[2300AD] Beanstalks

[Lemnoc]

Why are orbital elevators so slow?

Reportedly it takes 5 days to reach GEO. My rough calculation is that amounts to average speeds of less than 200 mph over the journey. Yet a vactrain, running on maglev rails through an evacuated tunnel, can reach theoretical speeds of up to 5000 mph in a vacuum. The orbital elevator car runs through vacuum for 99% of its journey.

I did a little research on the topic of G forces and it appears the human body can take quite a bit of it for very short duration bursts; however, one calculation I encountered estimated the vactrain could go from zero to top speed in 5 minutes with a transverse G-Force of only 0.76G.* Meanwhile, as the capsule rises, the perceived gravity falls off precipitously.**

I would posit that once the capsule is in relative vacuum (+100 miles) it might accelerate dramatically, perhaps to 2000 mph, with little or no discomfort to the passengers. They might have to strap in to accelerator couches for a few minutes until optimal speed is achieved.

In short, I think these orbital vehicles are probably able to, theoretically at least, make the journey to GEO—safely, comfortably, with plenty of margin—in one day. Not five.

Thoughts on this?

* Detailed in NASA, Effects of High Speed and Acceleration on the Human Body.
** Illustrated on page 26 of GDW's Beanstalk module

 

[rust]

A beanstalk would probably also be used by physically vulnerable
people like children, pregnant women, elderly people and so on.
With this in mind the maximum G force the passengers would ha-
ve to suffer at any moment should not be significantly above the
normal level of 1 G.

 

[Captain Jonah]

Physically vulnerable is one thing, making the entire trip at a speed slower than aircraft seems odd to say the least. Children and pregnant women don't drop dead on transatlantic flights.

Keeping accel to 0.5 Gs with a capsule that flips to keep "Gravity" down to the floor during the decel phase such a tethered car should be able to make the trip in a day. 5 days is a very odd time.

Is there considered to be some stability problem with the beanstalk cable. Do the cars have to keep the speed down to avoid creating ripples or shockwaves down the cable which would stress the anchor points ? ?

Frankly from a cost effectiveness point of view you can fly to orbit carefully enough not to shock the kids far more quickly than 5 days. a 5 day trip requires accommodation, food and drink, life support etc and keeps one car in use for a single batch of passengers for 5 days up and 5 days down. The fuel and maintenance costs may be a lot higher on a space plane or shuttle but the shuttle makes a run up or back ( or maybe up AND back) in a day.

Factor in the overhead costs of the beanstalk compared to the shuttle or space plane and you would seem to be making a lot more money running the shuttles. Yes governments subsidise the bean stalk but in terms of cost and income one car and 5 days of life support plus cabins, beds, steward type staff etc is going to be as expensive to run as a shuttle which has accel couches and a few stewards to serve drinks in zero G bulbs mid way.

The bean stalk only comes into its own for bulk cargos where time doesn't matter and no shuttle or space plane can lift them due to size or weight. For people, passenger cars on the beanstalk make no sense if it is a 5 day trip.

 

[rust]

I suspect that the speed of the climber is limited by the
mechanical friction between the parts of the climber that
are in contact with the cable and the cable. Even at the
climber's speed in 2300AD, approximately 300 km/h, the
friction would result in considerable wear on the cable, as
well as in considerable heat, which is difficult to get rid of
in a vacuum. To make the voyage of 35,770 km in a sing-
le day the climber would have to travel at a speed of ap-
proximately 1,500 km/h, and the mechanical friction cau-
sed could well result in a melted cable or well cooked pas-
sengers. To eliminate or significantly reduce the friction
would hardly be possible, because the friction keeps the
climber on the cable and enables it to move along the
cable.

Just some thoughts ...

 

[Lemnoc]

A beanstalk would probably also be used by physically vulnerable
people like children, pregnant women, elderly people and so on.
With this in mind the maximum G force the passengers would ha-
ve to suffer at any moment should not be significantly above the
normal level of 1 G.

My takeaway from the article on vactrains was the engineering took these ideas into consideration and it would still be within the parameters of safe travel. What is the G force from takeoff of a modern jet? What is the G force from an SST? Once optimal speed is reached (and there is no longer acceleration) the body feels as though it is at rest.

