Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Quote from: TrevorMonty on 01/29/2018 07:36 amReuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.Absolutely. A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.But if you take the latter as a given, then at that point the former becomes a distraction.It's a hell of a decision for Musk to have made, but he clearly made it. He who dares wins and all that.
Quote from: meekGee on 01/29/2018 10:12 amQuote from: TrevorMonty on 01/29/2018 07:36 amReuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.Absolutely. A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.But if you take the latter as a given, then at that point the former becomes a distraction.It's a hell of a decision for Musk to have made, but he clearly made it. He who dares wins and all that.Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
While knowledge from capsules and shuttle can be applied to BFS US design, they are still totally different aeroshapes.The only way to get BFS US design close to right first time is to fly subscale version.
They have zero competition for the Block 5 with booster-only reusability.Doesn't make competitive sense* to beat that dead horse.* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.
Quote from: AncientU on 01/29/2018 01:52 pmThey have zero competition for the Block 5 with booster-only reusability.Doesn't make competitive sense* to beat that dead horse.* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs. That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.
Quote from: ChrisWilson68 on 01/29/2018 02:40 pmQuote from: AncientU on 01/29/2018 01:52 pmThey have zero competition for the Block 5 with booster-only reusability.Doesn't make competitive sense* to beat that dead horse.* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs. That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.You are assuming that developing second stage reusability for Falcon will reduce their costs -- enough to justify the development effort. They are developing recoverable fairings because this reduces their costs (<$5M/launch) and/or streamlines operations. They are also working toward 24hr turn-around of flown cores. At this level of granularity, it is easy to see that these activities are more cost-effective lines of development than reusable second stages.They are soon going to be their own largest customer with Starlink launches... launch costs must already have their full attention, and they seem to be passing on second stage reuse for Falcon.
Quote from: JamesH65 on 01/29/2018 10:36 amQuote from: meekGee on 01/29/2018 10:12 amQuote from: TrevorMonty on 01/29/2018 07:36 amReuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.Absolutely. A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.But if you take the latter as a given, then at that point the former becomes a distraction.It's a hell of a decision for Musk to have made, but he clearly made it. He who dares wins and all that.Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!That's not true.Which law of physics?US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5You could double the mass of the US for reusability hardware and still be good.This is a business decision about schedule of development.
Quote from: meekGee on 01/29/2018 12:01 pmQuote from: JamesH65 on 01/29/2018 10:36 amQuote from: meekGee on 01/29/2018 10:12 amQuote from: TrevorMonty on 01/29/2018 07:36 amReuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.Absolutely. A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.But if you take the latter as a given, then at that point the former becomes a distraction.It's a hell of a decision for Musk to have made, but he clearly made it. He who dares wins and all that.Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!That's not true.Which law of physics?US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5You could double the mass of the US for reusability hardware and still be good.This is a business decision about schedule of development.Mass, speed, and air drag. US has a limited up mass, it's travelling very fast, often in the wrong direction, it needs to slow down before it hits atmosphere or it will burn up, it need fairly heavy landing gear. All these combined mean it's very difficult to get everything you need in the US to do a return, and still have enough left over mass to actually launch anything. It's not really big enough.Those ones.I'm not saying it's impossible, just very difficult to make it worth doing.
The only way to get BFS US design close to right first time is to fly subscale version.
Space shuttles and IXV have already proved what would be provable by reusable F9 upper stage. Wasting lots of resources to develop a new dead-end upper stage to F9 would have very little value.
Quote from: hkultala on 01/29/2018 08:29 amSpace shuttles and IXV have already proved what would be provable by reusable F9 upper stage. Wasting lots of resources to develop a new dead-end upper stage to F9 would have very little value.What shuttle proved that reuse of a re-entry vehicle is possible. Shuttle did not prove out the economics of said reuse, in fact it proved out the dis-economies of reuse.
I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.
US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5
I know a law of physics when I see one, and those weren't.Also, some of your statements of difficulty were plain wrong.The stage is not "traveling in the wrong direction". It is orbital. You wait a couple of orbits and aim the reentry for near the coast.You don't "need to slow down to avoid burning". You need to "slightly slow down just like any reentering orbital vehicle"You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements. I allowed for doubling the stage dry mass because of that.Also remember that many LEO missions are volume limited anyway.So no, no physical laws. Just a business decision. If BFS wasn't front burner, they'd be working on it already.
Quote from: meekGee on 01/29/2018 12:01 pmUS/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5Quote from: meekGee on 01/30/2018 01:35 pmI know a law of physics when I see one, and those weren't.Also, some of your statements of difficulty were plain wrong.The stage is not "traveling in the wrong direction". It is orbital. You wait a couple of orbits and aim the reentry for near the coast.You don't "need to slow down to avoid burning". You need to "slightly slow down just like any reentering orbital vehicle"You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements. I allowed for doubling the stage dry mass because of that.Also remember that many LEO missions are volume limited anyway.So no, no physical laws. Just a business decision. If BFS wasn't front burner, they'd be working on it already.I'm curious what the 1:5 ratio you mentioned is based on? I thought it was pretty clear that for adding recovery mass to the upper stage, it went 1:1 with payload. Actually, it may be even a tiny bit worse than that because there is also a minor effect on first stage performance as well.
Quote from: freddo411 on 01/30/2018 04:42 pmI'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights. In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts?