We have the technology to spin a spacecraft. Landing, building an automated smelter powered by mouse fart solar power or who the hell knows what and then launching again from mars a little less so.

Sure. We can spin a spacecraft. To get a 9 meter diameter spacecraft (Starship) up to 0.3g you'd have to spin it at 5.5 revolutions per minute. That means any given point on the skin of the spaceship is moving at 11.5 miles per hour. Add in, that with only a diameter of 9 meters the acceleration gradient between your head and feet will be severe.

If you are talking about spinning a larger ship or station, we can't do that any more than we can land on Mars, build an automated smelter, etc. Both are serious engineering problems and both are equally hypothetical at the moment.

Instead of a starship, it needs to be a ring. With the atmosphere and geography in the inside of the ring. Terrestrial tests are already underway.

They call that Coriolis effect in the Expanse books, and people closer to the center of spin (usually the poor) feel it much worse than those on higher levels (the more well off).  But they are spinning I think huge asteroids in The Expanse, not things less than 10m in diameter.

You would not spin Starship around its central axis.

You would link 2 Starships, nose-to-nose, with a scaffold like structure connecting them.  The effect of spin gravity now pushes 'down' such that the floor in space is the same as the floor when landed.  The longer the scaffolding the less spin you need.

Also probable to place a 3rd Starship at center point hub.  0G, cargo, etc.

Multiple ships provide a bit of emergency redundancy as well.  Move everyone to the healthy ship(s) while conducting underway repairs.

Ships come up to speed separately then link up in transit.  Ships separate prior to deceleration.

Want to get fancier?  Link more starships like the spokes of a wheel.

Be easier to just use a tether instead of scaffolding.

NASA has been testing them back to the Gemini days.

I don't know if there has been research that provided new data since then, but a few decades back there was a statement that to prevent any problems for the human body, the fastest you wanted to spin a station is one revolution every three minutes.

So what would be the required minimum diameter to spin no faster than that but still get .3g?

Looks like a radius of 2980.864156698396 meters.

https://www.artificial-gravity.com/sw/SpinCalc/

I think that Space X engines run on Methane. The good thing about Mars is that there is plenty of methane in the atmosphere.

I stand correct. It won't happen again.

And my memory may have inverted the data, since that site says that tests in 1977 showed that 3 rpm caused symptoms in test subjects, but at 1 rpm even the most sensitive test subjects didn't have any trouble.

ETA: And the calculator shows at 3 rpm you would need a radius of about 30 meters (diameter of 60 meters) for 0.3g, but warns that some people will require some time to adapt to the spin.  2 rpm is apparently the limit on the whole range of test subjects not needing time to adapt to the spin, and for 0.3g that would require a radius of 67 meters (diameter of 134 meters).

There is little to no methane in the atmosphere of Mars.  They have to convert Carbon Dioxide to Methane.

The atmosphere of Mars is around 95% CO2, but it may be easier and cheaper to mine frozen CO2 (dry ice) from the polar regions as the density of the dry ice is about 78K times that of the atmosphere.

A 1 rpm rotation to create 0.3 g would have a radius of 268.2777741028556 meters which would be much easier

So when we carry super heavy boosters into space to make into hab space, that's 135 super heavy sections in the rim of a circular station, and 43 on each spoke.  No problem
But of course you don't have to build the full ring right away (the ring is something like 2.25 million SF of floor space if there's only 1 level in each super heavy).

I need to look at Daniel Suarez's book Delta V to see what numbers he used.  He had a ship with 3 spokes and a pod on each end, spun for gravity during a long-term asteroid mining mission.

Edit:

I was going to say that 1 RPM sounded better to me too.  That would help things a lot.  That's only 8 super heavies to make a full diameter spoke.
(but muh 2.25 million SF of floor space )

Thanks for clarifying that for me.

Running through different numbers, the spin calculator indicates that 2 rpm shouldn't cause any problems for anybody, and for 0.3 g that would require a 67 meter radius.

It doesn't need to be a solid ring or solid spokes though.  

One Starship with a long tether attached to a counterweight (maybe another Starship) at the other end would work, and they simply revolve around a common axis.

One thing to remember about using a long object as the hab space and spinning them is that the calculation for gravity is at a specific distance.

So, if you get the gravity at the middle to where you want it, you will have less gravity at each end of the hab space.  You will need to curve the booster to get gravity that is continuous over the length of the hab space.

One more thing to think of is that the bottom of a 9 meter booster section would have about a 0.05 g difference than the top part under certain circumstances (2 rpm).

If you make a much longer radius, then the difference will be much less.

You can stack boosters next to each other though (side by side) to get more space

Methane is THE fundamentally operand in the entire Mars equation; within the context of SpaceX operations.

I was thinking more of a station than a transport.  Having to spacewalk from section to section would be a real drag.

I remember the bolo from Stephenson's Seveneves.  I suppose it could be done with modern control methods, but just getting the bolo balanced and working together, and then moving it somewhere by adding energy on the outside units while maintaining the balance, makes my head hurt.  Failure modes seem scary compared to even a truss (connection solid if not pressurized).

My original point about spinning a spacecraft was to show that we do not have the capability right now to spin a spacecraft for industrial activity, any more than we have the capability to de-orbit asteroids and refine them on the surface of Mars. Both are difficult engineering problems that need to be solved.

But let's look at the spinning thing.

