Atmospheric Surfboards

Void · 2022-11-06 11:23:58

Atmospheric Surfboards (Moderators go ahead and delete this if you don't like it).

The air braking footprint of Starship is likened to a skydiver. I would like in a similar fashion consider a surfboard.

Dark Star is the first encounter I had with the idea. It is a spoof of course: https://www.youtube.com/watch?v=IkjiDJUHPHM

https://www.bing.com/images/search?view … ajaxserp=0

So, I kind of think of this as perhaps being a bit like the footprint of Starship, but not necessarily having a pressurized tube as the main stiffness creator. Maneuvering thrusters will be needed. Perhaps even flaps, presuming the thing goes deep enough into the atmosphere.

Atmospheres it might work with at least could be Earth, Mars, Venus.

For Earth I think of an assistant that travels between Moon orbit and sub-LEO & an elliptical orbit, then an elliptical orbit sustainable. It might do multiple passes.

For Mars it might be a one-use device that would help a probe slow down and also maneuver to special locations by using the atmosphere to do turns. It would probably be disposed of before landing the probe.

Heat shields so far for the most part cannot exceed the footprint of the fairings of rockets from Earth. This might do so, and so have lower peak temperatures than is typical.

It might also be that this shield will be held out from a load by spacers, allowing heat flow out of the shield from its back side.

The device will not land on Earth, I expect, and likely would not land on the Moon.

Flying Nuclear reactors though the atmosphere is a real bad idea, so it would be solar powered, presumably with some energy storage ability. It might have solar panels that can fold into its back side during an entry event, or perhaps it might even be a solar concentrating mirror that either concentrates photons onto a smaller solar panel or onto a heat engine.

I tend to want this heat shield to be of metal, and so you could not tolerate as high peak heating as for the space shuttle or Starship, but heat tiles should not be ruled out.

Propulsion might in part be electric. Perhaps Argon will be available both from the Earth and the Moon.

So, a payload for this might be a Lunar Starship for a really big one, or a Lunar Terran-R or the like for a smaller one.

While this device might tow a ship to the Moon using efficient electric propulsion, it still could allow the ships to fly on chemicals, perhaps with an assist from a Nuclear Tug.

If you did have ceramic tiles and there was a failure, the worst that might happen could be a hole, and the payload might survive. I guess that would be a chancy situation. Not certain.

That is a start. It might be a way to use Aerobraking and also Electric Propulsion with Starship and Terran-R and the like.

Done.

Last edited by Void (2022-11-06 11:46:27)

Void · 2022-11-06 19:59:14

Well perhaps this will not work out. I guess then that will show what not to do.

But I am indeed very interested.

The Expanding Heat Shield for Vulcan's engines and avionics, expands in order to create a bigger footprint. So at least a bigger footprint may make sense.

So, that is yet another thing: https://spaceexplored.com/2022/10/27/vu … ield-test/
Quote:

Vulcan inflatable heat shield test launching on Atlas V in early November

Image Quote: https://spaceexplored.com/wp-content/up … e=1200,600

So, the point is, perhaps there will be further room to innovate for heat shields.

As I understand it, heat shields have typically been ablative or ceramic tile. And they typically are sort of glued/attached to the surface they are to protect, so they cannot radiate from their back side.

Exceptions to that would be for certain interplanetary probes which have used solar panels to do a very careful and gentle level of aerobraking. Here is an example: https://mars.nasa.gov/odyssey/mission/t … robraking/

There are quite a few things that I have in mind, and at this point it is not very wise to drill down deep on any particular one, and to then miss the possibilities of others.

A possibility may exist for a heat shield mainly metal, such as Stainless Steel, or maybe an anti-solar panel? Don't get too hung up on any possible option: https://www.solarsquare.in/blog/anti-so … lectricity.

In a way the heat shields I have in mind might be to some degree like a sail, except the inertia of the atmosphere acts against the inertia of the assembly. Some navigation might also be possible.

https://en.wikipedia.org/wiki/Solar_pan … ocylinders

Anti-Solar Heat Shield Braking Sails, might not tolerate very high temperatures, certainly there would be a limit. But these might generate electricity while aerobraking, and also when pointed appropriately at the sun. They might also double as a sun shield, to protect cryogenic propellants in some circumstances.

But perhaps the similar could be said for Solar-Panels. Some Solar Cells can tolerate 600 degC I believe. I will check.

We have this that we have looked at before: https://phys.org/news/2016-08-high-temp … solar.html

It suggests that high temp cells can be created. If like these however they may not function well in normal sunlight.

Quote:

In experiments, the new absorbers were shown to operate at a temperature of 800 degrees Celsius and to absorb light of wavelengths ranging from 300 to 1750 nanometers, that is, from ultraviolet (UV) to near-infrared wavelengths.

So pretty hot, but likely much heavier than a thin sheet of Stainless Steel.

Thinking of the heat shield like a "Sail" perhaps you could have a Stainless Steel "Sail", but you would need some kind of restraining frame to keep it from crumpling up like Aluminum foil. Good chances that the ability to alter flight with aerosurfaces would be a desire, if possible.

I might anticipate that this "Sail" might be of a thinner gauge than is that of the Starship.

Starship apparently goes down to 2 millimeters in some places, or that is the desire: https://answersdb.com/others/how-thick- … rship.html

The Starship is an inflated tube, so that gives some strength. But a Heat Shield sail might need other means. To some degree it might borrow some strength from a Starship riding in its lee, but of course struts would be mass as well.

Increasing the size of the "Footprint" would also add mass but would reduce peak heating per unit area.

Not diving too deep into the atmosphere would reduce the amount of footprint you would need.

