Author Topic: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 18, 2018  (Read 81146 times)

Offline gongora

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #160 on: 10/22/2018 07:33 PM »
I wonder if the GPS flights were always planned to be expendable when flying on F9?  If so then they may not be any more expensive than a corresponding commercial flight (which is supposedly around $90M for expendable).
« Last Edit: 10/22/2018 07:34 PM by gongora »

Online envy887

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #161 on: 10/22/2018 07:41 PM »
I wonder if the GPS flights were always planned to be expendable when flying on F9?  If so then they may not be any more expensive than a corresponding commercial flight (which is supposedly around $90M for expendable).

Why is that being expended? It's less than 4 tonnes and going to a very sub-GTO transfer...

Offline hopalong

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #162 on: 10/22/2018 07:42 PM »
I wonder if the GPS flights were always planned to be expendable when flying on F9?  If so then they may not be any more expensive than a corresponding commercial flight (which is supposedly around $90M for expendable).

Sorry, a bit confused here, why would the core be expended? GPS-III is sub 4 Tonnes to MEO, recovery to OCISLY should more then possible.

Offline russianhalo117

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #163 on: 10/22/2018 07:47 PM »
I wonder if the GPS flights were always planned to be expendable when flying on F9?  If so then they may not be any more expensive than a corresponding commercial flight (which is supposedly around $90M for expendable).

Why is that being expended? It's less than 4 tonnes and going to a very sub-GTO transfer...
I wonder if the GPS flights were always planned to be expendable when flying on F9?  If so then they may not be any more expensive than a corresponding commercial flight (which is supposedly around $90M for expendable).

Sorry, a bit confused here, why would the core be expended? GPS-III is sub 4 Tonnes to MEO, recovery to OCISLY should more then possible.
USAF awarded expendable flights so they got expendable flights.

Online TGMetsFan98

GPS III-1 is going to Middle Earth Orbit. More demanding performance-wise than GTO.

Offline gongora

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #165 on: 10/22/2018 08:51 PM »
GPS III-1 is going to Middle Earth Orbit. More demanding performance-wise than GTO.

I thought it was Medium Earth Orbit.  Now you're making me think about hobbits.

Online envy887

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #166 on: 10/22/2018 09:25 PM »
GPS III-1 is going to Middle Earth Orbit. More demanding performance-wise than GTO.

It's going to a MEO transfer, not direct to MEO. This is much less demanding than a GEO transfer, because MEO is lower than GEO and the inclinations aren't all that different.

Online TGMetsFan98

Ok, I didn't see that it was a transfer orbit, I was presuming direct MEO.

Online envy887

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #168 on: 10/22/2018 09:27 PM »
I wonder if the GPS flights were always planned to be expendable when flying on F9?  If so then they may not be any more expensive than a corresponding commercial flight (which is supposedly around $90M for expendable).

Why is that being expended? It's less than 4 tonnes and going to a very sub-GTO transfer...
I wonder if the GPS flights were always planned to be expendable when flying on F9?  If so then they may not be any more expensive than a corresponding commercial flight (which is supposedly around $90M for expendable).

Sorry, a bit confused here, why would the core be expended? GPS-III is sub 4 Tonnes to MEO, recovery to OCISLY should more then possible.
USAF awarded expendable flights so they got expendable flights.

They awarded a certain performance to a certain orbit on a new booster. Why would they care what SpaceX does with the booster after staging?

Offline gongora

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #169 on: 10/22/2018 09:28 PM »
We don't know the exact transfer orbit, and do we know if the second stage is going to deorbit or stay in a graveyard  orbit?

Online Alexphysics

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #170 on: 10/22/2018 09:29 PM »
GPS III-1 is going to Middle Earth Orbit. More demanding performance-wise than GTO.

It's going to a MEO transfer, not direct to MEO. This is much less demanding than a GEO transfer, because MEO is lower than GEO and the inclinations aren't all that different.

Well, yes, the inclinations are very different (55 vs <28.6), but obviously is not the limiting factor here

Online envy887

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #171 on: 10/22/2018 09:34 PM »
We don't know the exact transfer orbit, and do we know if the second stage is going to deorbit or stay in a graveyard  orbit?

It's a transfer orbit, it will decay eventually. Just like GTO launches.

Online envy887

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #172 on: 10/22/2018 09:35 PM »
GPS III-1 is going to Middle Earth Orbit. More demanding performance-wise than GTO.

It's going to a MEO transfer, not direct to MEO. This is much less demanding than a GEO transfer, because MEO is lower than GEO and the inclinations aren't all that different.

Well, yes, the inclinations are very different (55 vs <28.6), but obviously is not the limiting factor here

Not that different in terms of performance.

Offline gongora

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #173 on: 10/22/2018 09:45 PM »
We don't know the exact transfer orbit, and do we know if the second stage is going to deorbit or stay in a graveyard  orbit?

