Quote from: Jimmy Murdok on 04/12/2015 04:48 pmQuote from: GORDAP on 04/12/2015 11:50 amI think some of your figures might be a little off. The estimate I've seen several times for the ISP of a vacuum Raptor is 380, and the best estimate I've seen for the ISP of the present upper stage Falcon is 345. So this would be more like a 10% ISP improvement rather than 3.8%. And with the exponential nature of the rocket equation, this is quite significant.This ISP are between different fuels for same X engine. The big increase in ISP between merlin and raptor is mainly because of the full flow engine not because of the fuel. I think it would make a lot of sense to have a full flow engine for the upper stage and improve the ISP. What I don't see is the switch to methane. A mini raptor methane upper stage would fit and maybe in 5 years we will see it in case they have a mini-raptor, but FMPOV a kerosene mini raptor would fit better. The switch between kerosene and methane "is not a big deal", so I don't see that crazy that once they have a mini raptor they adapt it to kerosene. But thats lot of speculation.You're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.
Quote from: GORDAP on 04/12/2015 11:50 amI think some of your figures might be a little off. The estimate I've seen several times for the ISP of a vacuum Raptor is 380, and the best estimate I've seen for the ISP of the present upper stage Falcon is 345. So this would be more like a 10% ISP improvement rather than 3.8%. And with the exponential nature of the rocket equation, this is quite significant.This ISP are between different fuels for same X engine. The big increase in ISP between merlin and raptor is mainly because of the full flow engine not because of the fuel. I think it would make a lot of sense to have a full flow engine for the upper stage and improve the ISP. What I don't see is the switch to methane. A mini raptor methane upper stage would fit and maybe in 5 years we will see it in case they have a mini-raptor, but FMPOV a kerosene mini raptor would fit better. The switch between kerosene and methane "is not a big deal", so I don't see that crazy that once they have a mini raptor they adapt it to kerosene. But thats lot of speculation.
I think some of your figures might be a little off. The estimate I've seen several times for the ISP of a vacuum Raptor is 380, and the best estimate I've seen for the ISP of the present upper stage Falcon is 345. So this would be more like a 10% ISP improvement rather than 3.8%. And with the exponential nature of the rocket equation, this is quite significant.
If there was to be a higher(er) energy FH upper stage with an in-house engine, I'd expect it to be something like this> 5.2m barrel size (the same diameter as the PLF) and the same length as the kerosene-fuelled U/S. Whilst a 'Merlin-M' has not evidently in development, I'd certainly consider having it in a 'paper only' development phase to minimise delays if extra beyond-LEO performance is needed and Raptor is further off than a Methane conversion of the Merlin-VAC.There is a lot of 'ifs' in that and I doubt it would happen unless Musk were certain of a customer or two who needed the performance. That said, a 360-380s U/S would be an interesting addition to the vehicle.
Quote from: baldusi on 04/12/2015 12:36 amBut this is no case for SpaceX. They are going from RP-1 Gas Generator to Methane Full Flow. Big difference. And actual RSC Energyia engineer has calculated that a methane Falcon 9 with the same dimensions as v1.1, but engine performance as Raptor, would get 25tonnes to LEO and 8tonnes to GTO. That covers 100% of current market. And that's without the 10% tank lengething and propellant densification that SpaceX is implementing on the enhanced Falcon 9, nor 2050 aluminum tanks and other "cheap" enhancements. Probably could hit 30/10 with that.If they do a mini Raptor upper stage, they'll probably move the cores later. They'll have the performance margin for upper stage reuse and validate everything for MCT for a lot less money than a whole new development.Humm I cannot argue because I have no data but 25 tones losing 22% fuel mass is hard to believe. I would expect something similar to what you have now (13-14t to LEO). Zenit rocket with slightly less mass than F9 V1.1 and best full flow kerosene engine works 13500kg to LEO. Maybe could be slightly better, but 25 tones... anyway, time will tell.
But this is no case for SpaceX. They are going from RP-1 Gas Generator to Methane Full Flow. Big difference. And actual RSC Energyia engineer has calculated that a methane Falcon 9 with the same dimensions as v1.1, but engine performance as Raptor, would get 25tonnes to LEO and 8tonnes to GTO. That covers 100% of current market. And that's without the 10% tank lengething and propellant densification that SpaceX is implementing on the enhanced Falcon 9, nor 2050 aluminum tanks and other "cheap" enhancements. Probably could hit 30/10 with that.If they do a mini Raptor upper stage, they'll probably move the cores later. They'll have the performance margin for upper stage reuse and validate everything for MCT for a lot less money than a whole new development.
You're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.
Quote from: Robotbeat on 04/12/2015 04:59 pmYou're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.You mean that the production of a methane stage combustion engine is easier because methane produce less corrossion in plumbing and combustion chamber than the dirty kerosene?
For starters, F9 v1.1 actually does about 16.5/17tonnes to LEO. Second, the Zenit-2 has a smaller upper stage in relationship. And third, the F9 v1.1 is around 95% of pmf in both first and second, while the Zenit-2 is 92% and 90%, respectively. Zenit-2 was a compromise with the Energyia boosters and has too much T/W and is just too heavy.
More or less. The Raptor engine will be full flow staged combustion, so it will have both an oxygen-rich and methane-rich preburner. Kerosene-rich preburners just aren't done because they cause horrible coking problems in the turbine. There may be more to it to that, but that's my basic understanding of the issue.
