Fixing Planetoid Hulls

[Jeff M. Hopper]

Well, new data on planetoids shows that they are not as solid as we thought, and that they are structurally more similar to a conglomeration likened to styrofoam more than anything else. This produces a dilemma for two staples of Traveller, the belter and the planetoid hull. Belters have been covered elsewhere and I thought I'd take a stab at the planetoid hull problem.

Solutions include:

A) Handwavium - the problem doesn't exist. We all just ignore it and keep on playing as usual.

B) Slag It - The starship is created as a dispersed structure hull by the rules. This will be the framework around which planetoids are crushed and then layered, with each layer being fused by application of heat or a bonding agent. The dispersed structure framework is considered the "hollowed out" portion of the asteroid ship with the slag on the outside being an extra 20% or 35% of volume depending on which kind of plaetoid hull you'd like. The cost of the ship created using this method is both the cost of a planetoid hull of the final volume and the cost of the dispersed structure framework added together. You'd be essentially just be using the planetoid material as cheap, low-grade armor.

C) Niven It - In his essay Bigger Than Worlds, science fiction author Larry Niven suggests that a NI planetoid can be hollowed out, filled with water, the hole capped, and then heated slowly with solar mirrors while rotating. The planetoid melts from the outside in and when the heat reaches the water, the steam inflates the melted NI and you get a bubble once the whole mass cools down. I think this is plausible for large space structures that would not undergo acceleration or large stresses, like O'Neill colonies and space stations. The cost would be the same for the planetoid hulls we have in canon now, since the only real addition would be the water and the solar mirror - both of which wouldn't be that expensive to acquire.

D) Hot Potatoe - When it comes time to move the planetoid to the shipyard, drop the whole mass inward towards the star it orbits. With the planetoid on an orbit that closely approaches the star, the planetoid will melt and any pockets of gas will vent outward allowing the conglomeration of particles to collapse and coalesce (a tug with repulsor batteries will be needed for attitude control of the planetoid). As the planetoid starts on its outbound leg of its orbit, it will cool by radiative heating. Once it has cooled enough, it is tunneled out and used as a hull. Cost of this planetoid hull would be the same as in canon.

So, do these ideas make sense? What problems would a a ship yard have in using these methods? Are these techniques even plausible?

 

[atpollard]

[discussion moved here]

Originally posted by Bill Cameron:
</font><blockquote>quote:</font><hr />Originally posted by atpollard:
Why do you feel the CT prices are too low? Normal "ships" are made from "Crystal-iron" and "Super-dense", which sound to me like manmade compounds/molecules. A buffered planetiod is basicly a Wrought Iron hull (smelted gravel sounds similar to a cast iron hull).

AT,

CT says that planetoids are merely 'tunneled' out to create hulls. The smelting bit is something I assume may be used in certain cases.

Anyway, ton for ton, planetoid hulls are over two orders of magnitude cheaper than manufactured hulls. Consider the following:

Planetoid Hull of 10K dTons (8K dtons useful)
- Transport fee: 100Cr per dTon for 1MCr
- Tunneling fee: 1000Cr per useful dTon for 8MCr
- Armor fee: Factor 3 armor for 0MCr
- Total: 9MCr

Mnaufactured Hull of 8K dTons
- Construction fee: 100KCr per dTon for 800MCr
- Armor: 10% of hull is the average for Factor 3
- Armor fee: 0.6MCr per dTon for 480MCr
- Total: 1280MCr

Begin to see the problem? Now let's look at the planetoids themselves...

First, the vast majority of planetoids are going to be too big to use as ship hulls. Are pool of available cheap hulls just shrank drastically.

Second, we need planetoids that are not undifferentiated heaps of gravel with a density less than that of styrfoam. They're going to be used as a starship hull after all. Thermodynamics bites us really hard in this step. It works out that the larger a planetoid is, the less chance it will be a flying pile of gravel. Remember what I wrote about planetoid sizes? That most are going to be too big? Now we find out that the 'sturdy' ones are all big ones. That cuts our available pool of cheap hulls even further.

Third, just because a planetoid isn't a heap of flying gravel it doesn't necessarily follow that it also is a seamless body of NiFe close to the appropriate size we need. We'll need to carefully examine the planetoid looking for voids, bubbles, faults, and fissures. Think of flaws in a gemstone but on a huge level. Too many voids, bubbles, fissures, and faults means we need to find another candidate for our hull.

We can work around paragraphs two and three. We could carve the hull size we need out of a larger planetoid and we can 'repair' those voids, bubbles, faults, and fissures. However, look at the job we need to do before we even get the rock to the shipyard.

