Realistic Interface Transport in (GDW) 2300AD

Introduction

The formulae in the Naval Architects Manual are a mess. The fuel required for orbit is given as, using the correct order of operations:

(1)

 

 and the time to orbit is given as:

(2)

 

Both these are nonsense. There was an attempt to correct (2) in Challenge 37's Three Blind Mice, but it was also wrong.

The cost of lifting a ton to orbit (of payload) is ca. Lv4,500* in a shuttle or rocket or Lv3,000 with a spaceplane, which is about 1% of the current cost (ca. Lv200,000 per ton on a Falcon 9 Heavy to LEO, whereas 2k3 launches seem to be to a higher orbit). This is about in line with the current optimistic projections of what launches with fully reusable rockets would cost. SpaceX optimistically thinks they can get the price down to Lv2,500 per ton to LEO, with a fully reusable vehicle, which is close to 2k3 numbers.

Fuel is Lv100 per ton, and so the cost of fuel is ca. Lv600 per ton of dry weight, and if the vehicle is 50% payload (and non-thrust fuel) then the cost of fuel is Lv1,200 per ton of payload, or 27-40% of the cost to orbit. This is roughly in line with projections for SpaceX Starship's percentage etc.

From general principles, a hydrogen/oxygen rocket launching from Earth will require ca. 5/6ths of its' initial mass to be expended as fuel (and oxidiser). The fuel fraction vs dry weight should thus roughly be 5x dry mass one one (up). The 2k3 formula is explicitly two way - lift to orbit and return.

The Fix

Without giving derivations, the following formulae are approximately correct:

(3)

(4)

Tonnage should probably be dry mass.

Time to orbit should be 8-10 minutes for an Earth sized planet. Any quicker and the accelerations are liable to injure anyone onboard. Slower and the vehicle incurs additional gravity drag, and will have to expend even more fuel.

Both rockets and rocket planes are listed as taking 1 h to reach orbit, whilst scramjets take 2 h and so do catapults. Since the stutterwarp zone is about 10,000 km above the surface of Earth, once you've spent ca. 10 minutes getting to LEO, the rest is likely the orbital transfer.

Spaceplanes with airbreathing engines can use these engines in the lower atmosphere, but they rapidly get too high to get any benefit from airbreathing or lift surfaces. An option is for a shallower ascent than straight up, but this increases aerodynamic drag losses (remember, that lift is diverted acceleration) and gravity drag losses. A typical spaceplane might get upto about 25-30 km altitude and Mach 5 (1.7 kps, ca. one Mongoose Traveller "burn") before having to engage the rocket engine. From that point the fuel consumption etc. is similar.

The equation is for a round trip, although the majority of the fuel (> 90%) is burnt in the ascent.

Oddly, in terms of time, the spaceplane should be the one that takes longer to reach orbit, by both the table and common sense. Ergo, reverse the lift values for shuttles and spaceplanes. The advantage of a spaceplane is that there is no 3+ G acceleration, and the ride is acceptable for untrained non-astronauts. As described, most cargo goes to orbit in shuttles, whilst people take spaceplanes. Spaceplanes with air breathing engines can likely get away without external boosters, even if they have an external fuel tank.

The Effect

Yes, going up and down the gravity well is more difficult, or rather it is as difficult as described in the main rules.

No starship is going to be SSTO. Lifting a starship requires stacking on boosters (if the engine doesn't generate enough thrust, i.e. time to orbit isn't 10 mins for a rocket). Visiting a planet almost certainly means using landing craft. The gut check is whether the craft has 1 MW of MHD thruster per 120 tons of dry mass. Most of the fighters make this (the Bufer being the exception), as does the Aconit. The Yinma Lander doesn't, nor does the Hayabusa, LC-20 etc.

Most landers will require at least an external fuel tank to reach orbit. A Yinma, Hayabusa, LC-20, Thorez etc. will need to be stacked on a booster.

This gives problems for the likes of Bayern, but where are all the long runways on virgin planets for a spaceplane or shuttle to land on? Where are the cleared, level landing sites for thrust landings? Landing on a virgin planet, without infrastructure already in place, is a major issue.

Stutterwarps in Orbit

"Stutterwarp vessels can also leave orbit without using conventional drives."

2300AD Director's Guide, p. 62

It is continuously stated in the GDW books that stutterwarp does work inside the dead zone, and does provide enough movement for orbital maneouvres, but not enough for landings. It is explicit that stutterwarp equipped ships don't need rockets to leave orbit.

From the point of view of a starship, there is a certain truth to this. When a starship inserts itself into an orbit with stutterwarp, and makes no reaction burn, the orbit must either crash into the planet (or enter the atmosphere and land), or leave the dead zone at some point. Without a reaction drive, a starship simply cannot actually achieve a circular orbit below the threshold altitude. Thus it would never need a reaction drive to break orbit. If necessary, it could insert into an orbit with a very low perigee to launch landing craft.

For landing on the surface, one can devise deadglide strategies what obviate the need for a reaction drive to land, but for taking off, the reaction drive is necessary, and probably it's needed to reach the stutterwarp threshold.