Actually, if you were going to do that perhaps you would use the belly of the Starship itself as aerobrake and add sails to its footprint profile on its outside. I am thinking of the Lunar Starship of course, and you would not want to drop it too deep into the atmosphere.

The Starship metal gage being thicker perhaps it could "Sink" a bit of heat, and also radiate heat from the inside of its belly to the Leward side of the interior. There might be some tolerance there.

The thin gage "Sails" attached temporarily to the ship, may radiate a fair amount of heat from the lee side of the sails.

But of course, you could not push it to anywhere near melting.

https://www.costasteelsheets.com/stainl … /7491.html
Quote:

1400-1450°C

But you could get it pretty hot, it would seem.

So, it is beginning to look like feathers on a bird sort of the wings of a bat.

So, it might be desired, if possible, to not land with the wings/Feathers/webs on, when you land on the Moon, but to leave them in some orbit.

I have speculated that that assemble might have a space drive of its own, perhaps including chemical thrusters and even electric rocket propulsion.

Large wings attached to Lunar Starship might allow it to maneuver in very thin atmosphere, I would hope.

Exactly how the Starship and its wings assembly would "Path" their way to the Moon is open to options, I sort of think. But at the Moon at some point, they would likely join and heat back to Earth together.

At least that is what I am drifting towards at this point.

Of course, achieving some orbit of Earth where refilling was possible would be the desire, I would think.

Done

Last edited by Void (2022-11-06 20:50:24)

GW Johnson · 2022-11-07 10:16:12

I saw and enjoyed Dark Star many, many years ago. The astronaut trying to "surf" through entry on a piece of wreckage is quite the image.

Stagnation point convective heating is proportional to velocity cubed, to the square root of density, and inversely to the square root of the surface radius of curvature at the stagnation point. Unfortunately, for LEO and Mars entries, you typically measure it in watts per square centimeter, not per square meter. It's very high, almost no matter what.

Heating rates away from the stagnation point are lower. Where a lateral surface is still wetted by attached flow, heat rates are very crudely half an order of magnitude lower than at stagnation. For leeside surfaces immersed in a separation zone, heating rates are crudely a full order of magnitude lower than at stagnation. But they are still quite high.

That's for speeds under 10 km/s. Above it, radiation heating from the glowing plasma sheath dominates over convective heating. And it is more-or-less proportional to velocity raised to the 6th power.

There has to be a heat balance. You can cool the overheated surface by conduction into a heat sink somewhere, by re-radiation of heat to the environment, by active cooling with a sacrificial liquid, and by ablation where the mass flow rate of ablated material times its energy of destruction is the heat carried away in the ablation debris. Bear in mind that as the plasma sheath gets bright enough to heat radiatively, that it also becomes opaque to re-radiated thermal energy, so that re-radiation cooling becomes infeasible.

The astronaut trying to "surf" his way through entry on a piece of wreckage as a "surfboard" is betting that it won't all ablate away beneath his feet.

He is also betting that he can survive the heating he experiences in the wake zone behind the "surfboard".

While an order of magnitude lower than stagnation point heating, it is still quite high. If he cannot cool by reradiation at surface temperatures he can tolerate, he had better be able to tolerate his surfaces soaking out to near the effective gas temperatures (6 km/s = 6000 m/s ~ 6000 K effective gas temperature, by the old entry engineer's rule-of-thumb).

Mercury and Gemini, entering at only 7.9 km/s, had exposed superalloy metals for leeside skin structures, re-radiating somewhere in the 1000 F to 2000 F range. These were dark in color, for efficient re-radiation capability. Apollo, entering at 10.9 km/s, had an ablative coating on its leeside surfaces.

Spacesuits are usually light or white in color. They are very inefficient re-radiators, and so the equilibrium surface temperature would be higher than for a dark-colored surface. I don't think the astronaut "surfing" would really work, except at much lower speeds than a typical LEO entry.

But if the cargo delivered to Mars were dark in color, and could tolerate its surface equilibriating at around 1000-1500 F, then a sacrificial "surfboard" is one possible way to survive Mars entry at speeds up to around 7.5 km/s.

How you steer the thing correctly is another matter. It will require active control.

And, you will come out of hypersonics on Mars at around 0.7 km/s, angled steeply downward, only about 5 to 25 km above the surface, depending upon your ballistic coefficient. Quite unlike the end-of-hypersonics on Earth at around 40-45 km. The bigger you are, the bigger your ballistic coefficient is, because of the square-cube scaling laws. How you survive that landing is a whole other issue.

GW

Last edited by GW Johnson (2022-11-07 10:23:16)

Void · 2022-11-07 10:55:05

Science and Math again!

Yes, dark star is something special. It reminds me of when I was young and had planters' warts on my feet. The doctor would carve on them and then put some pads with a substance that caused a burning sensation.

At the final session when he was carving on me, I started laughing in involuntary manner. He said, "I think were done". I never returned. The warts went away.

I don't know if there is a pathway in human psychology where a situation gets so odd, that rather than Panick or Anger or Tears, you get into some strange sort of emotional state that might sometimes lead to a chance of survival.

Of course, the surfboard was not really going to work, but it was all he had. Very low to no odds of survival.

Dark Star seems to get close to it.

You are very much helpful, I appreciate that you say truth, but are willing to offer chances even slim ones.

Done.

Last edited by Void (2022-11-07 11:02:08)

kbd512 · 2022-11-07 11:57:09

HIAD is something of an "inflatable surfboard" that uses computer-controlled "mass shifting", meaning precisely moving the mass of the protected payload to "steer" the vehicle during reentry. I think you need a substantial thermal barrier protection around yourself.

