Quote from: Slarty1080 on 11/12/2018 10:04 am.. They must already have some idea, but they aren’t sure enough to risk a trial with a prototype BFR yet. It’s also not just about money. The loss of a prototype BFR at this stage would create delays whilst a new one was built, something that Musk would not be keen on...You need a BFR first stage to test full speed BFS re-entry. This would create delays, also :-) - BFS hopper: full scale, sub speed incremental testing, non destructive, grasshopper like. - Modified F9: sub scale, full speed, destructive testing, possibly enable F9 upgrades just in case.Hopefully they'll get enough points to refine mathematical model.
.. They must already have some idea, but they aren’t sure enough to risk a trial with a prototype BFR yet. It’s also not just about money. The loss of a prototype BFR at this stage would create delays whilst a new one was built, something that Musk would not be keen on...
You need a BFR first stage to test full speed BFS re-entry. This would create delays, also :-)
On the question of the M1D Vac nozzle being an issue during re-entry. Are the concerns because it may interfere with the aerodynamics of re-entry or some other reason? Lot's of ideas being floated about about how to get around the issue such as using sea level M1D. Is it possible SpaceX could discard the nozzle extension after ascent?
Making a precise sub-scale demonstrator used to be a daunting job. I am thinking that in these days of 3D-printing it is much more straightforward. Just reduce the dimensions of existing CAD models. SpaceX is already using a lot of 3D-printing.Yes, of course physics doesn't allow a reduced scale of all components, I of course know that. But the work should be a good deal easier than it would have been years ago.
Quote from: Oersted on 11/12/2018 04:25 pmMaking a precise sub-scale demonstrator used to be a daunting job. I am thinking that in these days of 3D-printing it is much more straightforward. Just reduce the dimensions of existing CAD models. SpaceX is already using a lot of 3D-printing.Yes, of course physics doesn't allow a reduced scale of all components, I of course know that. But the work should be a good deal easier than it would have been years ago. Having enlarged/reduced a bunch of scale model parts, I'd say that's not true unless they've been very clever in the original design. When you scale a part, you soon run into issues with wall thickness: the part becomes too thin to be printed (or when scaling up, way more expensive than necessary). You can design parts to account for this, but you'd have to do that from the start. Going back and editing existing parts for scaling can run into a full-on redesign.
I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.
How BFR lands is very much like F9 - just bigger. Their models are probably pretty close already. The hopper tests will deal with the precision landing details.BFS reentry is a whole new thing so using subscale models on their existing launcher is probably the fastest way to acquire the necessary data. It is not like a small model in a wind tunnel - it would still be close to 3.7m in diameter. I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.
Quote from: ThereIWas3 on 11/12/2018 03:56 pm I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.Scaled composites' machine never really gets past jogging speed so the info would only be of limited relevance and Scaled has gone with with a fold in half entry scheme which places the difficulty more on the mechanics of the folding structure than it does on entry aerodynamics.
Fundamentally, this is about as close as we're gonna get to an explicit admission from Spaceflight that they're going to incur a loss because of the drop to 50+ payloads from what was originally advertised as 70-100+ over the last year or two. Rephrased in a few words, Curt Blake is basically saying "not worth the effort or risk". https://twitter.com/pbdes/status/1062090419683708928
Quote from: ThereIWas3 on 11/12/2018 03:56 pm I would not be surprised if Scaled Composites paid money to SpaceX to get some of that data.And I would not be surprised if SpaceX refused to sell such data.
Quote from: oiorionsbelt on 11/12/2018 03:39 pmOn the question of the M1D Vac nozzle being an issue during re-entry. Are the concerns because it may interfere with the aerodynamics of re-entry or some other reason? Lot's of ideas being floated about about how to get around the issue such as using sea level M1D. Is it possible SpaceX could discard the nozzle extension after ascent?My concern was that it might not only interfere aerodynamicly but might disintergrate suddenly under extreme heat stress. Such a sudden loss of mass might destabilise the whole stage. But perhaps the payload adaptor is a bigger issue because when it disintergrates in the heat it will fall directly back into the top of the stage.
Quote from: Slarty1080 on 11/12/2018 03:57 pmQuote from: oiorionsbelt on 11/12/2018 03:39 pmOn the question of the M1D Vac nozzle being an issue during re-entry. Are the concerns because it may interfere with the aerodynamics of re-entry or some other reason? Lot's of ideas being floated about about how to get around the issue such as using sea level M1D. Is it possible SpaceX could discard the nozzle extension after ascent?My concern was that it might not only interfere aerodynamicly but might disintergrate suddenly under extreme heat stress. Such a sudden loss of mass might destabilise the whole stage. But perhaps the payload adaptor is a bigger issue because when it disintergrates in the heat it will fall directly back into the top of the stage.They can simply cut M1D Vac nozzle shorter as they did before, they dont need full performance for this mission.