Heat on aerobreak.

elderflower · 2018-09-15 03:52:53

Hi GW. What is the maximum stagnation pressure that you envisage during atmospheric entry at Mars and at Earth for a blunt conical body?

GW Johnson · 2018-09-15 08:26:33

That's kinda hard to say, since the flow is not normal ideal-gas compressible, due to ionization. But there is a way to estimate the average static pressure difference across the heat shield-and-body from deceleration gees.

Peak deceleration gees and entering mass give you the peak drag force. Divide that by the blockage area and the drag coefficient to get the dynamic pressure (or wind pressure) q at peak deceleration conditions.

If memory serves, the hypersonic stagnation pressure coefficient Cp is in the 1.8 to 2 range, depending upon whose theory you use. Multiply q by stagnation Cp to get Plocal - Pambient, knowing that at entry altitudes, Pambient is for all practical purposes zero.

Plocal is the average pressure near the stagnation point on your blunt object, figured at peak deceleration gee conditions. It's higher there than anywhere else on the heat shield.

Be aware that values you get depend exponentially-strongly on the steepness of the entry trajectory. Steeper is higher peak gees. Paths between about 1 and 2 degrees below local horizontal offer the lower gees that humans can tolerate, here on Earth, and that avoid impact while still hypersonic on Mars.

Shallow angles at entry interface speeds above escape present the risk of bouncing off the atmosphere, never to return, lost in space. That's true at Mars as well as here. Tilting the body to provide downlift until you are below local orbit speed, is the way to mitigate the bounce-off risk, at least partly.

Once below approximately orbit speed, you tilt the other way so as to prevent the trajectory steepening so fast with uplift. That last is particularly important on Mars, especially as ballistic coefficient exceeds about 70-100 kg/sq.m, in order to have time to do something about landing safely, once the hypersonics are over at local Mach 3 (about 0.7 km/s).

Be aware that there are only two supersonic parachute technologies currently ready to apply: the ribbon chute good to Mach 1.5 to 2, and the ringsail chute, good to Mach 2 to 2.5 (about .5-.6 km/s on Mars). You'll lose a lot of altitude waiting to decelerate from Mach 3 to Mach 2.5 as capsule-only in order to reliably deploy the ringsail on Mars.

High ballistic coefficient and steeper trajectory lead to very low Mach 3 altitudes at Mars: under 5 km, and if too steep, below the surface. This is the Mars "EDL dilemma" that JPL has been talking about for years, and why they have such difficulties landing anything over about a ton on Mars. That (plus weight savings for the Atlas-V) is why they had to use the Rube Goldberg "sky crane" scheme to land the one-ton Curiosity rover.

I think I once estimated a Red Dragon at ~6 metric tons at Mars entry, hypersonic CD ~ 1.5, and 3.7 m heat shield diameter, for a ballistic coefficient of 372 kg/sq.m. If peak deceleration gees on a 1-2 degree entry were about 4 gees, like some other things I investigated, then the Earth weight is ~ 60,000 N, for 240,000 N peak drag force at 4 gees. That's something like 15,000 N/sq.m dynamic pressure. Using stagnation Cp ~ 1.8, and Pambient ~ 0, I get a stagnation point pressure about 27,000 N/sq.m = ~27 Kpa = ~0.27 atm.

GW

Last edited by GW Johnson (2018-09-15 08:39:54)

SpaceNut · 2018-09-15 09:12:02

Your round up of the EDL shows why bigger is better for the heatshield diameter and why its also to increase the mass landed to the surface without using lots of fuel to slow before hitting the surface.
Nasa really needs to feed Space x developement money for retro propulsion landing if nothing else but for lunar landings to aid man at getting to the surface of the moon rather than orbiting it in the deep space gateway.

elderflower · 2018-09-16 03:05:08

Thank you GW. It seems rather low, much lower than I expected.

GW Johnson · 2018-09-16 10:51:12

Well, that's Mars, with lower entry speeds in the 3.5 to 6.5 km/s range. At Earth, speeds are higher, in the 8-11 km/s range. I've heard people talk about following the 5000 psf dynamic pressure curve, which would be a little over 2 atm. And peak gees can fall in the 4-11 gee range, too.

GW

Last edited by GW Johnson (2018-09-16 10:51:46)

Void · 2018-09-16 17:56:20

Alright then and I am giving a humble request. What do you think about this?
https://www.mlive.com/news/us-world/ind … d_aim.html
They have not really made it work prime time, but have done low level tests. If it works, how might it change what we think to do? If you wish to comment. Respects even if you decline.

SpaceNut · 2018-09-16 19:41:40

Void wrote:

Alright then and I am giving a humble request. What do you think about this?
https://www.mlive.com/news/us-world/ind … d_aim.html
They have not really made it work prime time, but have done low level tests. If it works, how might it change what we think to do? If you wish to comment. Respects even if you decline.

