Author Topic: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION  (Read 1087838 times)

Online ugordan

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #620 on: 02/12/2016 11:24 am »
Triangle to the right of SES on the starfield?

Err... their logo?

Offline Bargemanos

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #621 on: 02/12/2016 11:25 am »
Triangle to the right of SES on the starfield?

Err... their logo?


Correct!
« Last Edit: 02/12/2016 11:25 am by Bargemanos »

Offline kevin-rf

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #622 on: 02/12/2016 01:12 pm »
OMG, OMG, a mission patch that actually has the solar panels oriented correctly (North South, not East West)!!!!

Way to go SpaceX! We can quivel about the orbit being inclined some 60ish degrees later.
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Offline cscott

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #623 on: 02/12/2016 01:28 pm »
I guess it's obvious from the patch SpaceX care a lot about trying this recovery, regards of success.

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #624 on: 02/12/2016 01:28 pm »
Or the patch predates the mission profile change.

Offline cscott

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #625 on: 02/12/2016 01:40 pm »
Sure.  "Caring a lot" doesn't mean they'll actually perform a recovery.  Just that they will certainly, well, *try hard*.

Offline Norm38

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #626 on: 02/12/2016 03:04 pm »
So one less month of thrusting.  How much delta-V is that?  The XIPS thruster has a force of 165 mN when used in orbit-raising mode: ( http://www2.l-3com.com/eti/product_lines_electric_propulsion.htm ).  How much mass does the satellte have at this point?  From the fact that the chemical prop can get to a 24 hour (but not circular orbit), we guess about 1200 m/s delta-V.  At an ISP of 220 (typical for hydrazine), 1200 m/s implies a mass ratio of 1.744, so if SES-9 starts at 5330 kg it's about 3056 kg after the chemical engine burn.

Now 0.165 Newtons acting on 3056 kg gives 4.66 m/s per day of operation.  That's 140 m/s over a month.  So we guess the modified trajectory offers 140 m/s more.  Near the end of the first stage burn, the rocket should be accelerating at 4-5 Gs, or 40-50 m/s/s.  So SpaceX will run the 9 engines for 3 seconds longer than before.  This leaves less fuel for the re-entry burn.  Since this burn is made with 3 engines, not 9, it will therefore be 9 seconds shorter.

I have a question that I didn't see asked.  With the original trajectory, SES-9 would have provided 140m/s and burned 2274kg of propellant, per Lou's numbers.
So now that the F9 is providing that 140m/s, does that mean the SES-9 will have the extra 2274kg propellant for more service time in orbit, or that it will weigh 2274kg less on launch?  Or some split?

If SES-9 weighs less, doesn't that affect the amount of fuel F9 has left for the recovery burns?
« Last Edit: 02/12/2016 03:05 pm by Norm38 »

Offline gongora

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #627 on: 02/12/2016 03:33 pm »
So one less month of thrusting.  How much delta-V is that?  The XIPS thruster has a force of 165 mN when used in orbit-raising mode: ( http://www2.l-3com.com/eti/product_lines_electric_propulsion.htm ).  How much mass does the satellte have at this point?  From the fact that the chemical prop can get to a 24 hour (but not circular orbit), we guess about 1200 m/s delta-V.  At an ISP of 220 (typical for hydrazine), 1200 m/s implies a mass ratio of 1.744, so if SES-9 starts at 5330 kg it's about 3056 kg after the chemical engine burn.

Now 0.165 Newtons acting on 3056 kg gives 4.66 m/s per day of operation.  That's 140 m/s over a month.  So we guess the modified trajectory offers 140 m/s more.  Near the end of the first stage burn, the rocket should be accelerating at 4-5 Gs, or 40-50 m/s/s.  So SpaceX will run the 9 engines for 3 seconds longer than before.  This leaves less fuel for the re-entry burn.  Since this burn is made with 3 engines, not 9, it will therefore be 9 seconds shorter.

I have a question that I didn't see asked.  With the original trajectory, SES-9 would have provided 140m/s and burned 2274kg of propellant, per Lou's numbers.
So now that the F9 is providing that 140m/s, does that mean the SES-9 will have the extra 2274kg propellant for more service time in orbit, or that it will weigh 2274kg less on launch?  Or some split?

If SES-9 weighs less, doesn't that affect the amount of fuel F9 has left for the recovery burns?

Lou was saying the satellite would provide 1200m/s with its chemical propulsion system using that amount of propellant, then the smaller and more efficient thrusters would have to take over.

