[Spaceships] TL10 Space RV

[DataPacRat]

I want to throw together a relatively low-cost craft, for a wealthy biont to get from Earth to orbiting the other planets, as they see fit. (And to land on Titan, and anywhere under 0.1G surface gravity.) I'm a little nervous about pushing at the edges of Spaceships' simplifying assumptions, since I don't know where they start breaking; has anyone got any details on that? For example, is it really feasible to launch a craft with wings and a 0.1G drive from Earth's surface? (SS1 p39 says that it would take 2 hours 36 minutes.)

The setting is approximately THS, roughly TL10 with only a couple of pieces of superscience: a low-thrust reactionless drive (call it around the stats of Spaceships' Rotary Reactionless Drive, 0.1G per space) and as a spinoff of that tech, what's effectively a vacuum-energy power plant (though it uses completely different technobabble; call it SS7's Perpetual Motion Machine, 1 PP per space). Though if any non-superscience doodads get the job done for less investment, I'm open to using them instead.

(By the way, does anyone know how those two Spaceships systems compare to 3e Vehicles' "TL9 reactionless drive" and "TL10 zero-point energy generator" (the latter described as an NPU with +25% cost and unlimited lifespan)?)

Quickie design sketch: SM+4, streamlined, TL10 (mostly non-superscience).
- Design switches: Advanced Computers (as TL11), Exposed Radiators, Slower Industrial Systems
- Winged: $50k
- 1 spc: Armor, nanocomposite, dDR 3 (1 per facing), $50k
- 4 spcs: Cargo Holds, 2 tons
- 1 spc: Control Room, $20k
- 1 spc: External Clamp, $1k
- 10 spcs: Habitat: 1 SM+6 space: bunkroom for 2, total life support: $100k
- 1 spc: Power Plant, Fission Reactor, 1 PP, 75 years: $30k
- 1 spc: Reactionless Drive, rotary, accel 0.1 G, req 1 PP, $50k
- 1 spc: Weapon, central turret, improved laser, rapid fire: Major SM+4 battery (300 kJ, dDmg 1d+2, RoF 20/20s, rng C/S or 300/1000 mi), req 1 PP: $100k
-- Total cost: $401k
-- LMass 10 tons, length 10 yards, dST/HP 15, HT 12, Hnd/SR -1/4, dDR 1, Occ 2ASV.
-- Air performance: 800 mph. Hnd/SR 3/5.

? Self-Healing: +$200k, regenerate 1 dHP per 6.66 days?
? replace external clamp: Robot Arm, +$99k?
- Power Plant refueling: $3k every 75 years

How many cost-cutting corners can you think of, or other improvements that seem reasonable? (I'm open to using any of the SS books, or Pyramid articles offering more options.)



(In case you're wondering: Yes, I'm biting the bullet that such drives can be used to accelerate to high fractions of light-speed and impact a planet with devastating effects. I'm postulating a large-scale mutual-defense treaty that runs large numbers of UltraTech's non-superscience gravscanners as a detection net, and just one of the layers of interceptors being around 15,000 32cm missiles around a third of an AU from Earth. I currently plan on mentioning the existence of these two platforms as being public knowledge, and that there are further defenses that either aren't relevant to the game or are not-widely-known military secrets.)

[Michael Thayne]

This won't let you take off from Titan—Titan's surface gravity is 0.14G. The "extra large" habitat seems fine and I don't think it breaks anything even if it isn't RAW. I might consider more armor, even just for purposes of dealing with micrometeor impacts (IIRC Spaceships 5 has them doing 1d dDamage per 10 mps of velocity). If the laser is solely for micrometeor / missile defense you might make it very rapid fire—point defense is a major area where Spaceships can give odd or at least-counter intuitive results.

