Reaction Engines

[Laryssa]

Here are some TransHuman Space Reaction Engines I've converted for use with Traveller. The only one that works well is the High Thrust Fusion Pulse Engine, as it can sustain a continous 1-G acceleration for an hour given a fuel supply of 1.35 tons of nuclear pellets in a 50-ton ship. This table is for a single drive unit of this reaction engine type. Look up the amount of drive units each spaceship type requires based on hull size in the T20 Traveller Handbook.

I'm assuming that every 50 tons of ship's hull has a mass of 67.5 metric tons for the purposes of these calculations.

Reaction Engines
Type ________________ TL Cost __ Size _ EP ____ Mass _ RMC _ ISP __ Thrust
1-G Fission _________ 8 MCr 2 __ 2.5 __ +2.5 __ 10 ___ 235 _ 1,034 _ 67.5 tons
1-G Fusion Pulse (HT) 8 MCr 6.75 8.4375 +8.4375 33.75_ 1.35_ 15,000_ 67.5 tons

A scout ship would require a 67.5 ton High Thrust fusion pulse engine, and 2.7 tons of fuel pellets to accelerate for 2 hours at a continuous 1-G acceleration, leaving 29.8 tons for staterooms, the bridge and everything else besides the engines. Such a ship can reach a maximum velocity of 35.280 km/second using up half its fuel. A winged design would be best for lifting off planets with atmosphere as that acceleration would then go towards increasing velocity within that atmosphere rather than fighting gravity.

 

[Scott Martin]

Hello

A mass of ~10 metric tonnes per dTon is actually more reasonable. This give you an idea how badly HEPLAR is "broken"

For real world reaction thruster systems you really want a low accelleration high energy system for long duration flights, and a high thrust/weight system to move stuf to and from planetary bodies.

Nice having the conversion from a "harder" SF system!

Scott Martin

 

[aramis]

Laryssa:

Based upon MT and TNE, 50Td should mass close to 500Mg (tons metric). Which is still, BTW, less than a Specific Gravity averaging about 0.7

 

[Laryssa]

I was just going by what the T20 Book said about how to convert dtons to metric tons.

Now suppose you wanted to get rid of the standard Maneuver Drives in Traveller and you wanted to substitute realistic reaction drives. Now lets assume you keep the jump drives, but you remove the requirement for jump fuel, now they simply require energy inputs as listed in the T20 book. So the goal is now this create a bunch of standard Starships ranging from 100 dtons to 800 dtons, and give them reaction engines that can take them off the surface of an Earthlike planet and out to 100 diameters so it can activate its jump drive, and then bring them back down to the surface of another Earthlike destination planet, and suppose you have to sorts of drive available in Transhuman Space, could you do this? I think that in a frontier/exploration campaign, drives that require infrastructure such as laser rockets are out.

 

[Scott Martin]

Yup, this is a fairly "easy" conversion, and can probably be done by just "tweaking" existing designs.

That said, you will probably get much better efficiency if your "jumpships" carry landers to do the cargo shuttling, and contain a big J-Drive, lots of cargo space, a small high ISP (Ion?) thruster unit, and they never get within 100D of a planet.

small survey craft (Scouts) are likely to carry the largest J-Drive they can, since the fuel penalty is ONLY for reaction drives now, which will vastly extend their range.

If you want something like this, I can build you a TL-13 scout using FF&S

Some "unintended consequences" of your proposed changes

Scott Martin

 

[Laryssa]

Sure, go right ahead. Also in this universe there is no artificial gravity. gravity is produced either through spinning the space vehicle or through acceleration. Reactionless drives and artificial gravity are related technologies and neither one of them was discovered in this universe. The Jump drive was a suprise breakthrough utilizing string theory, basically it is able to bend space, but only in places where the gravitational gradient is low.

