That may well be so. I don’t actually recall if there was any coasting in the middle. But it makes sense that they would. At a constant acceleration of 1.5G, you would reach 90% of the speed of light in less than 8 months (ignoring relativistic effects, which I know you can’t do). So at some point, you reach a point of diminishing returns as you approach the speed of light, by expending energy while not achieving any appreciable greater velocity.
So for a journey of nearly 12 light years, it makes sense that the ship would accelerate to some large fraction of the speed of light, coast for several years at that speed, then turn around and decelerate.
Continuing to accelerate wouldn’t make much difference in when the solution could get back to Earth. But it would make a difference in how long you have to keep life support working on the mission.
Just watched PHM on Prime, and have a line of questions. (Presumably the book deals with the matter in medium detail.)
—Did the little black solar suckers provide Earth with a crazy simple source of not-quite-infinite power?
—Will humans be able to use that power after making Venus inhospitable for mating?
—Will humans use some of that power to try to save other stars — rather than face a future of a mostly starless sky?
—What are some other implications of dealing with little critters that consume suns, provide an insane power source, and have a known vulnerability?
The answer to the first question is unequivocally yes. Although it would be more precise to say that the astrophage provide a means of energy storage…as opposed to being a source of energy themselves.
The answer to the followup questions are related. First off, the astrophage—even if left unchecked—don’t kill stars. They “just” reduce the output—approximately 10% as I recall, before they naturally level off. Unfortunately this is enough to push the Earth into an ice age.
But with the taumoeba introduced, the population of the astophage is significantly reduced (though not completely eliminated) at a much lower equilibrium so as not to significantly affect the solar output of the sun.
It’s similar to other situations where a predator is introduced in order to keep the population of prey from expanding too much and causing problems.
In addition to astrophage being an excellent energy-storage medium, they also make it possible to make really cheap and easy solar panels. This is in fact how they made the fuel for the ship, but once the ship was fueled and launched, they still had all of that production capacity available. Part of how they Got Things Done in the book was by getting corrupt rich people on board, by offering them the profits from projects like that.
In the book, there’s no mention of any plans to “rescue” any other stars, but there’s also no communication from Earth after the mission. They might be planning other deep-space missions, since we now have the capability, but it’s probably for reasons more profitable than mere altruism. Also keep in mind that, while Grace’s mission was successful, it also took decades, during which time the Sun’s output was still decreased (with all of the implications of that), so Earth is probably in pretty bad shape economically.
It’d be more plausible that the Eridians might mount such a mission, since they weren’t hit as hard by the loss of solar energy (their planet has an extremely thick atmosphere, that makes it very slow to heat up or cool off), and they have a much higher base tech level (especially now that they also have access to essentially all of Earth’s scientific knowledge in addition to their own, a boon that Earth did not fully receive).
Thank you.
And of course this frees humanity from the confines of the solar system, and they’ll likely build bases around nearby stars and use energy from those stars to send probes to every possible habitable world they can reach.
Other than the astrophage itself, Earth didn’t really have the technology for interstellar travel - it never would have happened if it wasn’t utterly necessary for survival.
As mentioned above they had to cover all of North Africa with solar panels and wait several years in order to produce the fuel for a single ship to make a one way journey to Tau Ceti. A round trip would take more than 5 times as much fuel.
And their life support had a 67% failure rate. You’d probably want a better one before voluntarily getting on the ship.
Also, it wasn’t mentioned in the movie, but in the book only 1 in 7000 people had the gene that allowed them to survive the medically induced coma.
Thios puzzled me a bit. Relativity makes the acceleration phase shorter (according to observers on board ship). Does this reduce the amount of fuel used, or not? The motors are still using the same amount of fuel per second at any one point, surely? I know there is no free lunch involved, but how does one calculate the fuel use in this situation?
Same way you’d do it without relativity: You take the fuel usage per second, and multiply it by the time spent. You just have to make sure that the time you’re using is the time experienced by the ship (but that’s the same as the time you’d calculate for the trip if you didn’t know relativity).
Well, actually, it’s probably more complicated than that, since you’re probably going for constant acceleration, not constant fuel consumption rate. As you use up fuel and your ship gets lighter, the consumption needed for that acceleration decreases. So instead of just multiplying, you’d need an integral. But it’d still be the same integral you’d do without relativity.
Or Weir messed up. It happens. When the Martian was still web based, people were catching things and helping him update the science and engineering. We have teams of engineers for a reason. A single person just can’t think of everything.
It is mentioned they use margins of safety, as everybody should, so that is part of it. Due to the natural conditions of their planet, they were able to almost trivially generate astrophage fuel unlike Earth. So fuel generation was not an issue for them.
Yeah, he could have avoided that particular mistake by just saying that they included a safety margin that they turned out not to need, and since their ship was so much larger than the Hail Mary, their percentage safety margin was a lot of fuel.
He probably still would have wanted to include some sort of relativity-based mistake on the Erids’ part, since he wanted to show that, despite their advanced materials science, there were still some areas where we were ahead of them. Maybe have Rocky be a little extra worried about his star, since their scientists saw their star’s natural oscillation or rotation rate speed up while they were on their journey, and they’re not sure why.
We don’t know what technology or information the Eridians shared with Earth nor do we know what might be useful. At the very least, we might learn how they make xenonite. I like to think the two species cooperate from then on.
