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You’ll believe a water tower can fly

Some time in the next week or two, pending only FAA aproval, SpaceX is planning to fly Starhopper, a test device for their next generation Starship launch system. Starhopper looks like a water tower with an attached rocket engine, mostly because it is indeed a water tower with an attached rocket engine. Starhopper is planned to rise to 200 metres into the air and then land, testing control systems and engine technology. This is a follow-up to a previous 5 metre test flight.

The engine is a brand new design called Raptor, which has a high specific impulse, meaning it is unusually efficient. Eventually, Starship will use up to 41 Raptor engines.

The test flight will be an exciting moment. The reason space travel is so expensive is that conventional rockets get thrown away after only a single use. (Imagine how unaffordable a flight from London to Berlin would be if the aircraft were thrown out at the end of the trip.) While a Saturn V would cost roughly $1bn today, the fuel would only cost about $1m. The bulk of current spaceflight cost is thus the cost of expending an extremely expensive piece of capital equipment instead of reusing it.

So, there is an opportunity to reduce the marginal cost of getting objects into orbit by orders of magnitude. SpaceX have already achieved some re-usability with Falcon 9 and Falcon Heavy. However, Starship will be both much bigger (it will lift 100T or more into low earth orbit compared to Falcon Heavy’s 65T) and is the first ever fully reusable orbital launch vehicle (Falcon 9 and Falcon Heavy do not recover the second stage). It may even cost less to fly 100T into orbit than it currently does to launch a very small rocket like Rocket Lab’s Electron that lifts only 250kg to orbit at a price of about $7m.

Because it will be able to be refueled in orbit, it will also be able take that 100T to the moon or even Mars (albeit at additional cost because of the need for flights to loft the fuel.)

In other words, we are witnessing a revolution in space travel.

And with that stainless steel design, which can be transpiration cooled to avoid the use of heat shield tiles, it looks just like space travel was supposed to look back in the 50s.

23 comments to You’ll believe a water tower can fly

  • Gavin Longmuir

    https://www.youtube.com/watch?v=wv9n9Casp1o

    Sad thing is that the Delta Clipper DC-X was demonstrating this technology in the early-to-mid 1990s — a quarter of a century ago.

    We have wasted so much time with politically-driven concepts like the Space Shuttle, and wasted so much resources on junk science like Anthropogenic Global Warming and “renewable” energy.

    China performed its first test with a launch & return rocket only a few days ago. If we in the West don’t get our act together, we are going to be left far behind.

  • Brian Swisher

    Rockets that have fins and land on their tails — just as God and Robert Heinlein intended.

  • Bruce

    Not sure if I get the bit about the use of Methane as a fuel.

    Compressing and storing it can be a challenge.

    It has a MUCH lower energy per Kg than most “bigger” hydrocarbon molecules.

    Do they have a pipeline to the piggery?

    A bunch of us started fooling around with “effluent digesters” decades ago. Anaerobic decomposition at its finest… part of the problem is to get “pure” methane; with no traces of nasties like ammonia, etc. Yes. it can be liquified. It occurs naturally as a liquid in methane lakes…..on Titan, for instance.

    Amusingly, one minute the eco-nazis are rabbiting on about the evils of Methane as a “greenhouse gas”, then they want to burn the stuff, creating TWO “greenhouse gases”, CO2 and water vapour. Situational ethics ROOL!…..apparently.

  • MadRocketSci

    I’ll have to do the math: It seems counterintuitive that transpiration cooling can be any lighter than a non-ablative heatshield, but then again, with space travel, intuition needs training. They’ve probably thought about it.

    As for high isp – I don’t think anything beats hydrogen/oxygen due to exhaust molecular mass: I’ve heard claims that the bottom stage is supposed to be SSTO capable all by itself. I’ve seen claims of 500sec Isp for the raptor engine (that *has* to be wrong? sub-400 sec at any attainable chamber temp would be my guess). I’ve also seen claims back in the 90s that the DC-X followon (delta-clipper) was supposed to be SSTO just because the suborbital test vehicle was. Both claims clash with what I know: with the specific impulse obtainable by chemical propellants, any SSTO vehicle would need to be a >90-95% propellant mass fraction fuel balloon with barely anything leftover for the tank structure. Not impossible, but not easy to make reusable.

    The baseline design seems to have a booster, which I imagine anything chemical-propelled launching from Earth would have to have.

