Quote from: intrepidpursuit on 11/03/2017 02:32 pmQuote from: old_sellsword on 11/03/2017 12:04 pmQuote from: georgegassaway on 11/03/2017 03:57 amSo for one, they need some rear attachment system on the Octawebs that will either allow the outer boosters to pivot outwards, or for the rear attachments to actively push the rear of the boosters outwards during separation (but at less of an acceleration rate than the noses are pushed outwards, to produce an outwards yaw rotation rate). While the forward attachments will actively push the noses outwards pneumatically. Both the nosecones and the octawebs have pneumatic pusher mechanisms, and the octawebs also have a beefy connection point at the hold-down lugs. Whether or not that pivots before full separation is to be seen though.I am curious if the center engine(s) on the boosters will ever actually shut down. On RTLS missions we see the booster light back up seconds after separation and use the main engine TVC to aid in a speedy flip into the boost back burn. I can see using the center engine to help guide the boosters away from the center stage. After all, they have the most control authority over the stage while the engines are on.Seems likely to me. I am trying to imagine the center core continuing to thrust during booster separation, you will not want it to have to pull along the side boosters when they shut down. I would think that by providing just enough thrust on the side booster to zero out the forces on the attach points before separation would be the way to go.
Quote from: old_sellsword on 11/03/2017 12:04 pmQuote from: georgegassaway on 11/03/2017 03:57 amSo for one, they need some rear attachment system on the Octawebs that will either allow the outer boosters to pivot outwards, or for the rear attachments to actively push the rear of the boosters outwards during separation (but at less of an acceleration rate than the noses are pushed outwards, to produce an outwards yaw rotation rate). While the forward attachments will actively push the noses outwards pneumatically. Both the nosecones and the octawebs have pneumatic pusher mechanisms, and the octawebs also have a beefy connection point at the hold-down lugs. Whether or not that pivots before full separation is to be seen though.I am curious if the center engine(s) on the boosters will ever actually shut down. On RTLS missions we see the booster light back up seconds after separation and use the main engine TVC to aid in a speedy flip into the boost back burn. I can see using the center engine to help guide the boosters away from the center stage. After all, they have the most control authority over the stage while the engines are on.
Quote from: georgegassaway on 11/03/2017 03:57 amSo for one, they need some rear attachment system on the Octawebs that will either allow the outer boosters to pivot outwards, or for the rear attachments to actively push the rear of the boosters outwards during separation (but at less of an acceleration rate than the noses are pushed outwards, to produce an outwards yaw rotation rate). While the forward attachments will actively push the noses outwards pneumatically. Both the nosecones and the octawebs have pneumatic pusher mechanisms, and the octawebs also have a beefy connection point at the hold-down lugs. Whether or not that pivots before full separation is to be seen though.
So for one, they need some rear attachment system on the Octawebs that will either allow the outer boosters to pivot outwards, or for the rear attachments to actively push the rear of the boosters outwards during separation (but at less of an acceleration rate than the noses are pushed outwards, to produce an outwards yaw rotation rate). While the forward attachments will actively push the noses outwards pneumatically.
Quote from: Jcc on 11/05/2017 01:36 pmQuote from: intrepidpursuit on 11/03/2017 02:32 pmQuote from: old_sellsword on 11/03/2017 12:04 pmQuote from: georgegassaway on 11/03/2017 03:57 amSo for one, they need some rear attachment system on the Octawebs that will either allow the outer boosters to pivot outwards, or for the rear attachments to actively push the rear of the boosters outwards during separation (but at less of an acceleration rate than the noses are pushed outwards, to produce an outwards yaw rotation rate). While the forward attachments will actively push the noses outwards pneumatically. Both the nosecones and the octawebs have pneumatic pusher mechanisms, and the octawebs also have a beefy connection point at the hold-down lugs. Whether or not that pivots before full separation is to be seen though.I am curious if the center engine(s) on the boosters will ever actually shut down. On RTLS missions we see the booster light back up seconds after separation and use the main engine TVC to aid in a speedy flip into the boost back burn. I can see using the center engine to help guide the boosters away from the center stage. After all, they have the most control authority over the stage while the engines are on.Seems likely to me. I am trying to imagine the center core continuing to thrust during booster separation, you will not want it to have to pull along the side boosters when they shut down. I would think that by providing just enough thrust on the side booster to zero out the forces on the attach points before separation would be the way to go.Do you think Delta IV Heavy shuts down the core for booster separation? STS didn’t do it either. There’s no magic involved, just timing and establishing a good separation rate.
