Author Topic: Reusability effect on costs  (Read 136944 times)

Offline dante2308

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Re: Reusability effect on costs
« Reply #40 on: 05/30/2016 01:53 AM »
I don't know how much it has been stated, but the real issue I'm seeing is with second stage reuse being tied to Mars transportation. I'm not quite understanding the business case for reusing an interplanetary stage that makes 4 trips per decade (assuming Mars launch windows) unless it also doubles as a well-used transportation system to Earth orbit. However Elon is adamant that the Falcon line will take care of the satellite market for the foreseeable future and has indicated that the second state reuse plans aren't compatible with the Falcon rocket architecture.

I attached a porkchop plot showing the delta-v space for Mars as the sum of hyperbolic excess velocities. Sorry, I didn't spend any time making it pretty. The point the plot makes is simply that the Mars windows are not really voluntary.
Realize that the interplanetary stage will be reused multiple times per each mission cycle:
1) launch
2) refuel and fire again from Earth orbit toward Mars
3) landing on Mars
4) refuel and ascent from Mars
(possible refueling in Mars orbit, perhaps not required)
5) landing on Earth

The stage has to be intact at each stage, not shedding parts that it'll need in the rest of the mission. So you ALREADY need a reusable stage (really a spacecraft, but I'll stick with your terminology) just so the architecture works, so you might as well use it again. And getting 10-15 mission cycles out of each manufactured stage makes a non-insignificant reduction in cost! ...even if it is over 2-3 decades.

...additionally, SpaceX will require the stage to do refueler duty and cargo duty. They need the stage to be capable of a lot more than 10-15 reuses in those configurations.

And yeah, the potential cost reduction of 4-5 mission cycles per decade is still important. They need the cost as low as possible in order to achieve the sub-$500k/person ticket price, and at the full swing of 80,000 people to Mars per year, they'll need that reuse just to keep up.

The biggest problem I'm seeing isn't so much whether they have the opportunity to use it 10-15 times in 2-3 decades. It's whether it is even possible to iterate towards something that enduring and robust and fund the initial R&D and capital costs for something with such a long time horizon.

That obligatory bout of skepticism aside, I think it would do to sort of lay out the requirements for 80,000 people per year and $500k/passenger.

1) You have 4-5 launch windows per decade to lift 800,000 people onto TMI. If each ship holds 100 people, then that's 800 launches total. If you aren't loitering a city full of people in orbit, then that's at least 160 launches during window years or 3 per week if they are spread out over the year. With three pads, this is 1 per week per pad however, this still means people will have to loiter in parking orbit for up to 6 months.

2) If you reuse each interplanetary stage on subsequent launches, in one decade you have to manufacture at least 160 interplanetary ships or about 16 per year during the ramp up.

3) The cost per interplanetary ship must be at maximum $250m assuming zero fixed launch costs if the costs are to be recovered in one decade.

My take is that (1) is unprecedented, (2) is feasible but currently unfunded, and (3) is unprecedented but possible. The key is again producing a manned spaceship that lasts at least a decade and can function unaided for at least 6-9 months at a time for a sustainable cost. I agree that the mission architecture itself assumes that  craft survives planetary entry in a flight-ready condition, but that's only one of the technological blockers. There are no historical references for this kind of thing.
« Last Edit: 05/30/2016 02:05 AM by dante2308 »

Offline dante2308

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Re: Reusability effect on costs
« Reply #41 on: 05/30/2016 01:57 AM »
The reusable second stage will be shuttling enormous amounts of propellent and cargo in LEO, roughly 5000 tonnes per 100 people sent to Mars. That's not feasible with disposable upper stages.

5,000 tons? About a quarter of the LEO mass will make it to Mars. That's quite the haul.

Offline envy887

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Re: Reusability effect on costs
« Reply #42 on: 05/30/2016 02:01 AM »
The reusable second stage will be shuttling enormous amounts of propellent and cargo in LEO, roughly 5000 tonnes per 100 people sent to Mars. That's not feasible with disposable upper stages.

5,000 tons? About a quarter of the LEO mass will make it to Mars. That's quite the haul.