Now another thing the space drives I mention, they produce energy as a byproduct of their operation, that is the Fission Rocket and the High Thrust Fusion Pulse Rocket. (See the charts up above with the + signs for EP)

The fission rocket operates by utlizing an atomic pile that heats hydrogen into incandescence, it is basically a rocket whose exhaust is hydrogen gas. When you close the valve to the engine bell, the remaining hydrogen is shunted into a closed cycle that powers an electric generator, when the valve is open the exhaust gases still power the generator on their way out of the rocket and they also accelerate the rocket two. In other words the fission rocket engine can use its reactor to power the Jump drive and or weapons systems as needed.

The fusion pulse engine operates by a bank of laser beams converging on a nuclear pellet containing Helium-3 and Deuterium, the lasers implode the pellets causing them to fuse into helium-4 ions + a proton and some gamma rays, the high energy ions and proton can be used to generate a current as it leaves the rocket engine through magnetic induction, but their is no way to get this reactor to operate while on closed cycle, these nuclear explosions cannot be contained entirely by the space craft and most of the energy goes to propell the ship forward, it will need a separate closed cycle reactor to power the Jump drive, but the fusion rocket energy out put is available to power the weapon systems when the rockets are on.

 

[Jamus]

Originally posted by Laryssa:
I was just going by what the T20 Book said about how to convert dtons to metric tons.

Now suppose you wanted to get rid of the standard Maneuver Drives in Traveller and you wanted to substitute realistic reaction drives. Now lets assume you keep the jump drives, but you remove the requirement for jump fuel, now they simply require energy inputs as listed in the T20 book. So the goal is now this create a bunch of standard Starships ranging from 100 dtons to 800 dtons, and give them reaction engines that can take them off the surface of an Earthlike planet and out to 100 diameters so it can activate its jump drive, and then bring them back down to the surface of another Earthlike destination planet, and suppose you have to sorts of drive available in Transhuman Space, could you do this? I think that in a frontier/exploration campaign, drives that require infrastructure such as laser rockets are out.

Awsome.

 

[Uncle Bob]

Uh, you do know that neither the fission nor the fusion pulse engines can be used to take off from an inhabited planet? And if you are being realistic, at least 20 dton of your scoutship would have to be alotted to wings/aerofoils? Maybe 10 dton for a lifting body.

And 2 hr of accelleration is only 12 turns in Book 2, 6 turns in Book 5 combat. You are going to need a new combat system. Not impossible, but more work. And at 35 km/sec it is only about 8 hr to 100 diameters, but Earth-Mars takes about 1-3 months, depending. Not imposible, but suddenly jump drive becomes attractive for intrasystem travel.

 

[Laryssa]

1-3 months is not bad. Any of today's astronauts would not complain about such a speedy trip. I am using the T20 system by the way, in which the combat round is 1 minute within an atmosphere or 20 minutes in space, this is 3 combat rounds of acceleration and 24 combat rounds of cruise before 100 diameters is reached by your calculations. A fission rocket can accelerate for as long as its nuclear fule holds out if it is within an atmosphere, it only begins to use up stored reaction mass once it clears the atmosphere and an 8.5 minute burn should be enough to reach escape velocity at 1-G accelleration about orbital velocity + 5 km. Earth's escape velocity is 11.18 km/sec some of that velocity is obtained by accelerating through the atmosphere obtaining the reaction mass from that atmosphere as a scramjet would, so in addition to that velocity, the atomic rocket should be able to use its stored reaction mass to reach escape velocity. If it obtains the velocity of an outbound Apollo Capsule, it will reach 100 diameters in 10 days.

Now why do you say a fission rocket can't be used to take off from an inhabited planet? A fission rocket is basically a cousin of a chemical rocket, the main difference is that when a chemical rocket combines hydrogen and oxygen, its exhaust is water vapor, while the exhaust of an atomic rocket is either superheated air or hydrogen. The source of energy in the atomic rocket is the atomic pile, while that source in a chemical rocket is chemical combustion. A scramjet can achieve that combustion by obtaining oxygen from the air, this this requires an atmosphere with free oxygen in it. I think an atomic jet/rocket can be used in an atmosphere of an inhabited planet, but the inhabitants won't like it very much.

