Scroll down to read this post.


Please consider supporting my work here at Behind The Black by giving either a one-time contribution or a regular subscription, in any one of the following ways:


1. Zelle: This is the only internet method that charges no fees. All you have to do is use the Zelle link at your internet bank and give my name and email address (zimmerman at nasw dot org). What you donate is what I get.


2. Donate through Gabpay, using my email address zimmerman @ nasw dot org.

3. Patreon: Go to my website there and pick one of five monthly subscription amounts, or by making a one-time donation.

4. A Paypal Donation:

4. A Paypal subscription:

5. Donate by check, payable to Robert Zimmerman and mailed to
Behind The Black
c/o Robert Zimmerman
P.O.Box 1262
Cortaro, AZ 85652

Aerospike engine ready for ground tests

Capitalism in space: A demonstrator aerospike rocket engine being developed by ARCA Space is now ready [pdf] for ground tests.

The system will perform a series of ground tests that will ultimately qualify the engine for flight. After the ground tests, the same engine will be integrated into the Demonstrator 3 rocket that will perform a suborbital space flight up to an altitude of 120 km above the New Mexico desert. It will be the first ever flight of a linear aerospike engine and the first ever space flight of an aerospike engine.

Based on the results from these tests the company then intends to build a single-stage-to-orbit small rocket that they hope to fly by 2018.

Go to the company’s news website here to see some good images of the engine and the aerospike nozzle. It does not look like any typical rocket engine. If this effort is successful it will as significant a technological improvement to rocketry as SpaceX’s recovery and reuse of its Falcon 9 first stage.

Conscious Choice cover

Now available in hardback and paperback as well as ebook!


From the press release: In this ground-breaking new history of early America, historian Robert Zimmerman not only exposes the lie behind The New York Times 1619 Project that falsely claims slavery is central to the history of the United States, he also provides profound lessons about the nature of human societies, lessons important for Americans today as well as for all future settlers on Mars and elsewhere in space.

Conscious Choice: The origins of slavery in America and why it matters today and for our future in outer space, is a riveting page-turning story that documents how slavery slowly became pervasive in the southern British colonies of North America, colonies founded by a people and culture that not only did not allow slavery but in every way were hostile to the practice.  
Conscious Choice does more however. In telling the tragic history of the Virginia colony and the rise of slavery there, Zimmerman lays out the proper path for creating healthy societies in places like the Moon and Mars.


“Zimmerman’s ground-breaking history provides every future generation the basic framework for establishing new societies on other worlds. We would be wise to heed what he says.” —Robert Zubrin, founder of founder of the Mars Society.


All editions are available at Amazon, Barnes & Noble, and all book vendors, with the ebook priced at $5.99 before discount. The ebook can also be purchased direct from my ebook publisher, ebookit, in which case you don't support the big tech companies and I get a bigger cut much sooner.


Autographed printed copies are also available at discount directly from me (hardback $24.95; paperback $14.95; Shipping cost for either: $5.00). Just email me at zimmerman @ nasw dot org.


  • Edward

    Here is a nice explanation of how the aerospike engine works as well as why it does not lose as much efficiency at altitude, as happens with the classical bell shaped engine. (6 minutes)

  • wayne

    thanks for that video-link, highly informative.

    ARCA has a YouTube page with assorted short videos-

  • wayne

    I’ve only superficially followed this, but now I’m intrigued…

    (Tangentially, how do the folks at ARCA, get away without using respirators? Does OSHA know about this?)

    So, we had this technology 50 years ago, equipment & machines were designed, built & tested, millions of dollars changed hands, and they left it on the shelf??

    “The Linear Test-bed Program”
    NASA/Rocketdyne film

  • wayne

    “XRS-2200 Linear Aerospike Engine Test fire at NASA Stennis Space Center”

  • Wayne:

    “It’s unfortunate, but the way the American people are, now that they have developed all of this capability, instead of taking advantage of it, they’ll probably just piss it all away.”

