Alternative to drop tanks

Discuss the Traveller RPG and its many settings
Moppy
Greater Spotted Mongoose
Posts: 935
Joined: Sun Oct 04, 2015 12:42 pm

Re: Alternative to drop tanks

Postby Moppy » Thu Apr 25, 2019 1:46 pm

The grav bikes certainly aren't ridable without straps.

I agree that ships should operate slowly in atmosphere, but "hot-take off Han" and the millenium falcon look pretty impressive on the screen.

I don't see how a fuel scoop differs from a ramjet or scramjet. They both suck in air, process it, and deal with shockwaves and pressure. A key difference is that the maneuver drive continues to operate if you close the scoop for a bit and you don't lose power.

(A ramjet relies on supersonic forward speed to suck in air, slows it to subsonic via aerodynamics, and uses that air to burn fuel. A scramjet has supersonic airflow throughout the engine. A regular jet engine requires an air compressor instead of using forward motion to compress the air).
phavoc
Cosmic Mongoose
Posts: 4790
Joined: Tue Nov 04, 2008 6:13 pm

Re: Alternative to drop tanks

Postby phavoc » Thu Apr 25, 2019 6:00 pm

Moppy wrote:
Thu Apr 25, 2019 1:46 pm
The grav bikes certainly aren't ridable without straps.

I agree that ships should operate slowly in atmosphere, but "hot-take off Han" and the millenium falcon look pretty impressive on the screen.

I don't see how a fuel scoop differs from a ramjet or scramjet. They both suck in air, process it, and deal with shockwaves and pressure. A key difference is that the maneuver drive continues to operate if you close the scoop for a bit and you don't lose power.

(A ramjet relies on supersonic forward speed to suck in air, slows it to subsonic via aerodynamics, and uses that air to burn fuel. A scramjet has supersonic airflow throughout the engine. A regular jet engine requires an air compressor instead of using forward motion to compress the air).
The difference is that the air is flowing through the engine, and you aren't trying to scoop it up (let alone filter it simultaneously). If you look closely at airframes that travel at supersonic speeds you'll see how carefully (and sometimes oddly) every protrusion is around intakes. Airflow and drag have to be factored into the airframe design. Craft flying at slower subsonic speed's don't have as many issues. But even those you will notice that airflow is taken into account for things like speedbrakes, how the engines are positioned below (or above if you are Honda) the wings, or stuck to the sides of the airframe.

Scooping up gases means the atmosphere is flowing through the intakes, through piping/filters/supercoolers/ and into tanks. That means the amount of airflow is going to be restricted going though the piping. That airflow is going to have enormous pressure pushing it into the pipe system. With no place to flow the excess pressure will build up a wall at the intake source, causing a decrease in flow.

Ramjets slow the air down for combustion purposes, but they operate most efficiently when the craft is traveling at supersonic speeds. In all of the examples the air is flowing through, and there is no attempt to capture any of it.

Fuel scoops would need to sip at the air to ensure the internal tank pressure does not increase to the point that it would build a wall of pressure and prevent additional intake. Filtering out hydrogen from other gases at supersonic speeds would indeed be a feat - regardless of the air pressure question.
Moppy
Greater Spotted Mongoose
Posts: 935
Joined: Sun Oct 04, 2015 12:42 pm

Re: Alternative to drop tanks

Postby Moppy » Thu Apr 25, 2019 8:07 pm

You are aware that air is bled from airplane engines to drive or power other systems on the plane (pneumatucs) and pressurise the cabin? The usual source of air is the compressor of the jet engine and you will see a pressure release valve under the tail.

Edit 1: Random Google hit for "aviation bleed air systems": https://www.skybrary.aero/index.php/Air ... ir_Systems

Edit 2: This is also true of supersonic aircraft. The f-22 uses bleed air: https://www.globalsecurity.org/military ... 2-fcas.htm

Edit 3: Beyond using a pop-out molecular sieve I am not going to comment on how to extract Hydrogen because I am not a chemist.

