Author Topic: BFR and a bit of (hopefully) helpful scepticism  (Read 47825 times)

Online QuantumG

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #40 on: 05/16/2018 12:04 AM »
New Glenn will be fully reusable eventually. Probably sooner if BFR succeeds.

Where do you get that from?

It seems more likely to me that Blue has a design for a subsequent vehicle with that goal.
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Online butters

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #41 on: 05/16/2018 12:15 AM »
My skepticism about BFS is entirely confined to BEO mission profiles. Orbital propellant transfer and long-duration cryo storage (header tanks) are new but probably not a massive challenge. Mars EDL is new and certainly could be a challenge. I think SpaceX can possibly go it alone for Mars cargo missions, but I highly doubt they can go it alone (i.e. without NASA) for the first human mission.

But I don't think there's any compelling reason to doubt the satellite variant of the BFS or the BFR booster. SpaceX knows better than anybody how to develop a clean-sheet launch system. The lack of any delays or drama in the Raptor development program demonstrates a mastery of liquid rocket propulsion. Their avionics and guidance game is state-of-the-art to say the least. Their only notable shortcoming is a tendency to expect too much (and verify too little) from suppliers. If they can avoid shoddy strut syndrome, they should be fine.

Online QuantumG

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #42 on: 05/16/2018 12:19 AM »
I think SpaceX can possibly go it alone for Mars cargo missions, but I highly doubt they can go it alone (i.e. without NASA) for the first human mission.

They don't have any intention to "go it alone", but they're not waiting around for a contract from NASA either - and that's the real difference between SpaceX and everyone else - yes, even Blue Origin.

Quote from: butters
SpaceX knows better than anybody how to develop a clean-sheet launch system. The lack of any delays or drama in the Raptor development program demonstrates a mastery of liquid rocket propulsion.

They're also the best in the business at internal security, just saying.

I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

Offline TomH

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #43 on: 05/16/2018 01:27 AM »
Remember they want to land the US on a fully loaded booster stage. That's never been done anywhere ever.

Not sure what made you think that. They want to launch the full stack out of a cradle on the launch pad, then the booster returns, running on fumes, and lands in the cradle, already in position for refueling. The S2/spacecraft will land on its landing legs nearby and be hoisted into position atop the booster by a crane.

Offline Robotbeat

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #44 on: 05/16/2018 02:17 AM »
I for one, hope it works as planned.  Carbon fiber will make it lighter. 
No. Carbon fiber makes it possible at all.
Incorrect. Could do it with aluminum-lithium if you want. BFR isn't actually that sensitive to dry mass since it can refuel.
Quote
Quote from: spacenut
As mentioned SpaceX has landing covered, and engine reuse covered, and very well made engines. 
For the booster stage.
Remember they want to land the US on a fully loaded booster stage.
No, they don't.
« Last Edit: 05/16/2018 02:33 AM by Robotbeat »
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Ludus

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #45 on: 05/16/2018 03:40 AM »
Remember they want to land the US on a fully loaded booster stage. That's never been done anywhere ever.

Not sure what made you think that. They want to launch the full stack out of a cradle on the launch pad, then the booster returns, running on fumes, and lands in the cradle, already in position for refueling. The S2/spacecraft will land on its landing legs nearby and be hoisted into position atop the booster by a crane.

The alternative seems like something Elon might tweet and create enormous buzz until people realized the date was April 1st.

Offline envy887

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #46 on: 05/16/2018 03:46 AM »
New Glenn will be fully reusable eventually. Probably sooner if BFR succeeds.

Where do you get that from?

It seems more likely to me that Blue has a design for a subsequent vehicle with that goal.

Blue said that the NG upper stage was, and I quote, "initially expendable". That strongly implies that they will try to recover and reuse it eventually.

The switch to BE-3 strongly supports this, as it will make recovery much easier than with the original BE-4 upper stage.

Offline john smith 19

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #47 on: 05/16/2018 06:23 AM »
As mentioned SpaceX has landing covered, and engine reuse covered, and very well made engines. 
For the booster stage.
Remember they want to land the US on a fully loaded booster stage. That's never been done anywhere ever.

No, that is most certainly not what they want.
Remember they want to land the US on a fully loaded booster stage. That's never been done anywhere ever.

Wait, what? Where are you getting this from? That's absurd.
Watch Musk's presentation again.

1 Mars launch = 1 BFS in orbit + 4 BFS tanker launches.

That's take off, rendezvous with Mars BFS, propellant on load, RTLS and reload.

For that launch rate you need a lot of boosters and your tanker clocks up a lot of launches.

It is also one of Musks stated goals to eliminate landing legs on the US (I presume on the tanker only). Not surprising as the tanker has to be 30 tonnes lighter to make the propellant load numbers to refuel a BFS in LEO.
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Online RotoSequence

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #48 on: 05/16/2018 06:26 AM »
Watch Musk's presentation again.

