Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Starship is still not understood

caseyhandmer.wordpress.com

Post reply on HN
Print view View original

331–340 of 364 posts

Re: Starship is still not understood

#331

Post by qayxc »

atq2119 wrote: post #310
qayxc wrote: post #78

Earlier quoted context omitted.

Even 90,000 launches over 10 launch windows is 9,000 launches per window. Launch opportunities are about 30 days max per window (depending on the flight profile) so that'd be 300 launches per day or over 12 launches per hour . I'm not saying this is bonkers, but this is completely ridiculous and it doesn't matter whether it's 90,000 or 180,000 or even "just" 45,000 launches - it's completely impractical. Not to menti…

Genuine question: how important is the launch window when you start thinking about bulk transport to Mars? If you build thousands of starships, how much does it matter if some of them are slower to arrive? It's not like flying to Mars is impossible outside the launch window. It takes longer and probably needs more fuel, but by how much?

> how important is the launch window when you start thinking about bulk transport to Mars?

Launch windows aren't just about time of travel. They are primarily about the energy required to get to your target.

You can in principle launch to anywhere at any given moment, but the required energy will be much higher. So high in fact, that a Starship-type spacecraft would be unable to make the trip due to lack of fuel.

Hyperbolic trajectories require higher energies and the exact amount involves solving partial differential equations that depend on the exact orbital configuration (i.e. date and location of launch), so I cannot provide a general answer as to how much more fuel would be required.

Suffices to say it would take more fuel than a Starship is able to carry and a hyperbolic trajectory would require en-route refuelling, which is basically impossible since the tankers/fuel depot would have to move at the same speed.

Re: Starship is still not understood

#332

Post by imtringued »

ncmncm wrote: post #313
Factorium wrote: post #299

Earlier quoted context omitted.

Can we just build private space, lunar, and martian colonies? They could be financed by Tesla shareholders. The colonisation of the world by Europeans started with government investment, but eventually became self-sustaining. If these offworld colonies are free of political correctness, crime, taxes, welfare systems, and disease, and contain only beautiful, healthy, and intelligent people (via careful selection, incl…

Are you familiar with the term "Company Town"? We have, collectively, quite a lot of history with the concept. The Soviet Union did quite a lot more with the idea than western countries did. The GULag system was just one collection of data points. The nuclear weapons reservations, space launch complexes, and bio-weapons towns were others. The experience was not, on average, considered inspirational.

Oligarchs live well because they exploit their subjects.

Re: Starship is still not understood

#333

Post by qayxc »

ncmncm wrote: post #314
qayxc wrote: post #280

Earlier quoted context omitted.

> It gets ignored because it is a symptom of not being able to cheaply launch probes. Is it, though? Let's do a quick and very superficial analysis of the costs here. Say we want to send a probe the outer solar system, like the moons of Jupiter or the Saturn system. There are two unique challenges that such probes are faced with: • on Jupiter, the magnetic field of the planet requires hardened electronics and shieldi…

Just incidentally, a RTG powered by strontium-90 works as well as or better than a plutonium-powered one. Strontium-90 builds up as a waste product in ordinary uranium fuel rods, and can be (pretty) cheaply extracted from what we call nuclear waste. I suspect the use of plutonium for RTGs in spacecraft is mainly because people already had a pipeline for extracting and concentrating plutonium for the weapons industry.…

> I suspect the use of plutonium for RTGs in spacecraft is mainly because people already had a pipeline for extracting and concentrating plutonium for the weapons industry.

You suspect wrong.

In order to be a decent RTG power source, an isotope needs to have:

1. Good power density, since the current energy conversion efficiencies are quite low

2. Good half-life, since it is aimed to operate the spacecraft as long as possible

3. Require little to no shielding, in order not to interfere with sensitive instruments aboard and also to protect humans (i.e. scientists and engineers working on the spacecraft)

4. High power/mass ratio, to minimize the propulsion requirements to launch it into space (which would be less of a factor in this context)

Pu-238 is an ideal fuel due its very good performance in all of these characteristics. Nothing to do with nuclear weapons.

The next best fuel would be Am-241, which is more readily available but is a more aggressive alpha-emitter and therefore performs poorer in (3).

Strontium-90 has a lower power density and a significantly lower half-life. This makes it OK for terrestrial applications, where operation times of a decade are perfectly acceptable, but not ideal for interplanetary missions.

Keep in mind that a lot of power capacity is lost during transit if we're talking about missions to Saturn and beyond. Cheap cost to LEO doesn't pull the outer planets any closer so probes will still take the better part of a decade to get to their destination.

Overprovisioning is also not really an option, because excess heat needs to be radiated away, which is very difficult and costly to do in space.

Re: Starship is still not understood

#334

Post by maccam94 »

ncmncm wrote: post #306
modeless wrote: post #197

Earlier quoted context omitted.

Nitpick: the booster does not achieve orbit. If it did it would need a heat shield like the upper stage. What's new in Starship? Rapid turnaround. Catching the returning rocket with the launch tower. A durable heat shield that needs zero refurbishment for back-to-back flights. The sheer number of engines on the first stage and the volume of engine production needed for that. Orbital refueling. The landing flip maneuv…

Rapid turnaround is not demonstrated. Nor is it even, in fact, planned , in any real sense. I.e., to be clear, there is no evidence that they have any idea how to achieve rapid turnaround of a Starship orbiter. (Superheavy is a different story.) All this turns on the design of the heat-shield tiles. Those we have seen are basically the same as on the shuttle. Each individual tile needs a great deal of personal attent…

The tiles on Starship are much more uniform than on the Space Shuttle, so they are cheaper to produce and less complex to replace.