Hence, why older players get a little confused. The reaction drive is simply unnecessary.

 

* Note: this uses GDW Livres. Mongoose Livres are far less valuable, and pegged to the Imperial Credit.

The King Problem and How It Changed 2300AD

Preamble

I've been looking into historical stuff recently, and realised that many of the planets on the Colonial Atlas had serious flaws. The most egregious were Kie-Yuma (no planets can exist in the system), Kimanjano (explosive fuel-air mixture for an atmosphere), several worlds which are tide-locked but this isn't mentioned, and several worlds beyond the size for gas giant transformation.

I am aware that some people have played games on these worlds, as described in the Colonial Atlas, and would not want to change. Indeed, I think some changes should not be made, especially those caused by new observations. An example is that in 1989 it was found that Ellis' star is in fact a double star, which means the planet literally can't exist. However, if a true 3rd edition was ever to be written, I'd like the hard science to return.

King poses a particular issue, because the author actually rewrote the Human tech-level to make the planet work, and the author of the Mongoose edition pushed this revision to a logical conclusion, after stripping the DNAM tech of the dangers (which I revised here, to make follow the Mongoose rules). It serves as a wonderful example of the dangers of making an apparently small change to a setting. The DNAM's themselves changed during GDW's run (see appendix 1).

However. you are, of course, supposed to play the game as you see fit. I'm aware that I'm a stickler for consistency, scientific accuracy and continuity.

Introduction - Before King was Defined

In the pre-Colonial Atlas 2300AD, King was a rich planet colonised by America and Australia in 2194 and 2196 respectively. (1st ed. Player's Manual, 16 and the colony table) It was not designated a high-gravity planet, or one with a toxic atmosphere. At the same time, transfecting Humans to treat genetic disease was a new and experimental development in the year 2300. (1st ed. Player's Manual, 14)

In the non-canon Traveller's Digest issue 10 (September '87), William Connors gave King a toxic sulfurous atmosphere, and stated the Pentapods, at the Life Foundations' request, developed atmospheric filter symbionts (AFS). Of course, as a Pentapod invention, this places the AFS' introduction into relatively recent times, because the Pentapods weren't contacted until recently.

The high-gravity, tantalum motherlode King then appeared in William Connor's write-up in the Colonial Atlas (February '88), and it required a complete rewrite of Human genetic engineering. There is, however, a huge problem.

King is a Gas Giant (+)

When planets form, they do so from the local material, which is mostly hydrogen and helium. As they condense, their gravity will pull heavier materials into them, but cannot hold onto lighter ones. The temperature and solar winds have an effect, but in the habitable zone, these are roughly similar across all stars since the habitable zone is defined by temperature.

With smaller protoplanets, the gravity is insufficent to hold hydrogen and helium, and these gases escape from the planet. This leads to rocky or icy planets. If the gravity is strong enough to hold onto hydrogen and helium (which are the bulk of matter), the planet becomes a gas giant, and continues to suck in hydrogen and helium from the environment, snowballing into even bigger gas giants.

For worlds in the habitable zone, the boundary between these two states is about 1.35 G. Worlds with gravity below ca. 1.35 G loose their hydrogen and helium and become rocky or icy planets with a surface. Those with greater than ca. 1.35 G but less than ca. 1.6 G retain helium, not not hydrogen, and become failed cores (or Triton-type planets). Those with greater than ca. 1.6 G become gas giants, and may snowball into brown dwarfs.

King is far beyond this figure.

Now, GDW had sensible rules. In the 1st edition world building rules the limit to non-gas giants was given as 4 Earth masses, and that planets that had hydrogen-helium atmospheres were gas giants. Now, the mass and gravity tables changed between 1st and 2nd edition (the King gravity uses the 2nd edition table), but the minimum molecular weight retained (MMWR) didn't. The 1st edition rules lacked the snowballing rules, and these were added in the 2nd edition along with clarification that all worlds with MMWR of 4 or less were gas giants:

 

Connors made the largest and heaviest possible world under the planet generation system, which required rolling six 6's in a row on d6's, and then a 10 on a d10. The chances of this extreme roll were 1 in 466,560. The MMWR is zero (0) and thus the planet is a gas giant, and should roll for snowballing. Roll d6-2, and double diameter that many times. If another 6 was rolled then the diameter would be multiplied by 2^4 = 16 times, and King is a 480,000 km diameter gas giant.

The GDW planet creation system makes King a gas giant at the supplied values. 

How Big Could a Terrestrial King Be? What Would It Be Like?

To keep the spirit of the original, we need King not to bloom into a gas giant, but rather collapse into a terrestrial planet. At a density of 1.3 Earth's, the maximum diameter is 13,000 km, or just a bit larger than Earth. This would give a mass of 1.4 Earths and a surface gravity of 1.33 G. It is essentially the most extreme non-gas giant in the life zone the system can generate.

(As an aside, the size of icy cored planets was substantially increased in the 2nd edition)

King's star is a K7V. The actual star (Groombridge 1618) is more luminous than the 2300AD star, but we use 2300AD values. We'll use the stars' real mass of 0.67 solar masses. This is a small orange dwarf, and since the mass of the star is below 0.7, and since the planet is in the life or inner zone (actually inner, see below), it is tidally locked to the star. The distance from the star is not defined (but can be found from the orbital period, see below), but it is less than 0.32 AU, and this planet and King are in the life zone.

