Re: Martin Nova designs online: APR Extra
From: meiza (meiza_at_inva.com)
Date: 03/15/05
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Date: Tue, 15 Mar 2005 23:29:32 +0200 (EET)
In sci.space.history
Scott Lowther <scottlowther@ix.netcom.spamblok.com> wrote:
> meiza wrote:
>>Would the skirt be enough for stabilization during
>>entry and in other stages?
>>
>>
> Yup.
Funny, since the weight is aft, in the engines,
and the forward section is just empty light tanks,
but I guess they knew their stuff. It's fairly stubby.
>>I see no parachutes (they would have to be quite big
>>to make a difference). That would also make the terminal
>>velocity quite high. If it's 20 meters in diameter and
>>40 m in length, with weight about 700 tons, how fast would
>>it come down?
>>
> I may have that info somewhere...
I did some sketchy calculations..
With a coefficient of drag 0.3 to 0.5 the terminal velocity
comes to about 300 to 200 m/s .. 0.9 to 0.6 Mach!
With 8 of Star 48 -sized solid motors (5.8 million Ns, weight
2.5 tons apiece) you'd get only 70 m/s deltav, clearly too
little. With GEMs (35 million Ns) there'd be 400 m/s,
if you ignore their weight of 14 tons each (112 tons
total).
So it's something between these two, I doubt the impact
speed could ever have been 100 m/s.
Quite a hefty braking system it must be anyways - and
I wonder what would the solids more precisely be like if
that whole thing would slow down at a few gees, making them
burn out in maybe 10 seconds. Isn't burn time a problem for
big solids, relating to not enough surface area? Even
with 2 g's and 10 seconds burn time, the burn distance
would be one kilometer, giving some serious gravity losses
(i.e. decelerating high is not wise since you only re-
accelerate again by gravity on the way down), which
I haven't taken into account.
And also, not much thrust imbalances can be tolerated
since the motors are located on the outer ring of the
vehicle and there's no compensation systems. What were
the solutions to these problems?
-- meiza "Crash programs fail because they are based on a theory that, with nine women pregnant, you can get a baby a month" -WvB
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