    LBJ to Apollo 7 crew after a factory tour.

  • wayne


    We really did…. “fail to seize the moment.”

    Not that this is a perfect technology, but it’s an example of many things that have gone on.

  • Edward

    I have heard an estimate that $500 million has gone into the research and development of aerospike engines. “The Linear Test-bed Program” video helps show why a rocket engine costs so much to produce, and helps explain the high amount of R&D cost. Over the past five decades, quite a few linear and annular aerospike engines of various sizes have been built and tested. I will be interested to see how they perform under flight conditions. Hurrah for ARCA space!

    If you are really into rocket manufacturing, and have too much spare time on your hands, ARCA has a video series, “Flight of the Aerospike” (no, I haven’t watched them all, either, but a comment in the latest, 14th, video suggests that an annular aerospike engine has previously flown but not reached space):

    Later in the video, the narrator talks about the linear aerospike that they built as having 20 combustion chambers, but earlier he mentions a single annular combustion chamber. Because of the physics, even an annular aerospike may want to have multiple combustion chambers. The propellant gasses (exhaust gas) must reach mach 1 at the narrowest point in the nozzle for it to accelerate against the expansion section of the nozzle. Unlike a river, which slows down when it widens, a compressible gas (sonic or supersonic) will accelerate as the nozzle expands. The math works out that way.

    The equation is the same for the river and the gas as it reaches the narrowest part of the flow, but the gas can reach — but not exceed — mach 1. This is a limitation for a rocket engine, meaning that in order to increase the mass flow, the designer has to increase the chamber pressure. However, this limitation also works to an advantage, because while the equation during expansion is almost exactly the same, the sign changes due to the sonic speed of the flow. The sign change is one of the magical phenomena of physics.

    Yes, magic is real, and it occasionally shows up in the real world, not just Harry Potter’s world.

    With the sign change, the compressible gas accelerates when it expands, causing a force against the expansion section of the engine and adding additional propulsive force than if there were no expansion section.

    What a lot of fun rocket science can be. As long as the rocket doesn’t blow up, that is.

  • Michael

    This is amazing stuff. Thanks for the tip. It is now on my watch list.

    And thanks for the youtube link. I have not watched it all but it really interesting.

  • Edward

    I got so excited about the expansion section that I forgot the purpose of my previous comment. If the area of the throat, the narrowest part, of the annular engine is too large, then the gasses will not reach mach one. In order to solve this problem, multiple combustion chambers — thus multiple throats — can be used, just as multiple combustion chambers are used on the linear aerospike engines. Sometimes things don’t scale up as well as we would like, but adding multiple units can sometimes be the solution.

    Multiple combustion chambers aren’t magic, but they add to the fun of rocket science.

    You can count 20 combustion chambers on the near side of the linear aerospike in wayne’s “XRS-2200” video. You can also count eight combustion chambers on each side of ARCA’s Haas 2CA rocket (mockup?) shown in both of Robert’s links.
    At $1 million per launch, ARCA expects to put 100 kg (220 lbs) into low Earth orbit for $10,000 per kg ($4,600 per lb). This seems competitive with other smallsat launchers that are soon to come on the market.

    This is yet another reason that I think the next few years will continue to be exciting times for the space industry. Reusable first stages and reduced launch prices were just the beginning. Smallsats and smallsat launchers are another installment in the excitement. Suborbital space tourism and commercial space stations seem to be close behind.

  • Cotour

    Building an annular Aerospike from the inside out.

    CNC / additive laser deposition manufacturing. Building in a more organic process from the inside to the outside rather than a more component / assembled manner allows the design and construction of devices that have not been possible previously.

    Less components, much simpler designs at a very high degree of precision and strength. CNC / 3D manufacturing good and can only get better.

