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Comment by sandworm101 | Hacker News Reader

I think people underestimate the rocket equation. In the last fifty years very little progress has been made on the basic ratios between rocket fuel, size and payload. If you want to land on the moon, in 1960 or 2026, you are still going to need the same amounts of fuel and supplies. Your landers will by necessity be similar too.

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Sure, but rocket launch costs are orders of magnitude higher than the cost of fuel to launch payloads. Once we nail down reusability, then we'll see space access become much more affordable. And once we have ships that only operate in space, we'll be able to carry much more fuel along (aerodynamics and structural strength are much less important).

The problem is that, no matter how cheap your fuel is, you have to build a launcher that can lift off while carrying all that fuel. It's expensive to make a pressure vessel that strong and light and large, engines that powerful, etc.

If launch gets cheap enough given current launcher sizes, you can get into in-orbit assembly, but that requires immense investment into robotics or a lot of spending to support (machine-assisted) human construction workers. i.e. you can't launch Apollo as a single package on Falcon 9s no matter how many you can afford, and if you want to send it up in multiple packages you need to either make the spacecraft bigger and bulkier and more expensive so that it's modular, or send up a few times the mass of the resulting spacecraft in assembly robots or construction workers' habitats.

(That's why Starship is so exciting even if it doesn't end up meeting Musk's cost targets, and why SLS has been so enticing for NASA despite its shitshow of a development process - putting up a single large payload in one launch is an advantage in and of itself.)

Most of the weight of Apollo package at the low earth orbit was fuel. Fueling in space was not considered I suppose as this was too difficult with technologies from sixties. These days it is considered possible, so launching Apollo-size package to the Moon should be possible with much smaller rockets and refueling in the orbit.

Please note that the ISS was assembled on orbit from many small components and subassemblies: the largest module was IIRC about 22 tonnes, while the ISS itself is around 420 tonnes. The Soviets pioneered this with Mir, and ISS was designed around a core that was originally intended to be Mir 2.0.

So we have quite a bit of experience assembling one big structure in orbit—a 25 year learning experience, basically, which has given us a toolbox of standards for docking adapters, compatible modules, external manipulators based on the Canadarm, and experience in on-orbit refueling and resupply.

Starship is big and (in theory) cheap, yes, but it's not obvious that we can't do this stuff with smaller and pricier tools.

Apollo didn't go for on-orbit assembly because they were in a blinding hurry (JFK set the "by the end of the decade" goal in 1961-ish) and it's taken us 25 years of plodding to get there. But we could do it now.

Not to toot my own horn too much on here, but I've written a fair bit about these issues going forward: http://heffern.net/rob/index.php/2018/08/25/note-1-kismayo-s...

The current NASA spending is ~$22,000/kg to get into orbit. Elon and NASA both see that getting down to ~$200/kg by 2070, only 50 years away.

When we're talking about $200/kg, the launch site's location relative to the equator will become a BIG deal. You'll see a ~4% difference in cost per kilogram (wildy estimated here) if you are more than 17 km off the equator. That means if you wnat to launch your 160kg-self more than 17km from the equator, it'll be an extra ~$1400.

For a lot of reasons that my posts explain much better, buying certain Somalian real estate is a VERY good move right now. Granted you have to be muslim to do so.

I remember when the Shuttle program was scrapped that the consensus was that reusable vehicles didn't offer the economy they promised, so what has changed since then?

Doesn't matter if you can reuse something if refurbishing costs as much as building a new one. Space just has a more sensible design with better materials and computers.

And SpaceX is doing a totally different thing. They are not putting anything like the shuttle in orbit (humand+cargo). Shuttle's other big thing was that it returned all of its engines to the ground for reuse. All shuttle threw away was the big orange tank. SpaceX had abandoned that concept, returning only the first stage and dumping the second/third stages into the sea. We will probably never see anything like shuttle again.

Starship is very similar to the shuttle in that it will be a reused second stage carrying humans and/or cargo (humans optional unlike Shuttle). Hopefully unlike shuttle it will be able to be reflown without extensive, expensive refurbishment.

Shuttle also had the insane design decision of requiring human crew to be sent up on every single flight, rather than as an optional payload.

Shuttle returned all of its engines by throwing the srbs to the sea. Maybe using a cheap replacement to those and expending it on each flight would be cheaper. At the same time spacex decided against reusing the second stage, essentially making that decision for it's own stack

The shuttle had to make tons of major design compromises in order to get funding, and that basically reduced its utility, limited its launch rate and capacity, and blew out the operational costs.

Critically, the shuttle dumped its engines into the ocean, which meant extensive rebuilding and refurbishing was required in order to make them flightworthy again. The fastest reuse time for a Space Shuttle after the Challenger disaster was almost 3 months (and before it was nearly 2).

The most expensive component of a rocket is the first stage (particularly its engines), and SpaceX lands those on a pad, which means no costly saltwater removal. SpaceX is aiming to reuse a rocket within 24 hours this year (So far the fastest they've done is 71 days, but they're being cautious).

https://en.wikipedia.org/wiki/Criticism_of_the_Space_Shuttle...

At least for launch, I doubt we'll improve those mass ratios for a long time to come - chemical rockets hit theoretical limits at exhaust velocities/specific impulses of e.g. ~5.5km/s for hydrolox, and SSME already got within 10-20% of that theoretical maximum. All of the systems that can get better specific impulse, like thermal rockets or electric thrusters, have thrust:mass ratios waaaaay too low to get off of Earth on their own. (Possibly nuclear thermal rockets? But I don't think people will be overjoyed firing those off in an atmosphere.)

If you reuse vehicles and refuel in orbit, you don't need to be more efficient.

If you have large reusable rockets and refuelling, you can carry a lot more. Thankfully SpaceX is working on just such a plan, which would mean landing far more mass on the moon and being able to take a lot back.

Their lander will look completely different (starship).

The biggest changes will be in-orbit refueling and rapid reusability. That makes 100 tons to Mars orbit feasible.

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