Author Topic: MCT Speculation and Discussion Thread 4  (Read 621450 times)

Offline AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #1040 on: 11/01/2015 09:50 PM »

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

I, for one, don't expect SpaceX to sell any purely commercial flights (comm sats, for instance) on BFR before heading to Mars.  Exceptions could be flights that advance the technology toward Mars such as large Bigelow habs, or Lunar technology demos, fuel depots, etc.  I think they will schedule (maybe quietly) trips at a sequence of Mars conjunctions, including the BFR when it is ready, and NASA will (maybe not so quietly) climb aboard.

If SpaceX advances the timeline by a large factor and scales up the scope of the expeditions, NASA will not pass up the opportunity to be aboard -- they won't wait until 32 SLS launches are funded (if ever) and 2039 rolls around.
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Offline Burninate

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Re: MCT Speculation and Discussion Thread 4
« Reply #1041 on: 11/01/2015 09:52 PM »

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

The business case and usage schedule is far more up in the air than than even the technical details of BFR & MCT.  We don't have high-quality speculation to offer.  All we know is that BFR launches will be cheaper with high launch rate than with low launch rate.  On this basis and on the expectation that only a long record of successful unmanned launches proves safety of a manned launch vehicle to *my satisfaction*, I expect them to seek out whatever customers they can.  It's arguably a prerequisite that they find these customers, before scaling up the Mars project;  For that matter, the business viability of the Mars project as a private passenger delivery system without Apollo-grade Congressional outlays is... questionable.
« Last Edit: 11/01/2015 09:56 PM by Burninate »

Offline AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #1042 on: 11/01/2015 10:12 PM »

Vehicle structural dry weight of 25mT is, in my judgement, about an order of magnitude too low for a reusable lander with integrated habitat that brings 100mT payload to the surface.  Yes, there's a question about whether ISRU gear is inside or outside the '100mT useful cargo' box, but the weight of the vehicle alone is at 100mT-200mT in most other people's scenarios, I just favor raising it to 300mT-500mT with my own special sauce.

The point is that a set of eight superdracos such as is installed on the (existing) Dragon 2 can land 125mT of payload on Mars, given that the Raptor engines have slowed the vehicle to near zero at a nominal distance above the ground.  If the vehicle itself is somewhere between 100 and 200mT (say 150) and the delivered payload is 100mT, then double the Dragon 2 complement will do the job nicely.  Doubling the complement, four quads instead of four pairs, or doubling the thrust of a pair seems to be an easy step technically.
« Last Edit: 11/01/2015 10:25 PM by AncientU »
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Offline MP99

Re: MCT Speculation and Discussion Thread 4
« Reply #1043 on: 11/01/2015 11:10 PM »



Vehicle structural dry weight of 25mT is, in my judgement, about an order of magnitude too low for a reusable lander with integrated habitat that brings 100mT payload to the surface.  Yes, there's a question about whether ISRU gear is inside or outside the '100mT useful cargo' box, but the weight of the vehicle alone is at 100mT-200mT in most other people's scenarios, I just favor raising it to 300mT-500mT with my own special sauce.

The point is that a set of eight superdracos such as is installed on the (existing) Dragon 2 can land 125mT of payload on Mars, given that the Raptor engines have slowed the vehicle to near zero at a nominal distance above the ground.  If the vehicle itself is somewhere between 100 and 200mT (say 150) and the delivered payload is 100mT, then double the Dragon 2 complement will do the job nicely.  Doubling the complement, four quads instead of four pairs, or doubling the thrust of a pair seems to be an easy step technically.

ISTM the SDs could have a vacuum nozzle for Mars, with associated Isp & thrust benefits.

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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1044 on: 11/02/2015 12:20 AM »

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

The business case and usage schedule is far more up in the air than than even the technical details of BFR & MCT.  We don't have high-quality speculation to offer.  All we know is that BFR launches will be cheaper with high launch rate than with low launch rate.  On this basis and on the expectation that only a long record of successful unmanned launches proves safety of a manned launch vehicle to *my satisfaction*, I expect them to seek out whatever customers they can.  It's arguably a prerequisite that they find these customers, before scaling up the Mars project;  For that matter, the business viability of the Mars project as a private passenger delivery system without Apollo-grade Congressional outlays is... questionable.

