• Welcome to the new COTI server. We've moved the Citizens to a new server. Please let us know in the COTI Website issue forum if you find any problems.
  • We, the systems administration staff, apologize for this unexpected outage of the boards. We have resolved the root cause of the problem and there should be no further disruptions.

Gravity Wells (how do you beat them)

  • Thread starter Thread starter Pickles
  • Start date Start date
P

Pickles

Guest
I'm currently struggling with an ATU that has a harder SF 'feel'. I'm not talking about removal of all handwavium here, just a departure from some concepts like gravitics and zapotron-guns.

The main thing I'm stuck on at the moment is a pretty basic prerequisite for Travellers: how do you get off planets on a regular basis, without resorting to thrust plates?
 
One ruleset reference would be MT Hard Times, which covers quite a few aspects about planetary lift off without gravitics.
Or FF&S supplies thrusting alternatives, too.

Generally speaking, you "just" need enough thrust to reach at least escape velocity e.g. 11,2 km/s on earth or 5 km/s on Mars..
 
Let us count the ways...

Chemical rockets, like the space shuttle, or a Saturn 5. Upside: Easy to build and fuel, all the players understand how they work. Downside: Lifing any significant mass into orbit requires very large rockets. One modification of this is to have all streamlined starships also have wings. They take off like airplanes, fly to 50,000 feet (or the equivelent) and rocket off from there.

Nuclear rockets: similart to above, but the rockets and fuel can be smaller, making for larger payloads. Downside: People have to get over the fact that every launch sprays radioactive waste all over the landscape.

Beanstalk: Favorite solution of all TUs which lack thruter plates. Starships dock at an orbital platform connected to the ground by a very strong cable. If there are no thruster plates, these will be common.

Linear launch accelerators: Cargo is loaded into a huge magnetic linear accelerator and launched. Downside: Cargo needs to be able to withstand very high acceleration (10s to 100s of Gs), so no people launching.

These are the most common approaches, probably. Here are some other less common approaches:

Laser launching system: Similar to a chemeical rocket, but the fuel is a special plastic which zapped by a high power laser. The repeated laser pulses turn the plastic to plasma which provides thrust. Downside: This gets you to orbit, but not anywhere else.

Orbital Skyhook: A platform in low orbit spinning with two (or four) very long teathers. The cargo airplane files up as high as it can go, and get's hooked by one of the teathers, which then flings it into orbit.

I can find others if you like. And if you want more details on each any of these, let me know.
 
HEPLAR would work, cost would be about 1 G-turn (30 g Minutes) of thrust: you'd need a requirement of thrust > local gravity OR AF hull form to allow takeoff.

I would argue that a "streamlined" hull configuration could enter atmosphere without gravitics, but it would need to be a "tail lander" and pay a substantial (2x? 3x?) fuel penalty for take-off and landing. I base this on calling the Apollo rockets "streamlined" but not "airframe" configuration.

HEPLAR "wilderness" landings should be in water or areas where you don't care about the wildlife: try this link for some of the physics in the "real world"

http://www.projectrho.com/rocket/index.html

Scott Martin

P.S. and remember that people posting from Europe use the "," as the decimal separator, not the "." that we use in north America (with the exception of Quebec) so Mert's 11,2 is 11.2 in North America.
 
Thanks for all the suggestions, everyone! It's a bit tricky, combining SF with plausible science. I've looked at a few of these ideas before, and there's no doubt some amount of handwaving is required for a playable universe. I've also concluded that beanstalks are likely the most practical solution, although they are somewhat vulnerable and tempting targets.

I'll probably go for a combination of all of these approaches. There will be a technological split between 'hardy' cargo and personal launch. Cargo can go by linear accelerator where feasible. There will be beanstalks on worlds that can afford the investment. Hybrid-engined 'space planes' for PC-compatible ships. Nuclear rockets are a possiblilty, due to widespread depopulation and devastation on many worlds.

The atmosphere I'm trying to achieve in this ATU is essentially retro/hard SF, a small universe with many states and relatively few people (there was a big all-out war withan alien species not too long ago, which wiped out most of the population). The biggest state won't control more than 20 systems.

Originally posted by Scott Martin:
P.S. and remember that people posting from Europe use the "," as the decimal separator, not the "." that we use in north America (with the exception of Quebec) so Mert's 11,2 is 11.2 in North America.
Click to expand...
Or, "Elf Komma Zwei", as they say where I come from. ;)
 
Hi Bromgrev !

Would You mind to list to key technologies, You would accept in YTU ?

I would prefer a combined launching system, too.
Perhaps carrying two kinds of propulsion types in one craft is not so efficient, so there might be carriers/launchers using fusion electrical powered jet propulsion, while actual spacecraft just use something like ion drives or Heplar.

Surely transport is more devided between planet and space....
 
