Wednesday, October 21, 2009

Spaceship Design 101

Discovery (from 2001, the novel)
A lot of us would like some system for designing spaceships, at least in outline, for use in games, detailed fictional settings or physical or virtual 3D modeling.

The procedure I have seen most often begin by defining a hull. This gives you the main dimensions of the spacecraft, its surface area and volume capacity, perhaps along with constraints such as maximum load and drive acceleration. This is a natural approach. I used it for my battleship-era warship specification sim, SpringStyle, and it is retained by its independent offspring, SpringSharp.

But for deep space craft it is seriously misleading. Ships and aircraft, says Captain Obvious, move through a fluid medium that shapes and constrains their design. Deep space craft do not. Their overall design constraints are more architectural: supporting the craft against its own thrust, along with stresses from attitude change maneuvers, the thump of docking, thermal flexing, spin loads, and the various other kinds of abuse that spacecraft are subject to.

This is as good a time as any to point you to the Atomic Rockets pages on basic and advanced design.

I will argue that deep space craft have essentially two sections that can largely be treated separately from one another. One section is the propulsion bus - drive engine, reactor if any, solar wings or radiator fins, propellant tankage, and a keel structure to hold it all together. The other is the payload section that it pushes along from world to world.

There are both conceptual and economic reasons to treat them separately. Conceptually, because a propulsion bus might push many different payloads for different missions, such as light payloads on fast orbits versus heavy payloads on slow orbits. A little noticed but important feature of deep space craft is that you cannot overload them. They do not sink, or crash at the end of the runway, or even bottom out their suspension. They merely perform more sluggishly, with reduced acceleration and (for a given propellant supply) less delta v.

A very large station or hab might well have a modified ship drive as its main stationkeeping thruster. Or it may rely on a ship coupling to it, as the ISS is shunted by Soyuz craft docked to it.

Conceptual logic is also economic logic. The outfits that build drive buses would like to sell them to lots of different customers for a broad range of assignments.

This is not necessarily an argument for true modular construction, with drive buses hitching up to payloads on an ad hoc basis like big-rig trucks and trailers. Building things to couple and uncouple adds complexity, mass, and cost - plug connectors, docking collars, and so forth. Moreover, drive buses intended for manned ships need to be human-rated, not just with higher safety factors but provision for supplying housekeeping power to the hab, etc. But these things, along with differing sizes or number of propellant tanks, and so forth, can all be minor variations in a drive bus design family.


The payload we are most interested in is, naturally, us. The main habitat section of a deep space ship closely resembles a space station. It is likely that habs intended for prolonged missions will be spun, for health, efficiency, and all round convenience. (Flush!) The design of a spin hab is dominated by the spin structure and - unless you spin the entire ship - the coupling between the spin and nonspin sections.

Because ships' spin habs have the features of stations they may be used as stations, and again we can imagine design families, with some variants intended for ships and others as orbital platforms having only stationkeeping propulsion. Habs are the one major part of a deep space ship that correspond fairly well to our concept of a hull. Spin habs are entirely different in shape, but the shape is constrained; once you build it you can't easily modify it, beyond adding another complete spin section.


Pause to question another familiar convention here. Since at least Heinlein days spinning ships have typically been given a control room located on the spin axis, and perhaps nonspinning, where the astrogators can use their instruments unhampered. But isn't this equivalent to the circular astrogation slide rule? The navigators will do their normal work on monitors. In the inevitable space emergency there will no doubt be coelostats available, or other workarounds. But there's no reason not to locate the ship's main operating control room in the spin section, closer to the people who work there.

Though I'd be happy to be persuaded otherwise. I have always liked Heinlein's penthouse style control rooms at the forward/top end of the ship (plus the fact that he never called it a bridge). If Hollywood came calling I'd bend realism here in a nanosecond, not least because a 'top' control station is visually easy to understand, a sort of Aha! moment for viewers. But I suspect it is a minor cheat.


For those with bank cards at the ready, buying a deep space ship might be not unlike buying a computer. If your mission needs are fairly standard, you check off options on a menu. Those with more specialized requirements can select major components - perhaps a drive bus from one manufacturer, a main crew hab from another, along with custom payload sections, service bays, and so forth, assembled to your specifications.

In fact, both technology and probable historical development suggest that fabrication and overall assembly will be two distinct phases, carried on in different places, quite unlike either shipyard or aircraft assembly practice. In the early days, large deep space craft will be built the way the ISS was, assembled on orbit out of modules built on Earth and launched as payloads. In time fabrication may move to the Moon, or wherever else, but final assembly (at least of larger craft) will continue to be done at orbital facilities. I call them cageworks, on the assumption that a cage or cradle structure provides handy anchoring points for equipment.


For game or sim purposes, my advice would be to treat drive buses and hab sections as the primary building blocks for ships, whether these components are permanently attached to each other or simply coupled together. Both approaches might be in use.

A couple of provisos. All of the above applies mainly to deep space craft, especially with high specific impulse drives. Ships for landing on airless planets have some similar features. Ships that use rapid aerobraking, however, are aerospace craft and broadly resemble airplanes, even if they never land or even go below orbital speed.

And I have said nothing of warcraft. Kinetics are essentially just another payload. Lasers, and other energy weapons such as coilguns, probably draw power from the drive reactor, calling for some modifications in the drive bus. These things don't much affect the overall configuration. Armor protection would, but discussions here have left me doubtful of its value against either lasers or kinetics. Laser stars and other major warcraft may not be dramatically different in appearance from civil craft of similar size.

61 comments:

Citizen Joe said...

This isn't at all different from our launch platforms. They consist of a booster with a payload on top. In multistage rockets, the payload is actually another smaller payload/booster package.

I'm a proponent of modular components, but that doesn't mean interchangeable. There's hundreds of different motors you can put into a car, but they aren't plug and play. Often you need some additional work to get things to mate up right. However, the mass production of engines have brought the price per unit way down.

The modules for the ISS were constrained by having to fit into the Shuttle's cargo bay. Trains are designed to fit through tunnels, as are tanks and hummers on the presumption that they would be carried on trains. Ships are designed to fit through the Panama Canal. There will always be some sort of restriction that will affect the parameters of construction.

Nyrath said...

Great stuff here! I'm reminded of Sir Arthur C. Clarke's early space science books. He noted that a nuclear powered spacecraft would probably resemble a dumb bell, that is, two spheres connected by a stick.

The hab module is the forward sphere, the nuclear drive is the rear sphere, the stick is long to provide some inverse square protection from radiation, and the propellant tanks would be on the stick, probably clustered near the nuclear drive.

Nyrath said...

