Triangle to the right of SES on the starfield?
Quote from: Lar on 02/12/2016 11:04 amTriangle to the right of SES on the starfield?Err... their logo?
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.
Quote from: LouScheffer on 02/10/2016 01:36 pmSo 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?
thought SES-9 was processed, fueled and stored ready for launch. Confusing
^^^ 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.
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.
Quote from: Roy_H on 02/13/2016 03:43 pmDoes 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?
Quote from: woods170 on 02/09/2016 01:23 pmConfirmed 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...QuoteOne 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.
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/
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.
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/
QuoteOne 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).
QuoteOne 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.