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Thanks, very useful information.
During an aero-gravity assist, after an atmospheric entry at 18-17 km/s, if plasma wake become opaque and radiate on the waverider spaceship, I suppose that the quartz windows on the upper surface must be closed with some kind of reflective panel to avoid radiation inside the cockpit. Is it correct?
Last edited by Quaoar (2020-03-18 08:19:41)
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Hi Quaoar:
To answer your question, I would think covering a window to stop radiation from the plasma heating up things inside would be beneficial, although it might not be required. Depends upon the vulnerability of what get irradiated, and how powerful the air conditioning is for that space.
We here in the US are having panic-buying difficulties, because people have been lied to by their favorite internet and social media sources. The business model is getting paid by more clicks, without regard to the truth of what is posted. That's why so much bogus BS is out there. I posted an article debunking this crap on "exrocketman" today.
I hope you get through the troubles in Italy soon. We here are entering a sort of lockdown that is not really a shelter-in-place lockdown. But essentially the restaurants, theaters, bars, schools, and sporting events have been shut down in Texas, and across most of the US.
This will go on for a few to several weeks until the infection rate peaks and drops. Then we have to deal with the economic recession that is the inherent fallout from this. This is not a lot different from the 1918 flu pandemic, and it is nowhere near as bad as the 14th century Black Death pandemic. We'll get through this. All of us. Everywhere.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Hi Quaoar:
To answer your question, I would think covering a window to stop radiation from the plasma heating up things inside would be beneficial, although it might not be required. Depends upon the vulnerability of what get irradiated
The crew.
We here in the US are having panic-buying difficulties, because people have been lied to by their favorite internet and social media sources. The business model is getting paid by more clicks, without regard to the truth of what is posted. That's why so much bogus BS is out there. I posted an article debunking this crap on "exrocketman" today.
I hope you get through the troubles in Italy soon. We here are entering a sort of lockdown that is not really a shelter-in-place lockdown. But essentially the restaurants, theaters, bars, schools, and sporting events have been shut down in Texas, and across most of the US.
This will go on for a few to several weeks until the infection rate peaks and drops. Then we have to deal with the economic recession that is the inherent fallout from this. This is not a lot different from the 1918 flu pandemic, and it is nowhere near as bad as the 14th century Black Death pandemic. We'll get through this. All of us. Everywhere.
GW
Hi, GW,
I hope you are well.
I have red your blog: what you say is correct.
Why not for you to join us on this topic:
http://newmars.com/forums/viewtopic.php?id=9317&p=6
We share our experiences in dealing with this pandemic, and your contribution is precious.
Last edited by Quaoar (2020-03-19 17:18:43)
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The shuttles came back without any shielding for the large windows but if you do not need to see through them during landing then draw a metal shield on the inside of them should do the trick. No need to get fancy able it just latch that swing over the panel after you push it up to the sealing surface.
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The shuttles came back without any shielding for the large windows but if you do not need to see through them during landing then draw a metal shield on the inside of them should do the trick. No need to get fancy able it just latch that swing over the panel after you push it up to the sealing surface.
Thanks, nice idea.
Space shuttle enter from LEO at 8 km/s. My novel is set in a red dwarf system with many planets, almost like Trappist-1. Simulations give me enter velocity from transfer orbit of about 18 km/s, so plasma radiative heating is more severe.
For my waverider, I thought to use quartz double layer windows with a sliding reflective metallic shield in the middle.
Even the upper surface has to be protected, so I thought to low-density white TPS tiles like those of the upper surface of the space shuttles, It's a right choice?
Last edited by Quaoar (2020-03-20 04:34:59)
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Quaoar,
AlON melts at 2,150C and also provides fairly impressive ballistic protection, with a hardness pretty close to that of Sapphire. Quartz melts somewhere between 1,600C and 1,700C. AlON's bulk density is about 1g/cm^3 greater than quartz, but there are advantages that come with that extra mass. It's about 9 times as thermally conductive as quartz and CTE is slightly higher, but maybe that's a good thing if this new stainless vehicle is going to use thermal soak and eschew the use of ablatives.