See my post #20 in this topic with some more of this and Gw's post 21 response....

This work Nasa is doing and it looks promising as it allows for a larger heatshield to be created from a much small diameter.
For mars atmospher a larger diameter shield makes for a larger payload to the surface.

GW Johnson · 2018-09-17 09:12:20

Landing heavy objects on Mars is already possible, the problem is that you cannot use parachutes, unless you have some sort of inflatable or extendable heat shield to reduce your ballistic coefficient (a technology not yet ready to fly). That leaves retro-propulsion.

In turn that means you do something different than you did before, which makes the staid NASA labs very uncomfortable.

But Spacex and Blue Origin already do this quite successfully, and I think that capability will improve further as time goes by.

The favored contractors Boeing and Lockheed-Martin have not yet attempted this, nor have the foreign rocket builders. But eventually, they will have to, because even the extendible or inflatable heat shields will prove to have size limits on Mars, just like chutes.

Retropropulsion has no inherent size limit. If the deceleration gees are too high to start thrusting at end of hypersonics, then start earlier. Spacex already substitutes rocket plumes for heat shields, doing their re-entry burns with Falcon first stages.

GW

tahanson43206 · 2019-06-19 12:58:26

The link below reports on awards for research and development projects ...

The one I'd like to point out, that fits into this topic, is the last one of the set of five ...

3D printing of heat shields ... As I understand it, this process will be employed in space, to create heat shields for entry into atmosphere.

Another of the awards is interesting (to me at least) because it will use a camera mounted on a mobile platform similar to the camera used in football games today, to provide a closeup overhead view of the action. In this case, the design is intended to provide close up, overhead views of the interiors of craters, without the disturbance of the site that a tracked or wheeled vehicle would produce.

The method could be applied to Mars or any other body with craters, but I think it was designed for first application on the Moon.

(th)

SpaceNut · 2019-06-19 16:05:46

Not sure but the 3D printing could be an off shot of the materials developed for the space shuttle layed over the correct shape so that it can have something to adhere to before mounting it on the craft. I am sure that in time that we will be able to make it from insitu materials at some point in the near future once we have begun landing on the moon or mars.

Void · 2019-07-10 11:37:10

We have seen this before, but I know some members want to have real footing with things that are perhaps emerging as relatively new.
https://www.space.com/nasa-spacecraft-m … dings.html

I am pretty much interested in the shape.

And I have read the recent posts, so I am aware that much of what I might say has already been mentioned in some manner. That could be a good thing, as in this case my level of speculation, may be considered reduced from the normal.

Vapor deposition, and 3D printing methods are attractive I think, perhaps to make big heat shields, (not inflatable), in orbit or on the Moon.

I am tempted to hope that perhaps these could have so much surface area, as to reduce the dire stresses placed upon the heat shields.

I guess, at the start, I would wish for a large stainless steel make. Just because SpaceX is using stainless steel. It's the in thing to start with.

But I suppose that after you had a durable structure, there would be nothing wrong with thinking of coating it with a ceramic ablative material. I know that Josh and others have discussed such elsewhere (I couldn't find that section).

I would think that if you did have a method to do it in orbit, it might be OK to get your main structural materials from Earth, at least for some time, but then perhaps in conjunction with extracting Oxygen from Lunar materials, you could add the ablatives as from the Moon materials.

…..

I am thinking about the reusability emphasis that SpaceX has, but contrasting it with disposable, and I hope re-purposed structures, these for Mars.

I got the impression that GW indicated that these types of heat shield structure might top out at some upper size. I don't know how big that would be.

At this time my impression is that NASA is just trying to do it at all with inflatables. And that is good. In that case I believe a one time use, and then throw away, because it would be charred.

I like the NASA layout. It implies that you can put a knock off of the Starship behind it. That Starship would then not require a heatshield on the ship for all cases. I presume you could dispose of some of the air braking mechanisms as well. Legs for landing I suppose are an issue, but that would be figured out after you were sure what you wanted to have for a total structure.

I guess what I would want to justify such a process, would be that you could get useful gain by re-purposing the heat shields on Mars. Scrap metal would be an option if nothing else. However I would be much nicer if you could in some cases re-work the structure into something useful.

One possibility, I suppose would be a solar tracking device. Either solar panels inside the cone, or actually doing something to capture energy in other manners. For instance, it is not the proper shape for a solar concentrating mirror, but perhaps working in that direction.
Else, maybe just blacken the inner surface, and put a glaze over it, something that can put up with U.V.

I don't know if the heat shield could be in the shape of a parabolic circular mirror, but if it could that might be useful.

The outer edge might function like a wheel, and roll on a properly made base surface. Of course you would have to include mechanisms to drive it, but it could follow the sun to some degree. It might need a tilt capability to aim at the suns position above the horizon, in addition to being able to roll.

