Keep in mind that most likely Falcon won't be going anywhere even once BFR flies. SpaceX is investing if 4 pads for it. Even if they were to turn 39A into a BFR pad at some point, that's still 3 pads. It's sized good for comsats, and you aren't putting a 4mt comsat going to GTO on something the size of Saturn V or bigger. Multiple payloads are a possibility, but ArianeSpace is moving away from that, not doubling down on it with Ariane 6. Otherwise, why not make an Ariane 6 that's larger than Ariane 5 and can launch 5 or 6 sats at once? Becuase it's a bit of a challenge to get just two sats going to close enough of the same orbits that can launch together...much less more. So I don't see comsats being launched in big clusters by BFR. That's what F9 is for and it'll do a nice job of that.Bigger than F9 would be an FH with 3 reusable boosters. So what -could- BFR/MCT launch besides crewed, propellant, cargo, or depot versions of MCT? Even a fully reusable BFR/MCT which requires only nominal processing between flights (unlike STS) will have a fair cost...but could be less than say a D4H, or an FH-E or A5-551 or whatever the heavy Vulcan variant is. So it could be the most affordable launcher for those big government birds.It could also do planetary probes with an expendable kick stage.It could do a Bigelow module or large space telescope or something too, but those would be pretty rare, more one time events. Big telescopes are expensive and you only need so many big Bigelow modules in orbit. Cargo service to a big Bigelow station is a possible routine job for BFR though. So those are some potential markets for BFR, I'm pretty sure it's not going to take over F9R/FHR's markets.
Unfeasible? I don't know about that. How so? Because keep in mind, even if you have a dedicated reusable 2nd stage, and MCT sits on top, that 2nd stage will still almost certainly be some sort of biconic. It might get away with a more blunted nose and ballistic reentry like the reusable Falcon 9 upper stage, but it will still have to come in nose first...just like MCT. And since it's likely to come back from GTO trajectories if it's to deploy sats where most customers want them deployed, it'll be coming in faster than from just LEO. Which an integrated MCT platform would already be designed to do. But would a dedicated S2 be designed for that? It'd only ever need to go to LEO for purposes of launching MCT, and taking propellant to a LEO depot. It'd need to have HEO return capability built into it's TPS...again, like the integrated stage already will have.Which is what RobotBeat has hit on in a few posts. These are complementary tasks, not competing tasks. Where there is overlap anyway, why not go with it? Why have a separate 2nd stage that will have to be designed to do basically the same thing as the MCT basic platform?And how will it be easier to launch unmanned payloads from a biconic 2nd stage that cannot carry people (in any version) than it is from a biconic 2nd stage that can carry people when configured in a certain way?I'm not seeing the advantage...or how the later is technically unfeasible. If you can do one, you should be able to do the other. Either way, you need some sort of payload carrier that can be built in behind the nosecone cap (which would be used for docking and propellant transfer in either the integrated or non integrated concepts), or have some sort of expendable payload fairly that would mount on the nose.The only real advantage of a dedicated 2nd stage, as best I can see, is to allow an MCT to launch unfueled with fast reaction whole-vehicle abort capability. Something that cannot be done with the integrated design. But that's immaterial for the purpose of launching unmanned payloads to space.
Lets look at all the ways they differActive time of flight: R2S (Reusable 2nd Stage): Hours MCT: MonthsEntry Velocity: R2S: 7.7 km/s MCT: >12 km/sAerocapture necessary: R2S: NO MCT: YESLanding Site: R2S: Spaceport concrete pad + support facilities MCT: Unprepared martian regolith surfaceLanded Payload Mass: R2S: Self dry mass MCT: Self dry mass + 100 mT cargo (mars) 25 mT (Earth)Payload Carrying System: R2S: Payload adapter at top of tank MCT: Internal cargo bay with doorsPayload Separation Conditions: R2S: Axial decoupling in zero-g MCT: Horizontal removal on mars surfaceSingle use disposable Landing systems allowed (parachutes, airbags etc): R2S: YES MCT: NOAbort system necessary: R2S: NO MCT: YESTake off Site: R2S: Upper atmosphere after stage separation MCT: Unprepared martian regolith surface
The differences are almost endless and I foresee a very different 2nd stage that is a fairly normal cylindrical shape about 20 m tall and 10 m diameter holding around 1200 mT of propellants and equipped with 7 Raptor engines. It would be recovered by using a petal segment heat-shield covering the engines (rather then the unstable head-first entry depicted in the old F9 reuse video). The petals would then open and act as landing legs, the heat shield material can be a single use ablative (PICAX) that is attached to the structural leg/rib. The tank sides would likely have a metallic sandwich TPS system to protect them as well. The top of the vehicle would deploy parachutes, decelerators and other disposable systems from underneath the payload adapter. Grid-fins and vernier engines for touchdown would likewise be positioned at the top. Dry mass fraction of 6% would yield a 75 mT dry mass.
The 1st and 2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.
Musk said, paraphrasing, that BFR is intended to get approximately 100 tonnes to LEO.Interpretation 1: 100 tonnes including MCT dry-mass.Interpretation 2: 100 tonnes in addition to MCT dry-mass.
An interesting all be it old study on fast transit trajectories to and FROM mars.http://www.dtic.mil/dtic/tr/fulltext/u2/a272591.pdf
(From a couple of pages back.)Quote from: philw1776 on 10/23/2015 02:13 pmThe 1st and 2nd stage need only be able to get the 100mT cargo plus MCT dry weight into appropriate LEO.Hmmm, this seems to be another point that people should clarify when they debate options.Musk said, paraphrasing, that BFR is intended to get approximately 100 tonnes to LEO.Interpretation 1: 100 tonnes including MCT dry-mass.Interpretation 2: 100 tonnes in addition to MCT dry-mass.These are vastly different requirements.(And that's in addition to discussing whether the MCT is the second stage.)
