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OPM — Orbit Parameter Message

Parses CCSDS Orbit Parameter Messages containing a single state vector with optional Keplerian elements, spacecraft parameters, maneuvers, and covariance data.

OPM 

OPM(originator: Any, object_name: Any, object_id: Any, center_name: Any, ref_frame: Any, time_system: Any, epoch: Any, position: Any, velocity: Any)

Python wrapper for CCSDS Orbit Parameter Message (OPM).

Scalar metadata is exposed as properties with getters and setters. Maneuvers are accessed via the maneuvers property which supports indexing, iteration, and mutation.

Example 
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from brahe.ccsds import OPM

opm = OPM.from_file("state.opm")
print(opm.position)
opm.object_name = "NEW_SAT"
print(len(opm.maneuvers))
m = opm.maneuvers[0]
print(m.ref_frame)
m.ref_frame = "RTN"

Initialize instance.

arg_of_pericenter property 

arg_of_pericenter: float

Argument of pericenter in degrees, or None.

Returns:

Name Type Description
float float

Argument of pericenter (degrees), or None

center_name property 

center_name: str

Center body name.

Returns:

Name Type Description
str str

Center name

creation_date property 

creation_date: Epoch

Creation date of the message.

Returns:

Name Type Description
Epoch Epoch

Creation date

drag_area property 

drag_area: float

Drag area in m^2, or None.

Returns:

Name Type Description
float float

Drag area (m^2), or None

drag_coeff property 

drag_coeff: float

Drag coefficient, or None.

Returns:

Name Type Description
float float

Drag coefficient, or None

eccentricity property 

eccentricity: float

Eccentricity, or None if no Keplerian elements.

Returns:

Name Type Description
float float

Eccentricity, or None

epoch property 

epoch: Epoch

State vector epoch.

Returns:

Name Type Description
Epoch Epoch

Epoch of the state vector

format_version property 

format_version: float

CCSDS format version.

Returns:

Name Type Description
float float

Format version

gm property 

gm: float

Gravitational parameter in m^3/s^2, or None.

Returns:

Name Type Description
float float

GM (m^3/s^2), or None

has_keplerian_elements property 

has_keplerian_elements: bool

Whether Keplerian elements are present.

Returns:

Name Type Description
bool bool

True if Keplerian elements exist

inclination property 

inclination: float

Inclination in degrees, or None if no Keplerian elements.

Returns:

Name Type Description
float float

Inclination (degrees), or None

maneuvers property 

maneuvers: OPMManeuvers

Maneuver collection, supporting len/indexing/iteration.

Returns:

Name Type Description
OPMManeuvers OPMManeuvers

Collection of maneuvers

mass property 

mass: float

Spacecraft mass in kg, or None.

Returns:

Name Type Description
float float

Mass (kg), or None

mean_anomaly property 

mean_anomaly: float

Mean anomaly in degrees, or None.

Returns:

Name Type Description
float float

Mean anomaly (degrees), or None

object_id property 

object_id: str

Object ID (international designator).

Returns:

Name Type Description
str str

Object ID

object_name property 

object_name: str

Object name.

Returns:

Name Type Description
str str

Object name

originator property 

originator: str

Originator of the message.

Returns:

Name Type Description
str str

Originator string

position property 

position: ndarray

Position vector [x, y, z] in meters.

Returns:

Type Description
ndarray

numpy.ndarray: Position [x, y, z] in meters

ra_of_asc_node property 

ra_of_asc_node: float

Right ascension of ascending node in degrees, or None.

Returns:

Name Type Description
float float

RAAN (degrees), or None

ref_frame property 

ref_frame: str

Reference frame name.

Returns:

Name Type Description
str str

Reference frame

semi_major_axis property 

semi_major_axis: float

Semi-major axis in meters, or None.

Returns:

Name Type Description
float float

Semi-major axis (meters), or None

solar_rad_area property 

solar_rad_area: float

Solar radiation pressure area in m^2, or None.

Returns:

Name Type Description
float float

Solar radiation pressure area (m^2), or None

solar_rad_coeff property 

solar_rad_coeff: float

Solar radiation pressure coefficient, or None.

Returns:

Name Type Description
float float

Solar radiation pressure coefficient, or None

state property 

state: ndarray

Combined state vector [x, y, z, vx, vy, vz] as a numpy array.

