Well said Chris! What do you think about Gwynne Shotwell from where you stand?
Allow me to quote the source statements that informed my posts above:10:25 - Dr. Livingston - "So I guess what I'm hearing is that there really isn't going to be a penalty on the reusable because you've already compensated for that in the existing rocket."10:35 - Gwynne Shotwell - "That's correct."There are probably as many ways to spin this as there are posters on this thread, including what I did, which was to not spin it at all and let her statement stand unvarnished. Personally I think that without knowing what is actually in her head, that is the only correct approach to understanding what she said. However - YMMV Let the spin doctors begin.
Just wanted to interject with a salient point.You can't take a rocket that was designed for reusability- taking a 30% payload hit in the process- then pretend you're going to get 30% more payload into orbit by burning it to empty with no legs on it. Fuel+legs is not the only aspect of reusability. It's a huge part (legs alone represent hundreds of lost kilos to orbit), but it's not the only part. So why would they ever advertise that they could do that when they are designing a rocket that can't? None of what she said was very surprising. Though it was encouraging!
Quote from: Dudely on 03/25/2014 06:57 pmJust wanted to interject with a salient point.You can't take a rocket that was designed for reusability- taking a 30% payload hit in the process- then pretend you're going to get 30% more payload into orbit by burning it to empty with no legs on it. Fuel+legs is not the only aspect of reusability. It's a huge part (legs alone represent hundreds of lost kilos to orbit), but it's not the only part. So why would they ever advertise that they could do that when they are designing a rocket that can't? None of what she said was very surprising. Though it was encouraging!Sure you can, especially when the majority of that 30% hit is the fuel reserves. What other parts do you think are a major contributor?
Just wanted to interject with a salient point.You can't take a rocket that was designed for reusability- taking a 30% payload hit in the process...
...then pretend you're going to get 30% more payload into orbit by burning it to empty with no legs on it.
None of what she said was very surprising. Though it was encouraging!
...The ways things are heading, there's a fairly good chance she will have her name etched into history when we see people on Mars.
Quote from: Lobo on 03/24/2014 09:16 pmQuote from: Jcc on 03/23/2014 11:42 amQuote from: manboy on 03/23/2014 04:03 amSince Gwynne said she believed Pad 39A would be too small for the BFG doesn't that implicitly confirm that it'll be three cores?Possibly, and there may be a single core version, too. You would think that a pad that could launch Saturn V, could handle a single core BFR at least, although if the pad is configured for F9/FH the support equipment would be incompatible, and they would not want to stop launching F9/FH there while they retrofit, so better to build new pad. Maybe 39C? Another thought, the BFR will probably never be required to launch anything to GTO, so there is less reason to launch eastward from a site nearest the equator.A 2-stage BFR with a RTLS booster and reusable upper stage could launch large NRO type payloads to GTO, or dual payload launches to GTO like Ariane 5, and have enough margin to allow for total reusability. Where FH will need to launch at least partially reusable, if not fully reusable, to get those big birds to GTO.A fully reusable 2-stage BFR could be cheaper to operate than a partially expendable FH. So I think there could very well be a business case for BFR-R to go to GTO, or other BLEO trajectories for unmanned commercial and government payloads.She said that the SHLV aka. BFR is for Mars missions so don't expect it to be used for anything else. F9 and FH will take care of the satellite markets although FH will likely expend the center core on the heaviest missions.
Quote from: Jcc on 03/23/2014 11:42 amQuote from: manboy on 03/23/2014 04:03 amSince Gwynne said she believed Pad 39A would be too small for the BFG doesn't that implicitly confirm that it'll be three cores?Possibly, and there may be a single core version, too. You would think that a pad that could launch Saturn V, could handle a single core BFR at least, although if the pad is configured for F9/FH the support equipment would be incompatible, and they would not want to stop launching F9/FH there while they retrofit, so better to build new pad. Maybe 39C? Another thought, the BFR will probably never be required to launch anything to GTO, so there is less reason to launch eastward from a site nearest the equator.A 2-stage BFR with a RTLS booster and reusable upper stage could launch large NRO type payloads to GTO, or dual payload launches to GTO like Ariane 5, and have enough margin to allow for total reusability. Where FH will need to launch at least partially reusable, if not fully reusable, to get those big birds to GTO.A fully reusable 2-stage BFR could be cheaper to operate than a partially expendable FH. So I think there could very well be a business case for BFR-R to go to GTO, or other BLEO trajectories for unmanned commercial and government payloads.
Quote from: manboy on 03/23/2014 04:03 amSince Gwynne said she believed Pad 39A would be too small for the BFG doesn't that implicitly confirm that it'll be three cores?Possibly, and there may be a single core version, too. You would think that a pad that could launch Saturn V, could handle a single core BFR at least, although if the pad is configured for F9/FH the support equipment would be incompatible, and they would not want to stop launching F9/FH there while they retrofit, so better to build new pad. Maybe 39C? Another thought, the BFR will probably never be required to launch anything to GTO, so there is less reason to launch eastward from a site nearest the equator.
