Suppose BFR has 30 engines on the first stage alone (FH will have 27). If BFR is developed first, as the very first application of Raptor, that means a huge probability of engine failure occurring at least once on a flight (in fact, I'd probably bet money on it... a little, not a lot)
Quote from: Robotbeat on 01/07/2015 01:07 amSuppose BFR has 30 engines on the first stage alone (FH will have 27). If BFR is developed first, as the very first application of Raptor, that means a huge probability of engine failure occurring at least once on a flight (in fact, I'd probably bet money on it... a little, not a lot)Huh? If you're expecting a failure in the first n flights of a 30-engine vehicle, you should also expect a failure in the first 3n flights of a 10-engine vehicle. It's the same number of engines flown. If there's going to be an engine failure in flight, there's going to be an engine failure in flight, and using a smaller number of engines just means it'll happen a little later.
BFR would be too powerful for LC39a. They'd need an entirely new launch complex, most likely.BFR may just be a step too far, with no near-term market need for that large of a vehicle. Mini-BFR, however, would be like a cost-optimized version of Falcon Heavy and could launch from 3 of their current 4 launch sites (as well as use their Texas test stand) and give Raptor a much nearer-term market, and with gradual improvements in thrust it could (like v1.0 to v1.1) organically grow along with the payloads (assuming larger payloads start appearing).I'm not saying it's a guarantee, just that it seems to be a credible next step. And it could certainly enable initial Mars settlement as well, as the Mars base is built up. And again, because it's much more optimized for cheap commercial launch than either FH or BFR, it'd also cement SpaceX's domination of the launch industry. (BFR would leave an opening for a better-optimized RLV which could still compete in the high-revenue Ariane5/Proton market.)
Development of any new RLV by spacex will be far more difficult and costly than the Falcon family, as it will need to be proven as an RLV to be marketable.
Quote from: Robotbeat on 01/06/2015 11:46 pm...because it's much more optimized for cheap commercial launch than either FH or BFR, it'd also cement SpaceX's domination of the launch industry. (BFR would leave an opening for a better-optimized RLV which could still compete in the high-revenue Ariane5/Proton market.)What do you see as the big differences in op costs (key driver's and guess of their cost difference) between the truly Big FR (aka transorbital railroad), and the smaller rocket you're suggesting? As you know, I lean strongly toward a "millions of colonists sooner" approach; whatever form that may take.
...because it's much more optimized for cheap commercial launch than either FH or BFR, it'd also cement SpaceX's domination of the launch industry. (BFR would leave an opening for a better-optimized RLV which could still compete in the high-revenue Ariane5/Proton market.)
You'd get some awful drag losses for the first stage with that kind of design.
I will repeat my suggestion from upthread -- why not just launch a partly-fueled BFR with only some of the Raptors lit? (So that the ~15 Mlbf BFR can launch from the 12.5 Mlbf maximum capacity 39A -- let's say that 24 of the 30 engines light up when launching from 39A.) The PMF would be worse due to unused engines and tankage, but you would have lots of spare capacity, so it doesn't matter all that much, other than some extra propellant being used over a 9-Raptor design.
Quote from: GWH on 01/07/2015 01:26 pmDevelopment of any new RLV by spacex will be far more difficult and costly than the Falcon family, as it will need to be proven as an RLV to be marketable.That's your assumption and not a fact. If the hypothetical RLV has lower overall operating costs AND lower one-time use costs than an F9 or FH with an equivalent feature set (e.g. payload), then depending on your time horizon for a net present value calculation, it may be entirely worth it to invest in its development.
it'd also cement SpaceX's domination of the launch industry. (BFR would leave an opening for a better-optimized RLV which could still compete in the high-revenue Ariane5/Proton market.)