# 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 ...

41

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 ...

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 ...

22

Thrust termination is the goal of Range Safety in the event of an errant rocket. Rendering the boosters inert is considered secondary, when possible. The Range Safety Officers don't rely on the current positions of the vehicle to decide to terminate, but instead are looking at the IIP (Integrated Impact Point) on a map. The IIP is the point where the ...

21

They do! Many propellant tank, especially those required to work in zero-g environments, do use just such a bladder-inside-a-tank for the fuel. Typically monopropellants for thrusters. It completely removes the requirement for Ullage of the propellants, but adds complexity, cost, mass and failure modes. Additionally, flexible bags are a bit hard to make at ...

20

Hydrocarbons are largely interchangeable when it comes to performance, and as long as no single one beats kerosene with a large enough margin, the hassle of changing infrastructure is generally not worth it. Compared to RP-1, butane has slightly (very slightly) higher specific impulse, and somewhat lower density, largely cancelling each other out. Butane ...

20

Hydrogen peroxide has a (perhaps not fully deserved) reputation of being hazardous to work with; it decomposes spontaneously, releasing heat, and the decomposition rate increases with temperature, so it's tricky to store safely. An old usenet discussion thread found on Yarchive discusses the hazards in more detail. It is used sometimes as a monopropellant (...

20

SpaceX chose to use RP-1 because the development path for a good RP1 engine was a full decade shorter! Plus many other factors favoring KeroLox for launch from Earth surface, for example the very high energy density of RP-1 allows smaller tankage, which is a great advantage when flying through the atmosphere. The Excellent thrust density of RP-1 also allows ...

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 ...

18

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

Partial answer: If one has solar electric power, one can use each kilogram of propellant much more effectively (i.e. higher delta-v through a higher Isp) if it is ionized and accelerated. Electrostatic acceleration can impart roughly 10,000 to 100,000 m/s (or higher potentially (pardon the pun)) velocity, versus circa 4500 m/s from an 2H2 + O2 chemical ...

16

The object of burning chemical propellant is to convert chemical energy to heat, using that heat to accelerate the propellant. If you are starting out with electrical power, you have no reason to limit the energy you put into a given mass of propellant to what you can store in it as chemical energy: just heat water directly, and you can reach temperatures ...

15

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 the oxidizer, we’ll miss the fuel as well. The smoking gun here is a sentence “...

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 ...

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, ...

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

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

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 ...

10

HTP will sustain a combustion reaction without a catalyst once ignited, but it's not clear to me if the reaction proceeds quickly and smoothly enough to be a good idea for rocket combustion chambers. As MSalters comments above, hydrogen peroxide "will undergo potentially explosive thermal decomposition" before reaching its theoretical boiling point,...

10

The Falcon 9 burns somewhere around \$200k-300k in propellant (stated to be \$200k in 2015, but the vehicle's grown in size since then). For non-expendable launches, it puts about 16000 kg into orbit, so that's about \$20/kg. Starship burns cheaper methane fuel, and propellant cost is estimated at about \$500k/launch when purchased in volume. Total payload ...

9

What is the theoretical fuel cost to launch 1 kg of payload to orbit on an ideal rocket (rocket with 0 kg dry mass)? We can use the rocket equation to get a rough idea of the fuel required. $$\delta V = v_e ln \frac{m_0}{m_f}$$ $\delta V$ required to reach LEO is 9.4 km/s $v_e$ is the exhaust velocity of the rocket, 3 km/s is pretty good for a chemical ...

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 ...

8

I did look at the video, thanks for starting it at the point of interest; what Manley says is simply wrong. On actual shuttle flights propellant was not dumped from the ET. Residual prop (both fuel and oxidizer) was dumped from the Orbiter after ET sep. He is describing this dump in a garbled, mistaken manner. There's no relation between this dump and the ...

7

As a rule of thumb, no rocket fuel (or oxidizer) will ever be able to detonate on its own. For the simple reason that the maximum flame front propagation through it needs to be slower than the fluid speed through the injectors, otherwise the flame would propagate back into the tanks. NO, no-one has ever managed to pump flammable fluids faster than their ...

6

It sure is, by some small portion of the industry. I don't think we'll be seeing any big EthyLox (if you'll excuse the neologism) boosters taking off as first stages, though: it's a complicated thing to deal with, Ethylene. it being a room temperature gas means it entails all the hassle methane or hydrogen brings (i.e. you need to chill it down in order to ...

6

PS to previous comment about refrigeration in the X-15. It had none, keeping weight absolutely minimal precluded it. Temperature was far more of an issue for the LOX than for the NH3. During captive carry to launch the LOX was replenished from a supply in the B-52 carrier aircraft; otherwise some degree of boil-off occurred. A special case of venting LOX was ...

6

The only reason near-Earth asteroids still have water is that it's bound up in hydrated minerals where it's become part of the crystal structure of those minerals. Freeing it from those minerals requires baking it out of at high temperatures (up to around 500 °C), the most easily extractable volatile ices are all long gone due to heat from the sun. In ...

6

Hybrid smallsat launch vehicle technology is currently being developed 100% in Taiwan1 by the Advanced Rocket Research Center along with all control electronics and algorithms. The video below shows a test with four hybrid peroxide oxidizer plus rubber thermoplastic solid engines being both vectored and throttled to implement stable hovering. I think that ...

6

The Multi-Mission Radioisotope Thermoelectric Generators (MMRTG) used by NASA are probably unfeasible for the purposes you are thinking of, although they are highly useful for space exploration. Multiple spacecraft have used these, including both Voyager 1 and Voyager 2, New Horizons, Curiosity, and the new Perseverance. This is due to their ability to ...

6

I was a missile tech on a SSBN in the '70s and worked on the Poseidon C3 SLBM. This missile had six "Thrust Termination Ports" arranged around the periphery of the second stage motor dome. Each TTP was a 10" diameter fiberglass tube angled outward from the motor dome to the side of the missile with det-cord at each end. When commanded by the ...

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