Quote from: philw1776 on 06/16/2015 03:32 pmQuote from: spacenut on 06/16/2015 01:50 pmIf the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn. There will be quite a bit of fuel left. So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down. Also, there will probably be only a crew return, not 100 people. Crew?Why?MCT should be able to return to Earth empty. (And as needed provide occasional return transport for humans needing to return)On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans. No astronaut corps test pilots needed, just FEs similar to on the shuttle.Crew mass & life support is wasted mass and money. You may be correct aboutthe need for a crew, but people are still a bit primitive. They'd be more than a bit nervous to trust their lives to nothing more than machines. I'm pretty sure that they'd want at least a minimal crew orf pilot, navigator/copilot and at least one engineer. (A dedicated doctor/medic would also likely be a good idea). If nothing else, to keep the passengers calm during the flight. While machines are pretty good at doing their jobs, nobody will want to risk a several billion dollar investment on the possibility that a IC chip will fry because of a stray cosmic ray and send the craft wandering off into space or worse, come c rashing down on Earth at 6 to 7 KMS.
Quote from: spacenut on 06/16/2015 01:50 pmIf the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn. There will be quite a bit of fuel left. So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down. Also, there will probably be only a crew return, not 100 people. Crew?Why?MCT should be able to return to Earth empty. (And as needed provide occasional return transport for humans needing to return)On the way out assuming several 10s of passengers it would be astounding if there were not several engineers capable of specialized training as "flight engineers" to repair anything repairable by humans. No astronaut corps test pilots needed, just FEs similar to on the shuttle.Crew mass & life support is wasted mass and money.
If the MCT is completely refueled on Mars for launch back to earth, all of the fuel will not be needed to get the TEI burn. There will be quite a bit of fuel left. So the MCT could fire and slow down before earth reentry, or it could slow down using aerocapture for a few orbits to slow down. Also, there will probably be only a crew return, not 100 people.
At the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.
Quote from: Lobo on 06/16/2015 05:41 pmAt the end of they day, F9R and FHR will be doing the vast bulk of the sat launches.Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)[I would think the customers would end up forcing the decision. In much the same way that few were interested in F1 when they could fly as a secondary payload on F9 for half the price.]
Quote from: Impaler on 06/16/2015 03:28 amThat brutal 12-14 kms entry to Earth is something everyone who is talking about this direct Earth return is glossing over, that is beyond Apollo speeds, the only thing that can survive that kind of heat, dynamic pressure and g-force is a dense capsule with thick heavy ablatives.This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth. It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.A 2nd stage that can return from Earth orbit is a vastly simpler thing to do because the speed is half (and the energy is a quarter), and it is fairly easy to slow down the 2nd stage by several kms with residual propellents, and to employ disposable things like parachutes because it only needs to perform ONE landing before servicing rather then two, and lastly it can be made much less reliable in landing because it's unmanned, no one dies horribly if it crashes or burns up on reentry unlike MCT.The thing is....this is all a moot point to your argument. Whether MCT is it's own 2nd stage to LEO or it sits atop a dedicated unique 2nd stage won't change the fact that MCT will need to have -large- tanks. It will be mostly propellant tank by volume just to do the TMI burn and Mars EDL retropropulsion....and to get itself off the surface of Mars, even if it were only going to LMO before getting refueled there rather than all the way back in one shot.It will be mostly a large propellant tank, with some legs, engines, and some cargo or hab internal volume.Having MCT be it's own 2nd stage rather than having a separate dedicated 2nd stage won't change that. MCT can't then become just a simple larger Dragon capsule. With a dedicated reusable 2nd stage, then it's just a giant 3rd stage, rather than a giant 2nd stage. Maybe a little smaller. Not much else changes. So it's a bit of a moot argument.Yes, designing a vehicle that is returning just form LEO is vastly more simple than designing one that's coming back from interplanetary speeds. You are correct. But, there's not an either/or option. SpaceX must figure out how to get a large rocket stage back from Mars and land it on Earth. They already need to solve that long pole issue. A vehicle they design to handle that, can already return to Earth from LEO easily enough, without the [easy] development of a separate LEO only vehicle even necessary.
