Author Topic: MCT Speculation and Discussion Thread 4  (Read 621682 times)

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #940 on: 10/28/2015 02:52 AM »

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.

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.

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.

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 differ

Active time of flight:  R2S (Reusable 2nd Stage):  Hours   MCT:  Months

Entry Velocity:    R2S: 7.7 km/s    MCT:  >12 km/s

Aerocapture necessary:   R2S:  NO    MCT: YES

Landing Site:  R2S:  Spaceport concrete pad + support facilities    MCT:  Unprepared martian regolith surface

Landed 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 doors

Payload Separation Conditions:  R2S:  Axial decoupling in zero-g    MCT:  Horizontal removal on mars surface

Single use disposable Landing systems allowed (parachutes, airbags etc):   R2S:  YES    MCT:  NO

Abort system necessary:  R2S:  NO    MCT: YES

Take 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.
« Last Edit: 10/28/2015 02:56 AM by Impaler »

Online MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #941 on: 10/28/2015 07:29 AM »
Lets look at all the ways they differ

Active time of flight:  R2S (Reusable 2nd Stage):  Hours   MCT:  Months

Entry Velocity:    R2S: 7.7 km/s    MCT:  >12 km/s

Aerocapture necessary:   R2S:  NO    MCT: YES

Landing Site:  R2S:  Spaceport concrete pad + support facilities    MCT:  Unprepared martian regolith surface

Landed 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 doors

Payload Separation Conditions:  R2S:  Axial decoupling in zero-g    MCT:  Horizontal removal on mars surface

Single use disposable Landing systems allowed (parachutes, airbags etc):   R2S:  YES    MCT:  NO

Abort system necessary:  R2S:  NO    MCT: YES

Take 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.

Online MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #942 on: 10/28/2015 07:35 AM »
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.

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.

Offline Paul451

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Re: MCT Speculation and Discussion Thread 4
« Reply #943 on: 10/28/2015 02:11 PM »
(From a couple of pages back.)

The 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.)

[ Edit: 100t to LEO is pulled from a comment on the MCT Source Info thread ]

--

Re: Commercial MCT use.

(Interpreted as MCT as second stage, with 100t + drymass to LEO.)

Musk mentioned ten cargo MCTs per passenger MCT, so 11 MCT's per 100 colonists.

However, orbital refuelling means multiple launches in addition to the main launch. So if you need, say, three launches of fuel per MCT-to-Mars, then you've 44 launches per 100 colonists.

If the price per colonist is $500,000, that puts the price of a single launch at $1.14m (less for the launch itself, since the total price includes all the extra orbital handling for refuelling, the ECLSS for 100day flights, etc.)

At a bit over a million per launch, BFR/MCT combination will be profitable as a commercial launcher if they carry a single 1 tonne satellite for $2m.

Even if these numbers are out by an order of magnitude (especially at the beginning), that's still 100 tonnes to LEO for a mere $10-20m. At that price BFR/MCT will quickly eat up the entire FH and F9R's launch market, just as F9 ate F1's market. (Better to fly as a secondary or multiple payload and use a bit of extra fuel to shuffle into your target orbit than buy the full capacity of F9R.)

That allows SpaceX to shut down F9/FH and Merlin production and focus on a single production line. And it allows them to incrementally test and improve BFR at someone else's expense. And to develop the simplest possible MCT as the first iteration (as a reusable BFR upper stage), before adding the complexity of orbital refuelling, 100-day ECLSS, Mars EDL/refuel/re-launch... etc.

Sounds like a plan to me.

When you think about how expensive BFR would have to get before it's not a viable commercial launcher, it's a lot higher than the point where it's no longer a viable Mars colony vehicle.
« Last Edit: 10/28/2015 04:51 PM by Paul451 »

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #944 on: 10/28/2015 02:42 PM »
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.

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.

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #945 on: 10/28/2015 02:53 PM »
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



I'll take a look at that document when I get a chance.  Thanks for the info Impaler.  I've not really taken the time to work up my knowledge in the area of orbital mechanics like this.

Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #946 on: 10/28/2015 03:00 PM »
(From a couple of pages back.)

The 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.)

On the contrary.  He said that MCT would get "100 tons useful cargo to the surface of Mars".  Meaning if I want to ship 100 tons of candy bars to the surface of Mars for Halloween, that is doable.