Offline Norm38

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #628 on: 02/12/2016 04:00 pm »
^^^ Yes, I see my error, thanks.  140m/s isn't much fuel for an ion thruster, (~2kg?)  so I assume that will be extra station keeping reserve.

Offline Jim

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #629 on: 02/12/2016 05:48 pm »

thought SES-9 was processed, fueled and stored ready for launch.  Confusing


It is.  The launch/flight profile is independent of that

Offline LouScheffer

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #630 on: 02/12/2016 05:54 pm »
^^^ Yes, I see my error, thanks.  140m/s isn't much fuel for an ion thruster, (~2kg?)  so I assume that will be extra station keeping reserve.
Yes, that's what I would guess.  Station keeping takes about 50 m/s per year, so if this plan works, in addition to taking a month less to go into service, it should have almost 3 years more station keeping fuel.  (Although with ion thrusters, I don't know if station keeping fuel is ever the lifetime limiting factor any more.)

Offline Roy_H

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #631 on: 02/13/2016 03:43 pm »
Does anybody know if the legs and grid fins will be removed? I would think that if they are going to splash it in the drink anyway, there is no reason not to save the weight and cost.
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Offline Coastal Ron

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #632 on: 02/13/2016 04:07 pm »
Does anybody know if the legs and grid fins will be removed? I would think that if they are going to splash it in the drink anyway, there is no reason not to save the weight and cost.

It depends on what re-entry objectives they want to test.

For instance, if they feel there will be enough fuel to attempt a controlled re-entry, then they would likely keep the grid fins on since they provide directional control once aerodynamic effects come into play.  But if they are not planning on landing the stage on a barge, and will just assume a water landing, then it would make no sense to attach the landing legs.  Legs are an option, and are not required for the primary task of moving payloads to space.
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Offline Lars-J

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #633 on: 02/13/2016 04:15 pm »
Does anybody know if the legs and grid fins will be removed? I would think that if they are going to splash it in the drink anyway, there is no reason not to save the weight and cost.

If they are still going for the barge (no matter the reduced probability of success), *of course* they will keep them.

Their performance hit is not as significant as people tend to assume, they are only on the first stage.
« Last Edit: 02/13/2016 04:16 pm by Lars-J »

Offline IntoTheVoid

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #634 on: 02/13/2016 04:46 pm »
Does anybody know if the legs and grid fins will be removed? I would think that if they are going to splash it in the drink anyway, there is no reason not to save the weight and cost.

anyone thinking grin fins on, no legs and (projected) location on water is the objective?

No

Confirmed by SES that the SES-9 launch will skip first stage recovery.

http://spacenews.com/ses-applauds-spacexs-willingness-to-sacrifice-falcon-9-first-stage-recovery-for-main-satelilte-mission/

They are risking recovery, not abandoning. From the same article...
Quote
One industry official familiar with the SES-9 mission said Hawthorne, California-based SpaceX has not abandoned hope of recovering the first stage after a landing on an offshore platform positioned for the mission. But the chances of success are much less given the launch trajectory agreed to with SES to reduce the time to arrival at its operating position.

Offline CyndyC

Quote
One industry official familiar with the SES-9 mission said Hawthorne, California-based SpaceX has not abandoned hope of recovering the first stage after a landing on an offshore platform positioned for the mission. But the chances of success are much less given the launch trajectory agreed to with SES to reduce the time to arrival at its operating position. http://spacenews.com/ses-applauds-spacexs-willingness-to-sacrifice-falcon-9-first-stage-recovery-for-main-satelilte-mission/

What I don't get about that statement is how the chances of success can be "much less", when you're trying to land a rocket with an 18m leg span on a barge 52m wide. Sounds to me like you either can or you can't. So if just 4 days ago there was only "hope", that implies SpaceX is still working on the calculations to assess the new margins of error. Frankly I'm a bit worried they might try to cut it too close. Anyone with any roots in Jacksonville knows the infamous Lynyrd Skynyrd plane crash happened because the plane ran out of gas (the air/fuel mix was turned up too rich because the plane had been backfiring). We don't even drive to the grocery store around here with less than 1/8th of a tank.

