Dragon v/s Orion

[DigitalMan]

Not really, no.  This morning I went to read up on the actual differences.  Reading the docs on PICA (I know SpaceX uses PICA-X, but the differences are not readily known nor obvious, so forced to use the source material for
....... <snip>
They're aiming for different needs.  Dragon is simpler, more direct.  Orion offers some added flexibility.  The two capsule shapes lend themselves to the same as well, with Orion's shape enabling more crossrange over Dragons, while Dragon offers more internal volume for the diameter.  They are different beasts.

since you're looking at worst case margin for Dragon, I would be curious to know what is the thickness and worst case ablation for Orion?

Dragon and its PICA-X has flown and they indicated it performed better than expected.   As more flights are done in the near term hopefully they will share more details.

[Downix]

Not really, no.  This morning I went to read up on the actual differences.  Reading the docs on PICA (I know SpaceX uses PICA-X, but the differences are not readily known nor obvious, so forced to use the source material for
....... <snip>
They're aiming for different needs.  Dragon is simpler, more direct.  Orion offers some added flexibility.  The two capsule shapes lend themselves to the same as well, with Orion's shape enabling more crossrange over Dragons, while Dragon offers more internal volume for the diameter.  They are different beasts.

since you're looking at worst case margin for Dragon, I would be curious to know what is the thickness and worst case ablation for Orion?

Dragon and its PICA-X has flown and they indicated it performed better than expected.   As more flights are done in the near term hopefully they will share more details.

I'd like to know as well, honestly.  I have the old Block I thickness, and I know the ablation rate depending on the particulars of re-entry, but with the changes in the past year it looks as if the heatshield thickness may have changed, so the numbers may no longer be accurate.  The figures I was given has it's thickness at ~12cm thick, pretty close to Apollo.

It is not as simple as Dragon's is to figure out, due to the fact that Orion is utilizing a sandwich for thermal protection. I'll include a diagram to help explain. The first layer is char layer of C, Si, O, Al, Ca and B.  This is ~6cm thick, and is designed to crack as it ablates.  This layer itself has three general zones, and becomes denser the further in you go.  The reason why is that underneath, sandwiched in the middle, you find a thin layer of a pyrolysis material that, when heated, releases a mixture of gaseous Nitrogen, Carbon, Hydrogen and Oxygen which acts as a buffer, in effect a second TPS. For the re-entry speeds we are discussing here, this gas is usually released ~60 seconds into re-entry.  Once this begins to release its gas, the gasses then take the brunt of the work for the next ~80 seconds.  Underneath this is the final layer, a honeycomb matrix made up of aluminum, novalac resin, and silica fiber, commonly called "Virgin."

The initial layer by itself, at these peak loads, ablates away at the rate of approximately 3.8/minute, making it comparable to PICA in this regards.  Add in, however, the other two layer, and you can see it is designed to take a far worse beating.

[Jkew]

This morning I went to read up on the actual differences.  Reading the docs on PICA (I know SpaceX uses PICA-X, but the differences are not readily known nor obvious, so forced to use the source material for reference) a particularly fast mars re-entry can use up to 6cm of ablation worst-case scenario.  Dragon has 8cm, so has a 2cm margin not accounting for any improvements to the formula.  Orion, on the other hand, uses a reformulated AVCOAT, which utilizes several techniques to reduce the rate of ablation along with enabling multiple ablation events.  Orion, in short, can skip across an atmosphere in order to improve crossrange.  Dragon's TPS is also lighter than Orions, at 270 kg/m^3 over 540 kg/m^3.  Orions TPS is also less fragile, and is a single piece as opposed to Dragons multi-tiled design.

They're aiming for different needs.  Dragon is simpler, more direct.  Orion offers some added flexibility.  The two capsule shapes lend themselves to the same as well, with Orion's shape enabling more crossrange over Dragons, while Dragon offers more internal volume for the diameter.  They are different beasts.

Do you have a reference for these sources? I'm curious how AVCOAT can permit multiple ablative scenarios while Pica can't.