That brutal 12-14 kms entry to Earth is something everyone who is talking about this direct Earth return is glossing over, that is beyond Apollo speeds, the only thing that can survive that kind of heat, dynamic pressure and g-force is a dense capsule with thick heavy ablatives.This is why it is not valid to design spacecraft by only looking at Delta-V and tank sizes and imagining that a giant 2nd stage can do the job of direct Earth return from Mars surface just because it can hold the propellents to launch to Earth. It would literally be crushed like an empty beer can against ones forehead when it hits the Earth's atmosphere.A 2nd stage that can return from Earth orbit is a vastly simpler thing to do because the speed is half (and the energy is a quarter), and it is fairly easy to slow down the 2nd stage by several kms with residual propellents, and to employ disposable things like parachutes because it only needs to perform ONE landing before servicing rather then two, and lastly it can be made much less reliable in landing because it's unmanned, no one dies horribly if it crashes or burns up on reentry unlike MCT.
Quote from: Paul451 on 06/16/2015 09:52 pmSurely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)....I can't imagine they have any plans of retiring FH or F9 once MCT starts flying. For several reasons.When you have a hammer, everything looks like a nail. But not everything is a nail. it's...a matter of the right tool for the job...It's hard to imagine them launching a big Saturn V size (or larger) LV for such a comsat, even if it's fully reusable.
Surely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)
Quote from: Paul451 on 06/16/2015 09:52 pmSurely once a reusable BFR is flying, F9/FH will be retired? Simplify to one engine line, one tank line, one type of launch infrastructure, etc. Reduces cost. (Especially if BFR is a single core and cheaper to integrate than a triple core FH.)[...] Semi trucks haul mail cross country because that's the most cost efficient truck for that task. Jeep sized vehicles deliver to local mailboxes because that is the most cost efficient vehicle for that task. You don't use a maul when driving a finish nail. You use a finish nail hammer. Vice versa when demolishing a wall. You use the right tool for the job, and there is no single tool that does every job.
I can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)
Quote from: guckyfan on 06/16/2015 07:19 amQuote from: Impaler on 06/16/2015 05:22 am500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass. This also has the advantage of eliminating separate crew and cargo variants.It is also extremely inefficient in structural mass. MCT is all about efficiency in structural mass.The most mass efficient thing is to NOT make it integral to the MCT. The time when structural mass efficiently maters most is take off, and if we indent to me offloading people and not taking them back to Earth then all that habitat mass would be pure dead-weight on take off.
Quote from: Impaler on 06/16/2015 05:22 am500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass. This also has the advantage of eliminating separate crew and cargo variants.It is also extremely inefficient in structural mass. MCT is all about efficiency in structural mass.
500 m^3 is a reasonable cargo-hold but their would be no integral habitat as many have speculated, it makes much mores sense to load a large module into the cargo-hold which can be removed and left on the Mars surface to minimize the return mass. This also has the advantage of eliminating separate crew and cargo variants.
A single MCT won't be billions of dollars of investment or the $500k per passenger figure will be impossible. An order of magnitude less like $100-400 million. Also, electronics can easily be made reliable enough. We have lots an lots of experience running spacecraft for years at a time without maintenance. 6-9 months won't be a challenge for a company that will launch thousands of satellites into LEO.
Of course, transit time is just ~3 months, not 8, so that's a big difference right there. Additionally, they likely did not sleep in shifts like you would on MCT colonization runs.
MCT is a radical design. Acknowledge that and move on.
