The Dream of Single Stage To Orbit

    One of the dream options for easier access to space is Single Stage To Orbit (SSTO). In theory, as usual, everything is beautiful - graceful ships accelerate along the runway, fly into the sky, accelerate to space speeds, go into orbit, unload the payload, slow down, and board the same runway. In reality, again, as usual, various problems, so imperceptible at the stage of dreams and preliminary design, led to the fact that such devices have not yet flown in the entire history of astronautics. In this post I would like to talk about why it happened. And also we will fly on Skylon'e in Orbiter.

    Let's put things in order in the definitions

    First of all, it must be said that “desired SSTO” usually means “SSTO + reusability”. Or "SSTO + reusability + wings (airplane take-off / landing) + oxidizer from ambient air." The fact is that creating a single-stage rocket that would put a small load into orbit now will not be particularly difficult. Even at the dawn of the space age, this was possible. The first stage of the Titan-2 ICBM could launch a very small payload into space, and the Atlas ICBM was constructively “almost-SSTO”. But creating a one-time single-stage launch vehicle does not make sense, because it will be very irrational. A single-stage rocket would have a mass of 100-150 tons, and in this case would output no more than a ton. At the same time, a two-stage rocket with the same PN will fit in 50-70 tons. These are interesting features of the Tsiolkovsky formula.
    Therefore, various SSTO projects almost always involved reusability. The designers hoped to benefit from lower operating costs that was lost on the inefficiency of one stage. Quite often, the device was winged, so that the wing's lifting force helped in flight. Also quite often quite unusual engines stood on the device, using the unique characteristics of which, the designers hoped to design an effective and profitable medium.

    Bit of theory

    Consider the various ideas proposed in terms of the advantages and disadvantages of each solution.


    Reusability alone is not a panacea. Reducing the cost of building new copies of the carrier does not necessarily offset the costs of preparing the carrier returned from the flight for the next flight. One of the posts in the series “Facilitating Access to Space” tells a sad story about the Space Shuttle program, the economic study of which turned out to be wrong.


    The wings for the spacecraft are also a double-edged sword. On the one hand, you can use their lift and make a controlled landing on the airfield. On the other hand, the wings are dead weight outside the atmosphere (and the atmosphere, which is dense enough to support it, ends depressingly quickly), you need to spend additional fuel for their acceleration and braking together with the device, and you need to spend additional mass on the heat insulation of the wings so that they do not burn out during braking in the atmosphere. In addition, the winged vehicle will accelerate along a more gentle trajectory than a vertically launched missile, which will lead to additional losses.

    Use of atmospheric oxygen

    It is a logical idea - why should we carry an oxidizing agent if we can collect it from the atmosphere during the flight? But reality is making its price again. Each jet engine is effective in its speed range; it is irrational to put many different engines on one device. And of epic complexity, the SR-71 multi-mode engine clearly says that this is not an option at the current level of technology. You can still cool the air (in the limit - to liquid oxygen), but here there are pitfalls. A refrigeration unit places high demands on materials, is a mass useless in space, something needs to be done with nitrogen from the atmosphere, and cooling also requires energy, and this energy must be taken with you in some form.



    Historically, Atlas ICBMs became the first and only almost-SSTO implemented in metal. It was built according to the “one and a half-stage” scheme, and during the flight dropped the tail compartment with two side engines, continuing the flight on the remaining central one.

    In this version, the launch vehicle could put into orbit about 1,400 kg with a launch weight of 120 tons. Subsequently, accelerating blocks (“Able”, “Agena”, “Centaur”) were placed on top of the rocket, increasing the payload, but, of course, losing the right to call it SSTO.

    What is curious, according to the same scheme, there was a project based on Saturn-V. Apparently, it was such a “downgrade” too powerful for the low Earth orbit of Saturn V. Theoretically, it would still be possible to save the tail part, but it seems that there were no serious studies of this.


    The project , developed from 1958 to 1963. It was equipped with various engines, from engines with atmospheric oxygen liquefaction to direct-flow nuclear engines. For the variant with atmospheric oxygen liquefaction, the following scheme worked: atmospheric air entered the heat exchangers, in which fuel - liquid hydrogen circulated. They extracted oxygen from the air, which was then fed into a buffer tank, from which it went to the engine. In 1960, a demonstrator engine with a thrust of 12 kilograms was even created, which successfully worked for five minutes. Due to the novelty of technical solutions, the project was quietly closed in 1964.

    Shuttle Alternatives

    The launch of the Space Shuttle spawned several alternative projects, including several SSTOs.
    Chrysler SERV
    Source 1 , Source 2
    A very unusual looking reusable SSTO project with vertical launch and landing.

    Gross weight is 2040 tons, MO for low Earth orbit is 52.8 tons

    Martin Marietta Langley SSTO

    Gross weight is 1925 tons, MO for DOE 29.5 tons. It is bewildering, where are they so many engines, and different?

    Boeing Langley SSTO
    Source The

    light version of 1,180 tons and the heavy version of 3,438 tons were in the project.

    Boeing LEO VTVL SSTO
    Another marvelous unit with vertical take-off and landing. The launching and landing sites were to be special artificial lakes with a diameter of five kilometers.

    In different versions, the starting weight is from 5400 to 10300 tons.


    Against the backdrop of the triumph of the gigantomania of the 70s, the HOTOL project looked practically feasible. The sane spacecraft was built around the unique RB545 engine . Little is known about the engine; for some reason it was classified. But the principle of operation is known, it is a familiar idea to us to use liquid hydrogen to cool atmospheric air with the extraction of oxygen from it.
    The project was closed in the 90s, when it became clear that the rear position of the engine shifted the center of mass back, which requires shifting the maximum center of pressure far back to ensure flight stability. In short, the design made sense to start over, and it seems that there was no more money or desire.

