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Commercialization

NASA and Ad Astra Sign New VASIMR Deal

By Keith Cowing
NASA Watch
August 10, 2015
Filed under
NASA and Ad Astra Sign New VASIMR Deal

Ad Astra Rocket Company and NASA move to execution phase of NextSTEP VASIMR partnership
“NASA’s Advanced Exploration Systems Program sponsors NextSTEP awards in a 50/50 cost partnership with industry. Under this award, Ad Astra will conduct a long duration, high power test of an upgraded version of the VX-200TM VASIMR prototype, the VX-200SSTM (for steady state), for a minimum of 100 hours continuously at a power level of 100 kW. These experiments aim to demonstrate the engine’s new proprietary core design and thermal control subsystem and to better estimate component lifetime. The tests will be conducted in Ad Astra’s large, state-of-the-art vacuum chamber in the company’s Texas facility.”

NASA Watch founder, Explorers Club Fellow, ex-NASA, Away Teams, Journalist, Space & Astrobiology, Lapsed climber.

66 responses to “NASA and Ad Astra Sign New VASIMR Deal”

  1. TheBrett says:
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    Is it still not much of an improvement over existing ion thrusters? Granted, we’re not exactly talking a ton of money here at $3 million a year – if NASA can afford to throw money after whatever nonsense Sonny White spends his time on, they can afford this.

    And who knows? I don’t think there’s any chance of them getting either the necessary nuclear reactor or amount of solar panels for a Mars mission with a transit time improvement over a six-month trip with chemical rockets. But a VASIMR engine with improvements over regular ion thrusters could be very useful for robotic probes.

    • Jeff2Space says:
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      5000 sec Isp is huge. The thrust level may seem low, but if this thing can be run continuously, it will cut trip time. Yes, it will need a huge power source (likely nuclear), but we’re going to need that on Mars for “in situ” fuel production for the return trip. Solar at Mars is possible, but dust is a huge problem, especially if you pre-position the return vehicle and do not want to send a crew until it is fully fueled.

    • SpaceMunkie says:
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      6N thrust out of a ion thruster is massive, usually they are somewhere in the 0.06N thrust range

      • TheBrett says:
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        That’s probably using a 200 KW power source, since they’ve got it generating 5 N using a 200 KW source on their website. It takes 40 KW to generate 1 N of thrust, which makes it inferior to an NSTAR ion engine – the NSTAR gets 0.092 N of thrust from 2.3 KW, or about 25 KW to generate 1 N of thrust (assuming you can scale it, which may not be the case).

        • Yale S says:
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          The engines have different roles. How does a a single 5000 Newton VASIMR compare with a cluster of five thousand 1 newton conventional ion engines if your goal is moving humans, not only cargo?

          • TheBrett says:
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            They’re both high-ISP, low-thrust electric propulsion drives. They’d have similar roles – it’s just that VASIMR gets less thrust from its power supply than NSTAR does.

          • Yale S says:
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            We are talking 3 to 4 orders of magnitude thrust difference.
            It is for very different roles.

          • TheBrett says:
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            I think we might be talking past each other. It’s true that VASIMR gets much higher thrust, but that’s because it has a significantly larger power source – 200 KW versus NSTAR’s 2.3 KW.

          • Yale S says:
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            Thrus matters if your goal is moving people fast. For cargo or sensors, multi-year sail times with low thrust ion engines is just fine.

          • TheBrett says:
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            Still think we’re talking past each other. VASIMR only reports higher thrust on their website because they’re using a much larger power source than we’ve used on NSTAR engines. An NSTAR equivalent with that kind of power might be better than VASIMR in terms of getting the same amount of thrust with less power.

          • Yale S says:
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            Circling back one last time. The question is, are ion thrusters limited in size vs the low constraint on VASIMR size. To handle the same 5k newton thrust with its enormous power demand, do you need 5000 ion thrusters vs 1 vasmir engine, or do ion thrust scale up nicely?

          • TheBrett says:
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            I pointed out that qualification in my original post. If NSTAR can’t be scaled, then the comparison is moot. And VASIMR does seem to be an improvement over some of the other higher-powered ion engines, like HiPEP.