Burninate you put your finger on the reasons the system needs to find some non-mars bound commercial business, basically cost amortization and flight history build up.  I would also add that splitting development up over time, having experience with large reusable vehicles that survive high speed entry at Earth before trying it on Mars, and finally having a the launchers lift capacity fully characterized and upgraded to it's maximum potential so you know your ceiling mass for the MCT.

To clarify my prior post, I think NASA (in the course of a large Congressionaly funded mars mission) is the only conceivable first customer for a mars transport system.  That transport system will be both the rocket and a mars lander and possibly other transport elements provided by SpaceX (such as SEP tugs, Propellant production equipment).   Think of it like Mars-COTS, SpaceX schleps people & cargo for NASA under contract. 

This is the only way SpaceX can actually make any revenue from mars, they might be able to direct their satellite launch profits into vehicle development but actually run the system they need huge payments at low volume and government is the only possible customer during that start up period even if you want to sell to private interest later, just as we are under no illusions that Dragon capsule would have been developed without the COTS program.

SpaceX will control the whole payload interface of the BFR and mars bound vehicle and design it for their goals, and these will probably not resemble any current interfaces, so NASA will design all of the cargo it wants sent to mars around the SpaceX vehicles cargo capacity both in terms of mass and volume.  That is going to take time and money and training, billions of dollars and perhaps a decade.

But NASA can't actually do anything like that when it is saddled with the Orion/SLS millstone which basically sucks up all it's money.  The BFR can lift this off NASA's shoulders IF it can match all the SLS capabilities, is drastically cheaper, safer AND SpaceX is manufacturing in enough states to get support or at least defuse opposition in the senate to the cancellation of these programs.  SLS won't go away until BFR has a solid launch history, the political forces will always be able to justify keeping it going if SpaceX isn't superior in every metric.

So the first priority is to get SLS retired, everyone knows that SLS and BFR would be in direct competition and the universe is not big enough for them both.  If SpaceX get BFR up and running quickly I could see SLS being canceled in about a decade after a few flights, probably ARM as a face-saving last mission.  That opens up $3 billion a year for actual mars systems.  Meanwhile SpaceX will be well into designing the mars bound vehicle/s and a it will be both politically and economically easy to slip into a parallel development course in which SpaceX finishes the mars vehicle while NASA gives out contracts for surface system development as consolation prizes to the folks who lose out when SLS/Orion ended.  In another 10 years both are done and your ready to land on mars.

Offline meekGee

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Re: MCT Speculation and Discussion Thread 4
« Reply #1045 on: 11/02/2015 02:41 AM »
But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.


...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Or did you mean that NASA is the only conceivable customer other than SpaceX itself?

I can't be 100% sure that the first BFR mission will head to Mars, but I'm pretty sure there won't be a "good long time" (years?) in which BFR is used commercially before it used for MCTs to Mars.   I can see how maybe during off-season they are used for commercial purposes since why not, but they are built for a purpose, and I expect the Mars program to be pretty efficient in that things will mature by the time they are needed.

The business case and usage schedule is far more up in the air than than even the technical details of BFR & MCT.  We don't have high-quality speculation to offer.  All we know is that BFR launches will be cheaper with high launch rate than with low launch rate.  On this basis and on the expectation that only a long record of successful unmanned launches proves safety of a manned launch vehicle to *my satisfaction*, I expect them to seek out whatever customers they can.  It's arguably a prerequisite that they find these customers, before scaling up the Mars project;  For that matter, the business viability of the Mars project as a private passenger delivery system without Apollo-grade Congressional outlays is... questionable.

