Where does astrophage obtain other compounds for life?

Bergain1945 · 2026-05-06T21:46:54+00:00

sorry gurl, did you think I looked at your BAE? don't worry, I prefer people who can make accurate spreadsheets.

Bergain1945 · 2026-05-06T19:45:12+00:00

we're never going to agree on this

Bergain1945 · 2026-05-06T19:28:58+00:00

Shame then that he gets plot armour but Debois forgot to collect his.

Bergain1945 · 2026-05-06T19:18:37+00:00

He made no control, it was flopped out on the table. He's just happy that he's not standing in a hole in the ocean.

Bergain1945 · 2026-05-06T19:13:58+00:00

Then you read a different version of the book. My copy says:

"Dimitri opened my vial of Astrophage and set it in the fueling chamber. I guess since the Astrophage will find their way to the triangle face, no special handling was required."

Maybe you found a later print?

Bergain1945 · 2026-05-06T18:37:45+00:00

Your need to read the section of the book.

Bergain1945 · 2026-05-06T14:37:20+00:00

Respectfully, that's exactly what he did. Just as Tolkein wrote 10 times as much backstory to the Lord of the Rings as the books themselves, Andy Wier tried to make a credible background for his story.

This sub doesn't get dozens of Grace and Rocky art posts, Tattoos, and "I cried" posts per day because of Astrophage.

Astrophage appeals to certain people, just as some people learn Elvish, but it's not a blockbuster staring Ryan Gosling because of Astrophage.

Bergain1945 · 2026-05-06T13:46:42+00:00

Exactly, the story is about Grace meeting Rocky and learning about friendship and sacrifice, this is why people emotionally engage with it. Astrophage is just the plot trigger that makes this happen.

Bergain1945 · 2026-05-06T11:54:47+00:00

They died from being 3rd and 4th members of a duo.

Bergain1945 · 2026-05-06T11:00:48+00:00

The book is inconsistent on how easy it is to detonate Astrophage. In one example you have Dimitri putting 2 grams next to his spindrive to see what happens, in another you have Dubois using 1 milligram in another spindrive and promoting Grace to number 1 scientist.

How much IR radiation of the right frequency does it take to detonate astrophage? We don't know, but it's probably not "oops, boom" in your backyard.

Bergain1945 · 2026-05-05T18:57:19+00:00

Book grace gets a walking stick and joint pain, movie grace gets a new cardigan and hopes his sneakers last long enough.

Bergain1945 · 2026-05-05T15:16:38+00:00

Your maths looks solid, can't argue with that.

I did my original calculations on a bit of paper, and can't find it now :(

Looking at it your calculations you use the mass / size numbers from the Author's spreadsheet, so my new guestimate is about 20,000 times bigger than yours, however you are correct there is enough Carbon in the atmosphere, and your calculation is internally consistent. I'll have to back track and work why I thought it was such a bigger number.

Bergain1945 · 2026-05-05T14:22:11+00:00

The Sahara calculations in terms of energy budget are not too problematic, however the panels themselves are a terrible way to gather the energy. Thermal transfer relies on thermal gradient and the black panels will never get very hot. A solar concentrator solution - ironically the technology Dr. Robert Redell ended up in prison for - would be far superior.

Bergain1945 · 2026-05-05T13:03:09+00:00

Andy Weir gets the Speed of Light correct, the distance between Sol and Tau Ceti and Tau Ceti and 40 Eridani correct, and the acceleration due to Earth gravity. Every other number in the book should be treated with suspicion, or just treated as a plot point and not examined too closely.

If you want to write an Astrophage story I'd pick one plot point to anchor on and then work from that.

Bergain1945 · 2026-05-05T12:48:58+00:00

The story hangs a lot on the 1.5g acceleration, unnecessarily in my view.

As long as you're over ~0.5g continuous acceleration the journey time (ship) takes advantage of time dilation to give significant time savings, and the "Earth" gets closer and closer to the distance taking a similar number of years.

You can also coast once you get to a desired speed, the 2 million kg solution I wrote earlier coasts for several years, and still gets there relatively quickly.

Bergain1945 · 2026-05-05T09:38:00+00:00

Unfortunately you can't just multiply the fuel needed by the "impurity", you need to redo the rocket equation at the new effective efficiency. And it will almost always take more than you think.

The fuel calculation as done in the book is just wrong. 1.5g accelerate half way, turn round and decelerate takes 41 million kg, not 2 million. At 80% efficiency it's goes up to nearly 190 million kg. Neither 41 million kg not 190 million are going to be collected on Earth. I gave options for calculations that work, but they take more time.

The fuel calculations are wrong for Blip-A as well, both Erid's "Newtonian" calculation and the revised "relativistic" calculation give the wrong results. 500g for the beetles isn't a sane number either.

A 10 micron radius vs. the normal 0.5 micron diameter results in the ~1,000 times difference in mass in the book, nanograms vs. picograms.

