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The "Real Aerospace" Thread 
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Post Re: The "Real Aerospace" Thread
So, I've just had a reeeeally crazy idea I've been mulling over for about two weeks, and I'd like to pass it by here.

Firstly, I started from the concept of the Nuclear Thermal Turbo rocket, an idea for a Air Augmented Nuclear Thermal Rocket, that uses air-breathing propulsion to lofts itself out of the lower atmosphere, transitioning from a ramjet type of system (powered by a turbofan spun by gasses leached from the reactor chamber), then to a scramjet (using the air directly by heating, and leaving the fanblades at idle angles of attack), then finally using standard NTR-type propulsion for the final ascent and orbital circularisation.

More on the ideea (and it's creator, John Bucknell) here:
https://forum.nasaspaceflight.com/index ... c=43344.20
http://www.projectrho.com/public_html/r ... rmal_Turbo

The kicker is the quite phenomenal promised (and I do stress "promised") mass fractions, that can be seen in the tables presented. This is due to the high average Isp of the thing (as air-breathing systems have Isp's in the thousands generally).

I thought, "great, but that pure rocket Isp is killing me. Looks so weak compared to the rest". So I started digging for more experimental types of NTR's. I stumbled onto MITEE, which uses a hybrid power system to dissociate some of the hydrogen into it's monoatomic state, thus achieving Isp of about 1350. There was also the NTER, the european concept that used hot gasses to drive what is essentially an electrothermal thruster.

But... then I realised that, since I already have a nuclear reactor onboard, how about going even more speculative...and mate it to this:
http://www.projectrho.com/public_html/r ... d-core_NTR
If it works (think I said that about half a dozen times) then I could literally get to Titan with an SSTO. And back (with the payload fractions in LEO plus a specific impulse of about 17,000 sec from the pulsed regime).

Finally, since I've got copious amounts of power onboard, why not use a more... exotic system to aerobrake for the return trip? Like the magshell:
https://forum.nasaspaceflight.com/index ... c=29912.80
https://selenianboondocks.com/2010/02/m ... rocapture/

There are MONSTROUS issues with the above concept:
1) making the turbo-fan airbreathing mode work (supersonic ducted fans are not really a thing).
2) transitioning between modes
3) getting rid of the excess heat from the pulsed NTR mode (radiators aplenty).

My initial vehicle would be almost entirely fuel, but that can be aleviated if one uses ISRU (pump the atmosphere of wherever it is you be landing into your tanks; NTR's don't care much what they propell out the nozzle as long as it doesn't gum up the works; water vapour, methane, ammonia, H2 produced by electrolisys and cracking, etc) and magnetoshell aerobraking.

Or you can split the mission, and use a Starship-esque upper stage that has the pulsed unit, along with a simpler airbreathing mode and a pumping station.

Monstrously complex, but, as you might know, I like thinking ludicrous...


Another, simpler mission, is to use a molten salt thorium reactor to melt my way into Europa. The thorium would produce U233, which fissions and gives off neutrons... but also U232, which fissions into Th (Thallium) 228, which is a HARD gamma emitter (at 2.67 Mev, it's the third most potent one known). The reactor and the submersible that follows it down would be bathed in hard gamma, thus resolving the issue of how to sterilise the craft (the most complicated problem in this type of Europa mission). the reactor would be fueled so that it's no longer critical by the time it finishes melting, and just plunks into the abyss. The submersible could have it's own, separate, reactor or RTG to do long duration surveys (and would transmit data to the lander on the surface by optical cable). Before landing, the craft could use high-power ground penetrating radar (remember, plenty of power available) to map the ice, and determine ideal landing spots (not too thin, or the reactor will continue to be critical as it finishes melting, and kill whatever is in the general vicinity of it's landing spot when it hits the bottom).


Mon Apr 01, 2019 12:06 pm
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Post Re: The "Real Aerospace" Thread
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.