Maybe scrap metal would be the only real use, but whatever the use, then I might think that such an option can be considered as to how it might help a Mars civilization grow.

I do understand why SpaceX wants Starship to be multi-capable, but I also think that there could be a good use for a one-way-piping of materials to Mars. Of course, I have presumed that a variation of Starship could launch back to orbit without the heat shield, and I guess to be used again for Mars it then needs a new heat shield that I suppose would be appropriated in Mars orbit. They could be stockpiled in orbit I am thinking. As for a return trip to Earth, then I suppose you would need a version suitable for that as well. There are always trade offs I guess. However, most mass should be going to Mars, not to Earth.

Talk is cheep.

Done.

Last edited by Void (2019-07-10 12:26:55)

SpaceNut · 2019-07-10 17:09:02

The article shows a hypercone device...this also is under the term Ballute and a few others...

Inflatable space parachute or escape pod - Just another use inflatable technology?

New Atmospheric reentry technique

Marsdrive Mission Design pg2

Void · 2019-07-10 20:51:11

I guess I made a mistake and left this out of my post #36. Was in a hurry to shut down my computer, as it was behaving very slow, constipated, and strange. Not the first time when I have been posting on NewMars where that happens. Does not happen for me anywhere else.

This apparently is the source for this:
https://www.permanent.com/index.html

https://www.permanent.com/space-industr … ition.html
Quote:

§ 4.7.1 Vapor and Droplet Deposition in Vacuum
Vacuum vapor deposition in space utilizes an electron beam to vaporize a metal sheet, billot or ingot target, and the vapor sputters off onto a mold, or is manipulated by a magnetic field to paint a mold. Parts of any shape can be made with great ease, speed and purity, using electron and particle beams. This will work much better in the vacuum and zero gravity of space.
Aluminum sheet and steel sheet have been commercially produced on Earth by vapor deposition despite the costs of creating a special environment to minimize oxygen embrittlement. (Of course, in the vacuum of space, there's no problem with oxygen embrittlement.) Electron beam guns have also been used to coat millions of square feet of architectural glass each year. "Extensive work has been done on developing high rate physical vapor deposition of metals and alloys and evaluating the mechanical properties of metals so deposited. ... [R]esearchers [have] determined that the mechanical properties of vapor deposited metals and alloys can be comparable to those of the same metals made by casting, rolling and annealing." (General Dynamics report) Thus, many standard Earth processes for deforming material by application of large mechanical forces can be replaced by vapor deposition in space.
Droplet deposition is a relatively new technique on Earth used to make unique parts, as opposed to mass produced parts, without using a mold, by adding small increments of material to an existing structure, slowly building it up into any shape desired. Machines are already available which do this by programming, using plastics, and are used to make prototypes for product development. Indeed, they have opened up a whole new industry called "rapid prototyping". It has been pointed out that there are advantages to doing this in zero gravity and without air. As of 1992, commercial droplet deposition was using only plastic, but a number of companies were working to develop rapid prototyping machines able to make metal and ceramic prototype products. This process is related to "shape welding" or "shape melting" whereby layers of weld material are fed and built up. This method has been used to make vessels up to many tons in mass.
The energy for all these processes to melt or vaporize the metal can be direct solar oven heating or electrical heating (induction, resistance, or electron beam).
Droplet deposition is slow, whereas vapor and spray deposition is fast. The process used depends upon whether the product is mass produced (justifying a mold) or unique. Droplet deposition lends itself to computerized design so that producing a new product just means reprogramming the computer to move the droplet depositor in a different sequence. Droplet deposition requires less power and lends itself to simple, flexible robots sent out to perform tasks without being in a great hurry.
One such company, Incre, Inc., has produced products by incremental droplet deposition using aluminum and other metals, presented a paper on the technique at the 1993 SSI/AIAA Princeton conference, and mentioned plans to do work with nickel and steel alloys such as is found in asteroidal metal.

So, where I am going with this, is yes because of needing to get through the troposphere in a small package, an inflatable is the beginning.
But I can see where Starship, and this technology of a wide heat shield can move in a progression.

As soon as Starship is up and running smoothly, I see no reason why the equipment and raw materials for it's use, cannot be put into orbit.

A block of metal will also have a compact character, like an inflatable needs to. So, you then build your heat shields in orbit. While I did suggest a variation of Starship to be coupled with such a heat shield, of course some other propulsion system could be used, perhaps.

I really do think I understand why SpaceX is focused on being able to make the generic Starship that can do it all. But of course that is already not true. They are already specializing plans for a sub-orbital people mover.

Others have pointed out that Starship, is an atmospheric transit device, which by refueling, can be made into a civilization transfer device. (GW, I believe for one, Dr. Zubrin for another). As such it makes the most sense to move loads to orbit, couple them to heat shields, and provide an interplanetary propulsion, and landing propulsion. If it is a variant of Starship, then it could make a number of passes to Martian orbit, without a heat shield, to pick up loads.

