Quote from: punder on 02/18/2015 06:38 pmOkay, so forget that part. (And I do appreciate the smiley.) Use the ring trusses as the sole thrust structure and align/dock the stages some other way. Anything else in the "big concept" that's utterly nonsensical?Back to the boil off issue, if you are only looking for a single impulse from the two stages then, as long as you dock them and get that impulse in the first orbit you should not have lost too much. However, if one of the reasons you wanted all this extra capacity for a probe included a high energy orbit change later on then you still need to solve the boil off (and operation power issues since the main solar panels won't be deployed until after the last high energy burn). I am not seeing how this gets you a solution that is cheaper than 3'rd stage.
Okay, so forget that part. (And I do appreciate the smiley.) Use the ring trusses as the sole thrust structure and align/dock the stages some other way. Anything else in the "big concept" that's utterly nonsensical?
Maybe we should stop trying to pack all the energy for any given mission into a single launch. ...
Quote from: nadreck on 02/18/2015 07:07 pmQuote from: punder on 02/18/2015 06:38 pmOkay, so forget that part. (And I do appreciate the smiley.) Use the ring trusses as the sole thrust structure and align/dock the stages some other way. Anything else in the "big concept" that's utterly nonsensical?Back to the boil off issue, if you are only looking for a single impulse from the two stages then, as long as you dock them and get that impulse in the first orbit you should not have lost too much. However, if one of the reasons you wanted all this extra capacity for a probe included a high energy orbit change later on then you still need to solve the boil off (and operation power issues since the main solar panels won't be deployed until after the last high energy burn). I am not seeing how this gets you a solution that is cheaper than 3'rd stage.There may not be a solution. This is what you guys call "hand-waving" after all! But:1. The 2nd flight US has a bunch of propellant. It had no payload, after all, other than the weight of the docking mechanism and any rendezvous sensors/computers. Maybe it only had a small expendable nosecone rather than a big heavy payload shroud. Seems like that would make for much larger payload than a 3rd stage added to a single launch.2. Common stages, common engines, common propellants, common software, common power, common procedures, common personnel. All from within SpaceX. No additional companies, personnel, procedures, safety concerns, or pad mods for a non-common stage. Each interaction between dissimilar items eats money and poops paper + lost time.3. The state of the art wrt cryo boiloff may improve. People have been working on depot tech for awhile now.
Quote from: punder on 02/18/2015 03:58 pmMaybe we should stop trying to pack all the energy for any given mission into a single launch. ...For anything like this, multiple launches don't make any sense.I'm not sure of the exact figures, but I'm pretty sure a small solid rocket kick motor is in the (perhaps low) single-digits millions of dollars range. Another launch (even fully reusable!) would be more than that.EDIT: A Star-48 is around $6 million, roughly: http://forum.nasaspaceflight.com/index.php?topic=33084.msg1109467#msg1109467
The Falcon 9 - Falcon Heavy upper stage would need a major upgrade to enable it for refuelling. A very much longer loiter time would be one of those. I also would worry more about RP-1 freezing than about some LOX boiloff.
Quote from: guckyfan on 02/18/2015 07:51 pmThe Falcon 9 - Falcon Heavy upper stage would need a major upgrade to enable it for refuelling. A very much longer loiter time would be one of those. I also would worry more about RP-1 freezing than about some LOX boiloff.Why major, why couldn't the the fuel depot attach to all the existing umbilical points? giving it the ability to circulate propellants (thereby controlling temps) and to provide power to the US and payload to keep it fresh?
Quote from: nadreck on 02/18/2015 09:09 pmQuote from: guckyfan on 02/18/2015 07:51 pmThe Falcon 9 - Falcon Heavy upper stage would need a major upgrade to enable it for refuelling. A very much longer loiter time would be one of those. I also would worry more about RP-1 freezing than about some LOX boiloff.Why major, why couldn't the the fuel depot attach to all the existing umbilical points? giving it the ability to circulate propellants (thereby controlling temps) and to provide power to the US and payload to keep it fresh?At the very least the stage must remain alive and active until docking is achieved.Also connections to the stage made in the HIF are not the same as needed for automated docking to a fuel depot. It needs a redesign.I have the very strong opinion it won't be done for a Falcon upper stage. It will need to be done for the BFR upper stage. But that would be designed from the beginning with this in mind.
F1US and it's Kestrel engine flew several times. It could provide the basis for a kick stage, though I believe it's only ~4t. Extra mass would be no problem as gravity losses are not an issue for a kick stage.
Quote from: Robotbeat on 02/18/2015 07:30 pmQuote from: punder on 02/18/2015 03:58 pmMaybe we should stop trying to pack all the energy for any given mission into a single launch. ...For anything like this, multiple launches don't make any sense.I'm not sure of the exact figures, but I'm pretty sure a small solid rocket kick motor is in the (perhaps low) single-digits millions of dollars range. Another launch (even fully reusable!) would be more than that.EDIT: A Star-48 is around $6 million, roughly: http://forum.nasaspaceflight.com/index.php?topic=33084.msg1109467#msg1109467But a Star-48 wouldn't accomplish the overriding goal of two launches and LEO rendezvous and ...Wait, that's not the goal?
Quote from: punder on 02/19/2015 02:31 pmThat's my main concern. Concepts long discarded may become feasible with that kind of cost savings. Maybe not this particular concept from some nobody on the Internet, but you see my point.This!!!Bring out those retired visionaries from both sides of the Atlantic and dust off those old bindered studies from when cost was no object (until someone actually tried to spend the money). We've spend a lot of breath on the economic of reusability, and a good deal of it was conceptualizing missions to take advantage of it....
That's my main concern. Concepts long discarded may become feasible with that kind of cost savings. Maybe not this particular concept from some nobody on the Internet, but you see my point.
This is like talking about moving the house across the street to this side of the street so you don't have to cross the street to get to it.A Star-48 is proven, relatively cheap, with only minor well-understood integration considerations. It is a no-brainer way for SpaceX to be able to provide high-energy escape trajectories for the small number of payloads that require it. Successful booster recovery and reuse doesn't throw any "wrench" into anything. It makes any mission cheaper. It doesn't mean it makes it sensible to throw multiple launches and all of the complexity that would entail at something that a $6 million kick stage solves.There are other concepts that could greatly benefit from something like the proposed architecture, but this isn't one of them.
If WE are thinking about FH upper stage, the next probabal step is a single raptor.
Quote from: dror on 02/20/2015 06:50 amIf WE are thinking about FH upper stage, the next probabal step is a single raptor.I've long wondered if any performance advantage can be gained from a methane-fuelled Merlin upper stage.