[Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

Life pods, drop capsules, and stealth capsules are small, one-use re-entry vehicles described in GURPS Ultra-Tech, on p.232. Each has a loaded weight of one ton, besides which the life pod will carry four people and half a ton of cargo, a drop capsule will carry 2 people and half a ton of cargo, and a stealth capsule will carry one person and 0.3 ton of cargo. Despite having half the capacity in the same loaded weight, the stealth capsule is "more cramped than the drop capsule": this is because the stealth capsule includes ECM equipment, decoys, and an extra parachute which allows it to "jink", i.e. to change its course unpredictably by expending a parachute.

I suspect that a stealth capsule is large enough for a drop trooper in commando battlesuit (UT, p.183), a [military] cybersuit (UT, p.185), a warsuit (UT, p.185) or any other armour that does not increase SM, but that a drop capsule would be necessary for a drop trooper in armour that increased SM, such as the heavy battlesuit (UT p.184), HEX suit (UT p.184), or dreadnought battlesuit (UT p.185), and that there would only be room for one armoured trooper in such a capsule. I don't know about powered combat armour (UT p.183, B.285)), which is seven feet tall but not noted as SM +1.

Drop capsules are listed as consumables in Spaceships (on p.47), with a reference to Ultra-Tech p.232. The term is used in Spaceships 2 on p.20, with the interesting information that the 24-cm missile launchers on the Hermes-class courier are intended to launch drop capsules—but merely for delivering packages from orbit. They are mentioned in Spaceships 5 (p.37) as a means of covert landing on a planet. "Re-entry capsules" are mentioned in GURPS Mass Combat (p.38), in connection with "airborne" troops that can be dropped from orbit. But unless there is something in Spaceships 4 (which I don't have) there is no statement of what is actually required to launch life pods, drop capsules, or stealth capsules. They can be launched through a missile launcher, but it is not clear how large a missile launcher is required.


One thing to observe is that a life-pod, drop capsule, or stealth capsule has a loaded weight of one ton, which is the weight per shot for 32-cm missiles (Spaceships, p.47). A 32-cm missile launcher can be carried as a spinal mount by a spaceship of SM+7 (~300 tons), as a major battery by a spaceship of SM+8 (~1,000 tons), or as one of several weapons in a battery by a spaceship of SM+9 (~3,000 tons) or larger. That's a 50-ton missile launcher including about 20 loaded capsules (20 tons of capsules). That seems reasonable.

On the other hand, if I scrunch up as much as I can, I am 50 cm across the shoulders, and space marines or drop troopers presumably include men who are broad-shouldered and muscular. Allow a few centimetres on either side for their armour and a few either side for the walls of the pod, and it seems unlikely that you will be about to fit them into a 56-cm capsule. 64-cm would seem to be the smallest possible diameter for a stealth capsule, and it would seem that drop capsules and life pods must be even larger. But the smallest spaceship you can get a 64-cm missile launcher into is SM+11 (30,000 tons, about the size of a WWII battleship), where it is a spinal battery (15% of the ship, 1,500 tons of missile launcher). And a one-ton loaded drop capsule with cramped space for one man is perhaps small compared with a 7.5-ton, SM+3 64 cm missile.


Life pods, drop capsules, and stealth capsules might alternatively be launched through hangar bays (see Spaceships, p.18). Hangar bay capacity is noted in tons, so it is not necessary to know the SM of a life pod, drop capsule, or stealth capsule for this purpose (though it would be nice to know when we are shooting at them). An SM+5 spaceship (30 tons) could carry a single life pod or drop capsule in a single hangar system. An SM+7 could carry a squad SM+8 a platoon, SM+9 a company, etc.

So it looks as though hangar bays are the way to go when launching life pods or drop/stealth capsules. The only hint of doing it otherwise is the Hermes-class courier's packet delivery missile tube. Why am I unhappy about that?

Well, UT (p.232) and Spaceships (p.47) agree that drop capsules "have small rocket engine clusters that provide limited maneuverability, but careful landing is a matter of good navigation. De-orbiting takes two or three rotations around a planet with an Earthlike atmosphere (more for a planet with a thinner atmosphere, such as Mars). During this time, radio, radar, and all passive sensors will be blinded due to plasma effects." That makes them very tactically limited. Two orbits around an Earth-like planet take three hours. And if plasma effects blind radar, radio, and all passive sensors, then the capsule is going to be a very conspicuous object, a brilliant fireball that circles the planet twice. The planetary defences might not be able to shoot a stealth capsule in re-entry, but they get plenty of warning to put all their military facilities on full alert. This isn't a Starship Troopers-style surprise raid. Neither is it a good way to covertly insert a first-contact team (Spaceships 5, p.37).

So I'm looking for a way to land drop troopers much more quickly and discreetly. That means less reliance on aerobraking and considerably sharper decelerations.

• One approach would be to equip each capsule with a drive with sufficient acceleration and delta-v to use engine braking. But that threatens to make the capsules far too expensive for non-reusable items (I already have qualms on that front).
• Another would be to use the ship's main drives to cancel most of its orbital velocity, launch the pods with a much smaller braking task, and then boost the ship back to orbital speed again. That sounds rather like a hair-raising manoeuvre to me, besides being expensive in propellant/delta-v and pretty conspicuous.
• Hoping to get a result that looks more like Starship Troopers, I'm thinking of launching the capsules from the ship at some velocity to kill part of their orbital speed. Sadly, it isn't a very promising approach. Supposing the drop troopers could stand ten gees and recover consciousness before landing it'd take 81 seconds to cancel their orbital velocity for a drop on Earth and require a launch tube 320 km long.