    I’m glad they’re at least trying to build what they plan, and I wish them luck. There seems to be a lot of almost manic claims made about SpaceX’s plans though, mostly by the fans. Is it weird to like what the company is attempting, but find the fans and “community” grating?

    PS: While LOX/LH2 has higher attainable Isp than just about any chemical fuel save exotic/unuseable stuff like LH2/LF2, it is a royal pain in the ass to store. I’m glad they’re sticking with hydrocarbons – far more practical IMO. While the specific impulse means the vehicle will weigh more, the density and liquifaction temp means it’ll be a lot smaller and can have lighter structure and less insulation.

  • MadRocketSci

    The efficiency of a chemical rocket is determined by the exhaust velocity of the propellant jet, which is governed by the specific energy of the propellant reaction (energy/mass ratio), and the molecular mass of the products. The rocket nozzles are actually pretty good (90ish – 95% efficient) at converting that energy into directed KE of the propellant jet, so there’s nothing to gain there. The reaction can be made denser by increasing the chamber pressure, which increases thrust, but within pretty narrow limits, the propellant choice governs the exhaust velocity (jet speed, which for historical reasons is given as “specific impulse”).

    Methane/Oxygen isn’t that bad. https://www.engineeringtoolbox.com/standard-heat-of-combustion-energy-content-d_1987.html

    55 kJ/kg methane is a little on the high end of what you can expect for hydrocarbons. (~50 kJ/kg is a good round number for just about all of them.)
    The exhaust molecular mass is also probably pretty comparable for stochiometric mixtures for all of them. (Only so many hydrogens you can stuff onto a carbon chain, no matter how long.)

    Kerosene rockets are usually in the 340ish – 360ish sec range for isp (3300 m/sec exhaust velocity).

    That’s probably the “why” behind methane/oxygen. Also, it was chosen as a propellant for Mars Direct, because there is a chemical process you can use to synthesize it from water and CO2 (driven by a nuclear reactor) on Mars to refuel for a return trip.

  • MadRocketSci

    Heinlein’s sci-fi novels often posit a theoretical material called “single-H” which was kept stable by undisclosed sci-fi materials science. If you could actually put that in a bottle and keep it from exploding until you want it to in the combustion chamber (by recombining to form H2), you’d get superlative exhaust velocity (something on par or better than nuclear-thermal hydrogen rockets) ~10000-15000 m/sec or so. And the solar system would be OURS! Unfortunately, we misplaced the materials scientist with the magic stabilizer.

  • MadRocketSci

    “China performed its first test with a launch & return rocket only a few days ago. If we in the West don’t get our act together, we are going to be left far behind.”

    You know, one thing that I’m increasingly cynical about as I’ve continued along is the competitive goad people try to use to motivate recalcitrant politicians and public support. The way it looks to me, the world is in serious danger of degenerating into a state where if we don’t get our act together, *no one* is going to be doing *anything* interesting. The competence will be gone, the organizations choked with bureaucrats and ladder climbers with engineers firmly at the bottom of their totem poles spending all their time making viewgraphs to try to sell their work to managers. (The Wright Brothers could not have invented the airplane had they worked in someone else’s bicycle shop. They didn’t have to *justify* themselves to *anyone*!!)

    Anyone competent is a breath of fresh air. The non-spacex American program is a zombie. The non-SpaceX American aerospace industry in general is … dead somehow. The Russian program is slowly degenerating to the point we might have to abandon the ISS soon. I haven’t heard *anything* about the Chinese manned program lately.

    This is why SpaceX is a breath of fresh air: At least they’re *doing* something other than making viewgraphs and trying to amuse bored managers.

    In my own field (undisclosed on a blog), the competitive goad is talked up in meetings, but the truth is if *anyone* was anywhere close to succeeding in ($field) there would be just about infinite money for all of us to “catch up”. Technological progress is not necessarily the inherently competitive zero-sum winner-take-all thing that corporate “wargamers” or politicians make it out to be. (Unless it’s wartime and they’re actively bombing you, then there’s a legitimate crunch!)

    The world, circa 2020 is in danger of being “left behind” by the world, circa 1950 in terms of having organizations that function.

  • Perry Metzger (New York, USA)

    Bruce asks:

    Not sure if I get the bit about the use of Methane as a fuel.

    Compressing and storing it can be a challenge.

    It has a MUCH lower energy per Kg than most “bigger” hydrocarbon molecules.

