Hot answers tagged

70

A bore in the solid propellant grain increases exposed surface area and allows for a higher burn rate to increase thrust. There might be several grain geometries used, to meet launch vehicle's ascent profile needs through grain regression and with it control flow rate as the solid propellant core burns. From Wikipedia on Solid-fuel rocket - Grain geometry: ...


35

53 m/s is the approximate terminal velocity of a human skydiver. The terminal velocity of a 7-ton metal dart is quite a bit higher. Larger objects tend to be affected less by atmospheric drag than smaller ones, all other things being equal. Terminal velocity also increases with altitude because the air is thinner. Assuming 7000 kg mass, 3.5 m2 cross ...


33

It’s a sense of scale issue. As much as the struts might look like flimsy bits of drainpipe, those rockets are around 15 meters wide, and the struts are more like the heavy steel beams used to hold up entire buildings. So yes, they’re just really strong.


33

Why would these be used instead of just using a larger first stage? Strapping on differently-sized boosters allows variance in payload mass without redesign of the first stage. The PSLV has flown with no (PSLV-CA), small as shown (PSLV-G), or big (PSLV-XL) solid boosters. PSLV-CA (no boosters) - can deliver 1100 kg to 622 km sun-synchronous orbit PSLV-G (...


32

It depends on the particular engine. Thrust from a solid rocket is approximately proportional to the burning surface area of the fuel (also called the grain). A long solid rocket motor with a channel along its length is burning more surface area than an "end-burning" motor, so produces more thrust. Typically solid rocket boosters are used to provide very ...


31

At their core nuclear rockets working by heating a working fluid and running it out a nozzle are still constrained by the same physics as a chemical rocket where exhaust temperature cannot be much higher than the melting point of nozzle (cooling the nozzle lets you cheat a bit), putting limits on how much energy can go into the fuel. Nuclear rockets get ...


25

It is no longer generally considered optimal to use a launch TWR of 1.5-3 in KSP. A little background: In KSP players who were optimizing for launcher weight would go for a TWR of 2.0 or higher, so players wishing bragging rights of "I launched 100t into orbit for only X tonnes of rocket" would go for a TWR of about 2.0 or even higher and this worked because ...


24

The reason for the SRBs is that the stack weighs something 7.4 million lbs. The two SRBs provide about 2.8 million lbs of thrust each. The three SSMEs provide about 600Klbs each. If you subtract 5.6 million lbs of thrust, and the SRBs weigh 1.3 million lbs each, then the remaining stack, about 4.7 million lbs only has 1.8 million lbs of thrust. So it ...


22

For Delta IV Heavy, according to Spaceflight101: The CBCs functioning as boosters are attached to the central core using thrust struts that interface with the interstage section of the launcher to transfer loads from the boosters to the rest of the vehicle. Additional attachment points reside in the base of the vehicle right above the engine heat shields. ...


21

The one exception to this fact is Project Orion Not quite. Project Timberwind was a solid-core NTR using a pebble-bed reactor design that combined high Isp with a moderate T/W of 30. The DUMBO NTR used a quite different core design, and had predicted T/W ratio of 70. Still somewhat shy of a good modern chemical rocket, but with a much better specific ...


21

The U.S. Vanguard rocket reached orbit three times with a first stage thrust of only 125 kN. The first stage of the three-stage Vanguard Test vehicle was powered by a GE X-405 28,000 pound (~125,000 N) thrust liquid rocket engine. Vanguard TV3 — NASA NSSDCA


20

The short answer is: Tsiolkovsky rocket equation. You need some velocity to achieve some position (an orbit or a body) in space. Farther a position - more velocity. More velocity - more propellant mass, and this relation is not linear and not in favor of velocity. $$\Delta v=v_e \ln(m_0/m_f)$$ where: $\Delta v$ - theoretical maximum increment of velocity, $...


17

TL;DR Without SRBs, by maintaining the real stack's thrust to weight ratio at ignition, you run out of fuel at about 167 seconds with (if we maintain the flight profile of the real stack) a velocity around 1.4 km/s and an altitude of around 70 km. Without SRBs, with an initial thrust to weight ratio of 1, you run out of fuel at about 289 seconds with (if ...


17

It perhaps become clearer when stating what rockets do. They change velocity. In space terms, that's delta-v. A rocket stage can only change your velocity some limited amount. Different targets in space require different amounts of velocity change (Low orbit: 8km/s, low Moon orbit: 12km/s) If your rocket stage can not give all the velocity change you need, a ...


16

The thrust acts on the nozzle and combustion chamber walls by virtue of the pressure differential they contain. Using the RS-25 (SSME) as an example, with illustrations from this pdf, I can highlight a few of the components. Page 11 (pdf page 17) shows the gimbal bearing assembly, a ball-and-socket joint assembly made from a titanium forging. That is ...


