713 views

### How open is NASA's “open source” GMAT software?

In answers and comments to What does it mean when a software is called open-source for US-release only? I found out that when NASA uses the term "open source" it does not mean open to everyone! ...
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### JGM-3 vs EGM2008 coefficients

I've implemented the Earth harmonics calculation in JGM-3 model, using the coefficients from here ...
149 views

### What is the formula for Legendre Polynomials from EGM96 calculated in F447.f program?

The F447.f program is designed to calculate the geoid undulation for EGM96. I'm trying to understand how it accomplish this calculation. I stuck in ...
382 views

### Earth geopotential effect on orbit propagation

I'm trying to take into account the Earth geopotential effect on the orbit. The only term I could consider, is J2. Are the terms (J2, etc.) change with time? I ...
1k views

### How are the coefficients in the EGM96 model normalized?

For my own interest I'm trying to implement the EGM96 gravitational model. I found the coefficients here. The readme file says that they are "fully normalized", but I'm not 100% sure what this means. ...
170 views

### Measuring the effect of Earth tides

In order to calculate the acceleration due to the geopotential, I've already implemented the EGM-2008 TideFree model, getting the coefficients from the link. Is the Earth tides effect already ...
179 views

### Is Dawn's upcoming low periapsis orbit for XMO7 “resonant”?

The Spaceflight Insider article Dawn will enter lowest ever orbit around Ceres says: In his Dawn Journal blog, mission director and chief engineer Marc Rayman discussed the challenges of bringing the ...
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### CSM velocity / apollo program

Reposting as a question. Uhoh's answer allows us to compute the velocity at a given r. Let's see what velocity is at $r=100000 \text{ km}$: \begin{align}\mathscr{E}_{tot} &= {1\over 2}v^2 - {...
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### Ceres gravity from spherical harmonics from Dawn, how to get the coefficients, definitions and potential?

update: I think I've found what I'm looking for. The file JGDWN_CER18C_SHA.TAB has what looks like spherical harmonics up to order 18, except I don't know the ...
210 views

### Why would the orbit of a satellite in GEO climb by 21 km in altitude over six months by itself?

This answer mentions several effects that tend to move geostationary satellites out of their "box" over time, but one really surprised me. According to the plot below (from there, but ...
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### Zonal vs Tesseral part of geopotential?

So I've only recent started to try to wrap my brain around geopotential models. I've done work with some special perturbations using $J_2$ before, however I've never dealt with a full spherical ...
184 views

### Calculating the Earth Geopotential effect

I'm calculating the acceleration due to the harmonics in ECEF frame. Gravity potential in spherical harmonics is shown here (I just removed "$1+$", as considering only harmonics effect). \$U_{har}=\...
158 views

### Simplified WGS84 or EGM2008 model for rapid computations?

I am searching for a simplified model of EGM2008 that can be used for rapid, repetitive computations. It needs to be valid only up to GPS altitudes. I'm thinking such a model already exists but cannot ...