Would you eliminate the current Falcon 2nd stage, or place this atop that?
For a manned flight to the Moon or Mars my feeling is that assembly and fueling in LEO is more practical than direct departure.
Probably a simple pressure fed upper stage using one or two Kestrel engines as this would match Spacex's habit of doing things in house.Plus fluids commonality with the other two stages.
Unless a hypothetical 3rd stage has mind-blowingly great Isp, it will never make sense. Stretching the upper stage will always be more mass *and* cost efficient.Replacing the upper stage with something else entirely - like a methane upper stage - would make the most sense if SpaceX planned on using FH for Mars missions.
Dry mass of second stage should be about 4000 kg.A two meter stretch should add only 300 kg of dry mass for additional 20000 kg of propellant.A stretch of second stage seems far easier than a third stage and quite good for performance still using MVac.http://forum.nasaspaceflight.com/index.php?topic=36045.msg1285819#msg1285819
Quote from: TomH on 11/27/2014 05:42 amWould you eliminate the current Falcon 2nd stage, or place this atop that?You don't add one, you eliminate the current 2nd stage.
Quote from: cambrianera on 11/27/2014 04:34 pmDry mass of second stage should be about 4000 kg.A two meter stretch should add only 300 kg of dry mass for additional 20000 kg of propellant.A stretch of second stage seems far easier than a third stage and quite good for performance still using MVac.http://forum.nasaspaceflight.com/index.php?topic=36045.msg1285819#msg1285819With the additional propellant, are current 9 merlins enough to lift all the mass?
Quote from: Jim on 11/27/2014 11:42 amQuote from: TomH on 11/27/2014 05:42 amWould you eliminate the current Falcon 2nd stage, or place this atop that?You don't add one, you eliminate the current 2nd stage.As Jim has said Merlin is good engine just undersized for 1st Stage and way undersized 2nd stage. Will they ever Marvel Team up Blue and put BE-3U on FH 1 stage & make an awesome Departure Rocket? Doubt it, they did do studies with Merlin 2 & Rapture when it was H2 + O2 stage for FHPS this is kinda of a duplicate thread with Falcon 9 3rd stage possibly be merged.
Quote from: Patchouli on 11/27/2014 02:50 pmProbably a simple pressure fed upper stage using one or two Kestrel engines as this would match Spacex's habit of doing things in house.Plus fluids commonality with the other two stages.Unless a hypothetical 3rd stage has mind-blowingly great Isp, it will never make sense. Stretching the upper stage will always be more mass *and* cost efficient.Replacing the upper stage with something else entirely - like a methane upper stage - would make the most sense if SpaceX planned on using FH for Mars missions.
Falcon Heavy (raptor) Reusable ExpendablePayload to LEO, kg 59'000 75'000
What sort of payloads to what destinations? The mission will dictate energy requirements, which could be very substantial.
Best idea for a perfect departure stage is whatever has sufficient performance and is cheapest. Chances are, that's /probably/ an existing FH upper stage.
Quote from: Tomness on 11/27/2014 04:59 pmQuote from: Jim on 11/27/2014 11:42 amQuote from: TomH on 11/27/2014 05:42 amWould you eliminate the current Falcon 2nd stage, or place this atop that?You don't add one, you eliminate the current 2nd stage.As Jim has said Merlin is good engine just undersized for 1st Stage and way undersized 2nd stage. Will they ever Marvel Team up Blue and put BE-3U on FH 1 stage & make an awesome Departure Rocket? Doubt it, they did do studies with Merlin 2 & Rapture when it was H2 + O2 stage for FHPS this is kinda of a duplicate thread with Falcon 9 3rd stage possibly be merged.Your sentence is unclear; Merlin 1D is undersized for the first stage, yes, that's why they use nine of them. However, Jim said (and I agree) that the entire upper stage is undersized, in part, because Merlin 1D vac is oversized for the second stage. It (the stage) has a very high thrust to dry mass ratio.EDIT: Also, we're losing sight of the thread. He's asking what's YOUR perfect upper stage(s), not what would the most likely for SpaceX to do. We have enough of that speculation already. Of course "perfect" is in the eye of the beholder in this case. Many would optimize performance, others cost, others manufactuability.
Quote from: Patchouli on 11/27/2014 02:50 pmProbably a simple pressure fed upper stage using one or two Kestrel engines as this would match Spacex's habit of doing things in house.Plus fluids commonality with the other two stages.If we're using the CxP definition of EDS, that it burns from LEO, then Kestrel has neither the thrust, nor the Isp needed for the job. Perhaps as a Star-48-style kick stage, but that wasn't the question asked. Cheers, Martin
I don't think Kerbal or rocket Lego is the intent of this thread. But with tongue-in-cheek, I agree wholeheartedly. But politically, nukes flying on a rocket that might - *gasp* - blow up during launch from KSC is literally not going to fly, I fear. Mores the pity. With evolved nuclear thermal; the moons of Jupiter and Saturn could be ours to conquer...
