RCgothic
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Posts posted by RCgothic
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I assume it will slip a couple weeks, but still a pretty good turn around. I wonder what the FAA has to say about the SN11 Investigation.
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Nice.
Round up of a few tweets.
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It's easy for shorter rockets to look quick. The same speed is more body-lengths which is how we tend to judge speediness.
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I did comment that the mystery frame looked like tension members. That's making more and more sense the more of it they build.
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1 hour ago, Piscator said:
Glad someone else did the math, although I think your calculation is off by two magnitudes. Using your numbers, the amount of stellar material swept up would be only 0.3 mg. Also, the human frontal area is closer to 5000 square centimeters rather than 500. This would give you 1.35 kJ of kinetic energy which is close to the 4 kJ I got.
Still, quite a significant amount compared to thermal energies involved.
I'm having an off day. Think I misplaced a kg for g somewhere, and 1k cm2 to a m2 instead of 10k cm2.
Thanks for the corrections. Think a 1cm/s kick would be more noticeable rather than seriously injurious.
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Nice to see Falcon Heavy getting more missions. I think we're overdue a few.
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The swept distance over a microsecond at 30km/s is 3cm. The average human is ~500cm² frontal area so you'd sweep out 1.5 litres of stellar corona. As a diffuse plasma it would reasonably be expected to penetrate skin rather than be deflected.
The density of the Corona at the edge of the photosphere is ~0.0000002g/cm3.
The 1.5 litres contain 0.3g of stellar material, 9kgm/s of momentum, 135kJ of kinetic energy, and approximately 15kJ of thermal energy.
This would all be transferred to the unfortunate traveller in addition to the radiative effects other people have outlined. A human is about 20cm thick and weighs 60kg, so the wind-facing 3cm would account for about 9kg. Those 9kg would be kicked backwards at 1m/s and heated by ~4 Kelvin near-instantaneously.
It wouldn't be a fun kind of 1m/s either. More like hitting a less-friendly concrete wall. Could come with severe deceleration injuries.
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Superheavy grid fin spotted.
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9 hours ago, tater said:
Starship has huge capability only after refilling in LEO (at least to move itself anywhere). Though it could deliver an Apollo upper stage sort of mass to LEO (and stage that off for the Moon).
Sure, but in this instance I was speaking purely in terms of propellant delivery to LEO.
In every case a means of transferring propellant would be required, but that's a necessary technology for getting to Mars. Full drop tanks would be harder. It'd be easier structurally to put up the tanks as payload and then transfer the residuals from the upper stage.
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The vast majority of what will be required for a Mars mission is fuel, so residual props isn't necessarily the wrong way to go.
So long as the booster can put up a lot of them on a reasonable timescale for a reasonable cost. That's not SLS by any measure.
It might be FH, or Vulcan, or New Glenn though.
Even if Starship never works reusably as intended, there's no serious reason not to think it'll be an enormously cheap way of putting up a lot of propellant cheaply and often.
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2 hours ago, wumpus said:
This basically assumes that Falcon Heavy can lift considerably more to LEO than Falcon 9 expendable. Which in turn assumes that Block 5 was designed with that in mind and provided the support for ~150 ton loads to orbit (as the infallible wiki claims). I'm a big fan of Falcon Heavy, and have seen no evidence implying that at all.
I made no assertion about Falcon Heavy at all in the section you responded to. I said "Some other Booster".
It may indeed be the case that Falcon Heavy can't lift more payload to LEO than Falcon 9. That doesn't change the fact that SLS is never assembling a Mars mission.
A reasonably worthwhile Mars mission will take over a thousand tons to LEO. SLS can't do that on any reasonable cost or timescale. If no other booster exists that can do that then we're not going until one does.
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12 hours ago, tater said:
Yeah, but it is funded, regardless. It will fly until there is some off the shelf alternative that makes it look stupid.
My point is that it could fly many more times than it will for the same money. The thing could be well under a billion a flight, and still make money for the contractors.
Yes, that's the thing that annoys me most. Not that it's a badly designed architecture that can't accomplish any mission by itself, but that it shouldn't be as expensive as it is and it could be flying over four times as often for the same money.
The opportunity cost is staggering.
12 hours ago, kerbiloid said:It seems to me that Orion will be the part of SLS getting to Mars and back.
Maybe even when fusion engines get ready.Because they anyway need an escape pod, and that's it.
If any part of SLS/Orion goes to Mars it'll only be because the vast majority of the work was done by some other boosters. It's completely incapable of constructing any practical mothership in either LEO or at Gateway at any reasonable cost or timescale.
