Every SpaceX Super Heavy Starship Decision is for Faster and Cheaper Development

Elon Musk and SpaceX have simplified the Raptor engine and the Starship engine design. Every decision that is being made from the use of stainless steel metal, reduced payload and lower powered engine is being made to speed up the development and lower the cost to achieve a working Super Heavy Starship.

Elon Musk had previously estimated that it would cost $2 to 10 billion to develop the Super Heavy Starship.

I think if the tests and launches go smoothly the first SpaceX Stainless Super Heavy Starship could be flying to orbit late in 2019 or early in 2020. This might only cost $1 billion.

Even if the payload capacity drops from 100 tons to 70 tons it will not matter, because it will be fully reusable and more powerful than a Falcon Heavy. If the Super Heavy Falcon Starhip only could manage six reuses it would still be a lower price per kilogram to space.

SpaceX has a working, durable and reusable heat shield with the PICA-X material. If they had to apply PICA-X to 20% of the Starship that needed more protection, the launch system would still be better.

44 thoughts on “Every SpaceX Super Heavy Starship Decision is for Faster and Cheaper Development”

  1. Hi GG
    A peculiar thing of power-limited propulsion is that the average speed needs to be 2/3 of the cruise speed. The maximum cruise speed is attained when the mass-ratio is 4.42 and the rocket spends ~2/3 of its time accelerating/decelerating. Thus, in your example, 200 years boosting to cruise (~40 yr/ly), 200 years coasting, and 200 years braking. That’s the ‘sweet-spot’ of speed-to-specific power.

  2. IMHO, TAE’s current reactor design is not suitable for a fusion rocket. According to the Princeton PFRC patent, Intense NBI Beams require large FRC plasma radius to hadle it. Their first commercial reactor is 350ft long. It is too big to carried by the launch vehicle. I think the magnetic pumping heating mechanism(published on TAE’s research library) might be a solution for the size problem.

  3. The thrust from the fusion products would be tiny. For launch you’d want to use the heat to push A LOT more hydrogen out the back. Think nuclear-thermal.

    But the real problem is the size of the reactor. Fusion is hard; compact fusion is extremely hard. A fission rocket is a piece of cake by comparison.

  4. Keep in mind that E ~ F*Isp. A higher thrust per watt means lower Isp, and vice versa. Low thrust per watt is bad, but low Isp is worse.

    If you want both to be high, you need LOTS of power (and you end up throwing most of it out with the exhaust; the ship gets only a small fraction). Therein lies the problem of interstellar rocketry (or even far interplanetary). Either you waste fuel (low Isp), or you waste energy (high Isp).

    Maybe some day we’ll find a way around this with some sort of propellantless drive, but barring new physics, that’s equivalent to finding a new energy source. And new physics may well be a requirement.

  5. Well, the real problem is one of “powers of 10”.

    To get an “interstellar” rocket, one has to require a significant (if modest) fraction of the speed of light as the “drift” velocity.  

    This in turn drives the total trip time between stars. 

    For 50% fuel-mass-fraction (acceleration), and 25% (deceleration), the “years per lightyear” drift velocity is about 45,000,000 / Isp.  

    Thus for Isp of around 30,000 … that’s 1500 years per light year.  

    But for Isp at 300,000 … it becomes 150 years/LY. 

    For our local neighboring stars (within 10 LY), human lifespans of 75 years, maximally say 20 generations (30 years each) for a trip of 600 years, well … the ship needs to get down to 60 y/LY. Isp thus needs to be 750,000. 

    Then the problem becomes the massive energies needed to get rid of that 50% of fuel in a reasonable (10%?) amount of total trip time. 30 burn years. 4 megawatts per launch-ton. 

    Just saying,

  6. geometric average of those:

    Fsp = √(5 N/MW × 10 N/MW) ≈ 7 N/MW

    Isp = 2/(9.81 × Fsp/1,000,000)
    Isp = 29,125 s

    dm/dt = 2⋅1,000,000 W/(9.81 × 29,125 Isp)²
    dm/dt = 24.5×10⁻⁶ kg/MW
    dt/dm = 1.29 megawatt-years per ton

    This of course means that if we’re somehow with unicorn dust able to produce a scaled up version of this that burns 1,000 MW continuously, that it’d be able to go thru 1,000 tons in 1.29 years. For a spacecraft having 50% of its rest mass as combo-fuel-and-reaction-mass, well … 

    7,000 newtons (7 per MW)
    1 GW = 773 tons a year
    25,000 tons = 32 years. 
    Ultimate speed, about 200 km/s or 0.07% speed of light.
    Drifting to Alpha Cen, 6,200 years. 

