# Tag Info

17

OK, I cannot give you the answer for the ISS, MEO and GEO off the top of my head. However, if you do insist for any specific objects, please post their catalogue numbers (five numbers at the beginning of every TLE line, i.e. columns 03-07) in comments. But here we go. First of all, I suggest having a look at how we represent multidimensional uncertainty as ...

11

The canonical references are Spacetrack Report #3 which is the original documentation of the SGP4 algorithm, and Vallado + Kelso's Revisiting Spacetrack Report #3 which has updates, analysis and modern* source code with discussion. * well, kinda :)

7

The current accuracy of the JPL Developmental Ephemerides released in September of 2013 is given by its authors in their article The Planetary and Lunar Ephemerides DE430 and DE431, quoted below: The present-day lunar orbit is known to submeter accuracy through fitting lunar laser ranging data with an updated lunar gravity field from the Gravity ...

6

TLE's already considers drag up to some point (check if BSTAR is negative, if it is, then the TLE is considering that maneuvers have been performed). A positive BSTAR reduces (mean) semi-major axis over time, an effect of drag. J2, J3 and J4 are each partially considered (think taylor series approximaiton with $J_2^2$ set to zero). If you have a sun-...

5

Comparisons between predicted orbits (numerically integrated) and fitted orbits (from tracking data) are usually done in an inertial reference frame, such as ICRF or Mean of J2000. Within these frames, the orbit comparison can take several forms, such as point by point comparisons, or comparisons of the orbital elements

4

I used PREDICT operationally for the first few Planet Labs tech demo missions (Dove 1 / 2 / 3). It's fine. The quality of your ephemeris data is going to be the limiting factor, not the software you use to propagate it.

4

With respect to what orbit propagator you should use, it depends. If you are designing a space mission that will operate in a Sun-syncrhounous orbit, then usually a J2 is better. In those cases, the mission usually have ways to keep itself on the designed orbit, avoiding the all perturbations but J2. Hence, a J2 propagator is better. On the other hand, if ...

3

Juno is looking for how Jupiter formed, which would say a lot about how all planetary systems form, and all theories regarding that are on the line. First, determining how much water it has would help determine where and how fast it formed. Oxygen is the 3rd most abundant element in the universe, including in our solar system, and its most common form is ...

2

PREDICT uses legacy SGP4 code. SGP4 code is usually referred to a 1km/day rule of error increase. (However that actually strictly depends on the orbit type and satellite.) The second thing to note is SGP4 was updated by Vallado in 2006 with some error fixes and PREDICT does not see to have implemented those fixes. Therefore, using an updated SGP4 ...

2

You may be asking about a couple of different things here. 1 Events at the surface of the sun Events at the Sun itself may or may not head in the direction of the Earth, but this is step one of a prediction system. I believe there are two approaches: a) look at what happened about a month ago and predict that it will be still there when that part of ...

1

Solar flares travel at about 2000 km/s. Radio travels at 300,000 km/s, so a spacecraft at L1 (1.5 million km out) like DISCOVR gives about 12 minutes of warning when the solar flare reaches it. Spacecraft like SOHO observe the sun, and these observations are used by e.g. NOAA to try and predict flares: Current methods of flare prediction are ...

1

First, you need to make sure both results (simulation results and laser ranging data) are converted into the same coordinate system. This is usually chosen as an inertial frame, like ECI. You can compare two orbits in ECI frame but you will only have one meaningful information from that: the magnitude of the error. However, in most papers, you will see ...

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