The idea of reusable hardware, has great value, but I think it is best suited to well developed infrastructure situations. Of course because we would not want to discard the "Raptor?" engines with one use, then we want to get them back into orbit, to bring down another load. But if the heat shields can be manufactured so as to serve their purpose, and also then serve a purpose on the surface of Mars, then why lift them back up, through the gravity well, and atmosphere?

So, then the notion here moves to what useful purposes could you use. How could they be useful structure.

And so I sort of deviated from the cone, and hoped for (Edited)>a convex heat shield with an opposite side concave mirror, as a possible repurpose of the heat shields.

Other things would be to reuse the metals themselves.

And the chalk board is open for other notions on what to do with heat shield structures.

Of course our hopes are that some day, all necessary metal processing can be done on Mars, including sourcing the metals from ore, but there is going to be a progression. And if you feed the right materials into the growing infrastructure at the right time, then you facilitate greater chances of economic success.

More:
https://en.wikipedia.org/wiki/Electron- … deposition
https://www.researchgate.net/publicatio … vaporation

So, for such heat shields, the asperation would be to start by using metal stocks from Earth, as I anticipate, that it will a fair time before they could be sourced from the Moon.

But I think that after you had a metal shell, it may be that a ceramic like material could be deposited over it. My hope is that in fact some types of Lunar material could be deposited, and just maybe also Oxygen could be released in the process. Oxygen to put into Starship(s) of various types, Oxygen sourced from the Moon materials.

Obviously I am a novice at all of this. But if you could get Oxygen from the ion beam process, and also deposit something of a refractory nature onto the heat shield, that would of course be going in the direction desired.

Done

Last edited by Void (2019-07-11 11:11:15)

Void · 2019-07-11 11:16:29

I am having fun with this, and more has appeared.

I would say that Starship Earth<>Mars, is like having a conveyor belt, putting a bucket on the feed end, putting a payload into the bucket, running the conveyor belt 1/2 spin, so that the bucket travels from the feed end (A) to the deposit end (B). Then you would reverse the conveyor belt and move the bucket (B)>(A). While sometimes I suppose you want a bucket to travel (B)>(A), you want most of the payload to move (A) to (B). You don't want the bucket to be out of service for ~2 years.

So, I have had further thoughts about the mirror/heatshield.

It did not occur to me before now that such a structure could be used in orbit, as a solar device. What I am now thinking of is the coupling of such with the Danish high temperature photo cells. And adding to that a two stage boil>boil thrust or a boil>Plasma.

It is just my feeling that moving mass in space being a large trouble, anytime you can cause that mass to earn it's keep, is potentially a plus.
So, this again:
https://phys.org/news/2016-08-high-temp … solar.html
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.

Now add steam powered spacecraft methods:
https://www.popularmechanics.com/space/ … pacecraft/
In this case I think they use solar cells and batteries and an electric heater. I Would not exclude those options.

But for the high temperature solar cells, which would generate electric power, I would include the harvesting of thermal heat, as a preheater for a steam>steam, steam>plasma propulsion. For now I will think in terms of steam>steam.

Using a mirror to directly heat water, has complications I think making it harder to direct your thrusters in the direction desired. In this case the solar cells being in the focus of the mirror/heat shield, I would think of a preheat. Up to ~800 C perhaps?

Then the electric power used in a heater to kick it up much higher, but as I have elected to leave plasma for another time, I would say up to almost plasma. In this way it may be relatively easy to direct the thrust as desired while pointing the mirror as desired. Add batteries, and then you can also thrust to an extent even if you are occulted behind a physical object, or when it is inconvenient to point the mirror at the sun. I feel as an offshoot, that this could be a very good device for accessing asteroids. You may or may not want the heat shield option. It may be that this device could land on Ceres with steam thrust, and take off from it.

……

So while I agree that Starship as planed might be a good expeditionary method to start with, there after there should be a move to mass production of these thrust devices, provided that a propellant can be economically secured. Water is a likely option, with CO2, and maybe Oxygen as other options. I am fully aware that boiling Oxygen to such high temperatures will be lots of trouble until mastered, (If it could be mastered). Of course I want Oxygen, as it can be attempted to get it from the Moon in large quantities, along with ores for ~Ceramics, and later perhaps metals.

But it may very well turn out that with better methods over time, water can be procured from asteroids or other sources. Water is a good one, it is a radiation shield, you can drink it, bathe in it, and boil it.

I think I will rest for a bit.

Done.

Last edited by Void (2019-07-11 11:37:28)

SpaceNut · 2019-07-11 20:33:23

The things that we could do with a slightly used heat shield seems to come to mind with your posts Void so as to turn them into a solar concentrator if the ship (BFR) is never going to return home.

The pica parts could be cut and reshaped into a focal point for such a device. Coat the surface with anything to produce as shiny as you need to reflect the solar. Sort of reminds me of the helistatic furnace hot salts which you have meantioned quite often sp as tpo create power.

