Will Mars-bound Starships actually be reused?

[Brigantine]

I can imagine Mars starships returning to LEO, but not to Earth. Why would you lug heat tiles all the way to Mars and back?

[spacenut]

Using some Starships for Sabatier processed fuel and water storage.  Those Starships could have their engines removed and shipped back to earth, or use them for replacement of a damaged engine on a returning Starship.  As noted previously, bringing a crane that can be assembled on Mars to remove upper cargo/crew of a Starship and take it to a prepared colony area away from landing/launching area would be nice.  Remember at about 0.38 gravity, a crane doesn't have to be as robust as a crane on Earth.  For extra mass on the crane for lifting, a container area on the rear of the crane could be filled with Mars regolith, by a another piece of equipment with a grading/scoop similar to a Bobcat. 

Front end loader was what I was thinking about. Since equipment on Mars would be electric, batteries may well serve as the offset mass for loaders and cranes.  Equipment should be designed for assembly by spacesuit wearing crews, and modular.  For instance, a front end loader could have a scraper attachment or a backhoe attachment, as well as being a truck or able to haul a trailer for hauling ice to the reprocessing Starship. 
 

[Robotbeat]

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.

[meekGee]

NOT reusing the starships puts a floor on the price that SpaceX can reasonably afford to charge passengers to Mars, and that floor is like $500,000-$1,000,000. If you reuse them, you could make reduce that cost to a third. That's not a small thing.

I'd be surprised if it saves even 50%, and then you need to add back the cost of shipping the ISRU storage tanks and other parts, also per colonist, from Earth.   This is also part of the floor.

But here's a fun fact.  Common learning curve discount is 20% per doubling in production volume.
When you go from two ships to two-thousand (10 doublings), the cost per ship goes down to 0.8 ^ 10 = 0.1 of the original cost.
This is what they should focus on.

You could use that argument to justify only using cars for one trip though: think about how many we would need to build, and how many doublings that is, so how cheap the cars would be using that formula.

The difference is that cars can be used more often than once every two years, and the size of the car fleet is not forecast to expand 100 or 1000x in the next couple of decades.

I was not arguing against reuse in general.

[Robotbeat]

NOT reusing the starships puts a floor on the price that SpaceX can reasonably afford to charge passengers to Mars, and that floor is like $500,000-$1,000,000. If you reuse them, you could make reduce that cost to a third. That's not a small thing.

I'd be surprised if it saves even 50%, and then you need to add back the cost of shipping the ISRU storage tanks and other parts, also per colonist, from Earth.   This is also part of the floor.

But here's a fun fact.  Common learning curve discount is 20% per doubling in production volume.
When you go from two ships to two-thousand (10 doublings), the cost per ship goes down to 0.8 ^ 10 = 0.1 of the original cost.
This is what they should focus on.

You could use that argument to justify only using cars for one trip though: think about how many we would need to build, and how many doublings that is, so how cheap the cars would be using that formula.

The difference is that cars can be used more often than once every two years, and the size of the car fleet is not forecast to expand 100 or 1000x in the next couple of decades.

I was not arguing against reuse in general.

But we’ve seen that even reuse of just 7-15 times makes a huge difference in cost. Not 7-15, sure, but 2-3x definitely and that makes a huge difference in the end!

[meekGee]

NOT reusing the starships puts a floor on the price that SpaceX can reasonably afford to charge passengers to Mars, and that floor is like $500,000-$1,000,000. If you reuse them, you could make reduce that cost to a third. That's not a small thing.

I'd be surprised if it saves even 50%, and then you need to add back the cost of shipping the ISRU storage tanks and other parts, also per colonist, from Earth.   This is also part of the floor.

But here's a fun fact.  Common learning curve discount is 20% per doubling in production volume.
When you go from two ships to two-thousand (10 doublings), the cost per ship goes down to 0.8 ^ 10 = 0.1 of the original cost.
This is what they should focus on.

You could use that argument to justify only using cars for one trip though: think about how many we would need to build, and how many doublings that is, so how cheap the cars would be using that formula.

The difference is that cars can be used more often than once every two years, and the size of the car fleet is not forecast to expand 100 or 1000x in the next couple of decades.

I was not arguing against reuse in general.

But we’ve seen that even reuse of just 7-15 times makes a huge difference in cost. Not 7-15, sure, but 2-3x definitely and that makes a huge difference in the end!

That's because the reuse happened quickly, and the size of the fleet hadn't changed significantly over that timeframe.

Also, there was no alternate value to once-used Falcons like there is to landed Starships on Mars.

[spacenut]

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. 

[Robotbeat]

If Mars can’t progress rapidly from everyone living in basically converted airliners, they’re never gonna make it and this whole exercise is moot.

You can’t settle Mars permanently that way.

