SpaceX Falcon 9 - Inmarsat 5 F4 - May 15, 2017 - DISCUSSION

[stcks]

The same performance would put 6820 kg to GEO-1800, assuming the stage dry mass if 4500 kg and MVac I_sp is 348 seconds.

I'm curious, can you explain how you got there?

[TrueBlueWitt]

So assuming that this is max performance for the F9, at least for the moment, and as noted above by others, a 6,070 KG payload to GTO-1570, does this give us a clue what the max payload would for a GTO launch? I seem to recall seeing GTO-1800 is acceptable for customers. I don't have the knowledge to either know that GTO-1800 is ok, or the math to work backwards to get the payload. I would be interested on any thoughts by those more knowledgeable than I. I also wonder what portion of commercial payloads would exceed the mass we now think F9 is capable of. It seems like a smaller portion is restricted to the competition.

The same performance would put 6820 kg to GEO-1800, assuming the stage dry mass if 4500 kg and MVac I_sp is 348 seconds.

So we are still no where near the 8300kg promise land... Figures... 

Ref http://www.spacex.com/falcon9

8300 is the GTO figure.

This number  is also presumably for Block 5 which has higher Merlin thrust  levels and other changes. All boosters prior to block 5, other than potential reflights,  are probably already spoken for.

[rsdavis9]

So could any falcon heavy payload be put on f9 expendable? Well up to 8.3MT at least. Is it cheaper to expend a F9 once in a while versus have to refurb 3 boosters for heavy?

[kevin-rf]

From the update thread -

42698   INMARSAT 5-F4   2017-025A      1401.67min   24.50deg   69839km   381km      
42699   FALCON 9 R/B   2017-025B           1410.43min   24.47deg   70181km   384km

Definitly Super-synchronous.

Certainly. Only thing is that upper stage will stay up there for a long time.

Can I ask Targeteer's source, Space-Track.org is still returning No Results to Display for 42698 and 42699.

I am assuming these did not come from them.

[envy887]

The same performance would put 6820 kg to GEO-1800, assuming the stage dry mass if 4500 kg and MVac I_sp is 348 seconds.

I'm curious, can you explain how you got there?

This launch was GEO-1570, or 230 m/s past GEO-1800. I just used the rocket equation to back out the initial mass that would give this payload 230 m/s less delta v: (4500 kg + 6100 kg) * e^(230 m/s / 3414 m/s) - 4500 kg = 6838 kg (I used 233 m/s the first time, it gives 6820 kg).

[envy887]

Can I ask Targeteer's source, Space-Track.org is still returning No Results to Display for 42698 and 42699.

I am assuming these did not come from them.

He frequently posts orbital parameters before they show up on the tracking sites. Inside source, I guess

[LouScheffer]

The same performance would put 6820 kg to GEO-1800, assuming the stage dry mass if 4500 kg and MVac I_sp is 348 seconds.

I'm curious, can you explain how you got there?

When I do this I get a different result.   The orbit they got (70000 km apogee, 24.5 inclination) requires about 377 m/s more than a minimal GTO to both raise the apogee and reduce the inclination.  (This assumes a 180km x 180km x 28 degree parking orbit.)  The payload was 6,086kg according to Inmarsat CTO.

Then assuming 111.5t of fuel, 4.5t empty stage, we get a delta v of ISP*g*ln(initial/final) = 348*9.8*ln(122.086/10.586) = 8339 m/s.

To get 357 m/s less (the remainder is the first stage delta), you need to increase the mass to 7,380 kg.  This gives 348*9.8*ln(123.38/11.88) = 7982 m/s.   So the same performance could put 7.38 tonnes into a minimal GTO (GEO-1800) from the Cape.

[envy887]

The same performance would put 6820 kg to GEO-1800, assuming the stage dry mass if 4500 kg and MVac I_sp is 348 seconds.

I'm curious, can you explain how you got there?

When I do this I get a different result.   The orbit they got (70000 km apogee, 24.5 inclination) requires about 377 m/s more than a minimal GTO to both raise the apogee and reduce the inclination.  (This assumes a 180km x 180km x 28 degree parking orbit.)  The payload was 6,086kg according to Inmarsat CTO.

Then assuming 111.5t of fuel, 4.5t empty stage, we get a delta v of ISP*g*ln(initial/final) = 348*9.8*ln(122.086/10.586) = 8339 m/s.

To get 357 m/s less (the remainder is the first stage delta), you need to increase the mass to 7,380 kg.  This gives 348*9.8*ln(123.38/11.88) = 7982 m/s.   So the same performance could put 7.38 tonnes into a minimal GTO (GEO-1800) from the Cape.

Yes... I wasn't calculating the most efficient way to get a heavier payload to the minimum GTO, just to get to the same inclination and perigee with a lower apogee.

[John Alan]

So... Looks like changes still coming will add the needed 920 kg to get the spec'd 8300kg to GTO..
(based on the 5 postings above this one)

AND... It's assumed that the website number they quote is the GEO-1800 (GTO) standard from the cape...
Makes me wonder sometimes... 

Either way... the leaving of depleted S2's in these higher orbits that will take a LONG time to decay is not a practice I'm real thrilled about... personally...
I really wish they could quote GEO-1800 with one more short burn later to get the S2 down in short order...
BUT... that's just me... 

