3 ms·
That isn't the reason. The reason is that this is a completely different use case. The second stage of a F9 is not meant to survive re-entry, so there is no n
by NikolaeVarius 7y ago
That isn't the reason.
The reason is that this is a completely different use case.
The second stage of a F9 is not meant to survive re-entry, so there is no need to do anything interesting in terms of heat shielding. Starhopper is meant to survive re-entry, so the calculation had to be made to have it survive the heat.
It was deemed "better" to rely on steel rather than an ablative heatshield and aluminum because inspection requirements are pretty high.
As for the 1st stage also being steel instead of aluminum like the F9. The 1st stage booster will be much larger than the F9 and so the strength of steel is an advantage since it avoids the issue of the structure not being able to stay upright unpressurized.
- elteto 7y agoI never claimed it was the _only_ reason, but it is certainly one of them. Even if you wanted to make F9 out of steel (for whatever reason) you still couldn't do it with Merlins in an economically feasible way. This is a simple fraction: thrust-to-weight ratio = thrust / weight. If you increase the denominator but keep your thrust the same then you lose payload capacity.
- NikolaeVarius 7y agoThis is incorrect. A T/W ratio by itself is meaningless since it ignores mass. The propellant mass fraction is what actually matters which takes into account the mass of the vehicle. The fact that the Raptor is more powerful than the Merlin is barely a consideration in the "Build the Starship out of steel discussion". They would have loved to not have to bite into their mass budget, but other engineering concerns triumphed.