Musk’s $500,000 ticket price for a Mars trip was derived from what he thinks is affordable."The ticket price needs to be low enough that most people in advanced countries, in their mid-forties or something like that, could put together enough money to make the trip," he said, comparing the purchase to buying a house in California. [Photos: The First Space Tourists]He also estimated that of the eight billion humans that will be living on Earth by the time the colony is possible, perhaps one in 100,000 would be prepared to go. That equates to potentially 80,000 migrants.Musk figures the colony program — which he wants to be a collaboration between government and private enterprise — would end up costing about $36 billion. He arrived at that number by estimating that a colony that costs 0.25 percent or 0.5 percent of a nation’s gross domestic product (GDP) would be considered acceptable.The United States' GDP in 2010 was $14.5 trillion; 0.25 percent of $14.5 trillion is $36 billion. If all 80,000 colonists paid $500,000 per seat for their Mars trip, $40 billion would be raised."Some money has to be spent on establishing a base on Mars. It’s about getting the basic fundamentals in place," Musk said. "That was true of the English colonies [in the Americas]; it took a significant expense to get things started. But once there are regular Mars flights, you can get the cost down to half a million dollars for someone to move to Mars. Then I think there are enough people who would buy that to have it be a reasonable business case."
Quote from: Paul451 on 06/17/2015 02:11 amI can't imagine a client wanting to use a semi-expendable rocket when a cheaper secondary/tertiary payload slot is available on a fully reusable HLV. People seem hung up over the size, all that matters is the price.(Those semis will often carry many small packages because the per-item cost is lower than carrying them individually in a smaller vehicle.)People seem to be trying to compare BFR cost to launch satellites with other existing or near term launchers (Ariane 5, SLS, F9 etc etc). But that is not what my argument is about, it is about which VISION FOR BFR is cheaper to launch satellites with. Musk's goal is not to slightly undercut existing launchers, it is to create massive paradigm-shifting reductions in $ to LEO, even if BFR launch blows every other launch vehicle out of the water it still needs to compete with variants of itself.I'm arguing that BFR with mostly normal reusable 2nd stage is better at launching satellites then BFR with the giant MCT combo 2nd stage. These latter will cost LESS because a 2nd stage even reusable is a much simpler and lower mass vehicle then the whole MCT which has MUCH more demanding requirements on lifespan, reentry heat, lifespan etc etc. The first stage is identical and presumably all other logical and launch related costs are too, so the only difference is in the 2nd stages, one which is conventional with a voluminous payload fairing which is light and designed for optimal mass delivery to orbit, the other is a huge heavy vehicle totally over engineered for this job and has a small cargo hold. Their is no contest the normal 2nd stage will out perform the giant vehicle to any orbit, just as an EELV booster outperformed the shuttle at launching satellites. And the normal 2nd stage is going to be vastly cheaper to develop as well, the only argument that anyone has left is that because Elon absolutely MUST have his Mars oriented vehicle he will choose to shoehorn it into every possible usage even for things it is not optimized for so as to amortize the cost over as many flights as possible. I don't recall that strategy working well for Shuttle. Musk is blessed with inordinate patience, he could have blown his money on a stunt ages ago but has always focused on building a viable BUSINESS first and foremost. In pursuit of greater revenue he is now getting into the satellite business. He doesn't leave any potential revenue source on the table. Se Musk is not going to pass on designing the best conventional satellite launcher simply because he also wants to use the vehicle for Mars adventures, he knows that it must be a viable vehicle in it's own right.
And please stop repeating that big-tank are the ONLY way, I have shown you several times how the vehicle can designed with much smaller tanks, your not a fan of these options but it is dishonest to begin your argument with your preferred solution as the only option, it is simply begging the question.First off you can go to LMO and then dock with a transit vehicle like Mars Semi-Direct, no one here can claim that they are unfamiliar with Semi-Direct. Second, inflatable tanks in the cargo-hold, even rigid tanks in the cargo hold if you think inflatables are to low TRL.
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...
Try crushing a beer can containing several bars of pressure against your forehead.
Quote from: fast on 06/17/2015 01:48 pmAnd 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.
Quote from: Lobo on 06/17/2015 04:29 pmQuote from: fast on 06/17/2015 01:48 pmAnd 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.