Since Gwynne said she believed Pad 39A would be too small for the BFG doesn't that implicitly confirm that it'll be three cores?
I am referring to the 10m single core LV, not the tri-core SHLV, which I'm sure is intended for sending the final version of MCT to Mars for colonization. As there's little else such a beast would be used for.
Quote from: Owlon on 03/24/2014 02:15 pmQuote from: clongton on 03/24/2014 01:42 pmQuote from: Elmar Moelzer on 03/24/2014 01:15 pmThey are loosing performance.Ms. Shotwell specifically said they are not loosing performance.Do you know something that she does not?They are most certainly losing performance, they just already have the reduced performance posted on the website. That's exactly what she said.Perhaps you didn't read my post entirely, or did not actually listen to the interview show. In any case she specifically stated that the 30% is reserved for the RTLS flight. Reserved means that it was never figured into the available performance. She stated that the figures quoted on the website are the available performance and represent what is available for a resuable launch vehicle. Her contention is that the launch vehicle is not loosing performance because it was designed for reusability. That 30% was never alocated for available performance, and because it was never available to the customer in the first place it is not lost performance. Most cars and pickups will drive 20-30 miles after the gas gage says empty. Only dumb drivers wait until they have burned up that reserve before getting more, because that's not what it's for. This is pretty much the same thing.
Quote from: clongton on 03/24/2014 01:42 pmQuote from: Elmar Moelzer on 03/24/2014 01:15 pmThey are loosing performance.Ms. Shotwell specifically said they are not loosing performance.Do you know something that she does not?They are most certainly losing performance, they just already have the reduced performance posted on the website. That's exactly what she said.
Quote from: Elmar Moelzer on 03/24/2014 01:15 pmThey are loosing performance.Ms. Shotwell specifically said they are not loosing performance.Do you know something that she does not?
They are loosing performance.
A 747 designed for reuse can be used in expendable mode as well. That doesn't normally mean that you're losing performance when you use it as designed.
Have you ever heard anyone say that reusable 747s were losing performance compared to expendable 747s? Has anyone ever included that in an analysis of the 747s capability? Was expending 747s ever discussed during their design phase?
Quote from: Hyperion5 on 03/24/2014 04:11 amImpulse Density Id = v_e(exhaust velocity)*d_p(bulk density) 1600.6 Ns/L = 4471 m/s*.358 kg/L (hydrolox rocket)3568 Ns/L = 3477.6 m/s *1.026 kg/L (kerolox rocket) So you see, despite all of the hydrolox rocket's added efficiency, the kerolox rocket will still pack 2.23X as much delta-v into a liter of propellants. This means your hydrolox rocket must have tanks at least 2.23X as large to compensate, and more if you factor in the added mass of the tanks and their insulation.It is not that simple. The formulas the your methane F9 family thread apply here too. You can't equate plain impulse density value directly to delta-v. Half of it (density) is inside the logarithm of rocket equation and you'd need more info to calculate actual desired delta-v. Or vice versa, you peg desired delta-v from which you calculate tank volume, or the handy "specific volume" (propellant volume divided by burnout mass) for different propellants to compare.For example if there's upper stage needing to do 6000m/s dv then your values give specific volume of 4.496L/kg for kerolox and 7.896L/kg for hydrolox, so volume ratio is 1.756Lower stages become more complex because reduced upper stage weights need to be taken into account. A first stage doing 3500m/s needs "only" 1.462 times larger tanks using hydrolox with above upper stage example adjusted for its lesser wet mass, assuming it's 80% of first stage burnout mass. Without adjusting the ratio would be 1.961Yes this is too simple and does not take into account tank mass per volume, insulation, different engine T/Ws etc. just wanted to point out it is not directly proportional to impulse density. Calculated numbers with too-messy-to-upload mathcad sheet.This is so OT isn'it it
Impulse Density Id = v_e(exhaust velocity)*d_p(bulk density) 1600.6 Ns/L = 4471 m/s*.358 kg/L (hydrolox rocket)3568 Ns/L = 3477.6 m/s *1.026 kg/L (kerolox rocket) So you see, despite all of the hydrolox rocket's added efficiency, the kerolox rocket will still pack 2.23X as much delta-v into a liter of propellants. This means your hydrolox rocket must have tanks at least 2.23X as large to compensate, and more if you factor in the added mass of the tanks and their insulation.
Quote from: Lobo on 03/25/2014 10:23 pmI am referring to the 10m single core LV, not the tri-core SHLV, which I'm sure is intended for sending the final version of MCT to Mars for colonization. As there's little else such a beast would be used for.Any vehicle with a Raptor engine is a decade away and will only be used for Mars launches. I don't know how Gwynne could have made this more clear. If you haven't already listened to the show, please do.
In responding to the question, "What was one of the things you never thought the internet would be used for, but has actually become one of the main reasons people use the internet?" he replied, "Kittens".
