Hot answers tagged

74

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 ...


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 ...


47

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

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 ...


32

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. ...


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

Urged on at a similar question on Chemistry SE, it seems that the idea of mixing liquid oxygen and liquid methane is an old one. And one that, using some of the answers above, seems to be cloaked in at least some hyperbole. Of relevance is R.L. Every and J.O. Thieme, Journal of Spacecraft and Rockets 2(5) 787-789 (1965) titled "Liquid oxygen and liquid ...


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

It absolutely could! First of all, water can be split in to hydrogen and oxygen, which can be enough to launch a rocket. Hydrogen requires a very low temperature, and the rocket engine doesn't have as much thrust as other options out there, but it is the same fuel that ran the Space Shuttle main engine, among others. Water and carbon dioxide, easily ...


20

In many cases, propellant is only dumped when the spacecraft’s mission is complete, so any minor changes to trajectory caused by the dump are unimportant. If you must avoid any trajectory or attitude change due to a propellant dump, the most straightforward way is to have multiple vents pointing in opposite directions, so the propulsive forces cancel out.


19

For shuttle: The oxygen was dumped into a basin to boil off (red arrow) or released through the External Tank vent valve, through the "beanie cap", and out a pair of vent ducts that ran through the "beanie cap" access arm. The "beanie cap" and vent ducts. The hydrogen was burned off in flare stacks (green arrow). The connection from the External Tank was ...


18

At STP: LOX's boiling point is 90.19 K Methane's freezing point is 90.7 K This does not a priori prove that a solution of the two can not exist. However it does mean that they can not be handled as liquids at the same temperature, making mixing the two more difficult. And so I've just asked Can a stoichiometric mixture of oxygen and methane exist as a ...


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", ...


16

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 ...


15

I think this is due to the SpaceNews article Hydrazine ban could cost Europe’s space industry billions from October 25th, 2017. Dawn Aerospace also mentions the article on their site for green propulsion: The current methods of satellite propulsion will not be tolerated much longer, with the European Union planning to ban Hydrazine by 2021. Our green bi-...


15

It's important to address two things: space flight is a tiny fraction of what these chemicals are used for, and nearly all mono-propellants are extremely hazardous to humans and like to spontaneously combust. This isn't a ban on "toxic propellants". It's a ban on an extremely dangerous and toxic chemical of which the aerospace industry uses a tiny portion. ...


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. ...


14

For the Space Shuttle: Using the same approximate curves (with all their assumptions and limitations) used in the answer to How does the Space Shuttle's SSME engine's thrust vary after ignition?, we can integrate the SSME flowrates to get a startup propellant consumption of: 416 lbm LH2, 2246 lbm LO2 per engine, and ~ 1248 lbm LH2, 6738 lbm LO2 ...


14

The Redstone's engine was based heavily on the engine of the German V-2, which also used 75% ethyl alcohol fuel with liquid oxygen. Robert Goddard's first liquid fueled rocket experiments used gasoline with liquid oxygen, which burned extremely hot -- Goddard burned out several nozzles and combustion chambers on his early flights. Figuring out how to cool ...


14

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 ...


13

Having the colder tank lower in the stack is marginally helpful for the thermal design, but in the case of the space shuttle, aerodynamic considerations dominate. For aerodynamic stability, it's desirable to put the center of gravity well forward of the center of aerodynamic pressure (which means roughly "where the drag is happening"). Think about a ...


13

Yes, the EU is aiming to end the use of hydrazine by ~2020. This has been in motion since about 2011. ESA's strategy do deal with this consists of two parts: they're trying to get an exemption, they're working on alternatives, inviting industry to develop propulsion systems based on less toxic propellants. While ESA is pursuing possible exemptions ...


11

Each technology has their own strengths and difficulties. It's really difficult to explain this without going in to a great detail about how rocket engines work, but let me try and give a brief overview. There are a number of different ways you can power a rocket engine. In general, for the same fuel and engine size, the higher the chamber pressure, the ...


10

They would stratify. Liquid oxygen is much denser than liquid hydrogen, with 1.141 g/cm3 for LOX vs. 0.07099 g/cm3 for LH. Thus, you need to install equipment to ensure proper mixing of the two liquids. This adds not only complexity to an already complex machinery, it also adds weight.


10

On the chemical/physical question of whether such a mixture can exist: Yes it can. There's a NASA report that looks into this: "ON THE SOLUBILITIES AND RATES OF SOLUTION OF GASES IN LIQUID METHANE", Hibbard and Evans, 1968 and concludes that such mixtures are possible. Starting on page 8: Figure 5(a) presents the curves for oxygen, argon, carbon ...


10

The existing answers do not accurately describe the procedure for the Space Shuttle system (or, I believe, for Apollo, but I am not 100% sure of that - see note at end of answer). The propellant tanks in the Space Shuttle's External Tank (ET) were never filled with nitrogen. The initial condition for LH2 loading into the ET LH2 tank was with the tank and ...


10

Fuel requirements will probably dominate food and other consumables by an order of magnitude or more, so you can't save mass by shortening the trip. The exact tradeoff depends on the assumptions you make. I'm just going to consider the outbound leg of the flight. NASA's trajectory browser offers me two missions to Mars in the 2025-2035 timeframe: ...


9

They say space is hard. If you simply plop a big tube full of fuel and oxidizer on top of a surplus engine and light it, you will not go to space today. To get a feel of the smallest shoestring you can have and still get to space, look at Rocket Lab in New Zealand. They've spent the last 10 years or so developing the ability to reliably go to space. Their ...


9

This is a diesel-electric locomotive TEM-2. The more powerful modification of TEM-1 diesel locomotives. In turn, TEM-1 locomotive is developed on the basis of TE-1 locomotives. The TE-1 is soviet copy of American Locomotive Company RSD-1. https://en.wikipedia.org/wiki/ALCO_RSD-1 Does it have an official name? "мотовоз"


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