RobertDyck posted about a similar contraption ("man out-of-space soonest"- I forgot the actual acronym used) that would allow a single suited astronaut to "fall back to Earth" from a stricken space capsule. That was back in the 1960s or 1970s, and it never progressed beyond conceptual design. However, the astronaut was completely enclosed in the flexible / inflatable heat shield material and there were some serious g-loads involved. The astronaut was essentially "laying on his back", and the spacecraft was shaped somewhat similarly to a surfboard, but with a retrorocket mounted to his backside.

That reentry technique would be a fatal stunt on Mars without near-immediate ground support available, meaning a pressurized rover or habitat to hop into after a successful landing. Heck, it could still be fatal on Earth, even after surviving reentry and making a soft landing.

kbd512 · 2022-11-07 14:24:06

Void,

Here it is:

Man Out Of Space, Easiest

It's not really a "surfboard", but...:

Void · 2022-11-07 14:26:05

Thanks, fellow members. Interesting actually.

I am going to cheat, and change the Topic from "Index» Interplanetary transportation» Atmospheric Surfboards"

To??? I am open to suggestions; think I can do it later. I also want to expand to various re-entry concepts.

It is not that much of a surprise that the Apollo used what it used. Fairing sizes mandated it I sort of feel.

Primarily, I am interested in methods that would skip off of the atmosphere, and so perhaps not experience the full heating problem.

However, in any case that it might be possible to then find a way to do more, coming from the notions for the lesser task, then that will be fine to have a look at as well.

GW Johnson did suggest ablation with an atmospheric surfboard. I believe that kdb512 questioned the center of gravity.

So, all valid.

I am moving in the direction of what to do with a version of Lunar Starship, and perhaps to give it flying squirl wings. Not wings that flap for lift, rather with air braking and perhaps some glide.

The disposable thing for Mars that GW Johnson proposed may well be a solution to what I had proposed for Mars.

With Starship, we are hoping for multiple reuses. One thing that has formulated is a one-use ablation method. You would have to apply the ablative substance to outside locations of the Starship. I am thinking Salts. While they are corrosive, and may flake off with vibrations and turbulence, it is a place to start. I want something that does not leave a char residue. The salts will not be wet, so that may reduce corrosion. It is possible that the flaking might be reduced with an additive of some type of fiber. I am presuming that this would be added with vacuum deposition prior to reentry.

This might also be done to wings, but if they flex a lot then flaking will be a problem.

I am thinking phase change for the salts, and hopefully evaporation from the high wind speeds, so, possibly 2 phase changes.

Salts have been recently talked about for energy storage at this site. https://en.wikipedia.org/wiki/Molten_salt
Quote:

Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 800 °C (1472°F) and a heat of fusion of 520 J/g.[1][2]
A salt that is normally liquid even at standard temperature and pressure is usually called a room temperature ionic liquid, and so technically molten salts are a class of ionic liquids.

https://bssa.org.uk/bssa_articles/melti … ss-steels/
Melting temperature of Stainless Steel: Quote:

1400-1450°C
According to 3 sources

So, maybe, OK???

Now for the glider wings, I see two parts, the webs of thin metal, and the tubular struts that will be like bones.

The webs, I think might radiate some heat out of their lee side. Salt might be used on the windward side, but I have indicated that that might tend to flake off.

For the tubular struts, I am thinking vacuum oil similar to a high vacuum pump.

Also, the struts may have a radiator fin on the leeward side that will also give strength.

The oil might vaporize on the windward side and condense on the leeward side. Any pressure buildup might tend to stiffen up the struts.
The salt trick might also be tried on the windward side as well, for the struts.

OK, not sure, but sort of thinking of this for the oil: http://hyvac.com/Products/Oil/pump_oil. … ac%20Pumps.

For the body of the starship, you have the two propellant tanks, the engines skirt, and the cargo compartments.

A possible trick for the two propellant tanks, is to inject a bit of water and/or CO2 into them after purging them of propellants. You might actually burn the remnants of propellants to get some of it. (This is on the trip from the Moon and does not involve the smaller tanks, which might not be used to land but might be wanted for maneuvering).

During the trip back from the Moon, you would face the belly to shadow, away from the sunlight, and inject the water and/or CO2. These would be expected to form a frost on the interior of the belly of the ships metal skin.

During deciliation into the atmosphere, the intent is to phase change from frost to vapors and so to pressurize the tanks and cool the skin. I don't know if these vapors would be vented for cooling. I might prefer that they would not be.

During entry, if all these are converted to vapor then a pressure as high as 6 bars might be tolerated, and in a temporary gravity simulation caused by deceleration convection should occur, moving heat from the belly to the back of the ship. 6 bars (are/is) rather thick, but I don't know if it can be tolerated.

They would need to be purged by some method prior to filling the tanks with propellants again.

For the engine bell, some notion of thermal shine through may apply, that is the backside of the windward side is exposed and may radiate.
Also, the salt trick might be used. Further, the engine skirt may be of a metal foam and allow heat distribution with the oil I suggested for the wing struts.

The Cargo compartment is a problem. I guess you might try some of the solutions already suggested for other parts. Of course, those cannot conflict with the wellbeing of the cargo, and especially human crew and passengers.

Last edited by Void (2022-11-07 15:17:36)

kbd512 · 2022-11-07 15:15:12

Void,

I'm questioning the ability to land where intended without computer control. It's possible that an ace pilot could pull off a manual reentry, by virtue of knowing every aspect of the procedures involved, back-to-front, in much the same way that Neil Armstrong pulled off a manual lunar landing, but you'd better be able to do the required calculations in your head and have alternative landing spots picked out ahead of time, or you could easily become another impact crater.

There's probably a few very talented pilots out there who can prevent a F-16 from swapping ends, mid-flight, but for the sake of everyone else, the jet comes equipped with triple or quadruple redundant fly-by-wire computer controls to keep it pointed nose-first into the oncoming airstream. Few things are impossible, but few people would commit to the level of training required to pull it off. On that note, nobody is gong to be "surfing" during reentry. Possible yes, but practical... probably not.

