4 ms·

I note the 'fins' at the top of the outside rockets are black, whereas on the middle one are white. Is that purely cosmetic?

phpnode 9y ago
The grid fins on the outer cores are aluminium, the centre core is titanium. Newer Falcons will have titanium grid fins (the outer cores have already flown once before) Edit. Looking closer I'm wrong - the titanium grid fins are on the side boosters and the the centre core is aluminium
brixon 9y ago
Guessing, but it is likely for visibility.
adwn 9y ago
The grid fins on the side boosters are made from titanium (and are larger), while the center core's ones are made from aluminum with an ablative paint. The titanium grid fins have a better heat resistance.
- mhandley 9y ago
  The titanium grid fins are also larger, which gives them better control authority. The center booster (like regular Falcon 9s) carries the interstage. This is light weight, but has significant aerodynamic effect when re-entering engines first for landing, like the feathers on an arrow. The side boosters lack this - the nose coses are much smaller - so are less stable aerodynamically. The likely reason for using the titanium fins is to give better control. They don't need the extra heat resistance for the side boosters - the center booster will have a toastier reentry as it's going much faster when it shuts down.
jacquesm 9y ago
Ablative material to avoid frying the aluminum.
- JshWright 9y ago
  No, the ablative material is white (like on the center core). The darker fins are the fancy new titanium fins (note they're a little larger too). Not sure why they went with the new fins on the side cores and not the center core... The side cores are going to have a pretty tame reentry (gentler than a Falcon 9 to LEO), while the center core will be coming in very hot. Currently they only use the titanium fins on very hot GTO reentries.
  - jacquesm 9y ago
    Ah right, thank you.
  - emilecantin 9y ago
    On the SpaceX subreddit, I've seen a few mention that it's probably because of the different aerodynamics with a nose cone; they need more control authority in that case.

phpnode 9y ago

The grid fins on the outer cores are aluminium, the centre core is titanium. Newer Falcons will have titanium grid fins (the outer cores have already flown once before) Edit. Looking closer I'm wrong - the titanium grid fins are on the side boosters and the the centre core is aluminium

brixon 9y ago

Guessing, but it is likely for visibility.

adwn 9y ago

The grid fins on the side boosters are made from titanium (and are larger), while the center core's ones are made from aluminum with an ablative paint. The titanium grid fins have a better heat resistance.

mhandley 9y ago
The titanium grid fins are also larger, which gives them better control authority. The center booster (like regular Falcon 9s) carries the interstage. This is light weight, but has significant aerodynamic effect when re-entering engines first for landing, like the feathers on an arrow. The side boosters lack this - the nose coses are much smaller - so are less stable aerodynamically. The likely reason for using the titanium fins is to give better control. They don't need the extra heat resistance for the side boosters - the center booster will have a toastier reentry as it's going much faster when it shuts down.

jacquesm 9y ago

Ablative material to avoid frying the aluminum.

JshWright 9y ago
No, the ablative material is white (like on the center core). The darker fins are the fancy new titanium fins (note they're a little larger too). Not sure why they went with the new fins on the side cores and not the center core... The side cores are going to have a pretty tame reentry (gentler than a Falcon 9 to LEO), while the center core will be coming in very hot. Currently they only use the titanium fins on very hot GTO reentries.
- jacquesm 9y ago
  Ah right, thank you.
- emilecantin 9y ago
  On the SpaceX subreddit, I've seen a few mention that it's probably because of the different aerodynamics with a nose cone; they need more control authority in that case.