Making any conclusion off of peanut gallery spreadsheet calculations using random figures from different locations on the internet is a fool's errand. (Even if that is one awesome spreadsheet.)
Quote from: fatjohn1408 on 12/19/2013 12:28 pmFirst off all that is one heck of a spreadsheet. I also calculate that s2 thrust @ 55% would mean acceleration of 2.74g at the start of the second burn and 6.37g at the end. (Doesn't SpaceX cap the acceleration at 5g though?) Calculations (green box)Quote from: fatjohn1408 on 12/19/2013 12:28 pmOnly other conclusion would be that they - just for fun - decreased the throttle setting a bit in the first burn and went full power in the second burn. Which does not make any sense.Why do you think they went full power in the second burn?
First off all that is one heck of a spreadsheet. I also calculate that s2 thrust @ 55% would mean acceleration of 2.74g at the start of the second burn and 6.37g at the end. (Doesn't SpaceX cap the acceleration at 5g though?) Calculations (green box)Quote from: fatjohn1408 on 12/19/2013 12:28 pmOnly other conclusion would be that they - just for fun - decreased the throttle setting a bit in the first burn and went full power in the second burn. Which does not make any sense.Why do you think they went full power in the second burn?
Only other conclusion would be that they - just for fun - decreased the throttle setting a bit in the first burn and went full power in the second burn. Which does not make any sense.
I'm getting a little lost at the various claims here, but SpaceX is claiming 375 seconds burn time at 801 kN on their site. http://www.spacex.com/falcon9
Quote from: ChrisWilson68 on 12/19/2013 09:51 amYou realize that the Merlin 1Dvac can throttle down to 70% thrust, maybe less, right? So even if the average thrust of the second stage was less than 801kN on the SES-8 flight, that doesn't mean the engine isn't capable of higher thrust.Since we don't know how much the engine was throttled down compared to what it's capable of, I don't see how you could possibly conclude it isn't capable of 801kN based on what happened on SES-8.Yes off course I realize that, but there is no reason to throttle if you do not hit 6g is there? Perhaps a structural reason but then the premise remains the same that the upper stage cannot produce 801kN.Otherwise why throttle? It increases gravity losses and decreases Isp.
You realize that the Merlin 1Dvac can throttle down to 70% thrust, maybe less, right? So even if the average thrust of the second stage was less than 801kN on the SES-8 flight, that doesn't mean the engine isn't capable of higher thrust.Since we don't know how much the engine was throttled down compared to what it's capable of, I don't see how you could possibly conclude it isn't capable of 801kN based on what happened on SES-8.
Quote from: malu5531 on 12/19/2013 11:26 amQuote from: fatjohn1408 on 12/19/2013 09:31 am=> NO WAY THAT THE MERLIN VAC 1D PRODUCES 801KN OF THRUST! ISP AND THUS MASS FLOW AND UPPER STAGE PROPELLANT AND BURN TIME ARE NOT CONSISTENT AT ALL.just if anyone is interestedMy model of M1DVac predict 147 isp/801 kN at full thrust. I believe SpaceX is underselling the M1DVac Isp on their website, or the inconsistency is due to different numbers assume different throttle + rounded for nicer looking numbers.Apologies if this was either already brought up or has no relation but hasn't it been established by Elon that the M1D is currently operating at -15% of capable thrust? An increase of which they will optimize for as they continue flight operations. Would this not also transfer over to M1DVacs current and future operating parameters?
Quote from: fatjohn1408 on 12/19/2013 09:31 am=> NO WAY THAT THE MERLIN VAC 1D PRODUCES 801KN OF THRUST! ISP AND THUS MASS FLOW AND UPPER STAGE PROPELLANT AND BURN TIME ARE NOT CONSISTENT AT ALL.just if anyone is interestedMy model of M1DVac predict 147 isp/801 kN at full thrust. I believe SpaceX is underselling the M1DVac Isp on their website, or the inconsistency is due to different numbers assume different throttle + rounded for nicer looking numbers.
=> NO WAY THAT THE MERLIN VAC 1D PRODUCES 801KN OF THRUST! ISP AND THUS MASS FLOW AND UPPER STAGE PROPELLANT AND BURN TIME ARE NOT CONSISTENT AT ALL.just if anyone is interested
My understanding was that he was saying he thinks a future rev of the Merlin 1 engine might be able to get 15% more thrust than the numbers currently claimed by SpaceX. So it would mean the Merlin 1Evac or Merlin 1Fvac could get 15% more than that 801kN thrust, not that they are currently getting 15% less than that.
