Author Topic: MCT Speculation and Discussion Thread 4  (Read 567717 times)

Online docmordrid

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Re: MCT Speculation and Discussion Thread 4
« Reply #120 on: 06/18/2015 07:52 AM »
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.
>

We should also note that the new Tesla Energy Corporation scored $800 million in orders for Powerwall (home) and Powerpack (business & utility) power storage packs in its first week,

Bloomberg....

They're gonna need more Gigafactories (and they're already planned).
« Last Edit: 06/18/2015 07:53 AM by docmordrid »
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Offline fast

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Re: MCT Speculation and Discussion Thread 4
« Reply #121 on: 06/18/2015 08:48 AM »
And back to design concepts, it is the most fun  :)

What if BFR and MCT will be the essentially same thing?
Kind of universal module sized similar to S-IC, 9 Raptors at the bottom, with lending legs, around 1900mt.
 
Than all thing will be three core (I know, Elon said one-core, but look at F5), MCT in the center will have less fuel load replaced by cargo bay and improved thermal protection, and probably have less than 9 Raptors(3?).

Just a thought to standardize and reduce cost...

Setting aside Elon's actual words aside for a moment about it being single core, the 2-piece concept myself and a few others have been debating about would do what you are doing, but with just two pieces rather than 3.  One big monolithic RTLS booster, and one combo upperstage/spacecraft that can get itself to LEO where it will be refueled prior to going to Mars. 

Actually this looks to me like the first innovative new idea for a while.

Elon Musk said single core. But the idea behind that was to my understanding, not a 3 core heavy configuration because the central core would go too fast for easy RTLS and would incur heavy payload loos for reuse. This concept avoids that problem.

This concept would be like a first stage in two parts, something completely different. The "central core" would be the MCT. The vac engine problem might be solvable with a retractable engine bell extension. The mechanism shown in that Falcon Heavy animation seems to allow fast efficient reconnection so should not be a major problem for simple operation.

Two side cores with 9 engines each plus a central core with 5? engines would give a total number of engines 23 for lift off. Most of them would be switched off as soon as the T/W ratio allows it to retain fuel for reaching orbit.

It is innovative (good job fast).  And it could work for the reason you say.  It eliminates the central core that's staging too fast.  There's also be a booster core for the intermediate size LV that's been discussed over on the SFR thread.

But, I just don't know that it has advantages over an in-line wider core?  Do you see where this would be an advantage?  Maybe if they weren't planning to build the cores near the launch facility, this concept would result in thinner cores that are more easily transported.  But that's really not a problem unless SpaceX changes from what they've stated.

And it'd result in a tall and skinny MCT.  That's probably the major issue with it vs. monolithic, that I see.



Proportion of MCT module (same as side booster modules), as I mentioned can be similar to S-1C, which are ~10m diameter and ~40m long, but can be wider. It is not anywhere as skinny as F9 :)d.

Advantage of the concept is this one standard core module (with features) can give SpaceX one universal reusable LV of reasonable size. And Falcons could be discontinued.


Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #122 on: 06/18/2015 09:28 AM »
But, I just don't know that it has advantages over an in-line wider core?  Do you see where this would be an advantage? 

It would use all engines at launch, including those MCT will bring to Mars. That might make for a better T/W if the use of two tanks does not eat that advantage. But it should not since a smaller diameter tank can be thinner. Higher production on the production line.

Plus, as you mentioned already. A single core may make a more cost effective launch vehicle for everything that now goes on Falcon 9 and Falcon Heavy with much smaller development cost.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #123 on: 06/18/2015 10:37 AM »
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.

A doubling of commercial sales -- 50 launches a year -- adds about $170m to this estimate and puts the effort at $450M yearly.  A great success of reuse might drastically affect profit margins, or it might not, since now you need to build fewer rockets for the same flight rate, but you also need to maintain reflown stages, and you might end up discounting your launch price anyways.  Imagining a 50% profit margin and doubled sales, SpaceX can spend $900M on Mars work yearly.

What I am getting at is that the scale of SpaceX's commercial rocketry business is borderline in terms of building and operating individual exploration craft.  Fleets of $500M MCTs are beyond SpaceX's independent means, even under optimistic expectations.

