Isn't the simplest solution to foreign object damage an engine that is robust enough to survive the odd pebble? And maybe some redundancy in case one engine breaks?I have a really hard time to imagine how something could enter an active combustion chamber against the flow of the combusted fuel.
I think the answer to this issue is landing on bedrock or somewhere else deemed reasonably safe.
Quote from: Oersted on 09/01/2016 12:04 pmI think the answer to this issue is landing on bedrock or somewhere else deemed reasonably safe. Is "landing on bedrock" compatible with ISRU, e.g. would you have access to water?
Isn't the simplest solution to foreign object damage an engine that is robust enough to survive the odd pebble? And maybe some redundancy in case one engine breaks?
Quote from: jpo234 on 09/01/2016 06:55 amIsn't the simplest solution to foreign object damage an engine that is robust enough to survive the odd pebble? And maybe some redundancy in case one engine breaks?The odd pebble?....So picture something with 2/3rd more power than what is depicted here, sitting on landing legs, a metre or two above hard flat surface. Even bedrock would spall. ...
But you can't test your engines before a launch into a direct Earth return trajectory, because there's no infrastructure that can withstand the test (or hold down the vehicle.)
Quote from: Paul451 on 09/02/2016 08:19 amBut you can't test your engines before a launch into a direct Earth return trajectory, because there's no infrastructure that can withstand the test (or hold down the vehicle.)Actually you could test the engines if they were sufficiently canted, and the ship was fully fuelled. For a T/W of 1 at launch, cos^-1(1/2. = 69.1°, so set the cant at 70° or more, and you could perform a short full thrust static fire.Admittedly, I have some trepidation regarding static fires at the moment.
Making the vehicle strong enough for a static fire in two different directions is a somewhat questionable design choice, even if we were to assume that the gimbals for canting posed no weight issues or technical unknowns.
I've tried to fit landing some methalox in, but even for a small portion of the vehicle (an 'escape pod'), the math doesn't work for return to orbit (much less return to Earth), it swamps other payload. If you could wring 4.5km/s out of an escape pod, you could return to MLO and a waiting lifeboat there for return to Earth. But that's too much. Landing mostly dry just works a lot better. Every kilogram of propellant landed reduces the ISRU gear landed by 1kg, which reduces the propellant generated by many kilograms per synod.Now... that's not to say landing *completely* dry is the preferred option. Liquid propellants are useful for a number of things other than full-on Mars ascent. Solar storm shielding, EDL mass redistribution maneuvers, and high-thrust RCS landing maneuvers are all made considerably easier if you pack a sizable quantity of, say, monomethyl hydrazine on board.
Who here still believes that some new pad at Cape Canaveral or some future pad at Boca Chica is still viable for BFR launches? Given the recent pad anomaly, I believe that more stringent safety zones will force the BFR to be launched off shore, assuming any US based launch site, which I do because of ITAR.There are shallow seas offshore from both SX launch sites. At first a platform could be anchored to the sea floor and serviced by barges and hydrofoils while launch rates remained low. A very expensive causeway could later be constructed to support higher flight rates.I do not feel that on shore launch remains an option assuming the BFR is really ~2x Saturn V size or more.The noise dB problem remains as RTLS sonic booms propagate tens of miles with little attenuation.
Who here still believes that some new pad at Cape Canaveral or some future pad at Boca Chica is still viable for BFR launches? Given the recent pad anomaly, I believe that more stringent safety zones will force the BFR to be launched off shore, assuming any US based launch site, which I do because of ITAR....
Quote from: philw1776 on 09/03/2016 05:09 pm...I do not feel that on shore launch remains an option assuming the BFR is really ~2x Saturn V size or more....I agree an offshore platform is the best option for the BFR we've been discussing. But with the schedule Elon mentioned there really isn't enough time to build a pad or platform before initial BFR testing. Maybe the BFR isn't going to be as big as we think. Perhaps the first generation BFS will be 50 tonnes cargo to Mars instead of 100 tonnes, requiring a BFR about the size of a Saturn V. That's still impressive. Pad 39A can handle that. We'll find out in a few weeks.
...I do not feel that on shore launch remains an option assuming the BFR is really ~2x Saturn V size or more....