Quote from: Herb Schaltegger on 11/05/2017 11:05 pmQuote from: Jcc on 11/05/2017 01:36 pmQuote from: intrepidpursuit on 11/03/2017 02:32 pmQuote from: old_sellsword on 11/03/2017 12:04 pmQuote from: georgegassaway on 11/03/2017 03:57 amSo for one, they need some rear attachment system on the Octawebs that will either allow the outer boosters to pivot outwards, or for the rear attachments to actively push the rear of the boosters outwards during separation (but at less of an acceleration rate than the noses are pushed outwards, to produce an outwards yaw rotation rate). While the forward attachments will actively push the noses outwards pneumatically. Both the nosecones and the octawebs have pneumatic pusher mechanisms, and the octawebs also have a beefy connection point at the hold-down lugs. Whether or not that pivots before full separation is to be seen though.I am curious if the center engine(s) on the boosters will ever actually shut down. On RTLS missions we see the booster light back up seconds after separation and use the main engine TVC to aid in a speedy flip into the boost back burn. I can see using the center engine to help guide the boosters away from the center stage. After all, they have the most control authority over the stage while the engines are on.Seems likely to me. I am trying to imagine the center core continuing to thrust during booster separation, you will not want it to have to pull along the side boosters when they shut down. I would think that by providing just enough thrust on the side booster to zero out the forces on the attach points before separation would be the way to go.Do you think Delta IV Heavy shuts down the core for booster separation? STS didn’t do it either. There’s no magic involved, just timing and establishing a good separation rate.Good point, but I didn't say anything about the core shutting down. The question is, are the DIVH side boosters completely shut down at separation or is there some residual thrust, and likewise the Ariane, Shuttle, and others. If separation is timed just right, perhaps there is enough residual thrust as those boosters are in the process of shutting down, to not place a load on the attach points.
Good point, but I didn't say anything about the core shutting down. The question is, are the DIVH side boosters completely shut down at separation or is there some residual thrust, and likewise the Ariane, Shuttle, and others. If separation is timed just right, perhaps there is enough residual thrust as those boosters are in the process of shutting down, to not place a load on the attach points.
Quote from: Jcc on 11/06/2017 12:30 amGood point, but I didn't say anything about the core shutting down. The question is, are the DIVH side boosters completely shut down at separation or is there some residual thrust, and likewise the Ariane, Shuttle, and others. If separation is timed just right, perhaps there is enough residual thrust as those boosters are in the process of shutting down, to not place a load on the attach points.One thing I will point out as a reminder. The final Falcon 1 failure was due to 'residual thrust' causing a collision between the booster and the second stage. I would therefore think that 'institutional history' at SpaceX would call for a complete shutdown to avoid any potentially similar issues.
Just spin the rocket and let the boosters go. :-)
Quote from: Eerie on 07/11/2017 03:55 pmJust spin the rocket and let the boosters go. :-)https://xkcd.com/1244/
I don't recall off the top of my head if the boostback is single engine or three engine.
Visually at least, the shuttle's SRBSs seemed to be still thrusting a little at sep.Which when you think about it, and you think about the inherent uncertainties of controlling/predicting the thrust rate of a solid, just makes the fact that they made the shuttle work at all even more amazing.
And what kind of aeroloads will FH be seeing at side booster separation? Will the trajectory be lofted simply to get out of most of the sensible atmosphere before booster sep?
If you watch some F9 launches like NROL-76, the booster and the upper stage coast along for several seconds with the booster broadside to the direction of travel, apparently under control of the cold gas thrusters. FH boosters will be higher, and the atmosphere density and drag halves about every 3 km at those altitudes.
Quote from: envy887 on 11/07/2017 04:15 pmIf you watch some F9 launches like NROL-76, the booster and the upper stage coast along for several seconds with the booster broadside to the direction of travel, apparently under control of the cold gas thrusters. FH boosters will be higher, and the atmosphere density and drag halves about every 3 km at those altitudes. I may be confused but I believe that since the FH is a 2.5 stage rocket the boosters will stage lower, not higher than an F9 S1. The center core will stage higher though, I think...