    So yes, while the 7 N/MW … Isp = 29,150 value is just awesome, the ultimate speed of the 75% fuel (50% for the acceleration, and 25% for deceleration) vehicle, burning a friggin’ gigawatt, still would take 6,350 years or so to get there. 

    Need a higher Isp. And WAY more power. 250 GW, 490 drift years, 21 years of acceleration, 7 years of deceleration. 520 years trip. 15 generations of people with ordinary lifetimes, given space radiation degradation hazard. 

    Just saying,

  7. Your computations are correct GG, but your implications missed my point – the fusion rocket will not perform as advertised. Still great performance, just not Interstellar Class.

  8. And… in particular, the higher the Isp, the combination of the less reaction mass is blasted out the tail end, AND the more energy it takes to get even fairly tiny amounts of acceleration.  

    F ≈ 2P/(G₀ Isp)

    So for a given power, the force a rocket produces drops inverse-linearly with respect to Isp increase. e.g. for 250,000,000,000 W “big boy”, and 360,000 Isp:

    F ≈ 2 ⋅ 250,000,000,000 / (9.81 ⋅ 360,000)
    F ≈ 142,000 N

    And it also turns out that:

    dm/dt = 2P/G₀ Isp)²
    dm/dt = 2 ⋅ 250,000,000,000 / (9.81 ⋅ 360,000)²
    dm/dt = 0.040 kg/s

    The problem becomes “if you have a REALLY powerful (250 gigawatts!) fusion generator, its going to weigh a huge amount. No way around it. Heat dissipation, at the very least. 50,000 metric tons? 100 thou? BIG.  

    Since we need to lose 50% of the base mass of the ship to obtain about 1% of speed of light, well.  at 0.040 kg/s, its going to take a LONG time to use up those thousands of metric tons.  

    100,000,000 kg ÷ 0.040 = 79 years.  To get up to speed. 
    At 0.014% of 1 earth gravity, rising to about 2x that mid-flight.

    My earlier calculations were off by a few factors of 2, 4 and different rest masses.  

    Alpha cen in 540 years! Yay! Have to grow a lot of food, raise a lot of kids, try not to “lose it” intellectually while careening to Centauri.

    Just saying,

  9. Yeah but this is a fusion plant (probably a thousand tonnes even if the optimistic projections work out) with a thrust of 3.8N. It won’t be launching from anything with more gravity than a small comet.

  10. …try launching from Earth’s gravity well with an ion engine, tho. 🙂

    …or Mars’.

    …or even the Luna’s or Titan’s.

  11. Although making a fusion rocket is apparently simpler than a viable fusion power plant, if the result is a multi-thousand tonne behemoth the size of a sports stadium then it will be rather difficult to get it into space where the low thrust will be useful.

    A multi-thousand tonne power plant on the other hand is just normal. You hardly have to get them into the air even once.

  12. That seems to be what they are saying, but your comparisons aren’t (as far as I can tell) relevant.

    Because although the ISP is fantastic, the total thrust is very low. 3.8 N for example from the table for the CBFR_D-T scaled to 100MW.

    A better comparison is with the various ion drives, where ISP of thousands of seconds is the norm.

  13. Radioisotopes aren’t a problem if you are expelling them from your ship at many km/s.

    Likewise, flammable fuel is not a problem if the nearest free oxygen is back on Earth.

    These designs are for use in deep space only.

  14. take off at sealevel with fusion engines”

    “I was wondering that too. Even if it does not have enough T/W for vertical takeoff then maybe from a runway. I think that requires a T/W of 0.33. The fact that it does not need a lot of shielding is a big plus in this regard. Potential STO. But I suppose it would not burn through much of its fuel before exiting the atmosphere where you would need more thrust to weight.

  15. Yeah, It would be good see past performance increases and how it lines up with their future targets. And then why they seem so sure that they will not run into unforeseen barriers.

  16. And № 3:

    The 50.8 MW design output would, fed into:

    E = ½mv²
    50,800,000 = ½m(G₀Isp)² (ISP = 360,000)
    dm/dt = 8.15 milligrams per second, or
    dt/dm = 1.42 days per kilogram
    dt/dm = 3.9 years per ton

    If the 50:50 ship mentioned in № 2 had a significant mass, say 4 × 250 tons = 1,000 tons), to burn off the 500 tons would take 1,944 years. At 50.8 MW. 