            Although there is one advantage to having multiple smaller engines versus a single larger one. A single engine failure would only reduce thrust on the multi-engine set-up, versus a potentially calamitous death for the crew on a VASIMR ship.

          • Yale S says:
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            Very true. Modular systems have an array of advantages.

        • SpaceMunkie says:
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          Power is cheap, propulsion mass is much more important.

    • Yale S says:
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      The thrust is low compared to chemical propulsion, but higher than ion engines currently in use. Energy efficiency is about the same as currently produced, in space ion engines.
      One difference is that current ion engines have operated non-stop for years, while vasimr tests have lasted only seconds, so far.

      • TheBrett says:
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        As I pointed out in my post farther down, the energy efficiency to generate thrust might actually be inferior to NSTAR and existing ion thrusters. The chart they have shows NSTAR generating 0.092 N of thrust from 2.3 KW of power, or about 25 KW to generate 1 N of thrust. Meanwhile, VASIMR has 5 N of thrust being generated by 200 KW, or about 40 KW to generate 1 N of thrust.

        Given that NSTAR has tons of lab testing and actual spacecraft testing with years’ duration in interplanetary space on Dawn and Deep Space One, it doesn’t bode well for VASIMR.

        • Yale S says:
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          The NSTAR ~25 KW/Newton

          The VASIMR bench test:
          RF Power: 200 kW;
          thrust: 5.7 N;
          exhaust speed: 50 km/s;
          thruster efficiency: 72 % (jet power divided by coupled RF power).

          Roughly 35 KW/newton (might be misleading because it is the “coupled RF power”, not the the power source. The efficiency is 60% as input power.

          As pointed out, the efficiency is about the same as other ion engines (as compared to other technologies), but the key feature is both the much larger thrust (useful in leaving the gravity well, shortening human flight time, and quicker ISS repositioning)) and the major jump in ISP.

          The 6 newton VASIMR is a benchtop model of a much more powerful flight engine, up to maybe 5K newtons.

          The issue is whether the mass and performance of a large VASIMR exceeds that of a large cluster of lower thrust ion thrusters.

          Whether it all shakes out as preferable in actual flight is what this testing is all about.

      • Rod Burton says:
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        We really don’t know what the thrust is, because the thruster has never been put on a thrust stand. Thrust could be half or less of the 6 N they claim.

        • Yale S says:
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          FWIW They have measured the plume and derived the thrust:

          To determine a quantity for thrust, we rely
          on a force target (plasma momentum flux sensor) technique that has been validated against a Hall thruster on a thrust stand. The force target is a graphite disk mounted to a sensitive strain gauge and scanned across the plasma profile to integrate a total force that we interpret as thrust.

          Here is a paper:
          http://www.adastrarocket.co

  2. se jones says:
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    Oh lord here we go again:
    Pretty picture of VASIMR in space + ignore the part about “tests will be conducted in…vacuum chamber” = MARS IN 39 DAYS!

    • kcowing says:
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      Did you even bother to read what was posted? It says “The tests will be conducted in Ad Astra’s large, state-of-the-art vacuum chamber in the company’s Texas facility.”

      • se jones says:
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        That’s ironic Keith, if *you* read *my* (admittedly) snarky comment, my point was that the usual suspects will not read the entire post, they will see the pretty picture, they will assume the test VASIMR is attached to ISS, then it’s off to Mars in 39 days.

        >>ignore the part about “tests will be conducted in…vacuum chamber”

  3. Neil.Verea says:
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    So where is the “nuclear in-space Power” development? Without it this, if it achieves it’s stated design spec”, will be nothing more then a massive paper weight. I say parallel investments need to be made in Power generation so that this and other needed power hungry systems required to go to Mars and other destinations are made feasible.

  4. RocketScientist327 says:
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    Without a megawatt reactor none of this matters. NASA should be working on nuclear reactors for space travel, not the SLS Titanic.