One can also imagine modules designed by diverse corporations being incompatible with others on purpose. "Not invented here" syndrome.

One can also imagine a tramp freighter composed of incompatible modules, being held together with bailing wire and spit.

Rick said...

Citizen Joe - This is another historical factor; we are already doing things that way. (Also one of the problems for reusable orbiters: Payloads have to be accommodated to a cargo bay.)

Good point about modularity and standardization in the broad sense not implying plug and play.


Nyrath - I used Clarke's double sphere for one of the ships in my header image. Though the hab sphere also has Heinleinian details; viewports around the waist, and an astrodome over the top deck control room.

Clarke's picture of deep space craft was more modern than Heinlein's, or maybe he just wrote them a few years later than Heinlein's juveniles.

But the biggest way real spaceships differ from the rocketpunk image, it seems to me, is all their solar and radiator arrays and the like. Someone made a point (I forget where I read this) that the ISS rather evokes a sailing ship.

Positioning these arrays so they don't interfere will be a major overall design consideration, and they may well dominate the visual appearance of deep space ships.

So what else is new? Apple hab pods won't fit atop Microsoft drive buses? This is good news for the full service cageworks industry.

But physical compatibility is only the tip of the iceberg. Software, electrical standards, breathing air mix and pressure, ecological cycle.

On the other hand there will be huge customer pressure to standardize, and we are talking powerful customers here, such as governments.

Citizen Joe said...

There are international standards out there for everything. While you could put out proprietary stuff, nobody would buy it unless it was the only thing available. At that point, you are the defacto standard to which everyone needs to adhere. First with technology is a hard hurdle to overcome. Basically, the next guy would have to have something so much better than your old tech that the new tech and thus standard appears as a wholly different technology. So the competition for tape drive technology, cassette vs. 8 track, VHS vs Betamax all got put on the way side when DVDs came out. Then Blue Ray came out, but it was insufficiently better than DVDs that it couldn't overcome the DVD standard. It is all just recording media though.

My concern here is that our assumption that things will be modular may be colored by our history in that it is the only way we've done it in the past. Sure, it works and there are many advantages, but that doesn't guarantee it is the best way.

qwert said...

Hello:

The compatibility between modules will mostly depend on how the market develops. One extreme maybe Hicrosoft, a monopoly that basically sets the standard, as everything has to adhere to it. The other one extreme is the current hardware industry. Your memories and components have to fit on every motherboard if you want to sell them.

On the field of big aircraft manufacturing, standarisation dominates almost everything... exceept the endproduct. If you manufacture engines, they have to fit on Airbus as well as on Boeings aircraft. The components industry is dispersed and competition is intense.
On the other side, a pilot trained to flight with a Boeing can´t inmediately swith to an Airbus without some training. Competition centers around two big players and nobody is interested in making life easier to the other.

In short: how spaceship components wil be build, will mostly depend on how the industry evolves. A monopoly, strict goverment regulation, competition between many small producers or a highly dispersed specialised components industry may benefit a system of standars.
On the other side competition between a small number of giants, may produce diferent incompatible systems.

Rick said...

True modularity is by no means a given. But some features of modularity, call it demi-modularity, are inherent to deep space technology.

You probably want to keep your propellant tanks separate from the corrosive, explosive stuff we breathe. Drive engines are essentially bolted onto the tail. Generally the major parts of a deep space ship don't have to fit together snugly. If you want to hang something out on a bracket you probably can.

Anonymous said...

The overall design philosophy of two "module" design of the Drive Bloc and Payload Bloc does sound simplistic and economic in theory, yet in the previous comments there have been statements about a module-esque design not only equating to interchangeable modules to allow for near-instant changes for the payload and/or drive Bloc for specific mission profiles (at least not without good reason a.k.a. government or global pressure) but also would not equate to companies not sharing standards with each other and it may not even be due to competition.

Imperial vs. Metric measurement, voltage and wattage standards of two or more continents, even to something as seemingly insignificant as different languages of both the hardware and software would cause incompatibility in an otherwise module-esque system. It may not be as Trust-like monopoly control as some would like to envision, but they are still factors that may impede any attempt at creating modular "plug and play" blocs as the overall design might suggests.

And then there are the more minor details that could make the "Plug and play" idea all the more difficult to implement and it is not the complexity and machinery as mentioned in the blog entry.

For example, as stated in the Atomic Rocket page, the radiators for the drive section cannot be utilized for removing waste heat from the passenger payload hab-mod (Habitat Module). It needs its own radiator for heat managing the life support and on board computer systems of the Hab-mod. And I have a feeling that having some maneuver rockets upon the Payload Bloc would help in rotational maneuvers more than just keeping all upon the Drive Bloc.

There is also the question of stimulating gravity of either rotation or thrust. However, one would estimate that rotational gravity would be more popular than thrust gravity if the overall thrust velocity and drive acceleration is significantly less than a full Earth G. Increase this speed and thrust gravity would be far more suitable and popular since it is less mechanically intensive than rotational.

As for a spacecraft having to have a certain design for aerobraking or even landing upon a planetary body, well I only have this quote to repeat:

"Any real spacecraft designer would design two craft: one surface to orbit shuttle, and one orbit to orbit vehicle."

If there really is no possible way to overload the payload section of the spacecraft, unless one is trying to make it into a speedster and get to where one needs to be as quickly as possible, why not have the payload section have an attached lander as well? Heck, it might even help in overall spacecraft maneuver.

- Sabersonic
Gmail Address

Anonymous said...

Rick- Your discription of how to divide up the construction of a deep spacecraft sounds like the Service/Command module division of the Apollo moon craft.

I think that the engine package, mated to a suitable tank, mated to a hab module, mated to a mission module (a seperate entity from the hab module) would (as the last step in design) incorporate the heat management system suitable to the final design. Then construction/assymbly would occure.

If there aren't landers/shuttles at the final destination and you need them, then you can carry landers/shuttles in place of cargo. A mission module may be an extended docking module that a number of small modules 'plug' into, (or your transfer craft).

Manuvering thrusters should be at mutliple points/modules (distributed from the 'nose' to the 'tail').

Of course, you could stand it all on it's ear and have the mission module be on the inside of the ship, the hab ring be around the middle (with its radiators in arcs between its connecting pylons),with the engines, tanks, powerplants, radiators, and nav sensors clustered around both ends of the mission module; and any docking would be at the tips of the mission module, or on the inside walls of the mission module. This ship's direction of flight would be edge on to the hab ring, instead of the ring having its widiest dimension facing the nose and tail.

Maybe the high endurance deep space passenger craft of the next century will look more like Von Bruan's space station than Heinlein's rocket cruiser.

Ferrell

Anonymous said...