Edit 4: bleed air is sometimes cooled before being routed onwards, so we're already doing some limited processing of it.

Edit 5: I'm unable to find out if hypersonic planes use bleed air because they're all secret military projects.
BigDogsRunning
Mongoose
Posts: 140
Joined: Mon Sep 11, 2017 9:54 pm

Re: Alternative to drop tanks

Postby BigDogsRunning » Fri Apr 26, 2019 1:40 am

NOLATrav wrote:
Tue Apr 23, 2019 5:02 am
Also if the tender is larger than the jumping ship, the refueled ship will need to accelerate away from said tender.

Not a big deal I suppose (what’s the 100-diameter distance of a 10,000 dton tanker?) but something to think about.
That's why you use long hoses, or a tank at the end of a tether. At the point where, if the ship were using drop-tanks it's finished with the fuel source, the hoses/tanks get hauled back in by the tanker, which is standing off a good distance. If they can to in-air refueling on bombers, and other long-range military aircraft, with drones no less, this should be child's play at higher TL. You either catch the tank with a magnetic cargo grappler, or you have a small maneuver drive built into it that guides it back to mama for topping off.

No explosive pins to replace, less worrying about whether the tanks will get clear. And no expensive tanks being wasted whenever you use them. Someone could make a good living selling, and then just recovering, drop tanks.
phavoc
Cosmic Mongoose
Posts: 4790
Joined: Tue Nov 04, 2008 6:13 pm

Re: Alternative to drop tanks

Postby phavoc » Fri Apr 26, 2019 3:12 am

Moppy wrote:
Thu Apr 25, 2019 8:07 pm
You are aware that air is bled from airplane engines to drive or power other systems on the plane (pneumatucs) and pressurise the cabin? The usual source of air is the compressor of the jet engine and you will see a pressure release valve under the tail.

Edit 1: Random Google hit for "aviation bleed air systems": https://www.skybrary.aero/index.php/Air ... ir_Systems

Edit 2: This is also true of supersonic aircraft. The f-22 uses bleed air: https://www.globalsecurity.org/military ... 2-fcas.htm

Edit 3: Beyond using a pop-out molecular sieve I am not going to comment on how to extract Hydrogen because I am not a chemist.

Edit 4: bleed air is sometimes cooled before being routed onwards, so we're already doing some limited processing of it.

Edit 5: I'm unable to find out if hypersonic planes use bleed air because they're all secret military projects.
Yes, it's used to extract air for both passenger and fighter aircraft. But it's also in much smaller quantities. A sip compared to the massive gulp of engines. It's not difficult to do it for smaller amounts. Though, to be fair, the F22 system has some gremlins in it and has been blamed for at least one crash and numerous incidents. Nobody knows why yet though. Brass says it's safe but pots are still reporting hypoxia incidents.

If such a system were used for hydrogen collection it wouldn't be an issue. However the amounts are much different. Maybe they figure all this out in the future.
HalC
Mongoose
Posts: 159
Joined: Wed Jan 10, 2018 3:42 pm

Re: Alternative to drop tanks

Postby HalC » Fri Apr 26, 2019 3:35 am

Ok, what does have to happen for Wilderness refueling to work?

1) sufficient volume of hydrogen and/or Dirty Hydrogen has to be ingested to fill up a given volume of space.

2) time spent in the "run" per GURPS TRAVELLER (which I largely suspect is taken from other prior sources) states in part...
"One pass through the gas giant’s atmosphere is sufficient to fill all tanks and takes about 2 hours and 20 minutes (7 turns). Transferring fuel to ship’s tanks takes an additional 40 minutes (2 turns)."

The 2 hours 20 minutes reference is the actual skimming phase, the 2 turns to transfer - is from shuttles to the main ship. If that is the case, why that oddly specific time duration of 2 hours 20 minutes? Does it take the same amount of time for a shuttle that can gulp in 50 dTons of fuel as it does for a 1,000 dTon hull handling its needs?

