Author Topic: BFS Design Requirements  (Read 32724 times)

Offline woods170

  • IRAS fan
  • Senior Member
  • *****
  • Posts: 12096
  • IRAS fan
  • The Netherlands
  • Liked: 18202
  • Likes Given: 12162
Re: BFS Design Requirements
« Reply #60 on: 03/12/2018 06:46 am »
There's no LAS on an airliner either, and AIUI Raptor engines have integrated frag shields which mimic the effect of Octaweb cells - so it should  have engine-out.

Correct. Remember that view of the BFS aft end from the 2017 IAC? I have it from SpaceX sources that the actual design is more "buttoned-up" with similar-function safeguards in place, for protection against engine RUD, as F9 has.
« Last Edit: 03/12/2018 06:49 am by woods170 »

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2611
  • Liked: 500
  • Likes Given: 1096
Re: BFS Design Requirements
« Reply #61 on: 03/12/2018 11:59 am »
There's no LAS on an airliner either
Airliners are 10,000x safer than rockets, so adding a "LAS" would only decrease safety.
Bingo.

a remarkable example of an aircraft LAS going the wrong way is the saga of the ejection pods on the B-58, XB-70, F-111, and B-1 (and later (never-happened) developments on Space Shuttle and Hermes, post STS-51L)

In most case classic ejection seats bet them any time, anywhere.

 The most extreme example being the Su-27 / Mig-29 / Buran K-36 seats.

http://www.proairshow.com/MiG%20Crash%20Seq.htm
« Last Edit: 03/12/2018 12:03 pm by Archibald »
Han shot first and Gwynne Shotwell !

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 39271
  • Minnesota
  • Liked: 25240
  • Likes Given: 12115
Re: BFS Design Requirements
« Reply #62 on: 03/12/2018 12:27 pm »
And ejection seats also aren’t very safe. They’d be a net reduction in safety if added to a typical airliner today.
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 IainMcClatchie

  • Full Member
  • ***
  • Posts: 394
  • San Francisco Bay Area
  • Liked: 279
  • Likes Given: 411
Re: BFS Design Requirements
« Reply #63 on: 03/12/2018 11:00 pm »
I would be rather surprised if the normal exhaust of the landing engines was anywhere near 1270 K. The SSME exhaust was about half that. The nozzle expands and accelerates the exhaust gas, and the energy to do that comes from the heat in the gas itself. An ideal nozzle would expand it all the way to the condensation point.

You're talking about static temperature.  That's not what is experienced by a surface on which the flow impinges.

The flow slows down as it gets very close to the surface, exchanging velocity for pressure and temperature.  For a rocket blasting at a flat surface, like on the ASDS, at the stagnation point where the exhaust has come to a stop, it's back up to the same total temperature that it was at in the combustion chamber.  I'm a little fuzzy on the details, but I think the total pressure (and thus density and heat transfer) is much lower because of expansion between nozzle exit and deck surface.

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2611
  • Liked: 500
  • Likes Given: 1096
Re: BFS Design Requirements
« Reply #64 on: 03/13/2018 06:10 am »
And ejection seats also aren’t very safe. They’d be a net reduction in safety if added to a typical airliner today.

Imagine 800 seats popping out of a crashing A380... what a mess it would be...
« Last Edit: 03/13/2018 01:13 pm by Archibald »
Han shot first and Gwynne Shotwell !

Offline niwax

  • Full Member
  • ****
  • Posts: 1422
  • Germany
    • SpaceX Booster List
  • Liked: 2040
  • Likes Given: 166
Re: BFS Design Requirements
« Reply #65 on: 03/13/2018 06:47 am »
And ejection seats also aren’t very safe. They’d be a net reduction in safety if added to a typical airliner today.

Imagine 800 sieges popping out of a crashing A380... what a mess it would be...

As the saying goes, please put on your seatbelt so we can identify the corpses by their seat number.
Which booster has the most soot? SpaceX booster launch history! (discussion)

Offline Hog

  • Senior Member
  • *****
  • Posts: 2846
  • Woodstock
  • Liked: 1700
  • Likes Given: 6866
Re: BFS Design Requirements
« Reply #66 on: 03/13/2018 01:11 pm »
There's no LAS on an airliner either
Airliners are 10,000x safer than rockets, so adding a "LAS" would only decrease safety.
Bingo.

a remarkable example of an aircraft LAS going the wrong way is the saga of the ejection pods on the B-58, XB-70, F-111, and B-1 (and later (never-happened) developments on Space Shuttle and Hermes, post STS-51L)

In most case classic ejection seats bet them any time, anywhere.

