Will Mars-bound Starships actually be reused?

[Slarty1080]

A lot of arguments against reuse boil down to assumptions that energy, propellant, etc, will never be sufficiently cheap to make it worthwhile… which also kind of implies energy and propellant costs too high for a viable largely-self-sustaining Mars city. So what’s the point of this exercise if sending thousands of people to Mars if stuff on Mars always is gonna be too expensive to reuse Mars ships?

I think people aren’t really following the logic far enough.

Yes, it’s challenging to economically justify Mars ship reuse, just like it’s challenging to justify full reuse of space launch, just like it USED to be hard to justify partial reuse (back when 10 flights per year seemed like a lot)…
…but if you exclude that reuse, you’re excluding the possibility of reaching that eventual end state.


The end goal is millions of people on Mars. You ultimately can’t be relying on just using Starships for buildings, etc. you need to have cheap energy. You need to have costs low enough that the typical middle class person could potentially choose to go. Those are the requirements. Excluding reuse because of high energy costs, etc, is including assumptions that preclude that end goal and create passenger costs too high to make the end goal viable.

Exactly.   The first few synods return will not be possible (no ISRU), or difficult (limited ISRU, no chopsticks).  Once the infrastructure is there on Mars to catch and refuel ships, a lot will return to be reused again and again.

They wont get hundreds of flights but 2, 3 even 20 might be achieved (until starship is superseded)

Why would they want chopsticks on Mars? Why not land and take off from the same place?

[meekGee]

Playing around with a spreadsheet, and assuming the Starship itself is as valuable as the cargo it contains (per ton), it would appear that it probably makes sense to return Starships if the ISRU fuel costs nothing.

It takes about 480t of fuel to return an (empty) Starship from Mars to Earth.  So it's a no brainer that leaving the Starships on Mars makes sense if there's no ISRU, it costs 4 times as much mass sent to return it.

That 480t of fuel is about 1/10 of the fuel needed to get to LEO, which the latter is is $1M in (Earth cost) fuel.

So if ISRU fuel costs 10x as much as is does on Earth then $1M of fuel means returning Starships still makes sense.

If the ISRU fuel costs 100x as much as it does on Earth then it starts to not make sense to return Starships.

So it would appear that returning Starships for reuse is going to be almost completely dependent on the cost per kg of ISRU fuel, which will be varying by several orders of magnitude over time.

There's probably a whole other thread on ISRU fuel production and presumably how much it costs.  Does anyone have a summary?

My spreadsheet takes into account:
- increasing launch cadence of 2x per synod
- reduction of fabrication coat of 0.8x per doubling
- reuse lag time of either 1 or 2 synods

But I haven't given value to the used ships on the surface.   All I'm showing is that the savings gained by reuse, even infinite reuse are minimal - as long as the fleet keeps doubling.

At some point this will stop being true, but hopefully not within the first two decades.

I think at some point before that, large high-ISP orbit-to-orbit ships will take over, and then Starships will live mostly on Earth or on Mars (different variants) and will get reused rapidly where they are.

[InterestedEngineer]

Playing around with a spreadsheet, and assuming the Starship itself is as valuable as the cargo it contains (per ton), it would appear that it probably makes sense to return Starships if the ISRU fuel costs nothing.

It takes about 480t of fuel to return an (empty) Starship from Mars to Earth.  So it's a no brainer that leaving the Starships on Mars makes sense if there's no ISRU, it costs 4 times as much mass sent to return it.

That 480t of fuel is about 1/10 of the fuel needed to get to LEO, which the latter is is $1M in (Earth cost) fuel.

So if ISRU fuel costs 10x as much as is does on Earth then $1M of fuel means returning Starships still makes sense.

If the ISRU fuel costs 100x as much as it does on Earth then it starts to not make sense to return Starships.

So it would appear that returning Starships for reuse is going to be almost completely dependent on the cost per kg of ISRU fuel, which will be varying by several orders of magnitude over time.