If you have an influx of gas being shoved through the air intake, you have to have an exit point for the gas to exit from or eventually, you have a full volume of gas in a chamber (Tank) and eventually, you can not fill it up any further. Is this process one that is desired, or do you essentially have a Stream of gas flowing through the pipes, some being diverted into the fuel tank, some being allowed to exit out some exit point - and you keep doing this until you have liquid Hydrogen in your tanks (or liquid dirty hydrogen that needs to be refined)?

When a tank pumps out its liquid hydrogen, what takes the the place of the now empty tank? Does it create vacuum - or is the tank eventually filled with some form of gas? If it is a vacuum, wouldn't said vacuum help when it came time to suck in more hydrogen during a gas run? What if it was just any old atmosphere (oxygen/nitrogen/argon/etc - and prior to the gas refueling run through the atmosphere, they pump it all out and turn it into a vacuum?

If you are travelling at any kind of supersonic speed, what is the pressure experienced by any "atmosphere intake"?

Just curious.
Condottiere
Chief Mongoose
Posts: 7375
Joined: Mon Sep 23, 2013 8:23 pm

Re: Alternative to drop tanks

Postby Condottiere » Fri Apr 26, 2019 5:01 am

1. There's probably some form of compression going on during skimming, and presumably that soup separates enough so that the hydrogen, in it's dirty form, is identifiable and pumped into the tanks while the remainder drains out.

2. Minus local gravity, and the rest of the thrust can be used to calculate forward velocity; the atmospheric resistance could at high enough speed turn the hull into a fireball, at which point external sensors could burn off, and armouring could become a factor.

3. As for hydrogen turbines during transition, time and flow through are obviously factors, presumably the requirement being anywhere from six minutes to damn near instantaneous.
HalC
Mongoose
Posts: 159
Joined: Wed Jan 10, 2018 3:42 pm

Re: Alternative to drop tanks

Postby HalC » Fri Apr 26, 2019 5:13 am

Now you know why I wondered what the atmospheric density would be at the point of skimming. If it were me trying to come up with a formula of some sort, it would look something like this:

Volume collected = Time * Density * compression effect

The compression effect would have to be the size of the intake opening, the density determines how much is collected at any given moment, and the time would be how long it takes to fill 13.6 (or 14 depending on what your views are of a dTon by volume) cubic meters.

Put another way? Let's say for the sake of argument, that we need a total of GigaAtoms (pulling names and numbers out of thin air so to speak) to fill one dTon. In one second, you can gain .00000001 GA's worth. We would need to either increase the GA's per cubic volume we fly though, or we would need to fly really really quick so as to go through a LOT of cubic volume, or - we'd need to go to where the density was sufficient to get a full GA worth of Hydrogen to fill up the entire fuel tank within 2 hours and 20 minutes time.

Go too fast, and you overheat the hull. On the other hand, if the density isn't high enough to burn your hull out, or you drop your speed to a sufficient level where you don't burn - then maybe it is doable. I don't know, I'm not a physicist. For me, the trick is to think of the Atmosphere as no different than water (because it appears that both are the same effect - fluid in nature).

To be blunt? The idea of risking a fatal plunge into a Gas Giant's atmosphere just to skim off fuel seems worse than jumping off a perfectly good airplane without a functioning parachute.

I understand the concept that as long as you're sufficiently far away from the center of mass for a Gas Giant, the gravitational pull exerted upon your space craft is less than if you were closer to the center of mass. A ship with only a 1 G acceleration has to be sufficiently high enough for its engines to pull you out, yet sufficiently close enough to skim hydrogen. How for for example, does a ship have to be away from the center of mass for its engine to work, and is it still within the atmosphere sufficiently to skim?
Annatar Giftbringer
Lesser Spotted Mongoose
Posts: 758
Joined: Wed Jul 25, 2007 10:35 am
Location: Uddevalla, Sweden

Re: Alternative to drop tanks

Postby Annatar Giftbringer » Fri Apr 26, 2019 10:59 am

The Traveller Companion has a chapter on gas giant operations and fuel skimming.
HalC
Mongoose
Posts: 159
Joined: Wed Jan 10, 2018 3:42 pm