Look at the prospecting we have to do, grubbing through the all that emptiness in the belt looking for likely candidates. Look at all the prepatory work we have to do too. We got to identify a possible hull inside the planetoid, remove the 'overburden' to get at it, carefully survey it to determine it's structural soundness, if it fails that 'soundness' examination we need to determine if we can 'repair' enough it to do so, and only then do we know whether we can tow it to the shipyard or whether we need to start looking all over again.

Do you really think all of that work will only cost 1,100Cr per dTon?

Planetoids hulls are far too cheap in CT.


Have fun,
Bill

P.S. We can probably 'smelt' or 'sinter' planetoid chunks to make the hulls we want, but that will be more than 1,100Cr per dTon too. </font>[/QUOTE]From a game mechanics perspective, I admit that the cost difference is suspicious. Just to try to justify a cheap hull, what about:

Inflate a kevlar-like balloon to form the core. Heat the "gravel" or slag from refining processes in a "light bulb" type fusion reactor and spray the molten rock over the balloon to build up the hull. Sprayed concrete is a cheap way to manufacture pools and domes in the real world. Could the molten rock (or iron-nickel) form granite like crystals or a glass-like finish (I was thinking about obsidian)? Could the velocity of the spray provide the compression to form a dense shell?

Fusion is cheap power and heat in CT. Iron and rock are plentifull. Could this create an 1100 credit per dTon "planetoid" hull?

Just trying to think outside of the box.

 

[Whipsnade]

Originally posted by atpollard:
Inflate a kevlar-like balloon to form the core. [snip of good ideas] Could this create an 1100 credit per dTon "planetoid" hull?

AT,

I've no doubt you could create a hull that way. Whether you could create a planetoid hull is another question entirely. You see, the fault lays with Traveller's three decade old idea of what planetoids are.

Even in the 70s the idea was suspect, but Traveller followed the hoary old sci-fi conceit of planetoids being 'flying mountains'. You know, huge tough slabs/blobs of magma, basalt, granite, and other rocks complete with veins of ore and all the toughness the word 'rock' implies.

Planetoid ships in Traveller were pictured as flying versions of NORAD's Cheyenne Mountain. You moved a big chunk of rock to your shipyard and then tunneled out the passages and spaces you needed. In normal planetoid hulls, you needed to leave 20% of the rock intact for structural purposes. That gives you 3 'free' levels of armor. In the buffered version, you leave 35% untouched and get 6 free 'armor' levels.

All that presumed that planetoids are the left over bits of destroyed planets. That's a very old sci-fi idea and one we now know to be very wrong. Planetoids are not the remains of lost planets, planetoids are the remains of planets that never formed. All that tough rock Traveller's planetoid hull concept rests on simply doesn't exist(1).

Now, in the OTU there are planetoid belts which are the remains of destroyed planets. Yaskodray (Grandfather) and his various kiddies made a few during that family squabble we call the Ancient's Final War. That means you can find the kind of planetoids you need for hulls in a few scattered belts, but they areno where near as commonplace as HG2 assumes.

IMHO, planetoid hulls should be removed from the ship building rules completely and, if such hulls are to be used at all, placed firmly in the realm of GM fiat.

Just trying to think outside of the box.

That is always a good thing and your suggestions are very useful in picturing how very large space habitats could very well be constructed in the OTU.


Have fun,
Bill

1 - As always there are loopholes. The bigger a planetoid the more likely it will contain tough, homogenous, rock. However, we're talking about Ceres and Vesta sized planetoids here and not ship-sized planetoids. Such planetoids would be larger than the Sky Raiders' generation ship.

Another loophole keeps belt mining in the picture, but does not provide ship hulls either.

 

[far-trader]

I like option D a lot! Though I can see it more as a "So you want a kton hot potato hull base? OK let's get the cowboys on it..." scenario. Out in the belt the seeker ships begin corralling the required mass into the big roundup. The Belters are happy, it's an easy job and a good solid paycheck at the end of the drive. With the rock herded into a tight group the cowboys start driving it starward. After a few months of careful herding the finished rock is brought into the orbital shipyard and tunnelling can begin. The belters are paid and head for the starport saloon to get drunk. Tommorrow it'll be back to the belt and prospecting, until the next call for another big roundup.

Cost of the rock is free as per the rules. However it was noted in CT that there would be a cost for the transport of said rock though it was never detailed. That's where the cowboys come in. I'd guess we could use the charter rates (broken as they are) and some ratio of cowboys to rock needed. Then all we need is a bit of a handwaved "lasso" for the Seeekers' turrets so they can get those little dogies along and keep them in formation while they swing by the star. Some small repulsor mount or something.