There's probably a whole other thread on ISRU fuel production and presumably how much it costs.  Does anyone have a summary?

My spreadsheet takes into account:
- increasing launch cadence of 2x per synod
- reduction of fabrication coat of 0.8x per doubling
- reuse lag time of either 1 or 2 synods

But I haven't given value to the used ships on the surface.   All I'm showing is that the savings gained by reuse, even infinite reuse are minimal - as long as the fleet keeps doubling.

At some point this will stop being true, but hopefully not within the first two decades.

I think at some point before that, large high-ISP orbit-to-orbit ships will take over, and then Starships will live mostly on Earth or on Mars (different variants) and will get reused rapidly where they are.

So you don't have ISRU costs then?

[Robotbeat]

2x per synod means that 65 years after the first ship, you’ll be sending 1 billion ships per synod. I think we’ll saturate WAY before that… and it won’t take a century to do so.


Even 1000 ships per synod is a freaking lot. 100,000 people per year. I don’t think you’ll have enough people who can afford $1 million ticket prices to pay for that. (And ticket costs won’t go lower without reuse…)

Making 1000 ships per synod would likely cost around $50 billion per year. 1 billion ships per synod is like quadrillions of dollars per year.

I don’t think learning curves for things made out of real minerals will keep reducing in costs like that. (Semiconductors can because you’re just getting things thinner or smaller, so material costs are similar but performance keeps rapidly improving.). I don’t think it’s reasonable to expect more starships to be made than airliners per year.

Exponentials with a fast doubling time but without an eventual logistical curve will just yield nonsensical conclusions.

A billion ships per synod would imply over 100 Terawatts of energy on average, when you include all the tankers and stuff. You would destroy the atmosphere. I think launch rate limit for chemical is somewhere between 10 and 100 million tons IMLEO per year before big atmospheric constraints start to take hold. This would be about 1000 times that.



Realistically, I’d put it at 10 doublings. 1000 made ships per synod. Reused 10 times for Mars (far more for tankers etc), and that’s 10,000 ships sent to mars per synod or about 100,000 to 1 million passengers per synod, depending on ratio of cargo to people.

[Robotbeat]

Making - a billion ships per synod means after 15 years, every person on earth could have their own starship LOL

[meekGee]

Playing around with a spreadsheet, and assuming the Starship itself is as valuable as the cargo it contains (per ton), it would appear that it probably makes sense to return Starships if the ISRU fuel costs nothing.

It takes about 480t of fuel to return an (empty) Starship from Mars to Earth.  So it's a no brainer that leaving the Starships on Mars makes sense if there's no ISRU, it costs 4 times as much mass sent to return it.

That 480t of fuel is about 1/10 of the fuel needed to get to LEO, which the latter is is $1M in (Earth cost) fuel.

So if ISRU fuel costs 10x as much as is does on Earth then $1M of fuel means returning Starships still makes sense.

If the ISRU fuel costs 100x as much as it does on Earth then it starts to not make sense to return Starships.

So it would appear that returning Starships for reuse is going to be almost completely dependent on the cost per kg of ISRU fuel, which will be varying by several orders of magnitude over time.

There's probably a whole other thread on ISRU fuel production and presumably how much it costs.  Does anyone have a summary?

My spreadsheet takes into account:
- increasing launch cadence of 2x per synod
- reduction of fabrication coat of 0.8x per doubling
- reuse lag time of either 1 or 2 synods

But I haven't given value to the used ships on the surface.   All I'm showing is that the savings gained by reuse, even infinite reuse are minimal - as long as the fleet keeps doubling.

At some point this will stop being true, but hopefully not within the first two decades.

I think at some point before that, large high-ISP orbit-to-orbit ships will take over, and then Starships will live mostly on Earth or on Mars (different variants) and will get reused rapidly where they are.

So you don't have ISRU costs then?

