Patent Description:
Various types of rockets are employed for launching objects into space. For example, various approaches are undertaken to make the launching of satellites into space more readily accessible. Irrespective of the kinds of objects to be launched, rockets have to deal with the issue that the structure and the fuel required for launching the rocket are very heavy compared to the object to be launched into space, commonly referred to as payload in terms of the rocket dynamics.

<CIT> relates to in-tank propellant mixing and discloses providing separate fuel and oxidizer compartments within a singular pressure vessel, which reduces the weight and complexity of the system, while maintaining the non-volatility of separately stored fuel and oxidizer. The fuel and oxidizer can be selectively mixed within the pressure vessel when desired.

Despite extensive efforts of increasing the efficiency of rockets in terms of minimizing the amount of fuel needed for a particular payload, the energy efficiency of state of the art rockets is still not satisfactory.

Accordingly, it would be beneficial to modify existing rocket designs for an increase in energy efficiency.

Exemplary embodiments of the invention include a rocket propellant tank arrangement in accordance with claim <NUM>, a rocket propulsion unit in accordance with claim <NUM>, a rocket in accordance with claim <NUM>, and a method of carrying propellant in a rocket in accordance with claim <NUM>. Further embodiments are given in the dependent claims.

Exemplary embodiments of the invention according to claim <NUM> include a rocket propellant tank arrangement for storing fuel and oxidizer for launching a rocket, the rocket propellant tank arrangement comprising an oxidizer tank for storing liquid oxidizer and a fuel tank for storing liquid fuel, wherein the fuel tank is at least partially arranged within the oxidizer tank, wherein the fuel tank has a generally cylindrical shape, with a fuel tank wall being generally cylindrical, and wherein the oxidizer tank has a generally hollow cylindrical shape, formed between the generally cylindrical fuel tank wall and a generally cylindrical oxidizer tank wall.

Exemplary embodiments of the invention allow for a rocket propellant tank arrangement that is able to store highly energetic propellants, while having a low structural mass and thus contributing to a high energy efficiency of the overall rocket. The arrangement of the fuel tank at least partially within the oxidizer tank allows for a particularly light weight construction of the rocket propellant tank arrangement, thus greatly contributing to the overall energy efficiency of a rocket equipped with the rocket propellant tank arrangement. It is possible to select the fuel for a particular rocket and the temperatures / pressures for the liquid fuel and the liquid oxidizer in a way that the structural burden on the separation between the fuel tank and the oxidizer tank is low. Also, the requirements in terms of insulation may be low. The separation between the fuel tank and the oxidizer tank may thus add much less weight to the overall structural mass of the rocket than the components required for supporting separate tanks that are surrounded by the outside environment. Accordingly, as compared to prior approaches, where a fuel tank and an oxidizer tank were stacked in a one above the other relationship, an equivalent amount of propellants can be stored with a considerably lower structural mass.

According to a further embodiment, the fuel tank is one of a propane tank for storing liquid propane, a propene tank for storing liquid propene, and a propylene tank for storing liquid propylene. In particular, the combination of liquid oxidizer, such as liquid oxygen, and liquid propane allows for an energetically beneficial propulsion of a rocket. At the same time, the arrangement of a propane tank at least partially within the oxidizer tank allows for a particularly light weight construction of the rocket propellant tank arrangement. The separation between the oxidizer tank and the propane tank does not require excessive mechanical strength and does not require excessive thermal insulation, because liquid oxidizer, such as liquid oxygen, and liquid propane can be stored at similar temperatures and similar pressures. Without burdensome requirements in terms of mechanical strength and insulation, the separation between the oxidizer tank and the propane tank can be implemented in a fairly basic manner and does not add much weight to the overall weight of the rocket. In addition, the arrangement of the propane tank at least partially within the oxidizer tank allows for a mutual cooling of the liquid oxidizer and the liquid propane. Also, the similar pressures within the propane tank and the oxidizer tank allow for the separation between the two tanks to be a mere mechanical barrier that prevents diffusion therethrough from any of the two components, without requiring large mechanical strength in terms of pressure gradients. The propane tank does not have to be designed for being surrounded by the outside environment. Analogous considerations apply to the combination of liquid propene and liquid oxidizer, such as liquid oxygen, as well as to the combination of liquid propylene and liquid oxidizer, such as liquid oxygen.