BTW, not attaching the legs if they choose to abandon recovery would add to the recalculations, unless that scenario has been precalculated. The legs weigh about 2100kg or 2.3 US tons (2.1 UK tons for our friends across the pond).
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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #636 on: 02/13/2016 05:59 pm »
Quote
One industry official familiar with the SES-9 mission said Hawthorne, California-based SpaceX has not abandoned hope of recovering the first stage after a landing on an offshore platform positioned for the mission. But the chances of success are much less given the launch trajectory agreed to with SES to reduce the time to arrival at its operating position. http://spacenews.com/ses-applauds-spacexs-willingness-to-sacrifice-falcon-9-first-stage-recovery-for-main-satelilte-mission/

What I don't get about that statement is how the chances of success can be "much less", when you're trying to land a rocket with an 18m leg span on a barge 52m wide. Sounds to me like you either can or you can't. So if just 4 days ago there was only "hope", that implies SpaceX is still working on the calculations to assess the new margins of error. Frankly I'm a bit worried they might try to cut it too close. Anyone with any roots in Jacksonville knows the infamous Lynyrd Skynyrd plane crash happened because the plane ran out of gas (the air/fuel mix was turned up too rich because the plane had been backfiring). We don't even drive to the grocery store around here with less than 1/8th of a tank.

BTW, not attaching the legs if they choose to abandon recovery would add to the recalculations, unless that scenario has been precalculated. The legs weigh about 2100kg or 2.3 US tons (2.1 UK tons for our friends across the pond).

The issue is the reentry burn being shorter or non existant.... if the stage survives reentry the chances of landing are about the same as before... worse due to the possibility of damage that is not realised from hotter reentry[1], better due to them improving their approach based on learnings from previous attempts.

1 - many in the forum are discounting this saying that there is not much likelyhood of damage that would cause the stage to malfunction but not break up
« Last Edit: 02/13/2016 06:03 pm by Lar »
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Offline Nomadd

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #637 on: 02/13/2016 06:09 pm »
Quote
One industry official familiar with the SES-9 mission said Hawthorne, California-based SpaceX has not abandoned hope of recovering the first stage after a landing on an offshore platform positioned for the mission. But the chances of success are much less given the launch trajectory agreed to with SES to reduce the time to arrival at its operating position. http://spacenews.com/ses-applauds-spacexs-willingness-to-sacrifice-falcon-9-first-stage-recovery-for-main-satelilte-mission/

What I don't get about that statement is how the chances of success can be "much less", when you're trying to land a rocket with an 18m leg span on a barge 52m wide. Sounds to me like you either can or you can't. So if just 4 days ago there was only "hope", that implies SpaceX is still working on the calculations to assess the new margins of error. Frankly I'm a bit worried they might try to cut it too close. Anyone with any roots in Jacksonville knows the infamous Lynyrd Skynyrd plane crash happened because the plane ran out of gas (the air/fuel mix was turned up too rich because the plane had been backfiring). We don't even drive to the grocery store around here with less than 1/8th of a tank.

BTW, not attaching the legs if they choose to abandon recovery would add to the recalculations, unless that scenario has been precalculated. The legs weigh about 2100kg or 2.3 US tons (2.1 UK tons for our friends across the pond).
There are more things to consider than fuel reserves.
 Lower fuel after higher staging and higher speed means less re-entry braking and much higher re-entry speed. The greater uncertainty is partly because they don't know for sure how much punishment the stage can take.
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Offline Kabloona

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #638 on: 02/13/2016 07:58 pm »
Quote
One industry official familiar with the SES-9 mission said Hawthorne, California-based SpaceX has not abandoned hope of recovering the first stage after a landing on an offshore platform positioned for the mission. But the chances of success are much less given the launch trajectory agreed to with SES to reduce the time to arrival at its operating position. http://spacenews.com/ses-applauds-spacexs-willingness-to-sacrifice-falcon-9-first-stage-recovery-for-main-satelilte-mission/

What I don't get about that statement is how the chances of success can be "much less", when you're trying to land a rocket with an 18m leg span on a barge 52m wide. Sounds to me like you either can or you can't. So if just 4 days ago there was only "hope", that implies SpaceX is still working on the calculations to assess the new margins of error.

In case you missed it, LouScheffer did some good BOTE calculations upthread estimating that the braking burn may be reduced from 21 seconds in length to about 12 seconds based on the additional deltaV to be given to the payload.

http://forum.nasaspaceflight.com/index.php?topic=34077.msg1490085#msg1490085

That reduction in braking burn length means the stage will be coming in "hotter" with lower chance of survival.
« Last Edit: 02/13/2016 07:58 pm by Kabloona »

Offline Johnnyhinbos

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Re: SpaceX Falcon 9 FT - SES-9 - March 4, 2016 - DISCUSSION
« Reply #639 on: 02/13/2016 08:44 pm »
Am I the only one who can't wait for the 24th? This sounds like a huge mission as far as capability, survivability, and payload. I'll bring the popcorn!
John Hanzl. Author, action / adventure www.johnhanzl.com

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