Void · 2022-11-07 15:19:46

If you read the above, then landing on Earth is not planned, and also landing on the Moon, hopefully would not involve the wings section.

I want the Lunar Starship to skip off of the atmosphere, and eventually get to an orbit where it can be refilled.

But yes, for that, probably good computers needed. You certainly know more about flight in that level of the atmosphere than I do.

But the Starship has to navigate that in any case.

Done.

Last edited by Void (2022-11-07 15:21:38)

Void · 2022-11-07 15:23:42

In addition to the materials of post #7, magnetic and transpiration methods may be considered, but I am not offering anything new for that. They simply exist as possible contributors to success.

Done

kbd512 · 2022-11-07 18:47:33

Void,

NASA's Mars ARES aerial drone had a total wet mass of 185kg. Its stall speed at that mass was 226mph, and cruise speed was 324mph. It had a wingspan of 6.25m and a length of 4.5m, with a wing area of 7m^2. To bring stall speed values down to something sane, you'd need a vehicle with 10m^2 of wing area, essentially the same as a Cessna 152, but with a total weight no greater than 185kg, including the astronaut. That's a pretty tall order, but perhaps doable with CNT fabric and aerogel foam. The heat shield would have to somehow break away as well, or the thing simply weighs too much to land at reasonable speeds.

Edit:
Design of a Mars Airplane Propulsion System for the Aerial Regional-scale Environmental Survey (ARES) Mission Concept

Edit #2:
BNNT fabric over aerogel foam insulation, 3D-woven for strength, over-wrapped with CNT fabric to ablate heat away during reentry. The CNT fabric would be sacrificial in nature. BNNT fabric handles high temperatures well, and so does CNT, but not in an oxidizing atmosphere, which means it should actually work on Mars.

Last edited by kbd512 (2022-11-07 18:59:59)

kbd512 · 2022-11-07 20:51:03

Void,

A "flying surfboard" wing:

I think this might be feasible, but it won't be practical at all until computer-control is included.

SpaceNut · 2022-11-07 21:50:29

Part of the scout class mission of cheaper faster had a couple of these designs.
2007 Mars Scout
Mars Scout -11

Void · 2022-11-07 23:24:20

Well good, for a probe to Mars, you guys are offering some interesting alternatives.

I am also. of course, interested in making a method to use aerobraking for the Lunar Starship or a variation of it.

As a part of that I am trying to come up with methods to stretch the heat tolerances.

If you had an attachable wing frame, then by just not dipping too deep into the atmosphere, some modification of orbit should be attainable without melting or burning the materials depending on what materials. I do understand that you must dip fairly deep, to have navigation by air structures. But if necessary then the Lunar Starship would only use the wings as breaks and an atmospheric skipping mechanism. Thrusters would then be needed to keep the ship oriented if the atmosphere were too thin.

I don't have the numbers, but I believe that becoming unpinned from an orbit of the Moon, could with some expenditure of propellants, intersect the Earth's atmosphere.

The needed tricks are to actually have a pull-down capability at some times, to try to cling to the rarified atmosphere. A sort of reverse, lift method, at times, while also being able to add some lift when appropriate.

The normal starship is supposed to be able to have a little lift at very high speeds which will allow it to dwell in the upper atmosphere for an extended time to shave off speed, while not exceeding the limits of the heat shield tiles.

If using only stainless steel for the wings and the starship, then you would not want to go even as deep as that.

Not going deep enough or not being able to force an extended "Dwell" in the atmosphere, would then not shave off as much velocity as might be desired.

In my previous post, I have explored some possible options to handle heat, without tiles. But tiles would remain a possible option.

As far as thruster navigation method, I just remembered that the Lunar Starship is supposed to have small engines rather well up on its frames. Those might work and might also serve to help in the atmospheric entry process, as rocket exhaust can help to cool a ship in some circumstances.

A very interesting trick for that might be to run the engines poor in Oxygen. Then they might expel a plume that is cooler and partly composed of Un combusted Methane. Of course, it might combust with the atmosphere pressing on it. A curious situation. Needs some more thinking.

But a "Warm" plume might help in certain portions of the skipping process.

In other words, let's say you push 25% of the Oxygen you normally push through, and yet 100% of the Methane you normally would push through. Then the output should be relatively cooler than if you did 100% & 100%.

If you had thrusters that could do that, it might help protect the ship to some degree.

You might even have thermal sensors on the ship that would give a signal to a control process that would spew the cooling gas to the degree necessary to keep away a metal failure from overheating.

Such thrusters might be places where needed.

Just another possibility that could be explored. If those thrusters could also assist in landing on the Moon with a 100% & 100% mix, then they would "Earn Their Pay".

The objective would be to get the Lunar Starship into an elliptical orbit where it could be refilled from a depot. Assistance from the atmosphere would possibly help to achieve that orbit. Some of the work might also simply be thrust from Metha Lox Engines, and if the wing assembly had solar electric thrust, then some from that as well, perhaps.

Done.

Last edited by Void (2022-11-07 23:45:59)

kbd512 · 2022-11-08 07:39:41

Void,

You're talking about aerobraking using a lifting body. That's doable, but also very high-heat. I fail to see how you do this without a very substantial heat shield. You avoid the screaming reentry by first aerobraking into orbit from interplanetary velocity, then performing a rather sedate 4km/s reentry at Mars, but you don't get to skimp on heat shield or lifting body mass and bulk. You have lots of surface area to protect and need lots of heat shield mass to either carbonize away to get rid of the heat, or to soak up the thermal load. You're not saving any mass over the screaming interplanetary reentry. It's no-win, just a question of what you want to devote mass to- lifting body structural mass plus heat shield plus propellant, or heat shield plus propellant for a direct reentry. If the goal is to land, then the latter is best, whereas the former makes the most sense if you want to stay in orbit.