According to a further embodiment, the rocket propellant tank arrangement comprises a fuel tank wall, which forms the fuel tank for storing liquid fuel. With the fuel tank being at least partially arranged within the oxidizer tank, the fuel tank wall can form an effective border towards the oxidizer tank at low structural mass for the reasons laid out above. The expression forming the fuel tank does not require the fuel tank wall to form an entirely enclosed space. For example, the fuel tank wall may be a cylindrical wall, with the fuel tank being closed by fuel tank caps.

According to a further embodiment, the rocket propellant tank arrangement comprises an oxidizer tank wall, arranged at least partially around the fuel tank wall, with the fuel tank wall and the oxidizer tank wall forming the oxidizer tank for storing liquid oxidizer between the fuel tank wall and the oxidizer tank wall. In this way, the fuel tank wall forms both the surrounding wall around the fuel tank as well as an inner wall of the oxidizer tank. In this way, liquid fuel and liquid oxidizer are stored adjacent to each other, with only the fuel tank wall separating the two volumes for storing fuel and oxidizer. Again, the oxidizer tank may be closed by oxidizer tank caps, provided in addition to the oxidizer tank wall.

According to a further embodiment, a plurality of fuel tank fixation elements are arranged between the fuel tank wall and the oxidizer tank wall. In this way, a positional fixation of the fuel tank within the oxidizer tank can be achieved with low complexity. As the temperature and pressure gradients between the oxidizer tank and the fuel tank are small, the fuel tank fixation elements can have a low structural mass and do not have to be load bearing.

In a particular embodiment, the plurality of fuel tank fixation elements may be a plurality of fixation fins. The fixation fins may be sheet-like elements extending between the fuel tank wall and the oxidizer tank wall.

In a further particular embodiment, the plurality of fuel tank fixation elements may be a plurality of slosh baffles. In this way, the fuel tank fixation elements may on the one hand provide a positional fixation of the fuel tank within the oxidizer tank, while at the same time reducing or eliminating undesired dynamic effects from the liquid oxidizer moving within the oxidizer tank. The slosh baffles may also have the form of fixation fins.

According to a further embodiment, the fuel tank wall is made of aluminium, steel, in particular austenitic stainless steel, carbon fiber based composites or composite overwrap aluminium. The latter material is aluminium, wrapped or coated with composite material, such as carbon fiber based composites. Aluminium, composite materials and composite overwrap aluminium are particularly light materials. The fuel tank wall may also be a mixture of two or more of the above material.

The fuel tank may also be of one or more of above materials in combination with one or more other materials.

According to a further embodiment, the fuel tank wall is made from aluminium and/or the oxidizer tank wall is made from composite overwrap aluminium. It is also possible that the fuel tank consists essentially of aluminium.

According to a further embodiment, the fuel tank wall is free of insulating material. In this way, the structural mass, spent on insulating the fuel tank in prior art approaches, can be eliminated, thus increasing the overall energy efficiency of the rocket. Further, with the fuel tank being at least partially arranged within the oxidizer tank, the lack of insulating material in fact allows for a beneficial mutual cooling of the liquid oxidizer and the liquid fuel.

According to a further embodiment, the fuel tank wall has a thickness of between <NUM> and <NUM>, in particular of between <NUM> and <NUM>, further in particular of between <NUM> and <NUM>. With this thickness, the fuel tank wall may provide an effective barrier between the liquid oxidizer and the liquid fuel, while only contributing little mass to the overall weight of the rocket. The fuel tank wall may also comprise enforcing elements, such as stiffeners, stringers, isogrid features, etc. These enforcing elements may be included in above thickness values or may locally add thickness. The enforcing elements may be arranged on the inside of the fuel tank.