OK, I don;t know why it double posted...Rick, could you please remove one of them? Thank-you!
Ferrell

Nyrath said...

Vaguely related: In Charles Sheffield's THE McANDREW CHRONICLES, the protagonist's ship is called "The Array". This is because it is assembled out of various modules to optimize the ship for the current mission.

Nyrath said...

Also, there are standards, and there are standards.

When I was getting started in computers, one of the biggest jokes in the industry was the so-called RS-232 "standard" for serial ports. There were entire books on how to construct a cable that would connect an RS-232 port on a computer manufactured by Company A to an RS-232 port on a peripheral device manufactured by Company B.

There might be a brisk trade in "interface modules", that would connect modules made by different manufacturers. I'm reminded of the Apollo ASTP Docking Module used in the Apollo-Soyuz mission. This was a tiny airlock module with a NASA style docking collar on one end, and a Soviet style docking collar on the other.

Rick said...

Ferrell - I made the duplicate post go away.

Maybe the high endurance deep space passenger craft of the next century will look more like Von Bruan's space station than Heinlein's rocket cruiser.

This is pretty much what I expect, at least for the forward end.

Incidentally, though, I believe that the Apollo service module had life support components as well as propulsion.


Sabersonic - Yes, I'm gliding over a host of devils in the details. The payload section will surely have attitude thrusters, for example, and these must coordinate with attitude thrusters on the drive bus end.

Aerobraking could be a factor for purely deep space craft that never land on any planet, but aerobrake from arriving transfer orbit to parking orbit. But this is probably not compatible with any type of electric drive.


Nyrath - 'Standards,' indeed! Again this is a promo for full service cageworks that will provide things like docking adapters.

Anonymous said...

Rick; Thank-you again...and you are right: the Apollo's did distibute their lifesupport systems; thanks for reminding me!

It occurs to me that spacecraft with different mission profiles might need different layouts; a high endurance passenger ship might ressemble the one I discribed earlier, but a cargo ship would probably look more like an open-frame rocketship.

Aerobraking could work out well for 'drop-offs' (payloads or capsules released from a fly-by vessel) that use an inflating heat shield. That would eleminate the need to decelerate the mass of the propellant, et all.

Ferrell

Tim said...

There's some interesting assumptions underlying some of the conclusions here. I think the main one is that humans will design spaceships for humans to build and humans to repair.
It seems to me that standards based engineering has been favoured for two main reasons: 1. It makes it easy to repair and modify things; since you only need a limited number of different types of spare parts, and you only need a small amount of information to design aftermarket parts, and 2. standardised parts by there very nature lend themselves to coonventional mass production processes.
But consider for a moment. Model T type assembly lines worked because you can use expensive tools like presses and moulds over and over again without replacing them, and you don't have the problem of constantly redesigning your product and reliably distributing information about design changes to the hundreds of people that put the things together.
But consider, in a modern 3D modeling package such as SolidWorks, its possible to link every dimension to a spreadsheet. Its also possible to send a model straight to a CNC machine for manufacture. If you can get the spreadsheet to do your design calcs, it is in principle possible to plug your requirements into said spreadsheet and produce a customised component each time.
Standard components make repair easier because you only have to keep track of so many things, but if you can easily measure and manufacture new parts on the fly (say with a rapid prototyper incorporating a 3D scanner) you don't have to keep track of all your component types, or keep a warehouse full of the things.
I think there's a tendency to divide the components of large engineering projects by specialty, but again as design becomes more computerised, this might disappear. I suspect the need to keep the mass of a spacecraft down will create a need for components that do more than one thing, like making power lines structurally integral, or using fuel tanks as radiation shielding. So you might get a much more integrated ship than one with a drive/cargo split.
I've made all this sound easier than it is at present, but as manufacturing becomes more computerised (especially if it incorporates more optimisation), I think it should be easier to produce customised designs as easily as mass produced ones.
Sorry about the long post, I still didn't say everything I wanted to!

Jean Remy said...

On standards:

Currently the main type of freight vessel is the container-carrier. They are favored because the containers can be loaded/unloaded easily, then simply popped on a freight train or a truck. I can see the same things for a cargo spaceship. There won't be a cargo "module" but rather anchoring hard points for standard containers. Those containers will be loaded on a booster to orbit, transferred onto a ship, then at the other end the container is loaded into a simple remote-controlled lifting body (for planets with an atmosphere, say, Mars) or just a simple frame with thrusters (for the Moon) where they will be loaded into maglev trains if needed, etc.

The command post/bridge:

I'd still put in in the non-rotational part of the ship, certainly on warships (you want it as deep inside the ship as you can for protection) Not only that, but I would stop rotation in combat: precession might alter your maneuverability, and damage might weaken the structure or cause a wobble which would rip your ship apart. I would also put it in the middle for a civilian vessel, as then the command module can double as storm cellar, or if there's a separate storm cellar, you'll still have access to the command post during a solar flare. It's also a good defense against micrometeorites. The command center is just too important to risk placing it on the outer rim of a ship, no matter how convenient or comfortable it would be to the crew.

Anonymous said...

I agree with Jean Remy on the notations of the Command Post (or in some military circles the CIC or Combat Information Center) should be buried deep into the framework and structure of the spacecraft, particularly the non-rotating portion. Heck, most of its gravity could be generated by thrust alone when G acceleration drives become available. I also agree with the idea of the CIC becoming its own storm cellar, either primary or for the CIC personnel when under thrust or combat. It just does not make much sense to protect the all important Carbon-Water based command crew from everything but background radiation.

Though computers and human crew require a kind of synergy between each other in which one compensates for the weaknesses with the strengths of the other rather then either one being the sole crew type as seen in many Sci-Fi media, that does not mean that the two have to intermingle with each other when it comes to the distribution of computer-driven systems and human-controlled systems. The natural environment of even civilian spacecraft is hostile enough to allow such segregation, especially since computer chips can tolerate such stresses and dangers more than the average homo sapien.

Even so, it would probably be prudent to not have all command, or at least navigation control, be monopolized by the CIC. At minimum and barring mass budgeting, there should be two for overall spacecraft control: One that is the CIC/Navigation primary with the second being the engine room for mostly emergency purposes. If only because for something as complex and (for the first few decades if not centuries of interplanetary travel, let alone interstellar) inevitably as fragile as a spacecraft, one should avoid "putting ones eggs into one basket" and to always "have a plan B". Space and interplanetary/interstellar travel is not a place for the ill-prudent, and that's just the natural dangers.