    • Paul451 says:
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      Inside of 2-3 AU from the sun, modern solar achieves a higher power-mass ratio. Therefore it takes less solar panel mass (including necessary extras) to achieve any given power requirement than nuclear reactors (plus necessary extras). And over time, as solar cells get more efficient and/or lighter, the “cross over” distance where nuclear is worthwhile has pushed steadily outwards. Today, even Jupiter missions are primarily solar.

      That would probably change if space-rated nuclear reactors were widely used (hell, just if similar sized reactors were routinely used on Earth). But while space-based solar panels benefit from every breakthrough in Earth-bound solar tech, plus have the market of every commercial satellite, nuclear reactors would be developed from scratch for an extremely limited number of programs.

      That limits nukes to outer planet probes. And that puts the entire development cost onto those first programs, which are invariably already scraping the limits of their funding.

      • RocketScientist327 says:
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        Paul – thank you for this logical response. My question to you is can you link me the study? I have heard this argued in some context with some data but when it comes to moving a lot of mass it always falls back to chemical propulsion.

        Specifically, Missions from Mars and inward are fine for solar. However, if we want to go deeper we really need nuclear power. I know JUNO used solar but the output at Jupiter was really low and the sensors and radios were truly “one in a million”.

        I think it would be logical, at some point, to start a real nuclear reactor program in space that can produce outrageous levels of power. Some people say we do not need that much power… I also remember some people in 1977 not everyone needs a personal computer.

        • Yale S says:
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          The chances of a US space reactor is minimal any time soon.

        • phoebus1A says:
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          It always reverts to a thrust to weight ratio, which is is a metric best described by specific power for electric propulsion systems. I agree that nuclear is the only way to robust space exploration and we need to starts somewhere. However, mass of the power conversion systems is very large. At present, I don’t see any credible way around this, even for theoretical MHD conversion systems. In order to get the specific mass of an NEP system down to a level that gives a competitive thrust to weight ratio, the reactor ends up having to be in the 10s to 100s of Megawatts, which involves a propulsion module that is a substantial fraction of the ISS in mass and dimensions, not to include the rest of the craft. Admittedly, we have to start going down this path to solve them, but I would argue the better near term solution that opens the door to exploration, while advancing the state of the art for high temperature reactor materials is NTP. Like I said in another post, debates over best propulsion systems have no end, so at this point, I welcome progress in any direction.

      • Gerald Cecil says:
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        Generous 25% efficiency of converting 1 AU sunlight to electrical power requires approx (4 m x 1 km) / MWe. Times the conversion inefficiency for VASIMIR. Conclusion: solar does not scale usefully, VASIMIR works only with a reactor.

        • Yale S says:
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          I think a more reasonable solar panel is not your 4mx1km, instead roughly 60 meters by 60 meters per megawatt. The ISS panels are 35 meters long or 70 meters end to end. At Mars the power drops by 60%.

          In any event, I think a 30%+ efficient Stirling/Rankine/Brayton engine using inflated reflectors make a lot of sense.
          Click the youtube logo to got to the page and then make it full screen.

          https://youtu.be/MG_ynhTbJZA

        • Paul451 says:
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          Now try a 1MWe reactor. The radiators alone will mass 160 tonnes.

          (Thermal conversion for such a small reactor is likely to be around 25%. So a 4MWt reactor. Radiators typically 1m^2 per 300w cooling, and mass 12kg/m^2. There are tricks to reduce that, such as droplet cooling, but you’re adding another tech development program to the list.)

          With the reactor, you are looking at 200We/kg (judging by SAFE). Say 5 tonnes for 1MWe. Plus you need the heat-engine converter itself (and whatever primary coolant you are using), the mass of which is usually ignored in published studies, annoyingly.

          NASA typically targets 200-400W/kg at 1AU for solar arrays in modern probes/etc, including all sub-systems. So a 1MWe array is 5 tonnes or less.

          The inefficiency of the ion drive is irrelevant, since that applies to both power sources.

          • Yale S says:
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            Damn, i just logged in to talk about radiators.
            I do see a difference in required radiator mass. I am not sure what temperature heat you are using. With a high temp helium or sodium cooled reactor I see a radiator mass at a still large approx 2 to 3 tons.

