The Concept of an Inflatable Reusable Launch Vehicle Valentyn Pidvysotskyi1 1 Independent Researcher, Ukraine (Letava), https://orcid.org/0000-0002-0028-757X Abstract This article discusses the concept of a launch vehicle with an inflatable reusable first stage. The first stage in the form of an inflatable streamlined thin-walled tank with a low bulk density (which may be less than the standard sea-level density of air) is proposed. Compressed light gases (hydrogen, helium) ensure the rigidity of the inflatable thin-walled tank. For return to Earth, the first stage is slows down in the upper atmosphere. In the lower atmosphere, the aerostatic lifting force exceeds the Earth's gravity. Thus, the first stage will float in the air (this will prevents its destruction). Then the first stage returns to the spaceport for reuse. The inflatable first stage of a launch vehicle will be very large. Therefore, the main purpose of this article is to study the influence of aerodynamic losses on the payload. The mass of the inflatable first stage and its vertical and horizontal stiffness will also be calculate (as a first approximation). These are the main questions that need to be answer for the opportunity further developed the concept. Therefore, this article should be consider as a preliminary study, not claiming to be complete. Keywords Inflatable; Reusable; Launch Vehicle; Propellant 1 Introduction Mars, Jupiter, Titan (the moon of Jupiter) (Burke, 2014). Parachutes was use for soft landing The main reason for the high cost of space flights is (splashdown) Space Shuttle Solid Rocket Boosters 1 the single use of flying machines . After the (NASA, 1988, NASA, 2008). One of the most recent acceleration of the spacecraft, the launch vehicle examples the use of this method in astronautics is (which is a technical masterpiece worth millions or return of the reusable Dragon spacecraft (Garcia, even tens of millions of US dollars) falls to Earth, 2018). In most cases, the disadvantages of this repeating the fate of the legendary Icarus. Therefore, method include the need to equip the spacecraft’s the need to create reusable space transport systems is simultaneously with multiple systems: thermal obvious and such projects arouse of great interest. protection, parachute system and soft landing system. Currently, there are several basic methods for returning flying machines to Earth. The third return method is the horizontal (airplane) landing of flying machines (or parts thereof). The The first return method is the vertical landing of the most famous are Space Shuttle (Launius and Jenkins, launch vehicles using their own engines. Projects of 2002, Fernholz, 2018) and Buran (Kogut, 2018, such launch vehicles were develop in the past (for Afanasyev, 2018). Also known projects: MAKS example, Delta Clipper) (SDIO, 1993). The New (Plokhikh at al., 2012), XCOR Lynx (Messier, 2018), Shepard project (Spaceflight101, 2017) is develop NASP (Rockwell X-30) (Heppenheimer, 2009, currently. The Falcon 9 project (SpaceX, 2021) is on Pattillo, 2001), HOTOL (Postlethwaite, 1989), the stage of commercial use. This method of RLV/AVATAR (Martin at al., 2009), RLV-TD returning launch vehicles has good prospects for (Mohan at al., 2017), Skylon (Hyslop at al., 2019, commercial application. The disadvantages include Arefyev at al., 2019), Boeing X-43 (Hanlon, 2004), the high consumption of propellant during landing. It Cold (Rudakov at al., 1999), Dream Chaser (Federal leads to decrease in payload, and the additional Aviation Administration, 2018), SHEFEX (Longo at consumption of the resource of rocket engines. al., 2006), SpaceLiner (Lariviere and Kezirian, 2019) The second return method of the spacecraft’s (or and others. The disadvantages include the need to parts thereof) is to use parachutes. Parachutes are equip spacecraft’s with wings, empennage and widely used in aviation and space technology. They landing gear (which increases aerodynamic losses, repeatedly was use for landing probes on Venus, complexity and mass of the construction). All of these methods can be use individually or 1 If buy a new Red Tesla car for every trip to the store for together (in various combinations). However, their groceries, then transportation costs can become comparable to the application did not lead to a multiple decrease in the costs of delivery to low Earth orbit. cost of spaceflights. Therefore, there is a need to fabric. Based on these measurements, the optimum develop other methods of return (for example, using stitching (or gluing) line of these pieces will be aerostatic force). For this purpose, we can use an calculated. A thin gas-tight film will be glue to the inflatable balloon folded inside a special container. If inner surface of the first stage. A special this balloon is made large enough (and filled with impregnation can use to seal the