It's a transfer orbit, it will decay eventually. Just like GTO launches.

A transfer orbit with a perigee over 1000km will not decay in the near future.  It will need to do another burn to either go into disposal orbit or lower the perigee to a few hundred km if it doesn't deorbit all the way.

Online Alexphysics

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #174 on: 10/22/2018 09:50 PM »
We don't know the exact transfer orbit, and do we know if the second stage is going to deorbit or stay in a graveyard  orbit?

It's a transfer orbit, it will decay eventually. Just like GTO launches.

A transfer orbit with a perigee over 1000km will not decay in the near future.

I think this is mostly why it is going expendable, it has to go into a transfer orbit with a perigee at least with a 1000km perigee and that takes up *some* performance.

Offline zubenelgenubi

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #175 on: 10/23/2018 02:27 AM »
New article
SpaceX lines up five launches to close out 2018, October 22, by Michael Baylor
Support your local planetarium!

Online envy887

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #176 on: 10/23/2018 12:29 PM »
We don't know the exact transfer orbit, and do we know if the second stage is going to deorbit or stay in a graveyard  orbit?

It's a transfer orbit, it will decay eventually. Just like GTO launches.

A transfer orbit with a perigee over 1000km will not decay in the near future.

I think this is mostly why it is going expendable, it has to go into a transfer orbit with a perigee at least with a 1000km perigee and that takes up *some* performance.

Not that much, though. NASA LSP indicates the performance of F9 FT with ASDS landing to 51.6 x 1000 km circular LEO as 12,280 kg. This is (I suspect) for an old version of F9, and definitely has lots of margin built in to meet LSP requirements, so it's a very conservative estimate. Performance to 55.0 x 1000 km circular will be about 200 kg lower, as it needs 25 m/s more to overcome the loss of starting rotational velocity.

That means the total IMLEO is about 17,100 kg, using a fairly conservative 5,000 kg upper stage mass. An additional 1,846 m/s is required to raise the apogee to 20,200 km for the MEO transfer. This requires 7,150 kg of fuel, leaving the 5 t stage and about 4,950 kg of payload in 55 x 1000 x 20200 km orbit. That's more than 30% more than the 3800 kg listed for GPS-III-1. (And this example is not the most efficient transfer, which would be a single burn to 1000 km apogee, then a 2nd burn to 20,200 km apogee, instead of the 3 burns I listed).

If they do a deorbit burn at at 20200 km apogee, it needs 99 m/s to lower perigee to 300 km, or 135 m/s to lower it to 60 km and guarantee reentry at first perigee. This 180 to 300 kg of propellant carried to apogee, plus boiloff for the extended coast, plus additional helium for re-pressurization. Unless, perhaps, the RCS is capable of providing that delta-v at apogee, which might be possible since the early F9 user guide offered up to 200+ m/s with a RCS burn from the "delta-v mission kit".

Add in the Block 5 upgrades and this should be well within the capability of F9 with ASDS.

Offline Nomadd

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #177 on: 10/23/2018 12:44 PM »
 Maybe the AF considers the recovery gear to add risk, and they have no incentive to change anything. Or, some numbnuts just can't bring himself to pay for an expendable launch and not get it. They're not like a regular (sane) company who would be thrilled to get a $30 million break on price. The oldest and dumbest of all rules, "If you don't spend it this time you won't get it next time"
« Last Edit: 10/23/2018 02:42 PM by Nomadd »

Offline LouScheffer

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #178 on: 10/23/2018 12:47 PM »
I think this is mostly why it is going expendable, it has to go into a transfer orbit with a perigee at least with a 1000km perigee and that takes up *some* performance.

Not that much, though. NASA LSP indicates the performance of F9 FT with ASDS landing to 51.6 x 1000 km circular LEO as 12,280 kg. This is (I suspect) for an old version of F9, and definitely has lots of margin built in to meet LSP requirements, so it's a very conservative estimate. Performance to 55.0 x 1000 km circular will be about 200 kg lower, as it needs 25 m/s more to overcome the loss of starting rotational velocity.

That means the total IMLEO is about 17,100 kg, using a fairly conservative 5,000 kg upper stage mass. An additional 1,846 m/s is required to raise the apogee to 20,200 km for the MEO transfer. This requires 7,150 kg of fuel, leaving the 5 t stage and about 4,950 kg of payload in 55 x 1000 x 20200 km orbit. That's more than 30% more than the 3800 kg listed for GPS-III-1. (And this example is not the most efficient transfer, which would be a single burn to 1000 km apogee, then a 2nd burn to 20,200 km apogee, instead of the 3 burns I listed).