    Only 19.4 years at 5 GW. Probably more massive though. Meaning longer again. I’m guessing that something practical would happen at 50,000 tons, with a 250 GW bank of thrusters. Burning together about 0.198 kg/s, or 1,250 tons a year. 0.5% of the original loaded mass each year, for a 20 year burn.  

    Initially producing ¹⁄₇₀₀₀ Earth G acceleration, and by 20 years later, ¹⁄₃₅₀₀ worth. Not much. 

    Thing is, “obviously”, the amount of energy really needed is almost impossible to grasp … in a 50,000 ton machine. A quarter terawatt.

    110 years to Alpha Centauri. But at least it stops when it gets there.

  17. TAE Technologies emailed about how they are not working on the fusion rocket. I knew they were not working on it, but wanted to publish the 2004 paper. I expect and agree that the handful of companies focused on nuclear fusion rockets are ahead. Still my point is that if a company can make a commercial nuclear fusion reactor on land then creating a nuclear fusion rocket would not be that difficult. Although, General Fusions design approach does not lend itself to conversion other than as a power source for a high efficiency drive. TAE also said 2023 is only the start of commercialization. Starting 2023 on commercialization is still aggressive. Going from no net power to net power in about 2 years and then to P-B11 are all huge leaps.

  18. Perspective № 2:

    Yes, it is. The specific energy per unit thrust is 1.8 MJ/N. That is a lot of energy per newton. If one’s space ship was composed 50% of fusion-fuel-as-reaction-mass, then from Tsiolkovsky’s Rocket Equation:

    ΔV = 369,000 × 9.81 × ln( 1 ÷ 0.5 )
    ΔV = 2,500,000 m/s or 
    ΔV = 0.84% of speed of light. 

    Supposing that the ship is actually 75% mass as fuel-reaction-mass, then one could burn the first 50% to accelerate ‘to speed’, and the other 25% to decelerate completely. 

    However, in the perspective of a 400 MW fusion thruster, knowing that the previous calculations tell of using 1.8 MJ/N (1.8 MW/N⋅sec), the thrust is only 222 N. How much does the smallest useful H-B aneutronic doohickey weigh? 100 tons? 250 tons? 1,000 tons? The ship has to be 3× more than its empty weight in fuel. 

    Just saying,

  19. Given that the Pearl Street Station started out serving 400 light bulbs from a 50×100 ft building, Edison could afford to build it himself. Edison didn’t develop the steam engines that turned the dynamos. He bought them from the Arrington & Sims Engine Company. The steam engine had been around for about a century, so the R&D for that part was already taken care of.

  20. Am I correct in reading that 1.4 ISP figure as meaning 14,000 seconds?

    Whereas the best chemical rockets can only hope to get up to 440 ISP or so?

    And NTRs would only get about twice (about 850 ISP in vacuum) that of chemical rockets?

  21. Careful about making fusion predictions, we haven’t had even sustained operation of these type of reactors. On paper everything looks good. From some simplistic over linear thinking reasons you tend to believe that technology moves single handily directed by some very bright individuals and companies. It only rarely happens like this anymore. Mostly, new technology is coming one piece on top of the other.

  22. Since the fusion products are charged particles and does not release neutrons, the system does not require the use of a massive radiation shield.

    Technically, that is not true as some neutronic reactions occur. As per this report, aneutronic fusion reactions are defined as a form of fusion power where no more than 1 percent of total energy fusion released is carried by neutrons (https://www.njleg.state.nj.us/2006/Bills/A3000/2731_I1.HTM)

    But for p-b11 reactions, it is just 0.1% that emit neutrons: 11B + α → 14N + n + 157 keV

    But for a rocket, who cares?

    I love that phrase ‘who cares?’. Meaning, for rockets you can say that about a lot of things regarding fusion, as this article makes clear. So why haven’t we developed nuclear fusion rockets already? I don’t see where the excuse lies, other than funding.

  23. The private sector is doing a great job all by themselves funding r&d for that impressive Direct Fusion Drive.

  24. Bear in mind that TAE’s current machine has confinement times that are short by a factor of 1000 from what they need and temperature that is short by a factor of 100 from what they need for p-B to be a viable commercial reactor.

    They need to improve by an order of magnitude per year to hit their targets.