I agree that if its not going to return home that we do reuse the engines, tanks and anything else for other purposes....

Void · 2019-07-12 09:01:18

I think that your version is an expansion of options.

I do believe that there will need to be a transition from interplanetary Starship, to bulk automated shipments with efficiency as a goal, to in situ self sufficiency. Self Sufficiency as a goal for abilities if necessary, but probably a continuing commerce adjacent to the potential of self sufficiency. I think that over time, the costs of shipments will continue down in general, and the capabilities will expand, so to make a determined effort to be completely self sufficient without reasonable cause, is not a primary objective.

I brought in the two sources for materials for Heat Shields/Repurposed Objects, as I think it would be an early way to gain from the materials of the Moon. I think as a trial balloon, to propose that sintered blocks of Moon materials could be lifted by chemical propulsion, to a location suitable for processing by electron beams and their associated methods.

In processing such materials, concerns may be the shedding of collision objects, and the loss of Oxygen produced. I presume a location selected, would be factored from multiple reasons. For now, lets suppose the notion of L1, but some Lunar or Earth orbit might do. In order to contain shed materials, collision objects and the presumed produced Oxygen, I think that a very low pressure containment shell would be useful. If an electron beam is to be produced, then solar methods could be mounted on it.

As my hope would be the mass production of objects including mirrors by vacuum deposition, I would expect that such mirrors could be included in a possible solar power method for the vacuum deposition process. And electrical power is not all that could be used. I spoke of sintered blocks. I think that they could be placed in a solar oven to be preheated, at the focus of a mirror. This should reduce the amount of energy needed to initiate the vaporized materials to do vacuum deposition, in the enclosure. I have had a look at simple Oxygen production methods just using heat, and then again you can get more complex by perhaps using Hydrogen which you would recycle as much as possible. But to keep it simple at least at first, I would suggest just heat, and hope somehow to deposit a layer of materials that can burn off, during entry to Mars, if the object constructed would be constructed to include aerobraking service.

Here is something, not quite my first choices, but potentials:
https://arc.aiaa.org/doi/abs/10.2514/3.48974
https://curator.jsc.nasa.gov/lunar/lnew … oxygen.htm
http://adsabs.harvard.edu/abs/2004cosp...35.2975S

In order to satisfy K.I.S.S. better, I would like to look at pyrolysis as a method. In this link it is suggested as possible without the resort to Hydrogen, Carbon, Sulphur, and so on. To use those chemicals might complicate the process more than would be needed.

On the surface of the Moon, the ore selected could be sintered into convenient shaped blocks of materials. This might release some Oxygen. I believe that some "Ores" are more suitable to release Oxygen from heat than others. Having a bit of released Oxygen on the Moon most likely would be useful.

In the method I am pondering, then these objects would be moved to an orbital processing facility, preheated by a solar oven, and bombarded also with an electron beam. In an enclosure, I presume Oxygen released could be collected by some means. Perhaps even as an ice, if you also have a location in the "Box" where the sun never shines. Electrical and Magnetic forces might help the condensation process. Oxygen is paramagnetic when cold.

In order to justify bringing sintered blocks up to an orbital location however, the solids should also be reformed to a useful purpose. The intention is to fabricate solid machine objects from metals and ceramics. Solid objects might be Mirror/Heat Shields, or, (We could hope),
linkable radiation protection materials, to expand the factory. Rather than resorting to something like bags of dirt, I would hope that these radiation protective devices would also be structurally valuable. Perhaps fitting together like puzzle pieces. It might be possible to "Weld" them together after assembly with again vacuum deposition.

While I have suggested Mirror/Heat Shields to fly to the surface of Mars with the assistance of other devices, I am hoping that propulsive navigation of the Earth/Moon system could be included in some device perhaps including Mirror/Heat Shields. Because I want to try out new things, I am going to hope that these devices will use Oxygen propulsion of some kind, and would like to see if any aerobraking with the Earth's atmosphere could be also incorporated.

I understand that Aero Maneuvering is a difficult thing to do. For Mars it has been done with a multiple dips, so it is not impossible.
A member has indicated that some use of magnetic heat shielding might need to be included, or some other method to "Throttle" and adjustment to atmospheric conditions. I actually am just finding an ~approximate potential for something that might be possible to master in the future.

Using Oxygen as a mono-propellant might be done by boiling, or actually I think casting out beads of solid Oxygen with a mass driver.
But if all else fails, then Starship of a modified variant might move Hydrogen to LEO, to be burned with Oxygen. Or of course water from the moon might be the monopropellant for a boiling system. At any rate discovering what method is best, and also achieving aerobraking abilities would allow these devices to navigate the Earth/Moon system and carry loads to where they would be wanted.