Edit:

If you want to land on the moon, then only rocket thrust prevents you from becoming the next crater. There's no propellant cost savings to be had, except maybe employing reusable tugs to almost but not quite achieve escape velocity, as GW has shown. If you had the propellant onboard, then you would go from LEO to lunar surface, which is what SpaceX is doing, except with a much much larger lander. I'm partial to the Centaur / RL-10 "crasher stage" concept, especially if you get to reuse the engines to come home, because then a single high-Isp upper stage engine is performing all of the in-space propulsion, with some of the propellant provided by the moon if you land at the poles.

Last edited by kbd512 (2022-11-08 07:46:49)

Void · 2022-11-08 09:58:58

At times I question if you are reading what I am typing.

Considering an unmodified Lunar Starship. Yes, I understand that it is rocket engines that land on the Moon, and only that.

I had suggested an attachment for the Lunar Starship, but for now it is not included.

Coming back from the Moon to the Earth's atmosphere would be a higher speed than from LEO.

The International Space Station orbits in the Earth's atmosphere and drag requires that it be re-boosted periodically. I don't believe that there is any friction heating that needs to be worried about.

Coming from the Moon the orbital Periapsis could only go down that far, and technically the ship would do some aerobraking, and its orbit would be modified just a little. Its orbit would be modified just a tiny bit. There would be no significant heating or even no noticeable heating. But doing this would be unproductive, and you would also fly through much of the space junk as well.

OK, I fished this up: https://www.quora.com/At-what-altitude- … -or-Apollo Selected quote:

Matt P.
Software developer, sailor and seeing life is a rogue wave in a quantum seaUpvoted by
Russell Salsbury
, BA Economics, Harvard UniversityAuthor has 19.8K answers and 103.3M answer views5y
Originally Answered: At what altitude does atmospheric reentry begin for manned space vehicles like the Space Shuttle or Apollo? At what altitude does it end?
The entry interface, the point where the air starts to get thick and induce reentry heating begins for all spacecraft starting around 400,000 feet of altitude. Actual reentry maneuvers occur slightly higher than that at 550,000–600,000 feet.
HSF - The Shuttle
The altitude that it ends at is simple: When the spacecraft is on the ground at zero altitude.

It helps me to do miles 400,000 feet ~ 75.76 miles ~ and for the Normals, ~ 121.90781 Kilometers

So, if you graze the Earth's atmosphere at that level, you begin to convert differential inertia to heat that you shed.

The Normal Starship does land, but prior to that it is intended to stay at an altitude to shed heat, to minimize peak heating. At very high speeds it does have a little lift, but it is not properly a lifting air body.

If the Lunar Starship was to go that deep, then it would be best to give it ceramic heat shield tiles, so that it could survive. Then it might skip back off into an orbit. It's resulting orbit would likely still be elliptical, but of a nature that propellant could be given to it by refilling methods. If it had no flaps, then it would rely on thrusters to orient itself during the path.

There are two issues here. Can you do it and is it worth it. At this point I am trying to identify what can be done, and subsequently if it is worth it needs to be answered.

I would like to have the Lunar Starship not have a ceramic tiles heat shield, to save on weight and maintenance concerns. So, it may not fly as deep in the atmosphere. If heating begins at 400,000 feet, rate of descent and how deep you go matters, if you are only dependent on Stainless Steel to endure the heat.

If you can get away with one pass, then you might make multiple passes. But that could get tedious, and it might be desired to try to get it down to one pass. If it is a crewed ship one pass would be preferred, but if just for cargo, then maybe 3 passes would do.

If Stainless Steel can work for the Starship itself, then it may be possible to increase its footprint size with more Stainless-Steel structure that could be attached to it for Re-entry.

If you like, these could be enlarged flaps such as the "Normal" Starship is to have. Those devices are established in the human mind, so the "Ice" is thick enough to walk on in terms of awareness of communications.

For "My" Lunar Starship, I do not want to land on the Moon with the "Flaps" attached, so they should not be landed anywhere.

The Ship lands on the Moon, and then comes up and attaches the flaps. Curiously its landing gear could be left on the Moon's surface as scrap metal or plastics. The ship heads back to Earth and does an aerobrake maneuver or two or three.

At this point the "Flaps" assembly could be detached and might have its own power supply and electric rockets to fly back to some proximity to the Moon. A Lunar orbit or some L4 or L5 location. However, the Lunar Starship might alternately carry the Flaps back with it to a Lunar orbit or L4 or L5. In that case the Flaps assembly might not have a large power and propulsion system on board.

In some cases, if the "Flaps" assembly did have propulsion it might tow the Starship to some extent, perhaps using electric thrust. Probably some other method to punch quickly through the Van Allen Belts.

And then depending on a source of appropriate propellant, Nuclear Fission might be included, a Nuclear Tug, somewhere to reduce reliance on other types of propulsion.

And in previous posts I have indicated some proposals to seek methods to assist the Stainless-Steel structures to survive such an atmospheric entry pass.

Done.

Last edited by Void (2022-11-08 10:42:12)

kbd512 · 2022-11-08 12:57:34

Void,

I read what you wrote, but that's how I interpreted it.

Now it sounds like you want some transpiration cooling to enable the use of bare stainless.

Using the engines to cool the entire vehicle?

I don't know about that one.

Stainless tends to distort if the thermal load is too high, FYI.

If you need tiles to reenter from LEO or lots of propellant, then your chances of surviving a reentry from the moon don't look so hot.

Void · 2022-11-08 13:30:42

Thank You for your reply. If I cease to respond, it may be because I cannot log on. For logging on at this time it often takes 3 or more tries.