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Mon Apr 01, 2019 12:49 pm
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Post Re: The "Real Aerospace" Thread
Well, it IS an idea... never said it was a good one :P .
To quote Bucknell himself:
"Exploding is not a thing with a monopropellant rocket (how often do aircraft explode?). As for fuel containment/reactor structure – if the rocket were to have a RUD event the core/shielding is largely metallic with a tungsten carbide gamma shield (six of the seven tons of core mass). It would put a large dent in anything it landed on, but that is a risk with any rocket (ie why launches are over water).

The radiation shielding included in the rocket is probably overkill – it keeps exposure to both payloads and launch site below terrestrial background radiation (0.2 rad/y) if less than five flights a year are flown. Gamma shielding is fully surrounding the reactor (tungsten carbide), and lithium hydride for neutron fore for payload protection. Details in the paper."

For details: https://www.nextbigfuture.com/2017/07/j ... tions.html

As for the Europa mission, the reactor is just a big dumb hulking piece of red-hot metal. Could be molten salt, but some sort of pebble bed might be better. It's physically separated from the submersible trailing behind it (wich can unspool a lenght of optical as it goes down. The ice refreezes as the melter/sub pair go deeper). Once the melter melts it's way through, it drops (it would be heavy) and sinks, but the submersible is then free to roam about, away from the sinking neon-blue metallic deathball. Radiation is probably sufficient to kill stuff within tens of meters of where the thing lands on the bottom (some tens to hundreds of km from the hole in the ice is, depending on depth), but water is decent at shielding from gamma rays (massive enough). The submarine, as stated, is independent, and has it's own power source. The interior should be sterilised by the on-board source plus whatever gamma makes it in while it is near the melter as they both descend. The exterior is sterilised by the far more powerful rays from the gamma (needs a vehicle which exposes it's surface as much as possible to do that efficiently).


Mon Apr 01, 2019 1:34 pm
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Post Re: The "Real Aerospace" Thread
NTRs are actually heavily reliant on having liquid hydrogen. Water drops you down to barely better than hydrolox chemical, while leaving you with the poor mass ratios and T/W of nuclear systems, and requiring you to deal with an oxidizing working fluid. High temperature CO2's also oxidizing, and well into chemical rocket performance territory. Methane's not oxidizing, but decomposes at the temperatures required for decent performance. Ammonia's the most workable, but least available (basically only Mars, Titan, Earth, and stuff out at the distance of Pluto and Neptune have enough nitrogen) and still involves throwing away most of your performance. You're realistically stuck with liquid hydrogen and its various problems.

As for air breathing: the rocket equation is: deltaV = Ve*ln(Mo/Mf).
Augmenting this for air breathing gives: deltaV = (Ve/2)*ln(Mo/Mf)/(1 + 1/(L/D*A/g)).

The high specific impulse of air breathing engines is exaggerated by a factor of 2 to begin with, in short because it's only that high at low speeds and falls off roughly in inverse proportion to speed. On top of this, you need both a good hypersonic L/D ratio and good acceleration (high T/W) or you lose most of it to increased drag losses. Air breathers and nuclear engines both have poor T/W ratios, and hypersonic L/D ratios are never that great and require compromises in vehicle geometry. All this means that the apparent gains of air breathing are nowhere near as significant as the specific impulse number makes it appear, and it involves a major increase in complexity and dry mass.

The main drivers of cost are complexity and dry mass. Propellant cost is in the rounding error. Staging allows for enormous increases in payload fraction and allows separating the propulsion and structural requirements for the two very different flight regimes encountered, while adding little cost and complexity. Adding on lots of complexity and dry mass...exceptionally expensive dry mass containing fission power systems and heavily optimized to minimize mass to orbit...with the goal of reducing propellant mass and eliminating staging is rather misguided.


Wed Apr 03, 2019 3:28 pm
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Post Re: The "Real Aerospace" Thread
Just for fun:

I don't know if some of you are also reading the Freefall webcomic.
The creator published todays comic as a short notice to explain that he made an error.
Image
In the link to the powererror, simply states
This is why NASA uses real engineers instead of cartoonists for their rocket equations.

