Agreed, someone said correctly, that another stage is easier to build than
a balloon with associated infrastructure.
K
On Mon, Mar 1, 2021 at 3:38 PM Troy Prideaux <troy@xxxxxxxxxxxxxxxxxxxxx>
wrote:
From my novice understanding, weather balloons will routinely reach
altitudes of 65kft?
If (say) that was the height you could achieve for the rocket launch;
the 3 things that a balloon launch buys you is (1) obviously reduced drag
(2) significant additional propulsion performance from the utilisation of a
higher expansion ratio and (3) potentially significant increases in mass
fraction from lower operating chamber pressures (which might be
counter-helpful for coasting though).
Saying that, balloon launches are generally a major PITA and not worth the
hassle.
Troy
*From:* arocket-bounce@xxxxxxxxxxxxx [mailto:arocket-bounce@xxxxxxxxxxxxx]
*On Behalf Of *roxanna Mason
*Sent:* Tuesday, 2 March 2021 10:20 AM
*To:* arocket@xxxxxxxxxxxxx
*Subject:* [AR] Re: Mini-rocket to space?
The point is 40KFt is at commercial jet altitudes and some business jets
like the Lear 24 service ceiling is 51KFt. Probably can go higher but 51K
is chosen because any higher death would result in a decompression event,
even with oxygen blood boils at body temp.
I think the point has been made that 40KFt drag is far from negligible.
Ken
On Mon, Mar 1, 2021 at 2:46 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Mon, 1 Mar 2021, roxanna Mason wrote:
Drag is quite significant at 40,000 ft...
Right and the SR-70 flys fine at 100KFt...
Not quite -- SR-71 service ceiling was 85,000ft. That's where it ran out
of lift at normal max speed, Mach 3.2. Going slightly faster was possible
in special circumstances, but wouldn't gain you more than another few
thousand feet. (The pilot's manual was almost completely declassified a
number of years ago, see <https://www.sr-71.org/blackbird/manual/>, and
its contents shot down a lot of overenthusiastic earlier speculation.)
Still a lot higher and thinner than 40,000, though...
...and most meteors burn up at even higher alt.
Much higher -- they start being visible at 80-120km, and the small ones
disintegrate up there. But that's thermal effects more than drag. Drag
starts to be significant for small solid ones around 70km, although that's
at very high speeds.
Henry