Well, restricting myself to propulsion technology (don't want to wander too far into other territories ;) , or this will turn into a IMTU topic), here's what feels right to me:

Beanstalks/space elevators - I can happily imagine materials technology advancing to a state where these become feasible. The downsides I see is that they represent a massive investment, they are vulnerable, and they are a bottleneck for PCs (a.k.a. smugglers and ne'er-do-wells).

Hybrid-engined spaceplanes - Clearly a very specialised beast, although possibly quite common as a shuttle option without the FTL drive. I see them taking off and landing as conventional aircraft.

Ion engines - Sufficiently advanced to provide lots more thrust than available these days, these will probably me a space-travel mainstay. What are the problems with using them for launch?

HEPLAR/nuclear rockets (I like to call them atomic rockets) - Probably mainly for use in space, but might be acceptable for launching from uninhabited 'rocks' and the like.

Laser launch - is this feasible on high-G (Earth equivalent) worlds? I thought the power requirement is outrageous. Even so, still useful.

Linear acceleration - probably only for low-G mining operations.

Solar sails can be used for long-range supply routes, where only the initial wait counts (eg. a regular asteroid or ore 'conveyor belt'). Continuous high-speed interplanetary transports on elliptical runs, fed by shuttles. Sling-shooting around planets. Chemical rockets will probably not feature much, due to their fuel requirements. BTW, there are no fossil fuels IMTU.

Engineer, I agree that orbital interface and space flight are likely to be two very different animals for the vast majority of applications. Nevertheless, I see a need for a ship which is both interstellar and capable of planetary landing and (more importantly) take-off. These will be scout vessels originally, but just the sort of thing PCs might get their hands on at a later stage.

There will probably not be many elements like nanotechnology, bio-engineering, ultra-miniaturisation and such.
 
Given the devistation of the previous war, I'd go with the simplest solutions first. Hybrid rocket/planes for places with breathable atmospheres (at least to the planes). Nuclear rockets where jets don't work (airless rockballs, places without oxygen).

I'd imagine most worlds would have an orbital station or two, even if they don't have a beanstalk. Getting a single ship which can land, take off and do jumps is too inefficient. It makes much more sense to have two (or three) types of space craft, the orbital system plane, an interplanetary hauler and interstellar starship. The PC Starship (if they have one), should come equipped with a lander craft rather than making the starship land.

Interplanetary craft I'd use Ion drive engines or solar sails. Both give low but contstant thrust for speedy transport around the system.

Interstellar craft I would design with nuclear drives, as the need to get to jump points quickly, but with smaller course matching requirements. Plus a jump drive of course.

HePLaR sounds nice, but is is almost as real physics violating as thruster plates. Plus it's too easy to use as a weapon.
 
Originally posted by tjoneslo:
I'd imagine most worlds would have an orbital station or two, even if they don't have a beanstalk.
Click to expand...
They are actually quite common, although many have been abandoned due to lack of manpower or traffic. Arcologies, too.

Getting a single ship which can land, take off and do jumps is too inefficient. It makes much more sense to have two (or three) types of space craft, the orbital system plane, an interplanetary hauler and interstellar starship.
Click to expand...
I'm tending more and more to this sort of sub-division, too. In the case of the aforementioned scout ships, the 'starship' part is mainly engine (think of the SDB jump shuttle), with the 'lander part containing most of the accommodation and control systems.
 
As I am always a bit late with this media stuff, I was able to watch a few Firefly episodes just recently.
Perhaps this kind of ship is the thing Youre looking for: kind of jet propulsion for athmospheric flight and "kind of" Helpar (?) for space.

Regardless which way to the sky You would like to choose, keep in mind, that it needs around 60 GJ of invested energy to get one ton of material significantly out of earth gravity well.

And Ion or Heplar drives can be fixed by simply adjusting fuel and thrust performance a bit


Guess, the starship/lander combination is a pretty good concept..
 
Hmmm...

Methinks that Mert uses a different definition of "a bit" than I do ;)

I largely use "unadjusted" HEPLAR so that people can use my stuff straight up for TNE, without having to juggle too many "IMTU" adjustment factors.

Most of the "hard" science proposals that I have seen use the lander approach. Mass drivers are more efficient than rockets, and less efficient than Beanstalks, but the Capital Investment required for increased efficiency gets pretty brutal.

Mass drivers (or even a big gun) can "throw" solid state components without fear of damage (most can take hundreds to the low thousands of G's) so a "supergun" like the one that Iraq was said to be building could also be used for your space program (cheaper than a mass driver) but on balkanized planets it's sure to make your neigbours nervous. OTOH, cheap solid state sattelites have a lot of useful applications...

Scott Martin
 
So "within an order of magnitude or two" is OK for deck plans too? That's about what I can generally accomplish ;)

It *would* explain those 10-foot tall beds...

Seriously, SF (even "hard" SF) usually has trouble even getting within a couple of orders of magnitude of the Real World(tm) so HEPLAR isn't *that* broken.