    You don’t compress it. You liquefy it, which leaves you with a very dense fuel. It’s less of a challenge to store than liquid oxygen. It has an enthalpy of combustion of 55.125kJ/g, while n-octane has an enthalpy of combustion of 48kJ/g, so it should be obvious that it has higher, not lower, energy per unit mass than longer chain hydrocarbons. (You perhaps were looking at tables of enthalpy of combustion measured in moles, but that is deceptive because a mole of n-octane weighs much more than a mole of methane).

    Methane has several substantial advantages: a deep cryo methalox engine has a much higher Isp (specific impulse) than kerolox (i.e. RP-1 + Liquid Oxygen, which is what the Merlin engines in a Falcon 9 burn), it cokes the engine much less (i.e. it leaves behind far fewer deposits from combustion, which means that the engine requires much less service between flights), and it can be produced using the Sabatier reaction on the surface of Mars using only CO2 plus H2O at the poles, which means you can refuel the rocket using only locally available materials.

  • Perry Metzger (New York, USA)

    MadRocketSci says:

    As for high isp – I don’t think anything beats hydrogen/oxygen due to exhaust molecular mass

    That’s true, but there are good reasons not to use LH/LOx in the first stage of a rocket. One wants high Isp of course, but one also wants very high thrust. Although there are high thrust LH/LOx engines out there (see, for example, the RS-25), they’re pretty expensive and complicated, and the liquid hydrogen, though energy dense per gram, is not very energy dense per liter. A LH/LOx lower stage thus has significant disadvantages. Typically, people use LH/LOx on an upper stage, like the Centaur stage used on many US rockets, which is powered by an RL-10 engine. The Saturn V used keralox on the lowest stage, hydrolox on the upper stages.

  • Gavin Longmuir

    MadRocketSci: “The world, circa 2020 is in danger of being “left behind” by the world, circa 1950 in terms of having organizations that function.”

    Some might argue that has already happened. In a number of areas, rather than standing on the shoulders of giants, we are now hanging on to their belts. On the other hand, we should not glamorize earlier days. The 1950s saw the Allies who had beaten Germany, Italy, & Japan struggling in Korea. And 1957 saw the Ford Edsel.

    One of the interesting aspects of recent commercial successes is that they tend to come from outsiders. It was not Arianespace or NASA who commercialized launch & return — it was SpaceX. It was not BP or Shell who demonstrated how to produce gas & oil from shales, it was little Mitchell Energy. This is quite consistent with Professor Charles Handy’s theory of the Sigmoid Curve. After a period of successful progress, organizations become top-heavy, inefficient, and averse to new ideas, making decline inevitable. See Arianespace & NASA … and unfortunately many other big names.

  • Eric

    I’ll have to do the math: It seems counterintuitive that transpiration cooling can be any lighter than a non-ablative heatshield, but then again, with space travel, intuition needs training. They’ve probably thought about it.

    Musk backed off the tranpiration idea. It looks like they’re going to go with ceramics.

  • Chester Draws

    People stopped investing in space when it became clear that there is no money to be made. We can put up satellites, and that’s about it.

    We don’t need to mine asteroids, because they have no minerals not found on earth. Mars is never going to be habitable outside, with no ability to hold a decent atmosphere and lethal radiation. Space travel is just vanity — there’s literally nothing there — and humans aren’t built to live for long times in zero gravity.

    The big advances are in areas where there is money — computers, phones, biotech, etc. The advances continue in cars, planes, domestic appliances etc. We don’t tend to notice them because they are incremental, but a 1950 car and a 1919 car aren’t close in terms of comfort, efficiency, reliability etc. And a 1950 person wouldn’t even recognise a 1919 phone.

    So space boosters, get used to nothing much changing. Until there is something important that must be produced in space, we’ll be staying on earth.

  • Perry Metzger (New York, USA)

    People stopped investing in space when it became clear that there is no money to be made. We can put up satellites, and that’s about it.

    We don’t need to mine asteroids, because they have no minerals not found on earth. Mars is never going to be habitable outside, with no ability to hold a decent atmosphere and lethal radiation. Space travel is just vanity — there’s literally nothing there — and humans aren’t built to live for long times in zero gravity.

    By that criterion, there was no money in the New World either. There were no minerals there not found in Europe, no cities for people to move to, no good reason to be there. And yet, of course, people built mines and cities and factories, and moved by the tens of millions.

    As for the claim that space is uninhabitable, O’Neill colonies, constructed from materials readily found in lunar regolith, asteroids, and comets, can easily and quite affordably provide housing for humans that’s at least as comfortable as living in places like Southern California, including large “outdoor” spaces and what feels like normal gravity. I recognize some people don’t believe this is feasible; they haven’t read the engineering studies.