As for standards, well, before standards could ever become "standard" for lack of a better word, there lies the inevitable "Format War" in one form or another that would occur when one believes that their system is more efficient and reliable than the other or worse: a new industry/business standard that has the potential to supplant the jobs of numerous Dock workers or in this case "Cage Workers" that could drive hostility and perhaps a little bit of political pressure before the whole matter is settled in one way or another. It would not be a full parallel to the Teamsters Strike that is basically Teamsters vs Trucks, but it would not be a completely quiet deal when paychecks are involved.

- Sabersonic
Gmail Address

Citizen Joe said...

Modern warfare is moving towards remote operations. So it doesn't matter if the command crew is in the spinning section or non-spinning section. Cameras, sensors and weapon launch platforms would probably be mounted on the non-spin section, but the camera feeds could be projected onto screens in the spinning/gravity sections. That has the added benefit of letting the human's natural sensation of 'down' act as an anchor. The drawback there is that the shielding's mass has to be supported by the structure, and would be even heavier since it would be outboard of the crew compartment.

An alternate solution would be faster spinning but smaller 'cockpits' inside the non-spinning section, protected from radiation by the 'weightless' tankage. In this case, you'd climb into a pod (probably reclining to minimize the head/foot differences in gravity. Gravity would largely be "eyeballs in" direction and all your sensory input would be projected onto screens in your pod. Thus you wouldn't notice (as much) the actual spinning. The pod output would then be sent to the 'stationary' points on the non-rotating sections.

Flight command would then be more like a Gravitron(tm) amusement park ride, but with pods instead of sleds. Individual pods could be used for either drones or robotics on the ship. They could even be 'hot bunked' where you switch between semi-automated systems.

Rick said...

Tim - CAD/CAM allows far more manufacturing flexibility, but my guess is that the effect will be more variations on a theme rather than complete one-offs.

The unavoidable minimum human input is the customer specification, and to simplify the customer's task you will probably offer a range or family of pre-cooked solutions, with adjustment sliders or the like.

The end result might be that no two ships of a class are identical, but they are all readily identifiable as class members.

My division of ships into drive buses and payload sections is more because of operational factors than manufacturing considerations.

For example, ships inherently have (at least) two big 'hull' structures, the crew hab and the main propellant tank. These are probably at very different temperatures, which right away is a big reason to keep them physically separate.

Using the propellant tankage as shielding is appealing, but even with a vacuum separation it means that your 290 K hab shell is dumping 350 W/m2 of waste heat right into your 20 K liquid hydrogen tanks.

Some of the other things you suggest, like having structural members double as waveguides, etc., are less problematic, and I wouldn't be surprised to see that sort of thing.


Jean - The containership principle seems highly likely for most space cargo, with the standard pod being defined originally to fit Earth orbital shuttle bays.

In this case, your typical space freighter is a drive bus pushing a rack structure with clamps for pods. The rack might be configurable so that you can also carry 'oversize' loads.


Jean and Sabersonic - In a parallel discussion at SFConsim-l, the question was raised whether civil ships need a 'control room' at all, or whether people could just stand watch from their regular work stations.

I think that any spacecraft with a fair number of passengers or crew will have a watch at the main life support panel, because life support is always running, has constantly changing loads, and things can go very bad very quickly. The life support panel will almost certainly be in the spin section, because that is where the life support is.

You may as well put the engineering panel here as well. There's no reason for an 'engine room' in the maritime sense, since the drive is mounted externally, and if it is nuclear you don't want to go anywhere near it.

No doubt you could maneuver and navigate the ship from here as well. But en route there is very little of this to do.

The only time you really conn a (civil) spacecraft is during rendezvous and docking, or similar evolutions. At these times you surely de-spin, but you might want a separate control station next to the main airlock, with viewports for maximum situational awareness.

Because of its location, this station would also naturally serve as the ceremonial 'quarterdeck' where VIPs are greeted, and ordinary mortals report aboard.

Warcraft are a whole 'nother matter, with protective considerations arguing for a control room at the center of the hab section.

But from our earlier discussions, protection of space warcraft may be fairly moot. Lasers target each other, and kinetics overkill if they get through at all.

Citizen Joe said...

The advantage to a control room is that it is easier to protect one room than a bunch of smaller rooms. If you also need life support, one room is probably easier than dispersing it. The drawback is all the eggs in one basket. If you DON'T protect it, you're totally lost.

That begs the question, does it really matter? If a small hit disables your ship, you're looking at a lingering death alone in space vs. the catastrophic sudden death. Unless there is some means of rescue, the quick death is preferable.

So, I'd guess that, in fleet battle scenarios, where a ship might still be capable of supporting life after an incident, the dispersed structure would be preferable. If you're out there alone, or your ship wouldn't be able to sustain life after an attack, you're better off with a small command deck.

Anonymous said...

It sounds as though most people are arguing for a type of 'Citadel' (or two) buried in the middle of the ship. This Citadel would be an armored, rad-shielded, chamber housing the control room, life support, damage control, avionics, and a small auxiliary power source. The crew could survive inside this citadel (cramped and uncomfortable but safe), and have a secure place from which to repair the ship or wait for rescue...if we have so large of a presence in space that there are regular flights to various planets or even enought to have space battles, then there should be some spacecraft within a few days or couple of weeks from a disabled ship...unless, of course, the ruined spacecraft can just coast to its destination and get rescued then.

Ferrell

Rick said...

Citizen Joe - I think human factors reasons probably justify some sort of main control room, effectively an onboard Mission Control.

But that is no reason why control functions couldn't be run from elsewhere in an emergency, basically anywhere you've got a keyboard and monitor with access to the control network.


Ferrell - even civil ships are going to need a storm shelter, and it is not a bad idea to configure it as an onboard 'lifeboat.'

An alternative for bigger ships is to have two full life support pods, each able to support all passengers and crew on an emergency basis.

Anonymous said...

On driving, cellphones, and distributed CICs:

The major problem with driving and talking on a cellphone isn't that you have one hand off the wheel. The major problem is that humans are built to pay attention to conversations, and processing language takes a lot more brain activity than we used to believe. Studies have found that even talking on a hands-free set leaves the driver as 'impaired' as if they were over .08. On the other hand, the same studies have found that it's actually less distracting to talk to a passenger than to someone over a cellphone. The passenger is in the same environment as the driver, and is responding to the same environmental cues as the driver. The conversation ebbs and flows as the passenger realizes that "Okay, the driver needs to concentrate now" or "Obstacle coming, I should redirect the driver's attention to the road" or any number of other subtle conversational cues.

The main reason to have humans overseeing spacecraft operations is to have oversight into unexpected situations, or to correct in areas where spacecraft designers couldn't anticipate all the variables. There should be some communication between the people monitoring these systems and making the corrections. I'm sure there are far more sophisticated studies for this kind of oversight, but the experience of driver and cellphone conversations suggests that it makes sense to have at least some of these people centralized. That way they can at least partially monitor each other and reduce some of the distraction/interruption risk.