Although the missile drives that KG is postulating on a thread in the fleet look like they convert upwards of 1% of their mass directly into energy, significantly more than current nuclear devices. I hope that their (non-nuclear, "3I approved") warheads have significantly lower energy densities!

Scott Martin
 
One problem which is raised by the starship/shuttle comination is the need to cater for atmosphere and vacuum planetfall. This might not be a problem for regular runs, but scouts, merchants and explorers would need capability for both.

Would you carry two shuttles? Or one with two sets of drives? Or a modular cutter, but one which swaps out drives rather than cargo modules?
 
Hi !

Scott, IMHO Helpar fixing is easy, because you might leave basic stats as they are (fuel and power reqs) as well as those 20 tons thrust per MW, and assume that the cute rest of the required energy comes from a "clean" fusion reaction of the fuel itself. Ok, that would be a fix of the operation principle.
Well, this results in Heplar being a kind of continuous working PAW (I figured out some 60GW power output per 20 tons of thrust). So it might not be a design problem but a problem of design consequences (?).
OTOH it make the launch of a free trader to look like a space shuttle start, cool


But as I said in the pre-last post. If You want to use somehow "realistic" reaction based drives (regardless which principle) You have to release a vast amount of energy to the environment.

Bromgrev, vacuum landing indeed seems to be more tricky, but perhaps Heplar use is less harmful here. Ground landing sites might look a bit different and occupy large areas...
 
Hey Mert

I believe that I was the idiot^H^H^H^H^H person who proposed the "fusing HEPLAR" fix, and yes, it does result in lots of energy. It also means that the drive "trail" is probably emitting in the range of 200 Gw per 20T of thrust, since the energy from "plume fusion" will be directed in all directions, not just out the back. A direct side effect of this assumption is that EMM and "Stealth" just won't be effective. (fire your weapons 5M in front of where the drive plume starts)

A free trader launch will still be boring if YTU used CG lifters. If it doesn't, then wear the SPF ten Zillion sunblock (An "active" drive plume will probably be kicking off radiation well into the gamma range) and it will be a lot more energetic that the shuttle launch. Preferred launch sites would probably be water, mountaintop or desert if you care about "habitat" or "about to be desert" if you don't.

Vaccum landings are "easy" in terms of choosing a reaction drive: use a nuclear drive! You are guarenteed to be wearing hostile environmental gear, so you won't care (much) if the ground is a bit radioactive ;)

Atmospheric landings in a hard SF universe are likely to need some kind of lifting body, because "clean" (non-radioactive, as distinct from non-polluting) reaction drives tend to have very poor specific impulse ratings.

Scott Martin
 
Hmm, trying to use "hard" SF in all its consequences is just tough. Especially for your environment.
Perhaps high spaceports really make sense here, in order to protect your planet from being roasted and devasted by interstellar commerce.

I will check if a high TL ramjet systems could be at least a solution for planets with an athmossphere...
 
Or you could just duct atmosphere past your fusion powerplant for atmospheric travel... it's only reaction mass after all ;)

I'm a fan of highports and "very" highports, but if this TU is after a devestating war, they do tend to make convienient targets...

...of course after said war, finding places where "a little more radiation won't hurt" is also pretty easy.

Scott Martin
 
Originally posted by Bromgrev:
Well, restricting myself to propulsion technology (don't want to wander too far into other territories ;) , or this will turn into a IMTU topic), here's what feels right to me:

Hybrid-engined spaceplanes - Clearly a very specialised beast, although possibly quite common as a shuttle option without the FTL drive. I see them taking off and landing as conventional aircraft.
Click to expand...

This would be my number-one choice for getting up if your concerned about the environment. Also a good idea for a ships boat.

Ion engines - Sufficiently advanced to provide lots more thrust than available these days, these will probably me a space-travel mainstay. What are the problems with using them for launch?
Click to expand...
The delta V due to high exhaust veleocity I beleive is what makes these engines nice and efficient and good for space travel. They are also going to be cost effective to put cargo in orbit, the downside is the low accelleration means passengers spend too much time in a planet's radiation belt than is healthy. If you eliminate that problem, they would be good for passengers too.

In the real world you don't get both high exhaust velocity and high accelleration (often noted as thrust), absent something like an Orion drive.

How about a hybrid ion drive/"nuclear" or chemical drive for PCs? You take off with the ion drive then kick in your high accelleration drive (e.g., "nuclear", etc.) to clear the radiation belts then back to your cleaner drive to not dirty up orbit. When in interplanetary space you can use your dirty "nuclear drive" to speed up, manuever or slow down (i.e., combat) and ion drive to coast. If you have them use the same fuel that would make it easier, or they could have different fuels. Different fuels is probably more realistic and maybe one way to tell a merchant from a warship is by the relative amount of each?
 
You must log in or register to reply here.
Back
Top