[Spaceships] Statting a STL Interstellar Probe

[DataPacRat]

I'd like to run some numbers for a small craft in a particular setting, and could use some help.

The fluff: In a Transhuman Space-ish setting, plus two tech advancements (a reactionless drive and a zero-point generator), a ship's mechanic puts together a probe containing several redundant copies of a ghost mind-state, sets it to accelerate to 1% lightspeed, where it'll drift for ten thousand years or so until arriving at a destination star. The probe is no more than SM+3, which makes it tricky to stat out with the Spaceships system.

(The drive-tech is set so if half a ship's mass is drive, it can accelerate at 1G, equivalent to SS1's "rotary reactionless". The zero-point generator is equivalent to SS7's "perpetual motion" power plant. The rest of the tech is hardish-SF; you can assume THS.)

I want to have some solid stats, so that I can work out any plot-points that could depend on the particulars of how the thing is built; eg, if one of these gets picked up by a PC for spare parts.


Does anyone remember how the ablation table on SS5 p40 was generated, so I could try extending it down to 0.01c for millennia?


Does anyone have any advice on how to figure out some decent numbers? Eg, should I just try extending SS's numbers down to smaller SMs?

[Fred Brackin]

Originally Posted by DataPacRat

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(The drive-tech is set so if half a ship's mass is drive, it can accelerate at 1G, equivalent to SS1's "rotary reactionless". ?

Problem one. This won't quite work. If half the ship is drive the other half has to be power plant (as long as your power plants only produce 1 pp per space). You don't have that much ship available. You have to have a Control Room and Front Armor.

You'll also probably want an Engine Room unless the whole thing is made of Living Metal. Otherwise, things that break don't get fixed.

[DataPacRat]

Originally Posted by Fred Brackin

Problem one. This won't quite work. If half the ship is drive the other half has to be power plant (as long as your power plants only produce 1 pp per space). You don't have that much ship available. You have to have a Control Room and Front Armor.

You'll also probably want an Engine Room unless the whole thing is made of Living Metal. Otherwise, things that break don't get fixed.

Low acceleration works here; if the probe takes a century to get up to 1%c, that's entirely acceptable.

I'm thinking of around three plant-plus-drive pairs, for redundancy; and as much armour as possible, to extend duration in case nobody's around at the first few stars.

"Living metal", as I understand it, is a bit above the setting's tech-level. (Though I'm open to slightly lower-TL technobabble for a 'self-healing' ship.)

[AlexanderHowl]

Unless there is a setting reason, there is no particular reason for a probe with a reactionless engine to take 10,000 years to get anywhere close. Heck, you could easily reach 0.02c with a staged probe at TL10 using realistic technology, allowing the probe to get from the Earth to Alpha Centauri in two centuries. Of course, the idea that there would be anyone who cared to listen to the return message would be rather laughable, as it be 200 years from the time that the probe left to when the signal was received even for the closest stars, and technology would have likely advanced enough by that time to allow orbital telescopes to far exceed the capabilities of a tiny probe.

If you wanted a probe though, it would be easy enough to make a probe with a rotary engine. At TL9, a SM+10 scout ship could easily have eight rotary engines, four fusion reactors, three armor, two habitats, two hanger bays, and one control room. We will assume that the rotary engine produces inertialless thrust, so the spaceship is not a WMD, and it will take it only 1 year to accelerate to 0.8c. A cryogenic crew could reach Alpha Centaur in 6 years, which is soon enough that people back home would care.

[DataPacRat]

Originally Posted by AlexanderHowl

Unless there is a setting reason, there is no particular reason for a probe with a reactionless engine to take 10,000 years to get anywhere close.

Well, there is one - if the sponsor is a lone individual, doing the equivalent of building a microlight plane in their garage. When shaving even a hundred euros from the cost is a noticeable savings, then there's an incentive to really skimp on the acceleration. (And on everything else that exceeds the minimum of 'mobile time capsule sending brainstate into deep time'.)

[DataPacRat]

To answer my own question; the SS7 ablation table seems to correspond to the vessel's kinetic energy, which implies that at 0.01c, it takes 50,000 years of travel to ablate 1 dDR.

A quickie sketch of an el-cheapo SM+2 ghost-carrying probe looks roughly like:

* SM+2: LMass 1 ton, Length 5 yards, dST/HP 7, Hnd/SR ?0/4?
* Unstreamlined
* Design Switches:
- Advanced Computers
- Exposed Radiators
- Accelerator Tube Limits
- Slower Industrial Systems
- Pyramid 3-34 Armor/Volume tweak; 17 armor systems, dDR*3
* Systems:
- Fore: 6x Iron Armor, $720, dDR 0.3*6*3=dDR 5.4
- Centre: 6x Iron Armor, $720, dDR 0.3*6*3=dDR 5.4
- Aft: 5x Iron Armor, $600, dDR 0.3*5*3=dDR 4.5
- Aft: Rotary Reactionless Engine: req 1 PP, $500, 0.1G accel
- Core: Control Room: $2k, Comm/sensor TL-9=1, Computer C5+1=C6
- Core: Power Plant, Perpetual Motion: 1 PP, $6k
* Total Cost: $10,540
* Range at 0.01c: 270,000 years, or 2,700 light-years

The less costly upgrades might be to improve the front armor to at least steel ($200/system), to add a cargo hold to bring along more in the time-capsule, or add a $2k level-3 enhanced sensor array. To add robustness, a second (or even third) set of drive+plant, and to spring for $20k for what SS7 calls a TL10 'self-healing' design feature.