Incidentally, the same studies have found that people who text message while driving are frickin' loons who should have their licences revoked.

Ian_M

Jean Remy said...

"But from our earlier discussions, protection of space warcraft may be fairly moot. Lasers target each other, and kinetics overkill if they get through at all."

"That begs the question, does it really matter? If a small hit disables your ship, you're looking at a lingering death alone in space vs. the catastrophic sudden death. Unless there is some means of rescue, the quick death is preferable."

Actually I had initially argued (with myself) about that: if a good hit is going to get a kill, why bother putting CIC/Bridge/DCC deep inside. On reflection I decided that really military hardware is over-engineered, and simulator runs (both at NASA and flight schools) tend to focus on completely unlikely series of cascade failures that still somehow leave you that one unlikely out if you do everything right. Basically the idea is to design vehicles and train crews to be effective even in the unlikely scenario that the first hit doesn't instantly kill them. That philosophy is not going to be abandoned when we go to space. If there's a 1000/1 chance that having the CIC deep in the ship allows the crew to survive ten more seconds, allowing them a 1000/1 chance to kill someone else, then CIC will be built deep in the ship.

Multiple Command posts: Yes. That's why I used the term command post rather than CIC, Bridge, DCC, Main Engineering. It was meant to be generic and refer to all these. There ought to be at least CIC and DCC, if not a redundant third post, all of them capable of doing every job, but each ideally suited to one. The ship is more efficient with all of them, but can still work with the loss of one or two.

Decentralized Command posts: Possibly, but I don't think it likely. First of all we could do that now, but we don't. Psychologically, I think crews want to have the "Captain on Bridge" so to speak. It is generally recognized that good officers are the ones who stick by their men when the going gets tough. Caesar rode into battle at Alesia, rallying his troops to victory when it looked uncertain. Washington rode with his men. Patton led from a tank. Now granted the captain of a ship can't go anywhere, but seeing him on the Bridge will be a boost to morale.

On terminology: I still favor the term "Bridge" over "CIC". CIC is the Combat Information Center. Their role is to take in, collate, analyze, interpret potentially large amounts of data, then summarize it, add their projections, and finally send it all to the Bridge for decision-making time. The Admiral is in CIC because he needs to know everything going on around him. The Captain needs to focus on driving his ship, and risks data overload if you simply give him all the raw data. The largest Lasertars will have a CIC, and a bridge. Small patrol frigates, only a bridge. The "engine room" or DCC (after all the only time you need someone in the engine rooms is when something goes wrong) will have to be on the other side of the shadow shield and nowhere near the engines themselves. I do not forsee any kind of serious propulsion that is not massively radioactive.

Jean Remy said...

Oh snap, Ian posted some very interesting stuff while I was writing my own post.

I was actually thinking one of the issues with decentralization was the intercom issue, but decided it might not be too bad and elected against including it. Ian's post tells me I was actually instinctively right, but unable ton formulate why.

Fascinating data on cellphones! Also, people who text while driving should be taken out and shot. I mean: have their licenses revoked.

And then shot.

Jean Remy said...

Er also I fail at math. I mean 1/1000 not 1000/1 chances.

Rick said...

The question of having a control room at all was in the context of civil spacecraft. If they have an sudden emergency it is most likely to be a life support crisis such as fire, for which the classic 'bridge' functions are fairly irrelevant.

Military craft are a special case, and I'd certainly expect them to have a control center.

And maybe all ships, because to extend a point Jean makes, existing space programs are quasi-military in origin. The military outlook toward emergency response is coded into their DNA, so to speak.

All human carrying deep space ships will need a storm shelter in any case, and it would be fairly natural to configure this as an emergency control center.

Growing up on Heinlein, who simply calls it the control room, must be why I am so averse to spacecraft having a 'bridge.' Plus it connotes a position like the bridge on an Imperial star destroyer, which looks cool but isn't very likely. :-)

As for bridge v CIC in current naval practice, I think a CO would position themselves wherever the relevant situational awareness is better. Under air attack I would probably 'see' more from the CIC than from the bridge.

My wife, by the way, regularly gives her students a hard time over driving while texting, and agrees fully with the sentiments expressed here.

Anonymous said...

A storm celler big enough to hold the whole crew plus passengers should also be big enough to hold control room functions, a life support function, and DCC (including emergency power); I'd think it would increase surviability greatly.

Ferrell

Tim said...

Hi Rick, that's an interesting point about heat transfer from the hab section to the fuel tanks. If you look at the HOPE design on the "Realistic Designs' section of Atomic Rockets, you'll find it has the hab section surrounded by fuel tanks as I suggested. Perhaps what could work is to have a bola style architecture, with the drive acting as the counterweight on the end of a tether that's spun for artificial gravity. it'd keep the sections separate during coasting, but you could design it so that the hab is nested in the fuel tanks when the tether is reeled in for thrust. That way the fuel tanks could act as shielding from the drive, when you're doing a burn, but they wouldn't be subject to heating during cruise.
Out of interest, where did the 350W/m2 number come from?

Citizen Joe said...

I'm assuming some sort of liquid hydrogen fuel/propellant. How feasible is it to simply store your hydrogen in ice form and then crack out the hydrogen (and oxygen) as needed. Presumably ice is easier to handle and has less issues with keeping it cold. Ice is also volumetrically denser in hydrogen than Lhyd. You'll still need to store a smaller amount of refined hydrogen.

The added mass of the oxygen is a concern, but humans need water anyway, so you can pull double duty. You can also use the oxygen as remass some how. It would probably be your high thrust/low specific impulse re-mass for dodging asteroids. Using the water directly as remass via steam would also allow for low impact launch system.

However, I think that the best part of the ice storage is that it alleviates the need to deal with cryogenic fuels.

Luke said...

Re: Shielding. It now seems likely that a plasma magnet generated by a low mass antenna could deflect any charged solar radiation, so the crew would be safe from flares and CMEs. It does not seem like a plasma magnet could stop galactic cosmic rays, GCRs are a steady source of background radiation, not the sort of thing that a "storm cellar" would help with. A plasma magnet also would not protect against neutral particle radiation, but the only neutral particle radiation likely to be a threat is man-made: neutron radiation from nukes and possibly high energy photons from x-ray or gamma ray lasers.

For those not in the know, a plasma magnet uses low frequency radio waves to produce a rotating field that induces a current in the surrounding solar wind plasma. This current forms a dipole magnetic field that deflects and reflects charged particles. The field is not strong enough to deflect solar wind protons, but it does deflect the electrons, leading to charge separation that pulls the protons back to the electron cloud before they reach the section being protected.

