Neighbors (2)
Nov. 7th, 2011 01:05 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
hwrnmnbsol_Sagan_ withdrew. Gliese 581f was a gas giant with beautiful violet whorled patterns and was well placed for refueling. Interrupting _Sagan_'s planned intercept of Gliese 581g had cost a lot of delta-V, more than could be passively gathered from the interplanetary void. The crew agreed that if they wanted to keep as many options open as possible, they would need to top off the tanks. Pulling back also meant they could monitor the Gliesian response and see what they would do. A few weeks of delay wouldn't hurt anything.
Korda deployed the scoop and skimmed the surface of Gliese 581f, drawing hydrogen up into the refinery unit in Module C. It worked perfectly. Back when he was a teenager, Korda had practiced the maneuver on Uranus before accelerating out of the solar system. It was good to see that the advanced planning of the mission designers was paying off.
Unfortunately, mused Korda sourly, the designers didn't predict the Gliese system being occupied by humans – humans who apparently weren't too happy to see their brothers and sisters arriving from out of town. Or perhaps they did. Korda and his crewmates were the answer to unexpected mission challenges – humans capable of synthesizing responses on the fly. Over the years Korda had wondered why this mission had required an actual human presence at all. He grudgingly admitted that perhaps that decision on the part of Earth Mission Control had been a good one.
Zenia buzzed Korda from the communications room. "I think we're going to have some company," she said. "Launches detected – a bunch of them, coming here. Significant chemical propellant signatures and very high accelerations – 5G sustained."
"Ridiculous," cut in Gold. "Over short durations, sure. Sustained 5G is unsafe."
"Unsafe for Terrestrials," Zhizhi reminded them all. "Gliese 581g has a higher mass than Earth."
"But also a larger surface radius," Korda objected. "Surface gravity will be higher that 1G, but not that much higher."
"You're assuming the launches came from Gliese 581g," said Zenia.
There was an awkward moment. "Didn't they?" Gold asked finally.
"No," said Zenia. "Gliese 581c, further in-system."
"Wait," said Korda. "You've been monitoring EM all over the system. Have you gotten any kind of signal from that planet at all?"
"Not a peep," Zenia replied.
"The plot thickens," Zhizhi said.
The crew reassembled and looked at the models of Gliese 581c on the viewer. Liang delivered his lecture standing up with his hands behind his back, back stiffened, exactly as if he were still lecturing at the Beijing Academy of Science.
"Gliese 581c is approximately 6 Earth masses," said Liang, "and a radius just short of twice that of Earth. Its density is therefore lower than Earth's, but surface gravity is roughly 1.5G. Composition is suspected to be higher in carbon and lower in iron and nickel, which explains the lower density."
"If it's high in carbon," mused Zhizhi, "and given the certainty that the system primary used to put out a lot more energy than it does in its current red dwarf form, it's likely that a lot of carbon dioxide leached out. Won't 581c have an atmosphere like that of Venus, with surface temperatures too high to support life?"
"I believe not," said Liang, somewhat perturbed at having been interrupted. "581c appears to be phase-locked to the sun, similar to 581g, and spectroscopic analysis of the side facing the primary appears to reveal a very thick cloud layer containing a lot of water vapor. Temperature of that surface is high, but not high enough to indicate significant runaway greenhouse heating from below. I suspect that this atmosphere is an insulator, and the planet's surface is quite cool. Actually, 581g appears to be the warmer of the two planets; it also has a thick atmosphere that averages the temperatures of the sunward and shadowed sides, and blackbody radiation numbers suggest that the surface temperature is in the 30 degrees C range."
"So 581g is warm, and 581c is cold," said Korda. "But both are in the range necessary to sustain human life?"
"Oh, yes," said Liang. "Both planets were identified early on as being in the Goldilocks range of masses and proximity to the primary – not too hot and not too cold to sustain life. Of course there's a lot of variance in those numbers; a planet that can nominally support life could still be very inhospitable to humanity. But now that we're here and can see them up close, there can be no doubt that both are very well suited to human colonization. There's even oxygen in sufficient concentrations, although it's probably on the high end on 581c."
"Two human-habitable planets in the same system," mused Zhizhi. "And rather close to each other, too. Unsurprising that both are inhabited. But this doesn't explain why we have so much radio traffic from one and not the other."
"I believe I have an answer to that," said Liang. "There seems to be a great deal of ionization of 581c's upper atmosphere. There's a continuous flow of charged particles sweeping across the atmosphere from the sunward face to the shadow side. It's probably high enough to generate an extremely high noise in most wavelengths."