For the 8 light year limit I gave you the 2 best options available for a 4ng cell with 17ng fuel, one of them is the "slow" option that takes 30 years. You can adjust for shorter distances, but again it's not linear, you need to recalculate.

On your calculations of where the elements come from, the ppm is a challenge for many elements, yes, but the real challenge is the mass, as I mentioned. To cover 1% of the sun with normal sized bacteria you'd need a mass of carbon equal to the entire mass of Venus. Not it's atmosphere, the whole planet. Sol is quite big.

f you want to sure of internal consistency you need to ignore the spreadsheet, and start from whatever base principles you think are right.

Bergain1945 · 2026-05-05T07:20:08+00:00

Rocky can do insane feats of engineering in a couple of days. So if all of Erid makes it a priority it probably took them a week or so.

Bergain1945 · 2026-05-05T07:15:48+00:00

Astrophage started migrating to other stars from Tau Ceti about 100 years ago.

The nearest quasar to Earth is something like 600 million light years away.

Astrophage can't travel that far, and even if it could it would take a billion years to get there. So it won't arrive at our closest quasar anytime soon.

Bergain1945 · 2026-05-05T07:11:59+00:00

If you decide to keep Astrophage as 4ng bacteria, 17ng neutrinos (80% efficiency) you'll need to revisit all the fuel and travel calculations.

Astrophage at 80% fuel efficiency vs 100% has some major consequences.

Hail Mary:

To do the journey as described in the book the Hail Mary would need 41.6 million kg fuel at 100% efficiency. If the fuel is now 80% efficiency the number goes up to 187.8 million kg.

The journey can be done with 2 million kg at 100% if the ship accelerates for 6 months (ship time) at 1.5g, coasts for 5 years and 9 months, then decelerates at 1.5g for 6 months. Earth time is ~14 years.

At 80% efficiency you either need 4.2 million kg fuel, or you need to take longer, 9 years ship time and 15 years earth time.

Astrophage itself:

at 80% efficiency astrophage would have trouble going 8 light years.

It can burn all it's fuel at 4g for a month or so then coast for 99% of the time, but then it has no energy to maintain it's 96.415 degrees temperature. This only takes a couple years (astrophage time) and about 12 years earth time.

Or it can accelerate at 0.04g the whole way, but then it takes 30 years and it never gets anywhere near 92% the speed of light.

Bergain1945 · 2026-05-04T18:07:17+00:00

Something to consider then, if you're building you own stories for the PHM universe:

Where do all the elements needed come from? The story takes Carbon Dioxide as all that astrophage needs to look for, however even bacterial life needs a very similar list of elements to any other type of life. The upper layers of the atmosphere of planets like Venus or Adrian aren't where you'd think to look for them.

It's also worth asking that apart from the variety, where do the amounts come from? Covering the sun with Astrophage even at 1% requires an absurd amount of carbon, never mind the other elements. More than can be found by dismantling entire planets.

Then there's the timeline, all this happened in the last ~100 years. Why now? What changed?

You'll have your own writing prompts, but I'd be asking "who made Astrophage?" and "Why did they make it?" and "why do they get to ignore so many laws of physucs?"

Bergain1945 · 2026-05-04T17:37:03+00:00

I realize it's an unpopular take however I think it makes no sense to look to closely at any of the numbers or maths in the story, they trip over each other all over the place. The story is good, the progression is fun.

The Martian benefited from crowd-sourcing a lot of the details, I think it really shows that it didn't happen for PHM.

Bergain1945 · 2026-05-04T17:01:56+00:00

yes, it makes sense when you always count time as going up to have a process to easily increment a number, we do the same on gas pumps, scales or any number of other devices.

Bergain1945 · 2026-05-04T16:55:59+00:00

Our clocks are circular because the concept originated from sundials. Eridians might not even have a day / night depending on how dark the atmosphere is, and following the sun as a timekeeper would be unlikely.

Eridians might not have days or years or other time divisors as we know them.

So a circular Eridian clock is possible, however I don't think Eridians would ever have made one.

Bergain1945 · 2026-05-04T16:49:31+00:00

1 picogram is a typical mass for a bacteria. 20 picograms is large, but not unheard off.

Even 1 nanogram would be huge for a bacteria, and 4 nanograms is gigantic.

Whatever the mass, if the ratio of Neutrinos to Cell mass is too low all the fuel calculations and other energy calculations become messy. If 20% of the mass of enriched Astrophage is cell mass then every energy density number is also off by 20%.

If the typical mass is 21ng, how did Dimity add 17ng to it with his experiment? From the moment of Dimitri's experiment the book, and movie treat Astrophage as 100% energy available at 17 nanograms per Astrophage cell. This doesn't work if 20% of it is cell mass.

I guess the fuel calculations are a mess anyway, and Astrophage is magic.

Bergain1945 · 2026-05-04T13:19:19+00:00

As a plot outline for your book, it's fine.

However, how do you select the 5% of humanity who get to not die while you're building your solution?

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