Your only allowing 900 m/s for all drag and gravity losses which looks to be too low by around 300 m/s as I can't find any vehicle with total losses of less then around 1200 m/s. That would drop your mass in LEO by about 25 mt and put the flight total at an even 8 which is roughly meeting in the middle of our earlier estimates. Alternatively stretching your vehicle will likely make up the difference.I'm willing to accept 8 as the best estimate for refueling flights needed to perform this all-chemical brute-force mission architecture when performing a fast crew transfer. Do you have an estimate for what could be sent on a slow cargo flight?P.S. Oops, 300 m/s is what you get from Earth rotation so looks good.
1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.
Quote from: Robotbeat on 06/13/2016 02:49 pm1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.That would indicate 30t of fuel is excessive for Earth EDL, as that's 0.85 to 1.0 km/s for a 100t tanker depending on the altitude/ISP. I don't anticipate anything with an orbital re-entry heatshield will do an entry burn (it's rather pointless in Earth's dense atmosphere), and terminal velocity on Earth will be under 200 m/s for a very large, relatively light vehicle.
Quote from: envy887 on 06/13/2016 03:02 pmQuote from: Robotbeat on 06/13/2016 02:49 pm1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.That would indicate 30t of fuel is excessive for Earth EDL, as that's 0.85 to 1.0 km/s for a 100t tanker depending on the altitude/ISP. I don't anticipate anything with an orbital re-entry heatshield will do an entry burn (it's rather pointless in Earth's dense atmosphere), and terminal velocity on Earth will be under 200 m/s for a very large, relatively light vehicle.Right. And you'll have enough thrust to do a high-thrust landing, which means low gravity losses.Also, 100t tanker is much too small.
Quote from: Robotbeat on 06/13/2016 03:03 pmQuote from: envy887 on 06/13/2016 03:02 pmQuote from: Robotbeat on 06/13/2016 02:49 pm1.2-1.5km/s is on the high end for EDL except if you decide to do a braking burn before entry.That would indicate 30t of fuel is excessive for Earth EDL, as that's 0.85 to 1.0 km/s for a 100t tanker depending on the altitude/ISP. I don't anticipate anything with an orbital re-entry heatshield will do an entry burn (it's rather pointless in Earth's dense atmosphere), and terminal velocity on Earth will be under 200 m/s for a very large, relatively light vehicle.Right. And you'll have enough thrust to do a high-thrust landing, which means low gravity losses.Also, 100t tanker is much too small.That's 100t dry. Would be 1200t or 1500t at launch.
100t dry is too high for a tanker, I think. And maybe try 1000t instead. And greater payload.
Phil, if I might ask, why do you have so much performance spec'ed into the upper stage?A fast (80-120 day) transfer to Mars rarely requires more than 4.5 to 5 km/s from LEO, but your numbers (1604t wet, 225t dry, 380 ISP) give 7.32 km/s of total performance with a 100t payload. Mars EDL will add somewhere in the 1.2 to 1.5 km/s range (I don't see an estimate in your spreadsheet), but even with that requirement your margins run from 12.6% to 28.4%. Since it can do a fast transfer and Mars EDL while only partly fueled, I get 4 to 5.5 refueling launches per fast Mars transfer.Earth return definitely can use that performance, but you don't include any numbers for that. By my estimates the poor alignments in the 2020's prevent even a 1604t wet, 125t dry vehicle from returning before the next synod's optimal launch window.
Quote from: Robotbeat on 06/13/2016 03:10 pm100t dry is too high for a tanker, I think. And maybe try 1000t instead. And greater payload.For a dedicated tanker which does not share the outer mould line of the BFS then 100 tonnes is too high (I reckon something like 70 tonnes, but SpaceX might be able to reduce that even more). However, the first tanker flights may not be a dedicated design, instead just standard BFS with extra fuel in their tanks and perhaps long duration equipment removed. Then 100 tonnes dry is probably a bit too little.Although a dedicated tanker design with all the excess mass removed would be cheaper in the long run, during BFR/BFS development it would be another craft competing for development funds and effort.
This other transaction agreement requires shared cost investment with SpaceX for the development of a prototype of the Raptor engine for the upper stage of the Falcon 9 and Falcon Heavy launch vehicles.
..."LEO esc 3.2Km/s + Fast transit ~1.7 Km/s + aerocapture + Mars landing 2Km/s ~ 7 Km/sec Delta V for 2nd stage MCT" Since I was sloppy and forgot to include the URL on my spreadsheet I'm not sure of the source. I was trying for the 7Km/sec to Mars and propellant tank volume for 8 something Km/sec for return from Mars with reduced payload, 25t, not 100t....
Or, this stage is a SpaceX long duration stage for bidding on the same contracts as Vulcan ACES.