Yes, indeed. While cartoonists and Sci-Fi authors are necessary to make us look forward and to the stars and see the possibilities, we still need engineers to make it happen.

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Thu Apr 04, 2019 3:10 am
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Post Re: The "Real Aerospace" Thread
hi hi

It's been a while since I read Freefall. Not since that really awkward moment on the forums where the author basically said a thread about having intercourse with domestic canines was more on topic than a thread about civil rights in the context of AI having to prove that they're worthy of civil rights. (which, at the time, seemed relevant to the comic.)


Thu Apr 04, 2019 9:40 am
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Post Re: The "Real Aerospace" Thread
Hmmm... I've never been on the forums. Never found the link on the comic's page.

So I presumed there is no official forum...

But that indeed sounds weird.
The question of dog/human relations may be interesting, especially since Winston/Florence is a thing.

But the AI-rights is a continuous relevant topic for this story too.
It's allabout artificial intelligence rights...

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Thu Apr 04, 2019 1:39 pm
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Post Re: The "Real Aerospace" Thread
Mjolnir wrote:
The high specific impulse of air breathing engines is exaggerated by a factor of 2 to begin with, in short because it's only that high at low speeds and falls off roughly in inverse proportion to speed. On top of this, you need both a good hypersonic L/D ratio and good acceleration (high T/W) or you lose most of it to increased drag losses. Air breathers and nuclear engines both have poor T/W ratios, and hypersonic L/D ratios are never that great and require compromises in vehicle geometry. All this means that the apparent gains of air breathing are nowhere near as significant as the specific impulse number makes it appear, and it involves a major increase in complexity and dry mass.


So...is Bucknell wrong? :
http://www.projectrho.com/public_html/r ... nttr12.jpg
http://www.projectrho.com/public_html/r ... nttr13.jpg
I'm an aero engineer, but avionics is my specialty. Aerodynamics is something I never felt I could fully grasp. My understanding is that, for airbreathers, ISP is dependent upon exhaust velocity and mass fraction used for fuel. In an atmosphere, since an SSTO uses no fuel, it should have far higher ISP. Eventually, there comes a point where the vehicle can no longer accelerate, due to drag. Where that point is depends on many factors, such as materials used, design, optimal regime, etc. The idea seems sound enough: use no propellant while getting to an altitude that gets you above 80 percent of the atmosphere (which doesn't have to be that fast; your burn time is not dependant on what you have onboard, but by the materials of the reactor), then tilt the thing and try to accelerate (using an engine with higher Isp than conventional ones), at first in feeble airbreathing mode, then in NTR rocket mode. This study gives an airbreathing SCRAMJET isp of about 1000 (which is neither low altitude, nor low velocity):
http://mragheb.com/NPRE%20402%20ME%2040 ... ulsion.pdf
I do think he's optimistic about his transition. A Mach 15 airbreather is no joke

As for the propellant, I was simply pointing out that it could be done. While a lower ISP is not very good, with, say, nitrogen, it WILL still allow you to reach orbit of Mars or Titan. Also, just crack the hydrogen out before launch, or let the molecules dissociate during engine run. This paper cites the ISP numbers assuming some dissociation:
https://ntrs.nasa.gov/archive/nasa/casi ... 001880.pdf


Thu Apr 04, 2019 2:19 pm
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Post Re: The "Real Aerospace" Thread
Mr.Tucker wrote:
Mjolnir wrote:
The high specific impulse of air breathing engines is exaggerated by a factor of 2 to begin with, in short because it's only that high at low speeds and falls off roughly in inverse proportion to speed. On top of this, you need both a good hypersonic L/D ratio and good acceleration (high T/W) or you lose most of it to increased drag losses. Air breathers and nuclear engines both have poor T/W ratios, and hypersonic L/D ratios are never that great and require compromises in vehicle geometry. All this means that the apparent gains of air breathing are nowhere near as significant as the specific impulse number makes it appear, and it involves a major increase in complexity and dry mass.


