Craig:
Let me suggest you make the acquaintance of the rocket equation which will
teach you that even air breathing all the way to Mach 25 will require about
25% propellant (assuming Isp = 3000).
As a practical matter, Mach 8 is as far as air breathing will take you
today; the cost of keeping the nose tip and leading edges from melting is
too high to justify any greater velocity but the best known technology
appears unlikely to get you past Mach 12 for cruise in the very upper
atmosphere, someday.
Given Mach 8 as a practical maximum for air breathing today, the rest must
be done with rockets. That in turn means such a vehicle will be at least
55% propellant (I’m being very generous here). But air breathing means
much higher structural mass than a pure rocket: 35% is probably
optimistic. Thus 10% payload is an absolute maximum payload fraction for
an air breathing / rocket launch system...a realistic estimate based on
actual engineering of such systems suggests 2-3% is much more likely.
All of which is further proof that analogical thinking is mostly useless:
sub and slightly super sonic passenger aircraft are simply not comparable
to fully reusable Mach 25 spaceships.
Bill
On Sat, 25 May 2019 at 13:20, Craig Fink <webegood@xxxxxxxxx> wrote:
Hi Rand,
It's been a while, how are you doing?
There is a physical reason, and it's that Oxygen is heavy. That's why the
payload mass fraction of an air-breathing vehicle to Orbit would most
likely be something akin to that of a 747, Concord.
This is the same reason that while we are seeing electric drones and a few
electric small airplanes that are being developed, they will never be able
to compete with aircraft that only carry Fuel and gather the Oxygen along
the way. The Battery weights the same at takeoff and landing, while a
Commercial Airliner's weight decrease the entire flight. For this reason,
any long distance electric aircraft will probably have a generator
supplying the electricity instead of batteries.
https://en.wikipedia.org/wiki/Fuel_fraction
40-45% for long haul aircraft.
Oops, these two pages don't agree, Apples and Oranges. The payload
Wikipedia page included fuel as payload? Hummm.
https://en.wikipedia.org/wiki/Payload_fraction
OK, Change all those 50% to 20%
On Sat, May 25, 2019 at 10:02 AM Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
There is no physical reason to expect that.
On 2019-05-25 09:48, Craig Fink wrote:
On Sat, May 25, 2019 at 9:39 AM William Claybaugh
<wclaybaugh2@xxxxxxxxx> wrote:
David:
SSTO is cheaper than a TSTO of the same dry mass because staging
adds about 10% additional integration cost (assuming expendables,
reusables cost still more due to recovery and refurbishment costs).
However, TSTO throws more payload into orbit than an SSTO; the best
anyone has ever done with any rocket is about 5% payload (Space
Shuttle, counting the Orbiter as payload) and so it follows that an
SSTO w/ that payload fraction will be lower cost than any similar
dry mass and payload multi-stage vehicle.
https://en.wikipedia.org/wiki/Payload_fraction
The 747 and Concorde are at 50%, I would expect air-breathing to Orbit
to be close to this when it's fully developed.
This thought experiment overlooks the effect of technology (any
technology that allows 5% payload on an SSTO should improve a TSTO
as well) but a more detailed analysis will show that the effect is
very small: at 5% payload the advantages of staging become small.
Bill
On Sat, 25 May 2019 at 04:24, David Summers <dvidsum@xxxxxxxxx>
wrote:
I sense something I could learn from!
Why do you say 5% to be the economical msss ratio? What drives the
numbers?
My guess: engine cost is much higher than tankage, and you drop them
with the tanks?
On Sat, May 25, 2019, 12:08 AM William Claybaugh
<wclaybaugh2@xxxxxxxxx> wrote:
Craig:
Are you being a jerk on purpose or have you just not followed this
conversation?
Second stage of the Saturn 5 was also capable of expendable SSTO if
re-engined with SSME’s. Expendable SSTO has be technically
feasible since the late 1950’s; it simply hasn’t been economic.
Nor will it be until 5% payload fractions are achievable.
Bill
On Fri, 24 May 2019 at 19:01, Craig Fink <webegood@xxxxxxxxx> wrote:
On Wed, May 22, 2019 at 7:34 PM Henry Spencer
<hspencer@xxxxxxxxxxxxx> wrote:
On Wed, 22 May 2019, anthony@xxxxxxxxxxx wrote:
Wasn’t the former Titan capable of SSTO, assuming a practical“zero”
payload?
The Titan II first stage could even carry a token payload into
orbit,
maybe 1t or so if you did things just right
Hi Henry,
Titan was a missile, how many 1t weapons did it take to orbit?
Or, Ascents did it perform SSTO?
--
Craig Fink
WeBeGood@xxxxxxxxx
--
Craig Fink
WeBeGood@xxxxxxxxx
--
Craig Fink
WeBeGood@xxxxxxxxx
