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Super Heavy has splashed down in The Gulf of Mexico

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Re: Super Heavy has splashed down in The Gulf of Mexico

#671

Post by dotancohen »

aeternum wrote: post #500
Zigurd wrote: post #450

Earlier quoted context omitted.

That doesn't work IRL. Space is insanely unforgiving. While Starship has a vastly better chance than STS had of achieving rapid reusability, you really can't launch with a rocket that isn't up to spec because adding robustness adds weight. Unlike a multi-stage expendable rocket, Starship uses all its fuel to get to orbit. To go to the moon or beyond, it requires refueling by several other Starships that also just get…

The vast majority of the weight however is oxidizer which you could theoretically eliminate since the rocket is surrounded with various amounts of oxygen depending on launch trajectory. A scramjet power first stage for example could overcome the tyranny of the rocket equation (at least on earth).

I asked that very question on Space.SE:

https://space.stackexchange.com/questions/6256/why-were-jet-...

The summary is that there isn't enough oxygen at the range of altitudes needed.

Re: Super Heavy has splashed down in The Gulf of Mexico

#672

Post by somenameforme »

MeImCounting wrote: post #529
somenameforme wrote: post #383

Earlier quoted context omitted.

Many basic materials, like water, make great shields if necessary. For Mars one plan is simply to organize the ship such that the water reserves can act as an radiation shield when necessary. You don't need anything particularly massive or overly fancy.

The problem is that paradoxically, thicker shields can cause higher doses of radiation due to secondary radiation production. Theres a balance there to minimizing primary and secondary dosage but you cant really get it below a certain threshold without some form of active shielding. Theres a lot of promising ideas for active shielding but they all require alot of power. All this to say that someone on a trip to mars…

The secondary radiation you're talking about is called bremsstrahlung (braking) radiation [1]. This is precisely why water is, to my knowledge, the current leading idea. It works not only as an excellent primary shield but also helps to minimize secondary radiation, and you also naturally have literally tons of it.

As an aside, this is why the original Moon missions used simple aluminum. One of the typical angles people who don't think we landed on the Moon used is that to safely get through the Van Allen Belts we would have needed massive lead shielding on the craft, when in reality it was shielded by a pretty thin layer of aluminum, precisely to minimize secondary radiation. If you put that thick lead shielding on the craft that people intuitively think you'd need, it very well could have killed the astronauts.

[1] - https://en.wikipedia.org/wiki/Bremsstrahlung

Re: Super Heavy has splashed down in The Gulf of Mexico

#674

Post by imtringued »

bombcar wrote: post #470
Zigurd wrote: post #450

Earlier quoted context omitted.

That doesn't work IRL. Space is insanely unforgiving. While Starship has a vastly better chance than STS had of achieving rapid reusability, you really can't launch with a rocket that isn't up to spec because adding robustness adds weight. Unlike a multi-stage expendable rocket, Starship uses all its fuel to get to orbit. To go to the moon or beyond, it requires refueling by several other Starships that also just get…

There's a difference between getting to space and being in space. A true space age will involve many ships that never enter atmosphere or land.

Lockheed Martin is building the cislunar transporter to travel between the moon and earth.

Re: Super Heavy has splashed down in The Gulf of Mexico

#675

Post by somenameforme »

me_me_me wrote: post #596
somenameforme wrote: post #383

Earlier quoted context omitted.

Many basic materials, like water, make great shields if necessary. For Mars one plan is simply to organize the ship such that the water reserves can act as an radiation shield when necessary. You don't need anything particularly massive or overly fancy.

1m3 of water weights a metric ton, do the astronauts stay in a broom closet for duration of the flight? You still need (literally) tons of water. And every ton you take increases fuel cost. Currently you need what 10-20 trips to fuel for moon. How many trips would you need to fuel trip to mars? You would need a fucking conveyor belt of starship to prep the mission. Who is going to pay for it? And why? Just because th…

You hit on two really different topics at the same time. So let's hit on the fuel topic first. People tend to draw intuitive parallels of rocket fuel with gas. A short trip doesn't need much, while a long trip needs a lot. But it turns out that's not really how it works in space. In space the way you travel is you point at something, accelerate a bunch, and then coast there. So the typical measurement for something analogous to fuel is called delta-v, or the total required change in velocity. The delta-v required to get to the Moon is around 19km/s. The total delta-v required to get to Mars is around 21km/s. Wiki has a nice table for the delta-v required to get to different locations here. [1] Not only are they very close, but you might also notice that you spend about half your delta-v budget just getting off of Earth's surface! That's why in-orbit refueling is so useful.

On the water topic, here's [2] a very readable little writeup on the mass inputs required for longterm space missions. Water makes up the overwhelming majority of your requirements. Starship, in its current form, can carry 150 tons. And that will be substantially increased once the tech is stabilized. A sizable chunk of that storage, for Mars missions, will be water. Also, the big threat is not the persistent ambient radiation, but infrequent extremely high energy bursts from solar weather.

