Brute force re-entry

Mike Miller wrote:

Orbiter with typical ET residuals (15,000lbs): 200,000lbs
Orbiter after expending residuals: 185,000lbs
Specific impulse of the SSMEs in vacuum: 455 sec^-1.

Specific impulse (when measured this way) is measured in seconds, not
inverse seconds.

(455 sec^-1) x (9.8m/s/s) x Natural Log (200,000lbs / 185,000lbs) =
347 m/s.

As this equation can attest to; s^-1 times m/s^2 is m/s^3, not m/s.

--
__ Erik Max Francis && && http://www.alcyone.com/max/
/ \ San Jose, CA, USA && 37 20 N 121 53 W && AIM erikmaxfrancis
\__/ Never had very much to say / Laugh last, laugh longest
-- Des'ree

Erik Max Francis wrote in message ...

Specific impulse (when measured this way) is measured in seconds, not
inverse seconds.

D'oh! But the number is correct, despite the misplaced unit?

Mike Miller, Materials Engineer

Mike Miller wrote:

Erik Max Francis wrote in message
...

Specific impulse (when measured this way) is measured in seconds, not
inverse seconds.

D'oh! But the number is correct, despite the misplaced unit?

Yep, or certainly close enough.

Isp is sometimes measured as x seconds because one pound of propellent will
give one pound of thrust for x seconds;

- or x pounds of thrust for one second. Two pounds of propellant will give
one pound of thrust for 2x seconds, or x pounds thrust for 2 seconds; and so
on.

I hope I got that right!


--
Peter Fairbrother

Since orbital velocity is 8000 m/s, sacrificing the entire shuttle payload
to carry fuel would only allow the shuttle orbiter to decelerate by 16% of
the amount needed to come to rest. The only result would be to enter the
atmosphere at a much steeper angle and thus suffer much greater reentry
forces and heat.
Well, it's not the angle that heats the reentry vessel, it's the SPEED. Speed
compresses the air in front of the vessel and that is what makes the air hot,
not the angle which the vessel is flying. Capice, once and for all, everybody?
Now. Descent, no matter what, uses less fuel than ascent to orbit. Ascent
burns fuel fighting against air drag while descent, of any flight profile,
fast, slow, steep or shallow, cannot help but use drag for braking.
So double or triple the 16% savings and you'll start to see the advisability
of engine braking for reentry.
^
//^\\
~~~ near space elevator ~~~~
~~~members.aol.com/beanstalkr/~~~