So...is Bucknell wrong? :
http://www.projectrho.com/public_html/r ... nttr12.jpg
http://www.projectrho.com/public_html/r ... nttr13.jpg
I'm an aero engineer, but avionics is my specialty. Aerodynamics is something I never felt I could fully grasp. My understanding is that, for airbreathers, ISP is dependent upon exhaust velocity and mass fraction used for fuel. In an atmosphere, since an SSTO uses no fuel, it should have far higher ISP. Eventually, there comes a point where the vehicle can no longer accelerate, due to drag. Where that point is depends on many factors, such as materials used, design, optimal regime, etc. The idea seems sound enough: use no propellant while getting to an altitude that gets you above 80 percent of the atmosphere (which doesn't have to be that fast; your burn time is not dependant on what you have onboard, but by the materials of the reactor), then tilt the thing and try to accelerate (using an engine with higher Isp than conventional ones), at first in feeble airbreathing mode, then in NTR rocket mode. This study gives an airbreathing SCRAMJET isp of about 1000 (which is neither low altitude, nor low velocity):
http://mragheb.com/NPRE%20402%20ME%2040 ... ulsion.pdf
I do think he's optimistic about his transition. A Mach 15 airbreather is no joke


Bucknell's engine sounds incredibly complex and difficult to design and the airbreathing feature seems a bizarre addition to something that flies a vertical trajectory. Getting above the atmosphere isn't the hard part of getting to orbit. Atmospheric drag losses tend to be ~100 m/s. The Saturn V only lost 40 m/s to aerodynamic drag. Gravity losses are an order of magnitude worse, but still an order magnitude short of the delta-v required to reach orbit. Air breathing can't make a really major difference without atmospheric flight at speeds that produce major heating and structural problems. It's really only relevant to SSTO vehicles that can barely get to orbit, and turning them into TSTO systems with a booster is a much simpler way of improving their economics.

"Mr. Bucknell notes that the only practical method of dramatically bringing down the cost of boosting payloads into low Earth orbit (LEO) is to lower investment and realize a large return on that investment. The implication is you want a low dry mass Single Stage to Orbit Resuable Launch Vehicle with a high payload mass fraction."

Bucknell's observation is correct, but the conclusion is bonkers. To maximize RoI, the last thing you want is a SSTO vehicle where the entire dry mass of the vehicle has to be highly mass-optimized and where you carry huge amounts of excess propulsion and extra hardware all the way to orbit instead of paying payload. You get far better return on your investment with staging. And you really do not want the immense costs of building and operating a nuclear system that operates 5 times a year, as Bucknell proposed when discussing the radiation issues...and his estimates on those seem really low.

Bucknell sounds like a propulsion guy who sees everything in terms of a propulsion problem. He's concocted a supertech propulsion system to solve the problem of space lift, but it's not a propulsion problem. He should think more on why Skylon failed...note that Falcon 9 is already cheaper than Skylon would have been able to achieve, despite not using anything like the list of exotic ultra-high technologies needed for Skylon. Reaction Engines doesn't even mention Skylon on their website any more, just vague mentions of the possibility of using SABRE for launch systems, including staged systems.

The most credible attempts at reusable launch vehicles now are using methane fuel, which doesn't even match kerosene in impulse density and falls well short of hydrogen in specific impulse. It's used because it has other advantages that outweigh its lower performance as a propellant. Insufficient specific impulse isn't what's made space expensive, that's been due to high operational complexity, low flight rates, and building-sized pieces of disposable aerospace-grade hardware.


Mr.Tucker wrote:
As for the propellant, I was simply pointing out that it could be done. While a lower ISP is not very good, with, say, nitrogen, it WILL still allow you to reach orbit of Mars or Titan. Also, just crack the hydrogen out before launch, or let the molecules dissociate during engine run. This paper cites the ISP numbers assuming some dissociation:
https://ntrs.nasa.gov/archive/nasa/casi ... 001880.pdf


If you're going to the trouble of involving a nuclear reactor, you want better return than "it'll allow you to reach orbit of Mars or Titan". You don't even need an especially high performance (and vastly cheaper and easier to operate) chemical propellant system to do that.

