Celetrak's A New Way to Obtain GP Data (aka TLEs) by Dr. T.S. Kelso 2020 May 27 explains the arrival a new infoblob format that in several ways is "better" than the ancient TLE, and contains the following:

The US government has provided GP or general perturbations orbital data to the rest of the world since the 1970s. These data are produced by fitting observations from the US Space Surveillance Network (SSN) to produce Brouwer mean elements using the SGP4 or Simplified General Perturbations 4 orbit propagator.

Many of you are familiar with this data in the form of TLEs or Two-Line Element Sets. TLEs were designed to provide the minimum data necessary to propagate the orbit of a resident space object (RSO) at a time when both bandwidth for transmission or digital storage were extremely limited. In fact, at the time, transmission might be via fax, hard copy (postal delivery), or even read over the phone and storage was handled using punch cards or magnetic tape.

While this format has served us well for many decades, it has not been without its share of problems. For example, the choice of a two-digit year caused many problems approaching Y2K—problems that were side-stepped by redefining what those two digits represented—but that Y2K problem persists fully 20 years into the 21st century. And now we are approaching another milestone where we will no longer be able to catalog all the objects we track within the 5-digit catalog number limitation of the TLE format.

One of the key drivers forcing us to consider tracking more than 100,000 objects is the activation of the Space Fence on Kwajalein Atoll. The Space Fence reached initial operational capability (IOC) on 2020 Mar 27 and is expected to track far more than the ~26,000 objects currently tracked by the SSN—perhaps by as much as an order of magnitude.

And we are expecting to see public availability of data from the Space Fence starting some time this summer (2020). The 18th Space Control Squadron (18 SPCS) has already transitioned internally to using 9-digit catalog numbers in support of these changes and we expect 18 SPCS to release data from the Space Fence using 9-digit catalog numbers.

Question: Certainly the housekeeping improvements are critical, but are there potentially orbital mechanical improvements over SGP4 propagation of traditional TLEs as well? I don't really understand what it is that is happening; is it strictly a formatting and indexing improvement, or is the amount of orbital information contained going to be modified and/or improved as well?


Skimming CCSDS RECOMMENDED STANDARD FOR ORBIT DATA MESSAGES, it looks to me like three different message types are defined: Orbit Parameter Message (OPM), Orbit Mean Elements Message (OMM), and Orbit Ephemeris Message (OEM).

OPM gives position and velocity and optionally "osculating Keplerian elements". It is "suited to exchanges that "do not require high-fidelity dynamic modeling".

OMM is essentially the same info as a TLE in a more readable (by both humans and modern software) format.

OEM "is suited to exchanges that require higher fidelity or higher precision dynamic modeling than is possible with the OPM" and "allows for dynamic modeling of any number of gravitational and non-gravitational accelerations." It includes optional spacecraft parameters like mass, solar radiation area and drag area terms, so it can be used with a fancy propagator that models those effects.

The Celestrak post you link says Celestrak will be providing OMMs, so it won't provide any functional improvement in propagation versus TLE, but OEMs potentially would.

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    $\begingroup$ This is a good summary of the formats themselves. To fully answer @uhoh's question, could you also add that an SPG4 propagation is not high fidelity at all. For high fidelity propagation of a LEO craft, one needs to account for Earth's spherical harmonics (e.g. EMG2008), SRP, Drag, and the motion of the Sun, Jupiter and the Moon (at the least). SPG4 might work well-enough for tracking of spacecraft over very short periods of time but isn't good enough for any mission design. $\endgroup$ – ChrisR Jul 1 at 5:21

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