Keith’s note: If the QM-1 SRB engine is going to burn for 126 seconds (per NASA) that means that 693 million pounds of propellant will be used – or 693 million tons – depending on which Tweet you believe. But wait: the whole SRB only weighs 1.6 million pounds. Hmm … NASA’s infographic says that it is only burning 5.5 tons per second. No “million” pounds or tons is mentioned. Clearly @NASASocial needs to spend a little more time reading before tweeting.

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member...

30 replies on “@NASASocial is a Little Confused About SLS”

  2. Man, I knew that solid boosters don’t have the best specific impulse, but I didn’t know they were that bad

    1. Yes, they’re *that bad*. The dry mass is also extremely high compared to a liquid stage because the “fuel tank” on a solid is also the combustion chamber and has to withstand the very high pressures which are needed for combustion.

      Plus there are the handling issues (fueled, heavy, segments must be shipped by rail and assembled at KSC) which add to the cost.

      But worst of all, IMHO, is the non-zero chance of a case rupture and the resultant “kaboom” and solid debris that makes any crew escape system “challenging” (to say the least).

        1. Ohhhh I think I get it!

          NASA is letting Boeing skip their inflight abort test because, since atles will use solids, it is unlikely the crew would escape without being shot down anyway.

          1. Well, they are doing an in-flight abort test of the Orion, and that uses 2 of the monsters tested today. I think in the case of the CST-100 it is not solid engines, it is solid gold that is the issue.

      2. “But worst of all, IMHO, is the non-zero chance of a case rupture and the resultant “kaboom” and solid debris that makes any crew escape system “challenging” (to say the least).”
        NASA plans to put humans on this bomb?

        Yet they don’t want to even consider reusing liquid rocket boosters?
        http://m.aviationweek.com/s…

        Whats the deal here?

        1. the Block II version of the SLS might have liquid fueled boosters. ATK is also developing an advanced SRB to compete with that idea.

          1. Probably not. The Liquid Booster team would have to fork out the money for a new Mobile Launcher, as the current one (originally designed for the much smaller Ares I) isn’t big enough for two more liquid fueled boosters. That will give SRBs a major price advantage.

          2. Liquid boosters weight much less as they are loaded with propellant at the pad. They would have to put in a new RP storage facility at the pad or upgrade the existing hydrogen ones.

          3. The only advantage of solids is in the short term they have lower development costs. For a cash strapped NASA, these lower development costs will be very tempting. This is the very same trade NASA made when they picked the overall space shuttle configuration.

      3. Let’s see: 3.6 million lbs of thrust at 5.5 million tons of fuel/s, I get a Isp of about 327 microseconds 😉

  3. 5.5 million *tons* of fuel per second would equate to [very] roughly 2.7 trillion pounds of thrust (if memory serves me well). Hope they checked their test rig carefully. 😉

    2. That much thrust would affect the rotation of the Earth, hope they have contracted with Superman to correct that.

    3. the more important question is, how much payload could we put in LEO with that much thrust??

        1. I think they’re working on an additive called incumbent-anium that stretches the pork out across many terms.

    5. hmm. my offhand guesstimates (might be off by an order of magnitude or two) suggest such a rocket would be about 1.3 trillion pounds, and would need to be about the size of the Empire State Building (that feels kinda small, but i don’t want to re-work the math to figure out the right size / what i did wrong). still, that’s a truly gargantuan SRB. dunno how much it would change the rotation of the Earth.

  4. Tomorrow’s test will burn 5.5 million dollars per second or roughly what ATK earned from NASA’s Exploration program since SLS was awarded.

  7. Lost historically, amongst NASA and Space.com‘s erroneous hype on this morning’s test firing, i.e., “world’s largest solid rocket motor”, is the 156″ solid rocket motor. As a youth, in the mid 60s, I worked at Lockheed Propulsion Co (LPC), now defunct, in Mentone Calif. I worked on the first design of 120″ segmented solid motor (the Space Shuttle solid and also the fore-bearer of the motor fired today) and I also worked on the 156″ segmented solid motor. At least one of the 156″ was fired at about 4.5×10**6 lbf as far as I can recall

    The 156″ motor was to be a mobile ICBM that could be launched from movile transporters at randomly placed locations about the US and moved about on the interstate highway system. In fact, the height of the overpasses on the interstate highway system was set to accommodate the 156″ motor and transporter. It is funny today but when the motor was transported from Mentone (the manufacturing facility) to the Protrero ranch (the firing facility) along an interstate, it was necessary to let air out of the transporter tires to get under an overpass. This was not funny at the time.

    At that time, there were competitors in the solid rocket industry. For the big motors, there were LPC, and aerojet in sacramento, and thiokol in Utah. The utah facilities survive under the ownership of Orbital. I don’t believe the others actually fired a 156″ but they made competing designs before the program was cancelled.

    The 120″ solid has just evolved over the last half a century not much changed from the designs of the 60s. At that time various thrust vector control approaches were tried. Nozzle erosion and case insulation depletion, etc, was studied then as it is now. This firing was hardly a technological breakthrough. The reporters and NASA PR people should look over their facts before they make erroneous pronouncements.

    Tom Kosvic

  8. I think maybe they got things confused with the NASA portrayed in Interstellar which was planning to launch large numbers of humans into space. Although the NASA in Interstellar was going to use anti-gravity propulsion which is purely fiction because I don’t think there is a very big lobby base for anti-gravity drives

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