          • Paul451 says:
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            I am not sure what temperature heat you are using.

            Oh, good catch. I was using generic NASA figures for spacecraft design. That includes habs, panels, ion-engine inefficiency waste heat. Those are all inevitably based on colder “hot-side” compared to a reactor.

          • Yale S says:
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            Whatever a working system radiators would be somewhere between our extreme values, it is still more than a PV power system would ever need.
            Altho, with my conjectured solar-thermal generator, you’re back to needing waste heat radiators.
            In addition, the radiation shielding requirement, with whatever combo of extended structure (or difficult to manuever cables) and massive shield adds to the mass and size of a spacecraft with a multi-megawatt nuclear reactor must be accounted for. With an extended truss or cable separator you do get the possibility of generating artificial gravity, so that is a potential positive, altho just storing propellant at the end can accomplish that.

          • Paul451 says:
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            Altho, with my conjectured solar-thermal generator, you’re back to needing waste heat radiators.

            That’s for solar-thermal electric. However, direct solar thermal thrust, the “cooling” is the exhaust stream. (Same with NTR.)

            Of course, until we invent fusion drives, the winner is fission fragment propulsion.

            In addition, the radiation shielding requirement

            Oh, I completely forgot about shielding mass.

          • phoebus1A says:
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            I agree, but I would argue that the specific mass of solar electric and nuclear electric both fall short in comparison to nuclear thermal propulsion. However, I will say that this is a type of argument that could go on forever, so I would welcome progress in any direction at this point.

          • Yale S says:
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            Here is an image of the predecessor of your namesake, the phoebus1a, the KIWI nuclear thermal rocket. This is the KIWI-TNT test where the reactor was jimmied up and forced to simulate an accident with an uncontrolled power excursion. You can see the fragments of incandescent core as flying sparks. The core was fresh to minimize fission products, but it still spread fallout quite a distance.

            http://nucleardiner.com/wp-

          • phoebus1A says:
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            Actually the TNT test was not a fresh core, the reactor had undergone previous high power testing and this was part of its end of life disposition. Also, the reactor did not simulate a normal reactivity excursion, in fact the reactor design was not capable of this type of excursion and they had to add extra reactivity (more fissile material and an accelerated drum roll rate) to make it destruct in this fashion. Regardless of fuel integrity (fresh or used) NTP reactors only operated at low power levels (compared to terrestrial power reactors) and for very short durations. As a result, the fission product build up is very low even at end of life, and the radiation levels at most points beyond a few hundred meters were back to background levels within a day and a half or less as the distance away from the test increased in the expected r squared fashion.

          • Yale S says:
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            (Reply 4)
            phoebus1a wrote:.
            the reactor had undergone previous high power testing and this was part of its end of life disposition.
            Not correct:

            LA-3395-MS
            Radiation Measurements of the Effluent
            from the Kiwi TNT Experiment
            “A slightly modified Kiwi B4 type reactor with no previous history was used for this test.

          • phoebus1A says:
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            Well of course the fuel was fresh, the previous firings saw core temperatures of ~2700 K which corrodes the fuel (of the time) to the point where it could not be used again. However, you said core, not fuel. The core implies the entire core assembly to include tie tubes, faster heads plenum assembly, and many other components. I have worked in the industry for some time and in the space and terrestrial power world, I have never heard the core to assume just the fuel. However, it would not have mattered, because even in the case of ambitious assumptions, even after ten hours of firing a multi hundred Megawatt core, which is the most ambitious total firing time considered, the fission product inventory is negligible after a few days of cool down, which Phoebus had far more than a few days since its last firing.

          • Yale S says:
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            (Part II-A)
            No you are still incorrect.
            You wrote: “..the previous firings saw core temperatures of ~2700 K which corrodes the fuel (of the time) to the point where it could not be used again”

            THERE WERE NO PREVIOUS FIRINGS.