Re: Alternative to drop tanks

Postby HalC » Fri Apr 26, 2019 9:17 pm

Annatar Giftbringer wrote:
Fri Apr 26, 2019 10:59 am
The Traveller Companion has a chapter on gas giant operations and fuel skimming.
Alas - without a job - not a viable option.
PsiTraveller
Greater Spotted Mongoose
Posts: 894
Joined: Thu Dec 04, 2014 11:47 pm

Re: Alternative to drop tanks

Postby PsiTraveller » Sun Apr 28, 2019 4:35 pm

Going back to the main topic. A tender using a long hose offers some interesting options if it is allowed.

The departing ship would have the connecting tonnage of drop tanks. Attached to that would be a drone with the hose end. The long hose to the tender sends in the hydrogen into the system just like a droptank sequence. Once the fuel is pumped in the disconnect sequence happens and the drone drags the hose away from the expanding jump bubble.

Once the departing ship enters jump the hose is reeled back into the tender and the tender can go to the next ship in need of fuel.

1st edition had droptanks surviving on an 8+ roll. After TL 14 they always survive. This has been removed in 2nd edition Highguard, ouch. That is a big change. (page 44 of 1st edition highguard, page 37 of 2nd edition)

On the flip side if your drone is cheap enough you may be okay with it getting destroyed. You just put a new drone and a new end on the hose. It could be cheaper than buying a new drop tank every few trips.
AnotherDilbert
Cosmic Mongoose
Posts: 3869
Joined: Wed Dec 23, 2015 2:49 pm
Location: Sweden

Re: Alternative to drop tanks

Postby AnotherDilbert » Sun Apr 28, 2019 6:13 pm

PsiTraveller wrote: 1st edition had droptanks surviving on an 8+ roll. After TL 14 they always survive. This has been removed in 2nd edition Highguard, ouch.
?
MgT2 HG, p37 wrote: When a drop tank is used and jettisoned, roll 2D. On
8+, the tank survives the ejection process and can, in theory, be retrieved and reused.
PsiTraveller
Greater Spotted Mongoose
Posts: 894
Joined: Thu Dec 04, 2014 11:47 pm

Re: Alternative to drop tanks

Postby PsiTraveller » Sun Apr 28, 2019 10:28 pm

1st edition High Guard:
When a drop tank is used, roll 2d6. On an 8+, the tank survives the
ejection process and can be retrieved and reused. Otherwise, it is
destroyed by the expanding jump bubble or warped by the jettison
explosion. At TL14 the use of drop tanks has been improved to such
a degree that drop tanks designed at this tech level or above will
automatically survive use.

2nd edition
When a drop tank is used and jettisoned, roll 2D. On
8+, the tank survives the ejection process and can, in
theory, be retrieved and reused. Otherwise, it is destroyed
by the expanding jump bubble or warped by the jettison
explosion. In addition, drop tanks are automatically
destroyed once their ship has lost 10% of its Hull points.


So why no Tech improvement for survivability in 2nd edition? That's a big change. Only a 45 percent chance for survival for a 25 000/ton device. Pricey system.
Linwood
Lesser Spotted Mongoose
Posts: 527
Joined: Thu Jun 29, 2017 12:41 am

Re: Alternative to drop tanks

Postby Linwood » Mon Apr 29, 2019 9:27 am

I think I’d house-rule that drop tank survivability increases with TL - every level above the minimum required adds a +1 to that 8+ roll.
Moppy
Greater Spotted Mongoose
Posts: 935
Joined: Sun Oct 04, 2015 12:42 pm

