SpaceX F9 - 5th Reuse - Iridium Next 31-40 - SLC-4E
Next post gives a hint why fairing has thrusters. Fairing recovery has been discussed in many posts. I believe somebody has links for you.
"The Falcon 9’s aerodynamic nose cone split open and fell away in two pieces shortly after the mission’s three-minute point, and control thrusters on the fairing were also visible pulsing to position the pieces for re-entry. SpaceX is experimenting with recovering the Falcon 9’s fairing off shore for reuse, as the company does with its Falcon 9 first stages."
Falcon 9 launch lights up Southern California sky – Spaceflight Now
"SpaceX was expected to try and retrieve part of the Falcon 9’s payload shroud downrange from Vandenberg after Friday’s launch. A fast boat linked to experimental fairing recovery attempts, named Mr. Steven, was relocated from Florida to California in recent weeks, and it sailed south from the Port of Los Angeles on a heading toward the Falcon 9’s projected flight path."
SpaceX launch dazzles, delivering 10 more satellites for Iridium – Spaceflight Now
ecarfan
Well-Known Member
What is your source for your apparently highly confident assertion that the fairing halves do not have thrusters?
ecarfan
Well-Known Member
Cold gas thrusters are only possibility. Since fairings are relatively light, small thrusters will be enough and re-entry heat load/area is small. Fairings must be aerodynamically stable. Thrusters are needed to set initial attitude.
ggr
Expert in Dunning-Kruger Effect!
Doug_G
Lead Moderator
Gyros are complex, and have limited ability to torque (due to their limited weight) and limits to the control authority (i.e. when the saturate at maximum speed). That's why satellites have both gyros and thrusters. The gyros are used for continuous stabilization, and the thrusters are used to unload the gyros.
Nitrogen thrusters would seem to be the appropriate technology for this purpose.
It’s a bit pedantic, but in context of space stuff, gyros are rate sensing devices and momentum or reaction wheels are the attitude control devices.
Also, rockets have gyros.
Fairings typically go through an oscillation stage immediately after separation and then a relatively low rate tumble ‘away’ from the rocket. That’s due largely to the fact that there’s intentional stresses in the encapsulated configuration (plus springs) that push the halves away from the payload/rocket—the det cord and pyro devices that actually break the halves apart can’t safely separate them on their own. The post separation motion is a very understood and modelable phenomenon, and so it’s probably pretty easy to derive the minimum amount of thrust/vectors required for a system like cold gas to stabilize the fairing halves. They’re so big and so light that it seems quite feasible for thrusters mounted on the top or bottom to right the ship pretty easily.
Lastly, I don’t think one can draw the conclusion that the fairings aren’t tumbling based on the home videos that show an apparent constant brightness. Even black MLI can sometimes be pretty shiney.
ecarfan
Well-Known Member
Good point, that likely explains what the videos appear to show. Thank you.
ggr
Expert in Dunning-Kruger Effect!
Yes, thanks for correcting my terminology.
I think from my tour that I remember the guide saying that SpaceX doesn't use pyro devices at all, for anything. I'm pretty sure the fairings are separated with springs.
ecarfan
Well-Known Member
My understanding is that it is a pneumatic process for stage separation and fairing separation.
Unverified opinion:
Nitrogen based pneumatics to retract the connecting pins with preloaded springs or pneumatic pushers for seperation.
I type slower than @ecarfan....
No. Really broad brushing this one, typically release mechanisms come in a few flavors—pulling/pushing pins, cut rods, or detonation cord. The devices that initiate those mechanisms are typically pyro charges, heaters, servos, and pneumatics.
For an example of a non-pyro rod cutter, check out Frangibolt - TiNi Aerospace, Inc.. It’s basically a cylinder that heats up, expands, and stretches a rod that runs through the middle of the cylinder until the rod breaks. They have a bunch of other products for other release gizmos to if you want to get an idea what these things actually look like.
Back to springs, they’re typically basic coils and are preloaded during installation so when the mechanism releases The Newtons happen. In the case of fairings they’re typically also preloaded with some internal ‘spring force’—I haven’t actually seen a falcon fairing being mated though so I don’t really know the configuration.