Quote from: fatjohn1408 on 12/19/2013 12:28 pmFirst off all that is one heck of a spreadsheet.Pardon me for not going through it all before replying but when you have the following given:A first burn of more than 337s (probably around 345)A second burn of more than 60 seconds in which you know 2860 m/s delta v is given => hence you know the mass ratio between the beginning and the end of the burn given a certain Isp and you know the fuel rate going on in this burn hence the average throttle settings.Using 71 second burn time and 2860 m/s delta-v, I figure the second burn was @ 55% throttle on average. (132 kg/s instead of 236 kg/s). In my model, this would mean there was 79500 kg of fuel for the first burn, or about 338 seconds @ 100% thrust. However, I don't believe they ran on full thrust for the entire first burn. I calculate there was about 500m/s delta-v margin left after stage 2 second MECO. I also calculate that s2 thrust @ 55% would mean acceleration of 2.74g at the start of the second burn and 6.37g at the end. (Doesn't SpaceX cap the acceleration at 5g though?) Calculations (green box)Quote from: fatjohn1408 on 12/19/2013 12:28 pmOnly other conclusion would be that they - just for fun - decreased the throttle setting a bit in the first burn and went full power in the second burn. Which does not make any sense.Why do you think they went full power in the second burn?
First off all that is one heck of a spreadsheet.Pardon me for not going through it all before replying but when you have the following given:A first burn of more than 337s (probably around 345)A second burn of more than 60 seconds in which you know 2860 m/s delta v is given => hence you know the mass ratio between the beginning and the end of the burn given a certain Isp and you know the fuel rate going on in this burn hence the average throttle settings.
why wouldn't they do the first burn at full settings? You lose a lot due to gravity losses that way.
I think they went full power until they hit 6G, which is the limit they acknowledge in the old F9 block2 user manual.After that I think they throttle to keep the g-forces at 6g.Is it difficult to change throttle settings continually?You assume one switch in throttle to 55%? Don't forget throtlleing costs Isp, 20+s worth of it if you throttle to 55%.Now I could agree with the one time switch to 55% of throttle level. And yes that would mean that my somewhat hysterical conclusion was a bit too trigger happy. But why wouldn't they do the first burn at full settings? You lose a lot due to gravity losses that way.
Quote from: fatjohn1408 on 12/20/2013 10:17 amI think they went full power until they hit 6G, which is the limit they acknowledge in the old F9 block2 user manual.After that I think they throttle to keep the g-forces at 6g.Is it difficult to change throttle settings continually?You assume one switch in throttle to 55%? Don't forget throtlleing costs Isp, 20+s worth of it if you throttle to 55%.Now I could agree with the one time switch to 55% of throttle level. And yes that would mean that my somewhat hysterical conclusion was a bit too trigger happy. But why wouldn't they do the first burn at full settings? You lose a lot due to gravity losses that way.I do not assume 55% throttle, it was an example of average thrust and I have no guesstimate for the thrust profile. My 55% was a counter example to show a possible average throttle which allows for a 71s burn, adding 2480 delta-v while leaving fuel for a 338s 100% stage 2 first burn. I.e, it's possible to find consistency in the numbers and you were way too trigger happy. As for low throttle; you gain precision at lower acceleration and there is very little gravity loss during S2 burn. They might even have kept later parts of first burn below a lower acceleration limit.
Quote from: ChrisWilson68 on 12/04/2013 09:19 amCelesTrack is showing something labeled "Object A" with a launch date of 12/3/2013 from Florida. It has international designator 2013-071A and NORAD catalog number 39460.The TLE for this object is:1 39460U 13071A 13337.40768818 -.00000413 00000-0 00000+0 0 372 39460 20.5531 242.7832 8534855 179.4250 185.5374 0.87290738 01So it looks like 397 km by 79341 km at 20.55 degrees.Neat. Decay is estimated to be on 25 Mar 2014.. after 174 orbits. The lifetime is 112 days.Using the same (wrong) guesses as before for drag.
CelesTrack is showing something labeled "Object A" with a launch date of 12/3/2013 from Florida. It has international designator 2013-071A and NORAD catalog number 39460.The TLE for this object is:1 39460U 13071A 13337.40768818 -.00000413 00000-0 00000+0 0 372 39460 20.5531 242.7832 8534855 179.4250 185.5374 0.87290738 01So it looks like 397 km by 79341 km at 20.55 degrees.