data record), it will not fully support
highly-precise radar delay and/or doppler observations. The user is
therefore strongly urged to ensure the current "eopc04.txt" file is
available for processing any radar observations.
IMPORTANT: The MPC is constantly certifying new contributing
observatories. If a user were to process an MPEC or MPCOBS file containing
observations from a new observatory that is not on the CODES look-up table, the
quality of derived data would be severely degraded. The user is therefore
advised to periodically either check this web site or contact me for updated copies of the "ObsCode.txt"
file. New versions of the file should overwrite the existing version in the
"codes" folder/directory.
Note: CODES supports observations and predictions for the
range 1800-2200.
When complete,
CODES will save the data to disk and return to the Level Two Menu.
The Near-Earth
Objects Dynamic Site (NEODyS) provides web-based data on every known Near-Earth
Object (NEO). Start at the search page,
and enter the name, number, or designation of an NEO; a web page is dynamically
created providing the user with data on that NEO.
Near the bottom of
the web page, under "Observational Information:", click on the
"ASCII file" link. The user will be provided with a formatted table
containing all known observations of the NEO. With some help from the user,
CODES can batch-process the entire set of observations, thus avoiding the need
for manual input.
Simply click on
"NEODyS". The next frame will ask the user to save the NEODyS file
from the web browser as ''neodys.txt'' in the ''codes'' folder, using file-type
"text file" or ''text-only".
Note: Users will often want to refine computed orbits (and
collision analyses) using additional observations as they become available.
However, NEODyS files list all observations of the subject minor planet,
including those which CODES has (presumably) previously processed. To avoid the
creation of duplicate entries, CODES checks each observation as it is being
processed; if an observation with the same date, observation location, and
measurement already exists, CODES will ignore this observation and skip to the
next.
When ready, simply
click on "Process".
The NEODyS format
allows CODES to extract the following data for each observation:
- UTC time of observation (receive-time for
radar observations)
- observational measurement plus uncertainty
(right ascension, declination, and visual magnitude for optical
observations, delay or doppler for radar observations)
- Observer location (including MPC observatory
code for fixed optical observations, and both transmitter and receiver
MPC observatory codes for radar observations)
CODES then either
reads or generates default Earth Orientation Parameters and processes the
observation.
IMPORTANT: CODES now supports use of the International
Earth Rotational Service's "EOPC04" tables. Simply download the current "Series from 1962 to
the current week" file, and save it in the "codes"
folder as "eopc04.txt". If the
file is present, and the observation date falls within the table's span, CODES
will automatically read the relevant EOPs and use them in determining the
observer's position. If the file is not
present, or if the observation date is not covered by the table, CODES will
generate default EOPs.
IMPORTANT: At present, the default EOPs determine observer
position to within about 1 km. While this accuracy is sufficient for current
optical observations whose precision average about 0.1 arc seconds (and
irrelevant for satellite observations, whose observer positions are read
directly from the observation data record), it will not fully support
highly-precise radar delay and/or doppler observations. The user is therefore
strongly urged to ensure the current "eopc04.txt" file is available
for processing any radar observations.
IMPORTANT: The MPC is constantly certifying new contributing
observatories. If a user were to process a NEODyS file containing observations
from a new observatory that is not on the CODES look-up table, the quality of
derived data would be severely degraded. The user is therefore advised to
periodically either check this web site or contact me for updated copies of the "ObsCode.txt"
file. New versions of the file should overwrite the existing version in the
"codes" folder.
IMPORTANT: There are currently no "roving observer" or
satellite-based observations of Near-Earth Objects in the NEODyS database.
Should they appear in the future, I believe "roving observer"
observations would be listed in a NEODyS file with observatory code
"247", while satellite observations would be listed with observatory
code "248" (Hipparcos), "249" (SOHO), or "250"
(Hubble Space Telescope). Since there is no fixed position associated with
these observatories, there is no way to accurately calculate the observer
position with the data provided. The user is therefore urged to get the data
for these observations from an MPEC or MPCOBS file.
