Will Mars-bound Starships actually be reused?

[steveleach]

There have been extended subthreads in a couple of other threads recently (and not so recently) discussing the idea that Starships will be so cheap to build that they won't be worth returning to Earth and reusing. Continuing those discussions there risks dragging them increasingly off-topic, so I thought I'd see if a new thread dedicated to that question will take off instead.

Everything I've seen from Elon and SpaceX suggests to me that they are expecting to reuse Mars Starships, but a lot of that information is old and so things might have changed. Things might also change in the future as they learn more.

Obviously some ships will be returned, when people need to return. And some ships will not be, maybe because they are obsolete or broken. I'm discussing the bulk of the fleet here.

Some points in favour of reuse...

* Elon is on record saying - multiple times - this is the plan
* The cost per mission of the vehicle is obviously a lot lower if it supports multiple missions
* Starship's current design only really makes sense if it needs to support two-way Earth/Mars transport

Some points in favour of one-way use...

* The materials used from scrapping the vehicle might be useful to the colonists
* They will need a lot less ISRU fuel production
* Starships being reused may need to spend a lot of time between missions just sat on Mars doing nothing
* The ship design could be optimised for one-way use

So what does everyone think? When we look back on the development of the first city on Mars, will the majority of the ships used to transport the people and material for it have been used just once, or multiple times?

[InterestedEngineer]

I think the first 50-ish starships will be one-way, with a few test returns when ISRU is running.

If starships cost $30M to mass produce then it'll save complicated cargo handling to build the first habitats out of the starships themselves.

Simpler than removing pieces habitats from a cargo starship and assembling them on the ground is to use 2 starships to lower a 3rd human rated starship to the ground flat. 

Human rated starships will already have 1-2m of plastic radiation protection, some can be added by lowering into a trench or a built-up berm.

When colonization takes off, then reuse will start in order to get the cost down.

at $20/kg to LEO, that's $15M in fuel/cargo costs.   With ISRU it'll drop the cost from $45M to $15M to get to Mars and back, a factor of 3 improvement.  So in the long run even a a very low cost of $15M/Starship still wants to be reused.

[waveney]

Well I have been looking at this in some detail for my book on early colonists of Mars (work in progress  for many many years...)

I think the majority of the starships for the first few cycles will remain on Mars.   A few will return with a few people.   This is likely to change from about the 4th/5th colonisation cycle when there is sufficient Mars infrastructure to catch, refuel and relaunch them back to Earth.   The early ships will be used as living quarters, storage tanks for the ISRU plants, cut up and recycled.

When they are able to send a few ships back, I have been wondering if they will send raptors back to be reused.  They could, but will it be worth it?

[lykos]

Many will go to Mars.
Most will stay. (Special the Cargo-SS)
Some will come back. (With people and for experience)
No need to do a second flight to Mars.
(There will be plenty of brand new (and better!) ones)

Reuse is for LEO (cargo/tanker and tourists) and Moon (crew and cargo)

[meekGee]

The point I made elsewhere is that unlike a rapidly reused ship (think tanker)tl that gets reused maybe 100 times per synod, a Mars ship gets used once every two synods, or maybe once per synod if you're willing to spend a large amount of propellant and reduced payload.

Not only that, but the financial incentive is spread over 20 years instead of two.  Basically, you won't feel the savings until a decade has passed.

Someone else pointed out that a decade later the ships will already be obsolete or worn down from surface and interplanetary wear.

I feel ship tanks on the surface are a 1:1 necessity for ISRU so why send them back...

Send the engines maybe, since they don't suffer from static wear, and there's no use for them on the surface. Definitely there will be use for various batteries, electric motors, valves and pumps. Those are things you'll need to ship, so just plan surface-use for them.

The only time IMO ships will go back is when Mars is so advanced that making thousands of storage tanks locally is easier, and messing with the ship becomes a nuisance...   (And the occasional crews heading back)

This point is not 50 ships away or 5000 or more.  Even on Earth making Starships was a giant industrial effort, not to mention making thousands of them.

SpaceX meanwhile says they'll reuse them. Last time they said that though was when SS was ITS, 12 m, and carbon fiber.

The nice thing is that soon we will get to see what happens.  What's a few years to wait?

[Alx]

One Starship left on Mars means 100 tons less precious equipment delivered in next two years.

[meekGee]

Another note about crews heading back.  While the possibility of going back should be open, I think most people won't.

Part of it is the fractional gravity for several years.  Another is that as people become experienced, their value increases since they know how stuff is done, they own a certain corner of colony life, and they're sort of elevated above the noobs - and that's a huge incentive to stay.

Go back to earth, to 1 g, and not only are you not an "old hand", but you've been out of it for several years.  That doesn't  sound like fun.

[nycdotnet]

A small percentage of Mars-bound Starships will be re-used for the return journey to Earth.  Some may be re-used for journeys to other bodies in the Solar System.

It is very unlikely that any Mars-bound 9 meter Starship that returns to Earth will ever be re-used, though, because by the time a ship makes it to Mars and back, its design, systems, and engines will be antiques.  The earliest this could possibly happen is in the early 2030s using a ship manufactured in the late 2020s.

