[Spaceships] Is This Legal?

[MatthewVilter]

Originally Posted by Flyndaran

Okay, I failed my reading comprehension roll.
An A.I. piloted booster rocket ship attached via an external clamp onto the manned ship works, right?

Yep.

Originally Posted by Flyndaran

I'm under the weather today, and am not comprehending things I otherwise would.

No worries! Any choice for what "on top" means for a vehicle type that takes off vertically, hangs out in freefall, and then lands horizontally is arbitrary anyway.



Okay so...I had to do some analysis...working notes follow...

Going for LEO at TL 8...

Booster Drone
TL 8 SM+(n) Winged Hull with Total Automation
Lifts a SM+(n-2) craft onto a suborbital trajectory. The payload will need a Chemical Rocket and it’s own fuel to make orbit.

Front:
1 x Metallic Laminate Armor
1 x Control Room
4 x Fuel Tank

Central:
1 x External Clamp //by RAW it is better to just use a Small Upper Stage and yeah, if the mount configuration was going to mass this much I think people would get pretty clever about building stable, vertically stacked, independently aerodynamic configurations - IRL either configuration would add some amount of mass and technical complexity
2 x Payload //just leaving this space unused makes the whole design process much easier, not really different from cargo I guess
4 x Fuel Tank

Rear:
1 x Jet Engine (1G, 1 hour/tank)
1 x Chemical Rocket (3G, 0.15 mps/tank)
1 x Jet Fuel Tank
4 x Fuel Tank


Next I run the numbers on the performance of some alternative engine and fuel configurations. I have not really looked at craft or fuel costs yet.

With 1 Rocket Engine:
14 RP-1/LOX (3.36 mps delta-V) = 3.36 => the payload will need 2.24 more delta-V (11 tanks) //for reference

With 1 Rocket Engine and 1 Tank of Jet Fuel:
12 RP-1/LOX, 1 Jet Engine (0.694 mps airspeed + 2.52 mps delta-V) = 3.21 => the payload will need 2.39 more delta-V (12 tanks) //this is the configuration in the listing above
11 RP-1/LOX, 2 Jet Engines (0.972 mps airspeed + 2.31 mps delta-V) = 3.28 => the payload will need 2.32 more delta-V (12 tanks)
10 RP-1/LOX, 3 Jet Engines (1.19 mps airspeed + 2.1 mps delta-V) = 3.29 => the payload will need 2.31 more delta-V (11 tanks)
9 RP-1/LOX, 4 Jet Engines (1.39 mps airspeed + 1.89 mps delta-V) = 3.28 => the payload will need 2.32 more delta-V (12 tanks) //you might run out of jet fuel before you clear atmo with these multi-jet-engine configs - they are fuel hungry and get marginal airspeed buffs...need to run the numbers...
8 RP-1/LOX, 5 Jet Engines (1.56 mps airspeed + 1.44 mps delta-V) = 3.0 => the payload will need 2.6 more delta-V (13 tanks) //this is the break point for fuel tank number

If you give the payload a Nuclear Thermal Hydrogen Rocket instead it can make orbit with just 6 tanks of LH2

If you use Nuclear Thermal Hydrogen Rockets for blastoff you can do SSTO and just forget the whole premise of this thread. ;)

With 2 Nuclear Thermal Hydrogen Rockets //runway takeoff
13 LH2 (9.36 mps delta-V) = 9.36

With 6 Nuclear Thermal Hydrogen Rockets //VTO at 1.2G
9 LH2 (5.67 mps delta-V) = 5.67

And if you are really serious about cheap fuel...

With 2 Nuclear Thermal Water Rockets:
13 H2O (3.12 mps delta-V) = 3.12 => the payload will need 2.48 more delta-V (12 water tanks)

Even if you read the NTR entry (p. 22) as a misprint where “...or 0.45 mps (TL8).” should read “...or 0.45 mps (TL9).” you can still do SSTO...

With 2 (definitely TL 8) Nuclear Thermal Hydrogen Rockets //runway takeoff
13 LH2 (6.24 mps delta-V) = 6.24


What we are working with:
TL 8:
Jet Engine (1G, 1 hour/tank)
Chemical Rocket (3G, 0.15 mps/tank)
Ion Drive (0.0005G, 3 mps/tank)
Nuclear Thermal Hydrogen Rocket (0.2G, 0.3-0.45 mps/tank)
Nuclear Thermal Water Rocket (0.6G, 0.1-0.15 mps/tank)
External Pulsed Plasma (2G, 3 mps/tank)

I am don’t think an Ion Drive is strong enough to take suborbital to orbital before falling back to earth. I am not even going to get into the Orion Drive... >_<

[MatthewVilter]

Originally Posted by scc

By playing some games using Large Systems on a SM+7 hull I can cram 265 tons of fuel into only 16 spaces, that equal to 17 and 2/3 spaces of fuel...

You are going to need to explain that one to me...

[scc]

Originally Posted by MatthewVilter

You are going to need to explain that one to me...

