Quote from: deruch on 11/08/2017 12:54 amQuote from: Mike_1179 on 11/07/2017 02:40 pm<snip>If you watch the re-entry burn from stage 1 landings, the stage accelerates right up until the burn starts. Then the burn slows the stage down AND gets it to a lower part of the atmosphere so that after the burn is complete, the stage is not accelerating anymore - the thickening atmosphere slows it down from there but not so much that heat loading on the bottom end is too much.<snip>In actuality, the stage accelerates again after the entry burn as well for about 10-12 seconds. But it doesn't gain all that much before the aerodynamic effects fully overcome gravity. On the order of +100 m/s. This is visible in the analyses of the webcast telemetry data, e.g.: http://forum.nasaspaceflight.com/index.php?topic=40328.msg1673183#msg1673183 Not all flights were like that, though. Check out the Echostar 105 / SES-11 webcast. It gained less than 10 km/h before starting to decelerate again.
Quote from: Mike_1179 on 11/07/2017 02:40 pm<snip>If you watch the re-entry burn from stage 1 landings, the stage accelerates right up until the burn starts. Then the burn slows the stage down AND gets it to a lower part of the atmosphere so that after the burn is complete, the stage is not accelerating anymore - the thickening atmosphere slows it down from there but not so much that heat loading on the bottom end is too much.<snip>In actuality, the stage accelerates again after the entry burn as well for about 10-12 seconds. But it doesn't gain all that much before the aerodynamic effects fully overcome gravity. On the order of +100 m/s. This is visible in the analyses of the webcast telemetry data, e.g.: http://forum.nasaspaceflight.com/index.php?topic=40328.msg1673183#msg1673183
<snip>If you watch the re-entry burn from stage 1 landings, the stage accelerates right up until the burn starts. Then the burn slows the stage down AND gets it to a lower part of the atmosphere so that after the burn is complete, the stage is not accelerating anymore - the thickening atmosphere slows it down from there but not so much that heat loading on the bottom end is too much.<snip>
What if you had a FH secondary payload that was essentially an Falcon family interstage adaptor with a Dragon heat shield attached? (underneath the fairing this payload would launch heat shield facing up).The second stage would:1) arrive in orbit.2) deploy primary payload3) perform deorbit burn4) deploy interstage adaptor with heat shield5) stage flips 180 degrees and docks with interstage/heat shield (this would cover the MVac for reentry).6) Entry interface through transonic, performs guidance with CGS - hopefully enough control authority since stage is smaller.7) Ejects heat shield after Max-Q (maybe use parachutes to recover interstage/heat shield).8/ Uses MVac for landing burn.
Quote from: mikelepage on 11/08/2017 02:07 pmWhat if you had a FH secondary payload that was essentially an Falcon family interstage adaptor with a Dragon heat shield attached? (underneath the fairing this payload would launch heat shield facing up).The second stage would:1) arrive in orbit.2) deploy primary payload3) perform deorbit burn4) deploy interstage adaptor with heat shield5) stage flips 180 degrees and docks with interstage/heat shield (this would cover the MVac for reentry).6) Entry interface through transonic, performs guidance with CGS - hopefully enough control authority since stage is smaller.7) Ejects heat shield after Max-Q (maybe use parachutes to recover interstage/heat shield).8/ Uses MVac for landing burn.I think you're missing a 2nd 180deg flip in that sequence if you want the MVac pointing in the direction of travel after it's locked onto its protective heat shield.
FWIW, there is a interesting article in the just out Physics Today called "The relentless pursuit of hypersonic flight", by Ivett A. Leyva. I'm looking at it in front of me right now.Recommended reading for those interested in understanding the challenges faced in handling a US about 5 minutes past EI, approaching max Q.
Quote from: mikelepage on 11/08/2017 02:07 pmWhat if you had a FH secondary payload that was essentially an Falcon family interstage adaptor with a Dragon heat shield attached? (underneath the fairing this payload would launch heat shield facing up).The second stage would:1) arrive in orbit.2) deploy primary payload3) perform deorbit burn4) deploy interstage adaptor with heat shield5) stage flips 180 degrees and docks with interstage/heat shield (this would cover the MVac for reentry).6) Entry interface through transonic, performs guidance with CGS - hopefully enough control authority since stage is smaller.7) Ejects heat shield after Max-Q (maybe use parachutes to recover interstage/heat shield).8/ Uses MVac for landing burn.Are you serious?
