Expendable launch system

-

Expendable launch system (ELV)

An expendable launch system or vehicle (ELV) is a launch vehicle that can be launched only once. After that its components are either destroyed during reentry or discarded in space. ELVs typically consist of several rocket stages that are discarded sequentially as their fuel is exhausted. These stages are designed to burn their fuel and provide thrust during different phases of the launch. Gradual discarding occurs as the ELV ascends, each stage is discarded in sequence as its fuel is depleted. The lower stages are discarded first, allowing the upper stages to continue the ascent. The vehicle gains altitude and speed as it throws stages. Finally, the payload, which is for example satellite or spacecraft, is released into the desired orbit.

Nowadays, there is trend to use them less compared to reusable launch vehicles. Companies such as SpaceX are developing rockets that can be reused for multiple launches, reducing costs and environment.

However they are still used because ELVs are generally simpler in their design than reusable rockets. In addition, they can then use all the fuel to accelerate its payload, which means that they can offer bigger payloads. 

A Delta IV Heavy rocket (left) and a Proton-M rocket (right). Source: Wiki

Schema of the flight

Space Launch System (SLS)

NASA's newest ELV, the Space Launch System was launched successfully in November 2022 after more than six years of delays.

The Space Launch System (SLS) is a super heavy-lift expendable launch vehicle used by NASA. As the primary launch vehicle of the Artemis Moon landing program, SLS is designed to launch the crewed Orion spacecraft on a trans-lunar trajectory. The first SLS launch was the uncrewed Artemis 1, which took place on 16 November 2022.

SLS Block 1 with the Orion spacecraft launching from Pad 39B; source: wiki

Development of SLS began in 2011, as a replacement for the retired Space Shuttle as well as the cancelled Ares I and Ares V launch vehicles. The SLS reuses hardware from the Shuttle program, including the solid rocket boosters and RS-25 first stage engines.

Core stage

Core stage, together with the solid rocket boosters, gets the upper stage and payload out of the atmosphere to near orbital velocity. Core stage contains liquid hydrogen and liquid oxygen tanks. Main propulsion system is composed of the four RS-25 engines. The core stage generates 7.44 MN of thrust, which gives approximately 25% of the vehicle's thrust at liftoff, for approximately 500 s. The rest comes from the solid rocket boosters. It is propelling for another 375 s of flight. The core stage lifts the rocket to about 162 km before it separates. It splashes down into Pacific Ocean.  

The structure of the core stage; source: wiki

The core stage contains five major sections: the engine section, the liquid hydrogen (LH2) tank, the intertank, the liquid oxygen (LOX) tank, and the forward skirt. These elements can be further divided into ten barrel sections, four domes, and seven rings, together forming the structure of the rocket stage.

The largest structures of the core stage are propellant tanks, built to carry approximately 987 tones of cryogenic propellants, liquid hydrogen and liquid oxygen. The extremely low cryogenic temperatures of these fluids −182.8 °C for liquid oxygen and −252.8 °C for liquid hydrogen causes substantial shrinkage in the propellant tanks. The liquid hydrogen tank shrinks about 15 cm in length and 2.5 cm in diameter after being filled, while the liquid oxygen tank's size decreases by 3.8 cm lengthwise and 1.3 cm across. 

The design of core stages comes from the Space Shuttle program. Rocket's diameter is 8.4 m, which is identical to the Space Shuttle external tank. 

Space Launch System Lift Capabilities | source: NASA


Solid Rocket Boosters

see previous short article: Space shuttle solid rocket booster

Blocks 1 and 1B of the SLS will use two five-segment solid rocket boosters. They use casing segments that were flown on Shuttle missions as parts of the four-segment Space Shuttle Solid Rocket Boosters. They have an additional center segment, new avionics, and lighter insulation, but they are missing a parachute recovery system, because they are not going to be recovered. 
The propellants for the solid rocket boosters are aluminum powder, which is very reactive, and ammonium perchlorate, a powerful oxidizer. They are held together by a binder, polybutadiene acrylonitrile (PBAN). The consistency of the mixture is like a rubber eraser. 
The SLS solid rocket boosters provide about 25% more total impulse than the Shuttle Solid Rocket Boosters.