EDIT: Also consider pairing the accel of the climber against the falloff of gravity at LEO. Could balance out.

But... even if we grant what you suggest, why would there not be one line of the beanstalk that crawls while other lines run at top speeds? As Captain Jonah suggests, time is money.

I suspect that the speed of the climber is limited by the
mechanical friction between the parts of the climber that
are in contact with the cable and the cable. Even at the
climber's speed in 2300AD, approximately 300 km/h, the
friction would result in considerable wear on the cable, as
well as in considerable heat, which is difficult to get rid of
in a vacuum.

I guess my thought is that the "pawls" on the climber would be via electromagnetic pulse (maglev) rather than mechanical in nature.

Is there considered to be some stability problem with the beanstalk cable. Do the cars have to keep the speed down to avoid creating ripples or shockwaves down the cable which would stress the anchor points ? ?

I read up on the physics of beanstalks, very similar to that of a suspension bridge. The maximum stress point on the line is at GEO. Oddly, the cables could actually be thinner and lighter at their anchor points. I imagine any shockwaves would be in atmosphere, and indeed you'd want to keep speeds down there. The most comfortable deceleration would be in vacuum.

 

[2330ADUSA1]

I wounder what would the service life time be on the whole thing, and what would the cost of the upkeep be on it, and would it actually ever pay for itself or not. Plus what would be the primart cargo that it lifted into space? If the other end of the Bean Stalk was a spce station/ship yards in space then it might be real useful. Still the cost would be fantastic.

 

[Lemnoc]

I wounder what would the service life time be on the whole thing, and what would the cost of the upkeep be on it, and would it actually ever pay for itself or not. Plus what would be the primart cargo that it lifted into space? If the other end of the Bean Stalk was a spce station/ship yards in space then it might be real useful. Still the cost would be fantastic.

If you were ferrying just 20 passengers per car at five (ten) days per trip, I don't believe the economics would ever pencil.

...But, the cost and complexity of building the thing are not so great as you might imagine. One strand of cable, capable of supporting its own weight plus that of other cables, could be lowered from a GEO platform. Other cables could be hoisted along that cable until you built a bundle with enormous carrying capacity.

And, yes, the outer end of the beanstalk exceeds escape velocity and would therefore make a great low-cost launch point for cargo and in-system ships.

EDIT: (my surmise would be stutterwarp ships would most efficiently launch out of GEO station, above the wall but below the shelf. Plus they'd stay where you parked 'em)

 

[Colin]

There are a few reasons for the relatively slow speed.

First, however, a little more detail on the Beanstalk. The two Beanstalks currently in operation have three "tracks" One supports upward traffic, one supports downward traffic, and one is kept clear for emergencies and to allow maintenance rotation.

Beanstalk cars travel in "trains" of up to 30 cars at a time. Spacing between trains is carefully regulated for load-balancing and to allow time to load and unload the cars.

Cars are loaded and unloaded in yards, not while on the track. A mechanism similar to a gun magazine loads and unloads the track.

The load on the track, up and down, has to be kept balanced.

The cars do not physically touch the track, but their weight still has to be accounted for. The emergency backup system does physically touch the track, and the speed has to be kept low enought that the emergency system doesn't shred the track if it has to deploy.

Higher speeds are possible, but less safe. Special cars on the emergency rail can manage up to 3,000 k/hr. However, in case of an emergency with the drive system, these cars don't deploy brakes. They are ejected to fall free, but have rudimentary reaction drives and a reentry system.

Speeds have to be carefully controlled to ensure that a resonant virbration is not induced in the structure.

The slow speed then, is for load balancing and engineering reasons, along with scheduling and safety.

 

[2330ADUSA1]

My thought on failure would be that each "Car" would disconnect from the rest and deploy massive parachutes to allow them to land safely...maybe the "car" specificiacally for passengers might also have "pop-out" wings and engines/drives to aid it to land safer as well.

