On Feb 23, 1:14*pm, Robert Clark wrote:
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...

In these examples of using the SSME engine on existing stages to turn
them into SSTO's, I was using the trajectory averaged Isp value for
the SSME that Gary Hudson uses he

A Single-Stage-to-Orbit Thought Experiment.
Gary C Hudson
http://www.spacefuture.com/archive/a...periment.shtml

Note that a trajectory averaged Isp is always higher than just the
midpoint value between the sea level and vacuum values because the
rocket spends most of the time at high altitude, where the Isp is
close to the vacuum value.
However, I myself have not seen this actually computed. I have not
even seen it stated anywhere else except in this calculation by
Hudson. It should not be hard to do this calculation. You would need
to know the value of the thrust over the flight of the shuttle. I'm
sure this exists somewhere, possibly in graphical form. For instance
it's presented here for the thrust of the SRB's:

Space Shuttle Solid Rocket Booster.
3.1 Ignition
http://en.wikipedia.org/wiki/Space_S...oster#Ignition

You could also get a fairly good approximation to this trajectory
averaged Isp by knowing the altitude over the time of the flight and
using the formula for how the thrust for a rocket varies with ambient
air pressure.
Anyone know where the thrust or altitude profile for the shuttle is
given over the flight of the vehicle?


Bob Clark