That's the spirit! It's detailed analyses like these what really contributes to this thread, as opposed to empty speculation.Well, I guess the matter is settled, then.
Quote from: nomadd22 on 02/20/2009 05:20 pm[ Looking at Spacex's prices, going from 3500kg to 5000kg gto is about a 60% jump in price, that is because they can't reuse the upperstage
[ Looking at Spacex's prices, going from 3500kg to 5000kg gto is about a 60% jump in price,
Noone does prevent you from calculating. Sometimes things are so way off, you don't need to calculate exactly to see something is wrong.
Quote from: Jim on 02/20/2009 05:56 pmthat is because they can't reuse the upperstageI though re-use was not accounted in the stated price list?
that is because they can't reuse the upperstage
Given that SeaLaunch's original capacity to GTO was 5 tons, launched on a Saturn class, 3 stage vehicle sitting on the Equator, its hard to imagine that a 2 stage vehicle with lower ISP, launched from Florida, would provide 4.5 tons to GTO. These numbers just don't make sense.
The Saturn IB was a two stage vehicle with a empty weight of 54500 lb. The first stage was an RP-1/LOX fuelled stage, the second stage was LH2/LOX S-IVB stage common to the Saturn V launcher. Its payload was 18.6 metric tons, not 5 tons, to a 185 mile orbit with 28 degree inclination. A 5 ton payload vehicle is not a Saturn-class launcher.
Incredible claims require incredible proof.
Here's a comparable LV, do they hold up using Ed's formulas?Zenit-2: (data from Astronautix.com)Stage 1Gross Mass: ~354 tonnesPropellant Mass: ~325 tonnes (mass fraction = 92%)Thrust: 835 tonnes S/L, (doesn't give) tonnes vacuumISP: 309 sec S/L, 337 sec vacuumStage 2Gross Mass: ~90 tonnesPropellant Mass: ~81 tonnes (mass fraction = 90%)Thrust: 93 tonnes vacuumISP: ~349 sec vacuumPayload: 13.5 tonnes (to 51.6 degrees)Delta-V: 9150-9200 m/s plus 200 m/sGross Liftoff Weight: 459 tonnes
Quote from: William Barton on 02/20/2009 05:59 pmQuote from: Jim on 02/20/2009 05:56 pmthat is because they can't reuse the upperstageI though re-use was not accounted in the stated price list?The current price is not accounting possible reuse AFAIK, but you're effectively paying for denying them any chance of 2nd stage recovery as I understand it - using up all available propellant in the launch.
I will eat my hat and post pictures of it the day someone reuses an ELV 2nd stage.
Jon makes a good point that mass fraction is the end variable to evaluate. Not unlike the DIRECT teams EDS mass fraction that is questioned by some.I do wish SpaceX well but I'll have to see it work before I believe it.
Quote from: wannamoonbase on 02/20/2009 08:03 pmI will eat my hat and post pictures of it the day someone reuses an ELV 2nd stage.Half of the second stages could be refuelled and used as Earth departure stages. They will need a restartable engine and to fly to a propellant depot.
Quote from: Danderman on 02/20/2009 04:50 pmGiven that SeaLaunch's original capacity to GTO was 5 tons, launched on a Saturn class, 3 stage vehicle sitting on the Equator, its hard to imagine that a 2 stage vehicle with lower ISP, launched from Florida, would provide 4.5 tons to GTO. These numbers just don't make sense.Its about the mass ratio of the vehicle.
The initial flights of the Falcon 9, currently planned in 2009 and 2010, use the Falcon 9 Block 1.Beginning in late 2010/early 2011, SpaceX will begin launching the Falcon 9 Block 2. Block 2features increased engine thrust, decreased launch vehicle dry mass, and increased propellantload ‐ combined with lessons learned from the flights of the Falcon 9 Block 1. This results inincreased mass‐to‐orbit performance for the Falcon 9 Block 2 when compared with Block 1performance.
Stage 2Gross Mass: ~46 tonnesPropellant Mass: ~43 tonnesThrust: 48.99 tonnes vacuumISP: ~340 sec vacuum
I just read the F9 User manual that the 2nd stage burns for 345 seconds. With an ISP of 340 and a thrust of 49 tons, that means that the propellant *consumed* during the burn must be > 49 tons. Since your gross mass for the stage is 46 tons, something is off here.