Musk estimated 10 cargo flights per passenger flight, all hauling 100t of payload and probably about as much dry mass (engines, structure, heatshield, etc.). That's thousands of tons in LEO, once you include propellent.

Offline dante2308

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Re: Reusability effect on costs
« Reply #43 on: 05/30/2016 02:03 AM »
The reusable second stage will be shuttling enormous amounts of propellent and cargo in LEO, roughly 5000 tonnes per 100 people sent to Mars. That's not feasible with disposable upper stages.

5,000 tons? About a quarter of the LEO mass will make it to Mars. That's quite the haul.

Musk estimated 10 cargo flights per passenger flight, all hauling 100t of payload and probably about as much dry mass (engines, structure, heatshield, etc.). That's thousands of tons in LEO, once you include propellent.

I think the likely explanation is that we're not talking about a 100t payload fully reusable launcher and/or we're not talking about only 100 people because I'm fairly certain that we're not talking about a 5,000 ton starship.
« Last Edit: 05/30/2016 02:06 AM by dante2308 »

Offline macpacheco

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Re: Reusability effect on costs
« Reply #44 on: 05/30/2016 02:08 AM »
There will be no frequent missions to Mars until there's full reuse. None.
Even with full reuse, SpaceX needs low cost turn around (gas up, perhaps reapply some ablative material here and there, and fly again).
I predict there will be a handful of FH missions to Mars (either with a M1D or Raptor 2nd stage) and just a handful of non Mars planetary missions.
I feel thorn apart here at NSF, since I'm part scientist, part engineer, part businessmen, with the norm of the overwhelming majority here being not business people at all.
SpaceX needs tens of billions in free cashflow to finish MCT design and build the first 10 MCT vehicles.

Stop mixing things up. Right now SpaceX primary concern is have a profitable cash cow, while designing Raptor engine+rockets, some of those rockets will be built to launch sats to GTO, and do some sort of Cargo/Crew missions to LEO (probably with a shuttle sized vehicle that will do about 2x a current cargo mission plus a full Dragon Crew load per flight).

Sorry to burst your bubble. Maybe I deserve a good smacking from the moderators.
Looking for companies doing great things for much more than money

Offline envy887

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Re: Reusability effect on costs
« Reply #45 on: 05/30/2016 02:09 AM »
I don't see how a bigger expendable launcher is any cheaper. Colonization isn't feasible unless the launcher is cheaply and quickly reusable, including the second stage. That's true no matter what the scale.

Offline dante2308

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Re: Reusability effect on costs
« Reply #46 on: 05/30/2016 02:13 AM »
I don't see how a bigger expendable launcher is any cheaper. Colonization isn't feasible unless the launcher is cheaply and quickly reusable, including the second stage. That's true no matter what the scale.

I don't mean to suggest that expendable launchers are cheaper. I'm just wondering how feasible it is to lower the cost of an interplanetary stage by aiming to reuse it 4 times/decade. It sort of seems like the goal you have after you've been building something similar for decades and all the investors are lined up though there is something to be said for "getting to the point." Unaided, this would take at least a century of steady progress and the combined resources of all space-faring nations it would seem.
« Last Edit: 05/30/2016 02:19 AM by dante2308 »

Offline envy887

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Re: Reusability effect on costs
« Reply #47 on: 05/30/2016 02:26 AM »
The vast majority of launches will not be interplanetary though. To send a 11 ships to Mars (one with 100 passengers, ten with 100t cargo each) will require not 11 but about 50 launches of 100t each to LEO (to orbit the 5000t I mentioned before).

A cheaply reusable super heavy lift upper stage is absolutely indispensable to making colonization work.

Offline dante2308

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Re: Reusability effect on costs
« Reply #48 on: 05/30/2016 02:33 AM »
The vast majority of launches will not be interplanetary though. To send a 11 ships to Mars (one with 100 passengers, ten with 100t cargo each) will require not 11 but about 50 launches of 100t each to LEO (to orbit the 5000t I mentioned before).

A cheaply reusable super heavy lift upper stage is absolutely indispensable to making colonization work.

I'm having a hard time wrapping my head around a ship that is equally useful as a LEO hauler and a manned Mars expedition ship. I would assume two separate versions under normal circumstances.