I only looked at the immediate savings due to reuse, and showed that they are minimal - nowhere nears multi-fold reduction in cost.

Things like ISRU cost and value-on-Mars will only tilt it further towards stay-on-Mars.  They're just difficult to forecast so I stayed clear.

[waveney]

A lot of arguments against reuse boil down to assumptions that energy, propellant, etc, will never be sufficiently cheap to make it worthwhile… which also kind of implies energy and propellant costs too high for a viable largely-self-sustaining Mars city. So what’s the point of this exercise if sending thousands of people to Mars if stuff on Mars always is gonna be too expensive to reuse Mars ships?

I think people aren’t really following the logic far enough.

Yes, it’s challenging to economically justify Mars ship reuse, just like it’s challenging to justify full reuse of space launch, just like it USED to be hard to justify partial reuse (back when 10 flights per year seemed like a lot)…
…but if you exclude that reuse, you’re excluding the possibility of reaching that eventual end state.


The end goal is millions of people on Mars. You ultimately can’t be relying on just using Starships for buildings, etc. you need to have cheap energy. You need to have costs low enough that the typical middle class person could potentially choose to go. Those are the requirements. Excluding reuse because of high energy costs, etc, is including assumptions that preclude that end goal and create passenger costs too high to make the end goal viable.

Exactly.   The first few synods return will not be possible (no ISRU), or difficult (limited ISRU, no chopsticks).  Once the infrastructure is there on Mars to catch and refuel ships, a lot will return to be reused again and again.

They wont get hundreds of flights but 2, 3 even 20 might be achieved (until starship is superseded)

Why would they want chopsticks on Mars? Why not land and take off from the same place?

If you use chopsticks to land, then you aren't carrying 10 tonnes of single use legs (or whatever the weight is).  Which is 10 tonnes of cargo you can then usefully carry.

Chopsticks to land and an appropriate launch mount for the ship to takeoff from.  Then the same method is used on both Planets.

[MickQ]

This talk of hundreds of Starships per synod makes me cringe 😖.

The infrastructure required to handle that amount of traffic on Mars would dwarf LAX.  C’mon guys.  It ain’t going to happen.  Starship will morph into something bigger, faster and more versatile long before we’d see 100 ships travelling together.

[oiorionsbelt]

This talk of hundreds of Starships per synod makes me cringe 😖.

Good thing they're not using the right numbers then.   

https://twitter.com/elonmusk/status/1217993568482025472?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1217993568482025472%7Ctwgr%5E60a93852e8fe3e75505547bd4f23de4364f79e95%7Ctwcon%5Es1_&ref_url=https%3A%2F%2Fwww.businessinsider.com%2Felon-musk-plans-1-million-people-to-mars-by-2050-2020-1

[Twark_Main]

Initially? Sure. Makes sense. Long term? It requires the assumption that Mars won’t have local industrial capacity to make affordable steel and buildings and propellant.

Starship will likely cost around $1000/kg dry mass initially, could reach $100/kg dry mass eventually (10 times cheaper than an airliner… I’m skeptical but am willing to entertain the point). So by not reusing Starships, you’re basically saying that you can’t make the shells of buildings and scrap metal on Mars for cheaper than $100/kg, ever. This is guaranteeing that Mars will never proceed beyond basically a highly Earth dependent research outpost or settlement like Antarctica. (which can have thousands of people! But no local industry. No mining allowed.)

This logic cuts both ways.

"Long term, reusing Starship requires the assumption that Earth won't have local industrial capacity to make affordable steel rocket ships."

"Starship will likely cost around $1000/kg dry mass initially, could reach $100/kg dry mass eventually (10 times cheaper than an airliner… I’m skeptical but am willing to entertain the point). So by reusing Starships, you’re basically saying that you can’t make the shells of starships and rocket plumbing on Earth for cheaper than $100/kg (plus the cost of return fuel from Mars!), ever. This is guaranteeing that Earth will never proceed beyond basically a highly localized LEO space economy with no settlements, like Antarctica."