Re: Alternative to drop tanks

Postby Moppy » Mon Apr 29, 2019 10:02 am

2nd edition
When a drop tank is used and jettisoned, roll 2D. On
8+, the tank survives the ejection process and can, in
theory, be retrieved and reused. Otherwise, it is destroyed
by the expanding jump bubble or warped by the jettison
explosion
. In addition, drop tanks are automatically
destroyed once their ship has lost 10% of its Hull points.
It's nice to know they don't know how to build a multi-stage rocket. Perhaps having invented the maneuver drive first, they ceased working on rockets.
AnotherDilbert
Cosmic Mongoose
Posts: 3869
Joined: Wed Dec 23, 2015 2:49 pm
Location: Sweden

Re: Alternative to drop tanks

Postby AnotherDilbert » Mon Apr 29, 2019 10:57 am

PsiTraveller wrote: So why no Tech improvement for survivability in 2nd edition? That's a big change. Only a 45 percent chance for survival for a 25 000/ton device. Pricey system.
Sorry, I misunderstood you. Yes, that was removed during beta.

I can only speculate, but I guess it was intended to make things like this more expensive:
viewtopic.php?f=89&t=118716
baithammer
Greater Spotted Mongoose
Posts: 912
Joined: Wed May 31, 2017 2:21 am

Re: Alternative to drop tanks

Postby baithammer » Mon Apr 29, 2019 11:12 am

Moppy wrote:
Mon Apr 29, 2019 10:02 am
It's nice to know they don't know how to build a multi-stage rocket. Perhaps having invented the maneuver drive first, they ceased working on rockets.
I'd imagine a jump being several magnitudes greater than booster stages of a rocket.
Sigtrygg
Greater Spotted Mongoose
Posts: 1303
Joined: Sat Aug 12, 2006 9:23 am

Re: Alternative to drop tanks

Postby Sigtrygg » Mon Apr 29, 2019 5:09 pm

In the Third Imperium setting drop tanks are destroyed upon use:
L-Hyd drop ships have only been in service for the last dozen years in the interior, being made possible by recent advances in the field of capacitor engineering, a joint press release explained. Commercial vessels equipped with the new generation of long-storage jump capacitors carry jump fuel in specially designed L-Hyd drop tanks in excess of their rated tonnage. Upon conversion of the fuel to the massive energy required for jump, the drop tanks are explosively jettisoned through the use of break-away connections and explosive bolts. Jump is executed when the remains of the tanks are a safe distance from the vessel.
Condottiere
Chief Mongoose
Posts: 7375
Joined: Mon Sep 23, 2013 8:23 pm

Re: Alternative to drop tanks

Postby Condottiere » Mon Apr 29, 2019 9:03 pm

Another instance where you have to decide whether you want to house rule it.

At least, you can cite historical precedent, unlike my buttplug spherical drop tank, only adopted because it's a cheaper configuration and is expelled naturally and directly away from the the starship and it's entry into the rabbit hole.
PsiTraveller
Greater Spotted Mongoose
Posts: 894
Joined: Thu Dec 04, 2014 11:47 pm

Re: Alternative to drop tanks

Postby PsiTraveller » Tue Apr 30, 2019 2:10 am

What was the cost of those L-Hyd drop tanks? It makes for an expensive transport if they need to be replaced each time.

https://calormen.com/tns/ct.html
L-Hyd tanks are not reusable, and thus increase the absolute cost per jump. However, experience has shown that the increase in cargo tonnage resulting from the elimination of internal J-fuel storage more than makes up for this, the press release explained.

So now we have a base number for the cost of the disposable tank. They have to cost less per ton than the income from shipping the cargo. The next question is is this based on spec freight or cargo profits?

For 2nd edition a J4 jump cargo price is 7000 credits per ton. The cost of a drop tank is 25 000 credits a ton. This is a problem if the tanks are not reusable. L-Hyd tanks are 200 000 credits a ton in 2nd edition. This is a price problem for the concept. Even the prices for passengers works out to about the same price based on how many tons a cabin takes up.

So if we look at the single shot jump drives a la Drinax, is there a cheap version of a jump bubble inducer we can cobble together? A Jump space Jato unit as it were?

Were prices for the disposable drop tanks ever published?

Who is online

Users browsing this forum: Tay and 14 guests