Offline DAZ

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Re: Reusability effect on costs
« Reply #49 on: 05/30/2016 02:44 AM »
It would seem having so much expensive infrastructure sitting around for 2 years at a time with nothing to do would doom such a project to economic failure.  Trying to move 100 – 800 people every 2 years with an eventual goal of 800,000 – 1 million spread over 2 to 3 decades would also appear to be a recipe for failure.  It would make more sense for the 1st few cycles to carry 10 – 20 people at a time with their associated equipment to establish the initial colony and then expanded the system into something much more efficient.

As has probably been discussed before, using a Mars cycler with transit stations at both Earth and Mars would make much more sense.  The cargo would go by SEP which could be launched at any time and spiral out until they can leave during the appropriate window.  When it gets closer to the appropriate window the people can launch and stay at a station at ELL2 and then leave to catch the Mars cycler.  At the Mars end they could depart and wait at the Mars station to catch the landing craft down.

The beauty of using a Mars cycler is that almost all of the living space, radiation shielding, power and food/water production is only launched once.  It doesn’t slow down at the Mars end nor at the earth end.  By using the infrastructure to build more infrastructure you are more akin to building a road than just a simple boat like the Mayflower.

On each cycle SEP tugs could bring more modules and supplies to the Mars cycler.  These cycles would be on both the inbound and the outbound trip thus doubling the number of opportunities.  The people would only be going on the outbound side.  On each outbound the people could add the new modules and thus increase the number of people this cycler could handle on each trip.  This means the system could be expanded and thus make use of all of the infrastructure over the entire departure Mars cycle instead of just being clustered around a small 2 to 3 week window.

As most of the people would be going outbound at 1st there would only be in need in the beginning for an outbound cycler.  As commerce increases eventually a Mars – Earth inbound cycler could be constructed.  In the beginning the most logical cycler to use would be the Aldrin cycler.  At the moment there are 18 other cyclic orbits known.  Each of these with different time periods per cycle and earth to Mars transit times.  But as the commerce between Earth and Mars increases it might make sense to add at least some of these other cyclic periods to the overall system.  This would increase the number of transit times available to Mars from approximately once every 2 years to an occasional of multiple times every 2 years.

What SpaceX’s long-term plans are only SpaceX knows.  But it would seem that the economics would force the maximum use of the infrastructure if a long-term project is to have any chance at all of succeeding.

Offline dante2308

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Re: Reusability effect on costs
« Reply #50 on: 05/30/2016 02:54 AM »
It would seem having so much expensive infrastructure sitting around for 2 years at a time with nothing to do would doom such a project to economic failure.  Trying to move 100 – 800 people every 2 years with an eventual goal of 800,000 – 1 million spread over 2 to 3 decades would also appear to be a recipe for failure.  It would make more sense for the 1st few cycles to carry 10 – 20 people at a time with their associated equipment to establish the initial colony and then expanded the system into something much more efficient.

As has probably been discussed before, using a Mars cycler with transit stations at both Earth and Mars would make much more sense.  The cargo would go by SEP which could be launched at any time and spiral out until they can leave during the appropriate window.  When it gets closer to the appropriate window the people can launch and stay at a station at ELL2 and then leave to catch the Mars cycler.  At the Mars end they could depart and wait at the Mars station to catch the landing craft down.

The beauty of using a Mars cycler is that almost all of the living space, radiation shielding, power and food/water production is only launched once.  It doesn’t slow down at the Mars end nor at the earth end.  By using the infrastructure to build more infrastructure you are more akin to building a road than just a simple boat like the Mayflower.

On each cycle SEP tugs could bring more modules and supplies to the Mars cycler.  These cycles would be on both the inbound and the outbound trip thus doubling the number of opportunities.  The people would only be going on the outbound side.  On each outbound the people could add the new modules and thus increase the number of people this cycler could handle on each trip.  This means the system could be expanded and thus make use of all of the infrastructure over the entire departure Mars cycle instead of just being clustered around a small 2 to 3 week window.

