Author Topic: Developing the BFS - Phase 1 Big Falcon Hopper (BFH) Discussion - THREAD 2  (Read 241538 times)

Online matthewkantar

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The rush to build this thing suggests to me that they need the information it will provide to make an important decision. If they are at a fork in the road, they may need this data to continue.

On the other hand, they are wasting time hanging some non engineering bling on it, so how big can the rush be?

Matthew

Offline moreno7798

The rush to build this thing suggests to me that they need the information it will provide to make an important decision. If they are at a fork in the road, they may need this data to continue.

On the other hand, they are wasting time hanging some non engineering bling on it, so how big can the rush be?

Matthew

Rush?

I am going to assumen you have not kept up with EM's presentations over the past 3 years. Otherwise, I will assume you're trolling.

If they had decided to build the hopper 3 months ago I would have considered some validity to this argument.

Offline Rei

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Quote
So while obviously you need to have maximum reliability in your advanced super-high performance engine, that seems to be about all that this platform will test, and not much more.

 * First time flying a spacecraft with such a high diameter
 * First time landing a spacecraft with such a high diameter
 * If a weight-match for Starship, first time landing a spacecraft with such a high mass
 * First time operating a spacecraft with CH4 onboard
 * First time operating a steel-framed spacecraft
 * First time operating a spacecraft with steel in contact with cryogenic propellants
 * Numerous subsystems developed specifically for the craft which may be tested in flight.

Probably many more things.
« Last Edit: 01/07/2019 12:47 am by Rei »

Offline su27k

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The funny thing is you have folks doubting that SpaceX could make a 2022 launch date for Starship cargo launches to Mars and you also have people wondering why are they moving so fast?

Make up your mind.

The two thoughts are not necessarily contradictory, you can hold both if you don't believe the hopper is on the critical path to a 2022 launch date. I don't think anyone figured out why hopper is on the critical path yet (assuming it is).

On a smaller scale, there's also the question why are they rushing the body work when the engine won't be ready for another month. It looks like the body would be done in a day or two, what's next?

Offline su27k

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Oh my. This has gone from "It's a water tower!" to "It's a space ship!" all too fast.

Can we reckon some rational development path? My take is this:

1. This thing is a pathfinder. It's there both for having something in halfway the right scale and shininess to show off as soon as possible (exploiting all the hopefully good press they get with DM-1) and to fly the 500 m landing tests once they have three flight-worthy Raptors ready. Do landings with one, two or three engines and explore failure modes and how to recover from them. Try to not destroy it, but if you have to, well, do it and learn from it.

2. While they'll be doing this they will build version 2 with movable wings, canards and bigger propellant tanks to fly the 5 km tests: launch, do a landing approach sideways to 1 km of height, move vertical with the moving wings and canards and RCS and land. Repeat with all kinds of failure modes and shake it down until it's routine.

This hopper should be able to do #2 easily. DC-X was able to do this using just the main engines, no RCS or wings required:



Quote
3. While doing this build the version 3, with actual full size tanks and a heat shield (active cooling) to fly suborbital trajectories and to test reentry with increasing velocities and thermal loads. THIS SpaceX won't be able to pull off without money from the outside, but hopefully in one way or another they will get more money to do that with all the publicity they managed to provoke with 1. and 2.

They got close to $1B outside investment this year, I doubt money is a problem for building the orbital test vehicle. Besides, Elon said they're already building it at the San Pedro site, now we just need some photos to see what's going on.

Online Cinder

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If the BFH is the sine qua non precursor to all crew SSs, then you would want as much flight time as possible before putting humans in it, never mind high profile humans like the DearMoon crew. 

It may be an unanswered question to ask what good reason SpaceX could have to not work around the clock.  Maybe this SHSS work speed is only remarkable because it's the only publicly visible SHSS work.
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Online Lemurion

The funny thing is you have folks doubting that SpaceX could make a 2022 launch date for Starship cargo launches to Mars and you also have people wondering why are they moving so fast?

Make up your mind.

The two thoughts are not necessarily contradictory, you can hold both if you don't believe the hopper is on the critical path to a 2022 launch date. I don't think anyone figured out why hopper is on the critical path yet (assuming it is).

On a smaller scale, there's also the question why are they rushing the body work when the engine won't be ready for another month. It looks like the body would be done in a day or two, what's next?

I think that while the specifics may not be public knowledge, the base reason why the hopper is on the critical path is obvious:

Itís Raptor. If Raptor doesnít work as designed, nothing else matters. The hopper is going to give them vital data on both takeoff and landing operations and landing is the hard part. Raptor has to be able to throttle down and land and SpaceX appears to think that the hopper is the best available, if not the only, way to demonstrate that functionality.

Online Mongo62

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The rush to build this thing suggests to me that they need the information it will provide to make an important decision. If they are at a fork in the road, they may need this data to continue.

On the other hand, they are wasting time hanging some non engineering bling on it, so how big can the rush be?

Matthew

Is it wasting time though? They presumably need to wait until the engines are ready, so they might as well make the hopper shiny in the meantime. The cost is tiny compared to the total SS/SH development cost, and the gain is considerable, in terms of positive public perception when video of the hopper flying goes public.

Online Johnnyhinbos

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I’m curious as to what Jim’s thoughts are on the BFH. Jim, you out there? Be interesting to get your take...

