Trajectories
A trajectory is a series of state vectors (position, velocity, time and covariance) related to a single object. Depending on the file format, it may contain other metadata as well.
Supported Formats
Our system supports both OEM (Orbital Ephemeris Message), Modified ITC, UTC, and NASA formats for trajectories.
If a file starts with "CCSDS_OEM_VERS", the system attempts to parse it as an OEM file. If the file contains the headers "time", "pos.x", and "vel.x" as the ephemeris data field headers, the system attempts to parse it as an UTC file. Otherwise, it attempts to parse it as a Modified ITC file.
OEM (Orbital Ephemeris Message)
OEM (Orbital Ephemeris Message) format is defined in Section 5, and Section 7.7.2, of the CCSDS spec (link)
We accept a subset of OEM-formatted trajectories, subject to the supported reference frames and time systems (below) and the general trajectory requirements.
Sample OEM File
CCSDS_OEM_VERS = 3.0
CREATION_DATE = 2023-11-06T02:08:15.481374Z
ORIGINATOR = SPACEX/USA
META_START
OBJECT_NAME = STARLINK-3179
OBJECT_ID = 31790
CENTER_NAME = EARTH
REF_FRAME = ITRF
TIME_SYSTEM = UTC
START_TIME = 2023-11-06T02:09:42.000000Z
STOP_TIME = 2023-11-06T02:15:42.000000Z
META_STOP
2023-11-06T02:09:42.000000Z -4.542752e+03 -3.316417e+03 3.877276e+03 4.819418e+00 9.779460e-02 5.717377e+00
2023-11-06T02:10:42.000000Z -4.243593e+03 -3.304426e+03 4.211322e+03 5.149116e+00 3.012760e-01 5.413318e+00
2023-11-06T02:11:42.000000Z -3.925285e+03 -3.280348e+03 4.526387e+03 5.457463e+00 5.005622e-01 5.084935e+00
2023-11-06T02:12:42.000000Z -3.589152e+03 -3.244456e+03 4.821057e+03 5.743052e+00 6.949538e-01 4.733722e+00
2023-11-06T02:13:42.000000Z -3.236600e+03 -3.197065e+03 5.094009e+03 6.004573e+00 8.837872e-01 4.361276e+00
2023-11-06T02:14:42.000000Z -2.869109e+03 -3.138526e+03 5.344019e+03 6.240812e+00 1.066436e+00 3.969275e+00
2023-11-06T02:15:42.000000Z -2.488230e+03 -3.069228e+03 5.569967e+03 6.450669e+00 1.242312e+00 3.559489e+00
COVARIANCE_START
EPOCH = 2023-11-06T02:09:42.000000Z
COV_REF_FRAME = RTN
1.000000e+00
0.000000e+00 1.000000e+02
0.000000e+00 0.000000e+00 6.400000e-01
0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
EPOCH = 2023-11-06T02:10:42.000000Z
COV_REF_FRAME = RTN
1.000000e+00
0.000000e+00 1.000000e+02
0.000000e+00 0.000000e+00 6.400000e-01
0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
EPOCH = 2023-11-06T02:11:42.000000Z
COV_REF_FRAME = RTN
1.000000e+00
0.000000e+00 1.000000e+02
0.000000e+00 0.000000e+00 6.400000e-01
0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
EPOCH = 2023-11-06T02:12:42.000000Z
COV_REF_FRAME = RTN
1.000000e+00
0.000000e+00 1.000000e+02
0.000000e+00 0.000000e+00 6.400000e-01
0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
EPOCH = 2023-11-06T02:13:42.000000Z
COV_REF_FRAME = RTN
1.000000e+00
0.000000e+00 1.000000e+02
0.000000e+00 0.000000e+00 6.400000e-01
0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
EPOCH = 2023-11-06T02:14:42.000000Z
COV_REF_FRAME = RTN
1.000000e+00
0.000000e+00 1.000000e+02
0.000000e+00 0.000000e+00 6.400000e-01
0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
EPOCH = 2023-11-06T02:15:42.000000Z
COV_REF_FRAME = RTN
1.000000e+00
0.000000e+00 1.000000e+02
0.000000e+00 0.000000e+00 6.400000e-01
0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 0.000000e+00 1.000000e-08
COVARIANCE_STOP
Reference Frame and Time Systems
SpaceX supports a subset of the reference frames and time systems outlined in the OEM format.