 The most extreme example being the Su-27 / Mig-29 / Buran K-36 seats.

http://www.proairshow.com/MiG%20Crash%20Seq.htm
bold mine
What "saga of the ejection pods" are you referring to?
Paul

Offline Archibald

  • Senior Member
  • *****
  • Posts: 2611
  • Liked: 500
  • Likes Given: 1096
Re: BFS Design Requirements
« Reply #67 on: 03/13/2018 01:13 pm »
replace "wrong word" by "long and unfortunate story"
Han shot first and Gwynne Shotwell !

Offline Slarty1080

  • Senior Member
  • *****
  • Posts: 2740
  • UK
  • Liked: 1871
  • Likes Given: 814
Re: BFS Design Requirements
« Reply #68 on: 03/20/2018 08:32 pm »
The issue of FOD on Mars has been discussed in this thread:
https://forum.nasaspaceflight.com/index.php?topic=37466.20

Quote from reply #24
ADDED: Your question deserves a better answer so I looked up what NASA scientists have found in their studies. The following statement is a verbatim copy of a summary that addresses the problem. It was a section of the Mars Design Reference Architecture, Addendum A,  published in 2009:

"5.9.1 Summary and recommendations
The predictions and recommendations for a 40-t spacecraft on Mars are described in summary in this section. The next section of the report will then explain in detail how these predictions were obtained.
The engine exhaust plume from a 40-t lander on Mars will blow dust, sand, gravel, and even rocks up to about 7 cm in diameter at high velocity. These ejecta will cause significant damage to any hardware that is already placed on the martian surface within the blast radius. However, the blast radius is modest, extending out to approximately 1 km. The largest debris is accelerated by the plume to lower velocities and, thus, falls closer to the landing site; and the smallest particles are attenuated by the martian atmosphere, also falling closer to the landing. Thus, maintaining the distance of about 1 km between the landing site and any existing surface assets will completely solve this problem for all sizes of debris.
A second concern arises because the exhaust from the large engines will form deep, narrow craters that are directly beneath each of their nozzles, and these craters will redirect the supersonic jet of gas with sand and rocks up toward the landing spacecraft. This has been demonstrated in large-scale engine tests in sand and clay (Alexander, et al, 1966) 25, small-scale experiments (Metzger, 2007) 26, numerical simulations (Liever, et al, 2007) 27, and soil dynamics analysis (see section 5.10.2.3), so there is no question that this will occur. It did not occur in the Apollo and Viking missions because the thrust was lower and/or because the lunar regolith had higher shear strength and less permeability than martian soil. These variables have been taken into consideration in this report. An example of a small-scale test is provided in figure 5-55. The impact of debris striking the lander will be sufficient to cause damage to the lander, possibly resulting in LOM and LOC, and therefore must be prevented. Of special concern is damage to the engine nozzles, because with a multiple-engine lander the debris that is ejected by one engine will be aimed directly at the other engines. One mitigation approach is to add shielding to the spacecraft to block the debris. This will increase the mass of the lander and, therefore, reduce the mass of the payload by approximately 1 t."

So FOD is a significant issue. Other points to consider from this thread:

* Mars gravity only 38% of Earths so less thrust required on take off than on Earth
* Mars atmosphere only 1% of Earths so more gas dispersion than on Earth
* Longer landing legs move the engines further away from the surface
* Landing sites are likely to be covered with large quantities of very loose materials
* If a large enough angle can be achieved, engine gimbaling could be very useful in deflecting FOD
* Either berms will be needed or the BFS will need to land perhaps 1km from the habitat due to FOD
* Take off will require more thrust with full tanks and will be over a pit excavated by the decent engines
* It might be possible to place deflectors under the engines to mitigate problems at take off
* Difficult to test scenario due to Gravity / atmosphere differences between Mars and Earth
My optimistic hope is that it will become cool to really think about things... rather than just doing reactive bullsh*t based on no knowledge (Brian Cox)

Offline tdperk

  • Full Member
  • ***
  • Posts: 369
  • Liked: 152
  • Likes Given: 95
Re: BFS Design Requirements
« Reply #69 on: 03/20/2018 08:48 pm »
The issue of FOD on Mars has been discussed in this thread:
https://forum.nasaspaceflight.com/index.php?topic=37466.20

Quote from reply #24
ADDED: Your question deserves a better answer so I looked up what NASA scientists have found in their studies. The following statement is a verbatim copy of a summary that addresses the problem. It was a section of the Mars Design Reference Architecture, Addendum A,  published in 2009:

"5.9.1 Summary and recommendations
The predictions and recommendations for a 40-t spacecraft on Mars are described in summary in this section. The next section of the report will then explain in detail how these predictions were obtained.
The engine exhaust plume from a 40-t lander on Mars will blow dust, sand, gravel, and even rocks up to about 7 cm in diameter at high velocity. These ejecta will cause significant damage to any hardware that is already placed on the martian surface within the blast radius. However, the blast radius is modest, extending out to approximately 1 km. The largest debris is accelerated by the plume to lower velocities and, thus, falls closer to the landing site; and the smallest particles are attenuated by the martian atmosphere, also falling closer to the landing. Thus, maintaining the distance of about 1 km between the landing site and any existing surface assets will completely solve this problem for all sizes of debris.
A second concern arises because the exhaust from the large engines will form deep, narrow craters that are directly beneath each of their nozzles, and these craters will redirect the supersonic jet of gas with sand and rocks up toward the landing spacecraft. This has been demonstrated in large-scale engine tests in sand and clay (Alexander, et al, 1966) 25, small-scale experiments (Metzger, 2007) 26, numerical simulations (Liever, et al, 2007) 27, and soil dynamics analysis (see section 5.10.2.3), so there is no question that this will occur. It did not occur in the Apollo and Viking missions because the thrust was lower and/or because the lunar regolith had higher shear strength and less permeability than martian soil. These variables have been taken into consideration in this report. An example of a small-scale test is provided in figure 5-55. The impact of debris striking the lander will be sufficient to cause damage to the lander, possibly resulting in LOM and LOC, and therefore must be prevented. Of special concern is damage to the engine nozzles, because with a multiple-engine lander the debris that is ejected by one engine will be aimed directly at the other engines. One mitigation approach is to add shielding to the spacecraft to block the debris. This will increase the mass of the lander and, therefore, reduce the mass of the payload by approximately 1 t."

So FOD is a significant issue. Other points to consider from this thread:

* Mars gravity only 38% of Earths so less thrust required on take off than on Earth
* Mars atmosphere only 1% of Earths so more gas dispersion than on Earth
* Longer landing legs move the engines further away from the surface
* Landing sites are likely to be covered with large quantities of very loose materials
* If a large enough angle can be achieved, engine gimbaling could be very useful in deflecting FOD
* Either berms will be needed or the BFS will need to land perhaps 1km from the habitat due to FOD
* Take off will require more thrust with full tanks and will be over a pit excavated by the decent engines
* It might be possible to place deflectors under the engines to mitigate problems at take off
* Difficult to test scenario due to Gravity / atmosphere differences between Mars and Earth

They'll bring a tiller, like from a vegetable garden.  Possibly a powerhead running that and a vibratory compactor. They will till in fiber and adhesive.  It is smoothed.  It sets, and problem solved.  Fiber, adhesive, and tools are all mass left behind.
« Last Edit: 03/20/2018 08:52 pm by tdperk »

Offline Lar

  • Fan boy at large
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 13463
  • Saw Gemini live on TV
  • A large LEGO storage facility ... in Michigan
  • Liked: 11864
  • Likes Given: 11086
Re: BFS Design Requirements
« Reply #70 on: 03/20/2018 11:34 pm »
This adhesive survives multiple landings and launches?  And can set up in a low pressure but high CO2 atmosphere?  Did you have a specific one in mind?

I think they will glassify things or put down mats. We'll find out.
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Online rakaydos

  • Senior Member
  • *****
  • Posts: 2825
  • Liked: 1869
  • Likes Given: 69
Re: BFS Design Requirements
« Reply #71 on: 03/21/2018 02:08 am »
This adhesive survives multiple landings and launches?  And can set up in a low pressure but high CO2 atmosphere?  Did you have a specific one in mind?

I think they will glassify things or put down mats. We'll find out.
Wasnt there an old topic talking about marscrete? How hard is that stuff to make in an automated enviroment?

Offline Slarty1080

  • Senior Member
  • *****
  • Posts: 2740
  • UK
  • Liked: 1871
  • Likes Given: 814
Re: BFS Design Requirements
« Reply #72 on: 03/21/2018 10:41 am »
The problem with marscrete would be too many uncertainties over the exact physical and chemical composition especially early on. I’m sure they will use that later, but on the first mission I’m not so sure.

One big issue is that the problem is hard to quantify. Where are we on the scale of 1 to 10 where 1 is take off from a smooth solid rock surface in a vacuum and 10 is take off from a desert demolition site on earth?

Other unknowns are how resilient the engines are to having rocks thrown at them at speed, the initial thrust and speed at lift off and the initial distance between the engines and the surface. Coupled with it being hard to test given 38% gravity and 1% atmosphere.

Anyone have any more ideas?
My optimistic hope is that it will become cool to really think about things... rather than just doing reactive bullsh*t based on no knowledge (Brian Cox)

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
Re: BFS Design Requirements
« Reply #73 on: 03/21/2018 05:51 pm »
Other unknowns are how resilient the engines are to having rocks thrown at them at speed, the initial thrust and speed at lift off and the initial distance between the engines and the surface. Coupled with it being hard to test given 38% gravity and 1% atmosphere.

