How to get real-time Satellite Ephemeris Data

NASA's Real-Time Mission Monitor (RTTM) allows the real-time access of satellite ephemeris data for many Earth-observing satellites currently in orbit (and even some that finished their mission long ago). These data can be accessed by the general public in the form of XML strings by submitting queries embedded in a URL string, and this page describes how to make such requests.

How to Request Ephemeris Data from the RTMM SOS Service

There are two products available for Earth-observing satellites: nadir and footprint. The nadir product is the satellite ephemeris (position) at a given moment. The footprint product is the corresponding area on the ground within that satellite's field of view at that moment.

To See the Capabilities for a Given Product:

Nadir: http://rtmm2.nsstc.nasa.gov/SOS/nadir?request=getCapabilities&Version=1.0&Service=SOS

Footprint: http://rtmm2.nsstc.nasa.gov/SOS/footprint?request=getCapabilities&Version=1.0&Service=SOS

To Request the Ephemeris of a Satellite at a Specified Time:

The URL string to use which will return the ephemeris data as XML has the basic form:

http://rtmm2.nsstc.nasa.gov/SOS/nadir
?version=1.0
&observedProperty=urn:ogc:sensor:satellite:nadirTrack
&Service=SOS
&request=GetObservation
&offering= <offering>
&format=text/xml;%20subtype="om/1.0"
&time= <time>

Specifying the Satellite (Offering)

Here are just a few of the properly-formatted names of recognizable Earth-observing satellites:

AQUA
ENVISAT
LANDSAT_5
LANDSAT_7
RADARSAT
TERRA
TRMM

Specifying the Time Span and Time Step

This is the tricky part; proper formatting (syntax) is key. The starting and ending times are specified in this format:

YYYY-MM-DDThh:mm:ss

Where YYYY is the 4-digit year, MM is the 2-digit month, DD is the 2-digit day, hh is the 2-digit hour (military or 24-hour time), mm is the 2-digit minute, ss is the 2-digit second, and T is a literal 'T' separating the date and time.

A time step must also be specified so that the service knows how many ephemeris data points to return in that time span. The time step must be specified in the following format:

PTcS

Where PT is a literal 'PT', c is the number of seconds, and S is a literal 'S'. Put together, the time span time step are formatted this way:

YYYY-MM-DDThh:mm:ss/YYYY-MM-DDThh:mm:ss/PTcS

Where the first date-and-time string is the starting date and time and the second is the ending date and time.

Putting the Pieces Together

An example RTMM query string looks like this:

http://rtmm2.nsstc.nasa.gov/SOS/nadir
?version=1.0
&observedProperty=urn:ogc:sensor:satellite:nadirTrack
&Service=SOS
&request=GetObservation
&offering=RADARSAT
&format=text/xml;%20subtype="om/1.0"
&time=2010-09-01T13:00:00/2010-09-01T13:30:00/PT60S

This query string should return an XML string that contains, among other information, 30 ephemeris data points, as we requested the ephemeris data of the RADARSAT satellite from 13:00:00 to 13:30:00 at intervals of 60 seconds (1 minute).