For position and velocity, we support:
- ITRF (specifically, ITRF2008)
- EME2000
Note the supported covariance reference frames diverge from the OEM standard which requires COV_REF_FRAME, if specified, to be one of RTN, RSW, TNW; however, the standard also says if COV_REF_FRAME is not provided then the covariance matrices shall be specified in the reference frame of the position and velocity. For this reason we support the following covariance reference frames:
- RTN
- ITRF
- EME2000
If COV_REF_FRAME is specified then it currently must be specified for every covariance matrix. Covariance timestamps should have a 1-to-1 mapping with state vector timestamps, so a covariance matrix should be present for every position. There may be more covariance matrices than position states, but this is not recommended and the additional matrices will be ignored.
The preferred reference frame for position and velocity is ITRF as this is the native frame that the system uses during screening.
Timestamps must be in UTC in a date time string format as specified by the OEM standard. The standard for OEM files suggests GPS time is supported, but does not specify a format for this field and thus is not currently supported.
Modified ITC Format
Modified ITC format is described in the 18th Space Control Squadrons SpaceFlight Safety Handbook, p. 19.
It consists of three header lines (which can contain any information), the covariance reference frame (which must be UVW), and then blocks of 4 lines, each with 7 space-separated elements.
The the first line in each block contains a timestamp in yyyyDOYhhmmss.sss format, followed by 3 values representing position (in kilometers) and 3 values representing velocity (in kilometers per second).
The next three lines in each block contain the 21 covariance values that comprise the 6x6 lower triangular of the position and velocity covariance matrix.
Sample Modified ITC File
Arbitrary header line 1
Arbitrary header line 2
Arbitrary header line 3
UVW
2024050151742.000 -2717.6470601984 -4974.3191485700 -4003.8489578142 6.8863163410 -1.5414737334 -2.7602780986
4.8636600485e-07 -3.9604629126e-07 7.8226290555e-07 4.2441083688e-11 2.6517660097e-10 1.2714198064e-06 8.3869086144e-10
-9.1266964668e-10 -1.1434249337e-12 1.9517000894e-12 -4.7079913171e-10 4.1138462966e-10 1.5765230207e-12 -8.2452740364e-13
5.0047937509e-13 1.4246847775e-13 -4.1273571730e-14 1.7106743443e-09 -5.6529845602e-16 1.9599736772e-15 5.4193431704e-12
2024050151842.000 -2298.9370987377 -5056.0774012191 -4160.7397897232 7.0656847685 -1.1828389855 -2.4675503309
5.3668884512e-07 -4.6349648374e-07 8.9188710483e-07 2.2657306466e-11 4.1969964753e-10 1.4901772822e-06 9.3834041889e-10
-1.0554116634e-09 -1.4669001660e-12 2.1644646970e-12 -5.2134920301e-10 4.7989466356e-10 1.9467875434e-12 -9.2510091658e-13