[macpacheco]

So... Looks like changes still coming will add the needed 920 kg to get the spec'd 8300kg to GTO..
(based on the 5 postings above this one)

AND... It's assumed that the website number they quote is the GEO-1800 (GTO) standard from the cape...
Makes me wonder sometimes... 

Either way... the leaving of depleted S2's in these higher orbits that will take a LONG time to decay is not a practice I'm real thrilled about... personally...
I really wish they could quote GEO-1800 with one more short burn later to get the S2 down in short order...
BUT... that's just me... 

You're mixing a whole lot of issues up.

I really, truly, seriously doubt SpaceX today is selling expendable F9 launches, period.

This was originally contracted as a FH launch, FH got delayed, SpaceX managed to substitute with a F9 expendable launch to keep the customer !

The most performance SpaceX is selling today for a F9 launch is likely the predicted ASDS recovery performance of a Block V F9.

Instead of expendable F9, they're selling FH.

But what's launching now, was likely negotiated 2 or more years ago.

Of course, there are dozens of F9 launches that have been sold a while ago that will require expendable performance. Once FH is flying, if the schedule permits, SX might try to renegotiate that into a FHR launch.

For new contracts, expendable only comes into play if FH can't handle it without expending a booster.

Ask Ariane, ULA and others what they do on their GTO launches about the upper stage, I doubt they always include extra margin for a deorbit. Its a BIG sky !

There's a very sophisticated system that predicts near misses. If you're going to be concerned, be concerned about the thousands of little pieces in orbit in LEO that the ISS has to track, those will stay there in orbit for decades.

[guckyfan]

SpaceX has done similar to other providers with loiter time on this flight. On lower orbits they do deorbit burns. With loiter times longer they may be able to do more in the future. It does not take much for faster deorbit. As long as the stage does not desintegrate.

Can anyone give a rough estimate how long this stage will take to deorbit? 384km altitude does mean it still experiences some drag on perigee.

[gongora]

So could any falcon heavy payload be put on f9 expendable? Well up to 8.3MT at least. Is it cheaper to expend a F9 once in a while versus have to refurb 3 boosters for heavy?

The only things on the manifest (that we know about) that couldn't use F9 expendable are the beyond LEO Dragon flights and STP-2.  (FH will be required for some Air Force/NRO missions that SpaceX would compete for in the future.)

[LouScheffer]

Can anyone give a rough estimate how long this stage will take to deorbit? 384km altitude does mean it still experiences some drag on perigee.

The rule is that the stage should de-orbit naturally within 25 years.  According to Twenty-five Years, more or less?, Figure 8, this is right about at that limit.

[macpacheco]

Would it be inconvenient in orbital mechanics to use a lower perigee orbit instead ? Just enough the 2nd stage would deorbit in less than a year.

[stcks]

Would it be inconvenient in orbital mechanics to use a lower perigee orbit instead ? Just enough the 2nd stage would deorbit in less than a year.

A lot of them do use a lower perigee. See: https://www.reddit.com/r/spacex/wiki/launches/gto_performance

[abaddon]

Does anyone really think a burn terminated almost exactly at 36,000km/hr was a burn to minimum residuals?  Seems very unlikely.  Probably close, but still a little gas left in the tank.

[Kasponaut]

42698   INMARSAT 5-F4   2017-025A      1401.67min   24.50deg   69839km   381km      
42699   FALCON 9 R/B   2017-025B           1410.43min   24.47deg   70181km   384km

Roughly a 1,570m/s deficit to GTO. That's almost Zenit-3SLB/Proton-M/Briz-M performance.

How is that a deficit to GTO? It is almost twice as high as a standard GTO orbit.
Or am I missing something?
And what do you mean with almost Zenit/Proton performance?

[Herb Schaltegger]

42698   INMARSAT 5-F4   2017-025A      1401.67min   24.50deg   69839km   381km      
42699   FALCON 9 R/B   2017-025B           1410.43min   24.47deg   70181km   384km

Roughly a 1,570m/s deficit to GTO. That's almost Zenit-3SLB/Proton-M/Briz-M performance.

How is that a deficit to GTO? It is almost twice as high as a standard GTO orbit.
Or am I missing something?

Not the altitude of the apogee, but the velocity deficit (measured in deltaV) necessary to reach GSO at 0 degrees inclination. The usual "standard" GTO for a launch from Floria is -1,800 m/s.

[stcks]

42698   INMARSAT 5-F4   2017-025A      1401.67min   24.50deg   69839km   381km      
42699   FALCON 9 R/B   2017-025B           1410.43min   24.47deg   70181km   384km

Roughly a 1,570m/s deficit to GTO. That's almost Zenit-3SLB/Proton-M/Briz-M performance.

How is that a deficit to GTO? It is almost twice as high as a standard GTO orbit.
Or am I missing something?
And what do you mean with almost Zenit/Proton performance?

Its just deficit to GEO. Means 1570 m/s to circularize at GEO at 0 degrees inclination

[Space Ghost 1962]

42698   INMARSAT 5-F4   2017-025A      1401.67min   24.50deg   69839km   381km      
42699   FALCON 9 R/B   2017-025B           1410.43min   24.47deg   70181km   384km

Roughly a 1,570m/s deficit to GTO. That's almost Zenit-3SLB/Proton-M/Briz-M performance.

Those have more stages too. Not bad for kerolox 2 stage.