[Downix]

This morning I went to read up on the actual differences.  Reading the docs on PICA (I know SpaceX uses PICA-X, but the differences are not readily known nor obvious, so forced to use the source material for reference) a particularly fast mars re-entry can use up to 6cm of ablation worst-case scenario.  Dragon has 8cm, so has a 2cm margin not accounting for any improvements to the formula.  Orion, on the other hand, uses a reformulated AVCOAT, which utilizes several techniques to reduce the rate of ablation along with enabling multiple ablation events.  Orion, in short, can skip across an atmosphere in order to improve crossrange.  Dragon's TPS is also lighter than Orions, at 270 kg/m^3 over 540 kg/m^3.  Orions TPS is also less fragile, and is a single piece as opposed to Dragons multi-tiled design.

They're aiming for different needs.  Dragon is simpler, more direct.  Orion offers some added flexibility.  The two capsule shapes lend themselves to the same as well, with Orion's shape enabling more crossrange over Dragons, while Dragon offers more internal volume for the diameter.  They are different beasts.

Do you have a reference for these sources? I'm curious how AVCOAT can permit multiple ablative scenarios while Pica can't.

http://www.planetaryprobe.eu/IPPW7/proceedings/IPPW7%20Proceedings/Abstracts/SessionP1/a499.pdf
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070014634_2007014732.pdf
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19740007423_1974007423.pdf
http://www2.aero.psu.edu/RGD_2010/PaperSubmission_Full_Uploads/Titov,%20Evgeny_219_PDF_revised.pdf
Gobs of information on the TPS systems, just grabbed the first few rather than fill the thread with too much.
And as I understand it, PICA is more fragile.  You could layer it over another TPS of course, but not something such as the pyrolysis material, for instance.
*edit* had to add one more, with the AVCOAT material breakdown.  I don't know if this is the exact Orion composition, but it is the composition I have data for.  So it, like PICA, needs to be weighed in accordingly.

[docmordrid]

PICA-X != PICA

Mueller said it exceeds legacy PICA in all regards, and is easier to manufacture. 

[Downix]

PICA-X != PICA

Mueller said it exceeds legacy PICA in all regards, and is easier to manufacture. 

As I said, for lack of more current documentation, have to use what there is.  I'd point out that Orion uses an updated AVCOAT as well over the legacy Apollo TPS.

That being said, we already established that even with the legacy PICA, Dragon already has a heat shield more than capable of a Mars return.  SpaceX says they've improved it, and I have every reason to believe them, which means well done!

[kkattula]

As a reference point, Dragon was designed to ablate up to 1cm of its 8cm thick PICA-X heatshield on a typical LEO re-entry.  Presumably actual ablation on the COTS-1 re-entry was significantly less.

A high speed (e.g. Mars Return) re-entry is a little less than twice the energy.

Dragon also can do lifting re-entries to reduce heating.

[Downix]

As a reference point, Dragon was designed to ablate up to 1cm of its 8cm thick PICA-X heatshield on a typical LEO re-entry.  Presumably actual ablation on the COTS-1 re-entry was significantly less.

A high speed (e.g. Mars Return) re-entry is a little less than twice the energy.

Dragon also can do lifting re-entries to reduce heating.

That would be a design that is 50% better than the original PICA, very welcome news indeed.

[baldusi]

Dragon's TPS is also lighter than Orions, at 270 kg/m^3 over 540 kg/m^3.

That would mean that the whole Dragon TPS is 0.83m³ [i.e (3.65m/2)^2*pi*0.08m]? So it would weight just 226kg? Doubling it shouldn't be that much of a weight penalty, would it? Not that it's necessary, just an hypothetical question.

[Downix]

Dragon's TPS is also lighter than Orions, at 270 kg/m^3 over 540 kg/m^3.

That would mean that the whole Dragon TPS is 0.83m³ [i.e (3.65m/2)^2*pi*0.08m]? So it would weight just 226kg? Doubling it shouldn't be that much of a weight penalty, would it? Not that it's necessary, just an hypothetical question.

