SpaceX Falcon 9 : Intelsat 35e : July 5, 2017 : DISCUSSION

[Mike_1179]

It's a little unfair to compare what another vehicle (like Atlas) can do when its listed performance is given for a guidance commanded shutdown vs a minimum residual shutdown that happened here. The former will always reserve some delta-V margin for performance dispersions like steering losses, engine underperformance, etc.

If F9 had to deliver a payload to a *specific* GTO-1720 orbit, the maximum payload mass would certainly be less than 6.7 tonnes precisely because they'd be sandbagging the performance to make sure they hit the target with some propellant margin to spare.

Totally fair point. Have EELVs ever done a minimum residual shutdown that could be used for comparison?

[guckyfan]

Have EELVs ever done a minimum residual shutdown that could be used for comparison?

If not, then why not?

[mme]

Don't remember acknowledgement of previous launches?

Congrats on another successful launch and satellite deployment.  Keep up the great work!  Charlie B.

https://twitter.com/cboldenjr/status/883012283160555525

Maybe one of his granddaughters is a new fan.

Charles Bolden‏  @cboldenjr

I have no idea how to use twitter so my granddaughters are probably going to be managing this #welcometotwitter #newbie

https://twitter.com/cboldenjr/status/835511790381453313

[Kaputnik]

2017-041A    42818    FALCON 9 R/B    775.27min    25.84°    42861km    293km
2017-041B    42819    INTELSAT 35      772.84min    25.85°    42742km    296km

About GTO-1719. Excellent performance.

And how does that compare to Atlas V performance?

It's in the ballpark of what an Atlas 531 could do.

For $142M basic list price.

With gas generator engines and RP-1 on both stages. Still kind of boggles the mind.

Which makes what they'll do with staged combustion & Methalox even more exciting.

[macpacheco]

2017-041A    42818    FALCON 9 R/B    775.27min    25.84°    42861km    293km
2017-041B    42819    INTELSAT 35      772.84min    25.85°    42742km    296km

About GTO-1719. Excellent performance.

And SpaceX is still warming up, supposedly the full Block V can do the same with at least 700kg more payload, maybe 1 ton more. If it could put 8300kg to GTO-1800m/s, couldn't it put a 7700kg payload 200m/s closer to GEO, assuming also a burn to depletion ?

[envy887]

It's a little unfair to compare what another vehicle (like Atlas) can do when its listed performance is given for a guidance commanded shutdown vs a minimum residual shutdown that happened here. The former will always reserve some delta-V margin for performance dispersions like steering losses, engine underperformance, etc.

If F9 had to deliver a payload to a *specific* GTO-1720 orbit, the maximum payload mass would certainly be less than 6.7 tonnes precisely because they'd be sandbagging the performance to make sure they hit the target with some propellant margin to spare.

Either way, what F9 did here is fairly impressive as is SpaceX's turnaround record with LC-39A.

Solids give a step change, not a continuous performance curve. According to ULA's website, the 531 is required for anything over 6453 kg to GEO-1800, and the price is the same $142M for 6453 kg all the way up to 7423 kg

So for some payloads requiring the 531, the F9 could hit a commanded orbit with some level of reserves. For others, it couldn't get there with a minimum residual shutdown.

Still, impressive performance. And expected to grow considerably more in the next few months...

[LouScheffer]

It's a little unfair to compare what another vehicle (like Atlas) can do when its listed performance is given for a guidance commanded shutdown vs a minimum residual shutdown that happened here. The former will always reserve some delta-V margin for performance dispersions like steering losses, engine underperformance, etc.

If F9 had to deliver a payload to a *specific* GTO-1720 orbit, the maximum payload mass would certainly be less than 6.7 tonnes precisely because they'd be sandbagging the performance to make sure they hit the target with some propellant margin to spare.

Totally fair point. Have EELVs ever done a minimum residual shutdown that could be used for comparison?

Sure, Atlas does minimum residual shutdowns

Refer to the Atlas Launch System Mission Planner’s Guide (Rev. 7) for a description of MRS. The Atlas V performance variations associated with MRS are in Table 2.6.2-1 and in the performance curves in Sections 2.12 and 2.13 for the Atlas V 400 and Atlas V 500, respectively. MRS has been successfully executed for 24 Atlas missions and has become the typical operations mode for GTO-type missions.

From the graphs in the presentation, it looks like they get about 200 kg more payload with a MRS.

[edkyle99]

MRS always made more sense to me than commanded shutdown for these transfer orbit missions.  Why not use up all of the gas in the tank?

 - Ed Kyle

[acsawdey]

MRS always made more sense to me than commanded shutdown for these transfer orbit missions.  Why not use up all of the gas in the tank?

 - Ed Kyle

Well, within reason, right? Don't want to accidentally TLI the payload just because somebody didn't notice where the moon was ...

[LouScheffer]

MRS always made more sense to me than commanded shutdown for these transfer orbit missions.  Why not use up all of the gas in the tank?