Quote:

Stainless tends to distort if the thermal load is too high, FYI.

A legitimate concern. I am also concerned about repeated heating and cooling. It may change the nature of the metals. So, if it is done at all, the process may have a limited lifetime before the ship would need to be put to another purpose.

I am hoping that something like 800 degC would be tolerated to some extent. But I certainly don't know at this time.

Quote:

If you need tiles to reenter from LEO or lots of propellant, then your chances of surviving a reentry from the moon don't look so hot.

I recall (Correctly or incorrectly), the relative speeds for 3 things. I prefer to use a number to represent the stresses, rather than speeds.
I have 8.0 for LEO to reenter. I have 6.5 to enter Mars from interplanetary space. I have 4.0 to enter Mars from Low Martian Orbit.

The stress for entering the Earth's atmosphere from the Moon or Interplanetary Space would be more than an 8.0, I think. So, I do believe it is intended that the "Normal" starship with tiles will be able to do it.

Quote:

Using the engines to cool the entire vehicle?

I believe that Falcon 9 does that at some point. It can only work when the plume is cooler than the reentry process, and it can only work for a while at peak heating, I think.

Here we are, I think: https://www.teslarati.com/spacex-elon-m … ing-video/
Quote:

The video more or less starts at the point that the heating caused by reentry becomes a concern for the booster’s health, signified by the immediate start of a three-engine reentry burn. With said burn, SpaceX quite literally uses the exhaust plume produced as a sort of brake or shield, protecting Falcon 9’s first stage from the worst of the leading-edge heating that would otherwise risk damage to its octaweb and Merlin engines.

As it happens Lunar Starship is supposed to have small engines partway up its sides. Not as high up as I would prefer though.

OK, this is going to be a problem. I think that they are hoping that they can eventually throttle raptor engines down enough to land on the Moon. But the original concept included engines on the upper sides to land, and that would possibly be useful for plume cooling.

I have considered a Methane excessive mix and an Oxygen excessive mix. The Oxygen version would perhaps act like a cutting torch, so then no.

The excess Methane version may combust with the compressed hot air impinging, so maybe not good.

I have considered an engine that might be able to include Nitrogen in a mix, but Nitrogen is hard to get.

Maybe Argon? Also, maybe water? Both might be able to come from the Moon.

Quote:

Now it sounds like you want some transpiration cooling to enable the use of bare stainless.

Yes, that might help in patches that other methods don't serve well enough, but there is a fear that the pores will plug, or I suppose the pumps/pressurization will fail. It might work with plume cooling, to cover and augment certain spots.

This again: Quote:

Stainless tends to distort if the thermal load is too high, FYI.

Using the side engines, I hope to use a "Klingon" effect. The idea is to go shallow but try to keep the nose appropriately down to keep wedged into the atmosphere, to prolong the time spent at that density level. It would be hoped that the Stainless Steel could be kept at a temperature below failure. So, at that time the upper surface would be heated the most, unless the ship were to be spined upside down for it.

So, in that case the upper portion gets heated when the lower portion is not so much heated. Rocket plume method might help, and also may help in the orientation of the ship. Transpiration or other methods may augment that. The nose would be harder to protect with Rocket Plume, so other methods would likely be needed for that. Maybe even tiles.

Once again, tricks needed would be to not go too deep into the atmosphere, and possibly to add to the footprint of the vehicle with a removable flaps section.

But by no means do a claim a successful concept, not yet, perhaps not ever.

Done.

Last edited by Void (2022-11-08 14:14:14)

kbd512 · 2022-11-08 18:57:21

Void,

From Thyssen-Krupp (pretty sure these guys know how to make steel):

304 has good resistance to oxidation in intermittent service up to 870°C and in continuous service to 925°C. However, continuous use at 425- 860°C is not recommended.

Translation:
Yeah, you can do it, but it's not good for the metal.

304/304L doesn't have any more yield strength at room temperature than 6061 Aluminum. It yields at 25ksi to 40ksi, and UTS is 70ksi. It may as well be silly putty at 800C, and you're counting on "heat sinking" blast furnace temperatures into the metal during reentry. The leading edges of Space Shuttle reached 1477C. 304 melts between 1400C and 1450C, so significant protection or significant mass flow to carry away the heat is required.

The high strength stuff is brittle and they deform the living daylights out of the metal to achieve that level of tensile strength. ARP makes stainless fasteners with fantastic tensile strength, but to do that they'll start with a 1 inch rod and squeeze it into a 0.5 inch bolt in a series of progressive forming operations with annealing steps in between. You're not doing that with a paper thin sheet. Same thing with stainless gun barrels and receivers, also typically made from 304 or 316 alloys. At lower temperatures, what started as a fantastically strong and tough material becomes rather brittle.

If you BBQ something as thin as Starship's tank structures, to within 200C maybe 300C of it's annealing temperature, then whatever little strength it has left is gone baby gone, and during that severe heating phase you're subjecting it to high g-loads. That seems like a dangerous way to stress the machine, but YMMV.

Void · 2022-11-08 20:18:57

I am glad that you continue. I have been very concerned about your recent materials. I am still concerned and confused.

I do have this I fished up because of your last post:

https://www.nextbigfuture.com/2019/07/s … oling.html

https://www.seradata.com/it-aint-going- … -starship/

This old and outdated per heat shield method, but gives some kelvin numbers for temperature.

Quote:

On Twitter, Musk noted that only a portion of the structure would need this active cooling. “1750K (degrees Kelvin) is peak heating expected on about 20% of Starship for LEO entry, ~1600K on 20%. Rest drops below 1450K, so no heat shield needed. Radiative cooling at T^4 takes care of 60% of the ship. Another reason for steel.”