Luke

qwert said...

Hello,

Just a comment about combat spacecraft:
I imagine space warfare as mostly happening between automatized "ships" without crew. The only reason why you want a manned vessel would be to avoid ligthspeed delays when taking decisions.
In other words crewed warships would direct the battle from as far from the danger as posible, preferably out of reach from anything but radiowaves, I imagine they would also be unarmed, as it wouldn´t make sense to try to compete against the entire firepower of combat-specialised vessels .
In other words the crew wouldn´t be in danger unless it becomes impossible to take them out, because the enemy reached them first after destroying your "fleet", which makes surrender a very sensible option. So hardened "bridges" inside the center of the spaceship wouldn´t be necessary.

Rick said...

Ferrell - In one way or another we'll surely want to provide an emergency backup for long missions, abel to provide survival basics.


Tim - I'll have to take another look at the HOPE design. Ships of this type may make more than half their trip under thrust, so solutions that only work in coasting flight may not help.

The 350 watts per square meter is the approximate blackbody radiation from an object at room temperature. (~290 K)


Citizen Joe - Cracking hydrogen out of ice to use as remass would leave far more oxygen than you need; you might as well dump most of it as remass as well. But H2O is an inefficient propellant.

Methane might be a compromise; it has to be kept cold, but not as cold as hydrogen, and it is denser, though it is still not as good a propellant as H2.


Luke - I seem to recall that someone on SFConsim-l did the numbers for magnetic shielding, and it required a humongously massive and powerful magnetic coil. But that may have been to stand up to CGRs, or particle beams.


Qwert - I tend to agree that most actual combat will be between robotic platforms, with manned ships basically in rear positions performing command and control and support roles. In which case they won't have combatant-style protective measures, but more what you would expect of transport or AWACS type platforms.

Jean Remy said...

However, those command ships will become the primary targets. Even if they are not armed, they'd better be well-armored and well-protected. They would be the equivalent of a general on a horse standing on a hill, broadcasting "hello, kill me." Not only that but the more complex the weapon system, the most likely it will need maintenance. Roughly a fifth to a quarter of a carrier crew are the mechanics necessary to keep the air wing operational. In case of a Laserstar, I can see a crew of "window cleaners" in charge of mirror maintenance. In the likely event sectioned mirrors are used, they would replace those sections damaged by accident (a micrometeorite hitting it). The laser itself might need replacement (once again, in case of modular solid-state lasers, the switching out of a module) Even if done by robotic means, I think you'll want someone to monitor the process. I agree there will be extensive automation, and even the largest of Laserstars massing in the tens of thousands of tons might just require 20 to 40 crew members, but I don't really see the human element being entirely removed.

Citizen Joe said...

All I'm saying is compare the mass of the oxygen (usable as remass) and hydrolysis equipment to the mass of the cryogenic equipment to keep H2 liquid.

I wonder if the compromise might be a mixed load of ice and methane where the byproducts get recombined into CO2 and that gets frozen into dry ice. Is dry ice easier to make than liquid hydrogen?

On a molecular level we're looking at 2 water molecules (H2O) and 1 methane (CH4) to produce 8H + C02. That masses out at 8 hydrogen per 44 byproduct... about 18% hydrogen by mass with no particularly special requirements for storing the dry ice. This is compared to water at 12.5% and methane at 33%. I suspect that a water/methane mixture could be frozen making it easier for storage as well.

By mass, straight up LHyd is the way to go. However, LHyd has so many handling issues that it may simply not be feasible.

Luke said...

Rick: That was me, and yes I was trying to stop GCRs. The plasma magnets wouldn't stop the solar wind protons either, when considered as individual particles - you need the plasma effects of the electrons to stop the solar wind. This lets you get by with a much smaller magnet.

Luke

Rick said...

Jean - I don't think many parts of a laser weapon are field repairable. On the other hand, if lasers are dominant and fight by eyeball frying, the risk to an onboard crew may not be that great.

A curious exception to your earlier general point about military thinking is modern era navies, which have pretty much totally abandoned armor protection even for 10,000 ton ships.


Citizen Joe - Whatever you carry as propellant, a high specific impulse drive will reduce it to plasma and break any chemical bonds. An exhaust velocity of 50 km/s is equivalent to about 250,000 K for hydrogen, and more like a million K if heavier nuclei are involved.

So hydrogen not only delivers more oomph than methane, or anything else, but does it at a much lower core temperature.

(To play along at home, think of atoms as billiards balls of varying mass, flying around and banging into each other.

If two hydrogen atoms collide, the distribution of energy and momentum is not changed. But if a hydrogen atom bounces off a carbon or oxygen atom, the hydrogen atom flies off much faster, carrying most of the kinetic energy but only half the momentum. The upshot is that you waste energy with plasmas of mixed atomic weight.

My opinion, worth what you paid, is that hydrogen is so much better than any alternatives that it is worth carrying a cryo plant to keep the stuff cold.


Luke - In other words, you're saying that an electric ship probably doesn't need a storm shelter, though there is still a CGR background dose for which the only protection is a) armor, or b) fast travel reducing exposure time.

I'm certainly happy to get rid of storm shelters, which are very inconvenient to do if your hab uses spin gravity. But deep space ships (or stations), far from rescue, should have some sort of life support backup, whether an onboard 'lifeboat' or a dual hab.

Mark said...

@Citizen Joe: Looking around at LH2 storage on the web it seems that the major component in most cryogenic storage is insulation, and vacuum makes great insulation. the big problem with LH2 is the volume, necessitating such large (& bigger means heavier) tanks. I read somewhere that hydrocarbons have more hydrogen by volume than LH2, but the questions are, is the mass of the carbon less than the mass of the extra tank? how do you separate the H to get the high isp? Can you just put the hydrocarbon through the engine? But aside from all that, how funny is it to imagine spacecraft running on gasoline?

Anonymous said...

Rick-"A curious exception to your earlier general point about military thinking is modern era navies, which have pretty much totally abandoned armor protection even for 10,000 ton ships."
I'm sure by this you mean that naval planners have shifted away from passive protection (armor) to active protection (guns, missiles, ect). AWACS planes also (usually) have escort fighters to protect them during missions. Combat Air Patrols (CAP) are meant to protect surface ships and direct combat support planes. I don't see that changing in Qwert's scenerio of fleet-type space warefare.

Ferrell

qwert said...

Thats exactly the kind of scenario i was thinking of. The crewed command ship is actively protected by the rest of your fleet.
It doesn´t make any sense to try to protect the crew if the enemy manages to defeat your active protection.