Zenia nodded. "That makes a lot of sense," she said. "They probably can't hear anything outside their atmosphere, and inside as well. Most forms of long-distance communication would be useless."
"Fine, but then why would the Gliesians keep rockets there, and how would 581g be able to tell them that there was anything out here worth intercepting?"
"All good questions," said Zhizhi. "But not questions we can answer. However, I think we can safely assume that this latest foray is hostile. They're sending thirteen separate vessels, all with vectors that will take them here, and that seems inconsistent with a diplomatic response. They're also accelerating very quickly, even given their native surface gravity, so they must be in a big rush."
"Actually," said Zenia, "there are two stray data points. Yes, thirteen launches are heading this way. But there are two launches that we detected only a few hours ago, and they have different vectors. It looks like they're headed for 581g. Same burn rate."
"Hmm." Zhizhi thought quickly. "It's a small system. We have to assume they can't keep up the high acceleration forever. Let's cap their peak acceleration at .01c for chemical rockets. Given the orientation of the planets, they can reach 581g in a matter of hours. What's the inner window for them reaching our location?"
Liang did some calculations in his head. "Three days," he said.
**
It was actually closer to seven days; .01c was far too generous an assumption. In that interval, the crew of _Sagan_ learned a lot. What wasn't uniformly clear was what, exactly, they had learned.
"There can be no question whatsoever," said Zenia firmly at their daily roundtable. "What we saw when the 581c ships reached 581g was a space battle. Radio chatter increased until they arrived and then dropped off; there were launches from 581g that coincided with the 581c ship intercept; signals from some of those ships were interrupted abruptly."
"Why would they fire on their own kind?" Vrouw demanded. "Even if we assume that there are divisions between the Gliesians, why would they choose the moment of our arrival to engage in hostilities?"
"For the one millionth time, I don't know," said Zenia, tearing up. "I wish Belletto were here." This was awkward. All members of the crew were close, having lived all of their adult lives in close proximity, but Zenia and Belletto were primary companions. Zenia's grief hadn't had a chance to run its course, and Matsen had advised her that a sedative might be necessary to get through the current crisis.
"All right," said Zhizhi. "So we don’t know if the Gliesians fight amongst each other. But we need to operate on the assumption that they mean harm to us, so let's plan accordingly. Korda, what do we know about their ship designs?"
Korda shrugged. "Not much," he admitted. "They're so damned simple, it's impossible to tell if they have very spare ideas of design, or if they're really just piloting giant bottle-rockets in our direction. The propulsion systems don't use the same technology as we saw in the ambush; they're a good deal cruder. There's no evidence that they have any kind of a reactor, and there is no electromagnetic footprint to their craft at all. I'm not just talking about communications; I'm not even certain they have electronics on board."
"Oh, go on," scoffed Gold.
"Look," said Korda, "Russians and Americans got to the Moon with very little in the way of automated processes that a human being couldn't do themselves in an emergency. These craft don't seem very different from those first few craft that left Earth's atmosphere; they're rockets, fuel tanks, a little space for crew, and that's about it."
"What about weapons?" asked Zhizhi.
"Ah," said Korda. "Yes, well – those they have, I'm almost sure of it. They're close enough for high-resolution visuals to reveal a little surface detail, and there's a lot of hard-points on the craft. They probably have kinetic weapons and rockets, although beam weapons seem unlikely. These things aren't very sophisticated, that's for sure."
"Yeah, but there's something weird going on," said Gold. "I've done a spectral analysis of the fuel. Very pure hydrogen, beautiful stuff, combusting under pressure. But look: given the size of the ship, we can assume the maximum quantity of fuel they're carrying. They've burned a huge amount of it accelerating up to their current speed. They might have a little something left in the tank for maneuvers and such, but they can't possibly perform a complete braking."
Zhizhi turned sharply to Korda. "Any sign of a scoop on those craft?" she asked.
Korda called up the images and cycled through them. "Mmmm… nope," he said. "Too many hardpoints; there's no place to connect the scoop. Also, anything you scoop up has to be refined, and Gold's calculations don't account for that inside the volume of the ships."
"That's true," Gold said.
