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Comment by idlewords | Hacker News Reader

It will be interesting to see how SpaceX approaches partially closed-loop life support. This is an unglamorous and refractory technical problem unrelated to what they've done well in the past, but required to achieve their loftier goals.

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Less important than you might think if you have as much mass margin as they do. You can do years with just oxygen (Starship HLS will use oxygen from the propellant tank) and regenerative CO2 scrubbers (which are pretty simple). Also, they have access to NASA’s technical expertise, and NASA has been working with closed loop life support for decades on ISS, now.

Tons and tons and tons of mass margin covers a multitude of sins. A lot of the difficulties of “must haves” for Mars are really just a side effect of substantial mass constraints. Relax those, and it’s much simpler with tech close to what they’ve already demonstrated.

> Tons and tons and tons of mass margin covers a multitude of sins

This is also why building spacecraft is so expensive - they need to be engineered to the absolute minimum mass that does the job and that takes the majority of the time.

Relax that and you cut design time to 10% of it used to be.

There's a nice writeup of what 100X more launch capability means for space missions on this blog: https://caseyhandmer.wordpress.com/2021/10/28/starship-is-st...

We'll see if SpaceX can actually achieve their cost-to-orbit goals. Progress so far is promising, but they have a long way to go still.

“ However, limited water, storage, crew time, and food preparation capability (e.g., add water, heat) restrict the crew to a limited choice of shelf-stable, single-serving food products either in their natural form or preserved by dehydration, retort thermostabilization, or irradiation.”

So “limited water, storage, crew time, and food preparation capability (e.g., add water, heat)” all sound like things that can be addressed either directly or indirectly by “giant rocket.” And using a freezer for food (which a big rocket would allow) isn’t in the list of options they mainly considered. Deep frozen food is a very straightforward way of preserving food and high levels of nutrients for a very long time.

And as far as SpaceX meeting their goals, I agree they haven’t done it YET, but in order for Artemis to work, they now have to achieve those goals. It takes on the order of 10 Starship launches per HLS mission, more than a Mars launch would require! And they’re only charging like $2.5 billion for that, which includes two HLS missions and HLS development. Starship working and meeting its goals (at least enough for initial Mars mission) is now something NASA is reliant on for the critical path for Artemis. NASA is effectively all-in on Starship now.

Everything's easy in space until it has to run for three years or more without breaking. The idea that mass margin fixes everything falls apart a bit when you get into details.

Some examples: there's no good way to analyze air/water for trace volatiles on a spacecraft (ISS flies samples down to earth), there's no food that stays edible for five years, water recapture (which has to be closed loop) has been a headache for the entire life of ISS, so has managing trash and human waste.

You're also wrong that ISS has had anything like closed-loop life support. They are entirely dependent on regular resupply, a full-time ground crew, and lab analysis done on earth. The closest they come to closed-loop anything is 93% re-use of water; a Mars mission (by NASA estimates) would need 99%+.

There's a large class of space flight problems you can't giant rocket your way out of.

On the contrary, I'm convinced weight can (ab)solve many sins. The JWST's solar shade would have been much less difficult to develop if it wasn't so weight constrained.

> Everything's easy in space until it has to run for three years or more without breaking.

Only 90% reliability ? So let's bring 5 of each, since we're not limited by weight, we get to 99,999%

> there's no good way to analyze air/water for trace volatiles on a spacecraft

How much weights a specialized lab for that ?

> there's no food that stays edible for five years

Its been solved a long time ago: dried and salted food, basically

https://www.atlasobscura.com/articles/ship-food-research-rec...

> Mars mission (by NASA estimates) would need 99%+

There are glaciers on Mars. Its about the only thing they wont have to bring.

You can bring 100 of something and still be screwed if it turns out to break because of a common cause. You'd think people on this site of all places would understand that reliability engineering is hard.

2. There is no specialized lab for it that works in space. It has to be invented.

3. Astronauts can't survive on ship's biscuit and space MREs. Malnutrition is already a problem on ISS.

4. There are no glaciers between Earth and Mars, and by the way you're not allowed to touch the Martian glaciers because of contamination risk.

On the contrary, the specialized lab for volatiles has been in space for years already on ISS. They bring samples back to prove it works, and it does.

You’re now moving the goalposts from “no food is edible for 5 years” to “MREs don’t count”.

And the trip from Earth to Mars is only like 4 months if you use a BIG ROCKET. :) 4 months without resupply is no huge challenge.

The volatiles analyzer on ISS works against a short list of known compounds. For anything else you just get a generic warning and have to rely on earth labs to figure out what's going on.

You can't subsist on MREs for five years. Here's a cite for you about the space food problem: https://academic.oup.com/jn/article/150/9/2242/5870322

However fast your imaginary rocket goes, you have to wait 26 months for the planets to align so you can use it.

> You can bring 100 of something and still be screwed if it turns out to break because of a common cause.

If it breaks in storage, without been used - yes. If it breaks in use, for reasons related to usage - no.

If your common cause is a 200A electrical fault, no number of spare 100A fuses will help you.

Component level repair is something NASA does actually do on ISS. And Big Rocket allows you to also bring dissimilar redundancy.

No, my point was that even similar redundancy helps. The example of 200A vs. 100A fuse is just an example of something which is not suitable for the problem - like, a tractor on the Moon helps little if you have a broken leg, you need to have medical supplies for that. But with big rocket you could, of course.

Ah, but did you try to put them in parallel? I've heard Apollo-13 crew were in position of necessity to improvise.

Of course its hard, the point that mass margin helps a huge amount is still true. A bigger rocket doesn't provide a solution but it provides a gigantic amount of more solution space and that matters.