No, but then you dive into the fragility.  PICA is not often used due to this issue, it cracks easily.  The thicker it is, the quicker it cracks.  ~8-10cm is typically the maximum thickness for this reason.

[MP99]

As a reference point, Dragon was designed to ablate up to 1cm of its 8cm thick PICA-X heatshield on a typical LEO re-entry.  Presumably actual ablation on the COTS-1 re-entry was significantly less.

A high speed (e.g. Mars Return) re-entry is a little less than twice the energy.

Dragon also can do lifting re-entries to reduce heating.

Elon Musk, 8th Dec 2010:-

This is the most advanced heat shield ever to fly. It is so powerful that it can potentially be used hundreds of times for Earth orbit re-entry with only minor degradation each time (like an extreme version of a Formula 1 car's carbon brake pads) and can even withstand the much higher heat of a moon or Mars velocity reentry. 

(My highlight)

cheers, Martin

[blazotron]

Not really, no.  This morning I went to read up on the actual differences.  Reading the docs on PICA (I know SpaceX uses PICA-X, but the differences are not readily known nor obvious, so forced to use the source material for
....... <snip>
They're aiming for different needs.  Dragon is simpler, more direct.  Orion offers some added flexibility.  The two capsule shapes lend themselves to the same as well, with Orion's shape enabling more crossrange over Dragons, while Dragon offers more internal volume for the diameter.  They are different beasts.

since you're looking at worst case margin for Dragon, I would be curious to know what is the thickness and worst case ablation for Orion?

Dragon and its PICA-X has flown and they indicated it performed better than expected.   As more flights are done in the near term hopefully they will share more details.

I'd like to know as well, honestly.  I have the old Block I thickness, and I know the ablation rate depending on the particulars of re-entry, but with the changes in the past year it looks as if the heatshield thickness may have changed, so the numbers may no longer be accurate.  The figures I was given has it's thickness at ~12cm thick, pretty close to Apollo.

It is not as simple as Dragon's is to figure out, due to the fact that Orion is utilizing a sandwich for thermal protection. I'll include a diagram to help explain. The first layer is char layer of C, Si, O, Al, Ca and B.  This is ~6cm thick, and is designed to crack as it ablates.  This layer itself has three general zones, and becomes denser the further in you go.  The reason why is that underneath, sandwiched in the middle, you find a thin layer of a pyrolysis material that, when heated, releases a mixture of gaseous Nitrogen, Carbon, Hydrogen and Oxygen which acts as a buffer, in effect a second TPS. For the re-entry speeds we are discussing here, this gas is usually released ~60 seconds into re-entry.  Once this begins to release its gas, the gasses then take the brunt of the work for the next ~80 seconds.  Underneath this is the final layer, a honeycomb matrix made up of aluminum, novalac resin, and silica fiber, commonly called "Virgin."

The initial layer by itself, at these peak loads, ablates away at the rate of approximately 3.8/minute, making it comparable to PICA in this regards.  Add in, however, the other two layer, and you can see it is designed to take a far worse beating.

I believe you have misunderstood the way ablators in general (and Avcoat in particular) perform.  The diagram you present actually shows the configuration of the Avcoat ablator once it has reached thermal steady state, not the initial composition.  The entire ablator starts as virgin (unblemished) ablator material, composed of novalac resin in a silica fiber honeycomb.  The pyrolysis and char layers are formed only as the virgin material breaks down due to the heat of reentry and progress through the virgin material as it ablates away.

Once the virgin material is exposed to the heat of reentry, it begins to pyrolize, which is the process where certain materials break down into gaseous products.  Once all of the volatiles pyrolize away from the surface, it is left with nothing but carbon, silica, alumina and other materials that have high vaporization points and burn off more slowly as they combine with oxygen or nitrogen from the incoming airstream.  This is the char layer.