John Hanzl. Author, action / adventure www.johnhanzl.com

Offline GWH

I am sure there will still be a lot of time spent with actual SpaceX employees crawling around inside this thing wiring up various sensors and everything else to make it flight (hop?) worthy. The rush now is to get ahead of that.

Online vaporcobra

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Guys, the idea that this development is being rushed because of the hours worked is straight up blind to history and known operational facts. SpaceX runs almost every single one of its facilities - ranging from Hawthorne to Redmond to McGregor - 24/7 or nearly so, and pretty much universally has two shifts (10-12+ hours for two, 10-14+ hours for one) for most conceivable tasks.

This is a very normal pace for SpaceX, modified by the fact that they're building a purely experimental and less-than-full-fidelity test article with almost no red tape whatsoever. The Grasshopper/F9R programs proceeded at very similar speeds once they got into the actual process of building and assembling hardware.

Online AJW

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One aspect of getting the hopper flying that is easy to overlook is the human factor.   Having a team without a real deadline teaches you little about how that team will work when they must meet hard targets.  Who are the real leaders.  Who on the team makes the right decisions, or the wrong ones.  Hopper is the rubber hitting the road and will represent the efforts of thousands.  Decisions made up to this point will soon face the toughest of judges.

The difference between theory and practice is that practice may not forgive you for forgetting something.

Offline georgegassaway

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This hopper should be able to do #2 easily [test for change from belly flop mode to tail-first descent mode]. DC-X was able to do this using just the main engines, no RCS or wings required:

DC-X most definitely had aerodynamic flaps near the base which assisted in steering it. It also had strakes on the nose section to get a bit of aerodynamic "bite" when the flaps steered to produce an angle of attack (strakes acting sort of like very long skinny canards with no control surfaces).



And DC-X did not have huge fins trying to stabilize it nose-first thru the air. 

 This new hopper will be unable to get  data on the aerodynamic maneuvering of the "real" Starship to flip to tail-first descent, since it wont have the canard, two articulated fins for the belly-flop mode, and not the same shape (length), among other things (landing configuration CP/CG relationship need to be the same as well as mass).   Also, unless they really are going to pressurize the skin of the mid and nose sections or do something to stiffen it up more than the bare bones structure it seems to have, it's not likely to hold up to high aerodynamic side loads.

They are going to need a different vehicle to accurately test for that.

Although they'll be able to use thrust vectoring to maneuver sharply if they want to (up to the aerodynamic and structural limits), but not the same as the real Starship.  They can certainly get some rudimentary (hopefully not RUD-imentary) info on fuel slosh behavior
« Last Edit: 01/07/2019 03:33 am by georgegassaway »
Info on my flying Lunar Module Quadcopter: https://tinyurl.com/LunarModuleQuadcopter

Online Lars-J

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EDIT - never mind
« Last Edit: 01/07/2019 03:42 am by Lars-J »

Offline Michel Van

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Looking at what happen a SpaceX launch site Boca Chica
it remind me of this...

one consideration for the 24/7 working is there is less likely to be things missed in the program as systems will not be assigned to just one person
kind of like a double double check if that makes sense


Offline hallmh

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Regarding the 'foil', it may be similar to material that I used a few years ago - thin stainless steel sheet (I used 0.1mm, but it does come thinner and of course thicker), mechanically polished on one face to a mirror finish.

Comes in rolls or sheets. Amazing stuff.

Offline Rei

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I agree that it looks like somewhere around 0,1mm stainless. That said, you're not going to build tanks out of 0,1mm stainless for such a large rocket.  Falcon 9's skin is 4,7mm alumium, for comparison.

I'm 95% sure that only the bottom portion is tankage (and it'll end up with a big hemispheric bulkhead intruding into the upper portion, as well as an internal bulkhead). The bottom portion is clearly built far sturdier than the top portion. Yes, that leaves a truly massive empty area at the top, but that's the point - Starship's passenger / cargo volume is supposed to be truly massive..  Final Starship will be significantly extended vs. the hopper, and all of that extra length will be tankage.

The key thing to look for going forward is bulkheads. Is there any sign of work being done on them?

Offline Llian Rhydderch

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Looking at what happen a SpaceX launch site Boca Chica
it remind me of this...

--- snipped out the image expansion---

"Amazing Stories"  cover art, "October"  "25 cents"
https://pbs.twimg.com/media/DwKECeBX4AA-5JG.jpg


If NSF is going to put up images from some magazine cover artwork website from time to time, I think we should be crediting that source and providing a link to it, not merely grabbing the artwork and adding it to our site.
« Last Edit: 01/07/2019 11:16 am by Llian Rhydderch »
Re arguments from authority on NSF:  "no one is exempt from error, and errors of authority are usually the worst kind.  Taking your word for things without question is no different than a bracket design not being tested because the designer was an old hand."
"You would actually save yourself time and effort if you were to use evidence and logic to make your points instead of wrapping yourself in the royal mantle of authority.  The approach only works on sheep, not inquisitive, intelligent people."

Offline woods170

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Iím curious as to what Jimís thoughts are on the BFH. Jim, you out there? Be interesting to get your take...



Jim hasn't been active here since Dec 26th, 2018.

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