COACC rocket vs. Hard Times rocket

[Carlobrand]

COACC rocket vs. Hard Times rocket: which is more "realistic"?

COACC offers a rocket for use as an engine in flying craft to permit craft to fly in space, among other things. Hard Times, of course, offers rocket engines too.

As near as I can tell, all other things being equal the Hard Times rockets burn 25 to 30 times as much fuel to achieve the same amount of thrust, they're twice as big (but roughly similar in weight), and they cost a lot less. I understand Hard Times engines were drawn pretty closely from real life - to the extent that real life examples existed.

Different rule sets, of course, but inquiring minds go where they will.

 

[atpollard]

IMHO Hard Times will work better in a hard-science (like 2300AD) setting since it is closer to 'reality'.

On the other hand, the COACC rocket will fit better in a 'Classic Traveller' campaign since the performance is more in agreement with the other Traveller magic technologies like Maneuver Drive/Anti-Gravity (no Conservation of Momentum) and cold fusion Power Plants (no giant radiators).

[This is not a rant against Traveller Tech, just an acknowledgment that it differs from hard science in some areas.]

 

[Carlobrand]

Thing is, I could embrace this as "magic tech" if it weren't for the tech level. One does not expect "magic tech" in the past.

Let's look at this:

Your basic Saturn-V F1 engine delivers ~6.67 million Newtons, burning roughly 430 metric tons (430,000 liters) of fuel in 168 seconds. So, about 2560 liters per second, with each liter delivering ~2600 Newtons. It weighed a bit under 8 and a half metric tons.

A space shuttle main engine (RS-25) is more efficient, delivering about 4500 newtons per liter burned (in vacuum; about 3600 in atmosphere). It weighs about 3 1/2 metric tons.

Your Hard Times TL6 liquid rocket delivers 40 tons of thrust, burning 605 thousand liters per hour, and weighs a ton. 40 tons of thrust in Traveller means enough thrust to push 40 tons at 1g, so 400,000 Newtons? 605,000 liters per hour is 168 liters per second, so each liter delivers 2380 Newtons, not quite the efficiency of the F1, but reasonably close - though it weighs twice as much for the same performance. The TL7 delivers 45 tons with 570 kl/h, better than 2800 Newtons per liter. There's nothing quite matching the Space Shuttle engine, more's the pity.

Your COACC TL6 basic rocket delivers 30 tons of thrust, burning 19200 liters per hour, and weighs a ton. 30 tons of thrust in Traveller means enough thrust to push 30 tons at 1g, so 300,000 Newtons? 19200 liters per hour is 5.33 liters per second, so each liter delivers better than 56,000 Newtons - which translates to better than 20 times the specific impulse of the F1. The HP rocket delivers more thrust per engine weight, but consumes more fuel. Neither delivers as much thrust per ton of engine as the F1, but their fuel efficiency compares with some ion engines (and they are very clearly not ion engines).

So, out of curiosity - just how accurate are the other COACC engines?

 

[aramis]

yes, 1 Ton of thrust is 10kN.

The COACC rocket has an issue - the fuel masses 1 ton per 1000L - which means it's not LHyd and O2.

The energy release is excessive in COACC plants - best to ignore them in favor of HT.

 

[atpollard]

The energy release is excessive in COACC plants - best to ignore them in favor of HT.

Just a question for clarity, but isn't the standard Fusion Power Plant /Maneuver Drive just as bad?

(I have vauge recolections of the rocket equation yielding the equivalent of FTL exhaust for all traveller drives.)

 

[mike wightman]

The standard fusion plant/maneuver drive is Traveller magitec, the rockets are supposed to be real world science.

 

[Dragoner]

Thing is, I could embrace this as "magic tech" if it weren't for the tech level. One does not expect "magic tech" in the past.

Let's look at this:

Your basic Saturn-V F1 engine delivers ~6.67 million Newtons, burning roughly 430 metric tons (430,000 liters) of fuel in 168 seconds. So, about 2560 liters per second, with each liter delivering ~2600 Newtons. It weighed a bit under 8 and a half metric tons.

A space shuttle main engine (RS-25) is more efficient, delivering about 4500 newtons per liter burned (in vacuum; about 3600 in atmosphere). It weighs about 3 1/2 metric tons.

Your Hard Times TL6 liquid rocket delivers 40 tons of thrust, burning 605 thousand liters per hour, and weighs a ton. 40 tons of thrust in Traveller means enough thrust to push 40 tons at 1g, so 400,000 Newtons? 605,000 liters per hour is 168 liters per second, so each liter delivers 2380 Newtons, not quite the efficiency of the F1, but reasonably close - though it weighs twice as much for the same performance. The TL7 delivers 45 tons with 570 kl/h, better than 2800 Newtons per liter. There's nothing quite matching the Space Shuttle engine, more's the pity.

