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Old November 8th 18, 04:14 PM posted to sci.space.policy
Torbjorn Lindgren
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Default SpaceX to fly mini-BFS prototype as Falcon 9 upper stage

Jeff Findley wrote:
Elon Musk tweeted yesterday that SpaceX plans to build and fly a mini-
BFS prototype as a Falcon 9 upper stage. This is to test the
lightweight thermal protection system as well as the aerodynamics of
their "belly flop" reentry and flight down to subsonic speeds.

The flight tests will not include vertical landing because Musk says
they already know how to do that (duh). I am speculating it may,
however, test the transition from the "belly flop" attitude to vertical
as that would seem to be a critical part of the BFS flight profile to
prove out.


Musk was asked this by Everyday Astronaut and specifically says "No,
we’re building a BFR dev ship to do supersonic through landing tests
in Boca Chica, Texas".

He earlier say "Ultra light heat shield & high Mach control surfaces
are what we can’t test well without orbital entry" (IE this mini-BFS
conversion).


I'm also speculating recovery might be by parachute. You know, because
you might want to fly the thing more than once. Plus, if they fly a
mini-BFS prototype more than once, they'll be in the record books for
flying the first fully reusable TSTO. You know, because you've actually
got to reuse it to call it reusable.


It doesn't actually say anywhere that it's going to be recovered...

Obviously recovering the stage do have benefits (like inspecting the
TPS) but has to be balanced against the increased development cost and
time.


Elon Musk also tweeted that the first flight of this prototype is
expected by June. But, of course, that's Elon Musk time, so I'd expect
a delay of at least a few months.


The time-frame feels tight even by Musk standard if they do plan to
try recovery but I guess it's possible. It seems likely it would be
faster/easier not add that.

They may think they get that data from various Dragon flights. Or it
could even be done in stages, where the first one just has TPS and
fins while later they add parachutes if they want to down that route.


I'm sure SpaceX is doing this mostly for testing, but one could imagine
the utility of a reusable upper stage which integrates the payload
fairing into the design. This is especially true on the Falcon Heavy
since for some missions it's got the extra payload margin to handle the
increased mass of the upper stage.


Reusing second stages is certainly something that could be useful if
the timeframe for BFR/BFS slips sufficiently. Another possible use
might be that they're considering it to reduce the cost of launching
all those Starlink satellites.


My cite is the Elon Musk Twitter account. It's easy enough to find and
scroll down to yesterday's tweets.


https://twitter.com/elonmusk/status/1060253333116473344