5.5115563161e-13 -6.2106982707e-14 3.6103206656e-13 1.9303401098e-09 -1.2228009283e-15 2.5324132092e-15 5.1873702211e-12
2024050151942.000 -1870.3713992359 -5116.1597668306 -4299.7439511044 7.2147314742 -0.8192017657 -2.1642714468
5.9006079559e-07 -5.3882512561e-07 1.0195567578e-06 -1.3771040498e-11 6.3733209461e-10 1.7334464112e-06 1.0452685485e-09
-1.2166219092e-09 -1.8938654797e-12 2.3930449422e-12 -5.7506522394e-10 5.5642533914e-10 2.3795659970e-12 -1.0332529542e-12
6.0512086419e-13 -2.9804491596e-13 8.4437284811e-13 2.1186487133e-09 -1.9788406146e-15 3.1034656668e-15 4.9262055184e-12
2024050152042.000 -1433.7884241893 -5154.3126003016 -4420.2672971496 7.3328314432 -0.4521145181 -1.8517422544
6.4629918545e-07 -6.2231422941e-07 1.1673052992e-06 -6.9880168142e-11 9.2829929550e-10 1.9972680301e-06 1.1594136677e-09
-1.3978410559e-09 -2.4368514208e-12 2.6385236017e-12 -6.3176770168e-10 6.4127556470e-10 2.8710610744e-12 -1.1489225028e-12
6.6220600395e-13 -5.6414853767e-13 1.4047888592e-12 2.2723791834e-09 -2.8209246194e-15 3.6607115289e-15 4.6405757642e-12
2024050152142.000 -991.0605167036 -5170.3758219631 -4521.7947711535 7.4194907986 -0.0831429500 -1.5313016964
7.0518100260e-07 -7.1418173349e-07 1.3372285671e-06 -1.4882993649e-10 1.3018125275e-09 2.2773278566e-06 1.2806715117e-09
-1.6006203035e-09 -3.1070484611e-12 2.9019859455e-12 -6.9123111871e-10 7.3466570109e-10 3.4158648671e-12 -1.2719836762e-12
7.2218468549e-13 -8.5898387215e-13 2.0360902508e-12 2.3888998991e-09 -3.7334432682e-15 4.1915570184e-15 4.3356265560e-12
2024050152242.000 -544.0856347396 -5164.2835175237 -4603.8926704131 7.4743487591 0.2861406689 -1.2043205866
7.6644312550e-07 -8.1456800326e-07 1.5314682612e-06 -2.5366343254e-10 1.7657644294e-09 2.5690345067e-06 1.4088817061e-09
-1.8265087523e-09 -3.9126280543e-12 3.1845030192e-12 -7.5318689788e-10 8.3673660071e-10 4.0067533860e-12 -1.4022545288e-12
7.8478607542e-13 -1.1796772309e-12 2.7294684753e-12 2.4662168584e-09 -4.6970053365e-15 4.6842571860e-15 4.0168296254e-12
2024050152342.000 -94.7793264969 -5136.0641534569 -4666.2103603739 7.4971784041 0.6541639374 -0.8721961963
8.2978665389e-07 -9.2352896570e-07 1.7521907912e-06 -3.8718873889e-10 2.3263994870e-09 2.8675972585e-06 1.5438265252e-09
-2.0770408763e-09 -4.8584806577e-12 3.4871261888e-12 -8.1732733532e-10 9.4753916942e-10 4.6349705452e-12 -1.5394908176e-12
8.4969679543e-13 -1.5220529319e-12 3.4736021911e-12 2.5030064375e-09 -5.6890352084e-15 5.1279537308e-15 3.6898907529e-12
Reference Frame and Time Systems
Per the Modified ITC specification, position and velocity must be provided in the EME2000 reference frame, and covariance must be in the UVW (a.k.a RTN) reference frame. All timestamps must be in UTC.
JSpOC
JSpOC format ephemeris files contain "JSpOC Format Ephemeris Report" in its header.