    "Sivka" Feoktistova

    We also thought about SSTO. For example, engineer and cosmonaut Feoktistov developed the project of the Sivka rocket , weighing about one and a half thousand tons. The rocket had to take off vertically and land vertically.


    In this project, they decided to use a new type of engine - a hypersonic ramjet. The heat resulting from friction against the atmosphere was supposed to be collected by the heat carrier under the casing and sent to the combustion chamber. This approach promised to make available a speed of 20 M, and this is not far from the first space one. In various versions, the X-30 was developed as an ultra-high-speed passenger liner or spacecraft carrier. The total mass was 136 tons. It was supposed to use a mixture of liquid and solid hydrogen (sludge) as fuel. In 1993, the design was stopped due to budget cuts and technical concerns (for example, how will a device that has only one engine operating at hypersonic speeds take off on its own?)


    Prototype (scale model) of the SSTO vertical take-off and landing apparatus. Successfully tested in the 90s, like previous projects, fell victim to funding cuts. There are videos of successful flights and crash during landing:


    90s, vertical take-off, horizontal landing. The prototype, the large-scale model X-33 , was stopped in 2001 due to problems with the design (microcracks in the tanks of liquid hydrogen), problems with stability and excess weight, and, again, reduced funding.


    SSTO using helicopter blades. The blades, driven by jet engines at the ends, were to be used as the main engine during take-off, to operate the compressor at the launch and to slow the machine by autorotation at landing. A prototype with blades, without engines and thermal protection, successfully flew up, but the company went bankrupt in 2001.


    Implementation of the concept of "big simple cheap rocket." One stage, according to the design, up to a third of emergency starts are permissible. The starting weight is 130 tons, the payload is 1 ton, the rocket is designed as simple and cheap as possible - one engine, displacement feed, unless the use of liquid hydrogen is somewhat out of concept. The developer applied for the COTS (Commercial Orbital Transportation System) competition, the application was not selected, the project was closed.


    Probably the only living project right now. It is being developed in Britain, apparently, by people related to HOTOL, because it carries the same principles - horizontal launch and landing, wings, an engine with cooling oxygen from the air.
    Judging by the information from the company's website , in the summer of 2013 they received £ 60 million from the British government, and signed a contract with ESA for € 1 million to study the orbital transportation system. Parts of the engines are tested, the engine has not yet been fully tested. Accordingly, until the work is demonstrated (and the design characteristics for traction, fuel consumption, etc. are confirmed), it is too early to talk about any future project. Unfortunately, knowledge of the history of various SSTO projects is pessimistic.

    Engine with explanations. Material from the website of the company.


    In the virtual world, on the contrary, everything is wonderful. In particular, there is an addon with Skylon for Orbiter. We will need:
    1. Skylon C1
    2. Addon to addon - Skylon C2
    3. spacecraft3 and multistage2
    4. Universal Cargo Deck 4
    5. Velcro Rockets

    By the way, enthusiasts from the VK group Orbiter made the Russification of the program (without MFD, unfortunately). If you wish, here is the link .

    After installing all this stuff, we launch the Skylon C2 script.

    Our task will be to enter a low Earth orbit (200x200 km) and a controlled landing on Cape Canaveral. It is assumed that you are already familiar with Orbiter from my previous posts.

    Switch to the view from the cockpit, set the trimmer all the way up, and turn on the engines (standard button, Num + ). Skylon will not be able to tear itself away from the strip, at its end you need to help take-off by pressing Num 2 . Immediately after take-off, turn around 90 degrees.

    The car keeps a steady course, after a turn no special intervention in control is required. Trimmer is enough for a steady climb. Fuel in the jet engine mode will be enough up to about 27 km in altitude and speed of 5 M. When the fuel remains a little bit, switch F3 to the “second Skylon” - “Skylon_rocketmode”. Turn on the main engine there.

    You can switch back to Skylon C2 and close the air intake flaps on Left Shift - Num 1 , but this is purely for beauty. We continue to disperse until the height of the apocenter is 200 km. We turn off the engine.

    We are waiting for the apocenter point, taking a position along the vector of orbital velocity, giving an impulse to raise the pericenter.

    We are in orbit!
    Unfortunately, there is not enough fuel to fly to the ISS, so we turn on the music and begin to prepare for landing.

    I recommend watching the video in full screen sometime later.

    Unfortunately, for the Skylon_rocketmode ship, the MFD card is shamelessly lying, so you need to switch to Skylon C2. Or just know that from the first turn we have enough horizontal maneuver for landing. The procedure is standard - at a distance of 17,000 km we slow down until the MFD Aerobrake shows a shortage of 1000-2000 km. Brake carefully, the engines have become too powerful for an empty Skylon.

    Orientation engines normally work only in Skylon_rocketmode, therefore up to ~ 100 km we support orientation by them.

    Now our task is to set the trimmer up and walk with a snake, maintaining a descent speed of about 100 m / s, extinguishing speed and tracking so as not to shift away from the spaceport. Virtual Skylon behaves very obediently in the atmosphere, I almost forgave the developer the need to switch between the two ships.

    Notice which snake Aerobrake MFD draws.

    Wings make the landing truly controllable. It is necessary to monitor the vertical speed, direction to the landing point, altitude and speed of flight. We continue to walk as a snake: We

    turn around behind the Cosmodrome

    Strip across, but it's not scary. If you played flight simulators, then you know that you need to aim somewhat away from the strip.

    Well, the strip is almost at the heading.

    Remember to release the chassis with the G button and sit down.

    Have a landing!

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