I am also skeptical of SpaceX trying to switch horses in midstream between kerolox Falcon and methalox BFR architectures with this cost structure.  Before they had an order book and DoD certification, they had a lot of freedom to change rocket configurations.  Now, they have an ongoing business of maintaining Falcon service and associated Falcon costs.  If SpaceX tries to leap directly to methalox and BFR in one go, that adds on Raptor costs and BFR costs and MCT costs all at once.  These are going to be Large Rocket Costs, much larger than those incurred for Falcon.  I am skeptical that the existing business can bear them.  SLS costs are $2.2b/year, and BFR is larger than SLS.  I don't see how SpaceX can develop a rocket larger than SLS and a very advanced upper stage / spacecraft capable of Mars EDL/ascent for a small fraction of the price.

I think Musk's comments about a "single monster boost stage" can encompass a range of monstrosity.  A single core equivalent of Falcon Heavy would, after all, be at least a smidge monstrous.  A craft that delivers "100 metric tons of useful payload to the surface of Mars" can be assembled in Earth orbit and does not need to launch intact from Earth's surface.

Ultimately I think that SpaceX might well achieve a manned Mars landing, but I am doubtful of their ability to independently fund a major colonization architecture. It does make me wonder if SpaceX might try to get into the satellite business to scale up their revenues in order to better follow up on the Mars goal.
They have enough revenues to develop Raptor and perhaps the first few MCT/BFR, but Mars will not be paid for by Dragon or F9/FH, but according to Musk, Mars will be paid for by new growth from the SpaceX constellation. Did you miss that?

The revenue from the constellation would be at least an order of magnitude (and perhaps 2-3 orders of magnitude) higher than launch revenues right now.
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #124 on: 06/18/2015 10:44 AM »
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.

...

SpaceX probably do not need to fund Raptor/BFR/MCT completely out of earnings. With investment funding they can probably spend about $7B on them over the next 5-6 years. That should be enough to get basic versions of them designed and built, but probably not enough for a full manned Mars architecture (long duration crew and propellant depots, etc.). Long term revenue from their constellation will help, but there won't be much revenue this decade.

I would not use SLS as a benchmark of what BFR/MCT costs might be, SpaceX have proven low cost development.

I can't see BFR/MCT replacing F9R/FHR, but any FH (expendable) payloads would probably be cheaper on BFR.

Long term I think that F9R/FHR will be replaced by a methalox rocket, sized at about 15 tonnes to LEO fully reusable and using a smaller full flow staged combustion engine in the Raptor family. But that is many years down the road, and the road may diverge from that track.

Assembly in LEO is not feasible in my opinion, it has proved extremely expensive to do any assembly in space. However docking might be possible. Splitting the MCT into two parts which are then docked might work, especially if those two parts are identical mini-MCT which then dock nose to nose.

Offline Eerie

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Re: MCT Speculation and Discussion Thread 4
« Reply #125 on: 06/18/2015 11:43 AM »
Assembly in LEO is not feasible in my opinion, it has proved extremely expensive to do any assembly in space.

What are you talking about? It was proven that ISS is expensive, but that's basically it. ISS is the second modular space station to ever exist, and it used the most expensive launch vehicle (STS).

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #126 on: 06/18/2015 12:43 PM »
Salyut 7 was modular, too.
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Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #127 on: 06/18/2015 12:57 PM »
Thanks for the link, this seems to be the key quote.

“And then one of the key questions is can you get to the surface of Mars and back to Earth on a single stage. The answer is yes, if you reduce the return payload to approximately one-quarter of the outbound payload, which I thought made sense because you are going to want to transport a lot more to Mars than you’d want to transfer from Mars to Earth. For the spacecraft, the heat shield, the life support system, and the legs will have to be very, very light."


It's largely as I suspected, Musk is describing what COULD be done and the constraints he would face in doing it, but it is by no means a commitment that this is how he will proceed even with the initial design.  I think the incredible lightness necessary to make it work will prove too risky of a development challenge, he could end up in Venture Star territory if just one of his lightening strategies fails to work the whole thing could collapse.

By setting low bars like Mars surface to Low Mars orbit and low entry velocity the whole design process becomes a much less risky and cutting edge.  SpaceX has traditionally not done high risk designs so I think it is far more likely that in the end he chooses the safer design even if it dose require a second SEP vehicle to function and a good deal of rendezvous in space for refueling.

And? You've done better? Musk and occasionally Shotwell are basically the ONLY source for anything about MCT. So like it or not, that's all we've got right now.

Actually their is a LOT of information on rocketry out their on the inter-webs and we can and should do our own research if we expect to speculate with any kind of informed way.  If Musk & Shotwell quotes were the only permissible source material then this thread would be nothing more then a religious war between the SpaceX fan-boys and the SpaceX haters.  If my analysis disagrees with anyone else's, even Musk's I have every right and indeed the responsibility to point that out and I will not heckled by you or anyone else simply because I don't own a rocket company.

