Space X tests re-entry material

By Phil Plait | February 24, 2009 2:00 pm

This picture is very cool. And very pretty!

Space X tests the PICA-X material

That’s a test of the PICA-X (Phenolic Impregnated Carbon Ablator) material, a variant of the material NASA uses on its heat shields to protect astronauts during re-entry. It was developed by the private company Space X to use on their Dragon capsule, which will ferry materials and astronauts into space. In the pictures, it’s being blasted by a very hot (up to 1850 C) arc jet at the NASA Ames Research Center.

When the Dragon capsule re-enters, it will violently compress the air in front of it. A compressed gas heats up, and that’s why materials coming back from space must be protected. PICA (originally developed by NASA) actually heats up, melts, and blows away (ablates), taking the heat with it. Enough material is coated on the windward surface to make sure it lasts through the whole process. In a sense, it’s like sweating, but on a somewhat grander and scarier scale.

Dragon is slated to launch sometime this year on a Falcon 9 rocket. Space X has not yet launched a Falcon 9, but plans on doing so soon.

Image courtesy Space X.


Comments (36)

  1. Nothing malicious against NASA but: Space X, kick those bureaucrats where it hurts and knock them to the side of the road! *cheers*

    While there are many good and noble functions to be performed by government agencies, we really NEED a successful and viable commercial industry in space if any vision of a human future in space is to be realized. I am rooting and cheering for these guys all the time.

  2. Try adding some silica microballoons (thermal insulator) or powdered silica gel. A very thin layer of molten silicate smears across the char, protecting it from oxidation but not inhibiting its radiative cooling. Ordinary glass belches sodum oxide, seeding the plasma with sodiumD-line emission.

  3. Try adding some silica microballoons (thermal insulator) or powdered silica gel.

    Bad idea. Someone would eat it.

  4. Didn’t some country use plywood as an ablative material on a re-entry vehicle?

  5. Patrick
  6. Larian, Space X gets quite a bit of money from NASA, as part of the COTS program. I’ve blogged about it before. They love NASA, and use their launch facilities too.

  7. GregInVancouver

    Funnily enough I was just browsing through SpaceX’s site to see what they were up to in wake of the OCO failure. Coming along nicely it would seem.

    They have a really great gallery of videos that show you various test runs of engines, ablation materials, stage and fairing separation, etc.

    The sound of a turbopump spooling up has to to be heard to be believed. Kind of like:

    “Atomic batteries to power, turbines to speed”


  8. Melts adn blows away? Man that’s something you’d want to get the right amount of on the first try.

  9. You think that using plywood is something, check out this article:

    (Yes, The Onion)


    So, we’ve had straw and wood, do we make the next system out of bricks?


  10. hale_bopp

    One of my prized possessions is an old Space Shuttle tile. NASA had a program where they would give them (excuse me, loan them for 99 years) to teachers. It is amazing material. The Shuttle tiles are not an ablative material as the test shown here.

  11. I know Dr. Plait, I was being a sort of “hyper” cheerleader for them. Eventually I’d like to see Space X and the like get to the point where they are perfectly viable without having to rely on NASA and the government. A sort of cultural revolution in the US where rocket scientists are sexy. Engineers are respected. Yeah, I know, maybe I’m living in a dream world.

  12. David

    Maybe thinking of the ablative impregnated-oak nose cap heat shield used on the Chinese FSW re-entry vehicles? I like the DX Clipper approach, tail down with a low-power engine burn. The exhaust gases are much cooler than the heat of re-entry.

  13. Go SpaceX

    Should Intern at NASA or SpaceX? (:

  14. Depending on how much dv you need for that manuver it may cost more in fuel weight than the savings in dry weight by not having to don a heatshield. Can that approach really work David? Is that what Blue Origin is going to do with the New Shepard vehicle?

  15. Shoeshine Boy

    I know that the BA has little control over the ads that appear on his blog, and someone has probably pointed this out already, but the Earth is rotating the wrong way in the banner ad for the 3D Earth Screen Saver.


    PS: Nice, simple explanation of how ablative materials work, Phil.

  16. @John Paradox…
    I saw that earlier, and, while I did laugh, I thought maybe the timing was a little off, seeing that there have been 3 disasters (Apollo 1 fire, Challenger in ’86, and Columbia in ’03) all around this time of the year. Don’t get me wrong, I love the Onion, but I think this one, mentioning American and Russian astronauts being killed was possibly over the line… Then again, maybe that’s just me.

  17. I am really beginning to wonder if we are ever going to see major advances in space exploration without turning to nuclear power. I know, it’s a dirty word, but, unless we come up with another technological breakthrough, it will have to be addressed again at some point. Back in the ’50′s and ’60′s NASA did consider another project Orion, that would have seen a massive vehicle detonate Nuclear bombs to power it.