At that point, additional heat entering the outer suface of the ablator travels into the surface of the char (burning off some of the char as it does so) and then into the underlying virgin material.  The heat causes the outermost layer of virgin material to pyrolize and release gas products that diffuse through the char.  This pyrolysis layer moves inward as more heat is added and the outer layer of the char burns away.  There is no distinct "pyrolysis material" in Avcoat: the pyrolysis zone is simply the region under the surface that has reached a temperature high enough to pyrolyze the virgin Avcoat. 

This is also the case with PICA and other ablators.  You will see a similar region of charred material and of virgin PICA material in Fig. 11 in this paper that you linked in a later post:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070014634_2007014732.pdf  The pyrolysis zone lies in a band between them. 

Figure 1 in this paper also has a good diagram of the structure of Avcoat after being heated.  The introductory paragraph describes the process in more detail.  http://www2.aero.psu.edu/RGD_2010/PaperSubmission_Full_Uploads/Titov,%20Evgeny_219_PDF_revised.pdf

[Downix]

Not really, no.  This morning I went to read up on the actual differences.  Reading the docs on PICA (I know SpaceX uses PICA-X, but the differences are not readily known nor obvious, so forced to use the source material for
....... <snip>
They're aiming for different needs.  Dragon is simpler, more direct.  Orion offers some added flexibility.  The two capsule shapes lend themselves to the same as well, with Orion's shape enabling more crossrange over Dragons, while Dragon offers more internal volume for the diameter.  They are different beasts.

since you're looking at worst case margin for Dragon, I would be curious to know what is the thickness and worst case ablation for Orion?

Dragon and its PICA-X has flown and they indicated it performed better than expected.   As more flights are done in the near term hopefully they will share more details.

I'd like to know as well, honestly.  I have the old Block I thickness, and I know the ablation rate depending on the particulars of re-entry, but with the changes in the past year it looks as if the heatshield thickness may have changed, so the numbers may no longer be accurate.  The figures I was given has it's thickness at ~12cm thick, pretty close to Apollo.

It is not as simple as Dragon's is to figure out, due to the fact that Orion is utilizing a sandwich for thermal protection. I'll include a diagram to help explain. The first layer is char layer of C, Si, O, Al, Ca and B.  This is ~6cm thick, and is designed to crack as it ablates.  This layer itself has three general zones, and becomes denser the further in you go.  The reason why is that underneath, sandwiched in the middle, you find a thin layer of a pyrolysis material that, when heated, releases a mixture of gaseous Nitrogen, Carbon, Hydrogen and Oxygen which acts as a buffer, in effect a second TPS. For the re-entry speeds we are discussing here, this gas is usually released ~60 seconds into re-entry.  Once this begins to release its gas, the gasses then take the brunt of the work for the next ~80 seconds.  Underneath this is the final layer, a honeycomb matrix made up of aluminum, novalac resin, and silica fiber, commonly called "Virgin."

The initial layer by itself, at these peak loads, ablates away at the rate of approximately 3.8/minute, making it comparable to PICA in this regards.  Add in, however, the other two layer, and you can see it is designed to take a far worse beating.

I believe you have misunderstood the way ablators in general (and Avcoat in particular) perform.  The diagram you present actually shows the configuration of the Avcoat ablator once it has reached thermal steady state, not the initial composition.  The entire ablator starts as virgin (unblemished) ablator material, composed of novalac resin in a silica fiber honeycomb.  The pyrolysis and char layers are formed only as the virgin material breaks down due to the heat of reentry and progress through the virgin material as it ablates away.

Once the virgin material is exposed to the heat of reentry, it begins to pyrolize, which is the process where certain materials break down into gaseous products.  Once all of the volatiles pyrolize away from the surface, it is left with nothing but carbon, silica, alumina and other materials that have high vaporization points and burn off more slowly as they combine with oxygen or nitrogen from the incoming airstream.  This is the char layer.

