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.
Quote from: Proxima_Centauri on 03/11/2018 01:26 amQuote from: docmordrid on 02/21/2018 11:07 pmThere's no LAS on an airliner eitherAirliners are 10,000x safer than rockets, so adding a "LAS" would only decrease safety.Bingo.
Quote from: docmordrid on 02/21/2018 11:07 pmThere's no LAS on an airliner eitherAirliners are 10,000x safer than rockets, so adding a "LAS" would only decrease safety.
There's no LAS on an airliner either
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.
And ejection seats also aren’t very safe. They’d be a net reduction in safety if added to a typical airliner today.
Quote from: Robotbeat on 03/12/2018 12:27 pmAnd 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...
Quote from: Robotbeat on 03/11/2018 11:56 pmQuote from: Proxima_Centauri on 03/11/2018 01:26 amQuote from: docmordrid on 02/21/2018 11:07 pmThere's no LAS on an airliner eitherAirliners 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
The issue of FOD on Mars has been discussed in this thread:https://forum.nasaspaceflight.com/index.php?topic=37466.20Quote from reply #24ADDED: 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 recommendationsThe 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
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.
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?
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?
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.
Quote from: Nate_Trost on 03/26/2018 03:29 pmHas 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.