Fusion pulse rockets require lasers to implode pellets containing fusion fuel, this is akin to the Orion rocket only with much smaller bombs. The designers of Orion believed that their ship could take off from the surface of the Earth and the initial plans called for it to be launched from a desert. A fusion pulse rocket doesn't require fissionable material, its exhaust consists of helium-4, hydrogen, some free neutrons where deuterium/deuterium fusion occurs + some gamma rays, most of which don't travel very far in Earth's atmosphere.

What doesn't work is something called a fusion torch rocket, as that requires a plasma to be confined by a magnetic field and also open to space. If it is sitting on Earth's surface, it will be open to an atmosphere instead. The fusion bottle must be sealed off from the atmosphere and the plasma comfined in a magnetic field within a vacuum chamber, but if it is to function as a rocket, the plasma must be allowed to leak out in one direction, but if you do that, the atmosphere will rush in and cool the plasma down to a gas and magnetic fields will no longer be able to confine it. Also the thrust is not sufficient to lift the ship off the ground even if it were standing in a vacuum, but fusion pulse is different as it uses lasers, not magnetic fields and the fusion only occurs for a brief moment in a pulse rather than continuously as in a fusion torch. I think the best combo would be an atomic rocket with a fusion torch or a scramjet with a fusion torch if you assume their is free oxygen in the atmosphere.

 

[Straybow]

MT/TNE cargo and structure mass is broken. dT = 14 m³ = 494 ft³ = 5 register tons. The 5:1 ratio is also consistant for the dimensions of wet navy displacement tons compared to dT.

 

[Border Reiver]

Not broken, just a poorly defined source. MT opted to use the freight ton for displacement. It is 40 ft³ or 1.133m³ (MT calls it 1.135) The displacement ton is 35 ft³ and the register ton 100ft³.

I'm not entirely sure where your figures come from.

 

[Laryssa]

Spaceships are supposed to be made with light materials anyway. I imagine the walls of spaceships are going to be very thin, at least the internal walls.. In many casesz the walls are going to be like the walls of a balloon. The important thing to consider after that is the density of the breathable air that keeps people alive. Additionally spaceships have some shielding requirements. Water makes the best shield against cosmic radiation. I think it was 5 feet or water or 5 meters of water provides the same protection against cosmic rays as being on the surface of the Earth. That said larger ships are going to have more internal volume in proportion to their cosmic ray shielding than smaller ships. At a minimum size of d100 tons per starship though that's going to be pretty big. I'm not sure if any current manned spacecraft approaches the volume of 100 dtons, maybe the International space station does.

 

[Andrew Boulton]

I think the shuttle is about 100dt.

 

[Uncle Bob]

Larrysa
I am not sure why you think the amount of free oxygen in the atmosphere will make the slightest difference to nuclear engines.
Fission drive in atmosphere: As you point out, local residents will not be pleased, particularly if they become a prosperous world with a busy trade. The prohibition is political, not technical.

Fusion pulse drives in current designs have the fuel pellet in vacuum so it can be precisely located. Even if you get past that, the neutron flux will not be trivial, even if you are fusing simple hydrogen to H4. Traveller seems to assume that an internal PP can control the side reactions, but this will not happen in an external drive. And the amount of energy demands the same number of fusion reactions no mstter pulse or torch. so you still generate the same number of neutrons.

Deep space Ships hulls have to protect against cosmic rays, solar radiation and meteors. Also Traveller ships have to be reinforced to handle multi-g maneuvers and aeodynamic stresses. These hulls resemble tanks more than aluminum balloons.

 

[Laryssa]

Larrysa
I am not sure why you think the amount of free oxygen in the atmosphere will make the slightest difference to nuclear engines.

What I had in mind was the Fission Air Ram, listed below with some other reaction drives from THS that I converted to traveller terms. Fortunately Fusion Pulse engines won't be required to get off the ground. Underdeveloped planets will probably prefer Fission Air rams, where free oxygen is not available in the planet's atmosphere, where free oxygen is available the Turbo-scramjet is preferred.