Your COACC TL6 basic rocket delivers 30 tons of thrust, burning 19200 liters per hour, and weighs a ton. 30 tons of thrust in Traveller means enough thrust to push 30 tons at 1g, so 300,000 Newtons? 19200 liters per hour is 5.33 liters per second, so each liter delivers better than 56,000 Newtons - which translates to better than 20 times the specific impulse of the F1. The HP rocket delivers more thrust per engine weight, but consumes more fuel. Neither delivers as much thrust per ton of engine as the F1, but their fuel efficiency compares with some ion engines (and they are very clearly not ion engines).

So, out of curiosity - just how accurate are the other COACC engines?

IMO, after having done the calc's (nice BTW), I would use the real world values.

To give the rules writers some credit, much was written pre-internet so their sources were limited.

 

[atpollard]

I think that Hard Times aimed for realism (and did a good job of achieving it).
I think COACC attempted to aim for better compatibility with the rest of the magitech.

 

[aramis]

Just a question for clarity, but isn't the standard Fusion Power Plant /Maneuver Drive just as bad?

(I have vauge recolections of the rocket equation yielding the equivalent of FTL exhaust for all traveller drives.)

That's TNE's HEPlaR. Which is near-C exhaust - it's throwing bay-weapon-level amounts of energy, and should be generating major radiation hits on the starport upon landing and takeoff...

The Maneuver Drive in MT is gravitic tech, not a particle thrower. It has effectively infinite ISP... as long as it gets power. In the inner system, it's possible to get a ship going quite impressively fast, even with T4's 1000 diameter limit on gravitic M-Drives.

 

[Carlobrand]

That's TNE's HEPlaR. Which is near-C exhaust - it's throwing bay-weapon-level amounts of energy, and should be generating major radiation hits on the starport upon landing and takeoff...

The Maneuver Drive in MT is gravitic tech, not a particle thrower. It has effectively infinite ISP... as long as it gets power. In the inner system, it's possible to get a ship going quite impressively fast, even with T4's 1000 diameter limit on gravitic M-Drives.

Suppose. when in atmosphere, you superheated atmosphere as the working fluid? Wouldn't need magically fantastic exhaust velocities.

 

[aramis]

Suppose. when in atmosphere, you superheated atmosphere as the working fluid? Wouldn't need magically fantastic exhaust velocities.

You could get roughly 28:1 expansion on the water in the air, and 16:1 on the air itself... but the HEPlaR is a vacuum capable near-C plasma torch.

I can't quite figure out the exhaust velocity, but I can say that it's 0.34cc of hydrogen fuel per kilonewton per second.... at least in FF&S 2.

10kN is 3.4cc, and takes a couple liters of drive and 50kW of power...

 

[Lycanorukke]

Finally found the old link I had for reaction thrusters - http://traveller.mu.org/house/thrusters.html

About halfway down the page is a somewhat modified version of the HT tables to bring it a bit more inline with the real world and examples as well as a few interesting side discussions.

 

[Carlobrand]

Just a question for clarity, but isn't the standard Fusion Power Plant /Maneuver Drive just as bad?

(I have vauge recolections of the rocket equation yielding the equivalent of FTL exhaust for all traveller drives.)

Belated thought: were you factoring in relativistic effects on the exhaust? As you add more energy to the propellant, the resulting exhaust becomes more massive relative to the vehicle adding the energy (therefore requiring more and more energy for each unit of increased exhaust speed, resulting in that lovely curve whereby a particle's mass approaches - but never reaches - infinity as its speed approaches the speed of light). At some point, the drive becomes a kind of particle accelerator: if you just happened to have :devil:infinite energy:devil: available, and could transfer that with perfect efficiency to the propellant, you could pump out exhaust of infinite mass travelling at the speed of light (which of course is absurd, but you get the general idea).

(Having accomplished that, you could then invent a handy time machine and go back in time to thoroughly violate causality.)

 

[McPerth]

The Maneuver Drive in MT is gravitic tech, not a particle thrower. It has effectively infinite ISP... as long as it gets power. In the inner system, it's possible to get a ship going quite impressively fast, even with T4's 1000 diameter limit on gravitic M-Drives.

But IIRC, neither in HT nor in COACC do the Fusion Rocket have this backfire effect, while in T4 (and I guess in TNE) there is, needing empty space behind or it is irradiated.

 

[aramis]

But IIRC, neither in HT nor in COACC do the Fusion Rocket have this backfire effect, while in T4 (and I guess in TNE) there is, needing empty space behind or it is irradiated.

That effect is NOT mentioned by the rules - it's a side effect of the 4M ISP and a very light fuel.