Starship is still not understood • Hacker News Board

Re: Starship is still not understood

#351

Post by garmaine » Sat, Oct 30, 2021, 2:56 AM UTC

Gravityloss wrote: post #329

moralestapia wrote: post #308

Earlier quoted context omitted.

Except it's not 10,000 launches, it's 170,000 (see other comments here). So that's 850M tons, about a 10% increase (on top of the 2nd most polluting country in the world), so yeah, not happening. I would personally rally against the govt. (and everything that allowed that to happen) if Elon gets a free pass on that.

Ok, I'm not that familiar with the plans with starship. I think the premise of the article is wrong anyway. I think no matter what the system is like, it still makes sense to optimize for mass in a reasonable way. That means, not sending dead weight to high delta vee. Leave big tanks or engines behind. It's a bit like you don't transport your car with the airplane. It would be madness. Exponentials are unintuitive. T…

> That's why I'm really skeptical of the architecture of landing atmospheric stages to the surface. They are just unnecessarily heavy. You have maybe quadrupled your total launch amount from the surface (haven't done an analysis).

Lunar starship is not an atmospheric stage.

Re: Starship is still not understood

#352

Post by Gravityloss » Sat, Oct 30, 2021, 9:22 PM UTC

garmaine wrote: post #351

Gravityloss wrote: post #329

Earlier quoted context omitted.

Ok, I'm not that familiar with the plans with starship. I think the premise of the article is wrong anyway. I think no matter what the system is like, it still makes sense to optimize for mass in a reasonable way. That means, not sending dead weight to high delta vee. Leave big tanks or engines behind. It's a bit like you don't transport your car with the airplane. It would be madness. Exponentials are unintuitive. T…

> That's why I'm really skeptical of the architecture of landing atmospheric stages to the surface. They are just unnecessarily heavy. You have maybe quadrupled your total launch amount from the surface (haven't done an analysis). Lunar starship is not an atmospheric stage.

In the fine article, in Casey Handmer's plan, Starship is landed to the surface and returns directly to LEO or even to Earth surface.

So yes the heat shield goes all the way down to the lunar surface and back.

https://caseyhandmer.files.wordpress.com/2021/03/artemisspac...

Re: Starship is still not understood

#353

Post by garmaine » Sat, Oct 30, 2021, 9:32 PM UTC

Gravityloss wrote: post #352

garmaine wrote: post #351

Earlier quoted context omitted.

> That's why I'm really skeptical of the architecture of landing atmospheric stages to the surface. They are just unnecessarily heavy. You have maybe quadrupled your total launch amount from the surface (haven't done an analysis). Lunar starship is not an atmospheric stage.

In the fine article, in Casey Handmer's plan, Starship is landed to the surface and returns directly to LEO or even to Earth surface. So yes the heat shield goes all the way down to the lunar surface and back. https://caseyhandmer.files.wordpress.com/2021/03/artemisspac...

The Starship actually being built by SpaceX under the HLS contract for NASA has no heat shield or atmospheric engines. It is meant to be expendable, or for reuse only in space without servicing.

Re: Starship is still not understood

#354

Post by Gravityloss » Sat, Oct 30, 2021, 10:10 PM UTC

garmaine wrote: post #353

Gravityloss wrote: post #352

Earlier quoted context omitted.

In the fine article, in Casey Handmer's plan, Starship is landed to the surface and returns directly to LEO or even to Earth surface. So yes the heat shield goes all the way down to the lunar surface and back. https://caseyhandmer.files.wordpress.com/2021/03/artemisspac...

The Starship actually being built by SpaceX under the HLS contract for NASA has no heat shield or atmospheric engines. It is meant to be expendable, or for reuse only in space without servicing.

Yes, which the fine article was criticizing.

Re: Starship is still not understood

#355

Post by panick21_ » Sun, Oct 31, 2021, 9:31 AM UTC

spacemark wrote: post #336

panick21_ wrote: post #318

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. 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.

There you go again, responding with insults rather then arguments. A debating in a forum that is about debating articles about technology shocking.

Re: Starship is still not understood

#356

Post by panick21_ » Sun, Oct 31, 2021, 9:37 AM UTC

rbanffy wrote: post #335

panick21_ wrote: post #319

Earlier quoted context omitted.

> 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, howeve…

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

Not when Plan A has well known well document problems.

> New developments based on new components, however Saturn V-like, are a risk.

Restarting production for RS-25 has risk. Using solids boosters for human space flight has risk.

The idea that magically the picked design has no are significantly less risk is questionable.

In terms of risk to human on the rockets the other designs out-performed the current design and they were cheaper.

> The only novel idea of Ares was putting people on top of an SRB, which was cheap,

I recommend you go back and check out how much Ares 1 cost. It was literally the opposite of cheap. It was a gigantic money pit for a non-commercially competitive rocket that was incredibly risky for human.

> but abandoned when they realised the vibrations would kill the crew.

