37

TL;DR: The low technology readiness, the very, very low thrust, and the need for a catalyst bed means this was and still is the wrong technology for the intended purpose of a launch abort system and maneuvering in low Earth orbit. Low technology readiness SpaceX began working on Dragon V2 over five years ago. At that point, AF-M315E had a rather low ...


36

At least for the Space Shuttle, freezing was OK, but thawing out was bad for piping. Hydrazine contracts when it freezes, so it can 'superpack' (more fluid flows in, then freezes, etc.)...then when it thaws out, there is more than can fit in the pipe, and it can burst. In the Space Shuttle's auxiliary power unit, hydrazine plumbing was allowed to sustain ...


33

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 ...


14

The Olympus satellite (1989-053A, 20122) lost pointing and power for long enough that all the fuel froze. It was recovered after a couple months and the fuel defrosted. I couldn't easily find what fuel was used, but it must either be hydrazine or a derivative. The 21-Sep-1991 New Scientist article Nine-week battle that saved Olympus explains: Engineers ...


9

MON according to Wikipedia: Mixed oxides of nitrogen (MON) are solutions of nitric oxide (NO) in dinitrogen tetroxide/nitrogen dioxide (N2O4 and NO2). The addition of a small amount of nitric oxide (1%-10%) makes the oxidizer less corrosive, but slightly less powerful as well, and changes the freezing point of the liquid. MON3 means 3% nitric oxide by ...


6

An exhaustive 42 seconds of googling reveals this on Stellar Exploration's website: As part of early R&D for a NASA funded deep space nano-satellite mission we have designed, built, and tested a miniaturized hypergolic bipropellant thruster. It provides 3 N of thrust with 285 sec specific impulse. The propellant is pressurized with gear pumps, allowing ...


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

It's mostly due to nature of how DARPA operates in general. They have few 'programs', they are project and result focused. DARPA tends to form a temporary project team, formulate desired outcomes, see it either fail or come through and move on. The results, if any, will end up in literature and in forms of IP in hands of contracted partners etc. Their ...


5

The use of MON, as distinct from N2O4, arose because the latter can cause stress corrosion cracking (SCC) of titanium alloys. This was first observed in the 1960's during the development of the Apollo systems. The mechanism for SCC is believed to relate to the presence of oxygen in N2O4. Addition of nitric oxide (NO) to the propellant eliminates O2 by ...


5

Using Wikipedia: The hydrazine tank of New Horizon has an elastomeric diaphragm separating the liquid from the pressurizing gas helium within zero gravity. There are 16 thrusters with redundant plumbing to the tank. The diaphragm prevents helium entering the plumbing, so all hydrazine within the tubes is trapped. If the elastic diaphragm does not fully ...


5

The volume change is negligible for most purposes. Ordinary liquids (water, organic solvents, hydrazine) are relatively incompressible in the sense that their change in density is negligible for easily accessible pressures. 22 bar is only 4 times what I pump my bike tires up to with a manual pump, so it's not that extreme. This 1977 US Air Force document ...


4

This is a minor elaboration on Organic Marble's and Ross Milikan's answers. The driving principle is the same superpack (I've not heard it called that before) concern as in Organic Marble's answer. There is a difference in that the freezing points of Hydrazine, Nitrogen Tetroxide and Mono Methyl Hydrazine are quite different (very roughly 2 deg C, ~-15 ...


4

This website suggests SDMH is incompatible with oxidizing agents, water. So it can be used for hypergolic purpose.This quote is from Sittig's Handbook of Toxic and Hazardous Chemicals and Carcinogens: Properties of SDMH Forms explosive mixture with air. A strong reducing agent and strong base. Violent reaction with strong oxidizers, strong acids, metallic ...


4

Several sources (close to the end) show a table with a rough breakdown of the fuel use. The total amount of fuel of 77 kg was used both for trajectory change and attitude control. The Δv = 242 m/s number does not include the fuel used for the latter. There are 29.3 kg of fuel reserved for attitude control, leaving 47.5 kg for propulsion. Making the same ...


3

According to this Spaceflight101.com article SLS Solid Rocket Booster to be fired up for Final Qualification Test , the HPUs are still hydrazine powered. The SRBs host their own hydraulic power units fueled by hydrazine that drives a turbine powering a hydraulic pump to provide working pressure to the two servoactuators that gimbal the nozzle by +/-8 ...


3

The success of SpaceX is based mostly on using the best of well-proofed technologies not on bold innovations. There are innovations in production process and in business model but very few in rocket design. High energetic monoprppellants are very dangerous. Hydroxylammonium nitrate (AF-M315E) is rated as an Explosive. It is probably unacceptable for human ...


1

For the abort tests in early 2020, according to documents filed with the FAA over a year prior, the Dragon flew with 2565 kg of propellant (1590 kg of NTO and 975 kg of MMH), but only about half of that was fired during the abort. Consumption rate for a single SuperDraco is about 31 kg/s (= 71kN thrust / 2300 m/s exhaust velocity), so for the suite of 8 ...


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