Kerosene doesn't coke if you use the right kerosene.
-R
On Sun, Feb 11, 2018 at 1:40 PM William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
John:
We may be making somewhat different assumptions about funding: I’m
thinking about a risk tolerant billionaire rather than a USG funded
technology effort.
Although it might be possible, I’m skeptical that using existing engines
is a wise choice in so highly integrated a design as an SSTO must be.
Taking a page from SpaceX, I’d look to multiple independent small(er) high
performance engines for low(er) development and production costs. This
points me toward a plug nozzle with integrated heat shield.
To get high expansion ratio the 40 or more thrust chambers need a long
plug which does seem to make room for a spherical kerosene tank below the
spherical hydrogen tank. (Or a dedicated landing / entry cooling tank.)
Thus my question about tripropellant.
Kerosene imposes a requirement for flushing the system after each firing
to limit coaking in a reusable; I assume the move to methane at companies
Blue and X is to get rid of that mass, cost, and complexity as otherwise
Methane is a wash with kerosene. This seems to me to play in a
tripropellant SSTO where the added mass of a purge system may be
unacceptable. Is tripropellant w/ methane no worse performing than kerosene?
Bill
On Sat, Feb 10, 2018 at 2:49 PM John Schilling <
john.schilling@xxxxxxxxxxxxxx> wrote:
I'd probably baseline tripropellant if there were a good tripropellant
engine available; not sure it would be worth the effort of a technology and
engine development program. If there were a good staged-combustion
LOX/Kerosene engine that didn't need Vladimir Putin's approval to buy, that
plus a couple of RL-10 equivalents might be worth considering for an SSTO
propulsion suite. And at least there are other people with good reason to
chip in on a western LOX/Kero staged combustion engine program, but I'm not
going to bet the farm on Aerojet.
Wings vs VTVL are close to a wash at this point; pre-SpaceX I was leaning
wings on heritage grounds, but the performance (i.e. weight) trades are
within the error bars every time I or anyone else does them. Wings I think
become a clear win if you are using air launch to make an almost-SSTO, but
I don't think that's a good trade unless you can use a COTS launch aircraft
which at present limits you to relatively small payloads. VTVL is a clear
win if your idea of using a cold-flow engine for TPS augmentation works
out, and I've had my own thoughts on that.
I would also, for a Mark I SSTO, baseline an objective ten, threshold
fifty flights between major overhauls (i.e. swapping engines and/or
replacing the TPS). If such a vehicle is even marginally economical for
payload delivery, it becomes a cheap way of validating whatever improved
propulsion/TPS concepts we are developing in parallel for a hopefully
100-1000 flight Mark II.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 2/10/2018 12:46 PM, William Claybaugh wrote:
John:
While better propellants do seems a distance away; I’m inclined to think
that printed staged-combustion engines (a la Ursa Major) are a big enough
performance (and cost) benefit to count as a propulsion improvement worth
including in a today technology SSTO.
I was at the time impressed by the honeycomb inconel and Titanium
(respectively) TPS panels developed for X-33; they aced arc jet testing and
were both much lighter and appeared much more operable than ceramic
alternatives. The ARC inconel warpped ceramic tiles seemed—to me—a
possibly heavier and less operable backup technology. The need for
carbon-carbon ceramic at the hottest spots on some designs seemed to me,
twenty years ago, sporty: I would have designed c-c out of my personal
SSTO; I still hold that view.
I agree that Al-Li would be a today baseline. Northrop’s follow-on (to
LM’s X-33) composite H2 tanks worked fine in limited cycle testing and
might be an option. I remain deeply skeptical of using composites with Lox
for a 1000+ flights vehicle.
Highly reusable H2 tank insulation seems to me an issue: none of the
three X-33 proposals did much more than assume that the existing (or
proposed) corporate experience would last forever on an RLV. This was
specially problematic—in my view—wrt the DC-X insulation technology which
was known to shed into the plumbing.
Today, I would want to carefully understand two technologies: very low
power thrusting during entry to provide a stand-off gas blanket (and
specially the mass of propellant required) and the exact trade between
landing propellant and wings: one existing trade suggests that wings weigh
about as much as landing propellant for two very specific designs.
Would you baseline tripropellant?
Bill
On Sat, Feb 10, 2018 at 12:44 PM John Schilling <
john.schilling@xxxxxxxxxxxxxx> wrote:
Hopping the upper stage doesn't help with the high-energy recovery
problem, which I think is going to be the hard part. He'll need the BFR
booster for that. Recovering an F9 or FH upper stage would get him a
head start there, as well as making a better general-purpose launch
vehicle in the near term, so I'm somewhat disappointed that he has moved
away from that.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 2/10/2018 11:20 AM, Rand Simberg wrote:
But he's working the upper stage first, because he recognizes that asmore
the harder problem, given Falcon experience. He said he wants to start
hopping it next year.
On 2018-02-10 11:12, John Schilling wrote:
Elon said it was "conceivable" that BFR could have its first orbital
flight in four years, and Elon's schedule performance suggests that he
is already thinking in Mars years. So, mid-2025 at the earliest, and
I'd wager against even that.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 2/10/2018 10:42 AM, Rand Simberg wrote:
Not far in the future, judging by what Elon said this week at the
launch. BFS is a reusable orbital stage.
On 2018-02-10 09:38, John Schilling wrote:
I believe it was achievable 20 years ago, just more trouble than it
was worth. It is probably more achievable now, but may still be
LOX-compatibletrouble than it is worth.
One useful change has been improved materials and manufacturing
techniques to reduce structural mass, which is critical for SSTO.
Friction stir welding of Al-Li, for example. And maybe
Thecomposites, depending on what happens with XCOR's "Nonburnite".
Another, I think underrated, change is increased skepticism through
hard experience of shiny technologies that we probably don't need,
like air-turboscramwarp drives and tankage shaped into elaborate
aerodynamic shapes.
Operational validation of VTVL reusables is a good thing to have,
given that given that expendable SSTO is an economic non-starter.
tanks!),best answer may still involve wings (attached to cylindrical
somebut demanding wings because that's how Shuttle worked and we don't
trust anything else is a needless and possibly crippling constraint.
The biggest obstacle I see remaining, is the ability to safely and
reliably recover an orbital stage without excessive TPS mass.
Unfortunately, SpaceX seems to have pushed their work on that one
farther into the future, so maybe that's one for DARPA, Blue Origin,
or some newcomer to the field.
Propulsion is, I think, not a major constraint. We've got at least
marginally reusable rockets with adequate performance. There are
fornice-to-haves we could work for on that front, but no showstoppers
a Mark 1 SSTO.
John Schilling
john.schilling@xxxxxxxxxxxxxx
(661) 718-0955
On 2/10/2018 9:01 AM, William Claybaugh wrote:
Dr. Schilling’s comments on SSTO got me thinking about Have
Region, DC-X, and X-33.
Technology is now about 20 years further down the road; is
chemical rocket reusable SSTO now achievable?
What is different?
Bill