1 Mars launch = 1 BFS in orbit + 4 BFS tanker launches.

That's take off, rendezvous with Mars BFS, propellant on load, RTLS and reload.

For that launch rate you need a lot of boosters and your tanker clocks up a lot of launches.

It is also one of Musks stated goals to eliminate landing legs on the US (I presume on the tanker only). Not surprising as the tanker has to be 30 tonnes lighter to make the propellant load numbers to refuel a BFS in LEO.

None of that makes landing the stage on top of the booster part of the equation. If they want to eliminate landing legs, they'd try to land each stage in its own cradle before they'd try propulsively landing a rocket stage on top of a rocket stage.  :o
« Last Edit: 05/16/2018 06:28 AM by RotoSequence »

Offline john smith 19

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #49 on: 05/16/2018 06:36 AM »
Remember they want to land the US on a fully loaded booster stage. That's never been done anywhere ever.

Not sure what made you think that. They want to launch the full stack out of a cradle on the launch pad, then the booster returns, running on fumes, and lands in the cradle, already in position for refueling. The S2/spacecraft will land on its landing legs nearby and be hoisted into position atop the booster by a crane.
Just to be clear that  profile takes a pretty substantial hit on booster payload and RTLS for the US needs either Shuttle size cross range or you'll have to wait till it's orbital plane rotates back over the launch site again.

I'd say if SX want to launch BFS to Mars quickly those wings are going to need to get an awful lot bigger.

I'll note I had thought SX could get away with a shot at 2022 if they didn't do that much TPS development, as the Mars BFS's only had to "go up" in Earths atmosphere once and come down in Mars atmosphere once.

But unless you're prepared to launch multiple BFS's in expendable mode to load up the BFS in LEO you have to get orbital grade TPS within the mass target.

« Last Edit: 05/16/2018 06:37 AM by john smith 19 »
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline dror

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #50 on: 05/16/2018 07:17 AM »
There are a lot of technical uncertainties regarding BFR but most of them seems solvable to me.
The only thing that I am truly skeptic about is water ice ISRU. That takes such a leap of belief that i just can't swallow.
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Offline Semmel

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #51 on: 05/16/2018 07:38 AM »
Remember they want to land the US on a fully loaded booster stage. That's never been done anywhere ever.

Not sure what made you think that. They want to launch the full stack out of a cradle on the launch pad, then the booster returns, running on fumes, and lands in the cradle, already in position for refueling. The S2/spacecraft will land on its landing legs nearby and be hoisted into position atop the booster by a crane.
Just to be clear that  profile takes a pretty substantial hit on booster payload and RTLS for the US needs either Shuttle size cross range or you'll have to wait till it's orbital plane rotates back over the launch site again.

I'd say if SX want to launch BFS to Mars quickly those wings are going to need to get an awful lot bigger.

I'll note I had thought SX could get away with a shot at 2022 if they didn't do that much TPS development, as the Mars BFS's only had to "go up" in Earths atmosphere once and come down in Mars atmosphere once.

But unless you're prepared to launch multiple BFS's in expendable mode to load up the BFS in LEO you have to get orbital grade TPS within the mass target.

Ok, none of this makes any sense. John, you are on this forum for such a long time and you have seen Elons presentation, you know their plans. I am surprised by what you write here.

First, No one is suggesting that the second stage lands on the booster. The animations show it clearly land nearby. Then, this has nothing to do with orbital mechanics or cross-range. The difference in orbital paths or cross-range between landing on the booster or 100m next to it is laughable. Not sure where you get that from or why you think there need to be bigger wings. Also, a tanker BFS probably cant launch, phase with the Mars BFS, dock, transfer fuel and execute the de-orbit burn on half an orbit (45 min). They need at least a couple of orbits to do that, meaning the minimum return time is 12 hours, when the orbital plane crosses the launch site after half a day. It probably will take longer, maybe one or two days.

The 2022 timeline has absolutely nothing to do with how fast you can refuel the BFS in orbit. It makes absolutely no sense to say that in this context. What are you getting at? Also, SpaceX is applying "orbital grade TPS" on BFS. Not for the first prototype since that is only doing short hops, but for the first orbital vehicle for sure. I dont know how you come to the conclusion they need to be prepared to throw away BFSs. Again, this makes no sense.

Offline rsdavis9

Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #52 on: 05/16/2018 11:18 AM »
Actually IIRC the real mission ending event was when the APU's ran out of MMH and (I did not know this) they had to be running (at idle) continuously




APU's only ran on boost and reentry. They needed hydraulic pressure to move aero surfaces and engine gimbal. If I remember correctly.

EDIT: what I am not sure about is whether the apu's were needed for the OMS burns. I don't think they were. But I do remember that the startup of the APU's on reentry was a big thing.

