On Feb 3, 2:46*am, Robert Clark wrote:
*The key point is that you have significantly better leeway in your
options and choices with relatively low financial risk.

*Another option for a manned launcher. In this report Boeing proposes
heavy lift launchers using existing components:

Heavy Lift Launch Vehicles with Existing Propulsion Systems.
Benjamin Donahue, Lee Brady, Mike Farkas, Shelley LeRoy, Neal Graham
Boeing Phantom Works,Huntsville, AL 35824
Doug Blue
Boeing Space Exploration,Huntington Beach, CA 92605http://www.launchcomplexmodels.com/Direct/documents/AIAA-2010-2370-65...

*One of the proposals is of a manned launcher for the Orion capsule
using a shuttle ET propellant tank and four RS-68 engines. This does
not use an upper stage but is not a single-stage-to-orbit vehicle
because the final push to orbit is made by the onboard thrusters on
the Orion spacecraft.
*However, it is interesting in this report comparison is made to the S-
IVB upper stage on the Apollo rocket. I was reminded of a suggestion
of Gary Hudson that the S-IVB would be single-stage-to-orbit with
significant payload if it used the high efficiency SSME rather than
the J-2 engine:

A Single-Stage-to-Orbit Thought Experiment.
Gary C Hudsonhttp://www.spacefuture.com/archive/a_single_stage_to_orbit_thought_ex...

*In Hudson's proposal the vehicle could lift 10,360 lbs, 4,710 kg.
This would be just enough to carry the crewed version of the
Dragon
spacecraft without cargo.

The point of the matter is that if you use highly weight optimized
structures and high efficiency engines at the same time then what you
wind up with will be a SSTO capable stage. The Ariane 5 core stage is
another weight optimized structure using common bulkhead design for
its propellant tanks. The Ariane 5 core stage will also become SSTO if
using high efficiency SSME's instead of the Vulcain engines.
The specifications of the Ariane 5 are given he

Ariane 5 Data Sheet.
http://www.spacelaunchreport.com/ariane5.html

The Ariane 5 generic "G" version could be lofted by a single SSME.
It's gross mass is listed as 170 mT, and the propellant mass as 158
mT, for a dry mass of 12 mT. The Vulcain engine is listed on this page
as weighing 1,700 kg:

Vulcain - Specifications.
http://www.spaceandtech.com/spacedat...in_specs.shtml

Switching to a heavier SSME engine would add 1.4 mT to the vehicle dry
mass, so to 13.4 mT for the dry mass. Using a 425s average Isp again
for the SSME, this would allow a 6,000 kg payload:

425*9.8ln(1 + 158/(13.4+6)) = 9,218 m/s.

We wish to use this for a man-rated vehicle though. The Ariane 5 was
originally intended to be man-rated using the Hermes spaceplane to
carry crew. However, it's not certain the degree this was followed-
through when the Hermes was canceled.
As with the Ares I upper stage, there are means to increase the
payload capacity. Subcooled densification allows 10% greater
propellant to be carried, so then 10% greater mass can be lofted to
orbit. This brings the total lofted weight from 19.4 mT to 21.3 mT.
This extra weight can go to extra payload, so from 6 mT to about 8 mT
in payload.
The Ariane 5 uses an aluminum alloy, but not the aluminum-lithium
alloy being used now for the lightest weight designs. Switching to
aluminum-lithium allows approx. 10% weight saving over the previous
aluminum alloy. The structural mass sans the SSME engine is 10.3 mT,
so about 1 mT would be saved that could go to extra payload.
I also mentioned before the new research that suggests 10% to 20% can
be saved in structural mass because of overly conservative design now
used. This would be another 1 mT that could be saved off the dry
weight. These weight savings could go to extra payload, bringing the
payload capacity to 10 mT.
ESA appears to be amenable to adapting the Ariane 5 core stage for
other uses, considering its agreement with ATK to use it for an upper
stage. So NASA or a private company should be able to make an
agreement with the ESA to use it for this purpose, based on getting
sufficient financing. In this regard, to get a prototype done at low
cost I suggest using the RD-0120 russian analogue of the SSME's. These
are in mothballs and probably can be obtained at greatly reduced
price. As a point of comparison the NK-33 was mothballed by the
russians and Aerojet was able to buy 36 of them for only $1.1 million
each(!) Aerojets version of the NK-33 is now on track to be used by
Orbital Sciences on their Taurus II launcher.
Then the Ariane 5 core version of this SSTO has the advantage over the
Ares I upper stage and S-IVB versions in being already built and in
current use. It also has now the capability when powered by an SSME or
RD-0120 to launch a SpaceX Dragon sized spacecraft to orbit without
having to use special fuel densifying or lightweighting methods.
NASA has said they want to support commercial space. Support for this
launcher would allow for a small, relatively low cost launcher that
would permit independent private companies to launch their own manned,
or cargo flights to space.



Bob Clark