 

[Lemnoc]

I appreciate the additional level of detail, Colin, and the attention to detail as well. And I think I understand the original META reason for the slow speed, which was to set a stage for an Agatha Christie style of hotel / train mystery and/or to provide literally a vehicle for adventure seeds for bored Travellers going to and from sandbox destinations. I get that.

So... thanks!

But... from the standpoint of declaring that this is a A Class Starport feature, I think the economics are off, for a lot of the reasons Captain Jonah described. The throughputs are off, for starters. The modern airline system has trouble staying solvent without a great deal of gov’t subsidy; and here you’re binding that up with, essentially, the hotel industry and its various attendant problems. I mean, as described, the beanstalk is more hotel than shuttle.

If there are a LOT of wayfarers, the system appears inadequate to meet the demand. If there are FEW wayfarers, the system (IMO) doesn’t have enough economies of scale to offset costs. Encumbering this, it doesn’t seem flexible to adapt to either those economies. In effect, rather than being a NATURAL and OBVIOUS superior alternative to the spaceplane (“Aha! I wish we had one of these in every starport”) it comes across as a subsidized vanity project, a boondoggle.

Class A = you’d have to be nuts to prefer any other way into orbit, IMO.

Without meaning challenge, let me propose an alternate model:

Six ribbons as opposed to three. Two up, two down. One generally on standby for trade imbalances... lots of stuff coming in, lots of stuff going out. One idle for emergency, for maintenance, for system rotation. Each ribbon carries about half the load you describe, so the load-bearing issues are eased and the system is a bit more flexible in case cars get disabled or delayed. Rotations occur at intervals to ease particular types of wear.

At the Top and Bottom terminals are rotators that receive the cars (think about bullets in a revolver) that detach and cycle the cars up or down, or to periodic scrubbing and maintenance.

A mechanism similar to a gun magazine loads and unloads the track.

Just so!

Speeds are very high. You step into a capsule and it rises out of the atmosphere in a leisurely way for 100 miles, then whoosh the kinds of high-speed accelerations attainable only in vacuum. This acceleration is paired with the gravity falloff of LEO, so the passengers hardly notice the exchange. Some cars carry nothing but heavy cargo. Some cars might be designated as express to Top or Bottom and whizz right through GEO Station (another good reason to have two tracks up and down).

Problems of resonance and constructive interference are engineering and design problems.

I do like your idea (and that of 2330ADUSA1) that the cars might detach in the rare, rare emergency (that players seem magnets for). This becomes a bit easier if, as you say, the ribbon is not load-bearing and the propulsion / lift function is maglev. Anything above 100 miles or so, the car would drift into a recoverable orbit... maybe.

If the beanstalk was built of carbon nanotubes the whole darn thing might act as some gigantic 74,000km long fiber-optic photonic device, with lasers doing periodic nondestructive testing of the system integrity, relaying billions of databits along its length. GEO Station might be an amazing place, a bit like Babylon 5 / Clarke's Rama / O'Neill cylinder that, along with a debarking terminal, sheaths the beanstalk along its rolling length for several miles, providing numerous docking hardpoints for dozens of stutterwarp ships.

Anyway, just some thoughts.

 

[2330ADUSA1]

OK it seems to have been a "Pork-Belly" project that actually some how was completely built.

Now I really like (Lemnoc's) description of what it could look like alot, that works for me. Maybe it is on a world where the atmospher makes it difficult to see and/or navigate or some such issue and this was a safer approach. Or maybe it was just a science experiment that actually got built by some Mega Corp as a promotionial PR showcase. There is always a way to explain anything and make it sound real good.

 

[Greg Smith]

If happened to be called 'The Coca-cola Beanstalk', and painted red and white, the costs might be mitigated somewhat. Like this

 

[2330ADUSA1]

Don't laugh, anything could be made to work.

Within my own Traveller campaign setting set in the Verge Sector for the past 25+ yrs I have created (3) Mega Corps:

Pell Corp.
GTE Corp.
Trekian Corp.