According to a further embodiment, the pressure within the fuel tank and within the oxidizer tank may be between <NUM> bar and <NUM> bar in operation.

According to the invention, the fuel tank has a generally cylindrical shape. In this way, the fuel tank has a shape that can be surrounded by the liquid oxidizer tank in a regular manner. Also a generally cylindrical fuel tank can be conveniently slid into the inner space, provided by the oxidizer tank wall, during manufacture.

According to the invention, the oxidizer tank has a generally hollow cylindrical shape. In other words, the space between a generally cylindrical fuel tank wall and a generally cylindrical oxidizer tank wall may form a generally hollow cylinder, with this generally hollow cylinder forming the oxidizer tank of the rocket propellant tank arrangement.

According to a further embodiment, the oxidizer tank may have a diameter of between <NUM> and <NUM>, in particular of between <NUM> and <NUM>.

According to a further embodiment, the oxidizer tank has an oxidizer tank elongation and the fuel tank has a fuel tank elongation, wherein the oxidizer tank elongation is between <NUM>% and <NUM>% of the fuel tank elongation, in particular between <NUM>% and <NUM>% of the fuel tank elongation. Further in particular, the oxidizer tank elongation may be substantially equal to the fuel tank elongation. In other words, both the oxidizer tank and the fuel tank may be lengthy structures, having respective longitudinal extensions each. The longitudinal extensions of the oxidizer tank and the fuel tank may be comparable to each other or deviate by less than <NUM>% from each other. In this way, a continuous arrangement of the oxidizer tank around the fuel tank over most of the longitudinal extension or the entire longitudinal extension of the rocket propellant tank arrangement may be achieved. The direction of the longitudinal extension of the oxidizer tank and the fuel tank may be the height direction of the rocket.

According to a further embodiment, the rocket propellant tank arrangement has a longitudinal extension of between <NUM> and <NUM>, in particular of between <NUM> and <NUM>, further in particular of between <NUM> and <NUM>.

According to a further embodiment, the fuel tank is substantially entirely enclosed by the oxidizer tank. With the fuel tank being entirely or almost entirely enclosed by the oxidizer tank, above described beneficial properties of a low pressure differential and a mutual cooling through the fuel tank wall may be made use of over the entire surface of the fuel tank wall.

According to a further embodiment, the oxidizer tank for storing liquid oxidizer is an oxygen tank for storing liquid oxygen.

According to a further embodiment, the oxidizer tank is configured to store cryogenic liquid oxygen. Alternatively / in addition, the fuel tank is configured to store cryogenic liquid propane.

Further exemplary embodiments of the invention include a rocket propulsion unit, comprising a rocket propellant tank arrangement, as described with respect to any of the embodiments above, at least one combustion chamber, coupled to the rocket propellant tank arrangement for receiving liquid oxidizer and liquid fuel, and at least one nozzle, coupled to the at least one combustion chamber, for ejecting exhaust gases from the at least one combustion chamber. The modifications, additional features, and effects, discussed above with respect to the rocket propellant tank arrangement, apply to the rocket propulsion unit in an analogous manner.

Exemplary embodiments of the invention further include a rocket, comprising at least one rocket propulsion unit, as described above, and a carrier structure for attaching one or more objects to be launched into space to the at least one rocket propulsion unit. The modifications, additional features, and effects, described above with respect to the rocket propellant tank arrangement, apply to the rocket in an analogous manner.