At odd numbered SM's for spacecraft there's this odd effect that a Large System is equal to 3 and 1/3 systems. For example, and this is from in my design, at SM+7 a Fuel Tank holds 15 tons of fuel and 3 hold 45 tons, but a SM+8 Fuel Tank holds 50 tons and occupies the same space as 3 SM+7 Fuel Tanks. Net result, 3 Fuel Tanks of SM+8 on a SM+7 design hold as much fuel as 10 tanks, but only take up the same space as 9

[MatthewVilter]

Ah.

How do I put this? ... That's not- ... You can't just- ...

Okay let me put it this way:

What is the mass of this craft? 50 tons of cargo + 265 tons of fuel + the three small systems which total 15 tons = 330 tons

Now a SM+7 craft is normally 300 tons which means that a small sized chemical rocket that gives a ship like that 1G acceleration is putting out 300 tons of thrust. Now technically by the RAW 1G acceleration is the minimum needed to take off into orbit from the surface of earth. Realistically that is a bit low but in any case that 5 ton rocket is only going give your 330 ton craft an acceleration of ~0.909G...

I guess you could get around that with wings but that is without even going into what this kind of thing does to delta-V calculations...and small+undersized control rooms...

[malloyd]

Originally Posted by scc

At odd numbered SM's for spacecraft there's this odd effect that a Large System is equal to 3 and 1/3 systems. For example, and this is from in my design, at SM+7 a Fuel Tank holds 15 tons of fuel and 3 hold 45 tons, but a SM+8 Fuel Tank holds 50 tons and occupies the same space as 3 SM+7 Fuel Tanks. Net result, 3 Fuel Tanks of SM+8 on a SM+7 design hold as much fuel as 10 tanks, but only take up the same space as 9

To the accuracy of Spaceships, that's probably a negligible difference. And I'm not sure it's that much of an advantage in what's mostly a space combat system. You have a little more fuel, but a lot more vulnerability - put one hole in your single big tank (or cripple your single fuel pump or whatever) and you have no fuel.

[Ulzgoroth]

Originally Posted by scc

At odd numbered SM's for spacecraft there's this odd effect that a Large System is equal to 3 and 1/3 systems. For example, and this is from in my design, at SM+7 a Fuel Tank holds 15 tons of fuel and 3 hold 45 tons, but a SM+8 Fuel Tank holds 50 tons and occupies the same space as 3 SM+7 Fuel Tanks. Net result, 3 Fuel Tanks of SM+8 on a SM+7 design hold as much fuel as 10 tanks, but only take up the same space as 9

If you're rules-lawyering it up, that doesn't matter: delta-V is always described in terms of number of tanks, not quantity of fuel.

If you're not, you wouldn't do that in the first place.

(No, this isn't a legitimate representation of bigger tanks being more efficient, because you can't be more than 100% efficient.)

[scc]

Originally Posted by Ulzgoroth

If you're rules-lawyering it up, that doesn't matter: delta-V is always described in terms of number of tanks, not quantity of fuel.

If you're not, you wouldn't do that in the first place.

(No, this isn't a legitimate representation of bigger tanks being more efficient, because you can't be more than 100% efficient.)

Fine then, let me put it this way, a SM+8 Fuel Tank is 3 and 1/3 times the size of a SM+7 Fuel Tank

[Anthony]

Originally Posted by scc

Fine then, let me put it this way, a SM+8 Fuel Tank is 3 and 1/3 times the size of a SM+7 Fuel Tank

This is what we call a 'rounding error'. It should actually be 3.16x bigger, but in practice it doesn't matter, because Spaceships describes everything in spaces.

[MatthewVilter]

Originally Posted by Anthony

This is what we call a 'rounding error'. It should actually be 3.16x bigger, but in practice it doesn't matter, because Spaceships describes everything in spaces.

Ah yes! That is the term I was looking for.

scc the fact that you were able to find this exploit makes me think that you probably know why it does not make sense. If I was your GM and you tried to pull this I would be shocked...

If you really don't see the problem I (or someone) can explain it more clearly but yes, with the RAW I think your 'large fuel tank folding trick' is Legal...I just would be surprised to see anyone using it let alone allowing it.

[Fred Brackin]

Originally Posted by MatthewVilter

If you really don't see the problem I (or someone) can explain it more clearly but yes, with the RAW I think your 'large fuel tank folding trick' is Legal...I just would be surprised to see anyone using it let alone allowing it.

I not only wouldn't allow it I don't think it's legal either. "Fuel Tank" as a larger system doesn't even make sense. A larger system should stuill only be 15% of your mass or the same as the 3 regular systems it replaces.

In particular it screws the calculation of "miles per second per tank of fuel". Fuel is never measured in Spaceships as anything other than "tanks" or miles per second". Never convert fuel tanks to tons, lbs, gallons or hogsheads of fuel when calculating performance.

It also screws up the bonus you get for having many tanks of fuel. See "Delta-V increase" on p.17 of Spaceships I.