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 <mailto: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 <mailto: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 as
> 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
<mailto: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 more
>>>> trouble 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
LOX-compatible
>>>> composites, 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. The
>>>> best answer may still involve wings (attached to cylindrical
tanks!),
>>>> but 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 some
>>>> nice-to-haves we could work for on that front, but no
showstoppers for
>>>> a Mark 1 SSTO.
>>>>
>>>> John Schilling
>>>> john.schilling@xxxxxxxxxxxxxx
<mailto: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
>>>
>>>
>
>