            In my Reply 4 above quoting Los Alamos:
            LA-3395-MS
            “A slightly modified Kiwi B4 type reactor with no previous history was used for this test.

            You wrote: “I have never heard the core to assume just the fuel.”

            It is routine to say in the industry things along the lines of, “we swapped out a third of the core during the last outage.” It is understood it refers to the fuel and not the hardware framework. Irrelevant tho, since BOTH the fuel AND the reactor were fresh and unused.

          • phoebus1A says:
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            Your on a crusade to prove you know more than anyone else and not have a discussion so this will be my last post. The total radiation (due to fission products and activated materials) is proportional to the burnup. The total burnup normalized to uranium for any of the NERVA/ROVER reactors was 3 to 4 orders of magnitude less than that which comes out of a terrestrial reactor after a mere one cycle and most fuel goes through three. In the cases you mention, a large fraction of the radiation was in the form of soft gammas and hard x-rays inherent from activation, and while the fission products also contributed a sizable dose, it was less than that caused by activation because of the short burn time. Yes immediately following shut down the dose is high, but most of the radiation is produced by activated products and fission products with half lives on the order of seconds to hours. At that point the accumulation of actinides and mid column products, which have half lives of years was very small. In short, the measured dose dropped VERY quickly to the point that two days later people were walking the site and picking up debris. I even worked with a guy who is now in his eightees with healthy children and grandchildren who was lowered by rope into the nozzle of a hot fired NERVA engine just a few days after irradiation to inspect the nozzle. You talk about ALARA rad standards that I dont think you understand. Yes, the annual dose set by the NRC for workers is 5Rm/yr, set by 10CFR20, but even the NRC admits that it is WILDLY conservative. They also admit that to date there is no firm understanding of how radiation acts on the body. More importantly there is not a firm grasp on the effects of accumulated dose or dose rate, because it is likely that the dose rate is more important that combined dose. But none the less for public perception reasons and because no good studies have been conducted into better understanding rad effects over prolonged time frames we keep the limit where it is. Regardless, no one is arguing that workers should have walked up to any of the NERVA/ROVER reactors immediately following a test, but because of the extremely small product inventory, of which most have very short half lives, the time to background levels of radiation is relatively short.

          • Yale S says:
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            You are comparing apples to oranges. Yes, a 4 gigawatt nuclear rocket engine running for an hour has less fuel burnup than a power reactor running for 3 years. That was never the issue.

            re-read your posts. Your claim were and are incorrect.

            BTW – your last post is the first to distinguish (as I have pointed out) the difference between radiation and fission product buildup. That confusion shows in the implication that the decay of intensely radioactive fission products (with half lives under a few hours) portion wiped out the inventory in a few days. Re-read your posts.

            I do understand ALARA and there are ARE standards, whether the industry (and its whimpering puppy dog, the Nuclear Regulatory Agency – NRC) likes it or not (and their attitude shows in the often poor performance).

            By request of Congress:

            HEALTH RISKS FROM EXPOSURE TO LOW LEVELS OF IONIZING RADIATION
            BEIR VII PHASE 2
            Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation
            Board on Radiation Effects Research
            Division on Earth and Life Studies
            NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES OF SCIENCE

            CONCLUSION
            The committee concludes that current scientific evidence is consistent with the hypothesis that there is a linear, no-threshold dose-response relationship between exposure to ionizing radiation and the development of cancer in humans.

          • Yale S says:
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            Phoebus1a wrote:
            “I even worked with a guy who is now in his eighties with healthy children and grandchildren who was lowered by rope into the nozzle of a hot fired NERVA engine just a few days after irradiation to inspect the nozzle.”

            Here is the what actually happened:

            But for some of the nuclear rocket tests conducted, there were occurrences in which participants were exposed to radiation environments in excess of the limits.
            In particular, after the first high power test of the Kiwi B1A reactor, Rocketdyne’s NTR LH2 Turbopump & Nozzle Section Chief was given permission to inspect the condition of the nozzle’s coolant walls once the nozzle had been removed from the reactor assembly, provided he only inspected the inside of the nozzle assembly for thirty seconds. This action was conducted, but the exposure saturated his radiation measurement badge so that it was unable to record the incident radiation intensity.

