41
votes
Accepted
Why are unused launch abort rockets jettisoned rather than used to augment thrust?
The thrust of the Launch Escape System (LES) might look significant, but the total impulse is not (that is, they burn for such a short time, they can't actually impart much delta-V, especially not ...
- 1,542
35
votes
Accepted
How can a rocket approaching the Karman Line then return to earth faster than 53 m/s terminal velocity?
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 ...
- 170k
35
votes
Accepted
Why does the Indian PSLV rocket have tiny boosters?
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 ...
- 187k
33
votes
Accepted
How is thrust transmitted from strap on boosters to the central core?
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 ...
- 2,267
31
votes
Why do nuclear rockets (e.g. NERVA) have such poor Thrust-to-Weight ratios?
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 ...
- 23.4k
28
votes
Why are optimal launch TWRs so different in KSP than on earth?
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 ...
- 4,231
22
votes
How is thrust transmitted from strap on boosters to the central core?
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 ...
- 170k
22
votes
Accepted
What is the lowest first stage thrust for a launch reaching orbit?
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 ...
- 2,549
21
votes
Why do nuclear rockets (e.g. NERVA) have such poor Thrust-to-Weight ratios?
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 ...
- 8,188
20
votes
Payload capacity of a rocket
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 ...
- 1,183
19
votes
How far would the STS get without the SRBs
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 ...
- 7,330
17
votes
Payload capacity of a rocket
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 ...
17
votes
Why are unused launch abort rockets jettisoned rather than used to augment thrust?
The thrust of the Apollo launch escape rocket was negligibly small when compared to the thrust of the Saturn V first and second stages. The burn time of the launch escape system was negligibly small, ...
- 49.3k
17
votes
Accepted
Does "% Throttle" refer to fuel flow or thrust?
For the Space Shuttle Main Engine, "% Throttle" (actually in shuttle vernacular, % Power Level), referred to the chamber pressure. It was the desired value of chamber pressure that was used ...
- 187k
16
votes
Where does the thrust act in a rocket engine and how is it transferred to rocket structure?
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 ...
- 17.4k
16
votes
Earth Launch System with Water Propellant
Electrolysis-based propulsion becomes practical only once you've reached orbit, where you can power the electrolysis with solar panels and where you don't need enormous thrust. Whatever you'd use to ...
- 12.2k
16
votes
How are thrust specifications for multi-nozzle engines given?
Instead of seeking sources, I'll do a little bit of calculation:
1000kN per engine:
1000kN is about 100 tons-force. Wikipedia lists R7 launch mass as 280 tons. 500 tons-force of thrust (5 engines x ...
- 55.3k
16
votes
Accepted
How high is the ISP of a fire extinguisher
A conventional CO2 fire extinguisher could be used as a cold gas thruster. The maximum Isp would be determined by the temperature of the gas. CO2 is stored as supercritical CO2 inside the bottle. It ...
- 24.8k
15
votes
Rocket engine test bed structure
It had a heavy concrete foundation to which the metal structure of the stand was attached.
Shown is test stand 1-C at Edwards Air Force Base.
And in use with an F-1 running.
There was an F-1 stand ...
- 187k
14
votes
Accepted
How much G force is applied when correcting an orbit around Earth?
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 ...
- 170k
14
votes
Merlin 1D Engine Throttling
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 ...
- 187k
14
votes
Accepted
Why do chemical rockets encompass a weird shape on this thrust vs. Isp graph?
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 ...
- 170k
14
votes
Accepted
Saturn 1 thrust mismatch
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 ...
- 49.3k
13
votes
Accepted
why do under-expanded engines have less than ideal thrust?
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 ...
- 6,961
13
votes
What is the lowest first stage thrust for a launch reaching orbit?
@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 ...
- 19.6k
13
votes
How are thrust specifications for multi-nozzle engines given?
The nozzle is not the engine.
Each nozzle is attached to one combustion chamber, but by convention, a complex of multiple combustion chambers sharing a single turbopump, such as the RD-107/RD-108, is ...
- 170k
12
votes
Why will SLS Block I bring less mass to LEO than the STS shuttle system did?
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 ...
- 170k
12
votes
Why are unused launch abort rockets jettisoned rather than used to augment thrust?
The weight and complexity of using the launch escape system negate any advantages.
Using the LE rocket as it was designed, i.e. to give a brief, powerful burst would have meant strengthening the ...
- 20.3k
11
votes
What is the correct thrust curve for a solid rocket with a simple circular hole, and why?
Underneath the diagrams in the Wikipedia article you link, there's a mention of the BATES grain geometry:
Circular bore: if in BATES configuration, produces progressive-regressive thrust curve
...
- 170k
11
votes
Accepted
What is the correct thrust curve for a solid rocket with a simple circular hole, and why?
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 ...
- 187k
Only top scored, non community-wiki answers of a minimum length are eligible