Telemetry data from SpaceX Youtube

On Jan/20/2016 7:46 AM, Jeff Findley wrote :
In article id,
lid says...

In sci.space.policy message -
september.org, Sat, 16 Jan 2016 11:57:11, Jeff Findley
posted:

In article ,
says...

wrote:

On Tuesday, January 5, 2016 at 3:11:55 PM UTC-5, wrote:
Well I am no rocket scientist, But I clicked through the telemetry


I got to thinking about the implications of the SpaceX data. One
huge design error of Falcon9 is the first stage release. Throttling
down and coasting as the method of separation causes a "re-launch"
at altitude. The rocket simply has to burn larger than it would of
otherwise. This is just a fuel waste issue.


Fuel is cheap, which is the point.

For Falcon 9, fuel costs are reportedly less than 1% of launch costs.
Any SpaceX engineer who was hell bent on minimizing "fuel waste" would
be fired. Aruging with the boss is not a good thing.

Stationary fuel at ground level is cheap. But fuel at MECO altitude and
velocity is not cheap.

Excuse my language, but I'm calling bull****!

Fuel cost is paid when the vehicle is loaded and each pound of fuel
added to the vehicle costs the very same amount. Your wrong headed
thinking about "performance" and "fuel waste" is the sort of wrong
headed thinking that has kept launch vehicles expensive for decades.

Again, who cares how much fuel is "wasted" when its cost is *less* than
1% of launch costs? Falcon 9 could "waste" far more fuel than it does
now and still charge customers less than the competition, still get
payloads to orbit, and still make a profit.

The metric to optimize is overall launch cost and today fuel costs are
quite simply lost in the noise. A good engineer does not try to
optimize away a cost that is less than 1% of the overall cost.

I kind of agree with both of you on this. Or maybe that is I don't agree
with neither of you, I'm not sure.

I don't think Mr Stockton is saying that fuel at MECO altitude and
velocity is so valuable that it shouldn't be wasted to recover the first
stage the way SpaceX is doing.

But fuel at MECO isn't quite like fuel on the ground. It's not the price
of the fuel per se that makes it different. It's because to bring it to
MECO altitude and speed you needed tanks (which are also cheap) and to
bring those tanks and that fuel you needed rocket engines, which aren't
cheap.

Another way of saying this, is that if fuel at MECO was cheap there
wouldn't be any point in having the "Just Read The Instructions" or the
"Of Course I Still Love You", you would return every first stage to
launch site. The Falcon heavy plans on using drone ships instead of
return to launch site because fuel at MECO isn't cheap.

So yes, fuel is cheap. Yes it is worth it to spend some extra fuel to
save the first stage and things like that. But you still need to be
careful with.


Alain Fournier

In article , says...
I kind of agree with both of you on this. Or maybe that is I don't agree
with neither of you, I'm not sure.

I don't think Mr Stockton is saying that fuel at MECO altitude and
velocity is so valuable that it shouldn't be wasted to recover the first
stage the way SpaceX is doing.

But fuel at MECO isn't quite like fuel on the ground. It's not the price
of the fuel per se that makes it different. It's because to bring it to
MECO altitude and speed you needed tanks (which are also cheap) and to
bring those tanks and that fuel you needed rocket engines, which aren't
cheap.

Another way of saying this, is that if fuel at MECO was cheap there
wouldn't be any point in having the "Just Read The Instructions" or the
"Of Course I Still Love You", you would return every first stage to
launch site. The Falcon heavy plans on using drone ships instead of
return to launch site because fuel at MECO isn't cheap.

Only for the core stage. The side boosters will stage at a low enough
altitude and low enough velocity that they can make it back to the
launch site. The core stages higher in altitude and velocity and yes,
getting it back to the launch site would require more fuel than is
available. But this isn't a function of the cost of fuel so much as a
function of when the core stages. Everything in engineering is a
compromise. In this case, you trade higher payload (more fuel) for a
lower likelihood of getting the stage back intact.

So yes, fuel is cheap. Yes it is worth it to spend some extra fuel to
save the first stage and things like that. But you still need to be
careful with.

Agreed in that you work within the constraints of the vehicle you've
designed and built. My point is that Falcon 9 was deliberately designed
to be bigger than necessary (# of engines, dry mass, fuel load, and
etc.) in order to incorporate reusability from the start. Other launch
providers simply do not do this and instead minimize # of engines, dry
mass, fuel load, and etc. in pursuit of "maximum performance".

Maximum performance does not equate to minimum cost.

Jeff
--
"the perennial claim that hypersonic airbreathing propulsion would
magically make space launch cheaper is nonsense -- LOX is much cheaper
than advanced airbreathing engines, and so are the tanks to put it in
and the extra thrust to carry it." - Henry Spencer

On Jan/24/2016 9:51 AM, Jeff Findley wrote :
In article , says...
I kind of agree with both of you on this. Or maybe that is I don't agree
with neither of you, I'm not sure.

I don't think Mr Stockton is saying that fuel at MECO altitude and
velocity is so valuable that it shouldn't be wasted to recover the first
stage the way SpaceX is doing.

But fuel at MECO isn't quite like fuel on the ground. It's not the price
of the fuel per se that makes it different. It's because to bring it to
MECO altitude and speed you needed tanks (which are also cheap) and to
bring those tanks and that fuel you needed rocket engines, which aren't
cheap.

Another way of saying this, is that if fuel at MECO was cheap there
wouldn't be any point in having the "Just Read The Instructions" or the
"Of Course I Still Love You", you would return every first stage to
launch site. The Falcon heavy plans on using drone ships instead of
return to launch site because fuel at MECO isn't cheap.

Only for the core stage. The side boosters will stage at a low enough
altitude and low enough velocity that they can make it back to the
launch site. The core stages higher in altitude and velocity and yes,
getting it back to the launch site would require more fuel than is
available. But this isn't a function of the cost of fuel so much as a
function of when the core stages. Everything in engineering is a
compromise. In this case, you trade higher payload (more fuel) for a
lower likelihood of getting the stage back intact.

So yes, fuel is cheap. Yes it is worth it to spend some extra fuel to
save the first stage and things like that. But you still need to be
careful with.

Agreed in that you work within the constraints of the vehicle you've
designed and built. My point is that Falcon 9 was deliberately designed
to be bigger than necessary (# of engines, dry mass, fuel load, and
etc.) in order to incorporate reusability from the start. Other launch
providers simply do not do this and instead minimize # of engines, dry
mass, fuel load, and etc. in pursuit of "maximum performance".

Maximum performance does not equate to minimum cost.

I started my previous post by saying I agreed with both of you or maybe
with neither of you. Well now I say I agree with you period.


Alain Fournier