Another thought: the S2 is coming in from orbit, so there's no penalty for RTLS. If fitting landing legs behind the plasma shield is a problem, the S2 could simply come in and land upside-down on SuperDracos in a fixed cradle with a blast trench underneath. It would reduce plume impingement/wash dramatically and really simplify the recovery hardware needed for the S2.Quote from: Digitalchromakey on 04/20/2017 05:17 pmHave been thinking about an approach similar to this, however perhaps everything necessary for a S2 landing could be contained within one self contained 'standalone' module (minus the PICA heat shield) fixed between a standard S2 and the payload adaptor, also with grid fins fitted to this same module, first using the Merlin 1D/grid fins for a stable re-entry similar to S1, then only once the stage has significantly slowed (perhaps after another short Merlin 1D burn) inverting the S2 for a RTLS Super Draco powered landing.Heat shield is a non-negotiable. Hypersonic retroprop won't work at orbital speeds.
Have been thinking about an approach similar to this, however perhaps everything necessary for a S2 landing could be contained within one self contained 'standalone' module (minus the PICA heat shield) fixed between a standard S2 and the payload adaptor, also with grid fins fitted to this same module, first using the Merlin 1D/grid fins for a stable re-entry similar to S1, then only once the stage has significantly slowed (perhaps after another short Merlin 1D burn) inverting the S2 for a RTLS Super Draco powered landing.
Quote from: envy887 on 04/20/2017 03:59 pmLegs can go straight through the heatshield, see Dragon 2. So can the landing thrusters, they just need to blow off a tile when they start up. Shouldn't need to add more than 1/2 a stage diameter to the height of the stage to fit everything in.The existing S2 is more than three times the height of the Dragon 2, so those stubby little legs wouldn't provide nearly enough stability to avoid tip-over. And blowing a hole in the heat shield doesn't fit with reuse plans.
Legs can go straight through the heatshield, see Dragon 2. So can the landing thrusters, they just need to blow off a tile when they start up. Shouldn't need to add more than 1/2 a stage diameter to the height of the stage to fit everything in.
Quote from: sevenperforce on 04/20/2017 04:40 pm... Block 5, supposedly capable of getting an L/D ratio of 1:1 on the first stage ...Here's Musks's comment:Quotethe new grid fins should be capable of taking a scorching and being fine. And they'll also have significantly more control authority, so, that should improve reusability of the rocket. It will improve the payload to orbit by being able to fly at a higher angle of attack and use the aerodynamic element of the rocket to effectively glide like a big cylinder. It does have an L/D of roughly 1 if flown at the right angle of attack, but you need control authority, particularly pitch control authority, that's higher than we currently have to achieve that. It's hard to tease this apart, but I think he's talking about increasing payload to orbit by by 'flying' the first stage which has a L/D of 1 at certain (high) speeds. Not clear if the gain comes from going uphill (engine gimbaling), or RTLS landing (less prop needed for boostback because cross range 'flying' with grid fins is increased). TL;DR I don't think this helps S2 landing scenarios.
... Block 5, supposedly capable of getting an L/D ratio of 1:1 on the first stage ...
the new grid fins should be capable of taking a scorching and being fine. And they'll also have significantly more control authority, so, that should improve reusability of the rocket. It will improve the payload to orbit by being able to fly at a higher angle of attack and use the aerodynamic element of the rocket to effectively glide like a big cylinder. It does have an L/D of roughly 1 if flown at the right angle of attack, but you need control authority, particularly pitch control authority, that's higher than we currently have to achieve that.
The legs can extend through the heat shield a bit sideways to make the footprint wider. If the CG is far enough forward for a forward entry, it's far enough forward for a stable nose-down landing. Especially with 6 legs.
Quote from: envy887 on 04/20/2017 07:12 pmThe legs can extend through the heat shield a bit sideways to make the footprint wider. If the CG is far enough forward for a forward entry, it's far enough forward for a stable nose-down landing. Especially with 6 legs.I'll believe it when I see it. The CG isn't great, not with that heavy Merlin up top. Note the feathered flaps for maintaining COP.
It's hard to tease this apart, but I think he's talking about increasing payload to orbit by by 'flying' the first stage which has a L/D of 1 at certain (high) speeds. Not clear if the gain comes from going uphill (engine gimbaling), or RTLS landing (less prop needed for boostback because cross range 'flying' with grid fins is increased). TL;DR I don't think this helps S2 landing scenarios.