Exemplary embodiments of the invention further include a method of carrying propellant in a rocket, according to claim <NUM>, and comprising carrying liquid oxidizer in an oxidizer tank, carrying liquid fuel in a fuel tank, with the fuel tank being at least partially arranged within the oxidizer tank, wherein the fuel tank has a generally cylindrical shape, with a fuel tank wall being generally cylindrical, and wherein the oxidizer tank has a generally hollow cylindrical shape, formed between the generally cylindrical fuel tank wall and a generally cylindrical oxidizer tank wall, and jointly controlling a liquid oxidizer temperature of the liquid oxidizer and a liquid fuel temperature of the liquid fuel. The liquid oxidizer may be liquid oxygen. The modifications, additional features, and effects, described above with respect to the rocket propellant tank arrangement, apply to the method of carrying propellant in a rocket in an analogous manner. The liquid oxidizer temperature and the liquid fuel temperature may be controlled jointly in a number of ways. For example, active cooling means may be provided that apply their cooling power jointly to the two tanks. It is also possible that the temperatures are controlled to be substantially the same or at least similar by selecting a particular fuel and a particular fuel pressure that yield a particular temperature matching the liquid oxidizer temperature. By jointly controlling the liquid oxidizer temperature and the liquid fuel temperature, the separation between the fuel tank and the oxidizer tank may be implemented with low complexity, in particular implemented with little or no means for insulation.

Exemplary embodiments of the invention are described in detail below with respect to the accompanying drawings, wherein:.

<FIG> shows a rocket propulsion unit <NUM> in a schematic vertical cross-sectional view, with the rocket propulsion unit <NUM> being in accordance with a prior art approach. The rocket propulsion unit <NUM> has three basic components, namely a rocket propellant tank arrangement <NUM>, a combustion chamber <NUM>, and a nozzle <NUM> for ejecting the exhaust gases.

The rocket propellant tank arrangement <NUM> has an oxygen tank <NUM> for storing liquid oxygen, which is a commonly used oxidizer, and a fuel tank <NUM> for storing RP-<NUM>, which is a commonly used rocket fuel. The oxygen tank <NUM> and the fuel tank <NUM> are stacked one above the other in a load bearing tank <NUM>. In particular, the fuel tank <NUM> is arranged above the oxygen tank <NUM>, with an insulating intertank structure <NUM> being arranged therebetween. A fuel supply line <NUM> extends through the oxygen tank <NUM>, such that both RP-<NUM> and oxygen can be provided to the combustion chamber <NUM>.

<FIG> shows a rocket propulsion unit <NUM> in a schematic vertical cross-sectional view, with the rocket propulsion unit <NUM> being in accordance with an exemplary embodiment of the invention. The rocket propulsion unit <NUM> has three basic components, namely a rocket propellant tank arrangement <NUM>, a combustion chamber <NUM>, and a nozzle <NUM>.

The rocket propellant tank arrangement <NUM> of <FIG> has an oxygen tank <NUM> for storing liquid oxygen and a propane tank <NUM> for storing liquid propane. The propane tank <NUM> is a particular example of a fuel tank for storing liquid fuel. The rocket propellant tank arrangement <NUM> of <FIG> is configured to storing liquid propane. However, it is also possible to provide an analogous or similar rocket propellant tank arrangement for propene or propylene.

The propane tank <NUM> is arranged within the oxygen tank <NUM>. In particular, the propane tank <NUM> has a generally cylindrical shape. The top and bottom ends of the propane tank have rounded propane tank caps for closing a generally cylindrical propane tank wall <NUM>, thus forming the generally cylindrical shape of the propane tank <NUM>. The oxygen tank <NUM> has a generally cylindrical oxygen tank wall <NUM>, which forms the outer wall of the oxygen tank <NUM>. Two rounded oxygen tank caps close the cylindrical structure to the top and to the bottom. The lower ends of the oxygen tank <NUM> and the propane tank <NUM>, i.e. the ends of the oxygen tank <NUM> and the propane tank <NUM> towards the combustion chamber <NUM>, are arranged at roughly the same height. In this way, both the oxygen supply line(s) and the propane supply line(s) to the combustion chamber <NUM> can be kept short.

The height extension of the oxygen tank <NUM>, i.e. the longitudinal extension of the oxygen tank <NUM>, is about <NUM>% larger than the longitudinal extension of the propane tank <NUM>. The oxygen tank <NUM> has the shape of a hollow cylinder along the length of the propane tank <NUM> and has a generally cylindrical shape thereabove. Liquid oxygen is stored all around the propane tank <NUM> with the exception of the very bottom thereof.