BFR is something Shotwell rather than Musk has been talking about;  A launch vehicle that can loft 180-210 tons IIRC.  It doesn't really make much sense to launch MCT 'full' of small cargo, because MCT can be substantially heavier given a finite-sized launch vehicle if it's not packed with, eg, food, during ascent to LEO.

The questions are further down the road:
Interpretation 3A: 100 tonnes to the surface of Mars not including the ISRU equipment necessary to return (and reuse) the MCT, which will be additional mass
Interpretation 3B: 100 tonnes to the surface of Mars including the ISRU equipment necessary to return (and reuse) the MCT
Interpretation 3C: 100 tonnes to the surface of Mars with no ISRU equipment onboard;  MCT will only be used with prelanded ISRU assets on a 1-synod cycle
Interpretation 4A: 100 tonnes to the surface of Mars not including the ISRU equipment necessary to return (and reuse) the MCT, plus return 100 tonnes of cargo
et cetera, et cetera

Musk has also said things about "100 passengers".  This necessitates quite a large mass of food, and they need a very high-volume hab besides.  Maybe this is a *subjective guess* as to the terminal capacity that fits into "100 tons", but only if everything goes right and a functioning colony is first established.  Maybe it's one-way, Mars One style.  Maybe it refers (in the worst-case) to a first mission, and we need to return 100 passengers using onboard ISRU.  Maybe not everything gets landed.  We can't be sure.
« Last Edit: 10/28/2015 03:06 PM by Burninate »

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #947 on: 10/28/2015 03:04 PM »
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.

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.

If I recall correctly, I think the term was 100 tons of "useful payload".

But yea, that pretty much indicates that number doesn't include the dry mass of the vehicle.


Edit:  Burninate beat me to it.
« Last Edit: 10/28/2015 03:05 PM by Lobo »

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #948 on: 10/28/2015 04:11 PM »

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.


Yes, they may upgrade Falcon in the future.  If their past is any indication, that's probably pretty likely. 
Will they go to methane or even Raptor?  Maybe.  Although the two issues with Raptor are too few and too powerful of engines on the booster (as you said) which would likely necessitate some other means to land it.  And that a single vacuum Raptor on the upper stage would probably be way over powered for F9US.  Whereas the Merlins are sized correctly. 

But that's somewhat immaterial, as the point is SpaceX has mad a lot of investment into Falcon, and it most likely won't be going anywhere once BFR/MCT is flying.  It will cost effectively service payloads from EELV-medium class on down with booster reusability, and cheap upper stage mass production.  (Economics of scale can reduce costs as well as reusability).  It may be a Falcon v1.5, or v2.0, but it will still be Falcon in some form, because that's the butter size.  And it's affordable to launch single sats to their specific orbits rather than run into an Ariane 5 issue on steroids with a BFR.


Offline Pipcard

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Re: MCT Speculation and Discussion Thread 4
« Reply #949 on: 10/28/2015 04:50 PM »
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.

What Impaler was trying to refute was the idea that anything MCT is supposed to do is as easy and simple as having a reusable second stage.
« Last Edit: 10/28/2015 05:04 PM by Pipcard »

Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #950 on: 10/28/2015 04:55 PM »

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 differ

Active time of flight:  R2S (Reusable 2nd Stage):  Hours   MCT:  Months

Entry Velocity:    R2S: 7.7 km/s    MCT:  >12 km/s

Aerocapture necessary:   R2S:  NO    MCT: YES

Landing Site:  R2S:  Spaceport concrete pad + support facilities    MCT:  Unprepared martian regolith surface

Landed 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 doors

Payload Separation Conditions:  R2S:  Axial decoupling in zero-g    MCT:  Horizontal removal on mars surface

Single use disposable Landing systems allowed (parachutes, airbags etc):   R2S:  YES    MCT:  NO

Abort system necessary:  R2S:  NO    MCT: YES

Take off Site:  R2S:  Upper atmosphere after stage separation    MCT:  Unprepared martian regolith surface

I'm not saying a dedicated 2nd stage couldn't be made cheaper and easier than an integrated MCT basic platform stage.  It's criteria aren't as harsh as for MCT. 
But, that doesn't speak to your original comment about an integrated design being technically unfeasible.  There may be other reasons to go with a dedicated 2nd stage, but I don't think those are reasons because the integrated design is some sort of impossible or implausible concept.