  18. @Larian LeQuella said: “Eventually I’d like to see Space X and the like get to the point where they are perfectly viable without having to rely on NASA and the government.”

    Not sure what your point is — SpaceX already is perfectly viable by itself. The COTS program Phil referred to in his response is “an effort by NASA to stimulate, and then take advantage of, a robust commercial market for spaceflight services” (NASA website quote). Elon Musk would probably have done SpaceX even without NASA’s assistance. He saw a business need and devised a way to fill it, something he is quite good at.

    There is no conflict with NASA (your first post) or dependency on NASA (your second post). I recommend reading more background at the SpaceX website and at the NASA Commercial Crew and Cargo site.

  19. IVAN3MAN

    Michael L:

    Back in the ’50’s and ’60’s NASA did consider another project Orion, that would have seen a massive vehicle detonate Nuclear bombs to power it.

    Factual trivia from Wikipedia — Operation Plumbbob:

    According to an urban legend, a manhole cover was accidentally launched from its shaft during an underground nuclear test in the 1950s, at great enough speed to achieve escape velocity. The myth is based on a real incident during the Pascal-B nuclear test, where a heavy (900 kg) steel plate cap (a piece of armor plate) was blasted off the top of a test shaft at an unknown speed, and it appeared as a blur in a single frame of a movie of the test. The plate was never recovered. A calculation before the event gave a predicted speed of 6 times the Earth’s escape velocity, but the calculation is unlikely to have been accurate and they did not believe that it would leave the Earth in reality. After the event, Dr. Robert R. Brownlee described the best estimate of the cover’s speed from the photographic evidence as “going like a bat!!”

    This incident was reputedly used as part of the technical justification for the Orion project for possible use of nuclear blasts for outer-space propulsion.

  20. Valis

    I remember reading back in the 70s about NASA having a program to develop nuclear powered rocket engines. It was called MINERVA, if I remember correctly. Don’t know what ever became of it, maybe somone on here has some information about it?

  21. What’s with this element 115? Ununpendium?

  22. steve

    speaking of reentry, did anyone see the sky over san francisco tonight?

    i did, i took a picture, but i can’t upload it til the 4th. i’m on vacation to my old and the BAs old stomping grounds, Santa Rosa, CA. I went down to the Haight, and saw something over the sky to the west about sunset. it looked like a reentry contrail to me, but the better description is a cloud with a dark border going about 40 degrees against the direction of the rest of the clouds, making it look like it was going toward the earth. I can have a picture when i get back to jersey

    am i the only one who saw this? any clue what it was?

  23. Nigel Depledge

    The BA said:

    In a sense, it’s like sweating, but on a somewhat grander and scarier scale

    Except in the sense of being correct.

    Sweating cools the skin by a phase change (liquid water evaporates, which is an endothermic process, the amount of energy taken away from the skin determined by delta-H0vap), leaving the skin entirely intact. What leaves is water vapour alone, and the process by which it cools is to conduct heat out of the skin during evaporation.

    Ablation is wholly different. Based on your description here, the ablative material heats up but, being a poor conductor of heat, heats only at the surface. Thus a steep temperature gradient is present within the material itself. The hottest material (i.e. a very thin layer at the surface) melts and falls away, taking with it the heat energy that it possesses. It does not in the process remove any heat energy from the material beneath which, as it becomes exposed to the hot compressed gas, will also heat up and, in turn, melt.

    Thus, sweating is a process by which a surface (the skin) is genuinely cooled down. An ablative heat shield does not cool anything down – instead, it forms an effective barrier that does not permit the capsule behind it to heat up. So I think your parallel is not a valid one.

  24. This article has been added to the Astronomy Link List.

  25. “a variant of the material NASA uses on its heat shields to protect astronauts during re-entry”

    Phil, it’s not a “variant” of the material, the Shuttle uses a different material with different properties. This particular material is a variant on the Stardust capsule heat shield material. It’s also the kind of material to be used on the Orion capsule. Other than that, it hasn’t been used before.

  26. I think the pancakes I made this morning would also act as a good heat shield material, aside from being far too heavy.

  27. JoeSmithCA Says: “Didn’t some country use plywood as an ablative material on a re-entry vehicle?”

    I don’t know of any vehicles, US or foreign, that used it operationally, although I’m sure it was tried early on.

    One place that plywood has been used extensively is in the nose faring of every FBM (Fleet Ballistic Missile) deployed by the Navy. From the Polaris A3 to the current Trident D5 they all have fairings made of Sitka Spruce. Some admirals worried that the other services would make fun of their “rockets with wooden nosecones” but no other material had the same combination of, weight, water resistance, RF transparency and strength against hydro and aero loads.

    - Jack

  28. Michael L Says: “Back in the ’50’s and ’60’s NASA did consider another project Orion, that would have seen a massive vehicle detonate Nuclear bombs to power it.”