Additional Notes: if a date field is provided in the header it will be parsed as the creation date for the Ephemeris File and the spacecraft field will be parsed as the object name field
Each ephemeris data line follows the following format where each piece of data is seperated by a whitespace:
yyDOYhhmmss.sss Pos.x(km) Pos.y(km) Pos.z(km) Vel.x(km/sec) Vel.y(km/sec) Vel.z(km/sec)
Sample JSpOC File
JSpOC Format Ephemeris Report
Signature: Temp
Notice: Temp
Extracted: 2025/05/20 05:00:00
Title: ECI Position-Velocity Ephemeris Report
Subtitle: State: 00000 in Temp.state [events from /Temp.event]
Ephemeris: Temp.out
Spacecraft: Temp
Equinox: J2000
UTC ECI Pos.x ECI Pos.y ECI Pos.z ECI Vel.x ECI Vel.y ECI Vel.z
km km km km/sec km/sec km/sec
25145000000.000 -10000.26301680 -10000.03352560 100.58630839000 2.971470157880 -1.317083147990 -1.433513532251
25145001000.000 -10000.30339340 -10000.52147570 100.45335376000 1.071084180040 -1.227153237990 -1.440123779379
25145002000.000 -10000.75405010 -10000.76670430 100.60602660000 1.166738206140 -1.132970061090 -1.445892812286
25145003000.000 -10000.04605150 -10000.27082080 100.55242578000 1.258249966530 -1.034713499170 -1.450809665145
25145004000.000 -10000.71747290 -10000.64569900 100.80674417000 1.345445086280 -2.932571160320 -1.454864993608
25145005000.000 -10000.40856400 -10000.61800650 100.88829053600 1.428157412950 -1.826738023250 -1.458051092148
25145010000.000 -10000.85671880 -10000.03351860 100.32050124200 1.506229328940 -2.717416067080 -1.460361908317
25145011000.000 -10000.89126910 -10000.86120140 100.62994576600 1.579512047410 -2.604813889230 -1.461793053867
25145012000.000 -10000.42809880 -10000.19706700 100.34532504500 1.647865891680 -2.489146310580 -1.462341812795
25145013000.000 -10000.46409930 -10000.26778540 -100.00353323300 1.711160558150 -2.370633969630 -1.462007146335
25145014000.000 -10000.07146780 -10000.43405250 -100.88668226500 1.769275361480 -2.249502905450 -1.460789694758
25145015000.000 -10000.39187280 -10000.19369980 -100.77506242500 1.822099461400 -2.125984130810 -1.458691776054
25145020000.000 -10000.63048000 -10000.18455040 -100.14150732000 1.869532071370 -2.000313196460 -1.455717381512
25145021000.000 -10000.04986280 -10000.18700830 -100.46174551000 1.911482648730 -1.872729746814 -1.451872168171
25145022000.000 -10000.96380450 -10000.12637940 -100.21539678000 1.947871066180 -1.743477067983 -1.447163448243
Reference Frame and Time Systems
Per the UTC specification, position and velocity must be provided in the EME2000 reference frame. All timestamps must be in UTC.
UTC
The UTC format is described in the 18th Space Control Squadrons SpaceFlight Safety Handbook, p. 22.
It consists of up to 21 header lines (which can contain any information) and then each ephmeris data line seperated by a newline character.
Additional Notes: if a date field is provided in the header it will be parsed as the creation date for the Ephemeris File and the spacecraft field will be parsed as the object name field
Each ephemeris data line follows the following format where each piece of data is seperated by a whitespace:
yyyy/mm/dd hh:mm:ss.sss Pos.x(km) Pos.y(km) Pos.z(km) Vel.x(km/sec) Vel.y(km/sec) Vel.z(km/sec)
Sample UTC File
Version: 1
Description: 123.eph
Date: 2010/10/07 13:43:20
Path: M://temp
Spacecraft: W
Ephemeris: /M=temp
Equinox: MEME of Epoch [JD2000] FKS
Attitude: AttitudeReference
Report Span Initial: 2010/10/07 00:00:00.000
Report Span Delta: 25.00 days
Report Span Final: 2010/11/01 00:00:00.000
Ephemeris Parameter Report
==========================
