82
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 ...
72
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:
...
55
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 ...
55
Like any perpetual motion machine, it won't work. In this case, there are two major reasons.
First, your "send back fuel" arrow is pushing mass forward; every action has an equal and opposite reaction, so pushing that mass forward pushes the rest of the rocket backward.
Second, the exhaust isn't fuel; it's already combusted, and the chemical energy ...
53
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 ...
50
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 ...
48
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 ...
45
Most of the propellant expended in sending a spacecraft to Mars immediately returns to Earth -- the fuel and oxidizer are combusted, combining into (typically) water vapor, CO2, and other simple compounds -- and ejected out the back of the rocket at high speed. The six month trip to Mars is "coasting", with only very small amounts of fuel used for ...
40
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 ...
40
As Organic Marble hints, there is about 140 degrees Celsius between kerosene's freezing point and oxygen's boiling point; there's no temperature at which both are liquid.
Even if the propellants were more thermally compatible, putting your fuel and oxidizer in the same tank is a really dangerous idea. Typically, propellant tanks are pressurized with helium ...
40
tl;dr as SF said in a comment "...they always packed a little more hydrogen than oxygen (for that ratio), so that at the end of combustion they wouldn't risk running oxygen-rich (and as result engine-rich)."
If you are interested in details, please refer to this propellant loading table for the following explanation.
The numbers indicated by the ...
38
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, ...
38
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 ...
38
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 ...
38
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 ...
35
Well, I can refer you to the Range Safety Wikipedia entry:
Two switches were used, ARM and DESTRUCT. The ARM switch shut down
propulsion for liquid propelled vehicles, and the DESTRUCT ignited the
primacord surrounding the fuel tanks. In the case of manned flight,
the vehicle would be allowed to fly to apogee before the DESTRUCT was
transmitted. This would ...
34
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 ...
34
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.
34
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.
...
33
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 ...
32
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 ...
32
It's the same reason SpaceX often does things differently: Krypton is a lot cheaper.
The satellites are designed to control costs. For example, each will maneuver with Hall-effect thrusters—ion thrusters in which propellant is accelerated by an electric field. The conventional fuel for such a thruster is xenon, which offers high performance. The Starlink ...
32
Most commercial commodity specifications for hydrocarbons such as gasoline, kerosene, Diesel fuel, jet fuel, naptha, mineral spirits, etc are fairly broad. RP-1 is kerosene that meets some particular specifications that are important for use as a rocket fuel, but not so important for burning it in gas turbines or diesel engines. The specifications for RP-1 ...
31
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 ...
29
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 ...
28
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, ...
28
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 ...
28
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 ...
27
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 ...
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