15

The variations in the centre of mass was handled by the huge gimbal range of over 20 degrees. Also, the heaviest part of the propellant, the liquid oxygen, was placed in the upper part of the external tank. That means that the centre of mass was pretty high, placing it far from the engines, and thereby reducing the deviation angle.


14

Interesting and non-trivial questions. Most propellants are not self-pressurized because as soon as the engines turn on the pressure would drop precipitously as the tanks quickly emptied and the propellant was unable to vaporize fast enough to keep up. LOX, RP, and H2 are the most common launch vehicle liquid propellants and none vaporize fast enough to ...


14

What's your engineering budget? This is a hideously impractical undertaking. Most of the mass of an orbital rocket is fuel and the tanks to hold it; even though your payload is tiny, all the rest of that stuff is big. The smaller a rocket is, the harder it is to design it with the high fuel-mass-to-dry-mass ratio that is required to attain high speeds, ...


14

SpaceX is not exactly forthcoming with detailed information about the Merlin's workings but we can figure some things out. Tom Mueller, designer of the Merlin, gave a brief description of the engine in this video. He drew a sketch of the engine schematic which I have screen-captured for your use. The only valves shown on this sketch were described by ...


14

I'm guessing that the chemical rocket envelope in the plot encompasses points representing actually-built rocket engines, rather than theoretical ones, hence some of the irregularity of the shape is due to historical accident. 10N is quite small for a chemical rocket engine. Such units are mainly used for attitude control of small spacecraft rather than ...


13

In practice, the g force applied for orbital corrections is very small. The satellite operator has plenty of time to make the correction, and if you are capable of accelerating the satellite at more than a small fraction of a g, it suggests that you brought too much mass along in the form of a rarely used, over-powered engine. For the ISS in particular, ...


13

The hard part is that $P_e$ isn't a completely independent variable. As the gas expands past the throat, thermal energy is being converted into kinetic energy. The gas cools down and speeds up. So if you shorten the nozzle (creating an underexpanded flow), there is greater pressure at the exit (good). But the exhaust speed $v_e$ is lower (bad). The $\...


13

There were different versions of the RL 10 engine with different thrusts. The retired RL10A-1, first flown 1962 had a thrust of 67 kN (15,000 lbf). The active RL10B-2, first flown 1998 has a thrust of 110.1 kN (24,800 lbf) The RL10B-2 engine is very different to the RL10A-1, it is much heavier, longer and has a much larger diameter. The third stage of Saturn ...


13

@2012campion's answer shows that this was not the lowest thrust The smallest rocket to reach orbit is the Japanese SS520-5. It had a peak thrust of $185 kN$ according to the same web page: Firing up its first stage, SS-520-5 shot up from its launch rail at 2:03:00 p.m. local time on Saturday with its aft fins sending the climbing rocket into a spin to ...


12

Obviously there are differences between implementations that will make a general rule very hard to define. For example, on the Space Shuttle, the 3 SSME engines were close together, and the two SRB's offset nearby. But when they looked at 4 or 6 RS-68A engines between the two SRB's for one of the many SLS/Ares iterations they found the heat load was too ...


11

In the way you defined it, no motion relative to the sun, it is not possible to stand still, because the sun itself is not a solid object. Instead different latitudes rotate with different velocities. http://en.wikipedia.org/wiki/Solar_rotation You could stand still with regard to the sun's equator by being in a tight orbit around the sun with an orbital ...


11

It's always difficult to make apples-to-apples comparisons between the space shuttle and other launchers, because the orbiter is ambiguously part launcher and part payload. This is compounded by the broadness of the term "LEO"; shuttle payloads went to a variety of altitudes and inclinations. However, since the title of the question specifies "mass to LEO" ...


10

Hill and Peterson "Mechanics and Thermodynamics of Propulsion", third printing, November 1970, page 385, has a diagram that agrees with your intuition. (sorry for poor scan quality) You are correct - as the surface area increases, so does the mass flow rate. There must be other factors in play in the graph from Wikipedia.


10

Newton's Third Law states that if object A pushes on object B with a certain amount and direction of force then object B pushes on object A with same amount and opposite direction of force. Notice how the two bulleted clauses are nearly the same, except A and B have swapped roles, and the direction is reversed? In a rocket, object A is the rocket and ...


9

You can; burning retrograde with respect to the sun lowers your perihelion. If you do it long enough your orbit will intersect the sun. If you ignore gravity assists this is the cheapest way of impacting the sun. Because the sun is not a point mass you don't even need to reduce your velocity to 0. Thrusting directly towards the sun would eventually work, ...


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