# Tag Info

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

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 ...

32

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. ...

31

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 ...

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 ...

22

Because it will almost certainly go KABOOM. Intimately mixed fuels and oxidizers are pretty much indistinguishable from explosives, and in particular, LOX intimately mixed with flammable hydrocarbons is wildly dangerous -- rather than being something you can handle, it tends to be set off by shock, vibration, or adiabatic compression that can be caused by ...

18

According to Clarke's Ignition! (1972), German rocket experimenter Johannes Winkler fired a methane-LOX rocket motor in 1930: This work led nowhere in particular, since, as methane has a performance only slightly superior to that of gasoline, and is much harder to handle, nobody could see any point to following it up. By 1970, NASA had experimented with ...

17

I do suspect there's an obvious way to work it out from the specific impulse, which I know is Ns/kg.. but I'm not quite sure how I use that information. Does it mean that an engine with a specific impulse of 12000Ns/kg, can put out 1N of force for 12000 seconds, using 1kg of propellant? Exactly so. "Specific impulse" is short for "mass-specific impulse", ...

17

Apparently, at least one OTRAG rocket test used diesel. OTRAG's intended fuel was kerosene with a nitric acid/$N_2O_4$ blend for oxidizer, so I would guess they used a similar oxidizer with diesel. Most large rocket engines pass the fuel through tubes surrounding the combustion chamber for cooling; normal kerosene and other common hydrocarbon fuels tend to &...

16

I don't have a great reference for this, but it was to reduce cost on the throw-away External Tank. By using the same interface into the Orbiter used to supply propellants to the main engines, the cost and complexity of adding a dedicated loading interface to the tank was avoided. It was not a tremendous complexity hit to the Orbiter Main Propulsion system ...

15

Yes, and it is currently being done on a few engines, notably SpaceX's Raptor engines. They run on liquid oxygen and liquid methane. These are run through turbopumps in two different mixture ratios, burning a small part of the fuel which spins the pumps and vaporizes the rest of the fuel. When they enter the combustion chamber they are both in gaseous form. ...

15

Helium was used to pressurize the RP-1 tank to save weight. Nitrogen is much cheaper but its density is 1.250 kg/m$^3$, helium is 0.1785 kg/m$^3$, so 1.071 kg is saved for every cubic meter of emptied tank volume. The first stage RP-1 tank volume of the Saturn V was 770 m$^3$, so 824 kg were saved by using helium instead of nitrogen. During the flight the ...

13

Because all you have to do to get gaseous oxygen is take liquid oxygen and warm it up a bit. That means just tapping off a little gas from the engine and routing it back to the tank to keep the ullage pressure where it needs to be. Contrast that with RP-1, which doesn't really vaporize enough to get the pressure where it needs to be. For that, they had to ...

13

It’s a long journey, but it’s all “downhill” — once the spacecraft leaves the moon’s gravitational sphere of influence, Earth’s gravity brings it home. The process of leaving the moon is called “trans-Earth injection” or TEI; the rocket engine on the CSM fires for about two and a half minutes, adding about 1000 m/s to the spacecraft's speed in lunar orbit, ...

13

Helium is used as a pressurant and purge gas. While no longer a "modern" launch system, the Space Shuttle made extensive use of helium to pressurize various systems and can perhaps serve as an example. Prelaunch pressurization of the External Tank liquid oxygen and liquid hydrogen tanks (on the order of 100 lbm of He for each tank) During standby ...

12

If there is a rocket using cryogenic hydrogen tanks, you need helium for it. Liquid hydrogen should not be mixed with air, oxygen or nitrogen. A mixture with oxygen is explosive and should be avoided for security. Nitrogen gas would liquify and even freeze at the temperature of hydrogen. Other noble gases like argon would liquify, even solidify at the ...

11

The 1976 NASA monograph Liquid Rocket Disconnects, Couplings, Fittings, Fixed Joints, and Seals defines "couplings" as Couplings are manually actuated separable connectors that require more than a few seconds for engagement or disengagement. and lists the following types: Flanged Threaded: Dynamic swivel couplings Shape memory alloy is not ...

