Author Topic: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION  (Read 1087767 times)

Offline eriblo

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #480 on: 02/08/2016 09:49 pm »


James has confirmed ASDS landing: https://twitter.com/flatoday_jdean/status/696816102010200065

Looks like the rocket/bottle bank's still open for deposit ;)

Wait, a super-synchronous insertion with a 5,300kg payload AND a stage 1 return?

O_o

This means more than 30% better GTO performance for the FT over v1.1 . It's a beast! (or some part of the information we have about the mission is incorrect).
Did anyone actually confirm that this was not subsyncronous on FT? Otherwise it might still be, just less so...

Offline nadreck

If there was no incl change doesn't super sync still mean less delta-v to circularize?

No, if you had a craft in an 0° inclination equatorial LEO then putting it into an elliptical orbit with an apogee equal to the perigee and apogee of the target circular GEO orbit it would require less impulse to in a single impulse at apogee to circularize the orbit than the sum of the two impulses needed to raise the perigee then lower the apogee. Though each of those impulses individually would be lower than the single impulse needed to circularize the orbit in the direct case.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline rsdavis9

If there was no incl change doesn't super sync still mean less delta-v to circularize?

No, if you had a craft in an 0° inclination equatorial LEO then putting it into an elliptical orbit with an apogee equal to the perigee and apogee of the target circular GEO orbit it would require less impulse to in a single impulse at apogee to circularize the orbit than the sum of the two impulses needed to raise the perigee then lower the apogee. Though each of those impulses individually would be lower than the single impulse needed to circularize the orbit in the direct case.
So the only advantage of super sync is to do the plane change at the lowest possible velocity.
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
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Offline nadreck

If there was no incl change doesn't super sync still mean less delta-v to circularize?

No, if you had a craft in an 0° inclination equatorial LEO then putting it into an elliptical orbit with an apogee equal to the perigee and apogee of the target circular GEO orbit it would require less impulse to in a single impulse at apogee to circularize the orbit than the sum of the two impulses needed to raise the perigee then lower the apogee. Though each of those impulses individually would be lower than the single impulse needed to circularize the orbit in the direct case.
So the only advantage of super sync is to do the plane change at the lowest possible velocity.
Yes and I have never sat down and calculated it, but along with the axiom that the greater the plane change the greater the savings, there is also a minimum plane change below which it wasn't advantageous to increase the apogee for, that in fact it would have cost you more ΔV to go supersynch and correct back down than you saved in the plane change. However obviously since they have been doing super synch plane changes, there is an advantage when the plane changes is 26° or more.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Dante80

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #484 on: 02/08/2016 10:14 pm »

Did anyone actually confirm that this was not subsyncronous on FT? Otherwise it might still be, just less so...

The actual mission profile has not been announced. We can speculate though, from this:

Quote
In order to minimise the impact of moving the launch from late last year, SpaceX is supporting a mission modification. The changed mission will reduce the time needed for SES-9 to reach its orbital slot, keeping the Operational Service Date (OSD) in the third quarter of 2016, as previously foreseen.

The only possible way to offset the delay is to have a super-synchronous insertion. A more energetic sub-synchronous would definitely not suffice for explaining this announcement.

Offline sewebster

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #485 on: 02/08/2016 10:16 pm »
If there was no incl change doesn't super sync still mean less delta-v to circularize?

No, if you had a craft in an 0° inclination equatorial LEO then putting it into an elliptical orbit with an apogee equal to the perigee and apogee of the target circular GEO orbit it would require less impulse to in a single impulse at apogee to circularize the orbit than the sum of the two impulses needed to raise the perigee then lower the apogee. Though each of those impulses individually would be lower than the single impulse needed to circularize the orbit in the direct case.

So would a "synchronous transfer orbit" (not sub, not super) still have an apogee beyond the GEO altitude? Put another way, the "simple Hohmann transfer" strategy where the apogee matches GEO altitude and all you need to do is raise perigee, that's subsynchronous, right?

Offline nadreck



So would a "synchronous transfer orbit" (not sub, not super) still have an apogee beyond the GEO altitude? Put another way, the "simple Hohmann transfer" strategy where the apogee matches GEO altitude and all you need to do is raise perigee, that's subsynchronous, right?

