Looking for some Calculation help

MargeS

This is the site I am referring to : https://epic.gsfc.nasa.gov/

Under the Image Information section is the following data:
Distance to Earth: 932,550 miles

If I only had access to the following information;

• centroid coordinates: Geographical coordinates that the satellite is looking at
• dscovr position: Position of the satellite in space
• lunar position: (Position of the moon in space
• sun position: (Position of the sun in space
• attitude quaternions: Satellite attitude

would I be able to calculate that number '932,550' for the distance to earth?

I'm trying to figure out how they worked out the distances and the SEV angle.

MargeS

I finally got an answer to this....it is possible to get the distance between 3d points:

d=√(x2−x1)2+(y2−y1)2+(z2−z1)2

A bit of Sums (#oldskool) later, and I managed to work out all the distances.

ps200306

But which two (x,y,z) points are you using? You don't have the coordinates of the Earth (I'm assuming those geographical coordinates are just latitude and longitude).

MargeS

ps200306 wrote: »

But which two (x,y,z) points are you using? You don't have the coordinates of the Earth (I'm assuming those geographical coordinates are just latitude and longitude).

For example, the coords of the DSCOVR satellite are;
x: -1283061.502946, y: -669893.465826, z: -130240.863464

The coords of earth are 0,0,0

Capt'n Midnight

MargeS wrote: »

This is the site I am referring to : https://epic.gsfc.nasa.gov/

Under the Image Information section is the following data:
Distance to Earth: 932,550 miles

Damn thing keeps moving :pac:

Distance to Earth: 938,254 miles


Satelite position can be determined by radar if close like the GPS ones , or by timing of signals if further away. You can tell the relative speed by measuring the Doppler shift too. Once you measure it a few times you know the orbital parameters so you can predict the orbit. GPS relies on this too as those satellites broadcast the parameters so receivers know where they are supposed to be.

https://www.esa.int/Our_Activities/Operations/gse/Flight_Dynamics

Measurements from a pair of widely separated ground stations are used to determine the position of a spacecraft as far away as 150 million kilometres – the mean distance from Earth to the Sun – to within less than 1 km. Only a few of the world’s space agencies have perfected this highly precise technique.

ps200306

MargeS wrote: »

The coords of earth are 0,0,0

Aha. You didn't mention they are geocentric coordinates. :pac:

That makes it a cinch if you are calculating the distance to the centre of the Earth. If it is to the surface at the centroid coordinates then you'd have to take into account the shape of the geoid. I guess they must know all the details pretty accurately as DSCOVR is in an unstable Lissajous orbit around L1, so needs station-keeping manoeuvres from time to time.