# What was the ambient air density was there when/were Starman/Roadster first started playing Bowie's "Life on Mars"

When the Falcon Heavy test flight 2nd stage fairing opened at about 115 km, David Bowie started singing "Life on Mars".

Okay, the Tesla Roadster's stereo started playing "Life on Mars", or at least it is said to have done that.

In this comment under this excellent answer I've suggested that a very sensitive microphone could have picked up the sound, that there was indeed sound and that this is an example of music having been played in space.

In order to calculate the sound pressure level, I need at least an approximate density for the ambient atmosphere at 115 km on that day. This requires at least a basic model of the atmosphere and possibly a check on the solar activity on that day because the density depends pressure and temperature, and solar heating affects this, although I am not sure how strong this effect is at such a low altitude. It's extremely important at higher altitudes where drag on satellites in LEO needs to be calculated or estimated.

If you would like to estimate the density boost of a supersonic shock wave, that would be even better, it only makes my comment "more correct" ;-)

The microphone may be more sensitive than a typical commercial product, perhaps using a small laser pickup. But for this question I'm just asking about the density. We can do the sound pressure level and detectability in the subsequent question.

Queued at 25:25 lower your volume first, there's lots of cheering!

• Here's an atmospheric model, see Table 8 "U.S. Standard Atmosphere, 86 to 1000km": braeunig.us/space/atmmodel.htm Aug 28 '18 at 10:00
• @BlueCoder That's quite handy, thank you! It's a lot shorter than reading ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770009539.pdf and yet has analytical expressions which this page doesn't have: braeunig.us/space/atmos.htm (which shows at the bottom that at maximum solar activity the density effect at this altitude is less than a factor of 2)
– uhoh
Aug 28 '18 at 10:09
• May be the pressure or density of the ambient atmosphere was so low that no sound transmission was possible. At least for the higher frequencies and shorter wavelengths of the human accustic range.
– Uwe
Aug 28 '18 at 11:19
• @Uwe I'd already checked, should be okay for the lower frequencies and the short distance of a meter or so. Save further comments for the the next question please, this one is only about density! We'll have to look at ballistic transport as well as normal sound pressure waves to do it right.
– uhoh
Aug 28 '18 at 11:31