Now, if the integrated design is feasible, that just leaves the question of if it's the better way to go or not?
Mike speaks well to that here:


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.

That's always been my point.  You have to have MCT anyway.  It already can do everything a cheaper/easier S2 can do anyway.  Why not just make it be the S2 then?

Will it be a little heavier than the dedicated S2?  Probably.  It probably won't have quote the payload capability of the integrated MCT platform.  But will that be a problem?  Probably not.  It's only going to be an issue for two potential MCT/BFR missions.

1)  Unmanned payload launching to space.
2)  Tanker service to depot.

The first shouldn't be much issue, because there's already nothing that needs 100mt of throw capacity (although it would likely be even more than that, because it would be stripped down to just the tanks, engines, and OML)  To my knowledge there's no current or near term future need for more capacity than D4H or FHE will have to LEO or to GTO.  And such an integrated BFR would have much more capacity than those.  So if you have 100mt to LEO instead of say 120mt to LEO for a dedicated lighter/cheaper S2, it doesn't hurt you from the commercial or government payload launching market.

As for a tanker, it probably wouldn't be able to get quite as much propellant to a depot per launch.  But then again, you have a reusable launch system.  So if it takes 5 BFR launches to fill up a depot prior to a Mars mission instead of 4, is that really a detriment? 
And again, when comparing the dedicated S2 to the basic integrated MCT platform...stripped of everything but the bare shell, tanks, engines, and landing gear, I doubt the difference would be all that much.

Also, as a satellite launcher, it wouldn't really need it's big MCT solar arrays.  And it would have large residuals of propellants.  So a little methalox fuel cell or IVF engine could generate the short term loiter power it needs, so it wouldn't even need to have the solar arrays.  A dedicated S2 would need something like that too....or a lot of batteries.  Either way that would be needed.


Payload Carrying System:  R2S:  Payload adapter at top of tank     MCT:  Internal cargo bay with doors

You could either have an internal cargo bay for MCT...as there will be an empty volume between the nose and tanks, or have a payload adapter on the nose like you say for the S2.  Either set up will have a TPS on the nose, so there's not much difference in have a payload adapter on one vs. the other. 


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.


Yes, there can be differences, but it doesn't change that MCT would do everything S2 would do, and much more.  So the advantage of going that way is you only need to develop one spaceship, and all of them have the same basic common platform.  Where as the two spacecraft you've described appear to have different landing legs, different TPS systems, and different methods of landing...a lot of different duplicated systems that cost more to develop and support, and add extra mass to the stack when launching MCT.
 I think there's a plausible argument than the economic and logistic advantage...as well as mass advantage to LEO of have the one common integrated system outweigh loosing a little mass efficiency as a tanker or satellite launcher...especially when it could still be very capable at both.
which gets to the larger point, I think as others have pointed out, MCT/BFR will be designed to do specifically one thing primarily...serve as a Mars vehicle.  It'll be able to do other things of course, (which can generate money to help fund the Mars goals...definately a good thing for SpaceX) but the hardware won't be designed around those things primarily, it'll be designed around going to Mars as safely and economically and efficiently as possible. 
An integrated design also has better throw capacity to LEO when launching MCT...which would be it's primary designed function.  Whereas with the dedicated S2, it would have more throw capacity to LEO when launching payloads other than MCT...which isn't it's primary designed function.
So (IMHO) a dedicated S2 will probably only be part of the system if there's a Mars-centric reason for it.  Like a whole vehicle fast abort option for MCT or maybe they want the most efficient tanker possible, which would be a dedicated S2-tanker.  Or some other Mars related reason.





Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #951 on: 10/28/2015 05:25 PM »

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.


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. 
(I think there are transfer orbits which go to near escape before coming back, just like a GTO.  So possibly it could launch a planetary probe with a kick stage to such an orbit, deploy it, and return while the kick stage does the rest of the dV to escape. If it could get itself and enough propellant to LEO to do it anyway.)

If you have an expendable stage, then it really doesn't matter if you drop off it GTO, or take all the way to GEO, the stage doesn't have to get home.  But for a reusable stage, getting home needs to be factored in.