Quote from: Paul451 on 10/28/2015 02:11 pmMusk said, paraphrasing, that BFR is intended to get approximately 100 tonnes to LEO.Interpretation 1: 100 tonnes including MCT dry-mass.Interpretation 2: 100 tonnes in addition to MCT dry-mass.That is not at all what was said and there is no ambiguity whatsoever. The number was 100t net payload landed on Mars.Which does not exclude the possibility that this capability will be reached only with the second or third iteration of MCT.
How Falcon and BFR split the launch manifest is certainly something to look at but if SpaceX is operating a full portfolio of reusable rockets the trading of launches between them becomes much less of an issue because your operating a fleet at that point.All the non-satellite launch missions for BFR I have stated already as well, and these would not actually require much modification if the vehicle is a conventional 2 stage rocket, though the Earth Escape probe would definitely need an escape stage I see something like Centaur just being put under the probe and treated as part of the payload and not something SpaceX provides.Finally their are potential savings by 'Raptorizing' the Falcon vehicles and retiring Merlin production, 4 Raptor engines should substitute for the 9 first stage Merline engines if a small landing engine/s is used either in the center or around the periphery. So far SpaceX has saved money by only making one turbo-pump fed engines, once Raptor is available the incentive is clearly their to get rid of the old engine and propellant mix, though I am not sure what would be done in the upper stage of Falcon, possibly a low thrust variant can be made.
So effectively MCT has a superset of the R2S requirements. Anything the R2S can do the MCT can do as well, so there is no need for the R2S.
That is not what I think a reusable 2nd stage would look like, this equivalency has been your core argument from the beginning, that a reusable 2nd stage and the MCT are so equal in performance that they might as well be the same vehicle but I couldn't disagree more.Lets look at all the ways they differActive time of flight: R2S (Reusable 2nd Stage): Hours MCT: MonthsEntry Velocity: R2S: 7.7 km/s MCT: >12 km/sAerocapture necessary: R2S: NO MCT: YESLanding Site: R2S: Spaceport concrete pad + support facilities MCT: Unprepared martian regolith surfaceLanded Payload Mass: R2S: Self dry mass MCT: Self dry mass + 100 mT cargo (mars) 25 mT (Earth)Payload Carrying System: R2S: Payload adapter at top of tank MCT: Internal cargo bay with doorsPayload Separation Conditions: R2S: Axial decoupling in zero-g MCT: Horizontal removal on mars surfaceSingle use disposable Landing systems allowed (parachutes, airbags etc): R2S: YES MCT: NOAbort system necessary: R2S: NO MCT: YESTake off Site: R2S: Upper atmosphere after stage separation MCT: Unprepared martian regolith surface
So effectively MCT has a superset of the R2S requirements. Anything the R2S can do the MCT can do as well, so there is no need for the R2S.For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.
Payload Carrying System: R2S: Payload adapter at top of tank MCT: Internal cargo bay with doors
For GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.
A 2nd stage would have similar terminal velocity to Dragon, if SpaceX can do fully propulsive landings with Dragon 2, they should be able to do do propulsive for a 2nd stage. Petals which open as landing legs may even give a lower terminal velocity than Dragon 2.Although I like the petal idea I can't quite see how they are configured during launch when they obviously cannot cover the engines.
Quote from: MikeAtkinson on 10/28/2015 07:29 amFor GEO satellite deployment MCT could be refuelled in LEO, transfer to GEO, drop off the satellites and return. Only one MCT per year is necessary for all the commercially competed GEO satellites, plus 1-3 tanker flights.I think it better to just have it go to a GTO, and then do what's typically done today, which is drop it off there and have the payload place itself in the GEO orbit. I think the propulsive hit becomes large when entering a GEO orbit to directly deploy the sat, and then have to deorbit from there.A GTO will bring it right back to Earth, where it can do a small deorbit burn and come right home.
Briefly butting in here. Consider gaining flight history on Raptor ahead of any BFR concept.And consider that FH's US is limiting factor in certain mission profiles.Only way I can factor in a non-BFR use of Raptor is as a oversized diameter US, flown on only FH. For a limited scope of missions. Which is against the SX economics as a whole I'll grant.Things that argue for this: * Raptor originally was a hydrolox US engine - clearly they earlier saw the need * Raptor was scaled up in size, then scaled down in size - launch architecture clearly being "tuned" around US and Mars ascent requirements * Environment to prove this would be in high/no atmosphere, not test stand * You'd also want long duration in space operations, not unlike what ACES/IVF is aimed for
Quote from: Impaler link=topic=37808.msg1439383#msg1439383 So what -could- BFR/MCT launch besides crewed, propellant, cargo, or depot versions of MCT? [/quoteIs there a chance to have a depot in a GTO orbit? Maybe an 80,000 km apogee. Deliver satellite, adjust orbit to meet up with depot, deliver prop load, then return to Earth. Once the depot is full, I believe it could make its way to EML with quite a low dV boost. Cheers, Martin
Is there a chance to have a depot in a GTO orbit? Maybe an 80,000 km apogee. Deliver satellite, adjust orbit to meet up with depot, deliver prop load, then return to Earth. Once the depot is full, I believe it could make its way to EML with quite a low dV boost. Cheers, Martin