Citizen Joe said...

There is also lithium hydride which stores hydrogen at about 12.5% by mass, but forms into salt crystals at standard temperature and pressures.

That yields about 100 kg of hydrogen per cubic meter of LiH compared to about 70 kg of hydrogen per cubic meter in liquid hydrogen form.

Cracking it out is easy too, just add water. In the meanwhile, you can use the LiH as coolant and shielding for your reactors without worrying about your habitat module heating it up.

Now you get to dump that shadow shield mass in favor of fuel. No huge hydrolysis processor. No cryo hardware. It's win win... so long as you keep it away from oxygen or water ;)

Rick said...

Mark & Citizen Joe - As best I can tell, the extra tankage for bulky hydrogen is still a lot less mass penalty than using any other propellant. Mass is a double consideration, because it also reduces acceleration, and electric ships spend a good fraction of their trip under thrust.


Ferrell & Qwert - True, the disappearance of naval armor has not meant the abandonment of protection, only of one layer.

That said, I pretty much agree with Qwert's point. The protection of a constellation is its armament. If that is defeated the constellation must withdraw, be abandoned (and perhaps 'scuttled'), or surrender.

Anonymous said...

Hmm...that seems to go back to the cost of the hardware and that of the highly trained crew...just because some designer doesn't think it's worth it to provide armor for crew protection, doesn't mean that the people who actually man those ships share that same opinions...

Ferrell

Mark said...

I kind of figured, but I thought the image of a space ship running on fossil fuel too funny not to mention.

But in all honesty, it looks like all the heavy cryogen equipment for hydrogen stays at the production facility, and the insulation to keep it cold doesn't mass much, (and even less in space where hard vacuum is easy to come by).

Luke said...

Rick - According to the simulations and experiments I have seen, your summary is correct. However, there is one possible additional method of mitigating the GCR dose - medication. As we learn more about cellular repair and cell "suicide", new treatments may become possible for both chronic and acute radiation poisoning (and oddly, you are likely to want the opposite reaction in these two cases - for chronic exposure, you want the damaged cells to destroy themselves to prevent cancer; for acute exposure you want the damaged cells to repair themselves to prevent anemia, hemophilia, a compromised immune system, and digestive difficulties). Incidentally, it has been shown that vitamin D helps with chronic radiation exposure, although the mechanism is not clear.

Luke

Anonymous said...

"Incidentally, it has been shown that vitamin D helps with chronic radiation exposure" - Luke

From what I have skimmed from the article,
some payload of the spacecraft's supplies might consist mostly of sea foods that are listed in the article.

That or install tanning salons on board or some way to dilute and channel sunlight into the ship into safe levels without allowing the nastier forms of radiation to enter as well for crew usage in addition to general or personal centrifuges to help with overall crew health.

Personally, and in disregard to Airplane lore, I'll take the fish.

- Sabersonic
Gmail Address

Rick said...

I'll take the fish, too.

UmbralRaptor said...

At the risk of nitpicking, I get 400 W/m^2 for a 290 K blackbody (350 is for a 280 K one, which will probably make the crew unhappy). I wonder if painting tank-facing parts of the hull white would help.

Citizen Joe said...

White reflects light not heat. The white surface trick tries to get rid of the visible light frequency photons before they turn into heat.

Citizen Joe said...

I think that there are still some issues with the tankage relating to whether or not the tank is ejected after the fuel is spent. From the stand point of mass to surface area exposed, a sphere is the best tank design. That is also useful for pressure reasons as well. But that means hanging on to your tank until it is completely dry before you can eject it. A more likely scenario is a grapevine style system with many smaller tanks. That however increases surface area and thus heat gain. Liquid hydrogen also has pumping concerns. Moving cryogenic fluids around puts a huge thermal shock load on materials.

I think what we might be looking at is the difference between a performance race car and a simple utility truck. The liquid hydrogen spacecraft would be fast and efficient, but subject to a lot of maintenance and finicky adjustments. It would also rely heavily on supplemental systems (like the cryogenic systems to make the fuel). Meanwhile the more utility space craft, which probably operates in orbit of a planet, would use hydrogen locked up in a more stable form, like LiH or H2O. The race car model might use fusion power while the utility model would use something simpler like a fission core or RTG.

Rick said...

UmbralRaptor - Welcome to the comments thread! You caught me in a quick and dirty calculation. But the real lesson here is that a small difference in radiative energy balance can make a big difference for human comfort.


Citizen Joe - Yes; white is for reflecting visible sunlight.

You have a point regarding hot rods v utility trucks. I concentrate on the hot rods because they are the human carrying ships. Most space traffic is the trucks, but they are robotic and sort of in the background. (But pervasively so!)

Citizen Joe said...

I was just thinking that the complex and possibly quite fragile nature of the 'hot rod' system may lend itself more heavily to the modular construction. The engines are going to be finicky and the fuel supply is going to be hell on the plumbing. Ejected fuel pods may also make the 'hot rod' expendable. In the end, that set up becomes a one way trip into the service station where it then undergoes a total overhaul. People won't want to wait a year for their power bus to be deemed space worthy, which leads to the payload pod sort of arrangement.

Payloads may be cargo, habitats, or even fully operational ships. Many settings use the carrier model (particularly with FTL jumps), which then deploy the smaller ships while the carrier 'recharges'. The hydrogen hot rot model would seem to move that concept from interstellar to simple interplanetary scales while the more durable short range vessels become orbital platforms.

Now the question becomes what would the models look like for 'reactionless' drives. I think I saw some concept for some spinning dohicky thing that somehow pushes against the rest of the universe. And then there is the idea of compressing space itself (warping). I'm sure both methods are power hogs but they don't use reaction mass (or they minimize it greatly). I think that in both instances the cycling rate will determine top speed whereas reaction drives are limited to top acceleration (well also their delta V and the speed of light).

francisdrake said...

This is a very interesting thread! Just a few thoughts that came to my mind while reading:

- Mass is critical.
Even with future powerful engines the overall effort and cost will be dominated by the vehicle mass. Spaceship designers will always try to achieve their goals with as little mass a possible.

- Size matters.
All spaceship components have to be transported to space, coming from Earth for quite a long foreseeable future. They have to fit into some kind of telephone-pole shaped rocket. I assume the aerodynamic shrouds will not exceed a diameter of 10 -12 m, with more contemporary designs like the Ares V being in the 8 m range.
So all modules (or building blocks) would not exceed this size, with their longitudinal axis maybe being twice that value.

