Units of Space Measurement

[RSWingman]

Surface measurement is apparently in Kilometers and the edge of Earth's atmosphere is about 100k. This is what one sees in the HUD and it's only good until you get into space.

But space travel uses a measurement where the edge of Earth's atmosphere is around 6 to 6.5M (Mega or Million something). And there's also (K)ilo, (G)iga & (T)era, then it goes to AU, then Parsecs.

What unit of measurement is this (M=Million what?) and what is the conversion? It can't be Miles. For example, I hear we were nearly missed by an asteroid by about 400k, so I want to plan a 400k pass to get a feel. How can these different measuring systems be correlated?

 

[James.Denholm]

I'm pretty sure it's in meters. But I'm not certain.

 

[David]

The unit of distance measurement, in Orbiter, is the meter (and, in fact, the units are in general those of the metric system [S.I.]). Additional notations such as you describe, represent the usual power-of-ten metric prefixes, including:

k (kilo) = *10^3 (= *1,000)
M (mega) = *10^6 (= *1,000,000)
G (giga) = *10^9 (= *1,000,000,000)
etc.

So, for example, an altitude of "100" means 100meters, while an altitude of "100k" means 100kilometers, and an altitude of "100M" would mean 100megameters (=100,000kilometers).

 

[RSWingman]

Hmm, if it is, it may be measuring from the Earth's center. I believe it does.

---------- Post added at 01:09 AM ---------- Previous post was at 01:05 AM ----------

Ok. Yeah, I completely understand the Metric system. I was wondering of the discrepancy between surface & orbital measurement. But it occurred to me that it's the difference between the Earth's center and surface.

So now I gotta find the Earth's radius to subtract. No prob.

Thanks.

---------- Post added at 01:23 AM ---------- Previous post was at 01:09 AM ----------

Got it!

100k (altitude to the edge of Earth's atmosphere) + 6371 (Earth's radius) = 6471k or 6.471M. And THAT makes sense.

 

[tblaxland]

100k (altitude to the edge of Earth's atmosphere) + 6371 (Earth's radius) = 6471k or 6.471M. And THAT makes sense.

If you are using the Orbit MFD there is a button (DST) that toggles between surface relative and centre relative measurements.

 

[RSWingman]

If you are using the Orbit MFD there is a button (DST) that toggles between surface relative and centre relative measurements.

Kick ass! That's exactly what I needed. I think that's the only button I didn't know on there.

 

[Rathelm]

Kick ass! That's exactly what I needed. I think that's the only button I didn't know on there.

And ironically it's one of the more useful ones.

 

[MajorTom]

Yes...whenever I set up a launch vehicle scenario, I always make sure the Orbit MFD is set to display altitude above the earth. It makes no sense to display the distance from the Earth's radius in this case.

Just set the MFD as you would like it, save the scenario, then you can use the saved scenario as the base for your new scenario design.