Unfortunately most ships probably won't have both fission air rams and turboscramjets

MANEUVER DRIVES
Type ________________ TL Cost _____ Size EP __ Mass_ RMC _____ ISP Thrust
Chemical Rockets
-Metal-oxygen _______ 07 MCr 1.0100 2.53 00000 10.13 253.00 MO 274 6-G (405 tons)
-Kerosene-oxygen ____ 07 MCr 0.2050 1.02 00000 4.091 220.00 KO 395 5-G (337.5 tons)
-Hydrogen-oxygen ____ 07 MCr 0.1640 0.82 00000 3.273 540.00 HO 514 4-G (270 tons)
Laser Rocket ________ 08 MCr 0.2025 1.01 0000* 4.050 40.500 P 1500 3-G (202.5 tons)
Mass Driver _________ 08 MCr 4.0500 10.1 -40.5 40.50 0.2025 RD 720 0.015-G (1.0125 tons)
Fission Drive _______ 08 MCr 2.0000 2.50 +2.50 10.00 235.00 H 1034 1-G (67.5 tons)
Fusion Pulse Drives
-High-impulse (HI) __ 08 MCr 3.3750 8.44 +8.44 33.75 0.3375 N 30,000 0.5-G (33.75 tons)
-High-thrust (HT) ___ 08 MCr 6.7500 8.44 +8.44 33.75 1.3500 N 15,000 1-G (67.5 tons)
Fusion Torch Drives
-High-impulse (HI) __ 08 MCr 6.7500 8.44 +8.44 33.75 0.3375 H 36,000 0.05-G (3.375 tons)
-High-thrust (HT) ___ 08 MCr 6.7500 8.44 +8.44 33.75 2.1094 H 18,000 0.125-G (8.4375 tons)
Atmospheric
-Fission Air-Ram ____ 08 MCr 8.1000 10.1 00000 40.50 n/a ____ n/a __ 3-G (202.5 tons)
-Turbo-Scramjet _____ 08 MCr 2.0250 5.06 00000 20.25 1.0000 J 13,333 3-G (202.5 tons)

Mass (in tons), Size (in dtons),
EP (1 EP = 1 MW; + indicates power output, - indicates power requirement),
RMC: Reaction Mass consumption to provide one hours worth of given thrust
ISP: The drives specific impulse; to calculate total change in velocity capable of:
Delta-V = 0.003 x ISP x ln[Loaded Mass (in tons)/Dry Mass (in tons). The symbol “ln” means natural logarithm, a function found on most scientific calculators.
* The laser rocket has no onboard power requirements, but must be energized by an external 20-GW laser beam per dton of drive (20-GW laser requires 40,000 EP of energy to operate at ground installation)

Reaction Mass, Coolant, and Fuel Table (per dton)
Type _______________ Mass Cost
Ablative Plastic (P) 12.0 MCr 0.001
Hydrogen (H) _______ 01.0 MCr 0.00035
Hydrogen-oxygen (HO) 3.50 MCr 0.0003
Kerosene-oxygen (KO) 14.0 MCr 0.005
Metal-oxygen (MO) __ 21.0 MCr 0.005
Jet Fuel (J) _______ 10.8 MCr 0.01
Nuclear Pellets (N)_ 12.0 MCr 0.006
Rock Dust (RD) _____ 26.0 Free

 

[Scott Martin]

I suspect that GURPS uses "free oxygen" to determine habitibility, so enough free oxygen means it's habitable, and you don't want to be dumping radiologicals around, low free oxygen means that you need hazardous environment gear anyway, so no-one cares about a few extre millirem of exposure...

Scott Martin

 

[Laryssa]

Most planets will have a population rating of 5, that is hundreds of thousands of people, the operation of a fission air ram probably won't be noticed on such a backwater planet. There is the laser rocket of course. So each planet will probably have its own smallships to ferry crews, passengers, and cargo parked in orbit. Fission air rams for those planets with exotic or unbreathable atmospheres, turboscramjets for those populated planets with breathable atmospheres, and laser rockets for populated planets with unbreathable atmospheres.