Upper stages

The Interim Cryogenic Propulsion Stage (ICPS) is the upper stage of SLS Block 1. It flew for the first time on Artemis 1. It is planned for Artemis 2 and 3. It is a used Delta IV 5 m Delta Cryogenic Second Stage powered by a single RL10 engine. The Artemis 1 ICPS used the RL10B-2 variant, while the ICPS for Artemis 2 and Artemis 3 will use the RL10C-2 variant. The ICPS will be human-rated for the crewed Artemis 2 and 3 flights.

The Exploration Upper Stage (EUS) is planned to first fly on Artemis 4. The EUS will complete the SLS ascent phase and then re-ignite to send its payload to destinations beyond low Earth orbit (LEO).



Comments

Post a Comment

Popular posts from this blog

Apollo 8 delta-v calculation

-
Image
The Apollo 8 Apollo 8 mission launched on December 21, 1968, and it was the second crewed spaceflight mission flown in the Apollo space program. The first mission, Apollo 7, stayed in Earth orbit. Apollo 8 mission was the first ever mission to leave the Earth's gravitational sphere, and to reach the Moon. The crew orbited the Moon ten times and returned home. It went without the landing. However, the mission was the first mission to see and take a photo of the far side of the Moon.  The mission consisted of three astronauts: Frank Borman, James Lovell, and William Anders.  Apollo 8 was the third flight and the first crewed launch of the Saturn V rocket.  Earthrise: Taken from Apollo 8; source: Wiki When building a rocket, it is a good thing to do staging. Staging basically means throwing away big, expensive parts of your rocket while the rest continues on the way up. The main advantage is not to carry dead weight.  When one has multiple powered stages, the question a...
Read more

Exercise on single stage vs. two-stage rocket

-
Image
Exercise: 1. Single stage rocket:  Before a rocket begins to burn fuel, the rocket has a mass of  m r,i =2.81×10 7 kg, of which the mass of the fuel is  m f,i =2.46×10 7 kg. The fuel is burned at a constant rate with total burn time is 510 s and ejected at a speed v e = 3000 m/s relative to the rocket. If the rocket starts from rest in empty space, what is the final speed of the rocket after all the fuel has been burned? What we know: initial rocket mass m r,i =2.81×10 7 kg initial mass of the fuel m f,i =2.46×10 7 kg t = 510 s v e  = 3000 m/s So, we can calculate the dry mass of the rocket m r,d =m r,i -m f,i =0.35×10 7 kg. The mass ratio is then R = m r,i  /m r,d =8.03. So, the final speed of the rocket is then: V r,f =Δv r =v e lnR=6250m/s. 2. Two-stage rocket:  Now, we have similar example, the same rocket as in the previous example, but the fuel will be burnt in two stages ejecting the fuel in each of the stages at the same relative speed (v e  =...
Read more

Specific impulse

-
Image
Specific impulse  I was many times using the term specific impulse. So, let's speak about it in more detail.    Specific impulse (usually abbreviated I sp ) is a measure of how efficiently a reaction mass engine, such as a rocket using propellant or a jet engine using fuel, generates thrust. A propulsion system which has a higher specific impulse uses the mass of the propellant more efficiently than a propulsion system with lower specific impulse. Now, in the case of a rocket, this means less propellant is needed for a given delta-v, so that the vehicle attached to the engine can more efficiently gain altitude and velocity. For all vehicles specific impulse (impulse per unit weight-on-Earth of propellant) in seconds can be defined by the following equation: Thrust is force, the thrust obtained from the engine (newtons or pounds force), g 0 is the standard gravity, which is nominally the gravity at Earth's surface (m/s2), I sp is the specific impulse measured (secon...
Read more