The diameter of oxygen tank wall is about three times the diameter of the propane tank wall. The propane tank wall is made of aluminium and has a thickness of about <NUM> in the exemplary embodiment of <FIG>. The oxygen tank wall is also made of aluminium and has a thickness of about <NUM> in the exemplary embodiment of <FIG>.

In <FIG>, both the oxygen tank <NUM> and the propane tank <NUM> are shown in a partially filled state. The oxygen tank <NUM> is filled to about <NUM>% with liquid oxygen. The propane tank <NUM> is filled to about <NUM>% with liquid propane.

As compared to the rocket propellant tank arrangement <NUM> of <FIG>, the rocket propellant tank arrangement <NUM> of <FIG> does not require an insulating intertank structure <NUM>. Also, with the propane tank <NUM> being arranged within the oxygen tank <NUM>, only two large end caps on the top and the bottom of the rocket propellant tank arrangement <NUM> are required instead of the four large end caps of the two tanks of the rocket propellant tank arrangement <NUM>. Also, the design of the fuel supply line is greatly simplified, eliminating the need for the long range fuel supply line <NUM> of the rocket propellant tank arrangement <NUM> of <FIG>. Also, the propane tank wall <NUM> is greatly reduced in thickness as compared to the wall of the fuel tank <NUM>. Further, the propane and oxygen can be jointly cooled and their temperature jointly controlled in the rocket propellant tank arrangement <NUM> of <FIG>, as compared to the separated systems of the rocket propellant tank arrangement <NUM> of <FIG>.

<FIG> shows a rocket propellant tank arrangement <NUM> in a schematic vertical cross-sectional view, with the rocket propellant tank arrangement <NUM> being in accordance with an exemplary embodiment of the invention. The rocket propellant tank arrangement <NUM> has an oxygen tank <NUM> and a propane tank <NUM>. The propane tank <NUM> is formed by a propane tank wall <NUM>, which is cylindrical in shape. Accordingly, the propane tank <NUM> as a whole has a generally cylindrical shape as well. The top and bottom ends of the propane tank <NUM> are closed with propane tank caps <NUM>, which are generally disk-shaped. Again, the propane tank <NUM> is an exemplary embodiment of a fuel tank. It is also possible that a propene tank or a propylene tank is provided instead of the propane tank <NUM>.

The propane tank <NUM> is arranged within the oxygen tank <NUM>. In particular, the oxygen tank <NUM> is formed between the generally cylindrical propane tank wall <NUM> and a generally cylindrical oxygen tank wall <NUM>. The generally cylindrical propane tank wall <NUM> and the generally cylindrical oxygen tank wall <NUM> are arranged in a concentric manner, i.e. they are arranged with their respective center axes coinciding. The generally cylindrical oxygen tank wall <NUM> has a somewhat smaller height extension than the generally cylindrical oxygen tank wall <NUM>. The oxygen tank <NUM> is closed at its top and bottom ends by rounded oxygen tank caps <NUM>. The oxygen tank caps <NUM> are annular, thus closing the oxygen tank <NUM> of generally hollow cylindrical shape. Due to their rounded three-dimensional shape, the oxygen tank caps <NUM> make sure that the propane tank <NUM> and the oxygen tank <NUM> have the same height extension at the contact points of the oxygen tank caps <NUM> and the propane tank caps <NUM> in the exemplary embodiment of <FIG>.

As liquid oxygen is stored all around the propane tank wall <NUM>, the propane tank <NUM> is considered to be fully arranged within the oxygen tank <NUM>.