There's never been a sat to GTO that D4H couldn't carry (to my knowledge), at 11.4mt to GTO (1500 m/s to GEO) or 13.4mt to GTO (1800 m/s to GEO).  An MCT-sat launcher could take such a 11-13mt Sat plus around 90mt or more of propellant to LEO.  Someone would have to run the numbers to make sure that's sufficient to get it's own dry mass plus the payload to a GTO 1800 m/s to GEO orbit, with enough left to do a little deorbit burn and land.  Probably only need one central Raptor to do the GTO burn and the deorbit burn.   If there's a DoD requirement that the LV put the sat directly into GEO (which I think they have with EELV, although I don't think it's done that way often) then SpaceX always has FH to use, as the upper stage isn't coming back.

Note:  MCT-sat launcher would be the basic integrated MCT platform, less anything not needed to launch sats, to maximize payload mass.  Essentially a shell with tanks, engines, and landing legs...with a short term power source like a methalox fuel cell or IVF generator.



Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #952 on: 10/28/2015 05:31 PM »
I think you are right Lobo.  SpaceX has the same diameter S2 on Falcon 9, and the same engine optimized for vacuum.  It makes sense to have the same Raptor engine second stage optimized for vacuum, same fuel as first stage, even the same landing legs.  Either a clamshell heat shield for the S2 engines that doubles as interstage, or the conical one side coated heat shield on the second stage/MCT for atmospheric entry.  Like you said, a dedicated S2 might through 20 more tons into orbit, but then you have three things going on.  S1, S2, MCT.  Cheaper would be S1, S2/MCT combo.  Both build robustly and reusable for cost reusability cost effectiveness.  Same with airlines.  Same planes are for either passengers or cargo.  Only the guppy versions for large diameter items are different.

Offline Space Ghost 1962

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Re: MCT Speculation and Discussion Thread 4
« Reply #953 on: 10/28/2015 05:49 PM »
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

Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #954 on: 10/28/2015 06:55 PM »
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.

I see the petals staying closed on re-entry until the last kilometer, much as the legs on F9 only deploy just before touch-down.  The primary engines don't fire within the atmosphere and the actual landing engines are outside the petals.  As for how you configure for launch, the petals are closed and inside the inter-stage space, the top of the first stage would be concave and the stage separation pushes directly on the closed petals and they spring open once clear of the first stage and then the second stage engines ignite.

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #955 on: 10/28/2015 06:59 PM »
Methalox will have a higher ISP than kerolox on Falcon 9.  I/we are assuming BFR will use a minimum of 9 Raptors, probably about 24.  Therefore upperstage/MCT will use a minimum of 5 raptors if scaled like Falcon9.  5 may be needed to blast off Mars but probably only one will be needed to land the upperstage/MCT.   Once you get 100 tons to LEO, this much payload is not limited in scope.  Refueling you go to Mars or the Moon.  Or you off load multiple satellites to be sent to GSO.  Metholox would be easier to keep cold in long term space than hydrolox.  Less power required to keep liquid. 

Online guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #956 on: 10/28/2015 07:12 PM »

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.


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. 

Up to now I thought the same. But given the capabilities of a refuelled MCT GSO may well be the better option. No need to give com sats the capability to reach GSO on their own. GTO was so far the better option because the launch vehicle could be smaller and the upper stage can easily deorbit after placing the payload in GTO. None of the restrictions would be applicable for MCT, especially when refuelled but with few sats maybe even without refuelling.

Offline Lars-J

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Re: MCT Speculation and Discussion Thread 4
« Reply #957 on: 10/28/2015 07:20 PM »
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

Why are FH and F9 upgrades being discussed in this thread? Seems a bit off-topic.

Offline MP99

Re: MCT Speculation and Discussion Thread 4
« Reply #958 on: 10/28/2015 07:33 PM »
Quote from: Impaler link=topic=37808.msg1439383#msg1439383 So what -could- BFR/MCT launch besides crewed, propellant, cargo, or depot versions of MCT? 
[/quote

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
« Last Edit: 10/28/2015 07:38 PM by MP99 »

Offline spacenut

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Re: MCT Speculation and Discussion Thread 4
« Reply #959 on: 10/28/2015 07:49 PM »
With metholox having a higher ISP, has anyone figured if the MCT could make GTO as also a second stage?  Would a depot there be better? 

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