On Feb 23, 1:14*pm, Robert Clark wrote:
*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.
The advantages of a SSTO are best utilized as a reusable vehicle.
Then you would have to subtract from this estimated payload mass the
mass needed for reentry and landing systems.
However, this SSTO could still be useful as an expendable vehicle.
Then you could have up to a 9,000 kg payload without the reentry and
landing systems. This is close to the 10,000 kg payload capacity of
the Falcon 9.
I saw this article that had an estimate for the price of an
expendable version of the SSME's:
PWR Offers Shuttle Engine Alternative.
Jul 15, 2009
By Joseph C. Anselmo
"The company also would manufacture additional engines using the
existing SSME design while beginning work on a modified design that
incorporates advances in the construction of nozzles and combustion
chambers. That would be ready to go into production within 3-4 years.
Maser estimates the modified SSME would cost two-thirds to four-fifths
of the original model - depending on the number ordered - and would be
'a little more expensive' than the company's RS-68 engine 'but in that
ballpark.'"
http://www.aviationweek.com/aw/gener...%20Alternative
Using a price of $40 million for the current SSME's this would
correspond to a price of from $26.7 to $32 million for the expendable
versions. Considering the fact the engines make up the bulk of the
cost of an expendable launcher, this expendable SSTO launcher very
well could be comparable in cost to the Falcon 9 at $50 million.
Bob Clark