Wait a minute. If it can RTLS without penalty, and if it can fly itself to a pinpoint landing site via grid fins...why not just drop into a net, suspended above the ground? Nets are cheap. Terminal velocity can't be THAT high.
Quote from: Kaputnik on 04/20/2017 05:34 pmQuote from: sevenperforce on 04/20/2017 04:40 pmEDIT: back of the envelope...terminal velocity for S1 is slightly subsonic...S2 masses less than 25% of S1...estimating similar drag...grid fin L/D for S2 would be 4:1...Erm, that's not how it works. You're working off mass and drag. But you need lift and drag.An object with a L/D of 4:1 is essentially a crude glider. Think Shuttle orbiter, or jump chute. It doesn't matter how many grid fins you stick on the back of a rocket, it's not going to turn into a glider.Autorotation works a little differently. I don't know whether the AOA of the grid fins can be adjusted in real-time as readily as the collective and pitch on a chopper, but it's worth investigation.
Quote from: sevenperforce on 04/20/2017 04:40 pmEDIT: back of the envelope...terminal velocity for S1 is slightly subsonic...S2 masses less than 25% of S1...estimating similar drag...grid fin L/D for S2 would be 4:1...Erm, that's not how it works. You're working off mass and drag. But you need lift and drag.An object with a L/D of 4:1 is essentially a crude glider. Think Shuttle orbiter, or jump chute. It doesn't matter how many grid fins you stick on the back of a rocket, it's not going to turn into a glider.
EDIT: back of the envelope...terminal velocity for S1 is slightly subsonic...S2 masses less than 25% of S1...estimating similar drag...grid fin L/D for S2 would be 4:1...
I'll believe it when I see it. The CG isn't great, not with that heavy Merlin up top. Note the feathered flaps for maintaining COP.
You can't use spin stabilization with a empty stage top first, because the CG/CP are too separated and like a top heavy top, it'll tumble on its side.
Can you make the bell of the engine the landing gear and part of the rocket body? Say, S2 has a gimballed engine with a standard bell 'inside' the rocket body material at the level of the engine is shaped like a bell and also attaches to S1 and is reinforced in 3 areas to act as stiffened landing gear with crush zone adapters.So two different sized, nested dixie cups at the bottom of S2 (the bigger dixie cup being the diameter of the rocket), both essentially rocket bells. One outer bell for orbital operations, its stiffened outer area used for landing legs. The inner bell for landings. The need for a heat shield is largely obviated by use of the rocket plume during reentry. Small grid fins and perhaps gas jets could be added, leveraging existing systems in S1 that are already well understood. You would not need any changes to the upper parts of S2, the fairings could be jettisoned and recovered as they are now. Would this be light enough to have enough fuel left over for landing like an F9 does now?
Anyone thought of airbrakes? Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down. The brakes deploy from the end (opposite end of the nose that has the heat shielding). Legs deploy from the nose to land. You can put the retropropulsive units in the base with the aerobrakes. The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net. What kind of lego model can I make to convince everyone it will work?
Quote from: BobHk on 05/08/2017 11:09 pmAnyone thought of airbrakes? Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down. The brakes deploy from the end (opposite end of the nose that has the heat shielding). Legs deploy from the nose to land. You can put the retropropulsive units in the base with the aerobrakes. The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net. What kind of lego model can I make to convince everyone it will work?Developing a non-detaching fairing doesn't make sense given that they are also developing reuse for detaching fairings.
Quote from: Ictogan on 05/09/2017 10:52 amQuote from: BobHk on 05/08/2017 11:09 pmAnyone thought of airbrakes? Large deployable carbon fiber airbrakes that pop out after atmospheric re entry nose down. The brakes deploy from the end (opposite end of the nose that has the heat shielding). Legs deploy from the nose to land. You can put the retropropulsive units in the base with the aerobrakes. The fairing can be attached and deployable then retract after sat deployment (making up the 'nose' of the S2).A heatshielded clamshell fairing nose that doesnt detach and Aerobrakes + retro propulsion just seem to be more viable than a parachute or a net. What kind of lego model can I make to convince everyone it will work?Developing a non-detaching fairing doesn't make sense given that they are also developing reuse for detaching fairings.GTO/LEO?