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Quaoar,
AlON melts at 2,150C and also provides fairly impressive ballistic protection, with a hardness pretty close to that of Sapphire. Quartz melts somewhere between 1,600C and 1,700C. AlON's bulk density is about 1g/cm^3 greater than quartz, but there are advantages that come with that extra mass. It's about 9 times as thermally conductive as quartz and CTE is slightly higher, but maybe that's a good thing if this new stainless vehicle is going to use thermal soak and eschew the use of ablatives.
Thanks for the tip.
A double layer of aluminium oxynitride might be also more effective against micro-meteoroid impacts.
I imagined a waverider with a shell in 3D carbon-carbon composite with white PICA-X thermal protection. For the windows I can use a AlON double layer with a reflective sliding shield in the middle.
How to fix PICA-X to the shell?
I read that brazing is better than gluing.
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Quaoar,
I would use AlON windows with RCC gap panels and metallic gaskets. The AlON plates would be mechanically sealed to the pressure vessel using the metallic gaskets and the gap panels would prevent gases from directly impinging on the seals / edges of the windows where they're affixed to the pressure vessel. Oxygen would still attack the RCC, but the idea is to have a very high-precision sub assembly that prevents the oncoming flow from directly striking the attachment points for the windows- in other words the exterior of the entire windscreen surface and interface with the rest of the pressure vessel are as smooth as a plate of metal.
In the Space Shuttle they had protrusions from the attachment points associated with the tiles surrounding the windows, which is what I'm trying to avoid to preclude creating local hot spots. It worked because the windows were on the leeward side, they entered with a high angle of attack, and thus the air pressure was something like 1/100th what the windward side experienced. Leading edges aside, if this is supposed to be a thermal soak design then we can't have drastically different localized surface temperature variations caused by aerodynamic heating effects associated with all those protrusions from the skin of the vehicle.
Given current technology, windows for hypersonic vehicles are mostly a psychological thing for humans, which is the only good reason I can think of as to why we still have them. If I was designing a hypersonic vehicle and had freedom of design decisions then my first priority would be protecting the vehicle's occupants and that means no windows, so there wouldn't be any. We'd have hundreds or maybe even thousands of tiny cameras with Sapphire lenses to provide a composite view of the outside world on displays, similar to what we did with the DAS (Distributed Aperture System- a series of multi-spectral cameras to provide 360 coverage of the outside world) on the F-35.
Ultimately, I would like to have a reentry vehicle that doesn't need to reenter in a very precise way in order to survive the ordeal.
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Quaoar,
I would use AlON windows with RCC gap panels and metallic gaskets. The AlON plates would be mechanically sealed to the pressure vessel using the metallic gaskets and the gap panels would prevent gases from directly impinging on the seals / edges of the windows where they're affixed to the pressure vessel. Oxygen would still attack the RCC, but the idea is to have a very high-precision sub assembly that prevents the oncoming flow from directly striking the attachment points for the windows- in other words the exterior of the entire windscreen surface and interface with the rest of the pressure vessel are as smooth as a plate of metal.
In the Space Shuttle they had protrusions from the attachment points associated with the tiles surrounding the windows, which is what I'm trying to avoid to preclude creating local hot spots. It worked because the windows were on the leeward side, they entered with a high angle of attack, and thus the air pressure was something like 1/100th what the windward side experienced. Leading edges aside, if this is supposed to be a thermal soak design then we can't have drastically different localized surface temperature variations caused by aerodynamic heating effects associated with all those protrusions from the skin of the vehicle.
Given current technology, windows for hypersonic vehicles are mostly a psychological thing for humans, which is the only good reason I can think of as to why we still have them. If I was designing a hypersonic vehicle and had freedom of design decisions then my first priority would be protecting the vehicle's occupants and that means no windows, so there wouldn't be any. We'd have hundreds or maybe even thousands of tiny cameras with Sapphire lenses to provide a composite view of the outside world on displays, similar to what we did with the DAS (Distributed Aperture System- a series of multi-spectral cameras to provide 360 coverage of the outside world) on the F-35.
