On Aug 7, 5:01*am, Robert Clark wrote:
On Aug 7, 4:45*am, Robert Clark wrote:





*There had been some suggestions to use the Atlas V Heavy as an
alternative to the Ares I. According to this article NASA rejected the
Atlas V Heavy for human missions because of the payload requirements:

Lockheed and Bigelow Human-Rated EELV deal.
Man Rating the Atlas V
September 21st, 2006 by Chris Bergin
"NASA considered and rejected the use of Atlas V as a Space Shuttle
replacement for human space flight during their Exploration Systems
Architecture Study (ESAS) last year. The ESAS stated that it deemed
both Boeing Delta IV and Atlas V development options as ‘high risk’
for an on-time 2011 operational capability to meet CEV mass
requirements."
...
"The reason for the NASA ESAS man-rating concerns was due to the 25mT
CEV mass requirement, which ESAS maintained could not safely even be
met by the massive Atlas V Heavy variant. According to a Lockheed
Martin paper unveiled this week at the Space 2006 conference, the
basic Atlas V 401 can meet FAA and NASA man-rating requirements with
little modification with a much smaller capsule mass of 20,000 lbs."http://www.nasaspaceflight.com/2006/09/lockheed-and-bigelow-human-rat...

* The Atlas V 401 definitely could not make the 25 mT payload
requirements to match the Ares I performance. This is an already
existing booster so was suggested as an alternative to the Ares I to
save cost. The Atlas V HLV is only a proposed booster and has not been
built or authorized. But its suggested payload to orbit would exceed
that of the Ares I.
*It uses 3 RD-180's in its lower stage with a thrust of about
3,000,000 lb which is about comparable to the Ares I solids, but with
a lower dry mass so should indeed be able to exceed the Ares I in
payload to orbit. NASA's claim that it could not "safely" reach the 25
mT payload goal is puzzling, unless it means "man rating" of the
engines but that should be true regardless of the payload mass.

*All Atlas V versions use a smaller engine, sometimes in pairs, for
the upper stage, the RL-10A:

RL-10.http://www.astronautix.com/engines/rl10.htm

*The J-2X engine planned for the Ares I upper stage has 10 times the
thrust of one RL-10A:

J-2.http://www.astronautix.com/engines/j2.htm

*Using two RD-180's, cheaper than the three proposed for the Atlas V
HLV, to replace the Ares I first stage, while also keeping the J-2X
for the upper stage, would actually allow you to increase the payload
to orbit.

*The same would be true of the RS-84 engine if development were
restarted. This engine was also planned to be reusable:

July 21st, 2003
Kerosene Engine Passes Design Milestone.
Written by Fraser Cain.http://www.universetoday.com/2003/07...-passes-design...

*This article from 2003 stated a full scale model would have been
ready for testing four years after that in 2007. The program was
cancelled in 2004 however. If you suppose there was an additional year
of development before it was cancelled in 2004, then conceivably a
full scale model could be ready for testing by 2012 if development
were restarted this year.

*So there are several options if the Ares I solids are to be replaced
with liquid fueled engines for manned missions. All of these could
surpass the Ares I in payload to orbit:

1.)Replace the solids with a single RD-171. This engine has been used
many times, but is a Russian engine. It would be cheaper. But I
consider it unlikely that the U.S. would want to be dependent on a
Russian engine for all manned flights for a long period.

2.)Replace the solids with two RD-180's and keep the J-2X engine now
proposed for the Ares I upper stage. The RD-180 has been contracted at
least to be made by an American manufacturer, Pratt & Whitney, but I'm
informed none have actually been made in the U.S.
This would be more palatable to be used for all near term manned
missions if the ones used are made in the U.S. The fact there are two
needed would increase the cost as well as the fact they would be made
by an American company.

3.)Use the Atlas V HLV with 3 RD-180's for the lower stage, with the
RL-10A, perhaps two of them, for the upper stage. Using 3 RD-180's
would be more expensive but you might save on the cheaper RL-10A's for
the upper stage compared to the J-2X.

4.)Restart development of the RS-84. Two of these would give
comparable performance to using 2 RD-180's with a J-2X powered upper
stage. This would be reusable so it gives you some more options for
saving money if a flyback booster capability is developed. Main
disadvantage is that it's still not completed. You would then have to
figure also development costs.

*Cheapest option is undoubtedly #1. But I consider it politically
impossible.
*My personal preferred option is #4 because it would be an American
engine and also because it would be reusable, though very likely more
expensive than the others.

* * *Bob Clark- Hide quoted text -

- Show quoted text -

since all this the number of astronauts has been cut from what 8 to 5?
something like that........

nasa intentially speced too many astronauts so existing expendables
couldnt be used