Fundamentally, the economic question isn't just "is Starship cheaper than Martian materials?", the question is "is reusing Starship on Mars and building a new one on Earth cheaper than deadheading Starship back to Earth?"

[Twark_Main]

Why not?  Starships could be split in half for quonset type buildings for crop growing or even habitats.

Buildings on Mars need to be pressurized, so you want to keep the (nicely Earth-tested and qualified) pressure hull intact whenever possible.

That pressure test certification sticker is the truly valuable / expensive part, not the raw material.

Of course you might reuse some damaged hulls as quonset huts to cover machinery (no agriculture or people inside though), but the distance between "minor hull damage that can be repaired and used as a pressure vessel" and "hull too damaged to even trust it as a quonset hut" might not be very large...

[meekGee]

2x per synod means that 65 years after the first ship, you’ll be sending 1 billion ships per synod. I think we’ll saturate WAY before that… and it won’t take a century to do so.


Even 1000 ships per synod is a freaking lot. 100,000 people per year. I don’t think you’ll have enough people who can afford $1 million ticket prices to pay for that. (And ticket costs won’t go lower without reuse…)

Making 1000 ships per synod would likely cost around $50 billion per year. 1 billion ships per synod is like quadrillions of dollars per year.

I don’t think learning curves for things made out of real minerals will keep reducing in costs like that. (Semiconductors can because you’re just getting things thinner or smaller, so material costs are similar but performance keeps rapidly improving.). I don’t think it’s reasonable to expect more starships to be made than airliners per year.

Exponentials with a fast doubling time but without an eventual logistical curve will just yield nonsensical conclusions.

A billion ships per synod would imply over 100 Terawatts of energy on average, when you include all the tankers and stuff. You would destroy the atmosphere. I think launch rate limit for chemical is somewhere between 10 and 100 million tons IMLEO per year before big atmospheric constraints start to take hold. This would be about 1000 times that.



Realistically, I’d put it at 10 doublings. 1000 made ships per synod. Reused 10 times for Mars (far more for tankers etc), and that’s 10,000 ships sent to mars per synod or about 100,000 to 1 million passengers per synod, depending on ratio of cargo to people.

Oh come on - Where did I say they're going to double every synod for a century?  I know you can read better than that.

I said it will take 10 doublings (20 years) to get to thousands of ships.

I said it'll take a century to get to the point where making Starships (or equivalent) on Mars will be so easy that you'll shrug off the benefits of having landed ships available for use on the surface.

I said that as long as there's a doubling every synod, sending ships back doesn't make sense.

What I think will happen after 20 years is that ships will become much larger and operate only orbit-to-orbit, with Starships mostly remaining local to their planet, used for up-and-down traffic.

At that point, they'll be like tankers, and definitely get reused.

[Coastal Ron]

Why not?  Starships could be split in half for quonset type buildings for crop growing or even habitats.

Buildings on Mars need to be pressurized, so you want to keep the (nicely Earth-tested and qualified) pressure hull intact whenever possible.

OK, but if it is vertical it isn't a good place for people to live (i.e. radiation, access, etc.), and laying a Starship down requires lots of internal work.

If you do lay down a ship, slice it in half from nose to tail, lay it on a flat surface and cover it with dirt, you could just inflate a pressure barrier inside of that space - sort of like a big plastic bag. So I'm not thinking it would be difficult to use a Starship in that way.

The same method could be used to line tunnels that are bored into the underground, so it shouldn't be a technique that would be unknown to the inhabitants.

Too many knowns to know for sure what the first colonists will need, and what they will be capable of doing, but if they want to use a Starship, then splitting it may be an option...

[Twark_Main]

Why not?  Starships could be split in half for quonset type buildings for crop growing or even habitats.

Buildings on Mars need to be pressurized, so you want to keep the (nicely Earth-tested and qualified) pressure hull intact whenever possible.