Ultimately, I would like to have a reentry vehicle that doesn't need to reenter in a very precise way in order to survive the ordeal.
Thanks, nice idea.
So, no windows, but external cameras and monitors. Cameras have to be placed only in the leeward side or even in the windward one?
P.S.
As a retired medical doctor, today I volunteered in a medical task force of Italian Civil Protection Agency, so in the next few days I might be enrolled and deployed on the battlefield. I hope to see the light ad the end of this tunnel.
Last edited by Quaoar (2020-03-21 17:00:22)
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Quaoar,
Roughly speaking, normal human visual acuity correlates with 1 arc minute, so anything more than about 300dpi is beyond your ability to distinguish what you're seeing on a display. Using modern digital imaging technology, cameras are the most practical way to protect the structural integrity of a hypersonic vehicle and also provide a stunning view of the outside world. Such vehicles are flown primarily with very accurate instruments and computers with high degrees of redundancy to preclude single points of failure compromising the ability to pilot the vehicle. The latest and greatest high-DPI displays are completely indistinguishable from what your could eyes pick up at normal viewing distances. There's no reason the entire cockpit couldn't be a gigantic continuous display that feeds hyper-accurate multi-spectral data to the crew for their viewing pleasure.
I hope your civil service goes well. I know perspective is a difficult thing to maintain in difficult times, but I think most of us are going to get through this. In the end, we're all going to the same place and no matter what we choose to believe there is no escaping that fate. Before you arrive at that place, do whatever you feel you must with the time you do have. When I arrive at the end of my life, I want to know that I made good use of the time I had and that I did what I felt needed to be done. As long as I do that, I can accept the final result.
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Quaoar,
Roughly speaking, normal human visual acuity correlates with 1 arc minute, so anything more than about 300dpi is beyond your ability to distinguish what you're seeing on a display. Using modern digital imaging technology, cameras are the most practical way to protect the structural integrity of a hypersonic vehicle and also provide a stunning view of the outside world. Such vehicles are flown primarily with very accurate instruments and computers with high degrees of redundancy to preclude single points of failure compromising the ability to pilot the vehicle. The latest and greatest high-DPI displays are completely indistinguishable from what your could eyes pick up at normal viewing distances. There's no reason the entire cockpit couldn't be a gigantic continuous display that feeds hyper-accurate multi-spectral data to the crew for their viewing pleasure.
So I've eliminated the windows. Given the waverider uses PICA-X thermal protection, which is also good as heat sink, the shell can be build in carbon composite or aluminium or it has to be build in steel or carbon-carbon?
Which kind of adhesive is used to fix the PICA-X to the shell?
Quaoar,
I hope your civil service goes well. I know perspective is a difficult thing to maintain in difficult times, but I think most of us are going to get through this. In the end, we're all going to the same place and no matter what we choose to believe there is no escaping that fate. Before you arrive at that place, do whatever you feel you must with the time you do have. When I arrive at the end of my life, I want to know that I made good use of the time I had and that I did what I felt needed to be done. As long as I do that, I can accept the final result.
Thanks,
I'm still waiting for the call. I will be probably deployed in Lombardy.
I fear my enemy, but I want to give my little help to win this war.
Last edited by Quaoar (2020-03-23 16:27:17)
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Quaoar,
The resolution capabilities of current display technologies is far beyond normal human visual acuity and the ability of modern purpose-built graphics chips to process frames of data from cameras is likewise far beyond the ability of humans to detect individual image frames. I think the entire cockpit could be a gigantic wrap-around display that combines inputs from thousands of cameras to show what's outside the vehicle in every direction. Furthermore, the display could have the ability to digitally magnify a scene to show distant objects that the pilots' unaided eyes could never pick up. Add in multi-spectral capability (IR and UV) like the F-35 has and you have a system that's generations beyond the human eye. When the F-35 was developed, high-frame-rate multi-spectral HD cameras were state-of-the-art and strained the capabilities of onboard computers. Today, an iPad can do the number crunching as computing technology marches on. Special UV reflective coatings could provide unmistakable markers for landing and docking maneuvers and provide visual input to assist with manual vehicle control by using the rendering system to compute closure rates. It would still be a backup to automated systems using radio frequency waves, but useful redundancy nonetheless. A Space Shuttle pilot would be envious of the view provided. In the near future, all high speed aircraft or spacecraft will essentially be flying computers with sophisticated sensor suites that monitor everything from position relative to other nearby objects to temperature to background radiation levels.