Is it possible for drop pods and particularly stealth pods to make a steeper re-entry and to aerobrake harder? Orbiting the planet twice in the course of aerobraking implies deceleration at only 1/25 of local gravity.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

I've posted on a similar thread recently, but in short, one option for re-entry involves gliding in. No plasma sheath, but protracted re-entry time. Another option is a ridiculously good thermal shield and inertial compensators to allow a steep entry. But even then, if you're hoping to have the atmosphere slow you enough to survive landing, its still going to take at least a minute or two I think.
Basically there's no quick way to re-enter in the manner you're talking about without superscience, as far as I can tell.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

I've thought on this and my take is that you aren't launching the drop capsules out actual "missile launchers," but rather that "drop capsule launchers" capable of launching a 1 ton capsules have the same stats as "missile launchers" capable of launching 1 ton missiles. The two types of launcher shouldn't be interchangeable.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

Yeah, the diameter difference between a drop pod and an equivalent-weight missile always bothered me. The other thing would be launch velocity. An unmanned missile can be shot out into space a lot harder than a pod carrying living things or potentially fragile cargo. On the other hand, I'd let a drop-pod launcher also launch probes and drop cans; just not missiles due to the diameter and launch velocity differences. This assumes your probes are designed for the pod launcher and not a missile-type launcher. A further stretch might allow bombs to be fired from a pod launcher since they don't need a hard launch and can be fatter.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

We already tried discussing drop pod construction in this thread. I guess one could simply scale down from SM+4 downward. Ideally, one should optimise the ratio of payload and engines depending on needed landing time. I suppose a single fuel tank should be enough for the requirements of only a vertical landing (SS1, p.40).

If your space marines can stand 10 Gs, three chemical engines should be enough.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

I took a prominent part in the discussion, and remember it well. Some of us were confused about the difference between a one-man disposable re-entry vehicle and a ten-man flying AIFV. We did not discuss launching the things.

No. I am talking about the life pod, drop capsule, and stealth capsule that are described on p. 232 of Ultra-Tech, which have a small rocket engine for manoeuvring only. A small spacecraft with sufficient engines to de-orbit and land by engine power is a different thing entirely. Launching such a landing boat does not raise the issues that launching a drop capsule does and which are the topic I started this thread to discuss.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

Well, that sounds tactically limited compared with an assault shuttle that can land in twenty minutes, but without the plasma sheath it might at least be stealthy. What sort of numbers are we looking at for "protracted" re-entry time? What would the launch requirements be, in terms of shedding enough orbital velocity to de-orbit?

A minute or two I can certainly live with, even as much as fifteen or twenty. One gee of deceleration (two experienced within the capsule) would be enough to shed orbital speed in under fifteen minutes in the case of Earth. I suppose that fit and well-trained drop troops might stand three gee for seven minutes and be able to operate within a minute after landing.

How steep a re-entry path are we talking about here? What is the delta-v from LEO? Do you suppose that GURPS TL10 materials would be up to the job of a 2-gee or 3-gee aerobraking re-entry?
Basically there's no quick way to re-enter in the manner you're talking about without superscience, as far as I can tell.[/QUOTE]

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

With sufficient biotechnology you probably ought to be able to do better than that. Most of the reasons why humans can't handle high levels of acceleration is that our circulatory system isn't at all adapted to it. There are some obvious fixes (both in terms of bio-mods and drugs), IMO.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

That seems completely reasonable to me.

Re: [Spaceships]/[UT] Launching life pods, drop capsules, and stealth capsules
 

I'm afraid I don't have solid numbers for you, the math is beyond me, and is strongly dependant on the vehicles aerodynamic properties. Glide-in period would be on the order of several hours to a day off the top of my head.

Launch requirements would depend on the orbit of the launching vehicle. For a launcher in low earth orbit, we're talking in the ballpark of a couple of hundred m/s max, potentially less.

I'm getting better numbers and will post when I have more.

I had the impression you were after a much more rapid entry than that. If you can live with 15-20 minutes, you're in luck. That's about how long the Mercury capsules spent between deorbit burn and splashdown. They underwent 8-12 G's during re-entry, although significantly these were the peak accelerations. The deorbit burn was only about 110 m/s as well (if my math is correct(approx 1.1G for 10 seconds)).

These were craft that were already just above the atmosphere when they started. Apollo took a little longer (30 minutes or so) to reach the atmosphere after de-orbit, but once they did, they took about the same time. The corollary to all this is that the time taken to reach the atmosphere is a very significant factor. Dropping from other than low orbit is going to involve transit times as well.

If you consider the re-entry (de)acceleration to take say, half the time from deorbit to impact, allowing some time for transit to atmosphere and the post deceleration coasting to impact/landing, and using a constant deceleration as an approximation gives the following:

time: 7.5 minutes = 450 seconds
delV: approx 7700m/s

accel = delV/time = 7700/450 = 17.1 = 1.7 Gs

that quick and dirty calc shows that what you're talking about appears to be possible.

Also note that smaller objects can survive the heat of heavier reentry accelerations as they have a greater surface area to mass ratio as a rule.