No, the simple Hohmann transfer orbit which is initiated at the point where the initial orbit crosses the equator and has an apogee equal to the altitude of a geosynchronous orbit is neither sub nor super synchronous.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline sewebster

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #487 on: 02/08/2016 10:26 pm »


So would a "synchronous transfer orbit" (not sub, not super) still have an apogee beyond the GEO altitude? Put another way, the "simple Hohmann transfer" strategy where the apogee matches GEO altitude and all you need to do is raise perigee, that's subsynchronous, right?

No, the simple Hohmann transfer orbit which is initiated at the point where the initial orbit crosses the equator and has an apogee equal to the altitude of a geosynchronous orbit is neither sub nor super synchronous.

Ok, maybe I'm misunderstanding some simple orbit stuff (realize this is probably getting off topic pretty fast). But isn't period proportional to semi-major-axis^(3/2)? Semi-major axis of GEO is the radius. An elliptical orbit with the same apogee but lower perigee would have a smaller semi-major axis and therefore a shorter period?

Offline nadreck



So would a "synchronous transfer orbit" (not sub, not super) still have an apogee beyond the GEO altitude? Put another way, the "simple Hohmann transfer" strategy where the apogee matches GEO altitude and all you need to do is raise perigee, that's subsynchronous, right?

No, the simple Hohmann transfer orbit which is initiated at the point where the initial orbit crosses the equator and has an apogee equal to the altitude of a geosynchronous orbit is neither sub nor super synchronous.

Ok, maybe I'm misunderstanding some simple orbit stuff (realize this is probably getting off topic pretty fast). But isn't period proportional to semi-major-axis^(3/2)? Semi-major axis of GEO is the radius. An elliptical orbit with the same apogee but lower perigee would have a smaller semi-major axis and therefore a shorter period?

Yes but when we speak of a geosynchronous transfer orbit, it is like speaking about a Mars transfer orbit, we aren't saying that the transfer orbit is synchronous, just that it is meant to take the craft to where it can maneuver into one. When we say sub synchronous we mean that it still isn't as high at apogee as the final orbit, and super means higher apogee than the final orbit. It is not referring to the period of the transfer orbit.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Online LouScheffer

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #489 on: 02/09/2016 01:28 am »
However, my point was that the change of inclination is done from apogee of a super synch orbit before you bring that apogee down.
To first order this is right, but it's still not the minimum delta-V strategy.  It's (slightly) better to remove some inclination with each burn.  So at apogee you remove most (but not all) of the inclination.  Then your final apogee-decrease burn removes the remaining inclination.  This works because you can always get a minor amount of sideways thrust for very cheap.  For example, generating 1% of your delta-V in a perpendicular direction only reduces your main thrust to 99.995% of the original values.  (In general, adding  a small fraction x of sideways thrust costs only (1-x^2/2) of main thrust).   

Here's a post where user BowShock pointed this out to me.  http://forum.nasaspaceflight.com/index.php?topic=36954.msg1342012#msg1342012 .   Leaving 1.55 degrees of inclination to be removed by the last burn saves 8 m/s over removing all inclination at apogee 80000 km.  Not a huge deal , but this could be a few months of operation for a satellite, which typically uses 50 m/s per year of station keeping.
Quote
EDIT: Lou also when I was suggesting that if they were expending S1 that they should use some of the extra impulse available in the 2nd stage to eliminate some of the inclination, it was rather than throwing that extra impulse away, or raising the Apogee beyond 100,000km
This I completely agree with.  As you add available delta-V, go from sub-synchronous to synchronous to super-synchronous.  Then at some point even higher apogees save very little, but cause significant complications, so better to use any remaining delta-V to reduce the inclination of the transfer orbit.  In theory you can embrace super-high apogees, and do tricks like using the moon to reduce your inclination.  But this adds a lot of complications - you now have timing constraints on launch, your satellite may have problems such as Earth sensors that cannot cope, etc.  Probably best to just reduce the inclination as you suggest.

Offline FireJack

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #490 on: 02/09/2016 01:46 am »
The big part of this launch is that a successful returned first stage will be reused.  This will hopefully let us know the economics of reusing rockets something both the ESA and Russians have said would not work.  How quickly can the first stage be turned around and at what price? How much new business will be created with these new prices? What will the reaction be from other launch providers?
Very exciting stuff.

Offline topo334

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #491 on: 02/09/2016 02:30 am »
Do you mean the SES9 launch uses a previously flown first stage? (no), or that the first stage if landed, will be re-flown? Inquiring minds etc.

