On Oct 21, 1:21 am, BradGuth wrote:
On Oct 20, 7:58 pm, wrote:





On Oct 20, 4:18 pm, BradGuth wrote:

On Oct 20, 9:00 am, wrote:

More information on this hypthetical moonship.

http://en.wikipedia.org/wiki/Gas_core_reactor_rocket

A gas core nuclear rocket sustainer with chemical rocket boosters for
take off and landing built out of Apollo era hardware, to build and
sustain a moonbase.

600,000 lbs lift-off weight
360,000 lbs propellant
180,000 lbs lox
180,000 lbs lh
30,000 lbs booster
150,000 lbs sustainer

150,000 lbs payload weight
90,000 lbs structural weight
45,000 lbs of this is the gas core nuclear fission engine
900,000 lbs thrust at lift off
(2x 400,000 lbs - lox/lh liquid fuele booster - J2)
(1x 300,000 lbs - lh fueled gas core fission rocket)
(8x 15,000 lbs - lox/lh liquid fueled maneuvering rockets - RL10)

Chemical booster 450 sec Isp
Gas core nuclear susteainer 4,000 sec Isp

Top speed;
Booster: Vf = 450*9.82*LN(600,000/(600000-210000))
=1,910 m/sec (4,256 mph)

Sustainer Vf = 4000*9.82*LN(390,000/(390,000-150,000))
= 19,070 m/sec (45,642 mph)

Combined: 20,980 m/sec (49,898 mph)

The volume of hydrogen is 1,168 cubic meters (41,277 cf)
The volume of oxygen is 68 cubic meter (2,386 cf)

total propellant volume is 1,236 cubic meters (43,663 cf)

This is about the same volume as the S-II second stage.

http://en.wikipedia.org/wiki/S-II

So, one can imagine a reduced oxygen tank size for the SII, and
increasing the hydrogen tank by moving the bulkhead between the two -
which achieves the 405,000 lb mass with the appropriate mass ratios.
Remove the centrally located J2 and add the 45,000 lb weight and
300,000 lb thrust gas core nuclear sustainer in its place. Drop 2 of
the 4 remaining J2 engines, keep 2 J2s at boosters at lift off from
Earth. Add 4 RL10S clusters (8 total) at 2 of the of old J2
locations
for take off landing and meneuvering around the moon.

The SIVB is configured for a moonbase module similar to skylab for for
operations at 1/6 gee instead of zero gee..

To deploy the SIVB modules on the lunar surface equip the SII with a
simple
loading crane to erect on the lunar surface and then to lift the SIVB
out of its position atop the SII and put it in place near the landing
point. Apollo 14 landing next to the Surveyor spacecraft on the moon
shows that even in Apollo days you could land pretty accurately on
the
moon. With a radio transponder the SII-GC version could land at the
same point precisely each time. So, the crane could be erected after
each landing to remove an additional payload bay. After a half dozen
flights a base would be established and the personnel carrier version
of the SIVB large enough to carry a crew of 30 - or 10 plus supplies
- for crew rotations - would maintain the base after it was
completed.

http://www.astronautix.com/lvs/wintu....nasaspaceflig...

The Model 979 flyback booster for the Saturn SIC - the first stage,of
the Saturn V - could easily be adapted for the smaller SII second
stage. A
large nose cone with cargo doors would carry the SIVB inside

.

? 600,000 lbs lift-off weight ?

By your own numbers, it seems as though your 600,000 lbs of lift-off
weight or GLOW is in error, especially if including all the realted
fuel, payload and infrastructure or inert mass. Or, is it just my
having missed something obvious?
- Brad Guth -- Hide quoted text -

- Show quoted text -

I dunno, did I add it up right?

600,000 lbs lift-off weight

360,000 lbs propellant

that leaves 240,000 lbs everything else

the 360,000 lbs propellant is broken down into

180,000 lbs lox

and

180,000 lbs lh

and the 180,000 lbs lh is broken down to

30,000 lbs booster
150,000 lbs sustainer

The 240,000 lbs everything else is

150,000 lbs payload weight

thet's the SIVB payload configured as a luna-lab

and

90,000 lbs structural weight

everything else. that 90,000 lbs is broken down into;

45,000 lbs of this is the gas core nuclear fission engine

and 45,000 lbs everything else (the SII booster)

So, it all adds up to 600,000 lbs...

We have 1.5 gees at lift off because we have

900,000 lbs thrust at lift off

Broken down as;

(2x 400,000 lbs - lox/lh liquid fuele booster - J2)
(1x 300,000 lbs - lh fueled gas core fission rocket)
(8x 15,000 lbs - lox/lh liquid fueled maneuvering rockets - RL10)

The engines are throttable. The nuclear engine is started midflight
and brought to full throttle during ascent. The RL10s and J2s at 100%
thrust produces 920,000 lbs at lift off - and as propellant is burned
off, and the nuclear engine brought up to full thrust, gees mount to 2
gees - at which point the RL10s and then the J2s are throttled back.

The vehicle ascends directly to lunar injection speed and then shuts
down until it gets to the vicinity of the moon and does its major
delta vee with the sustainer - doing a direct descent. The final
landing is with the RL10s and nuclear engine off. But they account
for only a very small fraction of the total delta vee as indiciated.- Hide quoted text -

- Show quoted text -

240/600 = 40% inert, which seems a wee bit on the high side for
getting 75 tons into leaving Earth behind in its nuclear dust, but
what do I know.
- Brad Guth -- Hide quoted text -

- Show quoted text -

Indeed, one wonders what you know given all that you post.

You would do well to learn the rocket equation

Vf = Ve * LN(1/(1-u))

where Vf = final velocity
Ve= exhaust velocity
LN( = natural logarithm
u = propellant fraction

And Ve = g0 * Isp
g0 = acceleration at Earth's surface = 9.82 m/s/s
Isp = specific impulse in sec

A gas core nucleer rocket if one were built would likely have a
pitiful thrust to weight ratio compared to a chemical rocket. So, you
would expect the propellant fraction to be dismal as well.

However, on the plus side, exhaust speeds would be astronomical. A
4,000 sec Isp means exhaust speeds approach 40 km/sec. Which means
with a 60% propellant fraction you can achieve;

Vf/Ve = LN(1/(1-0.6)) = 0.916

or 91.6% exhaust speeds. So, with an exhaust speed something like 10x
that of chemical rockets, final speeds even with dismal propellant
fractions approach 36 km/sec - 7x the stage speeds of chemical
rockets.
..