In the future, assuming Mars colonization has kicked-off in earnest, the ships then will plausibly be re-used, but they will probably not be the 9 meter Starships we see today.

Note: By reused I mean "sent for a second journey to Mars".  I expect they will be scrapped and the materials used to build new 12+ meter ships.

[Robotbeat]

Space shuttles were used for about 3 decades. That’s enough for 7 to 14 uses.

[steveleach]

It is very unlikely that any Mars-bound 9 meter Starship that returns to Earth will ever be re-used, though, because by the time a ship makes it to Mars and back, its design, systems, and engines will be antiques.  The earliest this could possibly happen is in the early 2030s using a ship manufactured in the late 2020s.

On this point, does it actually matter if there are more modern ships available? If your 20 year old ship can still get to Mars and back the way it always has done, will it really be a problem if it can't haul quite as much as some other ships in the fleet?

[meekGee]

Space shuttles were used for about 3 decades. That’s enough for 7 to 14 uses.

Remember the assumption that for the foreseeable future, the Mars colony is ever-growing.

So each year you need more ships.

To make it simpler, let's say the size of the outbound fleet increases by 2x each synod.

2 ships head out on synod 0
..
2000 ships head out on synod 9, 20 years later.
...
And so on, until it will linearize at some point.


Keep in mind that as you increase your production rate, newer ships are cheaper.

Also, any reused ships only make an impact on how many you have to build at least 2-3 synods down the line from when it was launched (depending on whether you can turn them around on either end without losing a synod.)  So AT BEST, you're reducing the amount you have to manufacture by 25%.  More likely by 12.5%.  Even less considering economics of scale and cost of money.

This multi-synod lag in the midst of an exponential growth period is a real downer.

It is very different from a once-and-done static fleet like Shuttle, where if you fly 20 times, you theoretically saved 95% of the cost.

[r1279]

What's the value and priority of the electricity, water reserves and atmospheric gases on Mars used to generate the propellant to send a ship back?

Unquestionably we need propellant to send people [and some scientific/engineering samples] back and have emergency reserves, but beyond that wouldn't those resources be better allocated to construction, fabrication, industrial processes, farming, recycling and mining/refining?

[That plus a ship bringing 150-200t of cargo is also 80-100t of useful metals and components, including the engines for its alloys.  Use that electricity for melting and reforming the metal.  Producing 100+ ships per year on Earth should keep the cost of replacement low]

[InterestedEngineer]

It is very unlikely that any Mars-bound 9 meter Starship that returns to Earth will ever be re-used, though, because by the time a ship makes it to Mars and back, its design, systems, and engines will be antiques.  The earliest this could possibly happen is in the early 2030s using a ship manufactured in the late 2020s.

On this point, does it actually matter if there are more modern ships available? If your 20 year old ship can still get to Mars and back the way it always has done, will it really be a problem if it can't haul quite as much as some other ships in the fleet?

Does anyone fly the original 737 any more?

737-200?   Barely, a few third world cargo airlines.

Now triple the depreciation curve rate on a 737.

Now when the Starship equivalent of a mature 737-600 (NG) comes out, then reuse might make more sense as the volumes of Starships goes up and production levels level off.

[meekGee]

We should talk about what it takes to reuse a Mars ship right away.

Normally, an outbound ship lands after the inbound launch window closes. Even if you try to fly faster (which costs a LOT of fuel/payload) you still have to figure on the time it takes to unload and refuel.

(And of course the huge cost in terms of Martian resources to refuel - all the power that could have been used to do other things, like make plastics, or concrete, or grow crops, or power digging machines...)

So the solution is to take an opposition trajectory back.  You can leave later, but it's a larger dV, more propellant spent, higher reentry velocity, and Venus assist is not always available. 

And even if you do that - you still arrive on Earth very late, with very little time before the beginning of the next launch window, and you need to inspect this ship (which has gone through a very rigorous 2 year mission) relaunch it, refuel it, and still leave on time.

Not impossible, but it has a lot of cost associated with it - which you need to compete against the cost of a new ship, and the loss of benefits of having that ship on Mars providing 100 tons of tankage, batteries, motors - which you now have to launch from Earth.

I don't see this as a winning trade.

[Robotbeat]

It is very unlikely that any Mars-bound 9 meter Starship that returns to Earth will ever be re-used, though, because by the time a ship makes it to Mars and back, its design, systems, and engines will be antiques.  The earliest this could possibly happen is in the early 2030s using a ship manufactured in the late 2020s.

On this point, does it actually matter if there are more modern ships available? If your 20 year old ship can still get to Mars and back the way it always has done, will it really be a problem if it can't haul quite as much as some other ships in the fleet?

Does anyone fly the original 737 any more?

737-200?   Barely, a few third world cargo airlines.

Now triple the depreciation curve rate on a 737.

Now when the Starship equivalent of a mature 737-600 (NG) comes out, then reuse might make more sense as the volumes of Starships goes up and production levels level off.

