[AR] Re: Just where does space start?
- From: "" <dmarc-noreply@xxxxxxxxxxxxx> (Redacted sender "JMKrell@xxxxxxx" for DMARC)
- To: arocket@xxxxxxxxxxxxx
- Date: Sun, 31 Aug 2014 16:37:43 -0400 (EDT)
The altitude of 120 km (400K ft) is where a reentry vehicle produces an
ionization trail. The measurable atmospheric pressure changes from 10-6 to
10-5 Torr.
The Air Force considers 50 miles as the minimum orbital altitude. This
figure could be from their extensive space debris tracking.
John Krell
In a message dated 8/31/2014 12:24:39 P.M. Pacific Daylight Time,
paul.mueller.iii@xxxxxxxxx writes:
I did a little searching on wikipedia and it seems the 100 km number does
have a mathematical basis derived by Theodore von Karman (more than just a
round number in the vicinity of where the atmosphere gets really thin):
_http://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_line_
(http://en.wikipedia.org/wiki/Kármán_line) (that URL has funny characters
because of the accents over
the "a"s in Karman).
It is the number used by the generally accepted governing body for
aeronautical and astronautical records, the Federation Aeronautique
Internationale
(FAI). The only one who use 50 miles is the US Air Force, from the days of
awarding Astronaut wings to X-15 pilots who flew that high.
Paul M
On Sun, Aug 31, 2014 at 12:35 PM, David Weinshenker
<_daze39@earthlink.net_ (mailto:daze39@xxxxxxxxxxxxx) > wrote:
Bill Claybaugh wrote:
> Perhaps it would be best to simply accept the mathematically
> convenient "100 km" number proposed by the EU and apparently
> accepted by this community for the last 20 years.
I prefer to accept the (equally mathematically convenient) "400 k ft."
figure of the Space Shuttle "entry interface" threshold. This at least
is a convenient number with the weight of an engineering (rather than
a political) decision behind it: that's the value someone came up with
for the altitude of the boundary between "coasting" and "gliding" flight.
No doubt it's biased on the high side, as is perfectly appropriate for
the intended use: the guidance logic would want to stop "zeroing out"
the dynamic pressure effects before they actually reached significant
levels. I'm not sure what the altitude is where the aero effects were
actually noticeable in the numbers.
-dave w
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