In the exemplary embodiment of <FIG>, the diameter of the oxygen tank wall <NUM> is about four times the diameter of the propane tank wall <NUM>. Depending on the relative height extensions of the propane tank <NUM> and the oxygen tank <NUM> as well as on the desired mixing ratio for combustion, other relative diameters may be used. Also, the propane tank <NUM> and the oxygen tank <NUM> may have other geometric shapes. For example, the propane tank <NUM> may be of generally ellipsoidal shape, being arranged in an oxygen tank <NUM> with a generally cylindrical oxygen tank wall <NUM> or with an ellipsoidal oxygen tank wall.

The rocket propellant tank arrangement <NUM> of <FIG> further comprises a plurality of propane tank fixation elements <NUM>. The propane tank fixation elements <NUM> are provided for ensuring a spatial fixation between the propane tank wall <NUM> and the oxygen tank wall <NUM> along the length of the rocket propellant tank arrangement <NUM>. The propane tank fixation elements <NUM> may be attached to the propane tank wall <NUM> or to the oxygen tank wall <NUM> or to both the propane tank wall <NUM> and the oxygen tank wall <NUM> in a suitable manner. While the attachment to one of the propane tank wall <NUM> and the oxygen tank wall <NUM> may be sufficient for ensuring a spatial fixation, an attachment to both of the propane tank wall <NUM> and the oxygen tank wall <NUM> may allow for a more robust overall rocket propellant tank arrangement <NUM>.

In the exemplary embodiment of <FIG>, the propane tank fixation elements <NUM> are embodied as sheet-like elements, also referred to as fixation fins. Further, the propane tank fixation elements <NUM> act as slosh baffles in the exemplary embodiment of <FIG>, preventing an excessive motion of the liquid oxygen stored in the oxygen tank <NUM> during operation.

<FIG> shows the rocket propellant tank arrangement <NUM> of <FIG> in a pre-assembled view. In particular, <FIG> shows that the propane tank fixation elements <NUM> are attached to the propane tank wall <NUM> and that the pre-assembled unit of propane tank wall <NUM> and propane tank fixation elements <NUM> is slid into the oxygen tank wall <NUM> during assembly, as indicated by the arrow in <FIG>. This combination of oxygen tank wall <NUM>, propane tank wall <NUM>, and propane tank fixation elements <NUM> is then closed via the assembly of the propane tank caps <NUM> and the oxygen tank caps <NUM>. Liquid propane and liquid oxygen may be filled into the propane tank <NUM> and the oxygen tank <NUM>, respectively, before the second set of an oxygen tank cap <NUM> and a propane tank cap <NUM> are attached. Alternatively, at least one of each of the oxygen tank caps <NUM> and the propane tank caps <NUM> may have a suitable opening for introducing the liquid oxygen and the liquid propane therethrough.

<FIG> shows the top section of the rocket propellant tank arrangement <NUM> of <FIG> in more detail. In particular, it is shown that the oxygen tank wall <NUM>, the propane tank wall <NUM>, and the oxygen tank caps <NUM> have respective flanges. With the help of these flanges, the oxygen tank <NUM> and the propane tank <NUM> are closed with the oxygen tank caps <NUM> and the propane tank caps <NUM> via suitable fastening means.

<FIG> shows a schematic horizontal cross-sectional view through the rocket propellant tank arrangement <NUM> of <FIG>. <FIG> illustrates that the propane tank <NUM> has a generally circular horizontal cross-section and that the oxygen tank <NUM> has a generally annular horizontal cross-section. Accordingly, <FIG> also shows that both the oxygen tank wall <NUM> and the propane tank wall <NUM> have a circular cross-section, with the two circles being arranged concentrically. In the cross-section depicted in <FIG>, four propane tank fixation elements <NUM> are depicted. With these four propane tank fixation elements <NUM>, the propane tank <NUM> is spatially fixed in two dimensions with respect to the oxygen tank wall <NUM>. It is also illustrated that the propane tank fixation elements <NUM> are sheet-like structures having a thin horizontal cross-section.

