United Launch Alliance introduces Vulcan next generation launcher

Slightly off topic question - what is the advantage of using CH4 as a fuel vice say RP-1? I understand that hydrogen is particularly hard to contain and keep cool, and so there is advantages there, but what else? I assume cost is a little lower since some kind of purified natural gas could be used? Also if CH4 is desirable, what prevented its use up until very recently?
 
Josh_TN said:
Slightly off topic question - what is the advantage of using CH4 as a fuel vice say RP-1? I understand that hydrogen is particularly hard to contain and keep cool, and so there is advantages there, but what else? I assume cost is a little lower since some kind of purified natural gas could be used? Also if CH4 is desirable, what prevented its use up until very recently?
Click to expand...
Autogenous pressurization of propellant tank. Cleaner than Kerosene for reuse (less soot)
 
Byeman said:
Autogenous pressurization of propellant tank. Cleaner than Kerosene for reuse (less soot)
Click to expand...

Fair enough. What has prevented people from using liquid methane before? If it can be contained on an LNG carrier, I would have thought hydrogen not particular worth the effort, despite its superior performance. Is hydrogen that more energetic per volume/mass that it makes a huge difference in structural size/mass? And if so, what has changed? It seems like all the popular kids on the space playground are making the switch to methane based fuel now (Landspace, Vulcan, Starship)
 
Josh_TN said:
Fair enough. What has prevented people from using liquid methane before? If it can be contained on an LNG carrier, I would have thought hydrogen not particular worth the effort, despite its superior performance. Is hydrogen that more energetic per volume/mass that it makes a huge difference in structural size/mass? And if so, what has changed? It seems like all the popular kids on the space playground are making the switch to methane based fuel now (Landspace, Vulcan, Starship)
Click to expand...
Methane replaced kerosene and not hydrogen. Nothing prevented it. Kerosene requires helium for pressurization and is messy for reuse.
 
Byeman said:
Methane replaced kerosene and not hydrogen. Nothing prevented it. Kerosene requires helium for pressurization and is messy for reuse.
Click to expand...

Were there previous issues with achieving the property purity of methane? I cannot imagine liquifying it has been a problem for many decades.
 
Josh_TN said:
What prevented CH4 from replacing RP1 then?
Click to expand...
Requirements

RP-1 is really good as a first stage propellent, it's relatively easy to make, handle, store, and energy dense. It's not anywhere near as efficient as LH2, but it's really good for overcoming gravity and aerodynamic drag in the atmosphere. LH2 is a really good fuel once gravity is overcome and there's no atmosphere. That's why a lot of rockets were RP1 first stage and LH2 upper stage. The downside is LH2 is not an easy fuel to deal with.

CH4 has some of the benefits of both LH2 and RP-1, with fewer of the drawbacks being less cryogenic than LH2 and easier to handle. Also, it's pretty easy to get (and can even be "green"). The main two requirements that now make it preferred are reusability (already discussed) and it can be made on Mars. Take those away, and RP-1 would still be a good first stage propellent.

It's insightful to look at the EELV program to see the tradeoffs.

Atlas V RD-180 860,000 lbs. thrust (SL) 311 SL ISP 12,000 lb. engine weight 12.5 ft diameter
Delta IV RS-68 660,000 lbs. thrust (SL) 365 SL ISP 14,500 lb. engine weight 16 ft diameter
SpaceX Raptor 2 507,000 lbs. thrust (SL) 327 SL ISP 3,500 lb. engine weight

If I had the BE-4 info, I'd post it. The Delta had a more efficient engine but gave it all up with a bigger heavier structure (also wasn't very good on the amount of thrust, RS-68A, cough). The RD-180 put out a lot more thrust, through a lighter engine with a lighter first stage structure (the insulation didn't catch fire either ;)) . When I worked EELV no one wanted to launch on a Delta unless they had no choice.

Now, Vulcan, SS/SH aren't in the comparison since they have pretty different requirements. Atlas V/Delta IV both were built for the same set of requirements and make the trade space closer to an apples-to-apples comparison.
 

Similar threads

Back
Top Bottom