Also how large of a population do you really need to have a world government? 100,000 people can just as easily be scattered all over the planet as living in on town with a government ansd starport. Is a planet with 1,000 people going to even bother to have a government? If the 1,000 people consists of scattered hemits and prospectors, its going to be impossible to enforce the law anyway.

 

[Uncle Bob]

I believe most high-thrust high-Isp reaction drives will be confined to high orbit and above, so I can certainly get behind a system of shuttles. A strong candidate early candidate would be VTOVL vehicles of the ROMBUS/Deta Clipper type. HTOHL vehicles require a thick atmosphere and TL8+. By TL9 the Beanstalk becomes feasable

 

[Laryssa]

I was thinking of marrying that to Warp Engines, the kind that need a gradual gravity gradiant to function, say starting at 100 diameters of Earth.

How do they work?

Well there is Warp 0, which is a black globe or a deflector shield however you like it, it is functionally equivalent to a black globe, and it functions 1 Earth diameter away from the Earth's center, closer than that it fails.

At 100 diameters warp 1 kicks in and since that allows travel at 365 times the speed of light, is crosses 1 light year in a day, the minimum size starship that you can instal a warp 1 engine is 100 dtons

Warp 2 200 dtons ect.

 

[Laryssa]

I think the Warp Scales will go something like this:

Warp _ Velocity _______ Minimum size ______________ USP
0 ____ 0 c (0 ly/day) _ 1 Drive Unit (50 dton Hull) ________ 1
1 ____ 365 c (1 ly/day) 2 Drive Units (100 dton Hull) ________ 1
2 ____ 730 c (2 ly/day) 4 Drive Units (200 dton Hull) ________ 2
3 __ 1,095 c (3 ly/day) 8 Drive Units (400 dton Hull) ________ 2
4 __ 1,460 c (4 ly/day) 16 Drive Units (800 dton Hull) _______ 3
5 __ 1,825 c (5 ly/day) 32 Drive Units (1,600 dton Hull) __ 3
6 __ 2,190 c (6 ly/day) 64 Drive Units (3,200 dton Hull) __ 4
7 __ 2,555 c (7 ly/day) 128 Drive Units (6,400 dton Hull) __ 4
8 __ 2,920 c (8 ly/day) 256 Drive Units (12,800 dton Hull) __ 5
9 __ 3,285 c (9 ly/day) 512 Drive Units (25,600 dton Hull) __ 5
A __ 3,650 c (10 ly/day) 1024 Drive Units (51,200 dton Hull) __ 6
B __ 4,015 c (11 ly/day) 2048 Drive Units (102,400 dton Hull) __ 6
C __ 4,380 c (12 ly/day) 4096 Drive Units (204,800 dton Hull) __ 7
D __ 4,745 c (13 ly/day) 8,192 Drive Units (409,600 dton Hull) __ 7
E __ 5,110 c (14 ly/day) 16,384 Drive Units (819,200 dton Hull) __ 8

The UPC number is similar to the UPC number of an equivalent Black Globe.

As you can see this system favors large Star Ships, and encourages them to have subordinate craft for landing on planets I have a Star Trek Style campaign in mind, but taking it in a more realistic direction. A deflector shield is simply a stationary Warp envelope and all warp drives have that capacity, the higher warp drives gives better protection and higher energy absorption. Each black globe/warp envelope stays on for a preset amount of time and the flickers off Typically they are on 50% of the time and off the other 50%, and a typical Warp Drive flickers on and off 100 times per second, so a ship with a deflector shield on looks 50% dimmer than it does with it off. The flicker rate is not adjustible, but the velocity and direction of the warp drive is. One can steer a Warp ship much as one does an airplane through the air, but once the warp drive shuts off the Star Ship retains its original velocity unless it fires a reaction drive while in warp. The GM has to keep frack of all additions to the ship's normal velocity while this happens, this is typically done to match velocities with the ship's intended target.