One question this raises for me is just how many people is the MCT supposed to bring back?  Because if we just bring back the ship for reuse, automatically, and do not have return passengers, we can do without the radiation protection.  As Musk mentioned it would be mostly water (how many tonnes?  I've been using 50), so it can be drained easily.  We can also do away with 20 to 25 tonnes of food, and 10 tonnes of crew and personal luggage.  So the return MCT could be 80+ tons lighter than in the other direction.  My other question : is the radiation shield a type of payload?  Because the hydrogen can be used as seed for fuel production, and the clean water can be used directly at the colony.  Even the food might be considered payload, since by the end of the trip it could be on the way to becoming valuable organic compost.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #128 on: 06/18/2015 02:07 PM »
Actually, you probably want to dump the water shielding before Mars entry. Mars has lots of water, and it will be absolutely essential to tap that water for any of this to work.

Additionally, clever arrangement of propellant tanks (and surface tension devices) could use your propellant as shielding. Methane is actually significantly more efficient than water for radiation shielding (Water has an average atomic mass of 6, while methane has an average of ~3). Only hydrogen is superior.

That would probably shift the expected fuel:oxidizer ratio to be more fuel rich than it otherwise would be (if you could adjust that ratio on the fly, you may depart EML1/2 with a more stoich ratio but do final burn above Mars with significantly more fuel rich).
« Last Edit: 06/18/2015 02:10 PM by Robotbeat »
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Offline nadreck

Re: MCT Speculation and Discussion Thread 4
« Reply #129 on: 06/18/2015 02:17 PM »
In 2016 SpaceX has bookings for ~$1.3B of rockets (22 at $57m via Google and the US launch schedule thread).  They receive about $650M annually from the CCtCap award ($2.6B through 2019) and about $200M from CRS, that's about $2.15B in revenues.  A very cursory search suggests that Tesla and Google both have 25% profit margins so let's assume that SpaceX gets the same and makes a profit of ~$550M.  Suppose half that profit goes into funding private Mars work, so that 1/8th of all revenue is being spent on internal Mars R&D and mission costs.  That's a $275m annual budget for Mars efforts, on the order of half their yearly costs on the CCtCap award.
Note that there are 3 CRS flights in 2016 and that is $400M

I would work on the assumption of a $10M margin per launch right now for commercial flights of the F9, and maybe double that for FH.




What I am getting at is that the scale of SpaceX's commercial rocketry business is borderline in terms of building and operating individual exploration craft.  Fleets of $500M MCTs are beyond SpaceX's independent means, even under optimistic expectations.

I am certain that the first MCT costs effectively a lot more than $500M, but I certainly don't expect them to cost that much after the first. I would also break down the cost between booster ($250M maybe) and MCT $100M and reusable tanker US $50M and resuable payload lofter $50M. The large fleet needs to be of MCTs, much smaller fleet of BFR boosters.

I am also skeptical of SpaceX trying to switch horses in midstream between kerolox Falcon and methalox BFR architectures with this cost structure.  Before they had an order book and DoD certification, they had a lot of freedom to change rocket configurations.  Now, they have an ongoing business of maintaining Falcon service and associated Falcon costs.  If SpaceX tries to leap directly to methalox and BFR in one go, that adds on Raptor costs and BFR costs and MCT costs all at once.  These are going to be Large Rocket Costs, much larger than those incurred for Falcon.  I am skeptical that the existing business can bear them.  SLS costs are $2.2b/year, and BFR is larger than SLS.  I don't see how SpaceX can develop a rocket larger than SLS and a very advanced upper stage / spacecraft capable of Mars EDL/ascent for a small fraction of the price.

Not sure of your logic here, it was not easier to develop Falcon 1 along with 2 engines, and design the F9 with a lot of latitude and zero cash flow. F9 development was paid for by NASA under COTS and one thing that F9 demonstrated was the fact that F9 development could be done at 1/3rd the costs of similar developments in the past.

As far as "leap directly to methalox and BFR in one go" I assure you that doing it in 2 steps would cost more both in $ and time.  There will be no issue on the F9/FH business as BFR/MCT is being developed.  There will be little ongoing development in F9/FH by 2018 it will have hit maturity.  Dragon is another story.  BFR/MCT will be manufactured in a new centre and that will cost money, but I am certain Elon will find a source for the capital to gear up for that either with new equity or more likely a deal that brings other sponsorship.


Ultimately I think that SpaceX might well achieve a manned Mars landing, but I am doubtful of their ability to independently fund a major colonization architecture. It does make me wonder if SpaceX might try to get into the satellite business to scale up their revenues in order to better follow up on the Mars goal.

