I'd assume the chief benefit of subcooling methane is better storage
density. At boiling-point it's around .4, IIRC (kero tends to run a bit
over .6.)
Possibly also longer on-orbit storage time without active cooling or
superinsulation, for longer more complex in-space maneuvering? But
then, why not just use kerosene?
Methane Isp, as I mentioned, is slightly better than kero, but only
slightly. 360ish seconds vac, versus 350ish.
Henry
On 12/24/2015 9:15 AM, Ian Woollard wrote:
This subcooled methane idea, how is it supposed to work?
I thought about it, and pulled some of the physical data, but I'm still
not quite getting it.
Presumably you cool it down so that the vapour pressure is low, so the
tank walls can be thin and light and I ran cpropep-web and looks like
you'll get nearly the same Isp as Kerosene. But the propellant density
and impulse density is unimpressive.
I can see some small wins, like you it helps having the two propellants
at about the same temperature, but no big win. What am I missing?
To be honest, Musk really needs a hydrogen upper stage.
And Musk's other idea of making everything bigger, it would help a bit;
but Falcon 9 is pretty big already; he'd mainly gain on the reduced
reentry shielding due to area/volume relationships.
On 24 December 2015 at 14:42, Findley, Jeff <jeff.findley@xxxxxxxxxxx
<mailto:jeff.findley@xxxxxxxxxxx>> wrote:
On Wednesday, December 23, 2015 3:09 PM Derek Lyons wrote:____
> Quoted for truth. "Everyone" expected him to stick the first barge
landing. And the second. And the third.____
> Yet the times he didn't and their predictions were wrong have already
gone down the memory hole.____
__ __
We’re skirting very close to “fanboy bashing”, which I’ve seen on
enough websites over the years. “The other side” has called Musk’s
Falcon 9 a “hobby rocket”, criticized the “low performance” of the
Merlin engines, and said that reuse would never happen (because
smarter minds than his have not been able to do it yet, so it must
not be possible). So, all of those predictions have also “gone down
the memory hole”.____
__ __
> As Bill correctly points out, there's good reason for healthy skepticism.
(Not the least of which is the track ____
> record of a very complicated and "sporty" landing sequence.)____
__ __
While true, Musk also has a mind for the future. Let’s draw some
parallels with Tesla...
The first Tesla was an extremely impractical car, but you have to
start somewhere (Falcon 1). The second Tesla was a quite impressive
car, but still far too expensive for most people to afford at about
$100k (Falcon 9 and Falcon Heavy). Eventually, Musk plans on
selling an “affordable” car, but it requires building the biggest
battery factory on the planet before he can even think about
starting production (LOX/methane fully reusable launch vehicle).____
__ __
Say what you will about Musk, but he thinks big, and he thinks very
long term. ____
__ __
Jeff____
__ __
--____
Jeffrey Findley____
Product Eng____
__ __
Siemens Industry Sector____
Siemens Product Lifecycle Management Software Inc.____
2000 Eastman Drive____
Milford, OH 45150 United States ____
Tel. :+1 (513) 576-5606 <tel:%2B1%20%28513%29%20576-5606>____
Fax :+1 (513) 576-2840 <tel:%2B1%20%28513%29%20576-2840>____
jeff.findley@xxxxxxxxxxx <http://jeff.findley@xxxxxxxxxxx%20>____
www.siemens.com/plm <http://www.siemens.com/plm>____
__ __
*From:*arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>
[mailto:arocket-bounce@xxxxxxxxxxxxx
<mailto:arocket-bounce@xxxxxxxxxxxxx>] *On Behalf Of *Derek Lyons
*Sent:* Wednesday, December 23, 2015 3:09 PM
*To:* arocket@xxxxxxxxxxxxx <mailto:arocket@xxxxxxxxxxxxx>
*Subject:* [AR] Re: Re spacex falcon 9 landing____
__ __
On Dec 23, 2015 11:44 AM, "William Claybaugh" <wclaybaugh2@xxxxxxxxx
<mailto:wclaybaugh2@xxxxxxxxx>> wrote:____
> Take care; there is a difference between doubt and >professional
caution: I'm inclined to the view that >competent engineers, given
good specs, will at least >meet their goals. Thus it seems likely
that Falcon 9 will >be easier to refurbish than previous examples
>of reusable hardware. But in addition to being designed >for reuse
it was also designed for very low cost as an >expendable. It is
worth considering whether the total >cost of reuse is going to
be lower than the intentional-->and demonstrated--low cost of
expending. That is not >doubt, that is a subject matter expert
thinking carefully >bout the the details.
>
> Just sayin'
>
> Bill____
Quoted for truth. "Everyone" expected him to stick the first barge
landing. And the second. And the third. Yet the times he didn't
and their predictions were wrong have already gone down the memory
hole.____
As Bill correctly points out, there's good reason for healthy
skepticism. (Not the least of which is the track record of a very
complicated and "sporty" landing sequence.)____
D.____
--
-Ian Woollard
Sent from my Turing machine