"Interesting," said Zhizhi. "If what you're saying is true, we're about to have an encounter with hostile aliens who have left their homeworld to intercept us – and they had no plans to return…"
**
The solution to the problem was obvious. With its ability to procure more fuel easily, _Sagan_ could maneuver indefinitely. The Gliesians were apparently unfamiliar with this capability, and had left 581c expecting that their objective would be just as trapped by the constraints of fuel consumption as they. Korda burned sunwards from 581f, a high-energy maneuver. The ships changed courses to intercept, but it soon became obvious that they didn't have the ability to match _Sagan_ on delta vee. The thirteen ships fanned out, killing their engines and drifting on whatever vectors they had been on before they realized catching up to the Earth ship was impossible.
"Let's let them get some distance between themselves," Zhizhi suggested, "and then catch up to one of them once it's isolated enough that it can't expect help. We need to gather more information."
"Why?" asked Vrouw. "That sounds dangerous. If they set out on a suicide mission, won't they just blow themselves up and try to take us with them?"
"Yes, that had occurred to me," Zhizhi said. "But we have to find out what's going on here. If we learn nothing from this, we'll be no closer to figuring out what to do with not one but two hostile worlds."
In the end, they had gone with Zhizhi's idea. _Sagan_ stalked the rearmost of the thirteen ships, creeping up on it from behind. The Gliesian ship used a little of its remaining fuel to turn to face them. They fired kinetic weapons at 100 km, at too far a range to be effective. They also had rockets – crude, but packed with a great deal of explosive material – that Korda's lasers disabled trivially.
Zenia broadcast a simple set of easily decodable messages indicating that the mission was peaceful and that the enemy vessel should stand down. In the event that the Gliesians truly didn't have any radio at all, they also broadcast the messages using a visible-light semaphore.
The Gliesians responded. The nosecone of their craft, a wicked-looking barbed affair, separated from the rest of the vessel. Driven by its own rocket, it homed in on _Sagan_.
"Have a look at the visuals," Zenia suggested over the comm. Korda looked.
There were people clinging to the outside of the barbed launch, using handholds that undoubtedly had been provided for that specific purpose. They were wearing brightly colored vacuum suits – suits long on personalized decoration but short on technology, as they mostly appeared to be mechanical armor with simple air bottles on the back. The helmets were large glass bulbs, and the faces of the Gliesians were visible. They had long beards, intricately woven, and all appeared to be generally pale of skin. Each of them carried a long tool, something like a lance or polearm, with a barbed head made for biting into the skin of enemy craft. The Gliesians were shouting and gesticulating, rapt in some kind of battle-trance, closing in a suicidal attack against a far superior enemy who they simply did not fear.
"Space… Vikings?" asked Matsen dubiously.
"You have got to be kidding me," Korda muttered.
Korda deployed the scoop and skimmed the surface of Gliese 581f, drawing hydrogen up into the refinery unit in Module C. It worked perfectly. Back when he was a teenager, Korda had practiced the maneuver on Uranus before accelerating out of the solar system. It was good to see that the advanced planning of the mission designers was paying off.
Unfortunately, mused Korda sourly, the designers didn't predict the Gliese system being occupied by humans – humans who apparently weren't too happy to see their brothers and sisters arriving from out of town. Or perhaps they did. Korda and his crewmates were the answer to unexpected mission challenges – humans capable of synthesizing responses on the fly. Over the years Korda had wondered why this mission had required an actual human presence at all. He grudgingly admitted that perhaps that decision on the part of Earth Mission Control had been a good one.
Zenia buzzed Korda from the communications room. "I think we're going to have some company," she said. "Launches detected – a bunch of them, coming here. Significant chemical propellant signatures and very high accelerations – 5G sustained."
"Ridiculous," cut in Gold. "Over short durations, sure. Sustained 5G is unsafe."
"Unsafe for Terrestrials," Zhizhi reminded them all. "Gliese 581g has a higher mass than Earth."
"But also a larger surface radius," Korda objected. "Surface gravity will be higher that 1G, but not that much higher."
"You're assuming the launches came from Gliese 581g," said Zenia.
There was an awkward moment. "Didn't they?" Gold asked finally.
"No," said Zenia. "Gliese 581c, further in-system."
"Wait," said Korda. "You've been monitoring EM all over the system. Have you gotten any kind of signal from that planet at all?"
"Not a peep," Zenia replied.
"The plot thickens," Zhizhi said.
The crew reassembled and looked at the models of Gliese 581c on the viewer. Liang delivered his lecture standing up with his hands behind his back, back stiffened, exactly as if he were still lecturing at the Beijing Academy of Science.
