The "Real Aerospace" Thread

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Mithramuse
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Re: The "Real Aerospace" Thread

Post by Mithramuse »

icekatze wrote:hi hi
Mithramuse wrote:Also, why the #%&^ weren't we doing this a whole lot earlier
We've done reusable space vehicles before, and the cost savings have never been great.
Sure, but we also never brought back bits to land. Closest I think we've really come to trying this out before was the McDonnell Douglas Delta Clipper, which got squished after NASA was essentially shamed into taking it and didn't support it properly. (There's a lot of backstory there, not really meaning to get into it; I think NASA does a lot of great stuff, but 20 years back being shown up by competition definitely ruffled feathers.)

A lot of what was done on the DC-X and -XA programs has informed SpaceX, Blue Origins, and others today, fortunately, but it's also something that really could have been done sooner if NASA's main contractors were actually interested in making spaceflight less expensive.
icekatze wrote:It's a shame we don't have hard numbers on how much it is costing Space X to inspect and refit their reused boosters because as a privately owned company they're completely opaque, but I think it is a safe bet that they're not launching rockets for 10% of the cost like some of Musk's earlier predictions. It's probably closer to more conservative estimates of 70-90% the costs. But it's anyone's guess how much of their current pricing system is profit margin, subsidy, and reduced cost.
10%, certainly not, agreed. Ars Technica had a piece recently that is at least a decent attempt to tease some numbers out, though also implies that SpaceX set their own price a bit low... so where that price is relative to their cost is still an unknown, but I'd say 90% is almost certainly too high.

SpaceX has acknowledged that refurbishing a Dragon capsule (from cargo missions) that splashed down in the ocean is nearly the same price as making a new one, but that refurbishing the returned boosters is a significant savings over new. Don't have an article for that one handy, it's from further back in time than the Ars piece, but can try to find if needed.

Edit: Fix URL, clarify one point in DC-X commentary

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icekatze
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Re: The "Real Aerospace" Thread

Post by icekatze »

hi hi
Mithramuse wrote:Sure, but we also never brought back bits to land.
The SSMEs on the space shuttle were brought back to land and reused multiple times. Even ignoring all the other parts of the shuttle program, the engines themselves didn't live up to the cost savings that NASA was hoping for. Presumably people have learned from that and will do better the current generation, but I wouldn't expect an order of magnitude improvement.

Anyway, not trying to get into a flame war or anything. Space X puts stuff into space and that's pretty cool no matter how you cut it. But re-using rockets, even when it is just being used multiple times on the same mission like the Beresheet, involves some added difficulty along with the cost savings.

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Mithramuse
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Re: The "Real Aerospace" Thread

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icekatze wrote:hi hi
Mithramuse wrote:Sure, but we also never brought back bits to land.
The SSMEs on the space shuttle were brought back to land and reused multiple times. Even ignoring all the other parts of the shuttle program, the engines themselves didn't live up to the cost savings that NASA was hoping for. Presumably people have learned from that and will do better the current generation, but I wouldn't expect an order of magnitude improvement.
Shuttle was... complex, to put it mildly, in a way that a VTVL rocket is not. (And I was more thinking VTVL, not VTHL like the shuttle, though no I never stated that explicitly; my bad.) The RS-25 is a wonderfully efficient engine, but there are a tremendous number of moving parts, some moving really, really fast (some of which I helped make, 20-ish years back, at a prior job... I've got some 'flown' fuel turbopump blades that I was given by Rocketdyne as a thank you, which is kinda cool :D ). But the initial design needed a complete tear-down of the turbopumps between uses, though this was mitigated somewhat in the Block II version. Refurb costs were also higher because the shuttle didn't actually fly very much... economies of scale still work for rocket engines too, whether new construction or refurbishment.

I don't know the ins and outs of the SpaceX engines, so I don't doubt there are similarities e.g. 30k+ RPM turbopumps, but some of the complexity is due to using hydrogen as fuel, and some because there were just three engines (vs. nine for SpaceX) so one failing would lead to an abort. (Though IIRC there was one in-flight failure, but late enough that the shuttle still made it all the way up.) This is why the Shuttle would light off the main engines prior to the SSRBs; there were... dunno, 8 or 10 Shuttle launches called off due to a main engine failing to operate, which was then replaced. (And relatively quickly, IIRC; they were designed for that.) I think there were 46 main engines used across all the launches in the shuttle program... something like 400 engine*launches in all? Which isn't too bad.