At that point, additional heat entering the outer suface of the ablator travels into the surface of the char (burning off some of the char as it does so) and then into the underlying virgin material.  The heat causes the outermost layer of virgin material to pyrolize and release gas products that diffuse through the char.  This pyrolysis layer moves inward as more heat is added and the outer layer of the char burns away.  There is no distinct "pyrolysis material" in Avcoat: the pyrolysis zone is simply the region under the surface that has reached a temperature high enough to pyrolyze the virgin Avcoat. 

This is also the case with PICA and other ablators.  You will see a similar region of charred material and of virgin PICA material in Fig. 11 in this paper that you linked in a later post:
http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070014634_2007014732.pdf  The pyrolysis zone lies in a band between them. 

Figure 1 in this paper also has a good diagram of the structure of Avcoat after being heated.  The introductory paragraph describes the process in more detail.  http://www2.aero.psu.edu/RGD_2010/PaperSubmission_Full_Uploads/Titov,%20Evgeny_219_PDF_revised.pdf

See, this is why I love this place, if I make a mistake (not being familiar with ablatives I made my best understanding of what I could find) someone comes along able to rectify the situation.

This does make sense, although now my curiosity as to why PICA over AVCOAT.

[hektor]

Another difference if the ESA/NASA discussions about MPCV/ATV reach an agreement will be that Dragon is fully US, while MPCV will have an international flavor.

[yg1968]

Could Dragon use ATV as a service module? What other changes would be needed for Dragon to become a BEO spacecraft?

Thanks in advance for your reply.

[Ben the Space Brit]

What other changes would be needed for Dragon to become a BEO spacecraft?

AFAIK, and this list should be treated as a 'bare minimum', not a comprehensive one.

1) A powerful, high-impulse MPS;
2) Better thermal and ionising radiation protection;
3) More life-support consumables;
4) Long-range communication system;
5) BEO navigation system.

At least three of these could be filled by replacing the trunk with a BEO service module.  However, it is considerably easier to type that than to do it.  In fact, although I suspect that the Dragon OML, the RCS/LAS groups and pressure hull would be broadly unchanged, just about everything else would need some level of modification.

[A_M_Swallow]

What other changes would be needed for Dragon to become a BEO spacecraft?

AFAIK, and this list should be treated as a 'bare minimum', not a comprehensive one.

1) A powerful, high-impulse MPS;
2) Better thermal and ionising radiation protection;
3) More life-support consumables;
4) Long-range communication system;
5) BEO navigation system.

At least three of these could be filled by replacing the trunk with a BEO service module.  However, it is considerably easier to type that than to do it.  In fact, although I suspect that the Dragon OML, the RCS/LAS groups and pressure hull would be broadly unchanged, just about everything else would need some level of modification.

I wonder how many of these enhancements are supplied by docking with a Bigelow BA-330?

[Moe Grills]

OK!   Over on another thread, they are discussing the viability
of using an European ATV converted into a CM for the Orion
capsule. doing away with (I suppose) the CM that NASA had
already designed for the Orion CSM.
  So that brings up an interesting option for those on this thread to discuss: Can an European ATV be modified/altered into a service module
for a (manrated) Dragon capsule?
   
It seems compelling, almost logical.
But then, which booster would you use (Ariane? Falcon 9 Heavy?)?
And what would be the destination for that combo Dragon(CM) + converted ATV(SM)? 

It's all still hypothetical of course.

[yg1968]

That's the same question that I asked above.

[snowintx]

Lockheed/NASA keeps trying to RAM Orion/Ares1 down our throats!!!! 

They try to trick us with cubic feet in Orion.  Cubic Feet does NOT matter when going to Mars in a return vehicle!  You have to have a separate vehicle like Bigelow Aerospace's space station module.  You don't want to be in any capsule for 280 days each way or the Astronauts will kill each other.  A couple of Dragons, Bigelow BA 330 module, and a MEM (Mars Exploration Vehicle).  We do NOT need a single lift like in SaturnV days.  We built ISS on several lifts, we can make a Mars vehicle with one Falcon9 heavy, and maybe 3 falcon9's.