"Gliese 581c is approximately 6 Earth masses," said Liang, "and a radius just short of twice that of Earth. Its density is therefore lower than Earth's, but surface gravity is roughly 1.5G. Composition is suspected to be higher in carbon and lower in iron and nickel, which explains the lower density."
"If it's high in carbon," mused Zhizhi, "and given the certainty that the system primary used to put out a lot more energy than it does in its current red dwarf form, it's likely that a lot of carbon dioxide leached out. Won't 581c have an atmosphere like that of Venus, with surface temperatures too high to support life?"
"I believe not," said Liang, somewhat perturbed at having been interrupted. "581c appears to be phase-locked to the sun, similar to 581g, and spectroscopic analysis of the side facing the primary appears to reveal a very thick cloud layer containing a lot of water vapor. Temperature of that surface is high, but not high enough to indicate significant runaway greenhouse heating from below. I suspect that this atmosphere is an insulator, and the planet's surface is quite cool. Actually, 581g appears to be the warmer of the two planets; it also has a thick atmosphere that averages the temperatures of the sunward and shadowed sides, and blackbody radiation numbers suggest that the surface temperature is in the 30 degrees C range."
"So 581g is warm, and 581c is cold," said Korda. "But both are in the range necessary to sustain human life?"
"Oh, yes," said Liang. "Both planets were identified early on as being in the Goldilocks range of masses and proximity to the primary – not too hot and not too cold to sustain life. Of course there's a lot of variance in those numbers; a planet that can nominally support life could still be very inhospitable to humanity. But now that we're here and can see them up close, there can be no doubt that both are very well suited to human colonization. There's even oxygen in sufficient concentrations, although it's probably on the high end on 581c."
"Two human-habitable planets in the same system," mused Zhizhi. "And rather close to each other, too. Unsurprising that both are inhabited. But this doesn't explain why we have so much radio traffic from one and not the other."
"I believe I have an answer to that," said Liang. "There seems to be a great deal of ionization of 581c's upper atmosphere. There's a continuous flow of charged particles sweeping across the atmosphere from the sunward face to the shadow side. It's probably high enough to generate an extremely high noise in most wavelengths."
Zenia nodded. "That makes a lot of sense," she said. "They probably can't hear anything outside their atmosphere, and inside as well. Most forms of long-distance communication would be useless."
"Fine, but then why would the Gliesians keep rockets there, and how would 581g be able to tell them that there was anything out here worth intercepting?"
"All good questions," said Zhizhi. "But not questions we can answer. However, I think we can safely assume that this latest foray is hostile. They're sending thirteen separate vessels, all with vectors that will take them here, and that seems inconsistent with a diplomatic response. They're also accelerating very quickly, even given their native surface gravity, so they must be in a big rush."
"Actually," said Zenia, "there are two stray data points. Yes, thirteen launches are heading this way. But there are two launches that we detected only a few hours ago, and they have different vectors. It looks like they're headed for 581g. Same burn rate."
"Hmm." Zhizhi thought quickly. "It's a small system. We have to assume they can't keep up the high acceleration forever. Let's cap their peak acceleration at .01c for chemical rockets. Given the orientation of the planets, they can reach 581g in a matter of hours. What's the inner window for them reaching our location?"
Liang did some calculations in his head. "Three days," he said.
**
It was actually closer to seven days; .01c was far too generous an assumption. In that interval, the crew of _Sagan_ learned a lot. What wasn't uniformly clear was what, exactly, they had learned.
"There can be no question whatsoever," said Zenia firmly at their daily roundtable. "What we saw when the 581c ships reached 581g was a space battle. Radio chatter increased until they arrived and then dropped off; there were launches from 581g that coincided with the 581c ship intercept; signals from some of those ships were interrupted abruptly."
"Why would they fire on their own kind?" Vrouw demanded. "Even if we assume that there are divisions between the Gliesians, why would they choose the moment of our arrival to engage in hostilities?"
"For the one millionth time, I don't know," said Zenia, tearing up. "I wish Belletto were here." This was awkward. All members of the crew were close, having lived all of their adult lives in close proximity, but Zenia and Belletto were primary companions. Zenia's grief hadn't had a chance to run its course, and Matsen had advised her that a sedative might be necessary to get through the current crisis.
"All right," said Zhizhi. "So we don’t know if the Gliesians fight amongst each other. But we need to operate on the assumption that they mean harm to us, so let's plan accordingly. Korda, what do we know about their ship designs?"