I believe the man-rating requirements for the Shuttle also increased the cost through additional mandated inspections, disassembly, and test firings, in a way that SpaceX is not yet seeing since they aren't flying people just yet, so we will need to see what happens there.
icekatze wrote:Anyway, not trying to get into a flame war or anything. Space X puts stuff into space and that's pretty cool no matter how you cut it. But re-using rockets, even when it is just being used multiple times on the same mission like the Beresheet, involves some added difficulty along with the cost savings.
Certainly true, on all counts.

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Arioch
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Re: The "Real Aerospace" Thread

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Mithramuse wrote:Also, why the #%&^ weren't we doing this a whole lot earlier... though yeah, I know, the Big Gov't Contractors just don't have any financial incentive to innovate in this way.
I think that the automated control systems that allow for perfect booster landings (or self-driving cars) just weren't practical 15 or 20 years ago. And I think it takes a leap of logic... it never would have occurred to me that the vulnerable-looking engine assembly of a conventional booster would be able to withstand the punishment of a tail-first reentry. It still freaks me out a little bit when I watch it.

It also still freaks me out a bit when I'm in my car and my phone is telling me directions, and I ask it a question and it answers. It's easy to forget that we're living in the future.

It may turn out that the Falcon 9 boosters may over time require more refurbishment than planned, and it may turn out that each booster can only be reused a limited number of times before they are no longer cost effective. In either case, I still think it's likely to be a huge cost savings over fully expendable launch systems.

The ridiculously long and expensive refurbishment procedure for the Space Shuttle (which it wasn't designed for) and the incredibly inefficient refurbishment procedure for the solid rocket boosters (which was very little different than building a new one from scratch) are not, I think, good examples to follow.

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Re: The "Real Aerospace" Thread

Post by Mjolnir »

Arioch wrote:
Mithramuse wrote:Also, why the #%&^ weren't we doing this a whole lot earlier... though yeah, I know, the Big Gov't Contractors just don't have any financial incentive to innovate in this way.
I think that the automated control systems that allow for perfect booster landings (or self-driving cars) just weren't practical 15 or 20 years ago. And I think it takes a leap of logic... it never would have occurred to me that the vulnerable-looking engine assembly of a conventional booster would be able to withstand the punishment of a tail-first reentry. It still freaks me out a little bit when I watch it.

It also still freaks me out a bit when I'm in my car and my phone is telling me directions, and I ask it a question and it answers. It's easy to forget that we're living in the future.

It may turn out that the Falcon 9 boosters may over time require more refurbishment than planned, and it may turn out that each booster can only be reused a limited number of times before they are no longer cost effective. In either case, I still think it's likely to be a huge cost savings over fully expendable launch systems.

The ridiculously long and expensive refurbishment procedure for the Space Shuttle (which it wasn't designed for) and the incredibly inefficient refurbishment procedure for the solid rocket boosters (which was very little different than building a new one from scratch) are not, I think, good examples to follow.
The technologies needed would have been far more expensive to develop a vehicle around and build, not quite as accurate and reliable, but DC-X essentially proved the technology was available back in the 90s. Progress stalled with all parties getting hung up on the idea that any reusable vehicle had to be SSTO, and NASA forgetting the reason for its existence and getting territorial about space launch with the X-33 (much as they have been recently with the lunar architectures and Europa Clipper requirements concocted to give the SLS a reason to exist).

The Shuttle came in late and over budget, and completely failed at the cost reductions it was intended to achieve. NASA then flew it for 30 years without addressing its basic design flaws. That was the last launch vehicle NASA successfully developed. The various attempts at replacements have all blown their budgets and timelines, and apart from the SLS have been canceled. NASA's never shown any success at or even real interest in cost reduction, which makes the Shuttle costs a particularly lousy argument against reuse. Hell, the SLS is built from the same technologies without any compromise for reuse, and certainly isn't any cheaper as a result.

