[Spaceships] Is This Legal?

[MatthewVilter]

Originally Posted by scc

OK, I'm kicking around the idea of a flyback booster, specifically a winged spaceplane.

Cool!

Originally Posted by scc

2) I'm thinking of using Jet Engines to get a better price per mps to orbit, the question is do I count the tank of jet fuel (Which I assume will be empty or nearly so) when calculating the Delta-V increase for chemical rockets?

Keep in mind that you will want some fuel in that tank for return and landing. Unless you plan to just glide in. In that case you can probably get away with a partially filled small tank at launch and dump whatever you haven't used by the time you run out of air.

Originally Posted by Ulzgoroth

Yes, no control room means no control. You could omit it if it uses a soft landing system, probably.

A small control room might suffice, though for atmospheric flight it might not.

It should be fine as long as you don't plan on any fancy flying, I would think. But yeah you do need a control room system for controlled flight (more for the RCS and control surfaces than for the room itself).

Originally Posted by Ulzgoroth

Definitely not.

If you want to account for those emptied tanks, you can multiply the number of tanks or rocket fuel by 20/(20-jet fuel tanks) and using that to calculate dleta-V. This isn't given in RAW, but it whoulc be correct.

And if you want to get really accurate numbers even for a rocket that still has partially full jet fuel tanks it is really not that hard to break out your slide rule. (Although doing that with a system where fuel tanks are 100% fuel and wings are a massless body feature might be overkill...)

Originally Posted by Ulzgoroth

It seems a bit questionable to allow a vessel that has a hughe hole in the front from where its forward parts flew away on their own to be streamlined at all.

Theoretically SpaceX will be doing this. But that is a conventional (non-winged) design that will be doing a vertical landing so in scc's case I think you're right. I mean I guess it would be possible to build an inline lift stage with wings that is aerodynamic after separation but...it would be hard.

For a piggyback configuration I would use an External Clamp. And if the spacecraft is also winged that is probably the way to go; stacking something with wings on the top of a rocket introduces a lot of instability.

An alternative is a Soft Landing System. I would be tempted to let something with wings use a smaller Soft Landing System...but that just brings us back to the streamlining problem.

Originally Posted by RogerBW

I think the "a ship one SM smaller as the front six systems of the big ship" approach is not necessarily appropriate for ships where the back section can operate autonomously. For the big plane with a spaceship on top, I'd be more inclined to have six systems of Hangar Bay or even Cargo in the midsection, or just a huge External Clamp (and change performance accordingly for the payload craft).

Agreed, as far as the clamp goes. I don't think that a Hangar Bay or Cargo Hold would represent this particularly well but I guess it does make things a lot easier...

Originally Posted by schmeelke

"A streamlined spacecraft must have at least one Armor system for its front hull or central hull (if a multi-stage design, only the uppermost section need be armored)." (p. 9)

I think this rule assumes the booster stage is discarded, rather than reused. I would assume that yes, it should be armored.

Originally Posted by RogerBW

If you do still want to use the Upper Stage approach, then armouring one of the central systems will be vital for a fly-back booster.

Agreed.

[Flyndaran]

Originally Posted by MatthewVilter

...
For a piggyback configuration I would use an External Clamp. And if the spacecraft is also winged that is probably the way to go; stacking something with wings on the top of a rocket introduces a lot of instability.
...


Agreed.

Wasn't that what the shuttle "on top" of booster rockets was?
Size-wise it was boosters with a smaller ship attached.

[MatthewVilter]

Originally Posted by Flyndaran

Wasn't that what the shuttle "on top" of booster rockets was?
Size-wise it was boosters with a smaller ship attached.

The shuttle actually works as example of my point. A conventional rocket has each stage stacked on top of the last. The shuttle on the other hand had a drop tank mounted along side and booters mounted on the sides of that. If the shuttle had been stacked on top of the external tank (like the Orion on top of the Space Launch System) the drag from its wings would make it want to flip over and the more it turned over the more drag the wings would cause.

(Of course, the other reason the drop tank was on the side was because the shuttle needed to carry the expansive main engines into space so that it could bring them home safe.)

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

[scc]

And it looks like I don't need a booster after all. 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, this gives me 5.83 mps from standard chemical rockets. A Large System cargo bay lets me carry 50 tons into orbit, and 3 small systems, a chemical rocket, control room and METALLIC LAMINATE Armor round out the design

[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]

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... >_<