[Smwg] AI 2015-0602-1

[Reinert, Jessica (GRC-LSA0)]

Greetings,

In response to AI 2015-0602-1, "Check the semantics of the Nav Stds multiple segments and start/end time and report to WG as it applies to the Trajectory Prediction Format", I have the following information.

It appears that the Orbit Data Message types of Orbit Parameter Message and Orbit Ephemeris Message, plus the newly defined (per a new draft of the Orbit Data Message Book) Orbit Hybrid Message allow for the transmission of data for multiple maneuvers within a single message. These message types also include start and stop times for the entire epoch covered by the message.

The presence of a CREATION_DATE parameter is common across all messages. The OPM includes an EPOCH parameter which displays the Start date and time for the entire epoch and also MAN_EPOCH_IGNITION to designate the start time for individual maneuvers.

The OEM includes an REF_FRAME_EPOCH, as well as START_TIME/STOP_TIME and USEABLE_START_TIME/USEABLE_STOP_TIME in addition to the EPOCH parameter used to show the start time for each ephemeris data entry.

The OHM includes an EPOCH_TZERO representing the start time for all ephemeris and/or covariance data included in the message. A START_TIME parameter which represents the Epoch of all time-relative time tags used in specification of maneuvers, orbital states and covariance data, specified in timing system "TIME_SYSTEM" and an STOP_TIME which is the end of the total time span covered by all ephemeris and/or covariance data in this message. In addition to being able to specify start and stop times for multiple maneuvers, using MAN_START and MAN_STOP this message allows for the specification of maneuvers for systems in a parent child relationship (for example launching a few cubesats from the ISS).

Given the variety of ways the ODM standard approaches start and stop times, I hesitate to repeat this information in the trajectory prediction message. It seems like the simplest approach would be to specify only the start time for the trajectory data in addition to the creation time for the trajectory message and leave it at that. I am not convinced it is even necessary to include the start time, but since we have a place for it in the SrvMgtHeader, there is no reason not to include it. I propose this simplistic approach due to the fact that this message has always been approached as a wrapper around the NDM/ODM messages.

I look forward to discussing this at Tuesday's meeting.

Regards,

Jessica


Jessica Reinert
Systems Definition and Communications Branch
NASA Glenn Research Center
Phone: 216-433-6249

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