In the future, I expect we'll need integration of structures that absorb both thermal and mechanical loadings associated with high speed flight. I don't think PICA is a good thermal protection material for hypersonic vehicles if reusability is a consideration. It's an ablative and I'm not sure it's capable of withstanding the mechanical loads associated with a wave rider.
If you haven't already read it, here's a good paper on where heat shield technology is headed:
That's a pretty good 20,000 foot overview of where we've been and where we're going, as it pertains to reusable high temperature insulation materials and strategies. It's over a decade old, but the only thing that's really happened between now and then is that we've done a lot more testing and refinement of the concepts and materials science involved- to the point that there's now a baseline level of competence with both the space agencies and contractors for fabrication of complex structures of the scale required for crewed spaceflight. Along with NASA and the US Air Force, the various European aerospace research agencies have expended considerable time and effort to develop sharp leading edges fabricated from very sophisticated CMC's that combine the attributes of multiple different materials for reliable and durable heat shielding of hypersonic vehicles for both defense and commercial purposes. The end of the article does a good job of listing the various significant challenges associated with progressing from fabricating a coupon of material that can withstand a blow torch to having a working structure that can withstand the operational environments that a hypersonic vehicle will see.
If it were up to me, I'd keep working on integrated thermal / mechanical CMC aircraft structures and methods to combine those structures with heat pipe systems to, to the extent practical, create nearly isothermal structures that evenly distribute the heating loads over the entirety of the skin of the vehicle while maintaining the mechanical strength required to deal with the aero loads imposed by hypersonic flight.
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Just to let you know: PICA was developed by NASA long ago for surviving free returns from Mars at up to 17 km/s entry speeds. The Apollo ablative would not survive that. Their material was expensive and difficult to deal with. It was never used, and languished unused for a long time.
Spacex took that material and updated it to the PICA-X form for less expense and easier-to-use characteristics. It is well-proven on their Dragon capsules, and was intended to survive free returns from Mars. In contrast, the new ceramic-matrix composite materials are still laboratory demo items that have never yet been proven ready for application in flight. They will be successful, but that's still years off.
PICA-X is an ablative, yes, but it is a tougher one than anything we have seen except maybe carbon-carbon composite, which has a fragility problem that PICA-X does not, in addition to its expense. So far, Spacex has reflown Dragon heat shields. They say they will do this up to 5 times from LEO, and that is also their plan for a PICA-X-protected Starship.
Their prediction is it will survive 2 returns from the moon at just almost 11 km/s, and it will survive once the combination of a 7.5 km/s entry at Mars and an up-to-17 km/s entry at Earth. We will eventually see.
At any rate, it is definitely a ready-to-apply material technology. Essentially off-the-shelf, ready-to-go. Those other things are not, except for low-density ceramic tiles that won't survive past about 9 km/s, heavy thick reinforced-phenolic shields (long used), and rather fragile and expensive carbon-carbon, which would survive 5 or 6 times from LEO at 8 km/s.
Personally, I don't know what glue is used to secure PICA-X to a substrate. As for what substrate you can have, that depends fundamentally on the shield thickness, which controls the backside soak-out temperature. That's figured with finite-difference analysis on a time-transient basis, not steady state, because most entries are brief events.
GW
Last edited by GW Johnson (2020-03-24 08:45:11)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW,
Experimental though it may be, the X-37 uses TUFROC on the leading edges and windward side of the vehicle and the X-43 and X-51 hypersonic "wave riders" are using CMC's in their sharp leading edges. Furthermore, the SHEFEX series of sharp leading edge hypersonic vehicles are also using CMC's. The various Hafnium and Tantalum based CMC's and TUFROC use mechanical fasteners to affix them to the Aluminum or steel airframes, but they themselves are also load bearing structures that comprise part of the airframe, especially for the control surfaces.