[1] - https://en.wikipedia.org/wiki/Delta-v_budget#Delta-vs_betwee...

[2] - https://ntrs.nasa.gov/api/citations/20190027563/downloads/20...

Re: Super Heavy has splashed down in The Gulf of Mexico

#676

Post by tialaramex »

dotancohen wrote: post #665
andrewflnr wrote: post #655

Earlier quoted context omitted.

It was an ancestor of things with military value, but it had little to none itself. You need a guidance system for a useful cruise missile, and the V1 had essentially none. No points for "military utility" as a "research program" when you're actively launching them at civilians; whatever it is, that's not a research usage anymore.

The German strategy was to pressure the British civilians into pressuring their government for an end to hostilities against Germany. They were demoralizing the British, and to that end the weapon was actually effective though the government did not capitulate. Additionally, reports of damage to the British capital city was very morale-raising for the Germans who saw mostly the destruction of their own cities. That a…

V1 launches begin in June 1944. One week after Overlord ("D-Day") and prompted by it. The obvious release for the London public's fear of these weapons was to destroy the capability not capitulate to Germany, and by October of the same year V1 launches against Britain were no longer possible because Allied forces controlled all the launch sites in range.

Re: Super Heavy has splashed down in The Gulf of Mexico

#677

Post by grishka »

api wrote: post #120
delichon wrote: post #81

Watching pieces of the ship melt off, but then seeing it make a relatively controlled landing, is perversely confidence building. If it can survive that kind of damage on a control surface maybe it's a quite robust craft.

I’ve said for a while that we won’t be ready for the real space age until you can have a rusty pickup in space. What I mean by that is that we have it down well enough that the tech exceeds tolerances and can degrade gracefully. You see this in some sci-fi where there are rust bucket old ships that work.

This is unlikely. We don't really do this on airplanes, where servicing procedures and airworthiness criteria are very strict, and space is orders of magnitude more unforgiving than flying in the atmosphere at ~10km altitude.

If there's cabin decompression on a plane, you get an oxygen mask and land safely in the nearest airport. If there's cabin decompression on a spacecraft, you're dead. If there's a problem with engines on a plane, you can still glide and land somewhere. If there's a problem with engines on a rocket, guess what, you're dead.

Re: Super Heavy has splashed down in The Gulf of Mexico

#678

Post by tsimionescu »

hrnnnnnn wrote: post #653
cubefox wrote: post #591

Earlier quoted context omitted.

"will have had", "will have been" - amazing construction

Future perfect and future perfect continuous, respectively, if you're interested in the names.

They're both future perfect I believe, of the verbs "to have" and "to be". Future perfect continuous is "will have been filming", this was "will have been fine".

Re: Super Heavy has splashed down in The Gulf of Mexico

#679

Post by imtringued »

somenameforme wrote: post #675
me_me_me wrote: post #596

Earlier quoted context omitted.

1m3 of water weights a metric ton, do the astronauts stay in a broom closet for duration of the flight? You still need (literally) tons of water. And every ton you take increases fuel cost. Currently you need what 10-20 trips to fuel for moon. How many trips would you need to fuel trip to mars? You would need a fucking conveyor belt of starship to prep the mission. Who is going to pay for it? And why? Just because th…

You hit on two really different topics at the same time. So let's hit on the fuel topic first. People tend to draw intuitive parallels of rocket fuel with gas. A short trip doesn't need much, while a long trip needs a lot. But it turns out that's not really how it works in space. In space the way you travel is you point at something, accelerate a bunch, and then coast there. So the typical measurement for something a…

Why does this matter? The delta V requirements are so steep Starship can't return from the martian surface. It is a completely different game to go to Mars than to the moon unless you are planning on building a mars gateway in orbit and never landing anywhere.

Re: Super Heavy has splashed down in The Gulf of Mexico

#680

Post by tsimionescu »

notact wrote: post #217
pixl97 wrote: post #68

What the hell, half melted starship actually did the landing flip and hit the ocean slow!!! That was amazing!

Can someone explain why reentry must be so hellish? The energy gained during the rocket burn into orbit must be bled off during reentry, and that energy is enormous. However, why must reentry occur so quickly? It seems if the descent into the atmosphere was slower, the heat shield would be able to radiate the heat energy away more effectively, thus lowering skin temperatures, and significantly reducing the engineerin…

It's because slowing down from 26000 km/h to something that wouldn't cause extreme heating (say, 1000km/h) would only be possible by firing thrusters in the opposite direction. Otherwise, any contact with a medium that could slow you down would lead to the same extreme heating.

And of course, the thrusters you'd need would add huge complexity for the shape, and need extra fuel in the stage 2 itself, greatly reducing its cargo capacity.

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