OK, but if it is vertical it isn't a good place for people to live (i.e. radiation, access, etc.)

Eh, I don't think this is a given.

For radiation, chopping the Starship in half makes it much easier to bury. All you really need is a vertical Reinforced Earth Regolith retaining wall, then shovel a couple meters of washed regolith on the floor of the "Concert Hall." Top with organics and plant, and now you're using that huge window to grow food and oxygen. 

As for access, I haven't seen any compelling argument that Starship is suboptimal. I have seen a lot of silly Starship interior concepts, of course.

and laying a Starship down requires lots of internal work.

Personally I don't like the concept of laying Starship down, but presumably if you wanted to go that way you would plan out the interior with that in mind, building it out like that on Earth.

If you do lay down a ship, slice it in half from nose to tail, lay it on a flat surface and cover it with dirt, you could just inflate a pressure barrier inside of that space - sort of like a big plastic bag. So I'm not thinking it would be difficult to use a Starship in that way.

A non-rigid pressure barrier will just inflate to form a cylinder, so your quonset hut won't sit flat on the ground.

A rigid pressure barrier with a flat floor will have sheer stress, which makes it highly inefficient (ie not a thin-walled pressure vessel).

If you want to lay down a pressure vessel, don't try to cut a cylinder in half. It's a classic mistake. If you want a flat floor, just build one (or more) inside a full cylinder.

The same method could be used to line tunnels that are bored into the underground, so it shouldn't be a technique that would be unknown to the inhabitants.

It's not really the same.

In tunneling the liner doesn't hold any air pressure load. You're relying on the surrounding rock (probably reinforced with grout and rock anchors) and/or the surrounding ambient earth regolith pressure.

With a quonset hut, the lifting force of the internal atmosphere would be far greater than the weight of the shielding regolith above.

[MickQ]

This talk of hundreds of Starships per synod makes me cringe 😖.

Good thing they're not using the right numbers then.   

https://twitter.com/elonmusk/status/1217993568482025472?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1217993568482025472%7Ctwgr%5E60a93852e8fe3e75505547bd4f23de4364f79e95%7Ctwcon%5Es1_&ref_url=https%3A%2F%2Fwww.businessinsider.com%2Felon-musk-plans-1-million-people-to-mars-by-2050-2020-1

Even worse.   That’s 33.33 ships per day leaving Earth and arriving at Mars.  That’s more than 30 ships landing each sol for a month.  The landing zone will look like a corn field .

Processing that many ships in essentially a vacuum, even over a 2 year period, to get them cleared out before the next synod’s fleet arrives    Not possible without manning and infrastructure that will not be available until our grandchildren’s grandchildren’s grandchildren are having kids.

[meekGee]

This talk of hundreds of Starships per synod makes me cringe 😖.

Good thing they're not using the right numbers then.   

https://twitter.com/elonmusk/status/1217993568482025472?ref_src=twsrc%5Etfw%7Ctwcamp%5Etweetembed%7Ctwterm%5E1217993568482025472%7Ctwgr%5E60a93852e8fe3e75505547bd4f23de4364f79e95%7Ctwcon%5Es1_&ref_url=https%3A%2F%2Fwww.businessinsider.com%2Felon-musk-plans-1-million-people-to-mars-by-2050-2020-1

Even worse.   That’s 33.33 ships per day leaving Earth and arriving at Mars.  That’s more than 30 ships landing each sol for a month.  The landing zone will look like a corn field .

Processing that many ships in essentially a vacuum, even over a 2 year period, to get them cleared out before the next synod’s fleet arrives    Not possible without manning and infrastructure that will not be available until our grandchildren’s grandchildren’s grandchildren are having kids.

Well if they land and don't have to come back, there's another good argument for one-way ships.

[jimvela]

Processing that many ships in essentially a vacuum, even over a 2 year period, to get them cleared out before the next synod’s fleet arrives    Not possible without manning and infrastructure that will not be available until our grandchildren’s grandchildren’s grandchildren are having kids.