 

[Whipsnade]

Originally posted by far-trader:
After a few months of careful herding...

Dan,

It's going to take more than a few months of heating. And it's going to take years to cool sufficiently. Counting on the heat to radiate away naturally would mean years numbered in centuries. Space is a vacuum, vacuum as in 'vacuum thermos bottle'...

Nothing says we can't help the cooling process along, but we're talking about heat migrating through rock. Large concrete installations get cooled for decades after pouring. The Hoover Dam still has working cooling tubes embedded in it after 70 years.

Drilling out passageways and carving out spaces could help us cool it faster or...

... could result in uneven cooling that produces faults and other flaws that show up under accleration or in battle.

Cost of the rock is free as per the rules. However it was noted in CT that there would be a cost for the transport of said rock though it was never detailed.

HG2 says the transport fee is 100Cr per dTon.


Have fun,
Bill

 

[far-trader]

Originally posted by Bill Cameron:
</font><blockquote>quote:</font><hr />Originally posted by far-trader:
After a few months of careful herding...

Dan,

It's going to take more than a few months of heating. And it's going to take years to cool sufficiently. Counting on the heat to radiate away naturally would mean years numbered in centuries. Space is a vacuum, vacuum as in 'vacuum thermos bottle'...

Nothing says we can't help the cooling process along, but we're talking about heat migrating through rock. Large concrete installations get cooled for decades after pouring. The Hoover Dam still has working cooling tubes embedded in it after 70 years.

Drilling out passageways and carving out spaces could help us cool it faster or...

... could result in uneven cooling that produces faults and other flaws that show up under accleration or in battle.</font>[/QUOTE]Awww, drat and tarnation yer right. And it was such a nice idea. Maybe we can save it...

What if we skip the solar bit and maybe just use the Seekers' fusion mining turrets to both move the rocks together and insystem and melt them into one big lump on the way?

Still the cooling issues but maybe it could be managed by working it together in layers? And so what if it's still warm (very very warm but not molten) when the yard boys start fusion tunnelling it, it'll just make it easier right.

Cost of the rock is free as per the rules. However it was noted in CT that there would be a cost for the transport of said rock though it was never detailed.

Originally posted by Bill Cameron:
HG2 says the transport fee is 100Cr per dTon.


Have fun,
Bill

So it is, I'd forgotten. Still that's way too cheap too I think. Should be 10 times that maybe.

Carry on.

 

[Whipsnade]

Originally posted by far-trader:
Still the cooling issues but maybe it could be managed by working it together in layers? And so what if it's still warm (very very warm but not molten) when the yard boys start fusion tunnelling it, it'll just make it easier right.

Dan,

I don't see why not. After all, we're using the Hoover Dam even while we're still cooling the concrete poured seven decades ago!

Having the body still 'toasty' could help the yardbirds more easily find and fix those faults, fissures, bubbles, voids, and other flaws they find.

Traveller ships already deal with waste heat in some magical manner(1), so having operational 'smelted' or 'sintered' planetoid hulls tackling the heat still left over from their construction should be a trivial task.


Have fun,
Bill

1 - Waste heat is generally 'handled' by ignoring it!

 

[Jeff M. Hopper]

The cooling of molten rock is a problem, so change the manufacturing process? How about crushing the rock into gravel or powder and spraying that mixed with some epoxy unto the framework structure? Remember the two part primer used in the Navy to paint hulls, imagine that mixed with high-NI powder as the planetoid structure.

And come to think of it, if the molten NI is vapor deposited on a series of capillary tubes filled with liquid hydrogen (the fuel tanks) then you could use the heat from the cooling rock to naturally circulate the fuel as well.

Either of these plausible?

 

[Whipsnade]

Originally posted by Jeff M. Hopper:
Either of these plausible?

Jeff,

Sure, why not?

It all depends on whether those techniques provide some benefit over other techniques. And that benefit needn't be across the board, it could be limited to certain cases or applications.

It's the old faster, cheaper, better question. In HG2 planetoid hulls are cheap and give you 'free' armor but they also can't be streamlined and include 'waste' volume. So, you decide what sort of trade-offs you need for the type of vessel you're building. Sometimes planetoids hulls are the best choice, sometimes they're not.

I can see structures built like folks are suggesting here being big honkin' space habitats. All that rock gives you built-in rad protection for the worst case situations when your shielding goes down(1).


Have fun,
Bill

1 - The CT 'Belt Strike' module says m-drives provide a rad shield of some sort for the ship. You can then infer that such powered shielding is also part of a station's powerplant. It would be nice to have a couple meters of rock between you and the rads when or if your plant goes down.