Starship is still very much a developmental vehicle and I think it needs CMC's for sharp leading edges, combined with heat pipes for thermal soak over the entire control surface, plus TUFROC, reusable up to 3,000F and ablative to 3,600F, on the leeward side, and PICA-X on the windward side. We can't have leading edges ablating away during reentries. If they're serious about doing transpiration cooling then it could be TUFROC for everything but the leading edges and it's lighter than RCC and slightly heavier than HRSI or PICA-X but definitely more reusable and currently flying on the X-37. Starship is not a single-use capsule. It has to survive a minimum of 2 reentries with predictable aerodynamics for both Mars and Earth reentries and, ultimately, it needs to be maintainable and cost-effective. It's just my opinion, but I think the best way to do that will be by making use of reusable non-ablative control surfaces and maybe a toughened ablative like PICA-X on the belly of the beast.
Mechanical fasteners that provide strain relief will most likely work better than adhesives for long duration flights with multiple extreme heating and cooling cycles and since the CMC's or TUFROC would be mechanically fastened to stainless I think that combination would be hard to beat for durability and maintainability, as it's easier to remove and replace than a heat shield using adhesives.
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The materials then are for not only high speed returns from the moon or mars but for launch speed protection as well.
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Thanks to all,
Having entry speeds of about 19-17 km/s, I think to use PICA-X ablative TPS on an aluminium honeycomb skin, for my waverider, and to change the PICA-X tiles every new mission (I don't know if TUFROC or CMC can withstand entry speeds of such order).
I chose an aluminium substrate instead of a steel one, because the weak link of the chain is the glue to fix the PICA-X tiles on the shell: the best silicon adhesive I've found has a maximum temperature of about 620 °K, that is less than the maximum temperature of the best high-temperature aluminium alloys, like NASA-398, which is about 640 °K.
Steel might worth the weight penalty only if using some kind of high-temperature resistant adhesive method like brazing, but I don't know if PICA-X tiles might be brazed on a steel surface.
Are my thoughts right?
Last edited by Quaoar (2020-03-24 12:27:44)
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Quaoar,
If you actually allow Aluminum to reach 620K / 656F / 347C, then it's likely to be a problem for structural reasons. Aluminum only starts to melt at 1,200F, but it rapidly loses strength before you get it that hot. At 600F about half its strength is gone, so you're either going to make the airframe pretty stout or the airframe won't survive. 656F is nearing the annealing temperature range for certain types of alloys. I think 6061-T6 is annealed at 775F, but can't recall off the top of my head. That said, the non-reusable Apollo capsule was designed for a maximum allowable service temperature of 600F during reentry, prior to main chute deployment, at the bond line between the heat shield and the capsule, so maybe this would work if some kind of sacrificial Aluminum honeycomb and ablative heat shield are replaced or maybe you could thermally soak the entire airframe (windward and leeward side) using heat pipes to slow the temperature rise. The Space Shuttle's primarily Aluminum airframe was limited to 350F, which was an acceptable limit over its design service life criteria.
Edit:
When they designed the Space Shuttle, NASA determined that the mass savings differential between using Titanium (600F maximum allowable service temperature) and Aluminum (350F maximum allowable service temperature) was less than 10%, so they went with Aluminum anywhere they could because Titanium was 2.5 times more expensive and the thing already cost as much as a B-2 stealth bomber. I think they used Titanium in the engine mount. The engineers and fabricators were also highly experienced with using Aluminum alloys and less experienced using Titanium alloys, so even though Titanium could've made the structure lighter they stuck with Aluminum and took the mass hit on a TPS that was somewhat heavier to prevent the airframe it was protecting from getting any hotter than 350F. I've noticed that as attractive as Titanium appears at first, nearly everyone who designs aircraft avoids using it except for certain high temperature fasteners and engine mounts in military aircraft and airliners.