  • Cotour

    Supporting real world additive manufacturing illustration:

  • wayne

    would that $500 million, be in 1970’s money? Price level has gone up at least 6X’s since 1970.
    –I’d want to know where all the blueprints are stored! And did they sell all that hardware as scrap, or is it in a warehouse somewhere??

    tangential Q:
    Is Rocketdyne a grandfather, of the current ATK?
    Does anyone have a “Family Tree” of our current aerospace corporations?

    Interesting video!

    This appears to be well suited for relatively small designs. I’m wondering about their ability to scale-up in size?

    Sample some parts of that “Linear test bed,” video I reference. It’s was a massive structure.
    It would be interesting to know which parts could be additively manufactured, and which parts they could not.

  • Cotour

    I would think that those modular linear Aerospike combustor’s that were manufactured using investment casting, which is very labor intensive, exacting and limited will certainly be able to be made using additive manufacturing and I would not be surprised if they were able to make much more complex geometries and if it were not being worked on right now.

    What is the limit?

    Depending on the possible need to control the manufacturing environment and the material that is being worked with or some similar concern is probably the limiting factor. What size do you want to work with? This allows much more complex thinking related to component design with a much easier inside out ability to manufacture. Plus I believe that different materials can be incorporated into one part. I know that is being done in the 3D plastics end of the technology, I am not certain that right now it is being done in metal.

  • wayne

    Very interesting stuff! Thank you.

    I don’t know what “investment casting” means. (I get the additive vs subtractive, but I know way less about “working metal,” than I would like.)
    That term comes up a bit, in the video I referenced.
    And yes– it looks labor intensive, although I know improvements have been made in the whole metal-casting process(es) since the 70’s.

    (tangentially–I believe Musk is able to make about 300 units/year (engines). Does anyone have video links for any SpaceX engine manufacturing processes?

    It will be interesting to see what the people at ARCA can accomplish.

  • Robert Pratt

    “Demonstrator 3 will perform a suborbital space flight up to an altitude of 100 km above the New Mexico desert in August 2017,” reads the 15 June press release. Did this happen or is it a typo that should have read 2018?

  • Robert Pratt: The flight has not happened. They met their contract obligations to build the engine test stand within 60 days and on schedule. After the static fire tests they will then do the suborbital flight. I therefore suspect this was a typo.

  • pzatchok

    As for an aerospike engine, how well do they operate in space?

    Whats the thrust curve vs air pressure/altitude?

  • Edward

    wayne asked “would that $500 million, be in 1970’s money? Price level has gone up at least 6X’s since 1970.

    The estimate is from recent reports or videos that I have seen, so it is probably a relatively modern value with historical expenditures adjusted for inflation. I also expect that it is a rough estimate of the R&D spending.

    wayne asked “Is Rocketdyne a grandfather, of the current ATK?

    ATK (now merged with Orbital, now purchased by Northrup Grumman) was once known as Morton-Thiokol.

    Robert Pratt asked: “‘Demonstrator 3 will perform a suborbital space flight up to an altitude of 100 km above the New Mexico desert in August 2017,’ reads the 15 June press release. Did this happen or is it a typo that should have read 2018?

    In June, ARCA was expecting it would take a whopping two months to get ready to perform their first launch, which would have been August, so I suspect that it is a typo. They are now suggesting that they will perform their launch in only two months, which would be November.

    (Did anyone notice that I tried to hide the month-for-month schedule slip? Now that I point it out, please feel free to ignore this parenthetical statement, because month-for-month slips aren’t a particularly good sign.)

Readers: the rules for commenting!


No registration is required. I welcome all opinions, even those that strongly criticize my commentary.


However, name-calling and obscenities will not be tolerated. First time offenders who are new to the site will be warned. Second time offenders or first time offenders who have been here awhile will be suspended for a week. After that, I will ban you. Period.


Note also that first time commenters as well as any comment with more than one link will be placed in moderation for my approval. Be patient, I will get to it.

Leave a Reply

Your email address will not be published. Required fields are marked *