True. Elon Musk said by next year they expect to be doing short hops of
the BFR upper stage to test its capability as a point to point transport.
This is interesting because the point-to-point transport application during
his earlier presentations on the BFR were only in regards to the full
two-stage vehicle.
. With these short hop tests of the upper stage perhaps they only intend
it to be under a partial fuel load. They might need it to have 9 engines
instead of the planned 6 to be to lift off with a full fuel load. With a
full fuel load, calculations, show the BFR upper stage can be SSTO. The
SSTO application and the point-to-point transport application have the
potential to allow high flight rates to make SSTO's economical.
Bob Clark
On Wed, Feb 14, 2018 at 8:19 PM, Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
A necessary condition for economic SSTO is very high traffic rate to a
specific delta vee. e.g., a facility, or facilities, in equatorial orbit.
Because off-nominal performance of SSTO, regardless of engine type, is
awful.
On 2018-02-14 17:15, William Claybaugh wrote:
Evan:
Thanks, I had missed this.
I find myself wondering what an advisor would have said if Henry II
(of England) had asked for an iPhone: is SSTO a technology that is
more economic in future rather than today?
Because multiple analyses show SSTO at a limit price around $50 per
Kg., it seems likely to be the preferred answer in a century or so
when demand has reached levels that justify that solution. The
question I’m—in part—trying to answer is whether a significant
investment today can move forward the time when SSTO flight rates are
justified.
In the timeframe of SSTO viability it appears probable that “peak
oil” will be reached and thus that simpler hydrocarbons may be
favored over highly refined ones (because simple hydrocarbons can be
relatively cheaply derived from organic feedstock). Thus Propane over
Kerosene.
Bill
On Wed, Feb 14, 2018 at 1:00 PM Evan Daniel <evanbd@xxxxxxxxx> wrote:
On Wed, Feb 14, 2018 at 1:55 PM, William Claybaugh
<wclaybaugh2@xxxxxxxxx> wrote:
If we are considering tripropellants, then the Hydrogen wouldpresumably be
used as the coolant (optimizing Isp by altitude is achieved byvarying the
percentage of Hydrogen and Hydrocarbon being burnt). But thatstill leaves a
potential coking problem at the hydrocarbon injectors and upstreamafter
shutdown; a hydrocarbon that evaporates w/o residuals seems likelyto be a
better choice than one that does not (like kerosene) if one islooking to
avoid a post firing purge.
Part of XCOR's approach was to use a kerosene that evaporated
without residuals.
Doug's post on 3/29/17 to this list includes a photo and AIAA paper:
https://www.freelists.org/post/arocket/LPL-IPA-Effects-on-Copper,5
And a selected quote that the archives don't seem to display:
"...dry-residue-free fuels are strongly advisable, so that greasy
films cannot be created by fuel spills. We have had good results in
using 99% isopropyl alcohol as fuel; we even use the same supply for
the cleaning solvent to prepare the oxidizer plumbing. In the
transition to kerosene based fuels, we have settled on a grade of
kerosene equal or even superior to RP-1, a multiply-distilled
product
with no non-volatile components. Conventional Jet-A or JP-4 has too
many high molecular weight species, aromatic compounds, and [too
much]
sulfur content to be used in a long-life regeneratively cooled
rocket
engine where low coking is mandatory. The jet fuels leave long
lasting
residues, incompatible with oxygen, if spilled."
Evan Daniel