1750K = 1476.85 Celsius

1600K = 1326.85 Celsius

1450K = 1176.85 Celsius or lower

It does seem very confusing. It may be that they have changed some things more than just the transpirational cooling. For instance, I think that they may be able to dwell higher in the atmosphere to bleed down some speed before the drop to thicker atmosphere.

It is an old article from before they decided to go with tiles on the windward and a little more of the surfaces. But these are the only temperature numbers I have gotten yet.

Maybe they have a trick to deal with the Oxidation problem at those temperatures? When they are high in the atmosphere the Oxygen should be much thinner, but to be truthful, I do not have myself convinced that I understand all of this well enough.

As you may have read, I have expressed a concern about the repeated heating and cooling of the Stainless-Steel metal. It may well have only a certain number of safe flights in it, but that could be a fair number. I just don't know.

I find it hard to believe that the high masters do not know what they are doing, and it would be even harder to believe that their competitors would not have called them on a mistake.

So, for now I have to presume that it might be possible to go as high as 1176.85 Celsius or lower, but I would think that a lesser number might be preferable if it can assist a modification of the orbit sufficiently.

Let me also re-mention that if tiles would be needed in some places, then I guess they might be used.

A curious though did enter my head. If the flaps were large and a thin material of Stainless-Steel, (With struts), it might actually be good if it becomes ductile from the heat. I do seem to recall that 304 is stronger when hot or cold. Let me check that.

I forgot, it is 304L or later their own special formulation

I don't have it yet, but this is somewhat useful: https://www.tesmanian.com/blogs/tesmani … steelalloy
Quote:

The 301 stainless-steel alloy uses a mix of nickel, chromium and iron, this kind of material is very resistant to corrosion and cheaper than carbon fiber -that other rockets are built from. At the conference, Musk did not give any specifics as to what type of stainless-steel alloy mix the company will be using in future.

It is strong at cryogenic temperatures.

Well this might do it: https://matmatch.com/resources/blog/elo … ess-steel/
Quote:

This is where the greatest advantage of stainless steel gets to shine. With stainless steel, the operational window in terms of temperature is expanded to about 1100 K. This lowers the requirements for heat shielding substantially. Moreover, Elon Musk introduced the concept of integrating several components like the tank structure and the heat shield into one, making stainless steel the ideal material for this particular application.

Well how about that 1100K converts to 826.85 C. It is somewhat in dispute with the other article though, but I spitball-ed 800 c.

Not that I trust that yet though............

I think that they are now using tiles on more of the ship than they originally planned, so maybe that works out.

This post was an attempt to respond to the previous post, so I think I will move onto another post.

I will say before I am done here, that I do not feel sure that an atmospheric entry for HLS or "Lunar Starship" or "Deep Space Starship", is the best way. It might turn out that it is better to bring propellants from Earth to the lunar orbits, with a normal starship, especially if Starships can be filled with Lunar Oxygen.

But on the other hand, if you can make Lunar Oxygen, then you might want to bring it to an Earth orbit to fill Starships, in which case an air braking Starship might make sense.

Curious thought: could you have a block of Oxygen ice as cargo in a Starship and use its phase change to a liquid to cool a Lunar Starship doing an aerobrake? Weird stuff.

I'm tired, I think I will leave it at that for tonight.

Done.

Last edited by Void (2022-11-08 20:55:49)

SpaceNut · 2022-11-08 21:40:16

https://ntrs.nasa.gov/api/citations/196 … 025920.pdf

https://nasa.fandom.com/wiki/Heat_shield

https://www.nasa.gov/centers/ames/resea … hield.html

kbd512 · 2022-11-09 11:40:52

Void,

So far as I'm aware, the primary structure of SpaceX's Starship is 304L stainless steel (a "weldable" variant of 304). 304L is very soft and has very little tensile strength left at 1,100K, so either the loads applied are exceptionally low or they're (a) protecting the metal from ever becoming that hot using tiles or (b) heat sinking the thermal load into other parts of that vehicle's primary structure or (c) not allowing it to actually become nearly so hot from some combination of "a" and "b". As of now, you see much more of Starship being protected from heat with tiles than was initially "tweeted out" by Elon Musk. The kinds of metal heat shields used in our Mercury space capsules were "one and done" affairs made from Rene 41, which retained considerable strength between 600C and 1000C, the parts were rather small, and generous margins were provided, relative to what we produce today, to account for our lack of experience. Starship's primary structure and engines are intended to survive 100 flights, with routine maintenance. Without significant thermal protection, that's a pretty tall order over that many cryogenic-to-blast-furnace thermal cycles.

Take a look at the strength of 304 at 649C (flip to Page 15 of the document and look at "Table 3"):
American Iron and Steel Institute - High Temperature Characteristics of Stainless Steels

At 649C, 304H stainless maximum allowable stress is 6ksi, or 30% of its room temperature value. By 800C, 304 has a lower tensile strength than Zinc does at room temperature. Any greater and the metal will permanently deform, which will progress to failure if the structure is under significant aerol loads and/or g-forces during that period of time. Pure Aluminum at room temperature yields near 4ksi and pure cast Magnesium yields near 3ksi for comparison purposes. Alloying those lighter alloys with other metals drastically improves strength, obviously, but what's less obvious is that the moment you [edit: REMOVE "don't have to"] elevate temperature much for them to lose a lot of that additional strength.

Last edited by kbd512 (2022-11-09 12:57:19)

Void · 2022-11-09 12:03:27

I agree, it is a puzzle. I do not claim to be expert, I do sort of inquire. Perhaps SpaceX has some unsaid tricks. In any case, as I have said previously and others have also proclaimed, if the bare metal will not do, then it may be needed to add some additional tricks, even tiles. But not much money was spent on this conversation, a little time, perhaps some frustration.