    Orion was not a NASA project. It was a private study by General Atomic in San Diego that was funded mostly by the Air Force. The thing that killed it, outside of the radiation contamination to the Earth’s surface,* was the nuclear test ban treaty with the Soviets, which went into effect just as the program was about to starttesting with actual nuclear devices.

    NASA didn’t want anything to do with Orion since they thought it would divert money from its own project Rover with the Kiwi reactor, which was a straight thermal exchange.

    There will be a chapter on Orion in Volume 2 of “Spaceship Handbook.”

    - Jack

    * Freeman Dyson was one of the project scientists on Orion and towards the end he calculated that even if you started the nuclear phase of operations in orbit, any ionized particles (which is to say most of them) will spiral down the Earth’s magnetic field lines and reach the surface. Not good.

  29. IVAN3MAN relates Factual trivia from Wikipedia: “during the Pascal-B nuclear test…a heavy (900 kg) steel plate cap was blasted off the top of a test shaft at an unknown speed, and it appeared as a blur in a single frame of a movie of the test. A calculation before the event gave a predicted speed of 6 times the Earth’s escape velocity…”

    While I’m sure that happened, any piece of steel moving that fast in the lower atmosphere would certainly reduce itself to an inverse meteor and leave an incandescent trail as it left the planet. Very likely nothing would have remained to ultimately leave.

    It should be mentioned that one of the inspirations for project Orion came from a musing by Stanislaw Ulam, one of the mathematicians on the Manhattan Project. After watching one of the early tests (it might have been Trinity) he thought that even a small amount of that energy, focused in one direction, could put something into orbit without all of the fuss and bother of rockets. He even got permission to do some informal tests using graphite spheres with some crude instruments inside, hung off of the bomb tower. No only did they survive, but they were found further away than expected with one side ablated away, proving that the ablating material provided some thrust to the sphere as it flew away.

    The Orion people had a saying, “while other Air Force projects are using spacecraft (rockets) to deliver nuclear bombs, we’re using bombs to deliver spacecraft!”

    - Jack

  30. Dennis

    Long time reader Phil and I must first say how much I admire your stance on critical thinking and all of your efforts to promote it in the world.

    Now I’m going to ask a question that will no doubt make me stupid, especially in the light of a couple of science degrees, but I’ll start my excuses by noting that I don’t claim to be any sort of physicist… :-) At worst my first comment might give someone some laughs!

    Anyway, the stuff in this blog about the heat shield material tests and your explanation of the violent compression of gases during reentry reminded me of something that occured to me the first time I heard that, namely: if the heat of reentry is caused by this violent compression rather than friction (as most people generally and I gather wrongly assume), why are reentry vehicles not made as streamlined as possible to minimise such compression?

    I guess there’s a simple explanation for this. Is it perhaps that the concentrated heating effect of compression at the tip of any streamlined shape would be even more perilous to the craft, or somesuch? I’m sure you or someone else far more knowledgable than I in this area will be able to put me straight!

    Keep up the good work!


  31. Dennis: That’s an engineering question, not a science one!

    It’s also an excellent question. You’ve got to remember what the goal of the system is, i.e. to not only have the craft survive reentry, but to slow it down so that it doesn’t land at multi-mach speeds. Since the source of all the energy that is causing the compressive heating is the kinetic energy of the craft, generating lots of heat (and sending it away from the craft through ablation) is a really good way to slow it down.

    A needle nose craft would be able to slip through the atmosphere with minimal heating, but it wouldn’t slow down much. Entry bodies with bombs in them (warheads) are usually cone shaped for this reason. The faster they go, the less their accuracy is disturbed by the thick lower atmosphere (I don’t know about other systems, but a Trident Mk 4 warhead hits the ground at about Mach 8).

    Another consideration is the payload. Non-human devices can be hardened against high decelerations (that Mk 4 body is decelerating at about 300 g’s at impact), but humans max out their tolerance at about 10 g’s for an extended exposure. A blunt body starts building up drag very early so burns off speed over a much longer period, limiting the maximum deceleration rate.

    The space shuttle takes a different approach. Since it has wings, it generates lift thus can fly in and spread the reentry heating out over a longer period. The wings also vastly increase the surface area, spreading the heating over a larger area which keeps the heat per unit area down (although the leading edges of the wings, tail and nose get pretty toasty).

    - Jack

  32. Jay

    Pica is and always was a poor choice, structuraly unsound, parasitic to the airframe, ineffecient as the carbon blows away and dosent stay put and ablate as required in a good carbon heatshield. Face it it’s furnace insulation dipped in phenolic resin was tried by Avco ~ 30 years ago and found to be uninteresting as a TPS material.

    For manned craft Jack is correct you go blunt or glide. TPS for Bombs are an other matter best left off the table


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