Korda shrugged. "Not much," he admitted. "They're so damned simple, it's impossible to tell if they have very spare ideas of design, or if they're really just piloting giant bottle-rockets in our direction. The propulsion systems don't use the same technology as we saw in the ambush; they're a good deal cruder. There's no evidence that they have any kind of a reactor, and there is no electromagnetic footprint to their craft at all. I'm not just talking about communications; I'm not even certain they have electronics on board."
"Oh, go on," scoffed Gold.
"Look," said Korda, "Russians and Americans got to the Moon with very little in the way of automated processes that a human being couldn't do themselves in an emergency. These craft don't seem very different from those first few craft that left Earth's atmosphere; they're rockets, fuel tanks, a little space for crew, and that's about it."
"What about weapons?" asked Zhizhi.
"Ah," said Korda. "Yes, well – those they have, I'm almost sure of it. They're close enough for high-resolution visuals to reveal a little surface detail, and there's a lot of hard-points on the craft. They probably have kinetic weapons and rockets, although beam weapons seem unlikely. These things aren't very sophisticated, that's for sure."
"Yeah, but there's something weird going on," said Gold. "I've done a spectral analysis of the fuel. Very pure hydrogen, beautiful stuff, combusting under pressure. But look: given the size of the ship, we can assume the maximum quantity of fuel they're carrying. They've burned a huge amount of it accelerating up to their current speed. They might have a little something left in the tank for maneuvers and such, but they can't possibly perform a complete braking."
Zhizhi turned sharply to Korda. "Any sign of a scoop on those craft?" she asked.
Korda called up the images and cycled through them. "Mmmm… nope," he said. "Too many hardpoints; there's no place to connect the scoop. Also, anything you scoop up has to be refined, and Gold's calculations don't account for that inside the volume of the ships."
"That's true," Gold said.
"Interesting," said Zhizhi. "If what you're saying is true, we're about to have an encounter with hostile aliens who have left their homeworld to intercept us – and they had no plans to return…"
**
The solution to the problem was obvious. With its ability to procure more fuel easily, _Sagan_ could maneuver indefinitely. The Gliesians were apparently unfamiliar with this capability, and had left 581c expecting that their objective would be just as trapped by the constraints of fuel consumption as they. Korda burned sunwards from 581f, a high-energy maneuver. The ships changed courses to intercept, but it soon became obvious that they didn't have the ability to match _Sagan_ on delta vee. The thirteen ships fanned out, killing their engines and drifting on whatever vectors they had been on before they realized catching up to the Earth ship was impossible.
"Let's let them get some distance between themselves," Zhizhi suggested, "and then catch up to one of them once it's isolated enough that it can't expect help. We need to gather more information."
"Why?" asked Vrouw. "That sounds dangerous. If they set out on a suicide mission, won't they just blow themselves up and try to take us with them?"
"Yes, that had occurred to me," Zhizhi said. "But we have to find out what's going on here. If we learn nothing from this, we'll be no closer to figuring out what to do with not one but two hostile worlds."
In the end, they had gone with Zhizhi's idea. _Sagan_ stalked the rearmost of the thirteen ships, creeping up on it from behind. The Gliesian ship used a little of its remaining fuel to turn to face them. They fired kinetic weapons at 100 km, at too far a range to be effective. They also had rockets – crude, but packed with a great deal of explosive material – that Korda's lasers disabled trivially.
Zenia broadcast a simple set of easily decodable messages indicating that the mission was peaceful and that the enemy vessel should stand down. In the event that the Gliesians truly didn't have any radio at all, they also broadcast the messages using a visible-light semaphore.
The Gliesians responded. The nosecone of their craft, a wicked-looking barbed affair, separated from the rest of the vessel. Driven by its own rocket, it homed in on _Sagan_.
"Have a look at the visuals," Zenia suggested over the comm. Korda looked.
There were people clinging to the outside of the barbed launch, using handholds that undoubtedly had been provided for that specific purpose. They were wearing brightly colored vacuum suits – suits long on personalized decoration but short on technology, as they mostly appeared to be mechanical armor with simple air bottles on the back. The helmets were large glass bulbs, and the faces of the Gliesians were visible. They had long beards, intricately woven, and all appeared to be generally pale of skin. Each of them carried a long tool, something like a lance or polearm, with a barbed head made for biting into the skin of enemy craft. The Gliesians were shouting and gesticulating, rapt in some kind of battle-trance, closing in a suicidal attack against a far superior enemy who they simply did not fear.
"Space… Vikings?" asked Matsen dubiously.
"You have got to be kidding me," Korda muttered.