Note: CODES supports observations and predictions for the
range 1800-2200.
When complete,
CODES will save the data to disk and return to the Level Two Menu.
This option permits
the user to review the observations that exist for the given minor planet, and
to exclude those observations (if desired) which are found to have
exceptionally high residuals.
From the Level Two Menu, simply click "Rev/Del". From the resulting
frame, the user can review observations five-at-a-time. The user can delete one
or more of the displayed observations by checking the box to the left of the
observation(s), then clicking "Delete Checked". When more than five
observations exist, the user can click on the "Next 5" and "Prev
5" buttons to cycle through the entire list.
When done, simply
click on "Done"; CODES will save the data to disk and return to the Level Two Menu.
Simply click on
"Compute". From the resulting menu, select one of the four options:
Once at least three
observations exist for a minor planet, it is possible to calculate an initial
orbit using two-body mechanics (This initial orbit can later be refined by
using integrated n-body mechanics to calculate a best-fit least-squares orbit -
see "Compute an n-body best-fit orbit"). If only two observations exist, an orbit can
be estimated based on additional user-inputs.
Simply click "Initial". On the resulting
frame, use the drop-down menus to select which three observations to use in calculating the initial orbit. (Note: Only the first two selections will be
used in Herget's method.)
Knowing which
observations to use requires some judgment. The objective is to cover a
significant arc of the full orbit. For distant minor planets such as
Trans-Neptunian Objects, it may be necessary to have an arc of data covering
tens or even hundreds of days to get a good initial orbit; conversely, a
Near-Earth Object or a minor planet in the main asteroid belt may require an
arc of just a few days. My best advice is to experiment. If all of the initial
orbit methods diverge or give absurdly high residuals, pick another set of
observations.
Once the user has
made the selections, simply press "Submit". From the resulting menu,
the user must now select which method of initial orbit determination to try.
I have attempted to
make these methods as robust as possible. However, each algorithm has inherent
limits.
- The Gauss method is clearly the very best, and
it is always my first choice. If the iterative algorithm is successful,
the calculated orbit will contain the three observations; thus, you can
immediately accept the orbit (and skip differential correction, since
the residuals will be near zero). However, Gauss is sometimes less
successful for Near-Earth Objects.
Simply click on
"Gauss". The resulting frame will display the calculated state vector
and derived orbital elements for the minor planet at the TDB time of the first
selected observation. The two-body residuals for each selected observation will
be displayed, as well as a message warning if the iterative algorithm has diverged
(in which case the first-approximation to the orbital elements/state vector is
displayed).
The user will have several options.
1.
If satisfied with the
initial orbit, simply click on the "Select" button next to
"Accept This Orbit"; the initial orbit will be saved to disk, and
CODES will return to the Level Two Menu.
2.
If the residuals are
non-zero, the user may elect to click on the "Select" button next to
"Apply Differential Correction". The same frame will appear, displaying
the resulting state vector and derived orbital elements for the minor planet at
the TDB time of the first selected observation. The two-body residuals for each
selected observation will be displayed, as well as a message warning if the
differential correction algorithm has diverged (in which case the original
Gauss method orbital elements/state vector is displayed). When differential
correction converges successfully to zero residuals, the user can accept the
orbit. But when differential correction diverges, it's usually necessary to try
another method, or to select
another set of three observations.
3.
If the Gauss method
and/or differential correction have diverged, the user may elect to click on the "Select" button next to
"Try Another Method". In this case, the three selected observations
are retained, and CODES returns to the menu of methods of initial orbit
determination.
4.
If none of the three
methods of initial orbit determination has converged successfully, the user may elect to click on the
"Select" button next to "Try a Different Set of Three
Observations". In this case, CODES returns to the frame with the drop-down
menus to select a new set of t