Offline macpacheco

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #492 on: 02/09/2016 02:43 am »
To make up for the delay the satellite will be delivered to a better orbit for faster arrival at GEO. Which probably means no landing attempt.

The cynic in me is wondering whether the F9FT performance is less than expected, precluding the original nominal mission *and* barge landing so SpaceX just went ahead and committed all of the recovery reserve to SES-9.

Less than expected by whom? The original nominal mission was a sub-synchronous expendable insertion with v1.1. One month after that, it changed to a sub-synchronous DPL insertion with FT. FT has never been advertised to send a 5,300kg sat to GTO-1800 and then do a DPL. They actually list far less on their website (assuming the max they do list is for a DPL profile).

My take on this is that SES and SpaceX decided to go for a super-synchronous expendable mission profile so as to have the satellite come online sooner than expected, thus offsetting the delays that have plagued this campaign.

It's a good decision for business imo, although less exciting for SpaceX fans (that want to see the company nail its first FT barge landing sooner rather than later).

Certainly less exciting, but a single mission that puts a 5.3 ton bird in super sync orbit will make a big splash in the launch market.
From an objective perspective, this would be just as exciting as a valid ASDS landing. I look forward to a 7 ton launch to a sub sync GTO mission (for a purely electric bird).
Looking for companies doing great things for much more than money

Offline Lar

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #493 on: 02/09/2016 02:52 am »
Do you mean the SES9 launch uses a previously flown first stage? (no), or that the first stage if landed, will be re-flown? Inquiring minds etc.
There's only one previously flown first stage available at this time. I think it's pretty unlikely that it would be reused. SES has given no indication of interest in doing that. So I'm pretty sure he meant that if the first stage was recovered, it might be the first stage reflown. But that's my guess.
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Offline Wonger

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #494 on: 02/09/2016 03:25 am »
Do you mean the SES9 launch uses a previously flown first stage? (no), or that the first stage if landed, will be re-flown? Inquiring minds etc.


Some months back, SES asked SpaceX if the first stage from SES-9 was recovered, if they could use it again on a subsequent launch for a discount.  I don't think we ever heard SpaceX's response.  Article here:


http://spacenews.com/spacex-early-adopter-ses-ready-to-reuse-falcon-9-%C2%AD-for-the-right-price/


Offline FireJack

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #495 on: 02/09/2016 03:29 am »
Yes I meant if the stage is recovered (which I think has a pretty good chance) it will likely be the first to be reused.
This will open the whole reused rocket market, which will be very interesting.

Offline Steven Pietrobon

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #496 on: 02/09/2016 04:43 am »
Perhaps an option would be for the second stage to do a three burn profile; orbit insertion, transfer orbit (burn at low altitude at equator) and then geosynchronous transfer orbit (burn at apogee). This requires the second stage to stay alive for several hours after insertion.
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Offline sewebster

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #497 on: 02/09/2016 05:21 am »
Given that it appears they are still going for the landing, it seems like one of the only things they could do (?) is eliminate the boost back burn, or most of it, and put that extra delta-v into the satellite. Any ideas how much that is? Not enough to get super synchronous, but closer? (hence reducing time to operation for the satellite). This has basically already been mentioned I think... but what else is there if they still try landing?

Offline 411rocket

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #498 on: 02/09/2016 06:32 am »
Yes I meant if the stage is recovered (which I think has a pretty good chance) it will likely be the first to be reused.
This will open the whole reused rocket market, which will be very interesting.

The previous plans that we know about, one landed stage will be re flown many times, at Space Port America, possibly until destruction. Another was to be thoroughly examined, maybe even dismantled, in the process of the exams & testing of components post-flight.

These were the plans, prior to Decembers Orbcomm flight & landing. So what has changed in the plans, aside from keeping that Booster, I think it is wait & see what happens....

Offline Star One

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #499 on: 02/09/2016 06:40 am »

The big part of this launch is that a successful returned first stage will be reused.  This will hopefully let us know the economics of reusing rockets something both the ESA and Russians have said would not work.  How quickly can the first stage be turned around and at what price? How much new business will be created with these new prices? What will the reaction be from other launch providers?
Very exciting stuff.

No the big part of this launch is delivering the customer's payload where & when they require it. Don't do that & quickly you will find that you have no business to do the rest.

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