Burninate you put your finger on the reasons the system needs to find some non-mars bound commercial business, basically cost amortization and flight history build up.  I would also add that splitting development up over time, having experience with large reusable vehicles that survive high speed entry at Earth before trying it on Mars, and finally having a the launchers lift capacity fully characterized and upgraded to it's maximum potential so you know your ceiling mass for the MCT.

To clarify my prior post, I think NASA (in the course of a large Congressionaly funded mars mission) is the only conceivable first customer for a mars transport system.  That transport system will be both the rocket and a mars lander and possibly other transport elements provided by SpaceX (such as SEP tugs, Propellant production equipment).   Think of it like Mars-COTS, SpaceX schleps people & cargo for NASA under contract. 

This is the only way SpaceX can actually make any revenue from mars, they might be able to direct their satellite launch profits into vehicle development but actually run the system they need huge payments at low volume and government is the only possible customer during that start up period even if you want to sell to private interest later, just as we are under no illusions that Dragon capsule would have been developed without the COTS program.

SpaceX will control the whole payload interface of the BFR and mars bound vehicle and design it for their goals, and these will probably not resemble any current interfaces, so NASA will design all of the cargo it wants sent to mars around the SpaceX vehicles cargo capacity both in terms of mass and volume.  That is going to take time and money and training, billions of dollars and perhaps a decade.

But NASA can't actually do anything like that when it is saddled with the Orion/SLS millstone which basically sucks up all it's money.  The BFR can lift this off NASA's shoulders IF it can match all the SLS capabilities, is drastically cheaper, safer AND SpaceX is manufacturing in enough states to get support or at least defuse opposition in the senate to the cancellation of these programs.  SLS won't go away until BFR has a solid launch history, the political forces will always be able to justify keeping it going if SpaceX isn't superior in every metric.

So the first priority is to get SLS retired, everyone knows that SLS and BFR would be in direct competition and the universe is not big enough for them both.  If SpaceX get BFR up and running quickly I could see SLS being canceled in about a decade after a few flights, probably ARM as a face-saving last mission.  That opens up $3 billion a year for actual mars systems.  Meanwhile SpaceX will be well into designing the mars bound vehicle/s and a it will be both politically and economically easy to slip into a parallel development course in which SpaceX finishes the mars vehicle while NASA gives out contracts for surface system development as consolation prizes to the folks who lose out when SLS/Orion ended.  In another 10 years both are done and your ready to land on mars.
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1046 on: 11/02/2015 03:53 AM »
But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.

It will be cheaper per kg to LEO, but it is by no means going to be cheap enough to build an adequate flight history (~12 launches) with nothing but dummy payloads all at SpaceX's own expense.  A rocket is typically tested only once with a dummy payload with subsequent launches being with paid customers who have satellites.  I expect prices of ~200 million per launch even with recovery (about $1000 per kg, Musk's optimistic goal) so it would cost Billions to do these launches without customers.

I expect that 1st stage recovered will be attempted on every single BFR flight with very likely full success from the start.  If first stage recovery works on the dummy flight and is declared a solved problem then the price point will likely be set such that SpaceX is fully covering the cost of the 2nd stage in case it is lost as I expect 2nd stage recover to require a long campaign of attempts with lots of failures and redesigns as we have seen with F9, the customer will not care any more about the success or failure of these recovery attempts any more then they care about 1st stage recovery attempts now. 

By the time you have your 12 flight history your close to getting the 2nd stage to recover reliably and can drop the price to perhaps 100 million and try to get more volume.
« Last Edit: 11/02/2015 07:52 AM by Impaler »

Offline Semmel

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Re: MCT Speculation and Discussion Thread 4
« Reply #1047 on: 11/02/2015 07:36 AM »

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


Is this a widely shared opinion? 

Developing BFR and MCT is a huge investment by SpaceX. I dont think they can make it without picking up money in some fashion along the way. Even the internet satellite constellation cant do that much on the time scales that are envisioned. Hell, BFR might even be used to get it to orbit.