EDIT:
https://en.wikipedia.org/wiki/Auxiliary_power_unit#Spacecraft
Quote
The Space Shuttle APUs provided hydraulic pressure. The Space Shuttle had three redundant APUs, powered by hydrazine fuel. They were only powered up for ascent, re-entry, and landing. During ascent, the APUs provided hydraulic power for gimballing of the Shuttle's three engines and control of their large valves, and for movement of the control surfaces. During landing, they moved the control surfaces, lowered the wheels, and powered the brakes and nose-wheel steering. Landing could be accomplished with only one APU working.[14] In the early years of the Shuttle there were problems with APU reliability, with malfunctions on three of the first nine Shuttle missions.[Note 2]
« Last Edit: 05/16/2018 11:39 AM by rsdavis9 »
With ELV best efficiency was the paradigm. The new paradigm is reusable, good enough, and commonality of design.
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Offline johnfwhitesell

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #53 on: 05/16/2018 12:19 PM »

Online matthewkantar

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #54 on: 05/16/2018 01:04 PM »
The fact Musk talked about some new TPS when discussing the Block 5 F9 suggests there are issues with PICAX in high frequency F9 usage already.

Musk was talking about the old first stage TPS, cork, being replaced with a new felt based hydrophobic TPS. Not replacing PICAX. You are mixing things up.

Matthew

Offline Hominans Kosmos

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #55 on: 05/16/2018 02:55 PM »
Remember they want to land the US on a fully loaded booster stage.
No.
Watch Musk's presentation again.
OK.
It is also one of Musks stated goals to eliminate landing legs on the US (I presume on the tanker only).
No.


Official video upload from 2016: 
https://www.youtube.com/watch?v=H7Uyfqi_TE8?t=18m57s 

Official video upload from 2017: 
https://www.youtube.com/watch?v=tdUX3ypDVwI?t=33m34s 
Also see t=27m13s in the above 

Segment from the above video (2017), showing the transplanetary passenger service, not tanker flights:
https://www.youtube.com/watch?v=zqE-ultsWt0?t=1m16s 

Gwynne Shotwell's 2018 TED interview:
https://www.youtube.com/watch?v=Dar8P3r7GYA?t=18m05s 

1) None of the operations diagrams and videos show any of the Ships, tanker or passenger, landing on anything other than the ground. 
2) Tanker landings are not shown in video, but are shown to be on ground in operations diagrams. 
3) 2016 and 1018(TED) versions of the tanker Ship clearly show them standing on legs, and flying with stowed legs.
4) All images of passenger Ship on planetary and satellite surfaces, show them landing, launching and standing on legs. 
5) There are no company representative statements about planning to use legless Spaceships. 
6) There are no company statements about landing Spaceships on top of waiting Boosters. 
7) Many of the other illustrations, where the Spaceships are not standing on surfaces, but are in space, presented otherwise have the 2017 version showcased in a form without legs. 

Are you misremembering and gone too far with misremembered info? 
Or have you taken my last point (7) to be an implied statement of plans by the company to develop a legless version, not just having omitted showing legs in illustrations where they are not mandatory, since the design is too premature?

[Edit: formatting, improved context, clarity]
[Edit later: failed double negatives, in my defense I was proofreading with a fever]
« Last Edit: 05/18/2018 06:21 AM by Hominans Kosmos »

Offline johnfwhitesell

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #56 on: 05/16/2018 04:04 PM »
5) There are no company representative statements about planning to use legless Spaceships.

I thought they had plans to land the BFS in a cradle without legs?

Online whitelancer64

Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #57 on: 05/16/2018 04:06 PM »
5) There are no company representative statements about planning to use legless Spaceships.

I thought they had plans to land the BFS in a cradle without legs?

That's for the booster.

The spaceship needs landing legs.
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Offline dglow

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #58 on: 05/16/2018 04:30 PM »
My goodness, are we actually debating this? Yesterday I thought john smith simply mistyped amidst a long post and a few of us pounced on it as amusing. (The notion of landing atop a fueled rocket stage is genuinely funny.)*

But there's no debate here. john smith 19, you were in error suck it up. Shall we move on?



* Though it would lend a new angle to the whole "Load 'n' Go" debate... 
« Last Edit: 05/16/2018 04:36 PM by dglow »

Online QuantumG

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Re: BFR and a bit of (hopefully) helpful scepticism
« Reply #59 on: 05/16/2018 05:31 PM »
Blue said that the NG upper stage was, and I quote, "initially expendable". That strongly implies that they will try to recover and reuse it eventually.

Here's your source: https://twitter.com/RSgroshn/status/844596259776278529

This is pretty thin compared to BFS, don't ya think?
I hear those things are awfully loud. It glides as softly as a cloud. What's it called? Monowhale!

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