# Tag Info

0

If Hydrogen and helium are being used as reaction mass, they will be molecular, not atomic, at non-ionizing exhaust temperatures. The atomic mass of hydrogen is 1 but the molecular mass of H2 is 2. The atomic and molecular mass of He are both the same =4. At the same temperature, the H2 will have 1.4 times the velocity of the He. ISP will be 40% higher for ...

2

Checking Google scholar for Jonathan Lun at Hypernova I found the title Development of a vacuum arc thruster for nanosatellite propulsion and then I found Lun's thesis Development of a vacuum arc thruster for nanosatellite propulsion I'm not going to read the whole thing, I think another answer author can do that. Instead, here I'll address materials issues ...

0

SpaceX has already developed a CH4/O2 ICE: the Raptor. It was a very difficult job since stoichiometricaly efficient CH4/O2 combustion produces temperatures above the melting point of available materials. The solution was a very complex staged combustion design where mixture was initially very rich (or very lean) to keep combustion temperatures down. The ...

2

For an intuitive understanding of the answer, it helps to keep a few points in mind: Momentum is not kinetic energy. Momentum is conserved, while kinetic energy is not (it converts to other forms of energy). Two colliding lumps of clay will conserve momentum, but not kinetic energy. Momentum is proportional to velocity; kinetic energy is proportional to the ...

0

Mere Speculation: The kinetics of that fuel's combustion may be too slow for a rocket motor. Halogens are known for their use as flame retardants.

7

"Why do we use ______ rocket fuel?" is complicated. I recently read John Clark's Ignition!: An informal history of liquid rocket propellants, which I highly recommend. It's exactly what the title implies, and covers the history of fuel development, touching lightly on the pre-WW2 era, then hitting every major development through the sixties (i.e. ...

2

Adding to above answers, the escape velocity from the surface of Mars is less than half that from Earth, 5.0 instead of 11.2 km/s. So the high ISP of LH2/LOX is not as hardly needed. Or to put it the other way around, the low ISP of CH4 is less a waste of PV energy than it would be on Earth.

42

They chose $\rm CH_4 + O_2$ because that is a much, much better fuel. $\rm CH_3Cl$ does burn with $\rm O_2$, producing: $$\rm 2CH_3Cl + 3O_2 \to 2CO_2 + 2H_2O + 2HCl + {\sim}1528\text{ kJ/mol energy}$$ This from a total atomic mass of $2(50.5) + 3(32) = 197\text{ g/mol}$. Your fuel, combusted with oxygen, thus delivers some $7.8\text{ kJ/g}$. However, this ...

20

For some background see this answer to Could JWST stay at L2 "forever"? this answer to What happens to JWST after it runs out of propellant?. From the 2nd linked answer (slightly edited): According to... James Webb Space Telescope Initial Mid-Course Correction Monte Carlo Implementation using Task Parallelism and Station Keeping Monte Carlo ...

10

The telescope trajectory changes direction for halo orbit insertion. Image source: https://jwst-docs.stsci.edu/jwst-observatory-hardware/jwst-orbit Such a large change of direction would require a lot of delta-v. The budget is 150 m/s, 10 years of station-keeping would require 20 to 40 m/s, so 110 to 130 m/s would be available for orbit insertion. The paper ...

5

What is the condition of the nozzle after burnout? is it asymmetrically eroded? That points to nozzle failure. If it is spitting chunky sparks, then your fuel grain is fracturing and you are operating not a rocket motor but a malfunctioning bomb. It is absolutely vital that your fuel grain remain mechanically intact and adhered to the sidewalls of the motor ...

Top 50 recent answers are included