Great photo of the wind tunnel model and with a wider fairing although probably already discussed. Which forum was this originally posted in?Thanks
Why are people coming up with all these Heath Robinson separation schemes when the booster CBCs on Delta IV have a perfectly sensible system? Boosters burn out, Booster Separation Rocket Motors (BSRM), located near the nose, fire, boosters tumble away from core. What do they Falcon Heavy boosters have conveniently located near the nose? Ah some, N2 thrusters which we know can flip a stage around in no time.....
Quote from: jak Kennedy on 07/04/2017 03:10 pmGreat photo of the wind tunnel model and with a wider fairing although probably already discussed. Which forum was this originally posted in?ThanksThe two pictures ([1], [2]) were originally posted by the official SpaceX Facebook page. It was linked on r/SpaceX, but then the original post on their Facebook page was removed.I wouldn't be surprised if NSF picked up on it before it was deleted either.
Great photo of the wind tunnel model and with a wider fairing although probably already discussed.
Quote from: Welsh Dragon on 07/04/2017 01:13 pmWhy are people coming up with all these Heath Robinson separation schemes when the booster CBCs on Delta IV have a perfectly sensible system? Boosters burn out, Booster Separation Rocket Motors (BSRM), located near the nose, fire, boosters tumble away from core. What do they Falcon Heavy boosters have conveniently located near the nose? Ah some, N2 thrusters which we know can flip a stage around in no time.....not the same thrust levels
Quote from: Jim on 07/04/2017 03:49 pmQuote from: Welsh Dragon on 07/04/2017 01:13 pmWhy are people coming up with all these Heath Robinson separation schemes when the booster CBCs on Delta IV have a perfectly sensible system? Boosters burn out, Booster Separation Rocket Motors (BSRM), located near the nose, fire, boosters tumble away from core. What do they Falcon Heavy boosters have conveniently located near the nose? Ah some, N2 thrusters which we know can flip a stage around in no time.....not the same thrust levelsPneumatic pushers can generate a large thrust over a short time, plus GN2 thrusters with a smaller thrust over a longer time. Used in concert, they should be sufficient.
Quote from: envy887 on 07/04/2017 10:25 pmQuote from: Jim on 07/04/2017 03:49 pmQuote from: Welsh Dragon on 07/04/2017 01:13 pmWhy are people coming up with all these Heath Robinson separation schemes when the booster CBCs on Delta IV have a perfectly sensible system? Boosters burn out, Booster Separation Rocket Motors (BSRM), located near the nose, fire, boosters tumble away from core. What do they Falcon Heavy boosters have conveniently located near the nose? Ah some, N2 thrusters which we know can flip a stage around in no time.....not the same thrust levelsPneumatic pushers can generate a large thrust over a short time, plus GN2 thrusters with a smaller thrust over a longer time. Used in concert, they should be sufficient.Thousands of pounds?
Quote from: GWH on 07/04/2017 02:01 pmQuote from: old_sellsword on 07/04/2017 01:52 pmQuote from: GWH on 07/04/2017 01:17 pmBecause there aren't any N2 thrusters at the base of the rocket, so the booster wouldn't be capable of lateral movement only rotational. Rotating both boosters about their center of gravity only would cause the tails to colide in the absence of any lateral movement. ...This is why they have two pusher mechanisms for each side booster octaweb. They detach and pivot the forward ends away using the N2 ACS, then they detach and push away the octawebs with the two outside octaweb connections (see Lars-J's helpful drawing).Yeah those two struts at the bottom of the wind tunnel model could definitely have a pusher component to them, Would simplify the whole arrangement a lot. Do you know this for fact or are you speculating?I know it for a fact.
Quote from: old_sellsword on 07/04/2017 01:52 pmQuote from: GWH on 07/04/2017 01:17 pmBecause there aren't any N2 thrusters at the base of the rocket, so the booster wouldn't be capable of lateral movement only rotational. Rotating both boosters about their center of gravity only would cause the tails to colide in the absence of any lateral movement. ...This is why they have two pusher mechanisms for each side booster octaweb. They detach and pivot the forward ends away using the N2 ACS, then they detach and push away the octawebs with the two outside octaweb connections (see Lars-J's helpful drawing).Yeah those two struts at the bottom of the wind tunnel model could definitely have a pusher component to them, Would simplify the whole arrangement a lot. Do you know this for fact or are you speculating?