My expectation is, that the first version of BFR will be a vehicle, purely used for commercial satellites. BFRv1 would be shorter than the one used for Mars and less capable of course. I expect it to have an early version of the Raptor engine, maybe even less engines in total. I also expect that a cargo version of MCT will ride BFR as an integrated second stage. It would have no pressurized volume, but large cargo doors to release satellites in orbit, up to GTO. It would be re-usable, test reentry and landing systems and would be a precursor to MCT in general.

I dont think SpaceX will be able to fund BFR to Mars from the get go. Not even if NASA hitches a ride. Development and production of BFR is way too expensive. They need tons of tests before cargo can be send to Mars for real. Better use BFR commercially as early as possible and refine designes on the way. Thats how SpaceX operated in the past and I assume will continue to operate in the future. Look at the development of Falcon 9 and Dragon. Its the same story, I expect history to repeate it self.

I voiced that view in before and from experience, most users here on the forum disagree with that view.
« Last Edit: 11/02/2015 07:36 AM by Semmel »

Offline Zed_Noir

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Re: MCT Speculation and Discussion Thread 4
« Reply #1048 on: 11/02/2015 10:12 AM »
But we know that SpaceX, even in the fast build-up scenario, needs to send multiple unmanned payloads to Mars first.

BFR is an Earth-to-orbit vehicle, and so you're not risking a two-year delay when you first launch it.  Yes, the first launch may not carry an MCT, but by the same token, it won't carry any other one-of-a-kind payload.  Being reusable, it's a complete non-brainer to fly a dummy payload.  If it works, you you relaunch.  It it doesn't, good thing you didn't.

Actually, once you're shifted to a reusable rocket, test flights are cheap enough that you could do multiple dummy payloads before you put an MCT on top - and it's not like you wasted multiple rockets doing it.

So I think the "build up flight history" argument doesn't apply.

<snip>

Maybe not a MCT. But using the BFR tooling SpaceX can make an austere BFR upper stage with one Raptor Vac and an adopter for the current fairing. An interim upper stage suitable for most interplanetary missions.

Hmm a 300 to 400 mT restartable upper stage should have some kick.


Offline AncientU

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Re: MCT Speculation and Discussion Thread 4
« Reply #1049 on: 11/02/2015 11:27 AM »
NASA is planning to fly crew on SLS flight #2... where is the 12 flight requirement originating?

If twelve flights are needed, hundreds (thousands) of tons of fuel and precursor hardware/infrastructure can and probably will be positioned in advance of first crewed expeditions to Mars. NASA will be aboard the entire way, but the timeline and scale will be SpaceX's.

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Offline GregA

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Re: MCT Speculation and Discussion Thread 4
« Reply #1050 on: 11/02/2015 12:09 PM »

...  I expect SpaceX to sell normal commercial flights on BFR for a good long time before it is use for mars ...

... As NASA is the only conceivable customer for a first mission they need to be courted to create a mission utilizing SpaceX as the primary contractor.... 


I'm catching up on this thread so apologies for necro-quoting, but is this a widely shared opinion?  Basically that by the time SpaceX is ready with BFR, they will not be ready with a mission for it?

Speaking for myself, I don't think that.

There are several people talking about BFR being for other missions first. I personally suspect most don't agree that would happen, but since we know we're about to learn a whole lot soon it's not hugely valuable to argue it. And absolutely I could be wrong.

However, I should qualify what I think a little.

I think the plan for Mars has no room for 10 years of BFR side missions, the plan has no room for distracting from the prime goal of Mars colonisation. But I think the plan has many big asterisks in it with the note "insert huge investment here". Musk is likely playing several angles on where that investment comes from, and no doubt space based commercial activity is part of it (since it already is...).

Musk's comment to the Royal Astronautical Society was headlined as 80,000 people on Mars, which he clarified was wrong and changed to a million... "more like 80,000 a year". But reading the calculations he was talking about a portion of GDP,  $36billion a year, and he wasn't saying for 1 year. He also spoke about charging $500,000 for the trip (which people misunderstood and put together, dividing 500,000 into $40billion to get 80,000 people.) 