Quote from: Jimmy Murdok on 04/12/2015 06:23 pmQuote from: Robotbeat on 04/12/2015 04:59 pmYou're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.You mean that the production of a methane stage combustion engine is easier because methane produce less corrossion in plumbing and combustion chamber than the dirty kerosene?More or less. The Raptor engine will be full flow staged combustion, so it will have both an oxygen-rich and methane-rich preburner. Kerosene-rich preburners just aren't done because they cause horrible coking problems in the turbine. There may be more to it to that, but that's my basic understanding of the issue.
Quote from: MP99 on 04/12/2015 08:02 amQuote from: spacenut on 04/11/2015 07:39 pmIf Raptor is 500k lb thrust and Merlin vacuum is 200k lb thrust, that is a lot more thrust. Would the upper be widened to hold more fuel, or stretched? Unless the Raptor vacuum can be throttled down. If you assume 550 klbf for the vac version (~250 tf), that would need a minimum ~20t payload for 6g burnout @ 50% throttle. Fine for LEO with FHR, but not for GTO / escape unless they go with FHE (maybe recover the boosters?) Good for a prop tanker for MCT, though. Cheers, Martin Wouldn't this be 6g only if the upper stage itself was massless? I think the present one is about 4 mt empty. Switching from Merlin to Raptor probably will add 1 mt. If it's to be reusable, then you also would be looking at adding TPS, legs, grid fins + hydrolics, etc., not to mention the landing fuel. I can easily see this approaching 10 mt total. So at 50% throttle and a 20 mt payload, you'd only be looking at about 4 g at burnout.
Quote from: spacenut on 04/11/2015 07:39 pmIf Raptor is 500k lb thrust and Merlin vacuum is 200k lb thrust, that is a lot more thrust. Would the upper be widened to hold more fuel, or stretched? Unless the Raptor vacuum can be throttled down. If you assume 550 klbf for the vac version (~250 tf), that would need a minimum ~20t payload for 6g burnout @ 50% throttle. Fine for LEO with FHR, but not for GTO / escape unless they go with FHE (maybe recover the boosters?) Good for a prop tanker for MCT, though. Cheers, Martin
If Raptor is 500k lb thrust and Merlin vacuum is 200k lb thrust, that is a lot more thrust. Would the upper be widened to hold more fuel, or stretched? Unless the Raptor vacuum can be throttled down.
Quote from: Owlon on 04/12/2015 06:36 pmQuote from: Jimmy Murdok on 04/12/2015 06:23 pmQuote from: Robotbeat on 04/12/2015 04:59 pmYou're missing the fact that part of the reason Raptor's engine cycle is feasible is because it's using methane instead of kerosene. So methane enables higher Isp by enabling a better engine cycle.You mean that the production of a methane stage combustion engine is easier because methane produce less corrossion in plumbing and combustion chamber than the dirty kerosene?More or less. The Raptor engine will be full flow staged combustion, so it will have both an oxygen-rich and methane-rich preburner. Kerosene-rich preburners just aren't done because they cause horrible coking problems in the turbine. There may be more to it to that, but that's my basic understanding of the issue.Well I can imagine that. But in this case I don't understand how the normal gas generator cycle can work. The gas generator is also kerosene rich and the gas gets pushed through the turbine just fine, before being dumped as one big black sooty stream of evil. So maybe the coking problem is with the injectors into the burning chamber instead? Those are fairly small orifices and should be much more vulnerable to coking.
COLORADO SPRINGS, Colo. — SpaceX says it sent the U.S. Air Force an updated letter of intent April 14 outlining a certification process for its Falcon Heavy rocket to launch national security satellites.SpaceX hopes to have its Falcon Heavy rocket certified by 2017, Gwynne Shotwell, the company’s president and chief operating officer, told SpaceNews in an April 14 interview.- See more at: http://spacenews.com/spacex-sends-air-force-an-outline-for-falcon-heavy-certification/#sthash.0Wzwy5m7.dpuf
SpaceX Sends Air Force an Outline for Falcon Heavy Certification - See more at: http://spacenews.com/spacex-sends-air-force-an-outline-for-falcon-heavy-certification/#sthash.0Wzwy5m7.dpufQuoteCOLORADO SPRINGS, Colo. — SpaceX says it sent the U.S. Air Force an updated letter of intent April 14 outlining a certification process for its Falcon Heavy rocket to launch national security satellites.SpaceX hopes to have its Falcon Heavy rocket certified by 2017, Gwynne Shotwell, the company’s president and chief operating officer, told SpaceNews in an April 14 interview.- See more at: http://spacenews.com/spacex-sends-air-force-an-outline-for-falcon-heavy-certification/#sthash.0Wzwy5m7.dpuf
Interesting. It is after all exactly what the last Assured Access Congressional Hearing was requesting. I believe it was something to the effect of, "Please have that FH ready as soon as possible." A 2017 certification, IMO, puts real pressure on ULA in that it makes needing to extend the RD-180 past 2019 a mute point. (Except for the VI issue) This is going to get very interesting. Not that it isn't already.
Shotwell said she expects the Falcon Heavy rocket to fly once this year, three times in 2016 and three to five times in 2017. “The market is huge,” she said. “The market is bigger in the commercial marketplace than it is for the single stick Falcon 9.”
Surprising...Quote from: Gwynne ShotwellShotwell said she expects the Falcon Heavy rocket to fly once this year, three times in 2016 and three to five times in 2017. “The market is huge,” she said. “The market is bigger in the commercial marketplace than it is for the single stick Falcon 9.”
Surprising...Very. I'm not saying that she's misstating but I do wonder who the potential customers in the 50t IMLEO/17t GTO market might be.
competitive with Proton without the issues of working with Russians.