Wow, that's a great video - and yes, that was the reaction control thrusters of the first stage firing. This is the best view of it that we have seen so far.I'm not sure where it was filmed, but that was some pretty impressive tracking to follow the second stage until it went below the horizon. If this was truly filmed all the way from Orlando, then WOW again! More rockets should launch at this time to have the same great lighting conditions.
Quote from: Lars_J on 12/05/2013 07:49 amWow, that's a great video - and yes, that was the reaction control thrusters of the first stage firing. This is the best view of it that we have seen so far.I'm not sure where it was filmed, but that was some pretty impressive tracking to follow the second stage until it went below the horizon. If this was truly filmed all the way from Orlando, then WOW again! More rockets should launch at this time to have the same great lighting conditions. I understand they use cold gas thrusters? Does that give the most energy compared to the weight of the total package? ISP is not that great for cold gas but don't know about total efficiency. What rcs options exist for that are relevant for a first stage reentry control? How much weight does the rcs package add? Thought they were going to maximize performance on this one.
@ Lars_J,I suppose there must be a point where carrying not-required weight is so detrimental that it outweighs the simplification of production. For example, I doubt that the landing struts would be on all flights after SpX-CRS-3. The performance penalty would be too great.
Probably the answer lies in how you've set up the leg design. Is it easy simply to leave them off or have you designed them to be an integral part of the first stage. Anyone?
...There is no propellant for a controlled deorbit in GTO missions. The stages have limited life and usually are dead before reaching apogee for a deorbit burn. Also, it might be a bad point to do the entry at that time.CCAM is not done with the main engine, it is done with thrusters. The depletion or inerting "burn" is not even a burn, it is just a dump of the propellants.
That's definitely a burn isn't it? Unless they decided to inject in a higher orbit than published in the first place...
Quote from: beancounter on 12/10/2013 01:10 amProbably the answer lies in how you've set up the leg design. Is it easy simply to leave them off or have you designed them to be an integral part of the first stage. Anyone?The stage has already flown without legs. So if not for performance, they will leave the legs off because they are not cheap. They are the only major component that distinguishes reusable from non reusable. Yes I know there are the avionics, the relight capability and the cold gas thrusters. All of these will probably be present on the expendable, because they are integrated.
http://www.americaspace.com/?p=46034Any idea how accurate the statements are about second stage burn times?Namely first burn of 320 seconds and second burn of 71 seconds?
Quote from: fatjohn1408 on 12/10/2013 02:27 pmhttp://www.americaspace.com/?p=46034Any idea how accurate the statements are about second stage burn times?Namely first burn of 320 seconds and second burn of 71 seconds?The wired article that musk tweeted quotes a burn of just 1 minute, but this could have been presumably taken from the mission kit which stated a burn of over one minute.http://www.wired.com/autopia/2013/11/spacex-thanksgiving-launch/?cid=co15077314
Quote from: fatjohn1408 on 12/11/2013 02:37 pmQuote from: fatjohn1408 on 12/10/2013 02:27 pmhttp://www.americaspace.com/?p=46034Any idea how accurate the statements are about second stage burn times?Namely first burn of 320 seconds and second burn of 71 seconds?The wired article that musk tweeted quotes a burn of just 1 minute, but this could have been presumably taken from the mission kit which stated a burn of over one minute.http://www.wired.com/autopia/2013/11/spacex-thanksgiving-launch/?cid=co15077314Wow, hadn't even checked it, was mainly focused on second burn of 71 seconds. But the first burn was not 320 it was at least 338 (before they killed the feed)Even if they do the transfer at constant 6G somehow miraculously, they would need an additional 49s.since there press kit states plus 1 minute and most articles state 71 seconds I'm willing to venture that the second stage burned for more than 400s. => 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
=> 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
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.
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.
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.
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.