Orbital Mechanics

[cameron]

I have a question about balloons & orbital speed.



If the ship is lighter than air and can "float" to an altitude of 62 miles, can it just "hang" there and not require orbital velocity?



Of course if you wanted to go anywhere you would need forward thrust, but is it unnecessary to go 17,000 MPH to maintain altitude?



And if it were hanging there, would you have gravity since you're not "falling" at orbital speed?



Would re-entry be insignificant since you're just floating back down, and not coming in at 17,000 mph?



Of course you would have to watch out for satellites who *are* moving at orbital velocity!

[Eduardo Blomar 1679]

The most information on the subject in one place I have found so far:



https://www.quora.com/How-far-could-balloons-go-can-they-escape-into-outer-space-what-happens-to-them-when-they-reach-their-topmost-point-and-what-are-the-scientific-reasons-for-such-an-inquiry" class="bbc_link" target="_blank" rel="noopener noreferrer">http://https://www.quora.com/How-far-could-balloons-go-can-they-escape-into-outer-space-what-happens-to-them-when-they-reach-their-topmost-point-and-what-are-the-scientific-reasons-for-such-an-inquiry



EB

[cameron]

Thanks for the link Eduardo! Good reference for designing the lifting envelope.



I was searching for "gravity calculators" and found this. https://www.calctown.com/calculators/acceleration-due-to-gravity-calculation



Does this suggest that gravity is 97% at 100km altitude vs. on the surface? Or are acceleration calculations different than weight calculations?



I was also thinking about geostationary orbit. Those satellites are essentially "hovering" over the same spot 36,000 kilometers high. Does that mean gravity is 2.3% that far out?



As long as the ship "floats" below low earth orbit (372 miles), it seems like gravity wouldn't be an issue (83% at 600km) unless you started travelling at orbital speeds.



Disclaimer: I don't know anything about orbital mechanics. Hoping someone else can help with the math.

[cameron]

I failed to mention tangential velocity. On the surface, you're moving ~1000mph. Geostationary satellites move at ~7000mph. Does this contribute to weightlessness even though you're holding the same position relative to earth? What would your speed be hovering 63 miles up?