Comment by themgt | Hacker News Reader

Comment by themgt | Hacker News Reader

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Yep, and in addition to both of these, Starship is also designed:

* to be fueled / ignited such that it can be refueled in-situ on Mars & then launched back to Earth, without advanced rocket fuels or the TEA-TEB chemical igniter.

* to be able to refuel from another Starship in-orbit

The combination of all of this, if they pull it off, will be the ability to send truly massive payloads to Mars, faster and cheaper than anyone could have imagined just a few years ago.

To me it does really show the benefit of taking a systematic approach, working backwards from the goal "get to Mars and stay" in a resource-constrained environment. They've very strategically targeted the technology/engineering required to bring the costs down to something reasonable, while NASA's approach for 50 years has basically been versions of "can you give us one trillion dollars?" (or "we can put a couple humans on Mars for 3 days for $100 billion")

Today's Starship hop is getting very near the nail in the coffin for SLS. I still have some concerns about their crazy re-entry flip, but the speed SpaceX is moving is leaving everyone else in the dust.

Also, since its mostly made from steel, it will be fairly simple (as far as rockets go) to conduct repairs, you just need a welding rod or two. This is important for early stage bases where you don't have the equipment/materials to make carbon fiber or exotic aluminum alloy replacement parts.

Given how much difficulty they've had with welds and materials to date, is it really feasible to conduct in-situ repairs without a ton of advanced equipment?

That's what I was thinking. At the very least, they'll either have to come up with some very fancy welding rod matrials, or train their welders in some interesting techniques. Reminds me of the difficulties in welding aluminum.

I feel the same way. Likely not to start but over time I think they would build up capability. I wonder how lesser gravity on Mars would help/hurt their efforts. Easier to heft heavy gear up high?

I'm also thinking on the flip side, say a Starship somehow gets irreparably damaged getting to Mars (but successfully gets there). With some basic gear they should be able to part it out and re-use the steel.

Like for a new door on all the Cybertrucks rollin' around up there. /s

The idea of using parts of the landing unit for materials to build local structures and machines is not new. Probably, with proper planning and construction of the lander unit parts, it can be facilitated.

But you have to plan for another mission to pick up the crew, unless you're on the Moon where you could use an electromagnetic catapult to achieve orbit, and then slowly ascend to the rocket that would take you home.

I didn't know that. Sure, it doesn't sound like a revolutionary idea, and I'm not surprised at all its been thought of. I was basing it on the assumption there are people there already who aren't leaving. With a colony on Mars/Moon it surely becomes more useful to have a vast amount of steel to reuse than some crazy alloy.

Electromagnetic catapult, huh. Sounds fun as hell.

The difficulty is making it light and strong. If you're doing an emergency patch repair on a small area you could sacrifice some cargo and use much thicker material and more welds to be sure it will hold. It wouldn't be easy but is much easier than the initial build.

Most importantly, you mostly need it light to escape Earth's atmosphere. (And somewhat to have enough fuel.)

On Mars, Moon or in space this constraint is reduced.

The difficulty is making a weld that doesn't weaken or anneal the parent metal through heat induced material changes.

Welding thick to thin is nontrivial because of the different heat input required in each substrate. You tend to burn through the thin part.

Patching may be possible but thick patches don't make things any easier.

It probably depends on what needs repairs. Repairs around the fuel tanks will be difficult as they would not readily have the equipment to purge the tanks of the fuel/oxidizer. Anything that is bulk structural is likely to be repairable to some extent.

I would not be surprised if part of the reason for building these in a tent is so they can gain experience for building/repairing these rockets with as little infrastructure as possible.

Still it's much easier to work with, compared to titamium, to say nothing of carbon fiber composites or silica-fiber tiles like the Space Shuttles used.

That is, something you can have a fair chance of fixing while in orbit or on Moon or Mars.

I wish I could invest into SpaceX. Such a slam-dunk rarely presents itself, and an opportunity to change the world for the better _while also making money_ is rarer still.

It seems you could buy a stake in a number of publicly traded companies and funds that themselves own a stake. Seems like Google and Fidelity each own about 4% of SpaceX, maybe Fidelity is offering it as a component of some fund?

https://en.wikipedia.org/wiki/SpaceX#Ownership,_funding_and_...

Google at least is a bad option. You won't actually get any value representation, any exposure, due to their extreme market cap.

Most likely close to 0% of the SpaceX ownership stake is represented in Google's stock. Let's assume though for the sake of argument that some large part is, say $1.3 billion of the stake is represented (3% of $44 billion). That's equal to about 1.3% of Google's market cap (~$1t).

Whatever you do never buy a stock on that kind of premise. Risking the other 98.7% of your capital to get a meaningless piece of something else (which is already a big something else at a $44b market cap). If SpaceX doubles in value, you'll never notice it (you put $1,473 into Google, SpaceX doubles, max scenario you might make $20). It may be one of the worst reasons to ever buy a giant like Google. People commonly make this mistake when buying Berkshire Hathaway or certain other conglomerates, thinking they're getting a 1-to-1 direct exposure to the Berkshire portfolio (among their equity holdings, only a few matter at all, as with the Apple holding at $110b). I often see it pitched as a form of bonus diversification. Cash and equity holdings on the balance sheets of public companies are essentially never represented at full value in the market cap. The larger the company and the smaller the asset in question, the more likely it is to have something more toward zero representation.

I don't get the Berkshire Hathaway analogy. If you buy that stock, in what way are you not getting "1-to-1 direct exposure to the Berkshire portfolio"? You're owning the same investments Warren Buffet owns, in the same proportions, to within a rounding error.

It would be a mistake to invest in BH because, say, you're really bullish on Dairy Queen, but that doesn't seem like the mistake you're describing.

Math check -- I think Google's SpaceX ownership stake would be closer to 0.13% of Google's value, not 1.3%. Is that what you meant?

To be fair to NASA, they would never have been allowed to pursue a Starship-like strategy. Look at the Space Shuttle, which had all kinds of requirements ladled on top of the program, such as DoD requirements.

Remember, NASA was the one that added the DOD requirements. To increase their budget, they lobbied congress to cancel the Air Force space program to make it a captive customer of the Shuttle.

> * (or "we can put a couple humans on Mars for 3 days for $100 billion")*

Is there actually a NASA proposal like that? As far as I know, orbital dynamics don't allow for this. One has to wait for a Hohmann transfer orbit window to return home.

There are faster transfer opportunities, but not 3 days. But I think he way saying 3 days of surface ops. Which is still an exaggeration. I think the NASA reference mission is 30 days?

I had a peek at the Mars Design Reference Architecture 5.0 [1], and under "trajectory options" they talk about two classes of missions.

"Opposition class missions" stay on the surface for 30 to 90 days. "Conjunction class missions" stay for 500 days or more.

That confirms the 30 days that you mentioned as a reasonable minimum.

[1] https://www.nasa.gov/pdf/373665main_NASA-SP-2009-566.pdf

There is a "short stay" option, where you return on the same synod. This requires a higher-energy transfer, involving Venus on at least one leg, to get there early enough to hit the return window and also have enough time to actually do something on the surface. Apparently you can get up to 90 days in some situations, but 30 is more likely, out of a total elapsed mission time of 400-650 days.

https://nssdc.gsfc.nasa.gov/planetary/mars/marsprof.html

Of course, this in in the "resource-constrained" mode of thinking. If you allow for giant vehicles with on-orbit refilling, SpaceX-style, you just spend a bunch of energy to get there fast instead of monkeying around with Venus.

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