Quote from: john smith 19 on 04/04/2017 08:49 pmThe problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble."Drag" something behind it.
The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.
Quote from: hrissan on 04/03/2017 10:04 pmMy bet is what user NovaSilisko suggested year ago.https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme. The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.
My bet is what user NovaSilisko suggested year ago.https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.
Quote from: john smith 19 on 04/04/2017 08:49 pmQuote from: hrissan on 04/03/2017 10:04 pmMy bet is what user NovaSilisko suggested year ago.https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme. The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.
Quote from: GWH on 04/04/2017 09:23 pmQuote from: john smith 19 on 04/04/2017 08:49 pmThe problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble."Drag" something behind it.Like a really big nozzle extension?
Quote from: envy887 on 04/04/2017 10:02 pmQuote from: john smith 19 on 04/04/2017 08:49 pmQuote from: hrissan on 04/03/2017 10:04 pmMy bet is what user NovaSilisko suggested year ago.https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme. The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.better to have a PICA-X nose on the S2 with a Ballute collar like the LDSD. that will work with initial atmospheric interface as well as post max-heating while falling tail first. shuttlecock would probably fold up like an umbrella in the wind. IMHO
Quote from: Wolfram66 on 04/04/2017 10:07 pmQuote from: envy887 on 04/04/2017 10:02 pmQuote from: john smith 19 on 04/04/2017 08:49 pmQuote from: hrissan on 04/03/2017 10:04 pmMy bet is what user NovaSilisko suggested year ago.https://forum.nasaspaceflight.com/index.php?topic=39314.msg1474695#msg1474695His post has a nice picture, in a nutshell - like a bottom half of Dragon2 attached to the top of S2 legs forward.P.S. If it adds 4000kg to the mass of S2, so be it. Good for experimenting when the payload to LEO allows it.Those people who've read "Frontiers of Space" by Bono & Gatland will recognize Bono's idea for an early PoC of Saturn 2nd stage reuse, including the nose landing scheme. The problem remains how to you ensure that a rear heavy cylinder stays nose down when every slightest disturbance wants to push it nose up, if not into an active end over end tumble.The stage probably isn't that rear-heavy. The Mvac is only ~500 kg without the nozzle (which likely adds a few hundred kg). A frontal heatshield probably weighs nearly that much, which would return the COM to near the COP.Add on a few deployable PICA-covered split flaps (like IXV, but launched inside the interstage) to move the COP further back and enter like a shuttlecock. Pop a guided chute and land in a bouncy castle like the fairings.better to have a PICA-X nose on the S2 with a Ballute collar like the LDSD. that will work with initial atmospheric interface as well as post max-heating while falling tail first. shuttlecock would probably fold up like an umbrella in the wind. IMHOThey would be controlled by actuators, just like the Shuttle's body flap...
That's what my petals do create drag...
Quote from: Rocket Science on 04/04/2017 09:52 pmThat's what my petals do create drag...That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.
Quote from: envy887 on 04/04/2017 10:29 pmQuote from: Rocket Science on 04/04/2017 09:52 pmThat's what my petals do create drag...That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.what happens when S2 flips to perform hypersonic retro-burn? are the pedals extended or retracted and what is the weight penalty for the pedal and actuator systems? just playing Satan's Barrister aka: Devil's Advocate
I've often wondered why SpaceX didn't go with a plug nozzle type engine for the second stage. It would do double duty as the heat shield. It was considered for the second stage of Saturn IB and Saturn V before they were cancelled. It was based on the J2 engine at that time. The Octoweb is almost like a plug nozzle using he engines as heat shield for the first stage. I know it might be more expensive to develop, but in the long run to get 2nd stage reusable, it may be the best overall to do. No need for heat resistant nose or sides, parachutes, etc. Just landing legs like the first stage.
Quote from: Wolfram66 on 04/04/2017 10:47 pmQuote from: envy887 on 04/04/2017 10:29 pmQuote from: Rocket Science on 04/04/2017 09:52 pmThat's what my petals do create drag...That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.what happens when S2 flips to perform hypersonic retro-burn? are the pedals extended or retracted and what is the weight penalty for the pedal and actuator systems? just playing Satan's Barrister aka: Devil's Advocate No flip or retroburn needed in the atmosphere; after the deorbit burn (in vacuum), the MVac does not relight. RCS reorients the stage for entry, and it maintains that orientation all the way to the ground. Landing either on dedicated thrusters or an airbag.
Quote from: envy887 on 04/04/2017 10:29 pmQuote from: Rocket Science on 04/04/2017 09:52 pmThat's what my petals do create drag...That's the idea, but those are probably 4x longer then they need to be. Don't want to cover up the MVac nozzle, it needs to radiate heat.A relatively small amount of "draggy" area will be more than enough to make it stable. The inflatable toroid is also a great concept.I made them long in order to protect the nozzle from entry heat, just like the Shuttle's body flap protected them. If you read my original post a couple of pages back I wrote in that they would move rearward, then expand in deployment in a controlled fashion, similar how an afterburner "turkey feathers" moves only outward more...#106 https://forum.nasaspaceflight.com/index.php?topic=42637.100
This is obviously not a finished design of the reusable second stage because there's no landing legs.