Last edited by kbd512 (2020-03-24 15:03:49)
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Quaoar,
If you actually allow Aluminum to reach 620K / 656F / 347C, then it's likely to be a problem for structural reasons. Aluminum only starts to melt at 1,200F, but it rapidly loses strength before you get it that hot. At 600F about half its strength is gone, so you're either going to make the airframe pretty stout or the airframe won't survive. 656F is nearing the annealing temperature range for certain types of alloys. I think 6061-T6 is annealed at 775F, but can't recall off the top of my head. That said, the non-reusable Apollo capsule was designed for a maximum allowable service temperature of 600F during reentry, prior to main chute deployment, at the bond line between the heat shield and the capsule, so maybe this would work if some kind of sacrificial Aluminum honeycomb and ablative heat shield are replaced or maybe you could thermally soak the entire airframe (windward and leeward side) using heat pipes to slow the temperature rise. The Space Shuttle's primarily Aluminum airframe was limited to 350F, which was an acceptable limit over its design service life criteria.
I found this paper about a high temperature aluminium alloy named NASA-389
https://ntts-prod.s3.amazonaws.com/t2p/ … TOPS-6.pdf
At 588 K or 600 F it conserve almost 60% of its strength, but even the adhesive at this point is very near to failure, so the substrate has to be kept at lower temperature (below 400 F or 477 K). That's why I see no reason to use steel, which is heavier, unless you do use some other kind of temperature resistant fixing method.
P.S:
We Europeans are very unfamiliar with Fahrenheit scale so we have to use online converters to realize what we are talking about. Many years ago in US, I carbonized the tomato sauce over a pizza before cooking the dough for setting the oven at 200 F, like an Italian oven which has to be set at 200 C to correctly cook a pizza.
Last edited by Quaoar (2020-03-24 15:14:48)
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Quaoar,
Those Aluminum-based CMMC's I messed with were a good example of an Aluminum alloy that retains substantially more strength at higher service temperatures, but good luck finding someone who wants to machine it. It's also as expensive, by weight, as a mid-grade stainless. I was only thinking of using welded stainless to permit much higher service temperatures as part of a complete thermal soak design. The stainless is definitely going to be stronger than Aluminum on a per-unit-mass basis at 600F+, but really it's the issue of having cryogenic propellants on one side and blow torch temperatures on the other that seemed like a significant thermal expansion and subsequent metal fatigue challenge if we stick with using Aluminum.
I presume this hypersonic wave rider vehicle will contain cryogenic propellants, right, or will it be an empty beer can when it lands?
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Quaoar,
Those Aluminum-based CMMC's I messed with were a good example of an Aluminum alloy that retains substantially more strength at higher service temperatures, but good luck finding someone who wants to machine it. It's also as expensive, by weight, as a mid-grade stainless. I was only thinking of using welded stainless to permit much higher service temperatures as part of a complete thermal soak design. The stainless is definitely going to be stronger than Aluminum on a per-unit-mass basis at 600F+, but really it's the issue of having cryogenic propellants on one side and blow torch temperatures on the other that seemed like a significant thermal expansion and subsequent metal fatigue challenge if we stick with using Aluminum.
I presume this hypersonic wave rider vehicle will contain cryogenic propellants, right, or will it be an empty beer can when it lands?
Yes I use LOX-LH2 with four 2.7 MN P&W Cobra (derived from SSME), but it never land and fly orbit-to-orbit using aerocapture at both ends plus an aero-gravity assist in the return flight to spare propellant. Probably a steel shell is even more resistant to fatigue. Do you think it's better to use steel even if the outer skin temperature is constrained by the silicon adhesive?
It's possible to fasten or brazing the tiles instead of gluing them?
Last edited by Quaoar (2020-03-24 16:15:22)
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Quaoar,
Hmm...