That's best argued in the financing thread of course! but I read it as $36billion a year in addition to ongoing individual trip costs.

So there's a huge amount of money he wants to make this happen. It's not going to come easy.  At some stage he will be making commercial deals using his developed technology. But I just don't see that as being part of "the plan" per se. I would possibly concede that the argument made by Semmel and others may be a way of raising funds, but it's not an MCT design speculation, it's a MCT or colony funding speculation.

And on that financing note... I don't think he'll make even a small portion of $36billion a year from BFR launches ... so he has a bigger challenge for funding, and adding this kind of implementation distraction could have some significant negatives.

edit: I should note that Semmel, Burminate and others do relate it back to the funding issues too. But I believe their argument falls into the trap that Musk is trying to avoid... and that's shifting the focus from Mars. The focus needs to be Mars in order for the ideal Mars design to be aimed for, AND for inspiring the population to buy into the vision and be willing to support it. (That doesn't mean it might not end up being necessary for the BFR to serve other uses.)
« Last Edit: 11/02/2015 12:19 PM by GregA »

Offline Semmel

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Re: MCT Speculation and Discussion Thread 4
« Reply #1051 on: 11/02/2015 01:38 PM »
GregA, we dont necessarily have a disagreement here. I dont think that BFR will be derailed by requirements that are unrelated to Mars. Unlike the space shuttle, which was designed to do crazy stuff that never happened.
But I do think that SpaceX will take opportunities as they arise. And they can only take them with a satellite delivery system to LEO and GTO. It provides nice revenue for reentry and landing tests that would otherwise be without a paying customer. Therefore, I do expect SpaceX to create 5 versions for MCT, all based on the same concept.
1: MCT-Satellite: Satellite delivery system as a pathfinder to create revenue and as a test lab for the 3 following MCTs:
2: MCT-Tanker: Tanker version for refulling. Direct offspring of MCT-Satellite, initially tested with MCT-Satellite. Will enable MCT-Satellite to do deep space missions.
3: MCT-Cargo: Cargo version for Mars, no life support, no pressurized volume, pure cargo transport. Direct offspring of MCT-Satellite, will also be the first MCT to land on Mars
4: MCT-Crew: Early crew version of MCT. Very limited living room for exploration missions. Offspring of MCT-Cargo and Crew Dragon.
5: MCT-Coll: The true collonial transporter, designed for colonization and many people. Probably no cargo at all Direct offspring from MCT-Crew.

MCT-Tanker, MCT-Cargo and MCT-Coll are what SpaceX is aiming for. But they need MCT-Satellite as pathfinder, both for finencial and engineering reasons. I dont see them coming up with a ready to go Mars fleet. Doing MCT-Satellite can do a lot of the testing they need anyway. MCT-Crew is basically the same as MCT-Coll, just with less living space and more space for redundency, equipmit of all sorts and in general outfitted for high survivability instead of large number of crew. It will evenutally phase out. MCT-Satellite will probably be around for a long time, simply because it makes sense to use BFR to launch satellites. Once a reusable system is developed, it makes no sense to also create a disposable fairing-based launcher.

I also expect the performance of BFR and Raptor to increase over time, similarly to F9. For MCT-Satellite, not the same level of performance as for the others is needed. So it is ok if BFR is not up to the collonial task right from the beginning.

Still, all this development is pointed directly at Mars. But the steps I think will happen are a little smaller than most of the folk here think.
« Last Edit: 11/02/2015 01:39 PM by Semmel »

Offline RonM

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Re: MCT Speculation and Discussion Thread 4
« Reply #1052 on: 11/02/2015 01:54 PM »
If SpaceX went that route, I would expect the first version of the BFR would be a scaled up Falcon, but with Raptor engines. Nine engine first stage and one engine second stage. That would make a good reusable satellite launcher and a possible Falcon Heavy replacement. Once they have experience with that system, then it's time for a full up BFR and MCT.