A similar device to transport Mirrors and materials to Mars might be a potential. In this case I would have no trouble seeing something like Starship boosting the device to high Earth orbit, where it would finish its mission to Mars as a robot. Obviously if the intent is to get the mirrors to the surface intact, then a chemical landing propulsion also needed at the end of the mission. However if the mirrors were composed of a scrap material desired, then perhaps a higher impact could be tolerated. I guess the object would need to be slowed down by "Any Means Necessary", and then let go to crash to the surface at a speed that would not vaporize it.

The mass production of Mirrors and associated machinery, then could satisfy needs many places, and the needs could justify the mass production efforts.

I do think it could be very useful to have such mirrors in LEO for various purposes. However I am not that much of a fan of power beamed to Earth. I really think that the Earths surface can provide energy needed and expanded energy potential with Shale Oil/Gas, Wind power, OTEC + Solar, ect. I think that orbital solar power production would make the most sense for powering orbital objects, perhaps with a growing population, in orbit.

So, I am really in all camps for space. The SpaceX plan, the Blue Origins plan, the protect the Earth plan + Other.

Done.

Last edited by Void (2019-07-12 10:00:35)

Void · 2019-07-12 11:07:41

Well, this seems promising, as it could indicate yet another method to get better solar cell efficiency for items proposed in the previous post.
https://phys.org/news/2019-07-carbon-na … nnels.html
Quote:

Carbon nanotube device channels heat into light
by Rice University
A scanning electron microscope image shows submicron-scale cavities patterned into films of aligned carbon nanotubes developed at Rice University. The cavities trap thermal photons and narrow their bandwidth, turning them into light that can then be recycled as electricity. Credit: Naik Lab/Rice University
The ever-more-humble carbon nanotube may be just the device to make solar panels—and anything else that loses energy through heat—far more efficient.
Rice University scientists are designing arrays of aligned single-wall carbon nanotubes to channel mid-infrared radiation (aka heat) and greatly raise the efficiency of solar energy systems.
Gururaj Naik and Junichiro Kono of Rice's Brown School of Engineering introduced their technology in ACS Photonics.
Their invention is a hyperbolic thermal emitter that can absorb intense heat that would otherwise be spewed into the atmosphere, squeeze it into a narrow bandwidth and emit it as light that can be turned into electricity.
The discovery rests on another by Kono's group in 2016 when it found a simple method to make highly aligned, wafer-scale films of closely packed nanotubes.
Discussions with Naik, who joined Rice in 2016, led the pair to see if the films could be used to direct "thermal photons."
"Thermal photons are just photons emitted from a hot body," Kono said. "If you look at something hot with an infrared camera, you see it glow. The camera is capturing these thermally excited photons."
Infrared radiation is a component of sunlight that delivers heat to the planet, but it's only a small part of the electromagnetic spectrum. "Any hot surface emits light as thermal radiation," Naik said. "The problem is that thermal radiation is broadband, while the conversion of light to electricity is efficient only if the emission is in a narrow band.
Rice University graduate student Xinwei Li, left, and postdoctoral researcher Weilu Gao used carbon nanotube films Gao helped develop to create a device to recycle waste heat. It could ultimately enhance solar cell output and increase the efficiency of industrial waste-heat recovery. Credit: Jeff Fitlow/Rice University
"The challenge was to squeeze broadband photons into a narrow band," he said.
The nanotube films presented an opportunity to isolate mid-infrared photons that would otherwise be wasted. "That's the motivation," Naik said. "A study by (co-lead author and Rice graduate student) Chloe Doiron found that about 20% of our industrial energy consumption is waste heat. That's about three years of electricity just for the state of Texas. That's a lot of energy being wasted.
"The most efficient way to turn heat into electricity now is to use turbines, and steam or some other liquid to drive them," he said. "They can give you nearly 50% conversion efficiency. Nothing else gets us close to that, but those systems are not easy to implement." Naik and his colleagues aim to simplify the task with a compact system that has no moving parts.
The aligned nanotube films are conduits that absorb waste heat and turn it into narrow-bandwidth photons. Because electrons in nanotubes can only travel in one direction, the aligned films are metallic in that direction while insulating in the perpendicular direction, an effect Naik called hyperbolic dispersion. Thermal photons can strike the film from any direction, but can only leave via one.
"Instead of going from heat directly to electricity, we go from heat to light to electricity," Naik said. "It seems like two stages would be more efficient than three, but here, that's not the case."
A Rice University simulation shows an array of cavities patterned into a film of aligned carbon nanotubes. When optimized, the film absorbs thermal photons and emits light in a narrow bandwidth that can be recycled as electricity. Credit: Chloe Doiron/Rice University
Naik said adding the emitters to standard solar cells could boost their efficiency from the current peak of about 22%. "By squeezing all the wasted thermal energy into a small spectral region, we can turn it into electricity very efficiently," he said. "The theoretical prediction is that we can get 80% efficiency."
Nanotube films suit the task because they stand up to temperatures as high as 1,700 degrees Celsius (3,092 degrees Fahrenheit). Naik's team built proof-of-concept devices that allowed them to operate at up to 700 C (1,292 F) and confirm their narrow-band output. To make them, the team patterned arrays of submicron-scale cavities into the chip-sized films.
"There's an array of such resonators, and each one of them emits thermal photons in just this narrow spectral window," Naik said. "We aim to collect them using a photovoltaic cell and convert it to energy, and show that we can do it with high efficiency."