    Perhaps Musk and the hundreds of other “New Space” entrepreneurs out there are complete fools, and no one has any real interest in anything other than launching some satellites. Perhaps the human race has no yen to expand out into the cosmos, perhaps this is all idiocy.

    Perhaps, though, the fact that at one point the US Government was paying up to $600M* to launch 30T to LEO on a Delta IV Heavy (about $20,000/kg) but a launch soon might cost under $100/kg on SpaceX hardware, a factor of 200 difference, and that it could easily drop another factor of five while still delivering them substantial profits, might have something to do with the fact that no one has had much in mind other than high value satellites until recently, and that people are beginning to dream again given vastly lower prices.

    It’s easy to dismiss something that’s far too expensive or otherwise infeasible as something no one wants to do anyway even if it were feasible and cheap. After all, who will demonstrate that you’re wrong? Sour grapes isn’t just an Aesop fable; it’s very much the way many people think about progress. I suppose we’ll find out soon enough if all the money being spent was foolish.

    (*It’s impossible to figure out the actual cost of ULA launches because of the various layers of payments the USG makes to ULA in order to make it hard to figure it out. The current price apparent price of a Delta IV Heavy flight is $350M, but it used to be much higher before SpaceX came on the scene. It appears that a $600M price tag for early flights is not an unreasonable estimate. At $350M, it’s still an insane price.)

  • djc

    By that criterion, there was no money in the New World either.

    Lots of money: gold and silver. With the unfortunate effect of causing inflation and eventually ruining the economy of Spain.

  • Runcie Balspune

    Anyone competent is a breath of fresh air. The non-spacex American program is a zombie. The non-SpaceX American aerospace industry in general is … dead somehow.

    The “American Space Program” seems to be the libertarian ideal of proactively letting private individuals do what they are best at, in that sense SpaceX et al _is_ the “American Space Program” simply because what they are doing they could not do under another less-liberal government. Not to mention the American government does throw plenty of taxpayer cash (directly for services or as subsidies on a par with other industries) at SpaceX, so saying this is a “zombie” program is not accurate.

    The problem with many other countries’ space programs is they are still bound by the inherent benefits the government is likely to get out of them, in most cases this is a military advantage, like it was during the cold war – once you demonstrate you can get a payload into orbit, you can effectively build a ICBM. Where American military technology is moving towards is suppressing missile technology (ABMs) and diversifying the reliance on humans on the battlefield (drones), flashy orbital missions are no longer required.

  • Johnathan Pearce

    Rockets that have fins and land on their tails — just as God and Robert Heinlein intended.

    SQOTD material, that one.

  • Perry Metzger (New York, USA)

    SQOTD material, that one.

    It is an old quip, though finding the true origin is hard.

  • Runcie Balspune

    just as God and Robert Heinlein intended.

    And Hergé!

  • The competence will be gone, the organizations choked with bureaucrats and ladder climbers with engineers firmly at the bottom of their totem poles spending all their time making viewgraphs to try to sell their work to managers.

    This is the inevitable result of success… winner organizations become complacent. Keep your eye on the ball… the real currency which makes the world go ’round is competence, whether at the individual or group level… and there is no limit at scale.

  • Duncan S

    Perry Metzger – re source of the quip.

    Perhaps a variation of this title from 1994 –

    Finally, space travel the way God (and Robert Heinlein) intended it to be

    Title: Finally, space travel the way God (and Robert Heinlein) intended it to be. Title Record # 2193378
    Authors: Arlan Andrews, Sr. and Marianne J. Dyson and Geoffrey A. Landis
    Date: 1994-05-00
    Type: ESSAY

  • Edward

    The Starship is cool enough on its own. The fact that it looks like something Professor Quatermass would have designed and Colonel Dare would have piloted makes it even more awesome.

  • Bruce

    just as God and Robert Heinlein intended.

    And Hergé!

    And Aardman (Wallace and Gromit, “A Grand Day Out”, https://daegucompass.com/arts-culture/2019/05/the-art-of-aardman-animations-a-grand-day-out/ )

  • Schrodinger's Dog

    Brian Swisher, reading this, I thought of Robert Heinlein too. It looks like he’s going to be proved right and space exploration will be largely accomplished by private business. It’s terribly sad that he didn’t live to see it happen.

    And that rocket in the second picture really needs to take off and land to the theme music from Thunderbirds.

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