Multiple versions and designed to be repairable. Common parts, 3D printers and so on.

We 100% will need to use martian water. Otherwise its impossible to go.

I have never heard of 2) can you provide a link with some information what is actually required?

This paper (Lessons Learned from the Integration of Monitoring Resources in Addressing an ISS Water Quality Anomaly) gives you a good sense of (2), and the resources required to track down mystery volatiles.

https://ntrs.nasa.gov/api/citations/20110012747/downloads/20...

You claim “ There's a large class of space flight problems you can't giant rocket your way out of.” …but every single one of your examples is wrong and proves the point that large rocket DOES solve it.

For example: > The closest they come to closed-loop anything is 93% re-use of water; a Mars mission (by NASA estimates) would need 99%+. Oh, really? Why precisely do you think NASA estimated 99%+ water recycling would be required? Because MASS.

>trace volatiles In fact, ISS has had trace volatiles measured in real-time for years: https://ntrs.nasa.gov/citations/20070030106 ISS sends samples back to validate the instrument because ISS is a testbed. It isn’t absolutely required.

> there's no food that stays edible for five years

Wrong. Anything will stay edible for 5 years if put in a deep freezer. And canned food lasts a LOT longer than that. “Oh, it’s not as yummy and the nutrient profile changes”, well sure. It’s nice to have fresh food. But the claim no food stays edible for 5 years is trivially false. All of us have eaten food that old, and the radiation environment isn’t enough to change that equation massively.

ISS can withstand long periods without resupply, and has done so when there has been launch failures. If you can prepare for it ahead of time, it’s just a matter of having a sufficient spare pool on-orbit instead of just having the spare pool on Earth. In other words, MASS.

Waste management is annoying if you don’t have canisters to place the waste in, but again, that’s also just MASS. You can put the waste in double sealed containers and then just place it outside the airlock. Can do that on orbit, so that’s actually one advantage Mars has over ISS.

And I don’t see why Mars can’t have a full time ground crew, too. Time delay annoying but not in any way a showstopper.

In fact, a large rocket solves these problems so completely, people who should know better still haven’t wrapped their heads around just how completely it changes the situation. The water recycling thing you repeated is illustrative of this. It literally is just mass.

Space-specific problems are: 1) weightlessness - but people can deal with that, and if needed, I'm sure centrifuges can help; 2) radiation - but large shields can alleviate this problem; 3) space debris, attacking with large speeds - but we can use radars, shields, plasma clouds to reduce problems from this.

With all of these problems large rockets do help.

Space debris is a much worse problem in LEO than anywhere else from here to Mars. Mars’ surface itself at likely landing sites is shielded from all micrometeorites by the atmosphere which burns them up or slows them down to a reasonable terminal velocity (low for micrometeorites, even in the thin Martian atmosphere).

A centrifuge solves microgravity problems, but no one has ever flown one at human sizes. Seems like a big to-do list item.

With cosmic rays, having a large mass of metal around you will actually increase your dose (because of secondary radiation). So you need to figure out shielding that helps more than it hurts.

Space is hard.

Large rockets still help, even if shielding is not straightforward though.

Certainly. And if we had a big enough rocket, we could put its fins on earth and the tip on Mars and just climb up the middle.

That all skips the interesting middle values of the problem parameters :) .

Seriously, for long time already it's not a rocket science.

Existing technologies - with engineering efforts - are capable to bring humans to any point between Mercury and asteroids. We'll likely develop something better, and Solar system would be all reachable without major breakthroughs. Certainly not of the kind "rocket fins on Earth, tip on Mars".

Shielding ESPECIALLY is straightforward, though. The parent was wrong about it being hard.

Why the heck would you use metal for shielding when cheap plastic works way better? But anyway, the “shielding increases dose” is only true for a small portion of the thickness curve at the very beginning. Vast majority of the time even metal shielding helps.

“Space is hard” is kind of a low-effort mantra. Space radiation shielding really is one of those things that is extremely straightforward to address with mass. Polyethylene, or actually any hydrocarbon solid, works fantastic.

I wish you'd read your own links. The machine that measures volatiles on ISS works against a target list of 20 or so compounds. This is an excellent solution as long as your compound of interest is on the list. But when it's not (like when siloxanes turned out to be a big problem for catalyst bed poisoning) then you are entirely dependent on an earth lab.

Here's the Journal of Nutrition saying that five-year stable food adequate for space flight doesn't exist: https://academic.oup.com/jn/article/150/9/2242/5870322. You should write them with the good news that this is trivially solved.

These arguments about "everything is trivial with big enough rockets" remind me a lot of trying to have a discussion with blockchain people. Yes, if you have a warp drive, you can resupply Martian astronauts daily with fresh foods. But maybe let's see it in action before we call it a solved problem.

5 year NON-FROZEN food “adequate for Spaceflight”doesn’t exist. But if you simply bring a big freezer, the problem is almost trivial. Why don’t they normally do that on ISS already? Fundamentally, MASS. Freezers are heavy (mass) and use a lot of power (mass).

Fun fact, but SpaceX has launched ice cream in a freezer to ISS before. This isn’t hypothetical.

See how many hidden assumptions there are which can be relaxed if mass constraints are relaxed? It’s just assumed freezers aren’t viable because they’re too heavy. There’s stuff like this all over the place. The entire field is built under the assumption that mass is extremely rare.

Thanks for highlighting the point that big rocket solves these problems in almost a trivial way.

(And what does blockchain have to do with it? Blockchain is simply a worse solution to a database problem.)

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