Quote from: MATTBLAK on 11/28/2014 05:32 amI don't think Kerbal or rocket Lego is the intent of this thread. But with tongue-in-cheek, I agree wholeheartedly. But politically, nukes flying on a rocket that might - *gasp* - blow up during launch from KSC is literally not going to fly, I fear. Mores the pity. With evolved nuclear thermal; the moons of Jupiter and Saturn could be ours to conquer...Would these be possible game changers? Reusable LVs that in a few years could have a track record of successful consecutive launches. The ability to launch from an ocean going vessel away from land and populated areas.
Quote from: Patchouli on 11/27/2014 02:50 pmProbably a simple pressure fed upper stage using one or two Kestrel engines as this would match Spacex's habit of doing things in house.Plus fluids commonality with the other two stages.Unless a hypothetical 3rd stage has mind-blowingly great Isp, it will never make sense. Stretching the upper stage will always be more mass *and* cost efficient.
LH2 technology seems to have been considered and selected against by SpaceX. ISP aside, why take this exit off the laid-out road to MARS? The FH is a major player in developing the infrastructure for Mars according to Shotwell, and FH will be used to ferry fuel to depots/departing missions, so logically and strategically, fuel should remain methlox.Remember, 'a perfect Earth departure stage for FH' has to be perfect for SpaceX.
Quote from: AncientU on 12/01/2014 11:38 pmLH2 technology seems to have been considered and selected against by SpaceX. ISP aside, why take this exit off the laid-out road to MARS? The FH is a major player in developing the infrastructure for Mars according to Shotwell, and FH will be used to ferry fuel to depots/departing missions, so logically and strategically, fuel should remain methlox.Remember, 'a perfect Earth departure stage for FH' has to be perfect for SpaceX.FH is kerolox, not methalox...
Quote from: Elmar Moelzer on 12/02/2014 01:29 pmQuote from: AncientU on 12/01/2014 11:38 pmLH2 technology seems to have been considered and selected against by SpaceX. ISP aside, why take this exit off the laid-out road to MARS? The FH is a major player in developing the infrastructure for Mars according to Shotwell, and FH will be used to ferry fuel to depots/departing missions, so logically and strategically, fuel should remain methlox.Remember, 'a perfect Earth departure stage for FH' has to be perfect for SpaceX.FH is kerolox, not methalox...As is, the upper stage is anything but perfect... A methlox upper stage (instead of the traditional LH2) would be best fit not SpaceX plans for the FH.
Anything but perfect?? Geez, hold the exaggerations.
Quote from: Lars-J on 12/02/2014 11:21 pmAnything but perfect?? Geez, hold the exaggerations.It is no exaggeration at all. It is vastly underpowered for the tri-core heavy.
..it is low on propellant....
Quote from: Lars-J on 12/03/2014 12:43 am..it is low on propellant.... Yes. It is mismatched with the heavy core. The US needs to provide more total impulse to match the capacity of the tri-core.
Quote from: TomH on 12/03/2014 01:24 amQuote from: Lars-J on 12/03/2014 12:43 am..it is low on propellant.... Yes. It is mismatched with the heavy core. The US needs to provide more total impulse to match the capacity of the tri-core.Even SpaceX has discussed a high energy upper, so they don't think the second stage is perfect. Note that this was even before FH was upgraded to v1.1 core and stretched boosters...So yes, the F9 upper stage is anything but perfect for FH... and I'll predict hat an enhanced version that takes advantage of most of the launcher capability will appear within the first few years of FH operations.
The market need isn't there at the moment (FH is overkill for the current market!), and such an upgrade won't happen unless there is a need for it. SpaceX wants a larger launcher, yes, but I think they see FH as an imperfect stop gap until the 'BFR'.