Maybe the single worst rocket design ever. Despite the issues there were others metnioned.

However the whole Constellation program got canceled because it was horrifyingly badly executed and a bad plan in the first place.

> Back then, SpaceX was science fiction.

By the time SLS was designed they were not. And just because SpaceX doesn't exist, doesn't mean you couldn't do much better then Ares or SLS.

Re: Starship is still not understood

#357

Post by panick21_ » Sun, Oct 31, 2021, 9:39 AM UTC

ncmncm wrote: post #343

panick21_ wrote: post #322

Earlier quoted context omitted.

> Once it becomes Somebody Else's Problem, and not NASA's, then NASA can quietly abandon it No, what happens is that you create a seriously powerful group of private institutions that will go full force into lobbying congress to not kill the project. Even more so then now.

What you describe is the present condition.

No, now you have many private groups with slightly different interest temporarly unified. Once you create one gigantic mega contractor, that group has a much more specific and target interested in lobbying for that one specific program.

Re: Starship is still not understood

#358

Post by panick21_ » Sun, Oct 31, 2021, 9:41 AM UTC

vanattab wrote: post #193

panick21_ wrote: post #184

Earlier quoted context omitted.

> You are being deliberately misleading with this statement. No, I wasn't. I simply stated he wasn't there, and he wasn't. I didn't imply anything beyond that he wasn't there. > proves the parents point. No it doesn't. People violate different things and are allowed to continue to operate. Virgin Orbit was just stopped from operating and had to go threw review. Doing a review of company and its safety culture is stan…

>No, I wasn't. I simply stated he wasn't there, and he wasn't. I didn't imply anything beyond that he wasn't there. Honest communication is about more then just making sure your statements a factually correct, context matters.

I don't know what is not clear about what I said. The person wasn't there, for a rocket launch that clearly implies the facilities where the rocket is launch from.

Not sure how one could interpret that any other way.

And you continue to not provide that evidence for that SpaceX treatment was particularly unusually and gives them a massive advantage (not to mention that by that point SpaceX existed for almost 20 year).

Re: Starship is still not understood

#359

Post by chernevik » Sun, Oct 31, 2021, 4:29 PM UTC

I'm more worried about NASA's goals than I am their costing strategy.

SLS and Orion are taking up much of NASA's budget, and I don't see the payoff. What science are we going to add with another manned moon mission? Going to the moon and returning with stuff like the Genesis Rock was important, but that's been done. Likewise I'm really not sure what science we've gotten from the Space Shuttle and the ISS, outside of biology on long-term human space flight.

Whereas stuff like Voyager, Galileo, Cassini, Juno, Hubble have had _clear_ science gains, and cost much less than manned missions. Now we the Webb Telescope and Lucy, we should be doing much more stuff like that.

Re: Starship is still not understood

#360

Post by ncmncm » Sun, Oct 31, 2021, 7:37 PM UTC

qayxc wrote: post #348

ncmncm wrote: post #342

Earlier quoted context omitted.

Strontium-90 has better power-density per unit mass than Pu, albeit with larger volume. Half-life is comparable. Safety is better: less gamma, no neutrons, no shielding needed. Overprovisioning is needed in every case, and excess power has to be dealt with the same way. Low cost to orbit means more fuel / more ∆V is practical to provide, thus much shorter transit times, translating to less up-front decay.

> Strontium-90 has better power-density per unit mass than Pu The power density of Sr-90 fuel is 15% lower by mass than Pu-238 - 0.46kW/kg thermal compared to 0.54kW/kg thermal. You must have been looking at the wrong figures. Since the Sr-90 fuel rod doesn't get as hot as a Pu-238 fuel rod of the same size, energy conversion efficiency drops significantly and you need up to 100% more Sr-90 fuel (and consequently mor…

Wikipedia claims strontium-90 emits 0.95W/g. But it also says SrTiO3 emits only 0.256W/g, which is consistent with your figure.

So, I am obliged to conclude Wikipedia's figure is off by 2x, undermining my argument.

That said, if there were no Pu, Sr-90 would have to do. It has the advantage of being very cheap, as radiothermal isotopes go, and not requiring G7-military-grade security. Its bremsstralung radiation is only in X-ray range, so easily shielded, yielding heat.

When it gets cheap to loft 150 tons to orbit, in a couple of years, the economic and timing verities of outer solar system transport will be up-ended. Cassini was lofted at 6 tons, and took 7 years to get to Saturn. Much of its cost was driven by limits on mass. Given 150 tons to work with, it is hard to imagine any detail of the mission remaining similar, except its rousing success. It certainly would not have needed 7 years to get to Saturn. It might not even have needed RTG power.

A four-year transit to Pluto using FRC direct fusion propulsion is more appealing than RTG-powered ion drive, with the additional advantage of much less likelihood of wholesale civilizational collapse in the interim. But FRC fusion needs development work; its research budget is currently diverted to dead-end Tokamak projects.