No argument there but if SpaceX can fund all of the set up and demonstrate the will to go to Mars anyway,  I can't imagine that they aren't years ahead of anyone else and that the can sell participation to other groups, probably sell enough to actually pay for the first manned expedition even though the other groups are a small part of it.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #130 on: 06/18/2015 02:32 PM »
Actually, you probably want to dump the water shielding before Mars entry. Mars has lots of water, and it will be absolutely essential to tap that water for any of this to work.

Additionally, clever arrangement of propellant tanks (and surface tension devices) could use your propellant as shielding. Methane is actually significantly more efficient than water for radiation shielding (Water has an average atomic mass of 6, while methane has an average of ~3). Only hydrogen is superior.

That would probably shift the expected fuel:oxidizer ratio to be more fuel rich than it otherwise would be (if you could adjust that ratio on the fly, you may depart EML1/2 with a more stoich ratio but do final burn above Mars with significantly more fuel rich).
So I guess it might be a good idea to jettison the water before the final injection burn to Mars orbit, that might reduce the fuel required for that manoeuver.  A linked question is would we want to jettison the waste, or is the compost value higher than the value of fuel saving?  Is the injection burn a large part of the overall fuel use for Mars transfer?  My understanding is the faster we go, the more fuel is required to stop at Mars, but for a 6 month mission, is the Mars burn a large portion of the deltaV requirement?

Online oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #131 on: 06/18/2015 02:39 PM »
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
« Last Edit: 06/18/2015 02:48 PM by oldAtlas_Eguy »

Offline guckyfan

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Re: MCT Speculation and Discussion Thread 4
« Reply #132 on: 06/18/2015 02:42 PM »
So I guess it might be a good idea to jettison the water before the final injection burn to Mars orbit, that might reduce the fuel required for that manoeuver.  A linked question is would we want to jettison the waste, or is the compost value higher than the value of fuel saving?  Is the injection burn a large part of the overall fuel use for Mars transfer?  My understanding is the faster we go, the more fuel is required to stop at Mars, but for a 6 month mission, is the Mars burn a large portion of the deltaV requirement?

I don't anticpate any Mars injection burn. MCT will come in hot for aerobraking, doing only a landing burn.

Offline lamontagne

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Re: MCT Speculation and Discussion Thread 4
« Reply #133 on: 06/18/2015 03:00 PM »
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
Thanks, this is a great summary.   I guess this means not much water based radiation shielding?  And if as Guckyfan proposes there is no final injection burn, not much fuel at the end for radiation protection either?

Online oldAtlas_Eguy

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Re: MCT Speculation and Discussion Thread 4
« Reply #134 on: 06/18/2015 03:05 PM »
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
Thanks, this is a great summary.   I guess this means not much water based radiation shielding?  And if as Guckyfan proposes there is no final injection burn, not much fuel at the end for radiation protection either?

One item I forgot to mention was the number of Raptors on MCT would be 5 to give a 3g liftoff at Mars with immediate 1 engine out continue mission capability. Later in Mars launch even 2 engines out would still enable continue mission. A very low risk value for mission success results from this.

Edit added: GLOW at Mars liftoff would be 965mt or 2.135Mlb more than 2x the GLOW of the F9v1.0. (65mt dry weight [40mt vehicle 25mt payload]). The MCT is not a small vehicle. It could conceivably reach Earth orbit as an SSTO witha  little payload about 20mt.
« Last Edit: 06/18/2015 03:25 PM by oldAtlas_Eguy »

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #135 on: 06/18/2015 03:29 PM »
From Statements made by SpaceX representatives:
- 100mt payload delivery to Mars
- 1/4 payload SSTO return to Earth from mars surface
- prop density 1m^3 for 1mt (LOX and CH4)
- 15m diameter vehicle (this was hited at not actually specified by SpaceX
- Raptor engines 380-385 vacuum ISP 500klbf

A vehicle like this results:
- Vehicle structure+engines+ shield =40mt
- Max propellant load 900mt
- propulsion section (engines and tanks) cylindircal or nearly cylindrical section at base 15m diameter and 6m tall
- bi-conal payload section (first section 15m to 10m diameter 10m tall) (second section 10m to 0m 10m tall) ~1800m^3 volume
-MCT can be its own 2nd stage on the BFR (BFR is basically just the 1st stage) would have ~7.5km/s delta v capability with a 100mt payload+40mt vehicle dry weight +900mt propellant load
-An MCT tanker variant would be a Cargo MCT without any cargo which could deliver ~150mt of propellant to LEO would have 6km/s delta v capability