Plenty of 30 year old planes are still flying.

More than 30 years doesn’t really matter to the economics of Starship, so probably best ignored.

But 7-14 potential reused is not nothing, it is roughly the average reused of Falcon 9. And it’s possible the ships could be used at Mars and Earth for other purposes while waiting for the planets to line up.

[Coastal Ron]

It is very unlikely that any Mars-bound 9 meter Starship that returns to Earth will ever be re-used, though, because by the time a ship makes it to Mars and back, its design, systems, and engines will be antiques.  The earliest this could possibly happen is in the early 2030s using a ship manufactured in the late 2020s.

On this point, does it actually matter if there are more modern ships available? If your 20 year old ship can still get to Mars and back the way it always has done, will it really be a problem if it can't haul quite as much as some other ships in the fleet?

Does anyone fly the original 737 any more?

737-200?   Barely, a few third world cargo airlines.

Now triple the depreciation curve rate on a 737.

Now when the Starship equivalent of a mature 737-600 (NG) comes out, then reuse might make more sense as the volumes of Starships goes up and production levels level off.

Plenty of 30 year old planes are still flying.

More than 30 years doesn’t really matter to the economics of Starship, so probably best ignored.

But 7-14 potential reused is not nothing, it is roughly the average reused of Falcon 9. And it’s possible the ships could be used at Mars and Earth for other purposes while waiting for the planets to line up.

The U.S. Air Force still operates versions of the Boeing 707, which ended production back in the mid 60's, so 60 years old or more, and they also operate the Boeing B-52, which ended production back in 1962.

A lot of factors are involved in whether it makes sense to keeping using a complex hardware system, but I'm thinking the early Starships should be able to get a couple of mission done before they are retired in favor of newer designs.

[redneck]

It is very unlikely that any Mars-bound 9 meter Starship that returns to Earth will ever be re-used, though, because by the time a ship makes it to Mars and back, its design, systems, and engines will be antiques.  The earliest this could possibly happen is in the early 2030s using a ship manufactured in the late 2020s.

On this point, does it actually matter if there are more modern ships available? If your 20 year old ship can still get to Mars and back the way it always has done, will it really be a problem if it can't haul quite as much as some other ships in the fleet?

Does anyone fly the original 737 any more?

737-200?   Barely, a few third world cargo airlines.

Now triple the depreciation curve rate on a 737.

Now when the Starship equivalent of a mature 737-600 (NG) comes out, then reuse might make more sense as the volumes of Starships goes up and production levels level off.

Plenty of 30 year old planes are still flying.

More than 30 years doesn’t really matter to the economics of Starship, so probably best ignored.

But 7-14 potential reused is not nothing, it is roughly the average reused of Falcon 9. And it’s possible the ships could be used at Mars and Earth for other purposes while waiting for the planets to line up.

 That seems like a plan. Use the Starships in the Martian economy between times. Phobos and Demos and the Martian surface for local. Near Mars Asteroid Missions? On to the Belt? Building up a Mars orbital infrastructure with local materials? Martian SPS?

[meekGee]

Plenty of 30 year old planes are still flying.

More than 30 years doesn’t really matter to the economics of Starship, so probably best ignored.

But 7-14 potential reused is not nothing, it is roughly the average reused of Falcon 9. And it’s possible the ships could be used at Mars and Earth for other purposes while waiting for the planets to line up.

10x potential reuse does not mean 10x reduction in cost - not even close.

In order to reach a fleet of 2000 ships, you need to double the fleet every synod for 10 synods. (~20 years) 

But when you double the fleet, even if you could reuse each and every ship you've ever built, you still need to make the same amount all over again.  E.g. if last time you launched 512, and you can reuse all of them, you still need to make another 512 new ships in order to meet the 1024 goal.

So as long as you're growing, even if you had infinite reusability, and only a 1-synod cycle time, it only buys you a 2x factor in cost - before factoring in economies of scale (since the new 512 are 20% cheaper than the last 256, and 44% cheaper than the last last 128, etc...)

And if it takes 2 synods to recycle, it immediately gets much much worse. If you could reuse all 256, and need to launch 1024, you still need to make 768 new ships...

So it's just not true that you can save multiple X on the cost.  In reality reuse with long lag time will save only a small fraction - but has a large cost associated with it.

This effect only goes away once exponential grows dies down - but that's a long way away, and probably several generations of Starship design too.

[oiorionsbelt]

"Will Mars bound Starships actually be reused?"
 Given the "unreasonably cheap" potential of Starships and the time between synods, most reuse after landing on Mars, may be focused on Martian P2P, Martian moon trips and journeys to the outer solar system. Only a few being reused in Earth bound missions.
 

[steveleach]

It seems that the majority of people posting in this thread think that SpaceX have, or will have, changed their minds on reuse of Mars-bound Starships.  I'm not sure I agree with that consensus myself.

It will be interesting to find out whether this is another case of Elon having a plan that is too revolutionary for people to get their heads around until they see it actually happening, or SpaceX just coming up against the cold realities of the engineering and economics of the situation.