Title: CMOC Ephemeris
Subtitle: 123.eph
Absolute Time ECI Pos.x ECI Pos.y ECI Pos.z ECI Vel.x ECI Vel.y ECI Vel.z
UTC.YmdHMs3 km km km km/sec km/sec km/sec
2025/04/25 00:00:00.000 123.030 123.601 123.940776 -1.65403338 1.0051482 -1.00052720904
2025/04/25 00:10:00.000 123.289 123.533 123.241643 -1.78487517 1.9736690 -1.00047552861
2025/04/25 00:20:00.000 123.480 123.865 123.511217 -0.91421506 1.9364935 -1.00042291383
2025/04/25 00:30:00.000 123.581 123.200 123.748969 -0.0418050 1.8936928 -1.00036946642
2025/04/25 00:40:00.000 123.713 123.188 123.954429 -0.1674005 1.8453490 -1.00031528977
2025/04/25 00:50:00.000 123.147 123.529 123.127192 -0.2907606 1.7915545 -1.00026048880
2025/04/25 01:00:00.000 123.295 123.984 123.266915 -0.4116488 1.7324127 -1.00020516972
2025/04/25 01:10:00.000 123.709 123.377 123.373320 -0.5298334 1.6680367 -1.00014943982
2025/04/25 01:20:00.000 123.081 123.606 123.446191 -0.6450877 1.5985502 -1.3407251e-05
2025/04/25 01:30:00.000 123.234 123.642 123.485380 -0.7571908 1.5240862 -1.7180857e-05
2025/04/25 01:40:00.000 123.125 123.542 123.490804 -0.8659278 1.4447875 -1.9130104e-05
Reference Frame and Time Systems
Per the UTC specification, position and velocity must be provided in the EME2000 reference frame. All timestamps must be in UTC.
NASA
NASA format is described in the 18th Space Control Squadrons SpaceFlight Safety Handbook, p. 16.
If a file starts with ephemeris data with the EPOCH time in the format of yyDOYhhmmss.sss, the system attempts to parse it as a NASA file.
Each ephemeris data line follows the following format where each piece of data is seperated by a whitespace:
yyDOYhhmmss.sss Pos.x(km) Pos.y(km) Pos.z(km) Vel.x(km/sec) Vel.y(km/sec) Vel.z(km/sec)
Sample NASA File
24139151515.941 1234.789233128217 1234.6679672997861 -1234.0632350510487 -1.280984952575874 -1.356520309663561 -1.452930500514071
24139151520.941 1234.638788344994 1234.982823505116 -1234.372714366011 -1.3490349592296207 -1.380459506678761 -1.408833822878206
24139151525.941 1234.809928643115 1234.05976081613 -1234.2372900871774 -1.4166665579039575 -1.4041036099782938 -1.363950721931851
24139151530.941 1234.30687936067 1234.9017444633027 -1234.6491263423895 -1.483871506347982 -1.4274497672210185 -1.318286885401791
24139151535.941 1234.133947974557 1234.5117680104026 -1234.6004446015413 -1.550641619196526 -1.4504951641337227 -1.271848093838132
24139151540.941 1234.2955235272575 1234.8928529724622 -1234.0835246008664 -1.6169687688438135 -1.4732370247832023 -1.224640219830324
24139151545.941 1234.796076044852 1234.0480484309956 -1234.0907052594293 -1.682844886323058 -1.4956726118518793 -1.176669227223457
24139151550.941 1234.640155946205 1234.9804306464578 -1234.614385587748 -1.748261962193282 -1.517799226916484 -1.127941170330231
24139151555.941 1234.832393443233 1234.6931026678906 -1234.6470255884838 -1.813212047433452 -1.53961421072891 -1.078462193133779
24139151600.941 1234.377497932218 1234.1891939397728 -1234.181147149108 -1.8776872543429026 -1.5611149434979614 -1.028238528477105
24139151605.941 1234.280257376076 1234.4718599060361 -1234.209334926385 -1.941679757445915 -1.5822988451703894 -1.977276497235064
Reference Frame and Time Systems
Per the NASA specification, position and velocity must be provided in the EME2000 reference frame. All timestamps must be in UTC.
Trajectory Requirements
Structure
In order to efficiently screen the catalog, we enforce the following constraints on trajectory files:
- We recommend submitting your trajectory file with covariance although it is not required. (See Note below.)
