Linked Questions

3
votes
1answer
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! ...
3
votes
1answer
554 views

JGM-3 vs EGM2008 coefficients

I've implemented the Earth harmonics calculation in JGM-3 model, using the coefficients from here ...
2
votes
2answers
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 ...
2
votes
2answers
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 ...
3
votes
1answer
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. ...
6
votes
1answer
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 ...
3
votes
2answers
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 ...
0
votes
1answer
88 views

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 - {...
2
votes
1answer
267 views

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 ...
2
votes
1answer
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 ...
7
votes
1answer
113 views

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 ...
3
votes
1answer
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}=\...
2
votes
1answer
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 ...
1
vote
1answer
92 views

What counts as “0 mGal” in these gravity maps?

In the following gravity map of Mars the changes in gravity are shown according to mass distribution: Map removed However, since no moon or planet other than the Earth with 9.80665 m/s² has a ...
3
votes
0answers
122 views

Quantitatively, how deep are the stable equilibrium points in GEO? How much delta-v needed to move from one to the other?

This answer discusses a spacecraft in GEO using a two-impulse (circular → elliptical → circular) raise & lower maneuver to move (phase) itself by 180 degrees in longitude then return to synchrony. ...