50

It's all to do with ullage in the fuel tanks. Newton's laws of motion mean that when a rocket is no longer firing and no force is being applied, the rocket receives no acceleration. It continues at its same velocity (if we assume a perfect model). The fuel in the tanks goes into free-fall, just as the astronauts do when they reach orbit. You've seen those ...


44

The first multistage rocket is much older then one might think. Its from the 14th century CE. Huolongchushui or fire dragon issuing from the water (Chinese: 火龙出水; pinyin: huolóngchushui; literally: 'fire dragon out of water') were the earliest form of multistage rockets and ballistic cruise missiles used in medieval China. The name of the weapon was used ...


43

There are some major challenges with this. For starters, the engines of the first stage produce far too much thrust for the last stage, which would require extra structural mass to allow the rocket to hold together, and would not allow manned rockets at all, as humans have fairly tight g-force limits. If you reduce thrust to manage these problems, you're ...


38

Keeping a burnt-out stage attached doesn't hurt until it's time to start the next stage. In fact, keeping it attached until shortly before it's time to ignite the next stage can improve the total launch delta V. Stage three separation occurred at an altitude of 184 km. There's still air up there. It's not very dense air, but for a vehicle going at close to ...


27

When you shut down a rocket stage, its acceleration drops to zero and the rocket becomes weightless. As a result, the propellants may start sloshing around their tanks. This could lead to gas entering the pipes leading to the engines (since the propellant will have 'sloshed' away from the pipe entrance). If a gas pocket were to hit the engine's turbopump, ...


23

Nathan's answer is good and cover almost everything but let me add a last bit: An engine nozzle can be optimized for only one given altitude ambient pressure. This has a great impact on the rocket performance. You probably wouldn't want to drag that heavy, inefficient engine all the way up, even if you could. Some designs attempt to circumvent this issue ...


21

There is a misunderstanding in your question "The engine bell(s) already support the entire compressional stress generated by the weight of the stages above it when the engine is firing..." No, the engine bells do not. (Sutton, 7th edition, Chapter 2.2) The bells mainly withstand the differential pressure forces from the gases flowing through them....


18

The service module of Polyus was too fragile to withstand heavy laser payload above it during the launch. I've found the answer at buran.ru (in Russian). www.buran.ru/htm/str163.htm According to Constantin Lantratov's article Polyus was designed of two parts - Skif-DM laser payload and service module. Service module was a ready TKS spaceship. It had ...


16

The coasting period is certainly to perform a Gravity Turn. It is a trajectory optimization that uses gravity to steer the vehicle onto its desired trajectory. ... the thrust is not used to change the ship's direction, so more of it is used to accelerate the vehicle into orbit. Once the vehicle has coasted into the right angle, P4 ignition takes ...


16

The initial exhaust from the upper stage fires at the first stage and is deflected and exits through the openings in the interstitial fairings, as shown in the markup of a Proton rocket below: The reason for this is to maintain the ullage of the upper stage tanks (if the fuel/oxidizer slosh forward at separation they won't flow into the pumps/engine evenly ...


16

I would mention works of Konstantin Tsiolkovsy. I think that he was first, who proposed to use multistage rockets for space flights. His most important work, published in May 1903, was Exploration of Outer Space by Means of Rocket Devices (Russian: Исследование мировых пространств реактивными приборами). Tsiolkovsky calculated, using the Tsiolkovsky ...


15

As @Rikki-Tikki-Tavi points out escape velocity is the velocity you would need at (or near) the surface of Earth to make out out of Earth orbit. Of course, just like anything thrown up into the air, the spacecraft decelerates as it moves away from the Earth. Having escape velocity means that your total energy (relative to the Earth in this case) is greater ...


14

It would be extremely unstable. There are 2 things that weight a lot on an empty rocket, the capsule and the engine. With the two of them on opposite sides, the rocket would become extremely unstable. Separating the two allows for the entire system to be more stable. This is particularly important when it is on the ground, where it could easily tip over if ...


14

From the description of Soyuz-U on the Roscosmos site: Разделение второй и третьей ступеней происходит по «горячей схеме». Третья ступень (блок «И»), состоящая из переходного отсека, бака горючего, бака окис­лителя, хвостового отсека и двигателя, уста­новлена на центральном блоке и соединена с ним с помощью ферменной конструкции. Блок «И» ...


14

The answer is a bit more nuanced than Organic Marble presents it. It makes sense to make a force balance to see what bits of engine can take which amount of force. First, let's look at the chamber. It has a static pressure $p_1$ which is balanced everywhere by the walls, except at the throat where there is a large gap. This results in a net force of ...