In order to get to Mars 6-9 tankers docking in LEO-MEO are required

Edit Added: BTW An MCT cargo used as the 2nd stage going just to LEO would be capable of delivering 180mt of payload. Note the 1st stage needs to be capable of ~3km/s delta v with a fully loaded MCT + 180mt of payload on top ~1120mt MCT+payload GLOW
15m diameter and other such details have not been mentioned. Please cite your sources and put the source quote in the MCT source thread so we know exactly what was said: http://forum.nasaspaceflight.com/index.php?topic=37839.0
« Last Edit: 06/18/2015 03:33 PM by Robotbeat »
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Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #136 on: 06/18/2015 03:44 PM »
- Vehicle structure+engines+ shield =40mt

I think you are being rather optimistic here, compared to the F9 upper stage 10x the dry mass for 10x the propellant mass is quite reasonable, but the MCT would need heat shield and other reuse components, long duration features (propellant cooling), beyond earth orbit features (solar panels, better comms) and a large fairing to encapsulate the payload (perhaps 2500 m^3 of volume).

I've guestimated 90 tonnes, others have guestimated down to about 50 tonnes, but this is the lowest I've seen.

Offline MikeAtkinson

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Re: MCT Speculation and Discussion Thread 4
« Reply #137 on: 06/18/2015 03:46 PM »
The MCT is not a small vehicle. It could conceivably reach Earth orbit as an SSTO with a  little payload about 20mt.

20 tonnes to LEO is not a little payload.

If the MCT could really achieve a dry mass of 40 tonnes it would make a very useful reusable SSTO.

Online Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #138 on: 06/18/2015 03:56 PM »
Except the Vac-optimized Raptors may not have enough thrust to get it off the ground nor the Isp to get to orbit. Just because it might conceivably get 9km/s in free space doesn't mean it is a SSTO.
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Offline Lobo

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Re: MCT Speculation and Discussion Thread 4
« Reply #139 on: 06/18/2015 04:06 PM »
I've extremely high doubts that once the BFR/MCT package is complete, SpaceX will just cancel its breadwinning Falcon9/Falcon Heavy lines and launch all commercial satellites on a Saturn V class rocket.

.. and assuming that's the case, what's BFR for? Annual (at best) launches of MCTs?

If MCT basically gets itself plus 100mt of payload to LEO, and gets refueled there, that means it'll take several tanker flights per mission to fill up one MCT prior to departure.  If two MCT's are going, then double that.  If there's just one MCT pad initially, that could keep pretty busy just supporting that.  I think a depot (basically an MCT modified for extra low boiloff and long LEO loiter) would allow for regular flights during the time between syniods.  So that the MCT facility can work and launch regularly, rather than in a flurry once every two years, with lag time in between.

In addition to that, I think any large payloads that might otherwise require an expendable FH could be launched on the MCT stack, as well as anything larger, if there is anything larger. 

I think all of that in the aggregate could keep an MCT construction/landing/launch facility busy year-round, with F9/FH taking care of payloads EELV-class and below.  Realistically, a single HIF probably isn't going to handle more than one MCT per month.  A single pad could be used for multiple HIF's, and thus it could launch a few a month possibly, depending on how much pad damage there is between launches.  A launch complex could be pretty busy then, year round.

Once things ramp up for full colonization down the road, probably additional pads would be needed with multiple depots needing filled up between synoids to fuel up multiple MCT's heading to Mars each launch window.

So it's not the 1 or 2 or 3 MCT's per synoid going to Mars that will keep the hardward and facilities busy, it's staging all that propellant in LEO for those MCT's that will keep them busy.  With some other non Mars related payloads sprinkled in there.  If MCT were to take on F9 and FH payloads too, they'd need quite a large complex for that sort of launch rate.  And then there's the issue of how they'd get some MCT's from their main East Coast facility to VAFB for West coat launches and Falcon would be otherwise handling.

I'd also not be surprised if NASA hired SpaceX to do some lunar missions ahead of getting on board with them for the early Mars missions, assuming MCT is capable of lunar missions.  Elon seemed to indicate he thought it would be.  MCT will still need to be fully fueled in LEO for a lunar mission, and possibly get some more propellant in lunar orbit, as it might not be able to get from LEO to the surface of the moon, and then back to the surface of Earth all on one tank.  So that'd also be a nice testbed for SpaceX to refine their operations and methods and launch rates and hardware before sending MCT with a crew all the way to Mars.  So they'd have a vested interest in doing it aside from profit, if NASA were to hire them for that.

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