Falcon 9 expendable performance and re-use penalty estimated from SES-9 mission

[John Alan]

Moving from v1.0 to v1.1 staging speed changed from 3000 m/s to 2000 m/s.
Less than this?

Yes... lower and slower yet... how much is not clear
Trade some fuel/lox up into S2 from S1 to make up the delta v needed...
The re-entry burn or boost back burn will be shorter too... IF it's doing so on that flight...

The whole idea seems "interesting" to ponder... 

On edit...
To clarify... my thought was exact same length, same gross fuel/lox weight... just a rebalance of S1/S2 split on consumables...
Does that get it closer to the 8.3t SpaceX is claiming expendable on their webpage now... 

[Stan-1967]

How long can they stretch F9?  It seems an underlying assumption that the vehicle at its max.   If not, and changes to GSE aren't a show stopper,  that opens the door to a bigger S2.

[hkultala]

Very interesting trade.  It's not just moving 10 ft ( or whatever amount) of tankage between S1 & S2 to get better mass staging ratios, I think the advantage of the M1-Vac burning at 348s ISP vs. 311 ISP would be the big kick additional performance. 

The original point about the tankage was about price of the stages, and the tankage is really cheap compared to engines etc.


But about the capasity:

It's also that how much tank mass has to go all the way up to GTO with the satellite. When more mass is in the first stage, less total mass has to be lifted to GTO, or bigger part of the total GTO mass can be payload mass

So a good question to figure out would be the altitude at which you can have a clean staging event, and ignition of S2 can take place without increasing too much gravity loss from the lower T/W of S2?

F9 is already staging very early compared to most rockets, and S2 is already doing huge part of the work.

 

[pippin]

Are we sure the 8.3t are from the Cape, not some theoretical equatorial launch site? And that they refer to the same GTO?

[Robotbeat]

Or Boca Chica, more likely.

[Lar]

Or Boca Chica, more likely.

That helps a little maybe but not that much to make up ~3T I didn't think.

[Robotbeat]

It's a whole bunch of little things together.

Boca Chica
Shorter hold down times
Slightly higher Isp
Lower gravity losses
More propellant (densification)
Lower dry mass
etc, etc...

[wannamoonbase]

It's a whole bunch of little things together.

Boca Chica
Shorter hold down times
Slightly higher Isp
Lower gravity losses
More propellant (densification)
Lower dry mass
etc, etc...

...a good tail wind.

Edit: In seriousness I've been thinking about the hold down times and with more flights they should know if there is any time to shave. 

[Robotbeat]

The last launch had a shorter hold down.

The Falcon 9 is an amazingly capable rocket. People underestimate its performance.

[IRobot]

It's a whole bunch of little things together.

Boca Chica
Shorter hold down times
Slightly higher Isp
Lower gravity losses
More propellant (densification)
Lower dry mass
etc, etc...

Less drag (from legs, fins)

[acsawdey]

It's a whole bunch of little things together.

Boca Chica
Shorter hold down times
Slightly higher Isp
Lower gravity losses
More propellant (densification)
Lower dry mass
etc, etc...

Less drag (from legs, fins)

Actually, wasn't there something Musk said in an interview about redesigned legs that could partially deploy earlier as a drag brake? Reducing the amount of fuel needed for re-entry and landing burns would increase the payload for ASDS and RTLS.
 

[Nomadd]

Could throttling be part of it? Or is payload the main factor in that? I also wonder if engine out has anything to do with the numers.

[pippin]

Sorry, but we're talking > 30% more payload here, it's not going to be small things.

[Jim]

Or Boca Chica, more likely.

That is going to less than the cape due to non optimal trajectory

[Robotbeat]

Sorry, but we're talking > 30% more payload here, it's not going to be small things.

Small things, in aggregate, can make a huge difference due to the exponential nature of the rocket equation combined with the fact that Falcon 9 is just two stages, neither of which are high Isp, and because we're talking about a high energy trajectory.

[pippin]

But not _so_ small things like hold down times and aerodynamics due to lack of legs can't play a role because they haven't been attached on previous expendable launches either.
Also, we are still talking about first stage changes

[Robotbeat]

Reduced hold down times is a new thing. And performance is already much higher than older legless launches.

[envy887]

First stage thrust is going up 17% over the SES-9 launch. That's not a small thing.

And high energy orbits are very sensitive to small changes. Just changing the upper stage fuel margins by .1% adds several hundred kg to the payload capacity.

[Stan-1967]

Could SpaceX be enabling this Block 5 with longer duration & multiple restart capability of S2, thereby enabling a Bi-elliptic transfer orbit to GTO?   Would this enable more efficient burns at periapsis & apoapsis, and thereby lessen the overall DV needed to get to GTO?

[Robotbeat]

Upper stage can already do multiple restarts.