 

[Piper]

Originally posted by Jeff M. Hopper:
Well, new data on planetoids shows that they are not as solid as we thought, and that they are structurally more similar to a conglomeration ...

I think the jury may still be out on this one:

"These results will have important implications for our understanding of asteroid interiors. ...Interestingly, these data/results are consistent with a picture where km-sized and larger asteroids, including those produced by large scale collisions (like Ida which is a member of the Koronis family), are not rubble piles."

Taken from here (page 13).
See also the Wikipedia article on M-type asteroids.

Do you have a link to newer data?

 

[Whipsnade]

Originally posted by Piper:
Do you have a link to newer data?

Piper,

It's not the rubble pile effect that makes mining (nearly) impossible. That's something I brought up regarding planetoid hulls. It's the fact that planetoids are undifferentiated. Every element in them is jumbled together with every other element. There will be no ores (maybe).

None of the conditions you find on planets that are required to create ore veins and bodies are present on planetoids. For example, gold will be in that planetoid but it will be in it in the same fashion it's in seawater. There'll be no economical concentrations.

I've been working on what might be a loophole in all this, but I've still got some more research to do before I come down on one side of the issue or another.


Have fun,
Bill

 

[Piper]

Originally posted by Bill Cameron:
It's not the rubble pile effect that makes mining (nearly) impossible.

I was actually more concerned with the use of nickel-iron asteroids as hulls.

That's something I brought up regarding planetoid hulls. It's the fact that planetoids are undifferentiated. Every element in them is jumbled together with every other element. There will be no ores (maybe).

You might want to take a look at the geology of Vesta.

 

[atpollard]

On the other hand, Piper seems to have found a natural mechanism for converting those really big "hard" rocks into ship sized pieces. Even one such colission could economicly produce a very large number of "mountains in space" for use as CT planetoid hulls. The "shipyard" where these hulls can be found appears to be clustered in a small region of space, so one need not search the entire belt for an appropriate hull.

While ore veins are good for miners, they are bad for starship hulls. Planetoid Hulls may not be quite so broken after all - they are just a little less plentifull than previously thought.

Perhaps 10,000 credits per dTon for planetoid hulls. More expensive (and rarer) than HG but still cheaper than a metal hull. The armor factor could also be converted to a HG formula of 5+5a with a minimum of armor factor 3 (20 percent).

 

[Piper]

Originally posted by atpollard:
On the other hand, Piper seems to have found a natural mechanism for converting those really big "hard" rocks into ship sized pieces. Even one such colission could economicly produce a very large number of "mountains in space" for use as CT planetoid hulls. The "shipyard" where these hulls can be found appears to be clustered in a small region of space, so one need not search the entire belt for an appropriate hull.

It might be easier to nudge them within the Roche limit of an uninhabited planet or gas giant (although I'm not really sure how practical that would be). Cracking workable chunks off with nukes is another option.

What we could really need is a decent set of towing rules

 

[Whipsnade]

Originally posted by atpollard:
On the other hand, Piper seems to have found a natural mechanism for converting those really big "hard" rocks into ship sized pieces.

AT,

Those V-class planetoids the articles talks about are kilometers in size. They're also made of olivine and not the NiFe we all love an enjoy.

Big planetoids keep their heat longer and differentiate into (roughly) the crust-mantle-core configuration we know from real planets. Sadly, big also means they're less likely to be ship-sized.

Perhaps 10,000 credits per dTon for planetoid hulls. More expensive (and rarer) than HG but still cheaper than a metal hull. The armor factor could also be converted to a HG formula of 5+5a with a minimum of armor factor 3 (20 percent).

That's a good idea.

I've also toyed with the idea that planetoid hulls are actually dug out of larger planetoids. Why not go to a body like Vesta whose mantle/core might be accessible thanks to collisions and carve out the chunk you need?


Have fun,
Bill

 

[Piper]

Sub-kilometer asteroids are difficult to detect.
Some asteroids formed a dense, metallic core and some of these have been shattered by impacts with other bodies.

We have found both very large and very small examples.

Smaller asteroids are more common than larger ones.

Given all of that, it seems reasonable to assume that hull-sized nickel-iron asteroids would be available in some quantity.

 

[Whipsnade]

Originally posted by Piper:
Given all of that, it seems reasonable to assume that hull-sized nickel-iron asteroids would be available in some quantity.

Piper,

No. It doesn't.

I did some research in 2005 regarding planetoid mining after read an article in SciAm on collisional heating. (That type of heating is the loophole I've been talking about with regards to mining.) This is what an astronomer at Brown told me.