Sounds like a great thing if it works out in real world processes.

Done

Last edited by Void (2019-07-12 11:08:43)

tahanson43206 · 2019-07-14 13:23:35

For void re #42

Thanks for providing the link in this post.

Because of your powers of imagination, combined with a respectable command of real world physics, chemistry and biology, I'm going to take a chance that you might appreciate a couple of speculative ideas. The first fits reasonably well with #42, and the second would be a better fit with some of the posts by JoshNH4H.

First ... the downpouring of fresh water by Hurricane Barry, in land locations which don't need it, combined with your post, inspired me to imagine there might be a way to pull thermal energy out of a mass of humid air before that mass reaches land fall. Water can be given thermal energy by shaking, using microwave waves to push and pull on the asymmetric magnetic field of water molecules. Water is often cooled by passing it near a cold metal surface, which itself has been cooled by gas. The heat collected by the gas is then transferred to another location, where it is given off to a receiving medium, usually gas but often liquid.

In the scenario I am imagining, and which I hope you will expand upon, the energy in water molecules would be (somehow) absorbed electronically, and that energy would be (somehow) conveyed to electric form where it could be stored (somehow) .

***
the second idea is more in line with some of JoshNH4H writings, but you might have fun with it.

In a recent issue of Analog, John Cramer (physicist) wrote about a dispute in physics. I've forgotten the details, but I do remember that one of the significant elements of the resolution was the observation that the mass of a proton is due to the relativistic bouncing of three quarks inside the bounds of the proton. I assume something similar is happening inside neutrons, but I don't recall if that came up.

At any rate, this discussion led me to wonder if an anti-matter shield might work effectively to block radiation in space. Nevermind the difficulty of creating such a field. For this post, I am inviting consideration of what the practical results might be of galactic radiation (in particular) interacting with a shield of anti-matter.

(th)

SpaceNut · 2019-07-14 14:34:42

Off topic:

Multiple posts that are not on the topic helps no one to collectively have all the details of developement or of discusion as to what we are missing for a mission. Also breaking these out as new topics will not help either as it just creates more off topic discusions that benefits no one.
Having all of the topic items for solar in a discusion is the normal way to create data for missions. Blending them into not a mission discusion means we lose the content...of what makes the best solar to bring.

Rant finished and it does not excuse it

Since its not about the heat of aerobreaking which is the use of a heat shield.....

Just going to give all the solar topics a bump.

Void · 2019-07-15 12:09:37

Very interesting thinking (th), however, I must respect the moderators guidance here. But I will be a bit of a turd, and rough that one up just a bit.

Spacenut said:

Off topic:
Multiple posts that are not on the topic helps no one to collectively have all the details of developement or of discusion as to what we are missing for a mission. Also breaking these out as new topics will not help either as it just creates more off topic discusions that benefits no one.
Having all of the topic items for solar in a discusion is the normal way to create data for missions. Blending them into not a mission discusion means we lose the content...of what makes the best solar to bring.
Rant finished and it does not excuse it
Since its not about the heat of aerobreaking which is the use of a heat shield.....
Just going to give all the solar topics a bump.

I appreciate that we need to have pruning, we don't want our conversations to turn into tumors. Such would not allow focus on chances of useful achievement. So, you have the responsibility to do what you do, and I support it. Yet, if dealing with the problems of space travel, it is mostly about moving mass around, and also when arriving, surviving. If too limited, then we cannot get the most out of the mass that we do move and appropriate.

It is a real problem. You have also requested/required that no new topic be generated for this. And yet silly things like the "Transformer" movies, indicate to me that in the collective subconscious, the notion of turning a robot into a car and back again, is an emerging fiction.

Being a fiction, is not bad, unless you let it interfere with proper process to achievements needed and wanted. So, a double edged sword as usual.

How is this to be handled? Is it to be handled?

Done.

Last edited by Void (2019-07-15 12:19:34)

SpaceNut · 2019-07-15 16:44:32

elderflower wrote:

Thank you GW. It seems rather low, much lower than I expected.

That is to make use of the thicker atmospher to slow the vehicle down. Which is the surface area and attack angle part of the equation GW spoke of. Since we are at speed and with thick part of the atmosphere which will generate heat from the airs friction to the surface of the incoming vehicle.

Void · 2019-07-15 20:53:45

Words are going to happen. I am not done. Show me where I may finish what I was working on please.