Re: Starship is still not understood

#335

Post by rbanffy »

panick21_ wrote: post #319
rbanffy wrote: post #301

Earlier quoted context omitted.

> Ares, SLS are basically just warmed up shuttle concepts Not really. They were started before SpaceX proved the idea of reusable boosters. They are a safe Plan-B, using engines and concepts that were already available. It’s a shame they decided to improve upon the existing hardware and took much longer than initially expected, but that’s what life with rockets used to be before SpaceX showed rapid iteration is a bet…

> They are a safe Plan-B I was the Plan-A back then during Constellation. And SLS was also Plan-A. > Not really. I would argue the forced existing hardware into those project to continue to employ the same contractors. Using a single stick solid rocket booster for your human launcher might be one of the worst ideas in the last 2 decades of rocket history. Not surprisingly the congress person from that state was heavi…

> I was the Plan-A back then during Constellation. And SLS was also Plan-A.

It makes sense for it to use the well known approach as Plan-A when the options don’t exist.

> NASA did a whole bunch of studies and these studies pretty much universally showed that the current SLS designs was flawed and a booster that looked like a modern Saturn V was the far better solution.

New developments based on new components, however Saturn V-like, are a risk. I have read a couple studies back then and, while I am not overly enthusiastic about the approach adopted, it offered minimal development risk.

The only novel idea of Ares was putting people on top of an SRB, which was cheap, but abandoned when they realised the vibrations would kill the crew.

Back then, SpaceX was science fiction.

Re: Starship is still not understood

#336

Post by spacemark »

panick21_ wrote: post #318
spacemark wrote: post #292

Earlier quoted context omitted.

Jeez dude, these were just random programs off the top of my head to illustrate industry distrust of launch vehicle promises. My comment wasn't meant to initiate a debate but offer the perspective of someone who is quite literally writing proposals about launch vehicle selection for NASA missions. But hey, you can read Wikipedia, so... In any case to those reasonable out there, don't worry. If SpaceX can prove reliab…

> Jeez dude, these were just random programs off the top of my head to illustrate industry distrust of launch vehicle promises. What you are insinuating is that people are unable to difference between a suborbital technology demonstrator and powerpoint vehicles and multi-billion $ projects that are deep in development. And non of the projects you mentioned would have a comparable impact to Starship. Maybe VentureStar…

Man, there you go again, trying to turn this into a debate where we pick apart everything the opponent says line by line. What a waste of time. Take care, good luck with your mental health.

Re: Starship is still not understood

#337

Post by Ekaros »

twic wrote: post #215
s1artibartfast wrote: post #134

Earlier quoted context omitted.

I'm curious in what ways a industrial cylinder wouldn't be vacuum capable. Pressure shouldn't be a concern. they operate at 5-10,000 PSI above the ambient environment, so an additional 14 PSI differential shouldn't matter. I'm guessing operating temperatures would be a big concern What failed in water?

I am very much not a rocket scientist. But off the top of my head: Cooling. In space there's no ambient cooling by air. If you want to cool something, you have to pump heat out of it and into a radiator. And since that is energy-intensive, you want to minimise heat production as far as you can. Volatiles. In a vacuum those will boil off and not come back. All sorts of polymers, possibly including those used in seals…

To add to list vacuum welding. Which happens in hard vacuum. Making it somewhat complicated to test and solve for on Earth. Specially if we talk about large scale machinery. Then I suppose large scale hard vacuum will be solved by hyperloop...

Re: Starship is still not understood

#338

Post by waltbosz »

oxplot wrote: post #114
gremloni wrote: post #102

Earlier quoted context omitted.

He’s a household joke the same way Elon is a household joke.

Bezos is a household joke even in Elon's household. Elon is a nightmare in Bezos'es. That's where the difference is.

Can someone explain the joke to me?

Re: Starship is still not understood

#339

Post by rbanffy »

vimacs2 wrote: post #330
rbanffy wrote: post #301

Earlier quoted context omitted.

> Ares, SLS are basically just warmed up shuttle concepts Not really. They were started before SpaceX proved the idea of reusable boosters. They are a safe Plan-B, using engines and concepts that were already available. It’s a shame they decided to improve upon the existing hardware and took much longer than initially expected, but that’s what life with rockets used to be before SpaceX showed rapid iteration is a bet…

> It’s a shame they decided to improve upon the existing hardware and took much longer than initially expected, but that’s what life with rockets used to be before SpaceX showed rapid iteration is a better path. Uhm, I think you're simultaneously doing a discredit to past rocket development and giving an easy pass to the mess that is SLS with this statement. It's just shoddy project management and prioritizing collab…

> Uhm, I think you're simultaneously doing a discredit to past rocket development and giving an easy pass to the mess that is SLS with this statement.

Not at all what I intended. Congress is to blame for some of the mess, NASA for the rest. They had shuttle parts and tools and the SLS is certainly not the best that could be done with those.

But, remember, NASA can’t really do much unless Congress gives them the money.

Re: Starship is still not understood

#340

Post by ncmncm »

maccam94 wrote: post #334
ncmncm wrote: post #306

Earlier quoted context omitted.

Rapid turnaround is not demonstrated. Nor is it even, in fact, planned , in any real sense. I.e., to be clear, there is no evidence that they have any idea how to achieve rapid turnaround of a Starship orbiter. (Superheavy is a different story.) All this turns on the design of the heat-shield tiles. Those we have seen are basically the same as on the shuttle. Each individual tile needs a great deal of personal attent…

The tiles on Starship are much more uniform than on the Space Shuttle, so they are cheaper to produce and less complex to replace.

That mainly affects cost, not turnaround time. And there are anyway many unique tiles, particularly around fins and on the nose cone.
Post reply on HN