The very first Falcon 9 booster to be reused cost less than half the cost of a new booster to refurbish, and they've presumably improved on that since. Musk's order of magnitude cost reduction predictions were for a fully reusable system that doesn't throw away a ~$10M upper stage for every launch. There's a reason they're working on a fully reusable system to replace the Falcon 9/Heavy.

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Re: The "Real Aerospace" Thread

Post by danuis »

SSTO's a grand step in the right direction, but IMO, SpaceX is going to shoot themselves in the foot with their Spaceship design. It's one of my main gripes with SpaceX now, along with cancelling stuff like Red Dragon.

SSTOs, in the niche of repetitively getting people from the ground to sub-orbit or orbit where they rendezvous with a interplanetary cruiser, allows for the cruiser to focus on the hard work and the SSTO on another. It's division of labor. When the cruiser gets to Mars, it breaks or coasts in orbit and the SSTO, acting as a shuttle, deposits people wherever they need to go.

See the problem, however? In using the SSTO as both the shuttle and the cruiser, you get a jack of all trades which is incredibly impressive but over-engineered and overworked. The cruiser shouldn't have to deal with re-entry; if even aerobreaking if we get powerful enough thrusters; cutting the heat-shielding and related systems. It focuses on getting from one orbit to another. The Shuttle can deal with re-entry and blast-off. This also cuts down on the sizes of both; instead of the cruiser carrying everything from blastoff to orbit to breakoff to coasting to de-accelerating and re-entry and then blast off and breakoff and coasting and re-entry again; with all the fuel, systems, and mass that requires; it'll basically be a tug or a pusher with one or two attached shuttles and a massive space for the passengers. More shuttles can be - and should be, out of redundancy, two or three is a good number - carried; as their job is just lifting off from Earth to landing on Mars and then lifting off from Mars to landing back down on Earth again.

I think Spaceship will be cut down even further, especially since the first Mars missions won't be dragging 50 or 20 or even 10 people to the Red planet at first. You build the ship for the mission; even if it's a general one, and that's why we've seen passenger capacity drop from 100 to 50 to...something less in the future, most likely, most likely around capacity for 10 carrying 6-8.

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Re: The "Real Aerospace" Thread

Post by Mjolnir »

danuis wrote:SSTO's a grand step in the right direction, but IMO, SpaceX is going to shoot themselves in the foot with their Spaceship design. It's one of my main gripes with SpaceX now, along with cancelling stuff like Red Dragon.

SSTOs, in the niche of repetitively getting people from the ground to sub-orbit or orbit where they rendezvous with a interplanetary cruiser, allows for the cruiser to focus on the hard work and the SSTO on another. It's division of labor. When the cruiser gets to Mars, it breaks or coasts in orbit and the SSTO, acting as a shuttle, deposits people wherever they need to go.

See the problem, however? In using the SSTO as both the shuttle and the cruiser, you get a jack of all trades which is incredibly impressive but over-engineered and overworked. The cruiser shouldn't have to deal with re-entry; if even aerobreaking if we get powerful enough thrusters; cutting the heat-shielding and related systems. It focuses on getting from one orbit to another. The Shuttle can deal with re-entry and blast-off. This also cuts down on the sizes of both; instead of the cruiser carrying everything from blastoff to orbit to breakoff to coasting to de-accelerating and re-entry and then blast off and breakoff and coasting and re-entry again; with all the fuel, systems, and mass that requires; it'll basically be a tug or a pusher with one or two attached shuttles and a massive space for the passengers. More shuttles can be - and should be, out of redundancy, two or three is a good number - carried; as their job is just lifting off from Earth to landing on Mars and then lifting off from Mars to landing back down on Earth again.