            And note this: even this nasty exposure from a NON-reactor component was with a small KIWI B1A that was 1/16th the power of the Phoebus-2a and the engine only fired for 36 seconds!

          • Yale S says:
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            (Part II-B)
            Again you are incorrect. You are confusing radioactivity with fission product inventory and are wrong on both.

            “even after ten hours of firing a multi hundred Megawatt core, which is the most ambitious total firing time considered, the fission product inventory is negligible after a few days of cool down, which Phoebus had far more than a few days since its last firing.”

            The little KIWI A, after a only 5 minute run at only 70 megawatts, and after a nine day cool-down, at 1 meter from the core, had an exposure rate of 10 REMS/hour (the general public maximum legal exposure is 1/20th of that over a whole year).
            Phoebus-2A was 60 times as powerful. and with your 10 hour run-time, would have been astronomically more radioactive. In actual space flight the burn time would be measured in 10s of minutes, not hours.

          • Yale S says:
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            (Reply 3)
            phoebus1a wrote:
            “.,, the TNT test was not a fresh core,”
            Not correct:

            Los Alamos report on 1965 Kiwi simulated accident
            Environmental Effects of the Kiwi-TNT Effluent: A Review and Evaluation,1968.

            :“There was no fission-product inventory in the reactor at the time of the test.”

            Now the ONLY way you do not have fission products in the core is to NEVER HAVE FISSION, ergo, a fresh fuel load. That is the Law of Nature.

          • Yale S says:
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            (Reply 2)
            phoebus1a wrote:
            ,,,in fact the reactor design was not capable of this type of excursion
            Not correct:
            As I said, the controls were modified to create a possible power excursion accident:

            It was a special flight safety test to study the behavior and effluent of a KIWI-type reactor undergoing sudden power surges or excursions as might happen if a chemical rocket booster aborted and dropped a non-critical nuclear reactor in the ocean (or lake, reservoir, or river) where the water, being a good neutron moderator, would increase the likelihood of fissions and could make the reactor go critical very quickly..

          • Yale S says:
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            (Reply 1)
            phoebus1a wrote:
            NTP reactors only operated at low power levels (compared to terrestrial power reactors)
            Not correct.
            These engines were among the most powerful reactors ever built.
            Phoebus2A exceeded 4,000 megawatts thermal (and was designed for 5000 MWt)
            This is greater than almost any commercial power plant ever built.
            For example, each of the Indian Point reactors outside New York City are only 3000 megawatts thermal.

          • phoebus1A says:
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            Consequently, although a side topic, there is a fascinating read on all the NERVA tests that can, or at least you used to be able to find on NASAs NTRS “Overview of Rover Engine Tests, Final Report, by J.L. Finseth, NAS 8-37814, published in 1991. It is probably the most detailed assessment of the tests that I have seen in one place.

          • SpaceMunkie says:
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            what if you use the propellant as the reactor coolant, make the system into a hybrid nuclear-thermal-ion propulsion?

    • se jones says:
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      So instead of SLS “Titanic” they should get to work on giant nuclear electric “Battlestar Galactica”?

      • DTARS says:
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        At least they might be able to figure how not to dump that in the ocean.

        Aquaman

      • Ben Russell-Gough says:
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        Robert Zubrin made that a term of abuse and I don’t think it deserves it, particularly as our understanding of space environment hazards improves and the baseline safe weight of the orbital transfer vehicle increases.