Let's assume we can build segments of a ring the size of Starship and put them in orbit and tie them together. We'll start with two attached by a beam (we can add more later to fill in the gaps).
Using the spincalc tool:
To get to .3g we need a 75m radius spinning at about 2 rpm. (Note: the whole thing would be 150m in diameter.) The velocity of the rim would be 33 miles per hour.
So each ship would have a 75 meter tower poking out of it attached to a central hub.
An empty Starship weighs about 220,000 lbs (100,000 kg) and I'm going to assume a habitation/industrial module weighs the same once you delete the engines and retrofit the interior volume to contain necessities for life and industrial production. (BTW, you're going to have to balance the masses of each modules.)
So, now we have 440,000 lbs pulling on that central hub from each arm. How much strain is on that connection?

Force = Mass * Acceleration.

Mass is 220,000 lbs (100,000 kg), Acceleration is 33 miles per hour per second (14.8 m/s^s). So the force is 332,717 lbf for each arm on the central spoke. or 665,434 lbf combined. ~330 tons of force trying to rip the central hub in half. I'm sure materials science can make this doable. But it's not insignificant. And it will only get worse as  you add rim segments.

But redoubt, once you get it up to spin there is no acceleration! Not in this case. The rotation creates constant acceleration, otherwise you wouldn't get "gravity."

Another consideration. How do you maneuver? You're going to need course corrections on your way to Mars. Even if you're building a space-station, you may need to avoid orbital debris. But you've created a giant gyroscope. Do you de-spin to make your maneuvers and spin it back up after? How much fuel will that take from your RCS system?

We can probably overcome these issues in the future. But right now, it's a hypothetical as anything else.

I think you need to double check the part in bold.

Then ask yourself: can starship be lifted by a cable at 1G on earth today?  There is certainly no materials science problem with tethering two starships and spinning at 0.3G.

Well, sure math. I got hung up in the rim speed.

So assuming we use .3g as acceleration in that equation we get 66,093 lbf for each side of the arm for a total of 132,186 lbf or ~66 tons of force trying to rip the hub apart. Way better. But as you add ring segments, that number is going to go up.

I think you need to use the formula for centripetal acceleration, not linear.

Assuming:

r = 75m
m = 100,000kg
s = 2.6m/s (circumference is 471m assuming 150m diameter circle, time to 1 rev is 180sec)

Your force ends up being just a tad over 2,000 lbs.

Someone check me, please.

A little late, imperfect but I just had to share this.

Attached File

SpaceX's Roberts Road facility at KSC is set for a major expansion ahead of Starship production, a previously stalled effort on the East Coast.

By Aaron McCrea (@AaronMc286)https://t.co/iYR81PsJiA

Chris Bergin - NSF  (@NASASpaceflight) November 1, 2024

https://www.nasaspaceflight.com/2024/11/roberts-road-10-31-24/

You're way off.

3rpms gives 1g at 99 meters.

CO2 can't be converted to methane because methane has hydrogen in it.

True. But Mars has ice which can be cracked to get your hydrogen. Byproduct is oxygen, so you can breathe.
Suck up some atmosphere and crack the CO2 to get your carbon atom and even more oxygen. Easy-peasy, chemistry-sie.

Hold up a second.

Describe for me, in your own understanding, how the chopsticks on the tower lift and lower the booster/starship?

The original question was 1 revolution every 3 minutes to give 0.3 g.

I just used 0.3 rpm instead of 0.33333333333... which gave the 2980 meter answer above.

If I used the 1/3 rpm (or at least the closest approximation that the web page could handle), the radius is 2414.4999669257013 meters.

Be easier to just mine the dry ice.  Density is much higher than running atmosphere through a converter.

Looks like a new method is out that requires lower temperatures now.

https://phys.org/news/2020-02-method-carbon-dioxide-methane-temperatures.html

The more starships you link the less you have to care about the balance of the contraption. Balance doesn't matter in space anyway.

The water ice was the thing I wanted you to find. Oxygen is produced from CO2 and H2O. CH4 is made. O2 is available for breathing and oxidizing.

On the Moon, steel is strong enough for a space elevator. Mars would require something we don't have yet.
Fun fact: If you enclosed a volume of Earth air at 14.7 PSI on the Moon, you could fly using your own muscle power.

SpaceX's first true Human Landing System prototype.
A structure shrouded in mystery that has been sitting at Starbase for over a year.

Today, that shroud is lifted. This is the interior of the prototype, featuring things such as crew bunks, life support, control panels, ect. \uD83E\uDDF5 pic.twitter.com/u6Gx713wej

TheSpaceEngineer  (@mcrs987) November 2, 2024

Bellyflop should be fun at that angle.

No belly-flop for the lunar landing. Belly-flop is an aerodynamic maneuver to slow the ship and steer it to the landing site. There's no atmosphere on the Moon. The HLS ship won't even have flaps. But it will have legs.

That just looks like some random render of what they guess the interior will look like. For one there is a header tank in the tip with a fuel transfer tube running down the center of the vehicle.

no way

I mean it's only says it in the render itself.

Is it coming back empty?

The HLS will never come back to earth.

Header tank can be moved for HLS. Its location in the nose is to improve center of gravity for reentry that won’t be happening.

It's a depiction of what the current subscale prototype @ Boca Chica looks like inside. It's not a random render, but the config will almost certainly change for the flight article.

They put the header tanks in the nose to balance the ship. They also reduced the size of the front flaps to lower the nose. Why not eliminate the front flaps, and move the header tanks into the main tanks at the top of the tanks, and add strakes or chines to the front end for balance and to house the catch pins? I think Elon talked about deleting the front flaps a few years ago.

The astronauts will be coming back to earth in the Orion Space Capsule.

Orion space taxi.