Adept

SpaceNut · 2016-01-07 21:28:53

We have been talking for quite sometime now about how to get large down mass to mars surface and that the way forward is by making the heatshield larger....

Nasa is working on a couple of technologies that would make it possible for a much larger mass than the rovers to be able to land safely on the surface.

NASA Completes Heat Shield Testing for Future Mars Vehicles

Space Technology Game Changing Development Adaptable Deployable Entry and Placement Technology

MECHANICALLY-DEPLOYED HYPERSONIC DECELERATOR AND CONFORMAL ABLATOR TECHNOLOGIES FOR MARS MISSIONS

Adaptive Deployable Entry and Placement Technology

Adaptable Deployable Entry & Placement Technology (ADEPT) for Cubesat delivery to Mars Surface

SpaceNut · 2016-01-24 20:59:50

We keep running into what can we get to the surface of mars in large chunks with this developing technology being trumpeted as the solution to the problem. The testing was 7 October 2015.

The ADEPT project is led by NASA’s Ames Research Center.

Progress in Payload Separation Risk Mitigation for a Deployable Venus Heat Shield

https://www.technology.org/2015/10/07/n … -vehicles/

ADEPT is a mechanically-deployable heat shield concept using carbon fabric: a flexible heat shield that expands to “open” like an umbrella. Recently, Ames’ engineers successfully completed heating simulation testing of an ADEPT model under conditions akin to entering the Martian atmosphere. Surface temperatures on the test article reached 3,100 degrees Fahrenheit or 1,704 degrees Celsius. The bluish-hue streaks, streaming away from the test article, are due to the decomposition of the resin-infused protective layers that prevent degradation of the stitched fabric joints.

I can see the usefulness of a large heatshield for venus as it would allow for more time in the atmosphere for testing and other research....

GW Johnson · 2016-01-25 10:49:46

This and the inflatable technology share essential features. Either makes a very good 1-shot solution, in my opinion.

Adept uses mechanical arms to deploy a flexible bluff body shape, while the inflatables use inflatable back structures to deploy a flexible bluff body shape. Both have protective substances embedded onto or into the fabric to protect it before and during entry; this stuff burns away, so you cannot fly this technology more than once, as it is now.

But it is remarkable.

Until these two technologies mature more, if you want to fly your vehicle more than once, then you have to go back to the non-extendible heat shield concepts. On Mars, this demands retropropulsion if your vehicle masses over about a ton or so at entry. Especially if you land anywhere besides the lowlands.

So for one-way deliveries, adept and inflatables look great. If you want to build a reusable lander, they do not. Not yet. Maybe they will in the future, but not yet.

I'd be very careful proposing aerocapture at both ends of a journey with either of these extendible technologies. Like I said, it's 1-shot. You'll need two of them.

GW

RobertDyck · 2016-01-25 11:46:15

It burns away? Oh. That's not good. I had envisioned this for aerocapture of a reusable spacecraft. Both aerocapture into Mars orbit, and Earth. On Mars, the spacecraft would remain parked in highly elliptical, high Mars orbit. So just barely out of the atmosphere at periapsis, and at apoapsis it would be so far it would barely be in Mars orbit at all. I got that idea from a presentation by Gary Fischer at a Mars Society convention. It minimizes propellant required to depart Mars orbit. But for Earth orbit, the craft would have to repeatedly aerobrake to drop into low orbit so it could rendezvous with ISS. This means using the heat shield multiple times. I got the idea of a deployable heat shield from Mars Direct, but had originally thought to use the same fabric as DurAFRSI: Durable Advanced Flexible Reusable Surface Insulation. That's the advanced thermal blanked developed by NASA's Ames Research Center. That fabric is Nextel 440. GW and I have discussed this several times on this forum. Then I read about ADEPT, and thought that would be even better. NASA is already working on it, so let's use it. Turns out ADEPT is exactly what Robert Zubrin and his partner read about when they devised Mars Direct. But if the carbon fibre fabric burns off, then it's not reusable. Perhaps Nextel 440 is better. Besides, my application is for aerocapture and aerobraking only, so the heat load isn't as great as actual atmospheric entry.

My mission architecture has a reusable ITV, but the lander will not lift off. That means the heat shield for atmospheric entry could be use-once. So ADEPT could be used for that. But if GW is right, that carbon fibre burns off, then the heat shield for aerocapture would have to be different.

SpaceNut · 2016-01-25 17:59:26

A space walk to replace the fabric on the returning adept could be done if we bring an extra on the ITV proposal for aerobraking into Earth orbit. Or we take along another heat shield that can be assembled in mars orbit that can tolerate the multiple entries as it tries to slow into earth orbit.

GW Johnson · 2016-01-25 19:05:44

I didn't say the fabric burned, I tried to say its coatings burned. Look at the color picture in post #2 above. Then look at the quoted caption just above the picture. The bluish fire is the coatings burning away. Just like it says.

It means you cannot reuse that fabric until you recoat it. So, it might be more effective just to replace it, I don't know.