... But all of that assumes that I haven't gone too far off the rails by extending the SS system down to SM+2. (Of course, if it does, then why not a SM+1, or even SM+0, version of the probe?) Does any of the above look wildly out of line with what's reasonable?

[Fred Brackin]

Originally Posted by DataPacRat

Low acceleration works here; if the probe takes a century to get up to 1%c, that's entirely acceptable.

It's probably not explainable though. With 1 G of thrust not limited by Delta-V you can approach c in 1 year. You can't ignore relativistic effects at that speed but it'll be far beyond your 1% of c target.

If you're trying to reach 1,862.62 miles per second at a conatant accelration of 1/10th of G (3.2 feet per second per second) it'll take 35 and 1/2 days.

I'd say that you should go to whatever speed your armor can stand. This would probably be good. I don't really think your Ghost's storage medium will be able to take 10,000 years of cosmic rays.

[AlexanderHowl]

I am curious at why someone with only a garage inventor's budget would want to send out such a slow interstellar probe, especially since they will be dust long before the probe gets to its destination. Anyway, the probe would likely malfunction within the first few months of operation without an engine room with total automation, which is not allowed for anything smaller than SM+5.

[DataPacRat]

Originally Posted by Fred Brackin

It's probably not explainable though. With 1 G of thrust not limited by Delta-V you can approach c in 1 year. You can't ignore relativistic effects at that speed but it'll be far beyond your 1% of c target.

If you're trying to reach 1,862.62 miles per second at a conatant accelration of 1/10th of G (3.2 feet per second per second) it'll take 35 and 1/2 days.

Eh, the above stats were a quick, nearly-thoughtless sketch. To save a good deal of money, the builder would probably use a smaller plant and drive - call it two SM's down, for 0.01G accel (and a total cost of $4,690). 'A year to accelerate to 1%c' works with the fluff well enough.

Originally Posted by AlexanderHowl

I am curious at why someone with only a garage inventor's budget would want to send out such a slow interstellar probe, especially since they will be dust long before the probe gets to its destination.

Partly the same reason anyone buries a time capsule, and partly because the ghost they're mailing into the distant future... is their own! Trying to stay alive for Very Long Periods is hard, especially with all the complicated events that keep happening near stars and planets, so sending a backup copy of oneself on a millennia-long time-out is plausibly worthwhile. (And since they're already a ghost, they're very likely more focused on the patternist theory of identity, which allows for branching and interruptions, than the more common bodily-continuity forms of identity.)

Originally Posted by Fred Brackin

I'd say that you should go to whatever speed your armor can stand. This would probably be good. I don't really think your Ghost's storage medium will be able to take 10,000 years of cosmic rays.

Originally Posted by AlexanderHowl

Anyway, the probe would likely malfunction within the first few months of operation without an engine room with total automation, which is not allowed for anything smaller than SM+5.

These, however, are sticking points worth trying to solve.

The fluff already mentions that the digital backup includes 'nonuple redundancy, plus checksums'; so that whenever one bit gets flipped by cosmic rays, there's nearly no likelihood that more than one or two other copies of the same bit get flipped at the same time, and even then the checksums won't match for the bad bits, which seems likely to be good enough to keep the data intact until the hardware itself starts breaking down.

Maintenance is... an issue. The fluff is that both drive and power-plant are effectively solid-state, without moving parts, which could help, but is hard to stat out. The systems are so small that they need 0 workspaces, which plausibly implies no need for a crew for maintenance. SS7 rolls all interstellar-impact damage into frontal ablation, which could imply that the probe only has to worry about impacts when within a solar system.

If the probes are cheap enough - and 'under $5k apiece' probably counts - than the builder may just try building a dozen instead of one, and just hope the odds end up that at least one avoids dangerous impacts long enough to connect with whatever civilization exists at the time. Or I could throw in a cargo space with a couple of maintenance bots, and hope they're good enough to handle the damage-repair rules on SS1p64 if something goes wrong. Or I could come up with fluff for $20k of self-repair capacity from SS7. Or something I haven't thought of yet.

Edit: Or maybe throw in a 'mining' section, dedicated to turning random astroid rock into replacement iron, steel, or stone armor to help replace what's been ablated away.


Does any of the above strike any ideas in your mind?

[AlexanderHowl]

Solid state objects still need maintenance, though it is a more modest requirement, especially when they are exposed to cosmic radiation for thousands of years. Another concern is that a SM+2 probe at TL11 would have a 'control room' with a Complexity 6, which is only good enough for a ghost of a rat, not the ghost of a human, so the entire vanity project would be rather pointless. In addition, most governments will not allow people to build and launch interstellar probes without permission, and they would definitely not give someone without substantial resources permission to do so.

I am confused about the endgame for the character though. Assuming that the ghost was stored in the cargo hold, who are they thinking would boot them up in the future? We had enough trouble recovering programs from 25 years ago, I cannot imagine the difficulties that would exist for a civilization 10,000 years in the future, especially if they are nonhuman. At best, the probe would probably end up as a museum exhibit without anyone realizing that there was a copy of an archaic ghost trapped within.