Quote from: Lars-J on 12/03/2014 05:46 pmThe market need isn't there at the moment (FH is overkill for the current market!), and such an upgrade won't happen unless there is a need for it. SpaceX wants a larger launcher, yes, but I think they see FH as an imperfect stop gap until the 'BFR'.Is true Specificaly FH is "addressing" the needs of the current market that are going to fall out of the F9 capability due to reuse. The FH is really going to be too much with a higher energy up stage. Useful of course, but not in the sense of the market F9/FH is actually aimed at.Right now cost rather than performance is the key metric and for that reason using the already existing stage manufacturing and equipment is prefered. Intellectually I fully understand that, however, my sense of "want-more" tends to over-ride that common sense response I personally find it hard to believe that SpaceX is going to dive head-first into Raptor development without trying a "small" methalox motor of some type and my "gut" feeling is they will end up developing a methalox upper stage for the F9 and FH using that motor. Such a stage while being more expensive I admit will put the F9 back into the "middle" of its market payload range even with first stage reuse which can't be anything but "good" for SpaceX. Such a stage on the FH? Out of the ballpark home run territory Randy
I disagree with the idea that Falcon Heavy should have a bigger upper stage. A bgger upper stage means a heavier empty mass to drag all the way to GTO/TLI, and while the delta V of the upper stage increases, at some point that of the lower stage decreases faster.I did some estimates a while ago for GTO payload of Falcon Heavy with different GTO payloads, I attached a graph. Assumed was a fixed 0.94 PMF for the upper stage, with the lower stages all having 385 tons of prop, 20 tons empty. It's not the exact figure that's important, but rather the relation between the payload and the upper stage propellant load.
Except that SpaceX is already diving head-first into Raptor development with component testing at Stennis as of last year and SpaceX management have consistently said Raptor is the only engine being developed.
Quote from: Waz_Met_Jou on 12/03/2014 07:22 pmI disagree with the idea that Falcon Heavy should have a bigger upper stage. A bigger upper stage means a heavier empty mass to drag all the way to GTO/TLI, and while the delta V of the upper stage increases, at some point that of the lower stage decreases faster.I did some estimates a while ago for GTO payload of Falcon Heavy with different GTO payloads, I attached a graph. Assumed was a fixed 0.94 PMF for the upper stage, with the lower stages all having 385 tons of prop, 20 tons empty. It's not the exact figure that's important, but rather the relation between the payload and the upper stage propellant load.I'm not sure exactly how big a difference it would make, but the PMF should actually get better with an increased propellant load, since adding additional length to the tanks will add a relatively small amount of weight to the stage. Certain parts and systems might need beefing up with a large enough propellant increase, but the PMF should increase regardless.
I disagree with the idea that Falcon Heavy should have a bigger upper stage. A bigger upper stage means a heavier empty mass to drag all the way to GTO/TLI, and while the delta V of the upper stage increases, at some point that of the lower stage decreases faster.I did some estimates a while ago for GTO payload of Falcon Heavy with different GTO payloads, I attached a graph. Assumed was a fixed 0.94 PMF for the upper stage, with the lower stages all having 385 tons of prop, 20 tons empty. It's not the exact figure that's important, but rather the relation between the payload and the upper stage propellant load.
It should probably be pointed out that main subject of the thread is an "Earth Departure Stage" for the FH not one for GTO/GEO launch For that particular criteria a kerolox stage just isn't the "right" one to be using at all and you REALLY want a higher energy propellant and higher ISP engine.Randy
I did some estimates a while ago for GTO payload of Falcon Heavy with different GTO payloads, I attached a graph. Assumed was a fixed 0.94 PMF for the upper stage, with the lower stages all having 385 tons of prop, 20 tons empty. It's not the exact figure that's important, but rather the relation between the payload and the upper stage propellant load.
Quote from: Waz_Met_Jou on 12/03/2014 07:22 pmI did some estimates a while ago for GTO payload of Falcon Heavy with different GTO payloads, I attached a graph. Assumed was a fixed 0.94 PMF for the upper stage, with the lower stages all having 385 tons of prop, 20 tons empty. It's not the exact figure that's important, but rather the relation between the payload and the upper stage propellant load.Surely, that would drop the liftoff T:W below acceptable levels? Wouldn't you need to offload some prop from core or boosters? Boosters, I think? Cheers, Martin
Quote from: MP99 on 12/10/2014 08:27 amQuote from: Waz_Met_Jou on 12/03/2014 07:22 pmI did some estimates a while ago for GTO payload of Falcon Heavy with different GTO payloads, I attached a graph. Assumed was a fixed 0.94 PMF for the upper stage, with the lower stages all having 385 tons of prop, 20 tons empty. It's not the exact figure that's important, but rather the relation between the payload and the upper stage propellant load.Surely, that would drop the liftoff T:W below acceptable levels? Wouldn't you need to offload some prop from core or boosters? Boosters, I think? Cheers, MartinNot necessarily. For TMI the payload is given as 13t. That's 40t less than to LEO. You can increase second stage fuel by app. 35t and get the same liftoff T/W ratio compared to LEO launchs considering some weight for tank stretch and increased payload.
How about no chemical TLI nor TMI stages? VASIMR, instead?And simply launch a VASIMR into LEO to rendezvous with a 53 tonne payload sent up by another FH?Too simple an idea, huh?