<FIG> shows a rocket propellant tank arrangement <NUM> in a schematic vertical cross-sectional view, with the rocket propellant tank arrangement <NUM> being in accordance with another exemplary embodiment of the invention. In particular, the rocket propellant tank arrangement <NUM> corresponds to the rocket propellant tank arrangement <NUM> of <FIG>, with the exception of the relative longitudinal extensions of the propane tank <NUM> and the oxygen tank <NUM> and the closing mechanism. In particular, in <FIG>, the propane tank <NUM> has a greater height extension than the oxygen tank <NUM>. The propane tank <NUM> extends beyond the oxygen tank <NUM> at the upper end. Such an arrangement may be chosen for providing easier access to the propane tank <NUM> for fueling. In the exemplary embodiment of <FIG>, the oxygen tank cap <NUM> is fastened to a flange that is spaced from the upper end of the propane tank <NUM>.

<FIG> shows a rocket <NUM> in a schematic view, with the rocket <NUM> being in accordance with an exemplary embodiment of the invention. The rocket <NUM> comprises two rocket propulsion units <NUM>, <NUM>', namely a first stage rocket propulsion unit <NUM> and a second stage rocket propulsion unit <NUM>'. The rocket <NUM> further comprises a payload <NUM>, such as a satellite to be carried into space, covered by a deployable aerodynamic fairing <NUM>.

The first stage rocket propulsion unit <NUM> has a first rocket propellant tank arrangement <NUM>, which may be in accordance with any of the embodiments described above. The first stage rocket propulsion unit <NUM> further has four first stage engines <NUM>, each having a first stage combustion chamber <NUM> and a first stage nozzle <NUM>, and four turbo pumps <NUM>. The turbo pumps <NUM> ensure that the fuel is provided to the combustion chambers <NUM> at suitable pressures. The pressure within the fuel tank of the first stage rocket propulsion unit <NUM> may be between <NUM> bar and <NUM> bar. The provision of turbo pumps allows for storing the fuel at moderate pressures, thus again lowering the structural mass of the fuel tank.

The second stage rocket propulsion unit <NUM>' has a second rocket propellant tank arrangement <NUM>', which may also be in accordance with any of the embodiment described above. The second stage rocket propulsion unit <NUM>' further has a second stage engine <NUM>', which has a second stage combustion chamber <NUM>' and a second stage nozzle <NUM>'. The second stage engine <NUM>' is surrounded by a deployable aerodynamic cover <NUM>. The pressure within the fuel tank of the second stage rocket propulsion unit <NUM>' may be between <NUM> bar and <NUM> bar.

The operation of the rocket <NUM> may be as follows. For take-off and the first flight phase, the first stage rocket propulsion unit <NUM> is used, with the fuel and oxygen of the first rocket propellant tank arrangement <NUM> being used in the first flight phase. After using up the fuel and oxygen stored in the first rocket propellant tank arrangement <NUM>, the first stage rocket propulsion unit <NUM> is discarded, i.e. de-coupled from the remainder of the rocket <NUM>. The second stage rocket propulsion unit <NUM>' is then used for the second flight phase. After the second flight phase, the second stage rocket propulsion unit <NUM>' is discarded, i.e. de-coupled from the payload <NUM>. With the deployable aerodynamic fairing <NUM> also being discarded, the payload is then, by itself, maneuvered to its target position, such as to a desired orbit in case of the payload <NUM> being a satellite.

Claim 1:
Rocket propellant tank arrangement (<NUM>) for storing fuel and oxidizer for launching a rocket, the rocket propellant tank arrangement comprising:
an oxidizer tank (<NUM>) for storing liquid oxidizer, and
a fuel tank (<NUM>) for storing liquid fuel,
wherein the fuel tank is at least partially arranged within the oxidizer tank,
characterized in that the fuel tank (<NUM>) has a generally cylindrical shape, with a fuel tank wall (<NUM>) being generally cylindrical, and in that the oxidizer tank (<NUM>) has a generally hollow cylindrical shape, formed between the generally cylindrical fuel tank wall (<NUM>) and a generally cylindrical oxidizer tank wall (<NUM>).