I think processing 1000 ships per departure window won't happen right away.

But it's worth noting that twenty years ago I would have insisted that it was "impossible" for anyone to create and operate a 4500+ spacecraft LEO constellation that would need replacing of individual spacecraft in 3-5 years time.  And "inconceivable" that any commercial service would be potentially profitable in the course of doing that.

I'd have said something about maybe in grandkids' grandkids' time frame.

And here we are.

[TheRadicalModerate]

Would the Starships need the TPS to land on Mars?  If not, those without TPS can be repurposed in order to handle a little more cargo, or radiation protection for habitats.

Even if you were willing to propulsively enter LMO (and that requires a very small payload/crew module and a fairly long transit time), entry speed would still be >3000m/s, which is roughly four times the energy of a Falcon 9 core.  You might be able to do that with stainless steel, but it seems a lot more sensible to use the TPS.  The TPS is what lets you get close to the theoretical max payload numbers.

I suspect that very short transit times are going to be a big selling point for Starship, and that requires aerobraking into LMO or doing direct EDL at the highest possible speeds.

[meekGee]

I want to state the observation made upthread more precisely:

Assuming 2x growth per synod for 10 synods, at any point during this growth, when Earth's industry is able to send X ships on the next Synod (and this works for X=1 or 512), Mar's industry won't be able to turn around that many ships in time for the next synod.

Consider if X=256, this means last synod was only 128 ships.  Where would they store all the propellant?  When would they have made it?  With what equipment?  Where's all the ground handling equipment coming from?

In order to process amd recycle those 256 ships in the 3 months before they have to leave, there must be a base that would have required many more landings, and many more years, to construct.

If OTOH, they just land and that's it, then there's no need for this capability, but also the landed ships actually help propel the base forward, being storage tanks and other core components themselves...

[TheRadicalModerate]

A lot of arguments against reuse boil down to assumptions that energy, propellant, etc, will never be sufficiently cheap to make it worthwhile… which also kind of implies energy and propellant costs too high for a viable largely-self-sustaining Mars city. So what’s the point of this exercise if sending thousands of people to Mars if stuff on Mars always is gonna be too expensive to reuse Mars ships?

I think people aren’t really following the logic far enough.

Yes, it’s challenging to economically justify Mars ship reuse, just like it’s challenging to justify full reuse of space launch, just like it USED to be hard to justify partial reuse (back when 10 flights per year seemed like a lot)…
…but if you exclude that reuse, you’re excluding the possibility of reaching that eventual end state.


The end goal is millions of people on Mars. You ultimately can’t be relying on just using Starships for buildings, etc. you need to have cheap energy. You need to have costs low enough that the typical middle class person could potentially choose to go. Those are the requirements. Excluding reuse because of high energy costs, etc, is including assumptions that preclude that end goal and create passenger costs too high to make the end goal viable.

If you have millions of people on Mars, it'll be just another air route.  But even airlines prefer to avoid deadheading planes back without fairly full cargo or passengers.

And the need to deadhead depends on how many passengers return to Earth (you seem to think that it's very few, which I think is probably wrong) and what the ratio of passenger flights to cargo flights is. (I'd take a SWAG that it's about 1:10 for the first ten synods, and maybe it drops to 1:1 within 100 years.)

The cost of the hardware is going to be nowhere near the dominant cost for a deadhead.  Even if you have unrestricted access to water, and power equipment (PV, nukes, whatever) comes from Earth for only a few hundred bucks a kW, the opportunity costs are huge.  Why return a few million in obsolete capital equipment instead of building out your base/colony faster?  Ultimately, SpaceX makes millions of bucks per colonist if the full Elon fever dream comes true.  Even if passage is only a few hundred $K, it's a company town, and hauling the capital equipment to get it to the point of self-sufficiency will swamp the cost of moving the meatware.  So feeding power into anything other than deadheading will be a winner.