Alumino-silicate fabrics like Nextrel 312 and 440 have been used for decades as fire curtain cloth in engine nacelles. That's a one shot application. For reuse, you cannot exceed the phase change temperature where embrittlement happens. That's somewhere near 2000-2200 F. Exceed that, and your flexible fabric suddenly becomes as fragile as an old gasoline lantern mantle. It'll crumble away if you just look at it too hard.

The Nextel stuff is white or not far from it, so its emissivity is crudely 20%. That's not anywhere near the radiation cooling needed to hold fabric temperature under 2000 F when the oncoming gas stream is so very much hotter. A crude rule of thumb says that with high-hypersonic ionization, the gas stream effective total temperature in deg K is numerically the same as its speed in meters/sec. Another crude rule of thumb says that's your stagnation-zone surface temperature, too, if there's no other cooling going on.

Carbon fiber does not suffer from embrittlement, but it does oxidize away or sublime away, once its temperature gets white-hot. That's around 4000 F (2000 K). Happens at crudely 4000 m/s = 4 km/s speeds. Depending upon what you expect it to do for you, it could easily be a one-shot material.

There's nothing magic about this stuff, it's just standard materials properties and behaviors known for a few decades now.

Carbon fiber is not much different from low-density graphite, just a different physical form. If it doesn't fast-oxidize sooner, it will sublime away by just over 4000 F. No way around that.

3M has several Nextel fabrics, but they're one or another version of doped alumino-silicate. Every one of them shares the same phase change embrittlement temperature near 2000 F, and every one of them melts at around 3250 F. Only the hot mechanical strength properties differ.

GW

SpaceNut · 2016-01-25 20:38:25

I heard of gel's that are used in welding that resist heat causing damage to surounding areas that could be effected by the heat of welding...

Something like these

http://www.google.com/patents/US20140124176

http://www.kgcoatings.com/products/protective-coatings

RobertDyck · 2016-01-25 22:35:10

Ok. That's a lot of great technical info. Mars Global Surveyor was able to use its solar arrays for aerobraking, so obviously that didn't generate much heat. I want to aerocapture, barely slowing enough to enter Mars orbit. At Earth, I want to aerocapture again, then aerobrake with multiple passes down to ISS. I imagine aerobraking at Earth is more complicated, to ensure you don't collide with a satellite. Could the carbon stuff do that without degradation: oxidation, sublimation, or embrittlement?

GW Johnson · 2016-01-26 10:58:23

I don't know how to figure aeroheating in free-molecule flow like aerocapture. There's more KE feed into ionization than internal energy at orbital speeds. That's why the effective temperature in deg K is roughly numerically the speed in m/s.

I do know that in continuum flow conditions, the heat transfer film coefficient is quite low due to the low density. So, in spite of what can be very large temperature differences stream to surface, the actual quantity of heat delivered to a unit area per unit time is lower than you might think. With radiation cooling available to space, you can perhaps establish an equilibrium surface temperature that is acceptable.

That energy balance is beyond what I can estimate for myself, because I don't know how to evaluate the convective heating at aerocapture speeds in such a rarefied environment, whether at Mars or here. But somebody at NASA (or more likely its contractors) does. That balance is how they survive the aerocapture maneuvers that they have done so far.

I wouldn't give up just yet on using adept or the inflatables for repeated aerocapture maneuvers. The limiting factor will be how much radiation cooling one can get, and may be more limited by coating loss than carbon burnup or sublimation. My unsupported hunch is that service life will be short, but not just one-shot. Unless you try to "overdo" it, by attempting too much drag deceleration in one pass.

GW

Last edited by GW Johnson (2016-01-26 11:01:00)

SpaceNut · 2016-01-26 21:52:05

Ask and yea shall recieve "aerocapture heating profile for Mars"....

AEROCAPTURE DEMONSTRATION AND MARS MISSION APPLICATIONS

Mars Aerocapture Systems Study

This one is large
Physiologically Constrained Aerocapture for Manned Mars Missions

GW Johnson · 2016-01-28 10:27:45

Many thanks, Spacenut. I've downloaded both documents. I glanced through them both. It was enough to see that aerocapture heating loads at Mars resemble Earthly heating more than previous Mars probe experiences. I'm not sure, but that suggests we could test such things here, and expect decent results at Mars.

GW

SpaceNut · 2016-04-17 16:18:43

It appears to me that we can create an airframe under this out stretched fabric to make it glide down though the atmosphere all that is needed is evelons and a rudder and we have a lifting body plane in a small package...

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#1 2016-01-07 21:28:53

Adept

#2 2016-01-24 20:59:50

Re: Adept

#3 2016-01-25 10:49:46

Re: Adept

#4 2016-01-25 11:46:15

Re: Adept

#5 2016-01-25 17:59:26

Re: Adept

#6 2016-01-25 19:05:44

Re: Adept

#7 2016-01-25 20:38:25

Re: Adept

#8 2016-01-25 22:35:10

Re: Adept

#9 2016-01-26 10:58:23

Re: Adept

#10 2016-01-26 21:52:05

Re: Adept

#11 2016-01-28 10:27:45

Re: Adept

#12 2016-04-17 16:18:43

Re: Adept

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