As most of the people would be going outbound at 1st there would only be in need in the beginning for an outbound cycler.  As commerce increases eventually a Mars – Earth inbound cycler could be constructed.  In the beginning the most logical cycler to use would be the Aldrin cycler.  At the moment there are 18 other cyclic orbits known.  Each of these with different time periods per cycle and earth to Mars transit times.  But as the commerce between Earth and Mars increases it might make sense to add at least some of these other cyclic periods to the overall system.  This would increase the number of transit times available to Mars from approximately once every 2 years to an occasional of multiple times every 2 years.

What SpaceX’s long-term plans are only SpaceX knows.  But it would seem that the economics would force the maximum use of the infrastructure if a long-term project is to have any chance at all of succeeding.

The Aldrin Cycler has several drawbacks. I've attached it here.

1) The synodic period of Earth-Mars cycling is extremely long and by definition requires multi-year transits. (Note the long semi-major axis). Each cycler class is a multiple of one synodic period (2.41 years).

2) Feasible launch windows are infrequent no matter how many cyclers exist since cyclers that come in on off years have huge excess velocities and are generally non-Hohmann.

3) Rendezvous are one-shot, risky, and require a LOT more delta-v.

4) You still have to transport the cargo and the fuel. In the end, you're just saving on structural mass and the fuel to accelerate structural mass.

If it's just about the optimal orbital mechanics of the Earth-Mars transit system, I'll post a paper here later on this summer I'm working on for NSF to tear apart if you wish. I'm working on something hopefully better than cyclers.

Attached after the image is a recent-ish paper with cycler classes and the source of the image.

Edit: I just wanted to add that most cyclers assume a gravity assist at Earth encounter so they come quite close to the planet at great velocity. In order for an SEP tug to meet a cycler, it would have to accumulate quite a bit of velocity and be a good bit of the way to Mars. It also might be functionally impossible to go from LEO to a cycler orbit with SEP in a time frame not measured in years. We're talking about mili-Newtons and tons and an extremely large delta-v. At the very least the rendezvous may happen after Mars.
« Last Edit: 05/30/2016 04:06 AM by dante2308 »

Offline envy887

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Re: Reusability effect on costs
« Reply #51 on: 05/30/2016 02:57 AM »
Probably three: manned, cargo, and propellent tanker, differing mostly in how payload is stored. They would use the same launcher and engines, and probably be built on the same production line. All would need about the same payload and Delta v performance, and all would need to be capable of Mars and/or Earth EDL.

I don't see how building one version to be reusable while the others are expendable saves any cost or time. They all need landing capability (and return, for Mars ships) anyway.

The vast majority of launches will not be interplanetary though. To send a 11 ships to Mars (one with 100 passengers, ten with 100t cargo each) will require not 11 but about 50 launches of 100t each to LEO (to orbit the 5000t I mentioned before).

A cheaply reusable super heavy lift upper stage is absolutely indispensable to making colonization work.

I'm having a hard time wrapping my head around a ship that is equally useful as a LEO hauler and a manned Mars expedition ship. I would assume two separate versions under normal circumstances.

Offline dante2308

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Re: Reusability effect on costs
« Reply #52 on: 05/30/2016 02:59 AM »
Probably three: manned, cargo, and propellent tanker, differing mostly in how payload is stored. They would use the same launcher and engines, and probably be built on the same production line. All would need about the same payload and Delta v performance, and all would need to be capable of Mars and/or Earth EDL.

I don't see how building one version to be reusable while the others are expendable saves any cost or time. They all need landing capability (and return, for Mars ships) anyway.

The vast majority of launches will not be interplanetary though. To send a 11 ships to Mars (one with 100 passengers, ten with 100t cargo each) will require not 11 but about 50 launches of 100t each to LEO (to orbit the 5000t I mentioned before).

A cheaply reusable super heavy lift upper stage is absolutely indispensable to making colonization work.

I'm having a hard time wrapping my head around a ship that is equally useful as a LEO hauler and a manned Mars expedition ship. I would assume two separate versions under normal circumstances.

I never suggested anything should be expendable.

Offline envy887

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Re: Reusability effect on costs
« Reply #53 on: 05/30/2016 03:11 AM »
I never suggested anything should be expendable.

Fair enough. Reusability isn't optional, for many reasons, so the cost savings for long term stuff will have to come from component commonality with hardware that's flown very often.