I think Spaceship will be cut down even further, especially since the first Mars missions won't be dragging 50 or 20 or even 10 people to the Red planet at first. You build the ship for the mission; even if it's a general one, and that's why we've seen passenger capacity drop from 100 to 50 to...something less in the future, most likely, most likely around capacity for 10 carrying 6-8.
Starship won't be SSTO...not on Earth, with any payload. Every Starship launched to orbit from Earth will lift off on top of a booster, because that booster makes the difference between being able to reach a short-lived very low altitude orbit at best with no payload and no propellant for return, and being able to deliver a hundred metric tons to LEO and go back home for another go.

Forget being able to supply vehicles making repeated trips to and from the surface, a "cruiser" would need enormous amounts of propellant just to enter orbit around Mars. Worse, reserving delta-v for doing so means it'd have to take far more time to get there, meaning it would have to carry more consumable supplies and expose its passengers to greater risk from radiation and other hazards of transit. A heat shield is worth many, many times its mass in propellant, especially if you're braking from a high energy trajectory. Nothing landed on Mars has stopped in orbit first since the Viking probes, everything else has used direct entry and descent.

Their goal is not to get people to Mars with the smallest spacecraft that can do the job. The first Starships sent to Mars carrying crew will need to set up a propellant mining operation. This is going to take hundreds of tons of equipment and supplies staged ahead of them on unmanned Starships, and likely thousands of tons to fully build out. They're not going to be carrying a hundred passengers, but not because they've been scaled down. The more payload capacity the better, as far as their Mars plans go.

A smaller craft could also never be as well equipped, and would either have to use a different engine (which would never be as well-tested as the Raptor used on the 31-engine booster and 7-engine Starship), or it'd have to cut the number of engines down...Starship lands on 3 engines so it can land safely if one of them fails. Smaller is not better here.

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Re: The "Real Aerospace" Thread

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Arioch wrote:The basic problem with any nuclear-powered aerospace vehicles is that such vehicles inevitably crash. A nuclear powerplant turns a routinely tragic loss of life and property into a full scale disaster.

As for the other proposal, it seems to me that the only reason to explore below the ice on Europa is to search for life, and I don't see how a probe can do that if it's radioactive.
That depends on if you consider this be a problem at all, apparently such a craft was planned as an automated bomber that after having dropped it's deadly cargo was supposed to fly around over enemy territory on low altitude salting the ground with radioactive exhaust for weeks or even months until it finally dropped to the ground causing a local environmental disaster.

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Re: The "Real Aerospace" Thread

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Sweforce wrote:
Arioch wrote:The basic problem with any nuclear-powered aerospace vehicles is that such vehicles inevitably crash. A nuclear powerplant turns a routinely tragic loss of life and property into a full scale disaster.

As for the other proposal, it seems to me that the only reason to explore below the ice on Europa is to search for life, and I don't see how a probe can do that if it's radioactive.
That depends on if you consider this be a problem at all, apparently such a craft was planned as an automated bomber that after having dropped it's deadly cargo was supposed to fly around over enemy territory on low altitude salting the ground with radioactive exhaust for weeks or even months until it finally dropped to the ground causing a local environmental disaster.
We're talking about civilian transport vehicles. And you may notice that though there were a variety of plans for nuclear-powered bombers and cruise missiles, none of them were ever actually built. (I think Russia may have got their nuclear bomber to the prototype phase, but it was a mess.) Even bombers and cruise missiles eventually crash in your own territory.

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Re: The "Real Aerospace" Thread

Post by GeoModder »

Arioch wrote:Even bombers and cruise missiles eventually crash in your own territory.
Or submarines sink in your own territorial (littoral) waters.
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Re: The "Real Aerospace" Thread

Post by Arioch »

GeoModder wrote:
Arioch wrote:Even bombers and cruise missiles eventually crash in your own territory.
Or submarines sink in your own territorial (littoral) waters.
Ships can sink without breaching their reactors. When aircraft crash, it's a different matter.

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Re: The "Real Aerospace" Thread

Post by GeoModder »

Not the case in littoral waters of course, but couldn't a submarine nuclear reactor implode when the water pressure gets high enough?
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Re: The "Real Aerospace" Thread

Post by icekatze »

hi hi

It's hard to say what would happen at the bottom of the Mariana Trench, but nuclear submarine losses in the Atlantic show that their nuclear components are reasonably stable. This isn't surprising since they are not pressurized with air, and any impact with the ocean floor is going to be slow and soft.