You're much better off devoting the same nuclear materials to cracking chemical propellants. Think in RoI terms again: you can have those materials working full time producing propellant for a fleet of vehicles, instead of spending most of their time coasting through deep space while hauling big blocks of radiation shielding around along with their payloads.


Thu Apr 04, 2019 4:38 pm
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Post Re: The "Real Aerospace" Thread
Unfortunately, the Beresheet lunar probe crashed. It had some kind of fault that shut down the engine during descent. They were apparently able to restart it, but it was unable to recover at that point and impacted at around 1 km/s. They did at least get some good images.

http://www.planetary.org/blogs/jason-da ... ashes.html

In better news, SpaceX did their first operational launch of Falcon Heavy, putting the payload in its target orbit and recovering all three first stage cores.


Thu Apr 11, 2019 4:06 pm
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Post Re: The "Real Aerospace" Thread
A reminder that spaceflight is still hard, despite SpaceX making it look easy.

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Thu Apr 11, 2019 4:33 pm
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Post Re: The "Real Aerospace" Thread
Arioch wrote:
A reminder that spaceflight is still hard, despite SpaceX making it look easy.


Watch their blooper reel and remember when everyone was suggesting parachutes and airbags, big nets, giant robot arms, physically improbable cable arrangements...

It's interesting how quickly they went from not being able to land a rocket to being able to reliably plant them in the middle of a drone ship at sea (though they're still not confident of doing so at the edges of the envelope...the next Heavy launch was scheduled to use a different center core, in case they lost this one). Which illustrates what you said...there were a lot of little things they had to get just right for it to work.


Thu Apr 11, 2019 6:09 pm
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Post Re: The "Real Aerospace" Thread
Mjolnir wrote:
Watch their blooper reel and remember when everyone was suggesting parachutes and airbags, big nets, giant robot arms, physically improbable cable arrangements...

It's interesting how quickly they went from not being able to land a rocket to being able to reliably plant them in the middle of a drone ship at sea (though they're still not confident of doing so at the edges of the envelope...the next Heavy launch was scheduled to use a different center core, in case they lost this one). Which illustrates what you said...there were a lot of little things they had to get just right for it to work.

I remember. And it says something about SpaceX that they have the failure reel on their own YouTube channel.

I expect their booster recoveries will always have a certain failure rate. There's a lot that can go wrong with a pitching unmanned platform in the middle of the storm-prone Atlantic. There's probably a point past which trying to raise the success rate above a certain percentage will cost more than the boosters they lose.

But I never get tired of watching the boosters land. And seeing the two Falcon Heavy boosters land side by side is just... poetry.

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Post Re: The "Real Aerospace" Thread
Arioch wrote:
But I never get tired of watching the boosters land. And seeing the two Falcon Heavy boosters land side by side is just... poetry.


This. Just so absolutely this.

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.


Fri Apr 12, 2019 6:38 am
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Post Re: The "Real Aerospace" Thread
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.

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.


Fri Apr 12, 2019 6:58 am
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Post Re: The "Real Aerospace" Thread
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


Fri Apr 12, 2019 7:31 am
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Post Re: The "Real Aerospace" Thread
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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Post Re: The "Real Aerospace" Thread
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.


Fri Apr 12, 2019 9:05 am
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Post Re: The "Real Aerospace" Thread
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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Post Re: The "Real Aerospace" Thread
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.


Fri Apr 12, 2019 8:07 pm
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Post Re: The "Real Aerospace" Thread
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.


Fri Apr 12, 2019 8:32 pm
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Post Re: The "Real Aerospace" Thread
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.


Fri Apr 12, 2019 9:42 pm
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Post Re: The "Real Aerospace" Thread
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.


Sat Apr 13, 2019 6:23 am
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Post Re: The "Real Aerospace" Thread
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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Sat Apr 13, 2019 9:19 am
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Post Re: The "Real Aerospace" Thread
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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Sat Apr 13, 2019 10:46 am
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