Offline envy887

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Re: Reusability effect on costs
« Reply #54 on: 05/30/2016 03:33 AM »
I'm just wondering how feasible it is to lower the cost of an interplanetary stage by aiming to reuse it 4 times/decade. It sort of seems like the goal you have after you've been building something similar for decades
...
I don't disagree with this part. There will be a massive upfront investment required to get any reusable system flying. The feasibility of it all is TBD.

Offline guckyfan

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Re: Reusability effect on costs
« Reply #55 on: 05/30/2016 06:05 AM »
I'm having a hard time wrapping my head around a ship that is equally useful as a LEO hauler and a manned Mars expedition ship. I would assume two separate versions under normal circumstances.

I see it working out this way: A MCT will have an engine section and a cargo or passenger section. The engine section will have tanks big enough to work as a tanker as well. With tanks that big it can do fast transfer even in unfavorable launch windows. It just needs another fueling flight.

So a new MCT will start its life as a tanker. No passenger or cargo section added, saving weight. Only a cap with heatshield on top. It will do 5 or whatever flights as a tanker until it is proven reliable. Then a cargo or passenger section gets added and it will do ~10 or whatever flights to Mars. At the end of its life the cargo section gets removed and it works as a tanker again. This way you can get at least 40 launches out of the expensive part, the engine section.

Offline Semmel

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Re: Reusability effect on costs
« Reply #56 on: 05/30/2016 06:42 AM »
Gucky, I like the plan. However, I would put less Mars flights on the menue. If they keep flying the same engine section ~10 times to Mars, they will need to support the same hardware, software, all the replacement parts, etc for about 30 years. Thats a pretty long time. It is more likely that technology advances fast enough to make a replacement of an MCT as a Mars shuttle every ~3 trips more likely. That way, they can phase out old technology every 10 years or something which is much more reasonable.

It doesnt really hurt either because the engine section can do just more tanker runs, or even cargo to LEO or GTO missions. In fact, a MCT for GTO missions would be quite cost efficient since the entire rocket gets re-used naturally. Dont know what the payload limits would be though.

Offline dante2308

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Re: Reusability effect on costs
« Reply #57 on: 05/30/2016 06:45 AM »
I'm having a hard time wrapping my head around a ship that is equally useful as a LEO hauler and a manned Mars expedition ship. I would assume two separate versions under normal circumstances.

I see it working out this way: A MCT will have an engine section and a cargo or passenger section. The engine section will have tanks big enough to work as a tanker as well. With tanks that big it can do fast transfer even in unfavorable launch windows. It just needs another fueling flight.

So a new MCT will start its life as a tanker. No passenger or cargo section added, saving weight. Only a cap with heatshield on top. It will do 5 or whatever flights as a tanker until it is proven reliable. Then a cargo or passenger section gets added and it will do ~10 or whatever flights to Mars. At the end of its life the cargo section gets removed and it works as a tanker again. This way you can get at least 40 launches out of the expensive part, the engine section.

I'm not sure the engine is the most expensive part of a manned interplanetary spacecraft.

What you prescribed is what I understood as the best case scenario, but that puts a floor on the price because the most complex and novel component, the cargo and passenger interplanetary stage, is the one that will be reused the least and will have to last an incredibly long time to be reused at all. Literally years in deep space. It raises the $15m question for Elon. Is his $15m 1/10th or so of a spaceship to Mars because in normal accounting, that's off by (at least) two orders of magnitude.

Gucky, I like the plan. However, I would put less Mars flights on the menue. If they keep flying the same engine section ~10 times to Mars, they will need to support the same hardware, software, all the replacement parts, etc for about 30 years. Thats a pretty long time. It is more likely that technology advances fast enough to make a replacement of an MCT as a Mars shuttle every ~3 trips more likely. That way, they can phase out old technology every 10 years or something which is much more reasonable.

It doesnt really hurt either because the engine section can do just more tanker runs, or even cargo to LEO or GTO missions. In fact, a MCT for GTO missions would be quite cost efficient since the entire rocket gets re-used naturally. Dont know what the payload limits would be though.