Quote from: GWH on 07/04/2017 01:17 pmBecause there aren't any N2 thrusters at the base of the rocket, so the booster wouldn't be capable of lateral movement only rotational. Rotating both boosters about their center of gravity only would cause the tails to colide in the absence of any lateral movement. ...This is why they have two pusher mechanisms for each side booster octaweb. They detach and pivot the forward ends away using the N2 ACS, then they detach and push away the octawebs with the two outside octaweb connections (see Lars-J's helpful drawing).
Because there aren't any N2 thrusters at the base of the rocket, so the booster wouldn't be capable of lateral movement only rotational. Rotating both boosters about their center of gravity only would cause the tails to colide in the absence of any lateral movement. ...
Works fine for second stage separation.
Quote from: guckyfan on 07/05/2017 05:23 pmMy understanding is that it is derived from the concerns about grid fins not being effective due to the aerodynamic cone on top of the side boosters.My non expert opinion is that the grid fins are not involved in separation so this discussion is off on the wrong track.Edit: There may be a cause for concern that the side boosters may not make it back to LZ-1 due to the grid fin issue. Not a huge loss.Grid fins will not be used in the separation, and they will not be opened until after boost-back.And what grid fin issue on FH boosters would prevent them from making it back?
My understanding is that it is derived from the concerns about grid fins not being effective due to the aerodynamic cone on top of the side boosters.My non expert opinion is that the grid fins are not involved in separation so this discussion is off on the wrong track.Edit: There may be a cause for concern that the side boosters may not make it back to LZ-1 due to the grid fin issue. Not a huge loss.
Quote from: Jim on 07/04/2017 10:32 pmThousands of pounds?Well, we can guess the thrust of the nitrogen thrusters. From the NROL-76 mission, we see they fire for about 3 seconds to start the first stage rotating. The rotation reaches 90 degrees, more or less, in 7 seconds. So one revolution every 28 seconds, or 0.224 radians/sec. To acquire this rate in 3 seconds means an angular acceleration of 0.075 radians/sec^2Let's make the crude assumption that the booster rotates around the engines, since that's where most of the mass is located (engines + remaining fuel). We know the empty stages masses about 27t. 9 engines mass about 7t, so let's assume the rest is a 20t cylinder, and that the moment of inertia of the cylinder dominates (the rest of the mass, engines and fuel, is close to the axis of rotation). Rotating a cylinder around its end has a moment of inertial of mL^2/3. Using a length of 47 meters and a mass of 20t, this gives a moment of inertia of 14,800,00 kg x m^2.The torque to accelerate this at 0.075 radians/sec^2 is about 1.1M N x m. Assuming a lever arm of 47m, that's a thrust of 23400 N, or 2400 kg-force, or 5250 lb-force. At a typical ISP of 73 for cold gas nitrogen thrusters, that's a flow of 32 kg/second.So the cold gas thrusters can generate thousands of pounds of force. On the other hand, separation rocket motors can generate even more force. The shuttle boosters had 8 motors per booster, each generating 20,000 lb-f for 1.2 seconds. Each motor massed 80 kg.
Thousands of pounds?
Quote from: LouScheffer on 07/05/2017 07:18 pmQuote from: Jim on 07/04/2017 10:32 pmThousands of pounds?Well, we can guess the thrust of the nitrogen thrusters. From the NROL-76 mission, we see they fire for about 3 seconds to start the first stage rotating. The rotation reaches 90 degrees, more or less, in 7 seconds. So one revolution every 28 seconds, or 0.224 radians/sec. To acquire this rate in 3 seconds means an angular acceleration of 0.075 radians/sec^2Let's make the crude assumption that the booster rotates around the engines, since that's where most of the mass is located (engines + remaining fuel). We know the empty stages masses about 27t. 9 engines mass about 7t, so let's assume the rest is a 20t cylinder, and that the moment of inertia of the cylinder dominates (the rest of the mass, engines and fuel, is close to the axis of rotation). Rotating a cylinder around its end has a moment of inertial of mL^2/3. Using a length of 47 meters and a mass of 20t, this gives a moment of inertia of 14,800,00 kg x m^2.The torque to accelerate this at 0.075 radians/sec^2 is about 1.1M N x m. Assuming a lever arm of 47m, that's a thrust of 23400 N, or 2400 kg-force, or 5250 lb-force. At a typical ISP of 73 for cold gas nitrogen thrusters, that's a flow of 32 kg/second.So the cold gas thrusters can generate thousands of pounds of force. On the other hand, separation rocket motors can generate even more force. The shuttle boosters had 8 motors per booster, each generating 20,000 lb-f for 1.2 seconds. Each motor massed 80 kg.Thank you Lou, I really like the use of Math and Physics instead of hand waving and authority. More of that please!