There are perhaps 1 million planetoids in our solar system. Approximately 80% are in the Belt. Only about a dozen were ever large enough to retain enough heat from their formation and isotope decay to differentiate. Even then, they don't differentiate into strata as 'pure' as those we find in larger bodies.

With the need for heat, differentiation, and impact fracturing to occur in that order, plus the lengthy time requirements for the first two, the chances that pieces of planetoid 'cores' have been freed from beneath their crust/mantles is slim. Especially when you remember that the planetoids most likely to have formed a core; the very large ones, are the planetoids most likely to survive an impact; again because they're very large.

Yes, the law of large numbers says it should happen, we're talking about +1 million planetoids after all, but the chances are extremely low. Most of the chrondites which show differentiation also show characteristics of being formed by collisional heating and not differentiation by the process of slow, lengthy internal heating. So, those chrondites are not from planetoid cores but rather are from surface and subsurface impact sites.

I am not saying a planetoid suited for a hull could not be found. I am saying that finding such a beast would not take a trivial amount of time, that's it's very unlikely it would be 'ship-sized', and that it's NiFe structure would not be as 'pure' as we'd like it to be.

They're out there. They won't cost 100Cr per ton though.


Have fun,
Bill

 

[Piper]

Originally posted by Bill Cameron:
They're out there.

So it seems.

 

[robject]

Say you're a towing company. What would you charge to procure them? What craft would you use?

It mainly boils down to time. Power is cheap; equipment costs and salaries will dwarf it.

So you find your hulls, then ship them back to be sold.

Assume you've got a tag-team of tugs for small starship hulls. When one finds a suitable planetoid (100t to 1000t) it tows it back and a replacement tug is sent. So there's at least two tugs needed to herd each planetoid and continue the business.

Assume a 95-ton M6 hull for the tug, and a distance of 3 AU from market to source. That's 2 days for dispatch, D days for the search, and up to 7 days to pull the planetoid back (3 days for a 100t hull, 7 days for a 1000t hull). Smaller tugs may reduce the equipment costs, but (for example) a 40t M6 hull adds up to 4 more days to the return trip. If salaries are less than equipment costs, then use smaller tugs.

Assume your crew consists of a boat pilot, engineer, and a specialist or two. Anyone else? I guesstimate the total monthly salaries to be under Cr30,000 per tug. Could be wrong.

Assume you carry an inventory of planetoids already captured, so that you don't have to waste time looking for a particular volume.

Assume you need ten sets of these tugs then, and on the average the hulls from 100 to 1000 tons show up in an even distribution.


So the price of a hull is directly dependent on D -- how many days it takes to find any hull at all.


Assume a 95t M6 tug costs MCr20. That's a monthly payment of appx Cr40,000 per month... pretty close to my guesstimated salaries per month, so I'll let this stay for the moment.

Add on life support for appx four people, and you get a monthly cost of appx Cr80,000 per tug.

About Cr2700 per day.

Two tugs required per planetoid: Cr5400 per day.

Nearly double it for profit: Cr10,000 per day.

Assume it takes 2 days to get to the belt, an average of 7 days to find a hull, and an average of 5 days to return it (average volume = 500 tons). That's 14 days at Cr10,000 per day, or Cr140,000.

The average price per ton, then, is Cr280 for small starship hulls across relatively short distances.


Now a pessimistic version. Assume it takes 4 days to reach the source, 30 days to find a planetoid, and 10 days to return it. That's 44 days total, or Cr440,000.

Average price is Cr880 per ton.


Larger hulls will incur a greater equipment and personnel expense...

 

[Lochlaber]

I would have some questions about the differention or lack thereof.
1. What is the difference between the unformed planet and the formed planet? By this, when during the formation process would the failure occur. It couldn't be too early because then the material would have remained very small, much like water droplets in a fog. At the very least, the cloud would have had to be well into the process to have created planetoids such as Vega. As such, why couldn't a lot of the differentiation have already occurred?

2. Given that observational data on the asteroid/planetoids is rather sketchy, are we sure about the idea that our asteroid belt was created by an unformed planet? By this I mean a planet still in the gasous phase. Also, how certain are we that this is the more prevalent method of planetoid formation in the universe?

Given that our knowledge of how planetary systems is limited, both in scope and the fact we have only observed the results of 1 such system's formation, we continue to work with planetoid hulls. There is no reason to suspect that planetoids in other systems won't follow the OTU manner of formation. Ater all don't we have fusion power planets that fit inside 100 dton hulls, jump engines, anti-gravity, etc..