Returns:

Type Description
ndarray

numpy.ndarray: 6-element state vector (position in meters, velocity in m/s)
Example 
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opm = OPM.from_file("state.opm")
state = opm.state  # numpy array [x, y, z, vx, vy, vz]

time_system property 

time_system: str

Time system name.

Returns:

Name Type Description
str str

Time system

true_anomaly property 

true_anomaly: float

True anomaly in degrees, or None.

Returns:

Name Type Description
float float

True anomaly (degrees), or None

velocity property 

velocity: ndarray

Velocity vector [vx, vy, vz] in m/s.

Returns:

Type Description
ndarray

numpy.ndarray: Velocity [vx, vy, vz] in m/s

add_maneuver method descriptor 

add_maneuver(epoch_ignition: Epoch, duration: float, ref_frame: str, dv: list[float], delta_mass: float | None = None) -> int

Add a maneuver to the OPM.

Parameters:

Name Type Description Default
epoch_ignition Epoch

Epoch of ignition

 required
duration float

Duration in seconds

 required
ref_frame str

Reference frame for delta-V

 required
dv list[float]

Delta-V [dv1, dv2, dv3] in m/s

 required
delta_mass float | None

Mass change in kg

 None

Returns:

Name Type Description
int int

Index of the new maneuver

from_file staticmethod 

from_file(path: str) -> OPM

Parse an OPM from a file, auto-detecting the format.

Parameters:

Name Type Description Default
path str

Path to the OPM file

 required

Returns:

Name Type Description
OPM OPM

Parsed OPM message

from_str staticmethod 

from_str(content: str) -> OPM

Parse an OPM from a string, auto-detecting the format.

Parameters:

Name Type Description Default
content str

String content of the OPM message

 required

Returns:

Name Type Description
OPM OPM

Parsed OPM message

remove_maneuver method descriptor 

remove_maneuver(idx: int) -> Any

Remove a maneuver by index.

Parameters:

Name Type Description Default
idx int

Index of the maneuver to remove

 required

state_in_frame method descriptor 

state_in_frame(frame: CelestialFrame | ReferenceFrame) -> ndarray

State vector expressed in frame at the state-vector epoch.

The message's REF_FRAME chooses the axes and its CENTER_NAME chooses the origin of the frame the data is expressed in, and the state is converted from there through the reference frame router. A message declared in TOD about Earth yields a GCRF state directly usable for propagation, and one declared in EME2000 about the Moon converts to any frame the router reaches from Moon-centered EME2000 axes.

A TOD message that also carries a REF_FRAME_EPOCH names the true-of-date axes frozen at that epoch, and its state is converted from TOD at the frame epoch before routing.

Parameters:

Name Type Description Default
frame CelestialFrame | ReferenceFrame

Target reference frame

 required

Returns:

Type Description
ndarray

numpy.ndarray: 6-element state vector [x, y, z, vx, vy, vz] in frame (position in meters, velocity in m/s)

Raises:

Type Description
BraheError

If REF_FRAME has no FrameAxes equivalent, if CENTER_NAME is not a known NAIF body name or ID, or if the router cannot convert between the two frames
Example 
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import brahe as bh
from brahe.ccsds import OPM

bh.initialize_eop()
opm = OPM.from_file("test_assets/ccsds/opm/OPMExample2.txt")
x_gcrf = opm.state_in_frame(bh.CelestialFrame.GCRF)

to_dict method descriptor 

to_dict() -> dict

Convert the OPM to a Python dictionary.

Epochs are serialized as CCSDS datetime strings for JSON/dict compatibility.

Returns:

Name Type Description
dict dict

Dictionary representation of the OPM

to_file method descriptor 

to_file(path: str, format: str) -> Any

Write the OPM to a file in the specified format.

Parameters:

Name Type Description Default
path str

Output file path

 required
format str

Output format - "KVN", "XML", or "JSON"

 required

to_json_string method descriptor 

to_json_string(uppercase_keys: bool = False) -> str

Write the OPM to JSON with explicit key case control.

Parameters:

Name Type Description Default
uppercase_keys bool

If True, use uppercase CCSDS keywords. Default: False.

 False

Returns:

Name Type Description
str str

Serialized JSON string

to_string method descriptor 

to_string(format: str) -> str

Write the OPM to a string in the specified format.

Parameters:

Name Type Description Default
format str

Output format - "KVN", "XML", or "JSON"

 required

Returns:

Name Type Description
str str

Serialized OPM string

See Also