[spacenut]

Why not?  Starships could be split in half for quonset type buildings for crop growing or even habitats.  They could be made as long as you want them.  At least initially. 

Sooner or later, almost all Starships will return for more equipment, pre constructed habitats, etc.  Like I said, if engines on Starship that are repurposed into tanks, storage, or initial habitats, could be returned to be reused on more Starships, as they would be the most expensive parts that could be returned. 

Who knows?  I would think SpaceX would do cost studies on the way forward after initial landings on Mars. 

[Robotbeat]

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.)

[Robotbeat]

It’s a lot like the argument that Vulcan ACES (back when that was a thing) won’t need recovery and reuse of ACES because it’ll just be used for stuff in-orbit. Every ACES delivering a new ACES in space stage.

It’s an assumption that either implies low flight rate or some weird obviously unsupportable growth rate. You’ll quickly saturate useful purposes of ACESes up there.

[steveleach]

NOT reusing the starships puts a floor on the price that SpaceX can reasonably afford to charge passengers to Mars, and that floor is like $500,000-$1,000,000. If you reuse them, you could make reduce that cost to a third. That's not a small thing.

I'd be surprised if it saves even 50%, and then you need to add back the cost of shipping the ISRU storage tanks and other parts, also per colonist, from Earth.   This is also part of the floor.

But here's a fun fact.  Common learning curve discount is 20% per doubling in production volume.
When you go from two ships to two-thousand (10 doublings), the cost per ship goes down to 0.8 ^ 10 = 0.1 of the original cost.
This is what they should focus on.

You could use that argument to justify only using cars for one trip though: think about how many we would need to build, and how many doublings that is, so how cheap the cars would be using that formula.

The difference is that cars can be used more often than once every two years, and the size of the car fleet is not forecast to expand 100 or 1000x in the next couple of decades.

I was not arguing against reuse in general.

Yep, I get the difference. Fundamentally, though, that argument doesn't have much power without the details, and the details simply aren't known at this point. We can all plug in whatever values we like for the variables; when you plug in yours, it says reuse isn't viable. When I plug in mine, it says it is.

[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)

[steveleach]

(until starship is superseded)

Why stop there?

There are plenty of old cars & trucks on the road, even though new models are now available. Plenty of old aircraft still flying, ships still sailing, trains still rolling.

[spacenut]

Mars first Starships will have to have landing legs.  Like someone said, until a catch tower can be made. 

I often wonder why not specialize Starships.  One for Mars shuttle between Mars and Mars orbit, one for Earth between Earth and LEO.  Then many for use in space only to ferry material and people between the planets.  Develop larger docking rings for transfer of materials and people. 

[Robotbeat]

I believe that likely will happen (already is happening with Artemis), but I think it helps conceptually to think of them as the same vehicle. Also, if there aren’t a lot of missions, it might not be worth it to pay the cost of developing separate, specialized ships. Also, if ships are more general purpose, they can be reused more.

[waveney]

(until starship is superseded)

Why stop there?

There are plenty of old cars & trucks on the road, even though new models are now available. Plenty of old aircraft still flying, ships still sailing, trains still rolling.

There aren't many 45 year old vehicles doing useful work.

At some point people will wont some thing bigger, much bigger.

[SDSmith]

(until starship is superseded)

Why stop there?

There are plenty of old cars & trucks on the road, even though new models are now available. Plenty of old aircraft still flying, ships still sailing, trains still rolling.

There aren't many 45 year old vehicles doing useful work.

At some point people will wont some thing bigger, much bigger.

True.

Look at the DC-3. it is still flying after 70 years.
https://en.wikipedia.org/wiki/Douglas_DC-3#DC-3_after_70_years

[meekGee]

It’s a lot like the argument that Vulcan ACES (back when that was a thing) won’t need recovery and reuse of ACES because it’ll just be used for stuff in-orbit. Every ACES delivering a new ACES in space stage.

It’s an assumption that either implies low flight rate or some weird obviously unsupportable growth rate. You’ll quickly saturate useful purposes of ACESes up there.

No it's not.

The basis of the "reuse doesn't help" argument is the one-two punch of very long reuse cycle time (2-4 years), and exponential growth for the next couple of decades.

Take one of those away, and the argument doesn't work.

I am not arguing against reuse in general, which is what you're counter-arguing against in many of the posts upthread.

--

Then, the point where mars can manufacture thousands of tanks and large motors and batteries and fuel so easily that it has little value for the same goods that just landed from Earth - that point is easily a century from now.

Even on well-mature industrial Earth, with an 8 billion soul economy, Starship is an industrial program of note, and wait till they make thousands of them.

By the time Mars can shrug off such goods sitting on the surface, Starship as we know it will be part of history.

[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?