Here is my second worry beyond the frequency of interplanetary stage reuse. How do you iterate towards the correct design? We all watched SpaceX redesign the Falcon 9 over the years before they got the stages to land and we can expect several more iterations before they achieve "rapid" reuse. That's just the nature of bleeding-edge engineering. How many chances do they get to nail down MCT's architecture in a way that really optimizes against any contingency in a sustainable way? How many flights before you even put people on that voyage? Rationally, the process to reusable interplanetary spacecraft should take at least half a century if we were in a rush.

However, rather than just be skeptical, might I suggest that perhaps a more sustainable path to this kind of thing might actually be the moon after all? So many technologies can be qualified getting there and it's only a few days away. Tickets will sell just as well or better too.
« Last Edit: 05/30/2016 07:00 AM by dante2308 »

Offline guckyfan

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Re: Reusability effect on costs
« Reply #58 on: 05/30/2016 08:04 AM »
It doesnt really hurt either because the engine section can do just more tanker runs, or even cargo to LEO or GTO missions. In fact, a MCT for GTO missions would be quite cost efficient since the entire rocket gets re-used naturally. Dont know what the payload limits would be though.

I see the problem with a long use time. However it is the only way to get many reuses. Airframes of planes are the same. They get used a long time despite changes to newer versions. Keep attachment points and fuel type the same so that different iterations can be supported by the same GSE.

Unfortunately you cannot get around this by doing more tanker flights. The ratio Mars/tanker is fixed at betwen 3-1 and 4-1. The only development that could get many flights and a shorter life span would be large demand for flights in cislunar space. This may happen but I doubt Elon Musk counts on it when doing his Mars design.

I don't see the cost for passenger compartments that high, at least not when they are produced in significant numbers. The complex and expensive part will be development. Development of ECLSS will be ongoing and changes towards lower production and maintenance costs will be implemented in existing stages I expect. It will be an evolutionary process as early passenger MCT will not have to support 100 people.

Edit: The propulsion unit has more cost than the engines. There are engines, thrust structure, tanks - probably insulated, the avionics, the sensor suite and above all the cost of integrating everyting.
« Last Edit: 05/30/2016 08:07 AM by guckyfan »

Online AncientU

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Re: Reusability effect on costs
« Reply #59 on: 05/30/2016 11:55 AM »

<snip>

Here is my second worry beyond the frequency of interplanetary stage reuse. How do you iterate towards the correct design? We all watched SpaceX redesign the Falcon 9 over the years before they got the stages to land and we can expect several more iterations before they achieve "rapid" reuse. That's just the nature of bleeding-edge engineering. How many chances do they get to nail down MCT's architecture in a way that really optimizes against any contingency in a sustainable way? How many flights before you even put people on that voyage? Rationally, the process to reusable interplanetary spacecraft should take at least half a century if we were in a rush.

However, rather than just be skeptical, might I suggest that perhaps a more sustainable path to this kind of thing might actually be the moon after all? So many technologies can be qualified getting there and it's only a few days away. Tickets will sell just as well or better too.

I believe that iteration toward the correct design has begun.  F9 is demonstrating or will demonstrate a set of technologies and approaches that will be directly applicable to BFR (and FH obviously), so that 15,000,000lbf booster can be born reusable -- a few iterations will no doubt be needed, but this is much more affordable if the basic scheme is proven.  In a similar manner, a reusable second stage can and I believe will be built for FH to iterate MCT technologies, those needed on Earth end, in transit, and at Mars end.  Refueling technology will be proven early with a reusable FH tanker.  Red Dragon is building on iterations with the tech on Dragon 2 which is building on the tech from Dragon (1).  EDL with RD will lay foundation for EDL with FH reusable second stage -- mini-MCT if you will.  And on and on.  It's iterations all the way down.

This is the key to SpaceX's potential to realize their vision... each thing they do is done in light of that vision.  By the time MCT flies, there will be little but the enormity (scale) factor to be iterated.

Notes:
1) The Moon is slated to be used as a proving ground.
2) By the time SpaceX lands people on Mars, they will have been working toward this reusable interplanetary spacecraft for a quarter century.  They work fast...


« Last Edit: 05/30/2016 12:17 PM by AncientU »
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