11

Any rocket flight will involve a burn in it's final orbital position. If you want to enter a 500km orbit your engine will shut down at 500km up. The profile shows it needs nearly 19 minutes to reach altitude but the rocket burn times only add up to 15 minutes. You can't magically make it get there in 15 minutes because you don't have extra fuel. Thus the ...


11

It is important at stage separation to remove as much as possible weight from the upper stage. The interstage weight does not count after separation, but any enhancement of the upper stage engine nozzle does. The interstage weight is small compared to the weight of the upper stages, but it is tiny compared to the weight of the lower stages. Of course the ...


10

Kerbal Space Program, the video game, teaches us that it is most effective to thrust at apoapsis (highest point of orbit) to increase our periapsis (lowest point of orbit). Waiting to fire the next stage there will make better use of fuel. Note that you want all the force applied at apoapsis, so you want to burn a little before and after it, since it is a ...


10

It depends on your definition of a stage. Soyuz' boosters cut off and separate at ~40km, but the core stage cuts off well above the Karman line, around 175km altitude. This article refers to the boosters as "first stage" and the core as "second stage" despite the fact that the core starts burning at liftoff. Single-stick launchers like Falcon 9 and Atlas V ...


9

Important new ideas are often thought by more than one person of a single nation. See this page about multistage rockets. In the 14th century the idea was developed in China and Korea using solid rockets made with gun powder. Later in Europe this idea apeared in Austria, Germany and Poland as already answered. Theoretical work was done by at least four ...


8

The first stage and the interstage ring both did fall uncontrolled after stage separation, landing somewhere in the Atlantic ocean. Stage separation occurs at about 2400 m/s and 67km altitude. That's fast enough for re-entry scorching, certainly, but not enough to burn up completely. In 2013, more than 40 years after flight, one of the first stages was found ...


8

Paraphrasing parts of an answer to a different question, hot-staging has a few advantages: It's less complex than staging using ullage motors since fewer parts are involved (whole rocket motors and their plumbing and tanks are missing, as well as the sensors and controllers to make them work correctly). Reduced complexity often means improved reliability. ...


8

For Apollo: more nuts than bolts, but vastly more non-threaded connectors Table I of Apollo Experience Report: Spacecraft Pyrotechnic Systems, NASA Tech Note D-7141, lists all of the pyrotechnics above the Saturn booster (e.g. the CSM, LM, escape tower, etc.). Of the more than 210 pyrotechnic devices, 8 were nuts and 4 were bolts: 4 frangible nuts held the ...


8

Stage separation by design is typically slightly propulsive. The goal however is not to add a significant amount of momentum to the part of the vehicle that still matters. It is instead to ensure that the part of the vehicle that still matters doesn't collide with the part of the vehicle that no longer matters. Stage separation is a risky event. Several ...


7

This is a suggestion, I'm not sure this was the end of the story, but... In 2008, a problem of arcing near the Pyro bolts was proposed as an explanation by the Russians. A Pyro bolt was later retrieved from a docked Soyuz (TMA-12 -- Also here), and returned to earth for examination. (source: ibid) TMA-12 undocked with the remaining Pyro bolts and ...


7

Referencing the Ascent Checklist Ascent Cue Card: There were no procedures for failed SRB separation, and nothing the crew or ground could do about it. 1 The ET separation sequence2 could be halted by either excessive vehicle rotation rates, or by failure of the shutoff valves in the main propulsion system feedlines to close (or indicate closed). The crew ...


6

There's 2 major reasons: safety and practicality Safety: If you look at the history of booster landings it is not a proven technology, the reliability is not good enough for safety. Don't get me wrong, it's amazing that they can land a booster for re-use, and it works a good portion of the time, however when it goes wrong it goes very, very wrong very fast. ...


6

I found a document about that theme: Apollo Spacecraft & Saturn V Launch Vehicle Pyrotechnics / Explosive Devices Some cites: More than 210 pyrotechnic devices per Apollo Mission. All devices required high reliability and safety Most devices were classified as either crew safety critical or mission critical. When complete system redundancy was ...


5

Some "coasting" phases are designed to limit the aerodynamic stresses on the spacecraft. The US space shuttle is an example of this. After around 26 seconds the main engines are throttled back for the next 34 seconds. In actuality this is called a "Thrust Bucket". While this isn't a true "coast phase" because the solid rocket boosters are still burning, it ...


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