79
First stages are generally run to depletion (though not complete depletion - I'll get to that later). First stage ascents often use a preprogrammed, open loop guidance system to get out of the atmosphere with a good chunk of downrange velocity. Because winds aloft and other factors may vary, first stage performance also varies somewhat.
Upper stage guidance ...
74
What “fuel more powerful than anything the West (had) in stock” put Laika in orbit aboard Sputnik 2?
Laika's magical mystery propellant was kerosene and LOX.
Sputnik 2 was launched on the 8K71PS launcher. This was a modified R-7 ICBM, and like all the R-7 derived launchers, its RD-107 and RD-108 engines burned kerosene/LOX. The Russian specification for rocket-grade kerosene is called RG-1, and it's similar to the American RP-1.
The specific impulse of ...
67
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:
...
52
The book 'Ignition!' tells the history of propellant research and has this to say about ozone from page 112 available here
For it has its drawbacks. The least of these is that it's at least as
toxic as fluorine. (People who speak of the invigorating odor of ozone
have never met a real concentration of it!) Much more important is
the fact that it's ...
52
Monopropellant systems such as catalyzed hydrazine thrusters are attractive at very small sizes, where the simplicity of a single propellant tank outweighs their relatively low performance.
According to Wikipedia, Cavea-B requires a small amount of UDMH or a similar hypergolic to begin ignition -- every time you want to fire it, which can be a frequent ...
48
LF2/LH2, or liquid difluoride liquid dihydrogen bipropellant (binary cryogenic fuel) has a specific impulse of 410 seconds (by weight) at sea level, which is more than e.g. LOX/LH2 (liquid oxygen liquid dihydrogen) with average specific impulse by weight of 391 seconds, also at sea level. As the oxidizer is in both cases on board and one of the binary ...
46
To quote John D. Clark's great book Ignition! (Chapter 11: The Hopeful Monoprops):
If Tannenbaum's mixtures were bad, that proposed at a monopropellant conference in October 1957 by an optimist from Air Products, Inc., was enough to raise the hair on the head of anybody in the propellant business. He suggested that a mixture of liquid oxygen and liquid ...
38
Or am I wrong and have there been attempts to build a methane rocket in the past?
Well, if there were, I figured that John D. Clark's famous book Ignition! (1972, free online copy) would be the place to find it.
And indeed, the index at the end of the book has a convenient entry for "methane, usefulness of" pointing to pages 8 and 191.
On page 8, Clark ...
37
The three main competitors for liquid fuel choices to date have been:
Hypergolics - easiest to get started with
Kerosene/LOX - Good thrust, low performance, but dense
LH/LOX - Best performance, hardest to do
So if you were starting a new space program with a clean sheet design, LOX/LH is out of the question, too hard. Hypergolics are well understood, ...
37
What a fascinating question!
Turns out it's less flammable.
Ground Supply Fluid—Because the flash point of RP-1 fuel, which
supplies the system in flight, is 110 to 139° F, it is classified as a
Class Ill flammable liquid, not suitable for ground operations. A
study was made to find substitute fluids with properties similar to
RP-1 that could be ...
36
The Merlin-1D engines are now tuned to use the super cooled fuel and oxidizer. Thus you would be running the engines in an out of normal state, if not using it the same as all other launches with warmer propellant.
It would imply different software to handle the different performance levels.
Last thing you want to do is run things differently, if you can ...
32
According to Clark's "Ignition!", German rocket scientists in WW2 had done the math on ammonia, and JPL had burned it with RFNA and WFNA oxidizers in 1949-1951.
Regarding the XLR99, Clark says:
But something more potent than alcohol was needed for the X-15 rocket-driven supersonic research plane. Hydrazine was the first choice, but it sometimes exploded ...
31
Let's start with a Fermi estimate:
The atmosphere has a mass of about 5.15×1018 kg, 20% of that is oxygen. A rocket launch uses on the order of 106 kg of oxygen. To use up all the oxygen (and assuming no oxygen is replenished by plants) requires 1012 rocket launches.
Of course, rockets are only a tiny part of all oxygen consumption. We burn 4×1012 kg of ...
31
In addition to what the other answer said, it would take very little provocation for such a situation to turn into a good way to test the blast resistance of nearby facilities.
31
The same system was used on Shuttle - allow me to discuss that, the design philosophy applies to Apollo as well (Shuttle deleted the fans though, and had a special Avoid-Apollo-13-circuit in the O2 tanks).
A supercritical fluid is any substance at a temperature and pressure
above its critical point, where distinct liquid and gas phases do not
exist.