    • ptolemy1977 says:
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      Hi All,

      I was thinking about this problem just lately. And, I thought why couldn’t we use both solar and lasers as a heat source to power a vasimr? This is what I mean, we could use the new super critical CO2 turbine https://www.technologyrevie… developed by GE to provide electricity from some heat source. This could of course be any number of heat sources such as focused sunlight on a solar furnace which would heat a container of CO2 to super criticality of about 700 deg C not so tough in orbits below that of Mars. Ground based lasers could also serve as a supplemental heat source, or even spent uranium might even be able to generate this much heat over extended periods of time. This turbine is small light and can generate up to 5 MWh of electricity at greater than 50% efficiency, it is reasonable that GE could develop an even smaller version for space flight. SpaceX uses a carbon fiber storage tank for its dragon rockets I would think that something like that could serve as a heat reservoir of super heated CO2 to be used generate power for the vasimr during flight, and of course throughout flight sunlight and laser light could be constantly recharging the heat reservoir. Think about it this is just like energy storage for ground based solar power stations. You could in fact charge up enough CO2 heat reservoirs to attach to the turbine which would provide electrical power enough to send the craft all the way to mars and setup a similar powering station around mars to assist with recharging such heat sinks for the return trip. One great asset to all of this is the potential to beam power, via lasers or solar concentrators, to such a setup for heating the CO2 to super criticality, read you have options. And, of course, you could bypass solar and lasers altogether with a heat source based upon spent nuclear, no not a nuclear reactor but spent nuclear as a heat source simple and uncomplicated.

      I am just wondering if anyone else thinks that this could be a viable solution to the power problems faced by the vasimr.

  5. Rod Burton says:
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    The numbers simply do not add up. A thrust of 6 N at 5000 s is an exhaust beam power of 150 kW, compared to an input power of 100 kW. This is an efficiency of 150%. Somebody made a $9M mistake.

    • Yale S says:
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      The input power is 210 kw

    • Tritium3H says:
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      What am I missing, here? I am off by a factor of 2.

      (5000 isp ) x (10 m/sec^2) = 50,000 m/sec exhaust velocity

      (50,000 m/sec) x (6.0 kg x m / sec^2) = 300,000 kg m^2 / sec^3

      = 300,000 W = 300 kW

      My brain hurts. What am I forgetting?

      • Yale S says:
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        Power = Thrust times exhaust velocity divided by 2
        6newtons times 50k m/s exhaust divided by 2 = 150kw

        • Paul451 says:
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          Why is the scalar 60 degrees for constant acceleration?

          [Since P = F * cos(s) * V :: hence, cos(s) = 0.5 for a(const) :: hence, s must = 60 degrees]

      • Rod Burton says:
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        You’re missing the factor of 1/2 in particle kinetic energy.

        • Tritium3H says:
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          Hi Rod,

          Ah heck yes. Power = (thrust Force x exhaust velocity) / 2.

          My brain must have taken a quick vacation to the Bahamas. Thanks.

  6. SpaceRonin says:
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    Nuclear thermal…. high thrust moderate Isp. Burns anything so you can refuel with any old gas you like… If the HX chemistry is amenable. NERVA redux. No need for a in situ prop factory. No need for radiators either. Isp related to temperature. If you use a directly heating reactor then you can max the Isp. If you use a HX loop on the reactor then the Isp is driven my the HX operating temp and the prop gas molecular mass. In the former case extracting electrical energy is not likely. Either way if you go to the trouble of putting a reactor in space putting a VASIMIR on it is unlikely to be a mission optimum approach. Unless validating VASIMIR is your mission! So acres of SA’s it is. ESA’s JUICE mission is all SA… they don’t do nuclear; not even RTG. YMMV

    • Kenneth Ferland says:
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      The ISP of a Nuclear Thermal rocket is dictated by the atomic mass of it’s propellant because temperatures are already at the limit of the rocket chamber materials (also don’t say burn when no oxidation reaction is occurring), The purported ~900 ISP of NTR is due entirely to the use of pure hydrogen propellant as soon as you switch to a hydrocarbon you get standard hydrocarbon ISP, if you use water you get standard hydor-lox ISP.

  7. Steven Rappolee says:
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    Lots of discussions here about radiators, I was thinking for outer planets missions you could replace RTG heat with radiator heat to keep spacecraft warm and to recover secondary heat by generating electricity

    http://yellowdragonblog.com

    in all of my posts the thought is the radiator is inside an existing spacecraft structure such as an expended chemical fuel tank or capsule pressure vessel with Argon or Xenon gas for stirling motors