If they do a deorbit burn at at 20200 km apogee, it needs 99 m/s to lower perigee to 300 km, or 135 m/s to lower it to 60 km and guarantee reentry at first perigee. This 180 to 300 kg of propellant carried to apogee, plus boiloff for the extended coast, plus additional helium for re-pressurization. Unless, perhaps, the RCS is capable of providing that delta-v at apogee, which might be possible since the early F9 user guide offered up to 200+ m/s with a RCS burn from the "delta-v mission kit".

Add in the Block 5 upgrades and this should be well within the capability of F9 with ASDS.
This makes sense, so from this I would conclude that the perigee will be much higher than 1000 km.  How much higher?  With recovery, F9 can put 5500 kg into GEO-apogee GTO.  This takes about 2400 m/s from LEO.  Reducing the payload mass to 4000 kg gives an extra 500 m/s.   So there is about 2900 m./s to play with, and still recover.

A little experimentation shows that starting with a 200x200 parking orbit, it takes 980 m/s to get to a 200 x 5000 km orbit.   Then you coast to the top, and fire again into a 5000 x 20200 orbit, taking 1931 m/s, for a total of about 2900 m/s.  The intermediate orbit is high enough so that de-orbit of the spent stage is not required.

This is a crude calculation ignoring the 55 degree orbit, boil-off, etc.  But I'd guess this means the perigee will be higher than 4000 km, if they don't de-orbit the second stage. . And once you give up recovery, there is additional performance.  This could be used for a still higher perigee, or stage de-orbiting.  Though de-orbiting is quite expensive from a 5000 x 20200 orbit, about 550 m/s or so.  So if they opt for de-orbit I'd expect a lower perigee, perhaps 3000 km-ish.
« Last Edit: 10/23/2018 02:22 PM by LouScheffer »

Online envy887

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Re: SpaceX Falcon 9 : GPS III-1 : SLC-40 : December 15, 2018
« Reply #179 on: 10/23/2018 03:24 PM »
I think this is mostly why it is going expendable, it has to go into a transfer orbit with a perigee at least with a 1000km perigee and that takes up *some* performance.

Not that much, though. NASA LSP indicates the performance of F9 FT with ASDS landing to 51.6 x 1000 km circular LEO as 12,280 kg. This is (I suspect) for an old version of F9, and definitely has lots of margin built in to meet LSP requirements, so it's a very conservative estimate. Performance to 55.0 x 1000 km circular will be about 200 kg lower, as it needs 25 m/s more to overcome the loss of starting rotational velocity.

That means the total IMLEO is about 17,100 kg, using a fairly conservative 5,000 kg upper stage mass. An additional 1,846 m/s is required to raise the apogee to 20,200 km for the MEO transfer. This requires 7,150 kg of fuel, leaving the 5 t stage and about 4,950 kg of payload in 55 x 1000 x 20200 km orbit. That's more than 30% more than the 3800 kg listed for GPS-III-1. (And this example is not the most efficient transfer, which would be a single burn to 1000 km apogee, then a 2nd burn to 20,200 km apogee, instead of the 3 burns I listed).

If they do a deorbit burn at at 20200 km apogee, it needs 99 m/s to lower perigee to 300 km, or 135 m/s to lower it to 60 km and guarantee reentry at first perigee. This 180 to 300 kg of propellant carried to apogee, plus boiloff for the extended coast, plus additional helium for re-pressurization. Unless, perhaps, the RCS is capable of providing that delta-v at apogee, which might be possible since the early F9 user guide offered up to 200+ m/s with a RCS burn from the "delta-v mission kit".

Add in the Block 5 upgrades and this should be well within the capability of F9 with ASDS.
This makes sense, so from this I would conclude that the perigee will be much higher than 1000 km.  How much higher?  With recovery, F9 can put 5500 kg into GEO-apogee GTO.  This takes about 2400 m/s from LEO.  Reducing the payload mass to 4000 kg gives an extra 500 m/s.   So there is about 2900 m./s to play with, and still recover.

A little experimentation shows that starting with a 200x200 parking orbit, it takes 980 m/s to get to a 200 x 5000 km orbit.   Then you coast to the top, and fire again into a 5000 x 20200 orbit, taking 1931 m/s, for a total of about 2900 m/s.  The intermediate orbit is high enough so that de-orbit of the spent stage is not required.

This is a crude calculation ignoring the 55 degree orbit, boil-off, etc.  But I'd guess this means the perigee will be higher than 4000 km, if they don't de-orbit the second stage. . And once you give up recovery, there is additional performance.  This could be used for a still higher perigee, or stage de-orbiting.  Though de-orbiting is quite expensive from a 5000 x 20200 orbit, about 550 m/s or so.  So if they opt for de-orbit I'd expect a lower perigee, perhaps 3000 km-ish.

There is little reason to deorbit from a 4,000 km perigee. Bump the apogee of the stage down a few hundred km with RCS after S/C sep (only takes a couple m/s), and that's a nice graveyard orbit.

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