[ericthered]

Originally Posted by DataPacRat

I want to throw together a relatively low-cost craft, for a wealthy biont to get from Earth to orbiting the other planets, as they see fit. (And to land on Titan, and anywhere under 0.1G surface gravity.) I'm a little nervous about pushing at the edges of Spaceships' simplifying assumptions, since I don't know where they start breaking; has anyone got any details on that? For example, is it really feasible to launch a craft with wings and a 0.1G drive from Earth's surface? (SS1 p39 says that it would take 2 hours 36 minutes.)

If you've got a reaction-less drive, a power source that doesn't run out, and you can make it to the extreme upper atmosphere? you probably can get into orbit, and once in orbit the size of the acceleration doesn't matter.


I think your bird can fly, but not strongly. The power to weight ratio on a jet liner is about 0.3, and you've got a third of that.



I've got some concerns about the play between air resistance, lift, velocity, and heating. You need to be in atmosphere to generate lift until you reach orbital velocity. atmosphere is going to slow you down as long as you're in it, and eventually create massive heating around your ship, not to mention drag. You can reduce drag by flying higher, but that also reduces your lift.

[Michael Thayne]

Originally Posted by ericthered

I've got some concerns about the play between air resistance, lift, velocity, and heating. You need to be in atmosphere to generate lift until you reach orbital velocity. atmosphere is going to slow you down as long as you're in it, and eventually create massive heating around your ship, not to mention drag. You can reduce drag by flying higher, but that also reduces your lift.

Yeah, I don't think there's any way you can make it to orbit with 0.1G thrust. Even doing it with 1G would be tricky. If you want a rigorous answer though you'd need to play around with a program like Orbiter or perhaps a heavily modded Kerbal Space Program.

[DataPacRat]

Originally Posted by Michael Thayne

This won't let you take off from Titan—Titan's surface gravity is 0.14G.

Yes, but it also has an atmosphere denser than Earth's; if the RV can fly into orbit from Earth, it should be able to fly up from Titan.

Originally Posted by Michael Thayne

The "extra large" habitat seems fine and I don't think it breaks anything even if it isn't RAW. I might consider more armor, even just for purposes of dealing with micrometeor impacts (IIRC Spaceships 5 has them doing 1d dDamage per 10 mps of velocity).

We're a bit squeezed for space; even upgrading to best-in-setting diamondoid armor, 2 spaces provides a total of 10 dDR to spread across 3 hull sections. ... Probably still a good idea.

Originally Posted by Michael Thayne

If the laser is solely for micrometeor / missile defense you might make it very rapid fire—point defense is a major area where Spaceships can give odd or at least-counter intuitive results.

I looked at that, and the trouble with a VRF beam seems to be that its kJ goes down so far it only does 1d-2 dDamage, which runs a 1-in-3 risk of not being able to vaporize a micrometeor even if it hits.

Hm... re-reading attack rolls, though, it looks like going from RF to VRF adds +5 to the attack roll, so any attack that would hit with a RF shot would like hit with at least 5 VRF shots, and there's more than a 99% chance of getting at least 1 damage with at least 1 of 5 shots. Looks like another change worth making.

Originally Posted by ericthered

If you've got a reaction-less drive, a power source that doesn't run out, and you can make it to the extreme upper atmosphere? you probably can get into orbit, and once in orbit the size of the acceleration doesn't matter.


I think your bird can fly, but not strongly. The power to weight ratio on a jet liner is about 0.3, and you've got a third of that.

By SS's RAW, the RV should be able to hit 790 mph, rounded up; I'm not worried about relatively poor in-atmosphere performance, as long as it's got at least some.

Originally Posted by ericthered

I've got some concerns about the play between air resistance, lift, velocity, and heating. You need to be in atmosphere to generate lift until you reach orbital velocity. atmosphere is going to slow you down as long as you're in it, and eventually create massive heating around your ship, not to mention drag. You can reduce drag by flying higher, but that also reduces your lift.

Originally Posted by Michael Thayne

Yeah, I don't think there's any way you can make it to orbit with 0.1G thrust. Even doing it with 1G would be tricky. If you want a rigorous answer though you'd need to play around with a program like Orbiter or perhaps a heavily modded Kerbal Space Program.