These three Corps do all sorts of things to increase the PR for their Company and to get a better PR to gain the large part of the Market share within the Verge Sector. With the Imperium in a full scale civil War, the forces to keep the peace are almost gone. These three Corps are almost like governments themselves and do fight amongst themselves as well too. BTW in my Traveller campaign the current year is 1132 and I Do NOT use the AI Virus at all I instead have use a Plague that is very much simular to the I am Legend style plague or The Rage Plague from 28 Days. Combine these two plagues together and that is the plague that spread accross the Imperium space. There is a cure, and these three Corps have it for a price. Each Corps cure is slightly different with different side effects and situations. The plague is rumored to have been a Bio-Engineered Weapon, that spread fast.

Anyway back to the Beanstalk...a Corp backed one would make a real good PR add.

Penn

 

[Captain Jonah]

A few more points.

Re strands. A twin strand set up with three pairs allows for a far higher rate of runs, especially if cars can be switched across to the other cable in the pair to allow overtaking, this means you can have slow on one line, fast on the other and express which weaves between the two.

Resonance and vibration can be ( and should be countered) by strategically places vibration generators along the length. You can create 180 degree reversed vibration patterns to cancel out any resonance in the lines.

The cars themselves could well be magnetic rather than physically clamped to the cables. It would be an interesting engineering problem to get them to hold steady and them move but this sort of thing should be doable by the 2300s. So no physical contact and less vibrations.

Women, children and small pets are safely able to ride 1 gravity lifts (elevators), a 1 gravity Beanstalk car is no more dangerous and maintaining a constant 1 G apart from the mid point flip is going to be far more comfortable than doing the late part of the trip at half a G or less (unless you need to acclimatize civilians). You could make the whole trip at 1 G, then quickly switch to a Wheel habitat that is simulating 1G as well.

Technically it makes no sense what so ever to take more time to go from the earths surface up to the GEO than it then takes to make an FTL run to another world.

From a game point of view you can have slow “Tourist” runs with luxury trains that make the run in days rather than hours for those murder/intrigue on the beanstalk type stuff but commercially getting goods and people to the GEO and down again is going to be cost driven. One 30 cab train making the run in 5 days maybe taking 1500 people but you then need 5 such trains going each way for a regular service. If the same train can do it in a day you have the same traffic rate with only two trains (plus spare).

If the Beanstalk is government funded then politicians are going to be wary of stories about how many billions the beanstalk costs each year, particularly when elections come round. For a Mega Corp it doesn’t matter how much PR it would generate, squeezing a few more Pounds/Yen/Dollars/Gold/French money out of it keeps the share holders happy and brings those all important bonuses to the execs.

Either that or it is a boondongle, a sad relic of government or corporate over reach. Maybe it takes 5 days to make the trip because the lowest bidder cable is flawed and cannot stand more stress than that. Perhaps its faded paintwork, scuffed and worn carpets and battered old furnishings are a reminder of a bright hope now faded by reality. Perhaps the beanstalk is rumoured to be a death trap waiting to kill you and only the desperate or the poor use it.

What is the nature of your campaign, is it all bright lights, heroic deeds and exploring strange new worlds. Or is it a dark future, a Gibsonesk/Giegeresk hell of state control, run down and faded glory and darkness with the threat of war and death never far away.

 

[Reynard]

This discussion intrigued me to look for info about space lifts as to why one would build such a structure. The comparisons in the corebook between a Beanstalk module and lifting vehicles such as the spaceplane or the cargo lift rocket disfavors the Beanstalk for maintanence and life support costs. From one source I read, costs for conventional rocket lift is predicted to be US$25K per kilogram to transfer to geostationary orbit compared to a space lift at around US$220 per kilogram! That is definately in favor of the lift.

From the reading, a space lift isn't under constant power. There are two forces at work along a space lift -gravitational pulling down and centrifugal pulling up. Depending on the size of a planet, there will be a point along the height that the forces are equal then the other force dominates as one continues either up or down. Power needs to be applied to overcome each force as you move away from it but no power is needed when you enter the opposite force except for slowing and stopping. The speed of the transit will be determined by the power of gravity or centrifugal force inheirent to that planet. The system only need to accelerated enough to counter the force on it and not much more to save money so travel will be relatively slow. For these reasons I too think 5 days may be excessive but we need to see the math to be sure. Also remember a beanstalk will be feeding on relatively low cost solar energy. This all should make the ticket price very affordable.