The given luminosity of the star is 0.057 of Sol, which is weak for a K7V (average about 0.1 of Sol). By the GDW world creation system the optimal distance is 0.24 AU, the inner limit is 0.17 AU and the outer limit 0.35 AU. From the second planets location, the system would generate from 0.15 to 0.24 AU, which places King at inner part of the life zone. However, since we have the length of a year, if we assume the mass of the star we can calculate the orbital distance using Kepler's 3rd law. At 0.67 solar masses, the orbital distance would be 0.14 AU, which places King in the inner zone, not the life zone. Solar intensity is 0.057/(0.14)^2 = 2.91 of Earth. This means the planet would have lost all water, and developed into a scorched rock. This is the actual definition of inner-habitable-outer zones.

On the topic of habitable zones, the formula in GDW is based upon the assumptions in Doles' 1964 book, but the numbers in the world generation table is a bit narrower. Doles was probably a bit optimistic, and spinning worlds in the 72%-86% (ish) of optimal are likely to only have water at the poles, and worlds in the 120%-145% (ish) of optimal range are likely to have massive glaciation, and liquid water only at the equator.

The CA write-up says there are only two zones on the planet King that are habitable. For a rotating world this would be correct, and they'd be the two polar regions. The incident energy from the star depends on the sine of the angle of incidence (i.e. latitude). Since temperature equivalent is the 4th root of the energy, the equator is hotter than the poles with a spinning planet. However, with a tide-locked planet this causes the hot pole to be hottest, and the temperature to drop as we head out to the terminator.

Back in the 80's it was assumed that only the twilight zone of a tide-locked planet would be habitable. This is only true of tide-locked planets in the inner zone. For planets in the life zone, the ring of habitability is going to be on the day side, especially if we have a lot of liquid water, which King does (67% of the surface is liquid water). However, King is in the inner zone, and the solar intensity is huge. The hot poll is well above 100 oC, and the dayside is a scorched desert.

Being technically in the inner zone, the planet would have had a runaway greenhouse effect, and be a Venus type world. Ergo, we have to move it outwards.

A Revised King

Since we want to have a real colony, we have an issue. The star's luminosity condemns it to being a tide-locked desert world, without a breathable atmosphere (because oxygen comes from plants). We simply cannot have a terrestrial world with an oxygen atmophere around that star. However, if there is still ice on the cold side, we can perhaps build domes over subterranian mines, and supply an atmosphere by hydrolysis, or even from the ore they're smelting, assuming they have relatively pure oxides.

The planet could be high gravity (1.2 to 1.3 G), but it would not require any genetic adaption.

Domes would be in the twilight zone, sited to be over ore deposits and close to a glacier. Each dome would likely be based around a nuclear or fusion reactor (early ones nukes, fusion is a later invention) which provides the power to sustain an atmosphere. Under the dome, mines are sunk and ore harvested. Old mines become living spaces.

Expeditions to the cold side glaciers to bring back water would be a major economic activity. The water is needed not just to breath, but to be made into rocket fuel for leaving the planet, and taking the metals to orbit. Ultimately, pipelines may be built, with colony domes on the night side whose only economic activity is ice-mining.

This world's domes would resemble the hives of some sci-fi.

How DNAM's Changed 2300AD

Colin Dunn was (and is) far more interested in cyberpunk and transhumanism than the hard sci-fi of the 2300AD. Indeed, he once wrote he never played 2300AD proper, but rather used elements of it in his CP:2020 campaign. It is of no surprise then that he focused in on the cyberpunk elements, including the DNAM's, and magnified them. This evolved over several iterations of the Mongoose editions and is, to my mind at least, antithetical to the original. That said, GDW did this to themselves by trying to shoehorn in cyperpunk.

Thus, whilst in the original DNAM's didn't exist for much of the run, and then were a special case that was being downplayed over time, in the Mongoose edition were get an explosion of DNAM's. In fact, Colin tried to make every single colonist a transhuman. This did not go down well with some, and I intend to look at this when I compare real genetic engineering with his DNAM's.

 

Appendix 1: DNAM Development

In fact, DNAM's changed slightly over time. As mentioned, DNAM's were, until the publication of the Colonial Atlas, actually written up as beyond Human technology. The Colonial Atlas introduced them, and around the same time Bayern came out, which was also written by Bill Connors. There is a King born character in Bayern. However, that character does not appear to be a DNAM when compared to the second edition boxed set.

In the 2nd edition, a DNAM character is included in the solo adventure "Terror's Lair" They, and another DNAM encountered, cannot breath normal air, and have to wear rebreather masks. (DG, 19) The character of Diane Kamahmo on the Bayern doesn't have to wear such a mask, which would be a major hazard for her and make her an ineffective officer.

As an aside, Bayern and Ships of the French Arm are in conflict with respect to the Vogelperspektive, because the ship hadn't left the near French Arm, and hadn't done any real exploring as of 2300.