I suppose another reality check might be to try to recreate the RV in 3e's Vehicles, and see it it still works. Let's see, that's Vp164's sidebar; if the craft's aerial top speed is below orbital velocity, it should be able to reach Earth orbit, though the sAccel is reduced by whatever portion is required to keep the craft aloft. However, SS doesn't get fine-grained enough to describe stall speeds; that's in VXii p30, and if I guesstimate a lift area of 70 sf and "good" streamlining, that's a stall speed of 250 mph. With SS's airspeed of 800 mph, then less than half of the craft's thrust is needed to keep it airborne, so the other half can still be applied as sAccel to get into orbit.

Though I've probably made all sorts of math errors in that paragraph, so somebody with more experience with GURPS vehicle-building should feel free to correct me. :)

[ericthered]

Originally Posted by DataPacRat

By SS's RAW, the RV should be able to hit 790 mph, rounded up; I'm not worried about relatively poor in-atmosphere performance, as long as it's got at least some.

By that particular equation, a boeing 747 can hit 1300 mph (about double the true number) and sixth generation fighter jets can hit 2500 mph (about 1000 mph high). The equation performs best for needle-like rocket shapes with 1G or more of acceleration. It also claims that 10 cm per second squared acceleration can get you to 250 mph in atmosphere, and that's even more obviously wrong.


I would not use that acceleration equation for anything under 1G. I do have an alternate equation, which is to remove the square root, and replace the 2,500 mph with 1,500 mph if its plane like rather than rocket like (and with that kind of thrust, it needs to be to take off). So I've got the top speed for the plane at 150 mph for sea level air pressure.

[DataPacRat]

Originally Posted by ericthered

By that particular equation, a boeing 747 can hit 1300 mph (about double the true number) and sixth generation fighter jets can hit 2500 mph (about 1000 mph high). The equation performs best for needle-like rocket shapes with 1G or more of acceleration. It also claims that 10 cm per second squared acceleration can get you to 250 mph in atmosphere, and that's even more obviously wrong.


I would not use that acceleration equation for anything under 1G. I do have an alternate equation, which is to remove the square root, and replace the 2,500 mph with 1,500 mph if its plane like rather than rocket like (and with that kind of thrust, it needs to be to take off). So I've got the top speed for the plane at 150 mph for sea level air pressure.

If we're going to get rid of SS's formula here, we might as well fall back to Vehicles'. The craft is SM+4, implying a volume of 301 to 1,000 cf, thus a surface area of 300 to 600 sf, which feeds into the drag formula. Given 2,000 lbs of thrust, then top aerial speed depends on the level of streamlining (for which I'll assume at least "good", since the frame is Spaceships "streamlined"): "good" streamlining, max aSpeed 275 to 385 mph; "very good" 355 to 500 mph; "superior" 500 to 705 mph; "excellent" 705 to 1000 mph; "radical" 1000 to 1415 mph.

I'm not really sure how best to estimate stall speed, since it depends mainly on wing area... and which is relevant here because, according to VXii, an aircraft's ceiling is 8,000 yards * ln (TopAirSpeed/StallSpeed). I'm also not sure how this ceiling figure meshes with Vehicles p164's ground-to-space equations.

[ericthered]

Originally Posted by DataPacRat

If we're going to get rid of SS's formula here, we might as well fall back to Vehicles'. The craft is SM+4, implying a volume of 301 to 1,000 cf, thus a surface area of 300 to 600 sf, which feeds into the drag formula. Given 2,000 lbs of thrust, then top aerial speed depends on the level of streamlining (for which I'll assume at least "good", since the frame is Spaceships "streamlined"): "good" streamlining, max aSpeed 275 to 385 mph; "very good" 355 to 500 mph; "superior" 500 to 705 mph; "excellent" 705 to 1000 mph; "radical" 1000 to 1415 mph.