I'm assuming the bulk of a beanstalk's economy is cargo that doesn't need life support costs or the high maintanence of the people movers and are very cheap to build. This way I think space lifts are comparable to railway vehicles, freight and passenger, versus airlines. Things get there faster in a plane but cost a LOT more. People in a hurry will take spaceplanes to make their starship connections and pay the price. The cost for using a beanstalk should be very affordable and preferable to the average person. Also there should be trainlines of passenger capsules coming and going carrying thousands of commuters. If, in fact, it doesn't take nearly a week to ride the stalk then I see capsules built more like a passenger car or airline cabin with people packed in tighter over the duration with amenities to match. Anyone for peanuts?

Why even go to the top of a space lift? Other than the star/spaceport complex, which should be huge and spectacular in itself, there will be hotels and attractions and shopping and other sights for tourists as a vacation stop with views you will not get planetside. This will be the place interplanetary travellers stay interim to going downside or before continuing to their next system destination.

 

[Lord High Munchkin]

Once one has integration with a planetary rail system it becomes even easier/cheaper/faster, as freight and passengers can be loaded elsewhere into the specialised cars. There is not even the need to use any facilities at the stalk base other than to connect to the cable assembly (modern trains can do more complex format changes already, such as gauge changes and sideways loading of units).

 

[Lemnoc]

This discussion intrigued me to look for info about space lifts as to why one would build such a structure....

Excellent points. Another factor would be the safety of the space elevator versus boosters, etc. Unless the Kaefers are around, blowing up your beanstalks, this is the best, safest, cheapest way to achieve orbit.

Why even go to the top of a space lift? Other than the star/spaceport complex, which should be huge and spectacular in itself, there will be hotels and attractions and shopping and other sights for tourists as a vacation stop with views you will not get planetside. This will be the place interplanetary travellers stay interim to going downside or before continuing to their next system destination.

The station at the top of the lift exceeds the escape velocity of the system and therefore is a very low-cost, low-power spot from which to launch cargoes and in-system ships.

---

It’s interesting to consider the dynamics of this in 2300AD. How many people are traveling into space in this period, on a weekly basis? Do cars need to leave hourly or twice per day? Thinking this through helps set the scale for your campaign.

 

[GJD]

Both Beanstalks also serve other functions beyond moving stuff into orbit. Both have extensive orbital habitats at their ends -essentially the highport for the planet. Both provide significant power to the planet as well, through solar energy and gravitational potential difference, and some sort of ionic charge differential between the upper and lower atmosphere, apparently (although I have no idea how either of these works in practice).

As Colin pointed out, even though the cars aren't actually attached to the beanstalk runners physically, there is still a load on the runner. In addition, running a magnetic field at speed along the runner will induce heating, as will repeatedly stressing and de-stressing as you are applying load to the runner. You'll need to limit the speed to allow that heat to radiate away between trains of cars. Space is a very good insulator, remember.

G.

 

[Yatima]

Here's a description of a trip from Earth to the Moon using a beanstalk at Libreville, from Alastair Reynolds excellent novel Blue Remembered Earth:

After clearing exit procedures in Libreville, he'd been put to sleep and packed into a coffin-sized passenger capsule. The capsule had been fed like a machine-gun round into the waiting chamber of the slug-black, blunt-hulled thread rider, where it was automatically slotted into place and coupled to internal power and biomonitor buses, along with six hundred otherwise identical capsules, densely packed for maximum transit efficiency. And three days later he'd awoken on the moon.

So there's beanstalk mass transit in action for you: 300 bodies in suspended animation traveling at high acceleration along a beanstalk, and then transported to the surface of the moon within three days, so less than a day from surface to Geostationary Orbit, I guess. Forget the math and gear-heading, this paragraph is all a 2300 player needs to know about beanstalks in the course of using one in game.

Earth in this book has a number of elevators and a Catapult - the 'Blowpipe' - running up Kilimanjaro, that's clearly inspired by Marshall T. Savage's work. A really nice read for 2300 players, I'd suggest.