  25. Hmm… 


    E = ½mΔv² (kinetic energy)
    F = mΔv (thrust)
    E/F = ½ΔV
    ΔV = G₀ Isp


    ½G₀Isp = specific energy per unit thrust
    50.8×10⁶ ÷ 28.1 = 1,806,000 J/N = ½ 9.81 Isp
    Isp = 369,000 

    Which is not 1.4×10⁶ s of course, but rather more like about 25% of 1.4×10⁶. While I agree something’s off, it mostly might be (½)² “in the wrong direction”. 

    Just saying,

  26. While TAE’s fusion drive ISP will be quite good I don’t know that their T/W will be that usable. Their p-B reactor has a length of 350m. not counting radiators, coolers for their cryogenic superconducting magnets, etc.

    Also it isn’t clear to me how a FRC just opens up one end to make a fusion nozzle. Generally a FRC has a plasma injector on both ends of the “warp core” (sure looks like one, mad props for that!)

    (edit: fusion rocket schematic may be for some other fusion rocket)

  27. wonder if you could take off at sealevel with fusion engines… obviously better than “nuclear fission” engines in terms of radiation fall out… was wondering about that because Russia was claiming recently to have developed a “nuclear” powered hypersonic missle… to the point of openly bragging about how fast they could destroy the world before a US missle defense interceptor missles could respond … of course I suppose that could be the CIA putting words in their mouth so they can motivate a US weapons programs… or maybe Vladimir is getting all macho…

  28. you need shielding… high energy ions are dangerous because they kill living cells… that’s how they treat cancer by killing cells with high energy ions. Maybe less shielding is needed because the output of the fusion reactor are not radio isotopes that take years to decay.. another plus is the fuel is entirely non-flammable and not no-radiactive as well…

  29. Governments can act as enablers and early investors for some technologies and societal developments (e.g. the settlement of the American West, nuclear power), but still, most technologies come without or despite the government’s intervention.

  30. That one is indeed impressive. A thrust per watt ratio of 5-10 Newtons per Mwatt is far above the figures mentioned by the link above.

    And it is already being actively researched for space use, which means a faster adoption if it pans out.

  31. “Technology typically progresses the other way. The natural gas plants that produce much of the electricity in the US are an evolution of jet engines invented by the military”

    Which military program, government program, DARPA grant, or Federal tax incentive built Edison’s Pearl Street power station in 1882?

    History began before jet engines and the private sector was providing power long before the government even knew what was going on. There was a thriving privately funded market for electricity and power plants long before your timeline began.

  32. Getting rid of excess heat will be a problem with most nuclear space propulsion. Most will need large radiators which will have high mass.

  33. The Exhaust Velocity figures are screwy. If the jet-power is 50.8 MW and the thrust is 28.1 N, then the effective exhaust velocity is a bit over 3,600,000 m/s. Still good, but inconsistent with the claimed 1.4 Ms Isp. I wonder how the newer figures on the energy balance of the Fission alpha particles affects this?

  34. Fusion will face fierce competition on Earth, considering the many mature power sources around and the long ramp up for any new comer to catch up.

    But it will be really at home in space, where vacuum conditions are easy to get and even some amount of leftover neutrons aren’t such a big problem.

    And where it can be adopted right away, for thrusting probes and even manned ships needing that thrust and power for long periods.

    But given it takes several years to develop a system for use in space, this probably will have impact by the mid 2030s. Enough time for some chemical rocket space travel economy to develop and require it.

    But then, oh boy. Manned trips to Jupiter, Saturn, etc. become feasible, the same for earlier interstellar missions to the Sun’s gravity lens or the Oort cloud.

    And of course, by developing it further, up to legit interstellar travels at 4-5% c taking 80-90 years to get to Alpha Centauri. Yeah, people in the 22th century will probably see that.

  35. Technology typically progresses the other way. The natural gas plants that produce much of the electricity in the US are an evolution of jet engines invented by the military. Nuclear power plants are commercial versions of military power plants. Velcro was used in space before it made it’s way to shoes.

    Monopolies are better at providing cost recovery for R&D than markets.

    If there is a viable monopoly application, the technology will be deployed there first. Maybe pulsed fusion for pulsed operation of rail guns or laser weapons. Maybe to be the first to get to 1% of light speed. I have no idea.

  36. They were accelerated by the same reactor, so the net thrust from the particles you catch is zero. It’s the particles that are not caught that cause the thrust.

  37. wouldent the alfa particles wich are converted into energy provide thrust? particles are “slowed down”

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