K-219 sank at a depth of 6,000 meters in the Hatteras Abyssal Plain and didn't suffer a leak in its reactor or missiles.

The USS Scorpion imploded at around 470 meters, tearing the vessel apart into multiple segments, and sank to the seabed at around 3,000 meters. Its fuel casing and nuclear tipped torpedoes showed no signs of leakage.

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Re: The "Real Aerospace" Thread

Post by dragoongfa »

People seem to forget that water is the best radiation shield in terms of density and availability while water is the de facto shield of neutron radiation since stray neutrons are rendered harmless by Hydrogen (H20 and all that :P).

Better explanation than I can manage can be found here: https://www.reddit.com/r/askscience/com ... on_shield/

EDIT: In short, if you have something that leaks radiation you have no better place to dump it than the bottom of the ocean.

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Re: The "Real Aerospace" Thread

Post by Mr.Tucker »

dragoongfa wrote:
EDIT: In short, if you have something that leaks radiation you have no better place to dump it than the bottom of the ocean.
'points towards above Europa mission' Exactly. Use the reactor to melt your way through the ice, while bathing the trailing submersible in hard gamma (it's trailing close behind so no significant water volume in front of it). Then once the reactor finishes digging, let it drop into the ocean bottom (100 km). It's a big piece of metal, so no significant stress from water pressure, and you can build it to use most of it's criticality while in the melting phase, so it can't carry on producing heat for a long time after finishing. Bonus points if it's a pebble bed reactor using passive circulation. Release the pebbles once the melting phase is over, and watch them become subcritical almost instantly due to not being in close proximity to one another.

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Re: The "Real Aerospace" Thread

Post by Krulle »

IF here's life in Europa's oceans, we can assume it going all the way to the bottom of the ocean, as light will be no factor in the lifeforms swimming in the upper layers of the ocean...
Such a reactor willinfluence local life. Likely even positively, as a source of heat and warmth.
Just hope that the rockets launching that reactor start all right and have no failure....
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Re: The "Real Aerospace" Thread

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Krulle wrote:IF here's life in Europa's oceans, we can assume it going all the way to the bottom of the ocean, as light will be no factor in the lifeforms swimming in the upper layers of the ocean...
Such a reactor willinfluence local life. Likely even positively, as a source of heat and warmth.
Just hope that the rockets launching that reactor start all right and have no failure....
If there's life in Europa's ocean, its more likely to be found on the bottom. More chance for volcanic/tidal fissures there, and less chance for exposure to Jupiter's radiation belts.
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Re: The "Real Aerospace" Thread

Post by Mjolnir »

GeoModder wrote:
Krulle wrote:IF here's life in Europa's oceans, we can assume it going all the way to the bottom of the ocean, as light will be no factor in the lifeforms swimming in the upper layers of the ocean...
Such a reactor willinfluence local life. Likely even positively, as a source of heat and warmth.
Just hope that the rockets launching that reactor start all right and have no failure....
If there's life in Europa's ocean, its more likely to be found on the bottom. More chance for volcanic/tidal fissures there, and less chance for exposure to Jupiter's radiation belts.
Jupiter's radiation belts will quickly fry anything on the surface, but 100 km of ice is going to block essentially all of it. I wouldn't be surprised if ambient radiation under the surface ice is lower than on the surface of any solid body in the solar system, and mostly due to radioactive materials dissolved in the water.

But yes, the main sources for energy are likely to be volcanic activity at the ocean floor. Convection of ice that has concentrated minerals and organic materials might support some life at the top of the water column though. It may even result in subduction of significant amounts of free oxygen (split from the water by sunlight and Jupiter's radiation).

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Re: The "Real Aerospace" Thread

Post by Zorg56 »

Even with 0.1G, i think that pressure in this ocean will be insane.

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Re: The "Real Aerospace" Thread

Post by Mr.Tucker »

By my (rough) calculations about equivalent to 20 km on Earth, or twice the pressure found in the Challenger Deep. High as hell, but doable. Might wanna watch what instruments you put on the thing, though.

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