Aluminum does okay with LH2, but stainless fares even better and steel sheet is some of the cheapest stuff you can buy and robotic welding is much faster and therefore cheaper than machining Aluminum plates with giant milling machines and then bending the "Aluminum potato chips" into propellant tank gores, anodizing them to prevent stress corrosion cracking, and then friction stir welding them (which can also be done with thicker gores of stainless). The Centaur upper stage is a non-standard thickness super-thin stainless balloon design that's custom rolled to be thinner and then planed after welding to be thinner still. All that extra work and cost only achieved a 5% decrease in structural mass fraction, but as Tory Bruno said, "it's the Ferrari of upper stages". This transport vehicle will be large enough that standard thickness sheet can be affixed onto jigs / tools and robotically welded with a friction stir welding machine.
If the vehicle had to fly under power at low speeds, then Aluminum is lighter for a given level of strength and therefore more cost effective to operate, which is also the entire reason why Airbus and Boeing switched to CFRP / GFRP- because it's even lighter for a given strength than Aluminum, but again only when temperature limitations are respected. Steel is by far the easiest material to work with and so long as its been properly designed and fabricated it'll provide years of dependable service.
I think you'll still be forced to pay the piper, in terms of structural mass, if you try to make the structure lighter by using a lighter but less heat resistant airframe, in terms of TPS mass to insulate the airframe. Skip the adhesive and go straight to mechanical fasteners. Those work well and the results are highly repeatable. Between maximum practical durability and maximum feasible payload performance, I'd choose maximum practical durability for a reusable spaceship every single time. Propellant is cheap compared to a dead crew and destroyed vehicle. SpaceX has the right idea, I just think it needs a lot of refinement and they're doing that.
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Quaoar,
Hmm...
Aluminum does okay with LH2, but stainless fares even better and steel sheet is some of the cheapest stuff you can buy and robotic welding is much faster and therefore cheaper than machining Aluminum plates with giant milling machines and then bending the "Aluminum potato chips" into propellant tank gores, anodizing them to prevent stress corrosion cracking, and then friction stir welding them (which can also be done with thicker gores of stainless). The Centaur upper stage is a non-standard thickness super-thin stainless balloon design that's custom rolled to be thinner and then planed after welding to be thinner still. All that extra work and cost only achieved a 5% decrease in structural mass fraction, but as Tory Bruno said, "it's the Ferrari of upper stages". This transport vehicle will be large enough that standard thickness sheet can be affixed onto jigs / tools and robotically welded with a friction stir welding machine.
If the vehicle had to fly under power at low speeds, then Aluminum is lighter for a given level of strength and therefore more cost effective to operate, which is also the entire reason why Airbus and Boeing switched to CFRP / GFRP- because it's even lighter for a given strength than Aluminum, but again only when temperature limitations are respected. Steel is by far the easiest material to work with and so long as its been properly designed and fabricated it'll provide years of dependable service.
I think you'll still be forced to pay the piper, in terms of structural mass, if you try to make the structure lighter by using a lighter but less heat resistant airframe, in terms of TPS mass to insulate the airframe. Skip the adhesive and go straight to mechanical fasteners. Those work well and the results are highly repeatable. Between maximum practical durability and maximum feasible payload performance, I'd choose maximum practical durability for a reusable spaceship every single time. Propellant is cheap compared to a dead crew and destroyed vehicle. SpaceX has the right idea, I just think it needs a lot of refinement and they're doing that.
Thanks.
Which kind of mechanical fastners? The tiles can be bolted, but in this case the holes for the nuts has to be covered with a PICA-X cork, this time glued. Do you know some kind of blind snap fastners?
Just another question: The lander is a single use 30 meters long biconical vehicle which detaches from the waverider before the arrive, makes a direct entry at 18 km/s in a super-earth atmosphere (surface gravity 1.3 g) then lands with four cluster of seven Apollo type parachute and airbags.
Being a one-way vehicle the lander can be done in aluminium or is better in steel?
Last edited by Quaoar (2020-03-24 17:13:05)
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Thanks I've found this UHT adhesive of 3M which resist up to 2000 F or 1366 K
https://www.3m.com/3M/en_US/company-us/ … 008&rt=rud
it might be OK to fix PICA-X tiles on a stainless steel shell
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Direct bond means that it will transfer to the shell but with layers of adhesive and blanket you isolate and slow that process of thermal conduction through them...
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