...
30
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 ...
29
The J-2 engine used on the second and third stages of the Saturn V has a "PU valve" (propellant utilization) on the oxidizer turbopump. Adjusting the mixture ratio with this valve primarily provides a mechanism to ensure that the hydrogen and oxygen propellants are depleted at the same time. Secondarily, it allows a tradeoff between specific impulse (fuel ...
28
The Apollo LM had three independent propellant supplies: tankage in the descent stage usable by the descent engine, tankage in the ascent stage for the ascent engine, and in the ascent stage for the reaction control system (RCS) thrusters.
Prior to the initiation of descent and landing, only the RCS would be used, and very little of it.
During the ...
27
They might appear as the flame is detached from the nozzle, but that's in essence merely an illusion and the burn is there, all over the plume of the nozzle exhaust. It is however nearly translucent due to high purity of cryogenic propellants and by the chemical reaction producing molecules having high translucency. Visibility of the plume, unless you're ...
27
Chemical rockets will never have more than 600 seconds specific impulse. Storing free radicals in propellant to defeat this limit is impractical.
Validated. Chemical rockets in use top out at 450-460 seconds, with a demonstrated test-stand record of 542 seconds.
~500km range rockets will use chlorine pentafluoride and a hydrazine derivative.
As far as I ...
26
In addition to all the issues raised by TidalWave, you also need to consider the exhaust products.
The space shuttle main tank carried about 730 tons of hydrogen and oxygen. Burning that produces about 730 tons of water, the happy chemical we all love. Burning about 730 tons of hydrogen and fluorine produces about 730 tons of very hot hydrogen fluoride, ...
26
Possible: yes.
Feasable: not really (at least not for power applications).
The main trick is energy density (per volume) - gases tend to be quite significantly less dense than liquids - and thus the tanks would need to be much larger and heavier - so they are commonly used in their condensed liquid form.
For small engines gases have been used - both as ...
25
A vertical Mentos-coke geyser through a not particularly optimal nozzle reaches an altitude of roughly 6 meters (by my eyeballing), implying exit velocity of a little over 5 m/s, equivalent to an Isp on the order of ~0.5s. (I also see references to 40-foot/12-meter Mentos geysers, implying that figures closer to 8m/s or 0.8s ISP are possible).
The ...
25
The helium is used to continuously re-pressurise the propellant and LOx tanks as they are emptied. It is stored in a COPV inside the body of the LOx tanks to keep the He at a lower temperature (and higher density) to maximise loading capacity. The helium is cycled around the Merlin engine to be heated before being fed into the tanks. This has two main ...
24
NASA's Space Transportation System (STS) vehicle, better known as the Space Shuttle, used two single engine Solid Rocket Boosters (SRB) as Stage 0, an engineless external tank providing propellant for the three Space Shuttle Main Engines (SSME) on the orbiter as stage 1, and additional two Orbital Maneuvering System (OMS) hypergolic liquid-propellant rocket ...
24
When you compare the waste products of LOX/Kerosene vs hydrazine/MMDH/etc, it is actually not too terrible at full combustion. (End up with CO2 and water, or CO2, Ammonia, and water).
However, if say, a fully fueled Proton looses control say 50 seconds into flight and collides with the ground, literally a million lbs of hydrazine is the definition on ...
24
The fuel used in the shuttle's Orbital Maneuvering System engines and used for the deorbit burn was not cryogenic; it was storable hypergolic fuel.
The cryogenic hydrogen and oxygen fuel burned by the main engines was used only during the ascent, which took only about 10 minutes.
22
The requirements of the first stage are that it deliver about 3340 m/s of delta v to a 690 ton payload (the upper stages and spacecraft), with an initial thrust-to-weight ratio of at least 1.16:1.
The best candidate for a first-stage hydrogen engine in the Saturn era would be the never-completed M-1. At sea level, it would be much less powerful than the F-1,...
21
John D Clark, Ignition!, p.165, on the testing of a Cavea B motor:
“Well, through a combination of this and that, the motor blew on startup. We never discovered whether or not the [detonation] traps worked —we couldn't find enough fragments to find out. The fragments from the injector just short-circuited the traps, smashed into the tank, and set off the ...
20
As small amounts of LOX boil off heat is removed from the remaining volume. Boiloff actively cools the fluid and helps keep the remainder liquid. Rockets typically have vents to aid in managing the boiloff rate and fluid feed lines to replace lost fluid while waiting on the pad.
During flight the consumption rate outpaces any boiloff losses and it is not an ...
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