I think he's also missing the need to develop autonomous docking between two spacecraft, implying independent three axis control of each element with RCS and GNC, and a suitable docking interface. All for a tech demo on a vehicle that is supposed to be retired within five years when BFR comes along.
Is your biggest objection the attempt to try and dock with your heat shield *after* you've performed the deorbit burn, or something else?
Quote from: Kaputnik on 11/08/2017 09:38 pmI think he's also missing the need to develop autonomous docking between two spacecraft, implying independent three axis control of each element with RCS and GNC, and a suitable docking interface. All for a tech demo on a vehicle that is supposed to be retired within five years when BFR comes along.I was going to leave the problem of precisely docking with one "dumb" (heat shield) element as accepted risk - isn't it a similar (or easier) control problem to a BFR booster precisely putting itself back in a "dumb" launch cradle? My follow up question was if the process of stage separation leaves the second stage "docking interface" in a permanently changed state? As in, if the second stage could place itself accurately enough inside the heat shield/interstage, would there be something for the interstage to latch onto?
Quote from: mikelepage on 11/09/2017 02:00 amIs your biggest objection the attempt to try and dock with your heat shield *after* you've performed the deorbit burn, or something else?The problem with this sequence is: * it requires a ton of special development of hardware * the interstage is not made for docking, it's clearance with MVac is way too small * the heat shield is an expensive piece of hardware to throw away, not well suited for a first flight of a rocket * the docking has to happen in less than a quarter orbit, say 15 minutes which is way too short to do it right * second stage and heat shield need independent guidance and flight control, which is expensive and takes a ton of work hours to develop, thrusters, nitrogen tanks, etc.The problem I have with ideas like this is that it takes very little thinking to see why it wouldn't work. The fact that you still put it here means you didn't do the thinking. What you essentialy do is you outsource the thinking part to other people because you can't be bothered with it. I am sure this is not a popular view on a party, but is this a party?
I'm still holding firm on my prediction of: mass simulator built by interns that apes a typical jumbo comsat targeted for FH (but nothing outlandishly heavy). With some unknown bonus surprise addition that amuses Elon.
I mused that the payload inside the PLF might be extra tanks for 2nd stage to allow for a de-orbit, entry, and landing burn (in the sea)?It would give FH demo something to lift. It wouldn't violate the fairing qualification(?) and it might validate some hypothetical questions - like: given enough fuel, how well/badly would the 2nd stage perform on re-entry.However then I thought that too many mods would be required to the 2nd stage pluming and the payload adapter. Would I be right?
Quote from: Nate_Trost on 11/09/2017 03:51 pmI'm still holding firm on my prediction of: mass simulator built by interns that apes a typical jumbo comsat targeted for FH (but nothing outlandishly heavy). With some unknown bonus surprise addition that amuses Elon.I like that suggestion. But a Dummy Mass simulator floating around GTO might not be good. Maybe a Mass Simulator that can maneuver and possibly deorbit itself [passive or active] or serve as DARPA satellite servicing / refueling target
Quote from: Wolfram66 on 11/09/2017 04:59 pmQuote from: Nate_Trost on 11/09/2017 03:51 pmI'm still holding firm on my prediction of: mass simulator built by interns that apes a typical jumbo comsat targeted for FH (but nothing outlandishly heavy). With some unknown bonus surprise addition that amuses Elon.I like that suggestion. But a Dummy Mass simulator floating around GTO might not be good. Maybe a Mass Simulator that can maneuver and possibly deorbit itself [passive or active] or serve as DARPA satellite servicing / refueling targetGiven aforementioned difficulties docking with a dumb (or dummy) payload, will it be a sufficient demonstration of FH for the second stage to put itself, plus a dummy mass simulator into GTO, and simply do everything but deploy the payload? Later on, the second stage would deorbit both itself and the (still attached) payload.