- Crew protection:
I fully agree on putting the most precious cargo (the crew) well protected inside the ship. While exposed fly-bridges look cool in Hollywood movies, you would not expose the crew more than necessary. There may be a lookout post with some windows to see nearby objects with your own eyes, but most of the information would be take by cameras and other sensors and displayed on screens.

- Placement of tanks:
While it seems obvious to place them near the engine, it might make more sense to pack them (or at least some of them) around the crew quarters as radiation protection shields. We have very little flight experience outside the Van-Allen belt, which protects us from a lot of stellar radiation. Only Apollo went out further, but just for days and they probably had delayed the launches in case of a major solar event coming up.

But on a month long interplanetary journey you may not be able to avoid solar flares. Fuel (or reaction mass) is always present. It would provide shielding without extra weight penalty, also for non-magnetic radiation like gamma rays. And if fuel runs out, you are either short before reentry into Earths atmosphere, or you are having really serious troubles, with radiation bring one of your least :-)

I don' think the heat transfer is much of a problem with this arrangement. There would be heat radiators anyhow, it should be no problem to orient them up front of or behind, edge-on to the tanks. And maybe NH3 would be a better storeable reaction mass than H2, providing nearly the same ISP at much lower requirements for tank insulation or active cooling. (CH4 is not so nice, as the C tends to deposit as soot inside the engine.)

Citizen Joe said...

Ammonia (NH3) is about 17% hydrogen by mass. It could be converted to water by burning it with oxygen which yields:
4NH3 + 3O2 => 2N2 + 6H2O
Presumably that heat, in the form of steam would be used to generate electricity to perform electrolysis that turns the water to hydrogen and oxygen:
6H2O + e- => 3 O2 + 6 H2
That oxygen would then be returned to the burning chamber to convert more ammonia.

Remixing nitrogen into something else is a difficult power intensive process probably best reserved for production facilities.

It still requires significant cooling to around 40 degrees below zero. Further cooling (or applying pressure) could turn it to ice around -60C.

I think that there would be a point where it is too difficult to maintain the cryogenic temperatures due to heat build up from the sun. I'm not sure how close that would be, but that would be a definite design consideration.

Rick said...

To keep cryogenic propellant from boiling off on long missions you will need active refrigeration, pumping heat out of the tank. Otherwise heat buildup will be inexorable.

The ship will be designed to keep the propellant tanks away from the main radiator fins and such, and generally minimize heat absorption from the rest of the ship, so the heat you mainly have to deal with is from sunlight.

The tanks will be painted white or silvery to reflect away most sunlight. I assume that you can reflect about 90 percent. For a spherical tank at 1 AU, that means about 35 W/m2 of absorbed solar radiation that you'll have to pump out of the tank.

A 20 meter diameter tank holds about 250 tons of hydrogen, or 1500 tons of methane. Surface area is 1250 m2, so at 1 AU you'd need 44 kW of refrigerating capacity, i.e. heat extraction, to keep propellant cold.

At Jupiter distance, 5 AU, solar flux is reduced by 96 percent, and you only need 2 kW of refrigeration for hydrogen - none for methane, which will stay liquid or even tend to freeze.

Suppose you put a 10 meter diameter hab inside the tank. (This only reduces tank capacity by 1/8.) But even with a vacuum layer you will have IR heating from the hab surface, at room temperature: 400 W/m2 * 314 m2 = ~125 kW.

So in this case putting the hab inside the fuel tank multiplies your propellant refrigeration bill by 4x. Which is a lot, but not horrible; the shielding might be worth it. But wrapping propellant around a spin hab is tougher.

Rick said...

francisdrake - You wrote: There may be a lookout post with some windows to see nearby objects with your own eyes, but most of the information would be take by cameras and other sensors and displayed on screens.

My solution, for story/cinematic purposes, is a position called the pilot tower. It would be manned for rendezvous and docking, or EVA activity, and for large ships has much the function and appearance of an airport control tower.

But there'd be no reason to have anyone posted there in cruise flight. In normal operation you are dealing almost entirely with life support and general engineering, so the center for those functions is where you'd probably keep your 'underway watch.'

Citizen Joe said...

What about the cosmic radiation being absorbed by the fuel?

Work out the extraction hydrogen from LiH crystals (which stay solid to almost 700C) and use that as your shielding material. Consider that, plus the habitat plus it's own power/drive system as the payload. Then stick that on a liquid hydrogen bus for long distance transport.

Another option is using Lithium Deuteride as fusion fuel and wrapping that around the habitat. I'm not sure about the proportions of remass to fuel to habitat size and radiation protection, but any time you can get double duty out of something that is better.

Rick said...

Alas, the cosmic radiation is enough to be dangerous without carrying much total energy to speak of.

Fun fact (for very specialized values of 'fun'): The fatal acute radiation dose has roughly the same total energy as a .45 slug.

dvincent said...

I discovered your blog the other day, and am delighted to have such a backlog to review.

Where did you get the picture of Discovery?

Somewhere (perhaps in 'The Lost Worlds of 2001') Clarke says that for the movie a decision was made to get rid of the radiators, so as to avoid making a viewer wonder 'why a spaceship should have wings'.

I like the Trillion Credit Squadron approach to choosing an overall ship shape. As I recall there were only a dozen or so. Some of the options were cone, sphere, close structure, and open structure. Not sure if cylinder was an option. Each option had consequences in the game. I suppose an open structure could not support much acceleration.

Thank you so much!

Rick said...

Welcome to the comment threads!

The image of Discovery almost certainly came from the Atomic Rockets website.

And I also remember reading Clarke make that point about why the ship in the movie had no radiators. (Today we would have no such problem, because solar wings are a familiar visual attribute of spacecraft.)

I don't think an open structure would necessarily have limited acceleration. The Eiffel Tower handles a 1 g field perfectly well! For that matter, the tripod and cage masts of WW I era battleships also stood up to the pitching and rolling motions of ships.

Jim Baerg said...

Rick October 28 2009 at 8:48 am said: "Aerobraking could be a factor for purely deep space craft that

never land on any planet, but aerobrake from arriving transfer orbit to parking orbit. But this is

probably not compatible with any type of electric drive."

This:
http://www.nasa.gov/content/magnetoshell-aerocapture-for-manned-missions-and-planetary-deep-space-

orbiters/
would allow aerobraking for relatively fragile spacecraft & in thin atmospheres like Mars' so maybe

electric drive craft would aerobrake into orbit around any body with an atmosphere at least as thick

as Mars'

I saw the idea of using propellant tanks for radiation protection rejected on the grounds that the

propellant would be cryogenic hydrogen. However, current ion drives use high atomic weight stuff like

xenon as propellant, which suggests that it should be possible to find a propellant that is liquid at

about 20 °C, in which case surroundin the hab section with propellant should work.