- Trajectory files must have at least some state vectors in the future
- Trajectory files must span less than 7 days
- Trajectory files must have at least 6 data points
- Trajectory files must span a minimum 42 seconds
- Trajectory files must be in a supported reference frame and time system
If an operator submits a trajectory file that violates any of these requirements, they will receive an HTTP 400 (Bad Request) response with a helpful error message.
Covariance Note: If covariance matrices are provided then every state vector must have an associated positive semi-definite covariance matrix. If no covariance is provided then Collision Probability will not be generated for conjunctions against this trajectory and the CDM file will have a NULL value for the COLLISION_PROBABILITY field (This diverges from the CDM CCSDS standard).
Trajectory Submission Types
The POST /api/v1/trajectory endpoint requires that an operator submits trajectories with an upload_type parameter, which is one of three options, described below:
Definitive trajectories indicate the trajectory a satellite is intended to fly. It is shared with all the users of the system, and the screening system's catalog assumes that the most-recently-submitted definitive trajectory is the best estimate for where an object is going to be.
Hypothetical trajectories provide a mechanism for operators to do one-off screening of maneuvers without updating an object's definitive trajectory or confusing other operators. They aren't inserted into the catalog for future trajectory submissions to screen against, and they (and their results) are only visible to the submitting operator.
Candidate trajectories provide a hybrid approach to save operators an API call; they are screened as if they are hypothetical trajectories, but if the system determines they are "safe" (according to a risk tolerance supplied by the operator), they will be converted to a "definitive" trajectory.
To summarize:
| Upload Type | Use Case | Catalog Semantics | Permissions |
|---|---|---|---|
definitive | A trajectory that an operator is planning to fly. | Inserted into the catalog, replacing the previously-uploaded definitive trajectory for the object if it exists. | Trajectory and associated events / CDMs are viewable by all users |
hypothetical | A trajectory that an operator is considering flying, but would like to screen first. | Screened once, but not inserted into the catalog. | Trajectory and associated CDMs only viewable by submitting operator. No events are created. |
candidate | A trajectory that an operator is considering flying, and if the system determines it is "safe" (see below), the system should "lock it in" as a definitive trajectory. | Screened once, and converted to either definitive or hypothetical on the next screening cycle based on safety criteria. | Trajectory and CDMs are private, unless the trajectory is converted to a definitive trajectory. |
Trajectory Screened Status
Each trajectory has an associated status, which starts as NotScreened. Success or intermediate errors can result in the following statuses:
| Status | Meaning |
|---|---|
Screened | Trajectory successfully processed. |
NotScreened | Not yet processed (default). |
CandidateToDefinitive | Trajectory upgraded from a candidate to a definitive type. Only visible for a single cycle when a trajectory is converted. |
TrajectoryInvalid | Trajectory file was invalid. |
TrajectoryTypeResolutionFailed | Trajectory type could not be resolved to one of the above types. |
Superseded | Trajectory was not screened because there was a newer definitive trajectory for that object in the same screening cycle. |
Superseded Trajectories
If there are multiple definitive trajectories for the same object downloaded in a single screening cycle, only the newest (by upload time) will be screened. New definitive trajectories for an object will also replace older definitive trajectories for the same object from previous cycles.
Using Candidate Trajectories
The POST /api/v1/trajectory endpoint has an optional auto_relinquish_pc_threhold parameter (defaults to 0.0). When specified with a candidate trajectory, it expresses the operator's risk tolerance for "locking in" a trajectory.
If all CDMs generated by the screening of a candidate trajectory have a collision probability less than or equal to auto_relinquish_pc_threshold, then the trajectory is upgraded to a definitive trajectory on the next screening cycle.
The name of the field comes from a second semantic meaning of the field, which is relevant when an object has pre-existing conjunction events. To learn more, read about coordinating on conjunction events.
SpaceX Trajectory Uploads
Starlink uploads ephemerides for every satellite in its constellation to the production space-safety.starlink.com roughly every 30 minutes, with a 24 hour time horizon, subject to change due to operational considerations.