Are you sure you've taken Wing surface area into account in those numbers? they feel rather high to me.


EDIT: you know what? never mind. I think we've established that the thing can get off the ground, and that it will take some really high-end streamlining to get it going at decent speeds. I'm not sure if living quarters at SM+4 can be streamlined that much and remain usable, but this thing can get into the atmosphere, and I'll bet you can get it into the upper atmosphere.


Vehicles 133 has a stall speed equation.

[DataPacRat]

Originally Posted by ericthered

EDIT: you know what? never mind. I think we've established that the thing can get off the ground, and that it will take some really high-end streamlining to get it going at decent speeds. I'm not sure if living quarters at SM+4 can be streamlined that much and remain usable, but this thing can get into the atmosphere, and I'll bet you can get it into the upper atmosphere.


Vehicles 133 has a stall speed equation.

By that equation, then assuming wings of 0.1 times the body's volume (as suggested in pV17), depending on the exact size of the ship and level of streamlining, I get stall speeds between 144 and 288 mph.

[Michael Thayne]

Originally Posted by DataPacRat

I looked at that, and the trouble with a VRF beam seems to be that its kJ goes down so far it only does 1d-2 dDamage, which runs a 1-in-3 risk of not being able to vaporize a micrometeor even if it hits.

Hm... re-reading attack rolls, though, it looks like going from RF to VRF adds +5 to the attack roll, so any attack that would hit with a RF shot would like hit with at least 5 VRF shots, and there's more than a 99% chance of getting at least 1 damage with at least 1 of 5 shots. Looks like another change worth making.

Unless you are using the Gravitic Focus design switch (Spaceships p. 30), you will never use the 3kJ or 10kJ entries in the beam weapons table. The weakest beam weapon will be 30kJ (3MJ / 100), which does 1d+1 dDamage. Furthermore, according to Spaceships p. 60, "If firing in point defense against incoming missiles or shells, don’t bother rolling damage – each weapon hit (including tractor beams) kills one missile or shell." I think this is totally plausible—that 1d-2 damage on the d-scale should be thought of as more like 6d damage on a regular damage scale. If you think about it in those terms, the attack is never literally doing zero damage, and should always be enough to vaporize a micrometeor or puncture the fuel tank (or ruin the guidance system, etc.) of an incoming missile.

By SS's RAW, the RV should be able to hit 790 mph, rounded up; I'm not worried about relatively poor in-atmosphere performance, as long as it's got at least some.

That's only slightly more than 0.2 mps. It's the sort of thing that matters for building a near-future spaceplane when every bit of delta-V counts, but won't really help you with the thing you're trying to do.

I suppose another reality check might be to try to recreate the RV in 3e's Vehicles, and see it it still works. Let's see, that's Vp164's sidebar; if the craft's aerial top speed is below orbital velocity, it should be able to reach Earth orbit, though the sAccel is reduced by whatever portion is required to keep the craft aloft. However, SS doesn't get fine-grained enough to describe stall speeds; that's in VXii p30, and if I guesstimate a lift area of 70 sf and "good" streamlining, that's a stall speed of 250 mph. With SS's airspeed of 800 mph, then less than half of the craft's thrust is needed to keep it airborne, so the other half can still be applied as sAccel to get into orbit.

The Vehicles sidebar ignores the fact that the earth's atmosphere isn't like an ocean, with a well-defined "top". Atmospheric pressure gradually decreases as you get higher and higher. This means that aircraft generally have a flight ceiling well below the altitude where it's possible to orbit for any length of time before de-orbiting (or even burning up) due to drag. The altitude record for an air-breathing aircraft is ~37 kilometers, less than half the commonly quoted "edge of space" of 100 km.

If you want launching from Earth's surface to be easy, I would recommend allowing fusion torches, standard/hot reactionless engines, and/or contragravity lifters. If you want space travel to be super-duper cheap I guess you could also arbitrarily declare that in your setting, those systems cost less than they do in RAW.