Mars_B4_Moon · 2023-11-28 06:46:48

Aerocapture is a Free Lunch in Space Exploration
https://www.universetoday.com/164482/ae … ploration/

When spacecraft return to Earth, they don’t need to shed all their velocity by firing retro-rockets. Instead, they use the atmosphere as a brake to slow down for a soft landing. Every planet in the Solar System except Mercury has enough of an atmosphere to allow aerobraking maneuvers, and could allow high-speed exploration missions. A new paper looks at the different worlds and how a spacecraft must fly to take advantage of this “free lunch” to slow down at the destination.
Aerocapture is an orbital transfer maneuver in which a spacecraft makes a single pass through a planetary atmosphere to decelerate and achieve orbit insertion. On the other hand, aerobraking uses a propulsive burn plus repeated dips into the atmosphere – i.e., atmospheric drag — to gradually slow the spacecraft and reduce the size of the orbit to achieve orbit insertion.
The new paper, by Athul Pradeepkumar Girija from the School of Aeronautics and Astronautics at Purdue University, notes that one of the significant risks associated with aerocapture is the uncertainty in the atmospheric density. While aerobraking takes place in the tenuous upper atmosphere of a planetary body where the density uncertainties are much larger, aerocapture occurs in the deeper atmosphere where the density uncertainties are smaller. For example, the atmospheric density that the Mars Reconnaissaince Oribter MRO actually experienced when aerobraking for its orbital insertion in 2006 was much different than what was predicted by a NASA model called GRAM (Global Reference Atmospheric Model) for Mars.

GW Johnson · 2023-11-28 11:21:45

When I run an entry with my spreadsheet (of 1953 methods), the peak deceleration gees and peak heating occur fairly deep into the atmosphere. Even for Earth, it is a bit more than halfway down from entry interface altitude, around 50-60 km. For Mars, it is even lower. Very much lower, like 20 km altitude or thereabouts. Or even lower.

If you don't reach the lower levels like that, you get very little in the way of speed reduction. But, if you reach the lower levels for great speed reduction, you also get large aero-heating effects. They do not occur at the same point, but they do occur quite close together in time. And you incur peak heating just BEFORE you incur peak deceleration gees! You WILL get very hot, if you decelerate significantly!

When approaching a planet from an interplanetary trajectory, the difference in orbital speeds gets changed by the 3-body interaction: your speed will be higher at entry interface altitude because of the gravity of the planet. You will be approaching the edge of its atmosphere substantially faster than its escape speed. If you are going to capture by aerobraking, you have only one shot at it: get from above to well below escape speed in one pass! I say "well below", because if you are "just below", your capture ellipse will have way too long a period!

Another thing for enthusiasts of fabric or inflatable heat shields to worry about is this: what makes you think that those materials can be used more than once? The NASA tests are all 1-use items. At entry peak heating temperatures, even carbon fabrics ablate, and there is always heat-induced embrittlement. Every time you do an aerobrake operation, you will very likely need a brand new heat shield!

GW

Last edited by GW Johnson (2023-11-29 10:53:59)

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#26 2018-09-15 03:52:53

Re: Heat on aerobreak.

#27 2018-09-15 08:26:33

Re: Heat on aerobreak.

#28 2018-09-15 09:12:02

Re: Heat on aerobreak.

#29 2018-09-16 03:05:08

Re: Heat on aerobreak.

#30 2018-09-16 10:51:12

Re: Heat on aerobreak.

#31 2018-09-16 17:56:20

Re: Heat on aerobreak.

#32 2018-09-16 19:41:40

Re: Heat on aerobreak.

#33 2018-09-17 09:12:20

Re: Heat on aerobreak.

#34 2019-06-19 12:58:26

Re: Heat on aerobreak.

#35 2019-06-19 16:05:46

Re: Heat on aerobreak.

#36 2019-07-10 11:37:10

Re: Heat on aerobreak.

#37 2019-07-10 17:09:02

Re: Heat on aerobreak.

#38 2019-07-10 20:51:11

Re: Heat on aerobreak.

#39 2019-07-11 11:16:29

Re: Heat on aerobreak.

#40 2019-07-11 20:33:23

Re: Heat on aerobreak.

#41 2019-07-12 09:01:18

Re: Heat on aerobreak.

#42 2019-07-12 11:07:41

Re: Heat on aerobreak.

#43 2019-07-14 13:23:35

Re: Heat on aerobreak.

#44 2019-07-14 14:34:42

Re: Heat on aerobreak.

#45 2019-07-15 12:09:37

Re: Heat on aerobreak.

#46 2019-07-15 16:44:32

Re: Heat on aerobreak.

#47 2019-07-15 20:53:45

Re: Heat on aerobreak.

#48 2023-11-28 06:46:48

Re: Heat on aerobreak.

#49 2023-11-28 11:21:45

Re: Heat on aerobreak.

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