For GTO, anyway.  If you're trying to rendezvous with something, you probably want to stop once you've got the right orbit.

Even for GTO, minimum-residual requires that the satellite and ground support can deal with the variable and super-synchronous orbit you might get.  As I understand it, some GEO satellites are not super flexible about working in other orbits, and maybe the customer wants a fast and predictable deployment.  It's also possible that with a light GTO payload, a minimum fuel shutdown would put it on an escape trajectory.  I believe that even a MRS has an upper apogee limit precisely to avoid this possibility.

[tp1024]

Did anybody else notice that the first stage shut down two seconds earlier than during the Inmarsat-5 mission? Staging also occured 3km lower and about 80m/s slower. So unless SpaceX put 4 tons less fuel into the stage, something didn't quite go as planned.

[Stevenzop]

Did anybody else notice that the first stage shut down two seconds earlier than during the Inmarsat-5 mission? Staging also occured 3km lower and about 80m/s slower. So unless SpaceX put 4 tons less fuel into the stage, something didn't quite go as planned.

It's a heavier payload, slightly increased gravity losses maybe?

(I'm not sure here, does it work like that?)

[Steven Pietrobon]

Did anybody else notice that the first stage shut down two seconds earlier than during the Inmarsat-5 mission? Staging also occured 3km lower and about 80m/s slower. So unless SpaceX put 4 tons less fuel into the stage, something didn't quite go as planned.

The earlier shutdown might have been caused by throttling the engine down a little later in time or just dispersions in the Isp and thrust of the engines. The lower and slower performance is probably due to the heavier payload.

[tp1024]

Did anybody else notice that the first stage shut down two seconds earlier than during the Inmarsat-5 mission? Staging also occured 3km lower and about 80m/s slower. So unless SpaceX put 4 tons less fuel into the stage, something didn't quite go as planned.

The earlier shutdown might have been caused by throttling the engine down a little later in time or just dispersions in the Isp and thrust of the engines. The lower and slower performance is probably due to the heavier payload.

Its just 0.7t heavier. First stage (empty) and second stage (full) have a mass of ~150 tons. It will reduce acceleration by 0.2m/s*s at the end of the flight. If that was true for the whole 170s flight (a gross exaggeration), it would account for a loss of 34m/s. It is actually much less.

[woods170]

Did anybody else notice that the first stage shut down two seconds earlier than during the Inmarsat-5 mission? Staging also occured 3km lower and about 80m/s slower. So unless SpaceX put 4 tons less fuel into the stage, something didn't quite go as planned.

Emphasis mine.

Bold assertion for something derived from watching a webcast whilst not having insight into what SpaceX had actually planned.
That said, first stage performance in this case does not matter. It's the final performance at payload separation that counts. And that was well above expectation.

[FutureSpaceTourist]

A write-up of the F9 performance, in terms of achieved orbit, for this flight:

http://spaceflight101.com/falcon-9-intelsat-35e/falcon-9-outperforms-expectations-with-intelsat-35e/

The achieved orbit is around 105m/s closer to the satellite’s operational Geostationary Orbit in terms of change in velocity needed by Intelsat 35e to reach GEO, equivalent to around two years of in-orbit stationkeeping

[edkyle99]

Did anybody else notice that the first stage shut down two seconds earlier than during the Inmarsat-5 mission? Staging also occured 3km lower and about 80m/s slower. So unless SpaceX put 4 tons less fuel into the stage, something didn't quite go as planned.

I noticed that it was two seconds longer than the number given in the press kit.  I have it as about one second shorter than during the Inmarsat launch.  Throttling differences possibly account for much of the difference.  These are the two longest first stage burns by any v1.2 variant.

Here are my notes:

Inmarsat 5 F4:  S1 165 sec, S2-1 342 sec, S2-2 56 sec
Intelsat 35e:  S1 164 sec, S2-1 346 sec, S2-2 57 sec
Intelsat 35e Presskit:  S1 162 sec, S2-1 344 sec, S2-2 52 sec

 - Ed Kyle

[kenny008]

Not an expert on this, but there is a g-limit (5 g's?).  Later in flight, as they hit the g-limit, the stage throttles down.  For a heavier payload, wouldn't it hit the g-limit slightly later, therefore staying at full thrust slightly longer and burning fuel quicker?  This would slightly shorten the overall 1st stage burn time.

[mn]

...
first stage performance in this case does not matter. It's the final performance at payload separation that counts. And that was well above expectation....

I don't know anything about the current mission and if there was indeed a shortfall or not, I have no idea.

BUT this statement is like saying there was nothing wrong with OA-6 !!

[abaddon]

I don't know anything about the current mission

I'll try and be helpful.  Intelsat 35e was a nominal mission with greater than expected performance.  OA-6 experienced an anomaly greatly impacting performance, but was able to (barely) achieve mission success due to excess performance being available.

In the future, I would suggest that commenting on something you admit you don't have any knowledge of ends up harming the content of your post.  woods170 is correct, and your analogy is invalid.