Offline philw1776

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Re: MCT Speculation and Discussion Thread 4
« Reply #1053 on: 11/02/2015 02:16 PM »

Developing BFR and MCT is a huge investment by SpaceX. I dont think they can make it without picking up money in some fashion along the way. Even the internet satellite constellation cant do that much on the time scales that are envisioned. Hell, BFR might even be used to get it to orbit.

My expectation is, that the first version of BFR will be a vehicle, purely used for commercial satellites. BFRv1 would be shorter than the one used for Mars and less capable of course. I expect it to have an early version of the Raptor engine, maybe even less engines in total. I also expect that a cargo version of MCT will ride BFR as an integrated second stage. It would have no pressurized volume, but large cargo doors to release satellites in orbit, up to GTO. It would be re-usable, test reentry and landing systems and would be a precursor to MCT in general.

I dont think SpaceX will be able to fund BFR to Mars from the get go. Not even if NASA hitches a ride. Development and production of BFR is way too expensive. They need tons of tests before cargo can be send to Mars for real. Better use BFR commercially as early as possible and refine designes on the way. Thats how SpaceX operated in the past and I assume will continue to operate in the future. Look at the development of Falcon 9 and Dragon. Its the same story, I expect history to repeate it self.

I voiced that view in before and from experience, most users here on the forum disagree with that view.

I agree with much of this.
I am directly in the camp that the 1st BFR launches may have less engines.  I do not agree with those proposing a mini-BFR configured similar to the Falcon 9 8:1 1st stage and single Raptor 2nd.  That's a whole different airframe development & tooling and flight testing than starting right away testing a less engine equipped BFR using THE intended airframe design but not necessarily full up with engines.
Early commercial satellite launch flights will likely serve as boilerplate MCT Cargo config proof of concept tests and yes purchasers could not care less if the 2nd stage MCT is recovered or not except that they will welcome a future price cut.
I am in the camp that the biggest risk for BFR development aside from additional Falcon 9 RUDs is financing the expensive R&D.  Right now SX is WAY behind on planned Q3 and Q4 revenue and most certainly has encountered large additional engineering, manufacturing and operations expenses preparing for RTF.
« Last Edit: 11/02/2015 02:17 PM by philw1776 »
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Re: MCT Speculation and Discussion Thread 4
« Reply #1054 on: 11/02/2015 11:53 PM »
...The size of boulders that would pose a problem for an MCT landing would be faaar to large to handle with a small rover. And boulders are only part of the issue, dust blasting may be more of a problem, and that certainly cannot be addressed by a small rover....

Boulders big enough to cause problems for MCT landing are easily spotted using MRO. You can just avoid them in the planning stages.


1) MRO can resolve objects of "about a meter across"...
MRO has a resolution of ~30cm per pixel. Multiple exposures of the same site from different angles and ESPECIALLY with the Sun at high angles (thus casting long shadows) can identify hazards.

Perhaps, but that kind of coverage does not exist.
What do you mean? You can, right now, go and request new images be taken of a certain area. There's plenty of "coverage" to take multiple images of the same small area at multiple times of day.
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Yes. And even when it does, it tells you nothing about the relative strength of the surface. It could be the Martian equivalent of quicksand for all we know.
Untrue, we have ground-truthing of multiple sites on Mar that allow us to calibrate the orbital instruments with on-the-ground measurements. We have day and night thermal IR, which allows us to figure out thermal inertia, etc. And there isn't such a thing as "Martian Quicksand," which requires a lot of liquid water. We can identify sand dunes, etc.

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But it is still irrelevant. MCT will need to be able to land on unprepared terrain, it will be necessary to allow of off-nominal EDL and abort scenarios. So it will need a sturdy gear, and you seem reluctant for some reason to admit that.
I am in favor of actual abort capability, instead of super heavy landing gear. Why do I need to "admit" something that has no basis in actual SpaceX communications, just some people's opinion on the internet? My mental model of MCT most resembles DC-Y and DC-I, which used fairly stubby landing gear and had real abort capability. (And yes, you'd need Soyuz-style cushioning thrusters on Mars in addition to a parachute. But the actual delta-v for that cushioning thrust is VERY low.)
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Offline Impaler

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Re: MCT Speculation and Discussion Thread 4
« Reply #1055 on: 11/02/2015 11:58 PM »
Lars/RB:  Can you each state how massive you expect landing gear to be, I've estimated 10% of touchdown mass.

Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1056 on: 11/03/2015 12:14 AM »
Probably because it's another nail in the idea that MCT will have single digit dry mass percentage.
Oh, give me a break. You have not come even CLOSE to establishing that single-digit-dry-mass percentage isn't possible. (Not that it'd be that bad... you can still get more than 6km/s out of it, thus within the range of my expectation for MCT of 6-8km/s.)

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Lets look at what landing gear will likely mass.  The primary driver is touchdown mass which would be 100 mT + vehicle dry mass + reserves from the landing propellants.  I'd call that all 200 mT, and no we do not get to deduct because of mars gravity, the vehicle has kinetic energy at touchdown which is independent of gravity.
That's false. Mars' lower gravity makes it easier to zero out the velocity more precisely than on Earth. So you have proportionally less kinetic energy (or, since kinetic energy is proportional to velocity squared, perhaps much, much less kinetic energy).

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The landing legs on F9R are said to be 10% of the empty stage mass (and that's with use of carbon-fiber) so I take this as my basis for MCT legs structure.  Around 20 mT, though I expect them to telescope inside the vehicle rather then be on the surface.
No, we can do much better. For a VTVL SSTO or similar, something like 3% is often assumed for parametric purposes in "common wisdom," but we can do much better.

"Gary Hudson pointed out a couple of years ago that, while 3% is common wisdom, the B-58 landing gear was 1.5%... and that was a very tall and mechanically complex gear designed in the 1950s. "

( http://yarchive.net/space/launchers/landing_gear_weight.html )

But why would the passenger version of MCT use the super heavy legs of the full payload version? F9R's legs are removable and added at the launch site, so it would make perfect sense to be able to use less massive legs if you aren't landing a huge payload and that was a big mass driver.

F9R's legs are very long due to the fact that F9R is very tall and skinny, and you would want a wide base for landing. While MCT will have around the same volume for tanks and such, it will likely have a much wider base, thus allowing an equivalently-wide stance while being very short, ala DC-X. That saves significant mass. If we can do 1.5% in the 1950s on Earth, then even a 1% mass for the landing legs (if they're short and you land on a prepared surface) is well within the realm of possibility. Though a 4% leg isn't a deal-breaker either.
« Last Edit: 11/03/2015 12:17 AM by Robotbeat »
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1057 on: 11/03/2015 12:19 AM »
SpaceX has not reached the pinnacle of landing leg design and manufacture; there's room for improvement. Others have done better.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1058 on: 11/03/2015 12:21 AM »
Musk is borrowing somewhat from Mars Direct (or is it Semi-Direct?) where an already-fueled ascent vehicle is fueled up on the surface. I don't see a good reason not to have a fueled up vehicle ready when they arrive.

I see no reason why to land the fuel production equipment at all.
It can do the same job on orbit.

you have said it yourself:
 http://forum.nasaspaceflight.com/index.php?topic=17984.msg620589#msg620589
CO/O2 is really neat, but orbital propellant collection is very difficult, and although I certainly support its development, I have absolutely no reason to think that's what SpaceX is planning. In fact, we can be reasonably certain that Raptor will use methane (and certainly it will use some sort of hydrocarbon), and that's what MCT will use.
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Offline Robotbeat

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Re: MCT Speculation and Discussion Thread 4
« Reply #1059 on: 11/03/2015 12:24 AM »
Subcooled ethylene isn't a horrible idea if you want to boost MCT's mass fraction. It's not a lot harder to make than methane on Mars, has similar Isp, but is much denser. It's also liquid at Mars ambient temperatures at ~1MPa, and requires less hydrogen than methane. And is really useful for making plastics and stuff for habitats, so you'd want to eventually make it anyway.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

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