Anyone have any more ideas?

You only care - for the initial vehicles - about 'will it explode or tip over'.
You do not care about relaunch, which makes things a little better.

There are many plausible approaches:
Pre-preparing the landing site using small robot vehicles or at least surveying in the synod previous to a landing.
Throwing out an ablative coated 9m diameter 'yoga mat' while traversing ballistically and then come back to it and land.
Land on parts of the various rover tracks that seem best.
Aerobrake into LMO and then throw out lots of sojourner class robots, in beagle 2 sized (70kg) entry packages, to do an immediate survey before landing.
Add landing engines at the top of the tanks of the vehicle canted out at 30 degrees, so nothing meaningful happens to the ground.
Yes, this would mean four engines, with a total thrust of some 100 tons for several seconds, and more complex piping.

There are no clearly obvious best solutions, especially with a cargo undefined beyond '150 tons of something'.


Offline wes_wilson

  • Armchair Rocketeer
  • Full Member
  • ****
  • Posts: 466
  • Florida
    • Foundations IT, Inc.
  • Liked: 542
  • Likes Given: 377
Re: BFS Design Requirements
« Reply #74 on: 03/26/2018 12:30 am »
The problem with marscrete would be too many uncertainties over the exact physical and chemical composition especially early on. I’m sure they will use that later, but on the first mission I’m not so sure.

One big issue is that the problem is hard to quantify. Where are we on the scale of 1 to 10 where 1 is take off from a smooth solid rock surface in a vacuum and 10 is take off from a desert demolition site on earth?

Other unknowns are how resilient the engines are to having rocks thrown at them at speed, the initial thrust and speed at lift off and the initial distance between the engines and the surface. Coupled with it being hard to test given 38% gravity and 1% atmosphere.

Anyone have any more ideas?

I wonder how much a launch cradle weighs?  Like the one used for BFR? And whether a BFS could carry a launch mount as a payload to Mars.  My assumption has always been that it would launch from the legs it lands on, but maybe that's not the case?  It's not using legs when it sits atop BFR before staging so maybe it takes off from a cradle at Mars. 
@SpaceX "When can I buy my ticket to Mars?"

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 39271
  • Minnesota
  • Liked: 25240
  • Likes Given: 12115
Re: BFS Design Requirements
« Reply #75 on: 03/26/2018 03:41 am »
Or just posts. Doesn’t have to be a full cradle at all. Could be really simple:

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 Nate_Trost

  • Member
  • Full Member
  • ****
  • Posts: 436
  • Liked: 47
  • Likes Given: 2
Re: BFS Design Requirements
« Reply #76 on: 03/26/2018 03:29 pm »
Has the ramifications of extensive composite use in BFS been discussed in terms of long-term radiation exposure through multiple Mars round trips? It immediately sprang to mind after the Roadster mission when there was talk about just how fast the carbon-fiber body of the Roadster was going to break down in the space environment.

Offline speedevil

  • Senior Member
  • *****
  • Posts: 4406
  • Fife
  • Liked: 2762
  • Likes Given: 3369
Re: BFS Design Requirements
« Reply #77 on: 03/26/2018 03:36 pm »
Has the ramifications of extensive composite use in BFS been discussed in terms of long-term radiation exposure through multiple Mars round trips? It immediately sprang to mind after the Roadster mission when there was talk about just how fast the carbon-fiber body of the Roadster was going to break down in the space environment.

The proper paint pretty much solves the degradation problem.
The issue is vacuum UV degrading the epoxy badly once the non-UV-rated paint flakes off.
With proper coating, it's pretty much not an issue.
There is no significant damage from other radiation.

Offline envy887

  • Senior Member
  • *****
  • Posts: 8144
  • Liked: 6801
  • Likes Given: 2965
Re: BFS Design Requirements
« Reply #78 on: 03/26/2018 03:53 pm »
Has the ramifications of extensive composite use in BFS been discussed in terms of long-term radiation exposure through multiple Mars round trips? It immediately sprang to mind after the Roadster mission when there was talk about just how fast the carbon-fiber body of the Roadster was going to break down in the space environment.

The proper paint pretty much solves the degradation problem.
The issue is vacuum UV degrading the epoxy badly once the non-UV-rated paint flakes off.
With proper coating, it's pretty much not an issue.
There is no significant damage from other radiation.
The entire BFS will be covered in TPS anyway. Even the back side will reach several hundred degrees C, so there will be little to no exposed or painted carbon fiber surfaces.

Tags:
 

Advertisement NovaTech
Advertisement Northrop Grumman
Advertisement
Advertisement Margaritaville Beach Resort South Padre Island
Advertisement Brady Kenniston
Advertisement NextSpaceflight
Advertisement Nathan Barker Photography
0