But remember, I do not propose to go as deep into the atmosphere as Starship will. If heating starts at 75 miles up, I don't believe that that indicates that it immediately goes to 100%. I certainly think that at 800 degC, it is questionable, perhaps very questionable. But let's say then 300 degC, and skip of the atmosphere, but try to stay in it at that level, using some tricks. Let's say you have to do 10 skips. That would not be suitable for a crewed ship but might be considered for say water or dry ice as a cargo.

And that is the direction I am heading. A certain doctor has indicated that heat sinking is also an acceptable method to handle heat, perhaps for landing legs that might be on the leeward side of the ship. (If there is one).

We have discussed, using a rocket plume to help to a degree.

I have also indicated putting frost into the inside of the tank's walls.

And so, I am looking now at transport of frozen water and CO2. To an elliptical or LEO orbit, from an external source such as the Moon, Asteroids or even other.

Pause for Coffee............

Lets try this crude notion for an atmospheric skim vehicle:

First of all, the blue is some kind of ice, maybe water, maybe CO2. Maybe something else.

If it is water, it would be totally wrong to load it as a liquid, rather to put it in as vapor, that would then condense to ice/frost, might work.

The Nose Engines assembly will be the most at-risk part for heating, I would expect. There could be a resort to assistive devices to protect it. Probably tiles, maybe some kind of ablative, maybe liquid cooling or gas cooling.

It is apparent that the propellant tanks are rather small in this picture. They are not for landing, but for navigation, possibly only using the nose engines.

I have left out how this object came to be in the Earth's atmosphere traveling from an orbit. It is highly likely that some kind of tug method is the answer. But it could have larger tanks and travel on its own.

As you can see, it is backwards to a normal ship with the engines in the front and the cargo at the back. But the water or CO2 is also cargo and a heat sink.

This could be cigar shaped or perhaps even flying saucer shaped. As indicated, it could have another engine compartment at its tail.

Then for this device we have some hopes of utilizing heat sinking, and also exhaust plume protection for much of the vehicle. It is possible that the exhaust plume could be cooled prior to exiting the nose engines.

If the purpose of this device was to transit between some orbit of the Earth, and the Moon, to bring cargo out towards the Moon, you really might not need an internal cargo hold, but could "Strap" stuff to the outside of the ship.

As far as tugs go, I guess it would be risky to have a nuclear tug in a lower Earth orbit, but near the Moon it could be a reasonable thing.

So, then you are not altogether chemical in propulsion. Of course, there are other collaborative options. A solar Electric Tug might be employed. But not sure where that is a best plan. Solar electric towing the ship out to the Moon, and then Nuclear boosting the solar electric towards the Earth again, and then boosting the atmospheric entry device as well?

I guess I don't want to obsess about the tug issues at this time.

It is a question if the nose engine "Wedge" could be protected by squirting something ahead of it. Maybe tiles would be better.

But during atmospheric entry, you could do both bottom and top impingement maneuvers, to distribute the heat over more of the surface than just the belly.

Of course, if you had big ice chunks bouncing around you would have real trouble, so, that has to be worked around to prevent it. Sudden changes could be the worst. But in general melt water should "Gravitate" towards the braking force, and also to gravity itself.

I would think you would begin by transporting materials from the Moon, but I don't want to see those squandered longer term, so you might hope to tap other sources in the solar system. It is not impossible that Hydrogen could come from the Earth and Oxygen from the Moon later on.

But I will grant greater liberty of use early on to boot things up.

Done.

Last edited by Void (2022-11-09 12:46:12)

Void · 2022-11-09 19:41:17

This is curious, because cigar and saucer shapes have been mentioned, (By me), but I also see after all that a surfboard shape might be tried.

Another curiosity is that "Nose Engines" might actually convert some of the heat to a use, of altering the plaining of the device in the atmosphere.

I think Apollo had only limited ability to alter its course when it would enter the atmosphere. Space Shuttle and Starship include thruster and air devices, I believe, to navigate.

So, if this would work OK, you might generate a steam, actively cooling the Nose Engine assembly, but could use the thrust to control what direction you would "Plane" in.

I think that the Appolo just mostly entered and was along for the ride, translating from an orbital path to a parachute drop.

Space Shuttle had much more active entry methods and translated from orbital to semi-lifting body method.

The "Surf from orbit to air drag to orbit again" could be passive or active, even beyond expected drag.

Where it might still have enough momentum to exit the atmosphere, and go to orbit, by aiming down properly, it might be possible to stay in the atmosphere beyond what the orbital momentum might by itself produce. So, I am hoping to stay in a thin atmosphere, and lower heat, but to prolong the process, to drain off more speed, while reducing peak heating.

Playing with fire is sort of normal for spacecraft. I am wondering about a stored cold mix of water and Hydrogen Peroxide. If conducted to the Nose Engines, of course then to be heated and to explode as thrust it would be hoped. The direction of the thrust would not itself slow the craft but speed it up, but it could help to control the altitude and angle of the surfing device and might also serve as a coolant that would protect the rest of the metal of the ship behind the Nose Engines. While it might be Oxidizing, it's expansion may also cool it a bit.

None of this should be considered certain, rather it is amateur hour, partially by me.

Lots of grains of salt then.

Done.

Last edited by Void (2022-11-09 19:56:28)

Calliban · 2022-11-09 19:53:25

Another cooling option is to have pores in the surface through which water or ammonia are bled. This cools the surface through evaporation and dissociation lowers the plasma temperature, reducing the radiant flux hitting the surface. Kind of like sweating. For really high velocity atmospheric impacts the plasma gets so hot it becomes opaque. Sacrificial liquids may be the only way of effectively cooling a heat shield under that circumstance.

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