"SLS /Orion is how we get to Mars" is one of those statements I classify as *lies to investors*.
8 hours ago, tater said:BTW, I added an edit to my last SLS cost post. ET-94, the light weight tank built for Columbia, and delivered to NASA in 2001, cost $75M brand new. SLS core is a little more than a third larger. Call it 50% larger to slop up the cost. Corrected for inflation and the larger than it should be increased size (50% larger), that's $171M, I said 112 I think. Oops.
Still, that drops the cost of what SLS should cost to 100(4*RS-25)+171(core)+88(25% larger SRBs)+60(EUS*) = $419M
In which case it'd be somewhat competitive to Falcon Heavy, we could build five times as many for the same price, four cargos for every crewed, and the extra launches would cover Orion's weak points.
That'd be the kind of SLS I could get along with.
9 hours ago, SunlitZelkova said:It is unclear. The most recent crewed Mars mission architecture with the Deep Space Transport has them leaving the Orion at the Gateway, and boarding the DST there and then going to Mars. But NASA is still making blog posts about Orion's heat shield stating it needs to "survive the heat of a Martian reentry".
Well they have to pretend Gateway is useful for something.
Even with full ISRU I'm not convinced fuelling a Mars mission at Gateway (LLO would be better) is worth it compared to assembling in LEO.
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SLS / Orion are the least essential bits of Artemis, tbh.
Take away the commercial support of Falcon Heavy, Vulcan, Starship or HLS, and people don't walk on the moon period.
Take away SLS/Orion and we can still make something work by Earth Orbit Rendezvous, probably for a good deal less money.
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Wow, I hope we get lucky and these two don't collide. That's a lot of debris to have in a highly inclined orbit.
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Humans are capable of self-motivating, so no syrup pipe for us!
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I also think catching starship in a net is nuts. Even with a ridiculously long breaking distance a net that size is not inertialess. An impact at 70+m/s isn't fun for reusability.
Lots of TPS on SN15:
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The first piece of SN20 has been spotted:
This being the first piece of the next major block of starship upgrades beyond the SN15-class of starships and potentially the first piece of a starship to orbit.
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On my last project a missed delivery slot for a 30t payload for 150 mile transport cost on the order of $15000. Three times further for $45k sounds about right.
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I'm pretty sure this is the sort of thing we could sim these days.
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1 hour ago, tater said:
In his article on teslarati, he mentioned they'd otherwise need to buy off the shelf 100,000 gallon tanks (there are some available for sale in McGreggor, TX google shows me).
Hard to find prices (sites here allow you to get a quote), but google results say 100,000 gallon water tanks run around $1/gallon to purchase. Alibaba has 100,000 gallon liquid propane tanks available for $26,000, less in quantity.
SpaceX need not build tanks for more than they can just buy them...
I estimate that GSE tank is ~2000m3, or about half a million gallons.
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https://en.m.wikipedia.org/wiki/Impact_depth
Newton's Impact depth approximation implies it'd struggle to escape the atmosphere.
It has to move through all space occupied by all the mass in its way, which must move faster than it to get out of the way.
But by conservation of momentum it can't give more velocity than it starts with to an equal or greater mass without coming to a complete halt.
The approximations look reasonable. Blunt body. High velocity. Non-cohesion of the impacted material.
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There's about 10 tons of air above every square metre. The plate at 100mm thick (4in) has an area of ~1.25m2 or ~1.2m diameter.
It'd therefore need to move between 11t and 1.1t out of the way on its way out of the atmosphere depending on how it tumbled.
If it survived it would necessarily be going a lot slower by the time it reached space.
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I wonder if the header tank imploded again.
Stir the tank, get an implosion, mix methane with oxygen, boom. They said they were taking the helium pressurant away again.
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Well, SpaceX's are. AJR's engines on the other hand...
Theoretically Cannot Any Mass Intiate Nuclear Fusion?
in Science & Spaceflight
Posted
Iron is the most energetically stable element. To fuse anything to a heavier weight than Iron takes energy rather than releases it.
All the elements heavier than Iron were created in Supernovae where fusion of comparatively vast quantities of light elements powered fusion of comparatively tiny traces of heavy elements as byproducts.
Dirt is mostly oxygen, silicon and aluminium though. These are all lighter than Iron, so you could perhaps expect to get some power out of fusing dirt. But you wouldn't get any power from, e.g. gold.
As alchemy though, transmuting one element into another, sure, go nuts. A civ capable of atomic manipulation and at-will fission/fusion could change anything into anything else. Justkeep in mind transformations towards Iron release power and away from Iron consume power. Vast vast quantities of power.