seams. After light gas), it can keep the spacecraft in the air. The stitching the outer shell, into the first stage can main disadvantage is the long deployment time of the pumped gas (air, etc.). After that, it is necessary to inflatable balloon. For example, during the VEGA sew on internal partitions, install systems and Venus balloon experiment, a balloon with a diameter mechanisms, etc. For made of inflatable first stage ≈ 3.4 m deployed in ≈ 100 s (Sagdeev et al., 1986). can used existing airship hangars. As the size increases, the filling time of the balloon will increase, which complicates their use. To solve the problem of balloon deployment (at 2 Materials and Methods limited time), the concept of an inflatable launch This section considers methods for calculating vehicle will be consider. It is assume that the indicators by which will be determined the main hydrogen balloon will be permanently deploy and is technical characteristics and parameters of the launch part of the launch vehicle. There are various design vehicle with an inflatable reusable first stage. The for multistage launch vehicles. As an example, the methods of calculating the aerodynamic losses, the tandem staging design (with a reusable first stage) mass of the propellant, the strength and mass of the will be consider. First stage as a streamlined thin- body is considered. walled cylindrical tank divided into three sections. These sections store separately: liquid methane, 2. 1 Comparative Calculation of Aerodynamic liquid oxygen and hydrogen gas (Fig. 1). Inside the Losses sections is create an increased pressure (several atmospheres) to maintain a stable shape. The size of Suppose a launch vehicle moves upward at a speed v the first stage2 is calculate so that when it returns to (at time t). The main factors determining the flight Earth, its bulk density is less than that of atmospheric dynamics of the launch vehicle are its mass m, the air. Due to the positive buoyancy, the first stage thrust of rocket engines Ft, the force of gravity Fg, (without propellant) will be able to float in the Earth's and the aerodynamic drag force Fd. Consider the atmosphere3. Then the first stage will move to the changes in speed dv over the time interval dt. The spaceport (using its own rocket engine or special thrust force Ft could provide a speed increase dvh (in tugboats). the absence of other forces). However, the aerodynamic drag force Fd will decrease the speed by dvd, and the gravitational force Fg will reduce the speed by dvg. With this in mind, the actual acceleration a will be: 1 3 5 dv dv−− dv dv a ==h d g (1) dt dt 2 4 The physical meaning of dvh is the change in characteristic speed, dvd is the aerodynamic loss, dvg is the gravitational loss. Aerodynamic and gravitational losses depend from the many interrelated factors, and their determination is a Figure 1. Schematic diagram of an inflatable launch vehicle (in the difficult task. At the preliminary stage, it can diagram, the exact shape and proportions are not respected): 1 – assumed that the gravitational losses of an inflatable nasal section of an inflatable launch vehicle (it includes the second launch vehicle are approximately equal to the stage, third stage and payload); 2 – upper part of the first stage (for gravitational losses of classic launch vehicles. For hydrogen gas); 3 – middle section (for liquid methane); 4 – aft section (for liquid oxygen); 5 – rocket engines aerodynamic losses, it is necessary to make an additional calculation (because of the large size of the inflatable launch vehicle). Suppose that a launch vehicle has mass m, and because of aerodynamic drag For the made of the inflatable first stage, it is propose loses infinitesimal speed dvd for infinitesimal period to use a super-strong fabric (for example, from of time dt. With this in mind, the aerodynamic drag graphene filaments). After cutting out need to force Fd will be: measure, the elasticity coefficient of each piece of mdvd Fd = (2) dt 2 By means of hydrogen section. 3 Upon return, the first stage will drift in the Earth’s atmosphere in a vertical position, since its stern will be heavier (due to the weight of the rocket engines). The aerodynamic drag force Fd depends from drag is Q. Using equation (8), the following equation it is coefficient Cd, drag area S, air density ρa, speed v. obtained: Taking this into account, it is written: 2rlP r QP== (9) C S v2 2ldl dl F = da (3) d 2 Using equations (7; 9), it is obtained: Using equations (2; 3), it is obtained: r m= 2 rl P (10) ttQ C S v2 dt dv = da (4) d 2 m After returning to Earth, the first stage contains inside light gases (hydrogen, helium). The density of For evaluate the aerodynamic losses of an inflatable atmospheric air is ρa, dry mass of the first stage is md launch vehicle, will be use a comparison method with (without propellant).