11

There is far more material to be gained from space exploration than will be lost from Earth in collecting it. A primary reason to explore space is to exploit mineral and organic resources that occur in abundance off earth. Within the "few centuries" you mention, the net change of mass on Earth may very well be positive due to an influx of precious ...

10

This paper, claims that metallic hydrogen at low temperatures might be relatively long-lived at pressures above about $50 GPa$ (with a large margin of error) which is about 500 thousand atmosphere and decay rapidly below that pressure. This does make it seem that tankage for a metallic hydrogen fueled rocket would have to be quite robust, and the ...

10

Liquid methane (Methalox) has never been used in an orbital, or even very high flying rocket. It's a long story, but the short is methalox requires a bit better metal alloys then were available until recently, and that is why the sudden heavy interest in it. Methane in and of itself isn't optimal for atmospheric or above-atmosphere range, but has a good mix ...

9

Until Masten Space Systems reveals the exact composition of the propellants, we can only speculate on the combinations they used. Based on what you have presented in question we can rule out options one by one, but we cannot be 100% sure especially for fuels because if we miss oxidizer than we will miss fuel to. The smoking gun here is a sentence “prepared ...

8

Goddard's first liquid fueled rocket in 1926 was pressure fed -- the engine was above the tanks, so gravity feed was not feasible. Liquid oxygen was vaporized with a small alcohol burner, and the resulting oxygen gas pressurized both the LOX and gasoline into the combustion chamber. The V2 is claimed to have the first "large rocket engine" to use a ...

7

Peroxydisulfates and acid itself would be a bad choice for rocket oxidizers for several reasons: H2S2O8 is actually a solid with melting point of 65°C, therefore unsuitable for liquid fueled rockets, In pure form acid is even more aggressive and corrosive than sulfuric acid, it's like sulfuric acid on steroids. It can explode in contact with organic ...

7

I'm not a chemist but I'll go out on a limb and suggest a way to resolve some issues in comments. It looks to me as though as long as you are above both the critical pressure and critical temperature at the same time, it's a supercritical fluid; thus the name. So as long as the pressure is above 50.4 bar and the temperature is above 154.5 K (-118.6 C) it's ...

6

To complement the answer: 1 L contains 1141 g of liquid oxygen 1 L contains 1 g of gaseous oxygen (at 1ATM) Of course you can compress it but the container will add more weight (highly undesirable). But that's not over! Rockets consume not only a lot of propellant, but they consume it fast. A Saturn V consumes 18000 kg every second. That would be ...

6

From the Waiver Request linked from the article in the question: The Boeing 702HPspacecraft design features a reaction wheel pointing control system. As all venting must occur within the capabilities of this pointing control system, the firing of thrusters for venting and to address momentum buildup must be of more limited duration and additional time is ...

6

To draw out a quote: Symmetrical dimethyl hydrazine turned out to be a dog (it's [sic] freezing point was only--8.9 [degrees]) Not only have I found a rare typo in the remarkable Ignition! (and in the second edition, to boot!), but there you go: SDMH was a good propellant, but it froze far too readily. To answer your question: yes, it was probably a ...

6

RP 1 fuel was red dyed for a thermal stability experiment on JP-8 and RP-1 fuel of various ratios. High Reynolds Number Thermal Stability (HiReTS) testing device. There are several factors that set the HiReTS machine apart from other thermal stability tests. The red dye of RP-1 was used to detect the various effects of parameters like temperature and ...

5

If you want to store as much oxygen in a given volume as possible, you have to increase the density significantly. There's two ways to accomplish that. Low temperature (cyrogenic liquid) High pressure (supercritical fluid) If you don't need to store it for very long (say during a launch), then cyrogenic liquid oxygen has lots of benefits. You get maximum ...

5

The difference in loading a flown booster and a brand new booster is the same. SpaceX starts loading RP1 and first stage LOX at T-35 min. RP1 fueling on the first stage finishes around the T-3 min and second stage around T-2 min time. For LOX fueling, they never really finish loading, they will keep topping off the LOX that's boiled off til about liftoff. So ...

Only top voted, non community-wiki answers of a minimum length are eligible