Quote from: TrevorMonty on 10/03/2014 07:39 pmCan the F9 deliver 2 dragons at once i.e stacked on top of each other. Once in orbit the dragons would fly separately.I doubt Dragon V2 has been designed to carry a payload on top of itself (i.e. another Dragon). That's a lot of load, and no obvious ways to elegantly (i.e. without a lot of extra weight) stack two inline. Even if you used Falcon Heavy I'm not sure why this would be a good idea...
Can the F9 deliver 2 dragons at once i.e stacked on top of each other. Once in orbit the dragons would fly separately.
The lack of ports may not be a problem as 2nd dragon with non-perishable supplies can stay in orbit free flying for a few weeks until the first dragon leaves. Unfortunately stacking 2 dragons on top of each doesn't' look feasible.
...Agree. Seems a simpler way for SpaceX to provide additional pressurized up volume and also allow for pressurized disposal would be a pressurized module in the Dragon trunk. If I read the dimensions right, something similar in size to standard Cygnus PCM (~2.6x3.1m) would fit inside the extended trunk (~3.1x3.6m), give or take a bit. Presumably similar could be done with CST-100 if they get rid of the LAS hardware for cargo flights, altho not sure of the resulting dimensions of such a CST-100 trunk. That might also provide additional freedom of design and operation by allowing a mix of docking/NDS and berthing/CBM for both Dragon and CST-100. Edit: Although of course such "dual pressurized" missions would also require the simultaneous use of two ports, which may be an issue.
Do we have any info on the interior dimensions of the Dragon V2 trunk?
Besides consuming manhours the docking ports are only rated for a relatively small number of cycles and they want to extend the station life. Presumably without bringing up more ports.
Quote from: TrevorMonty on 10/04/2014 01:54 amThe lack of ports may not be a problem as 2nd dragon with non-perishable supplies can stay in orbit free flying for a few weeks until the first dragon leaves. Unfortunately stacking 2 dragons on top of each doesn't' look feasible.However, even if feasible, that would not necessarily satisfy NASA's objective of minimizing the number of cargo missions/yr--with a minimum of four--where "missions" equates to "number of ISS cargo vehicle visits per year" (not the number of launches).NASA wants to minimize visiting vehicle traffic operations overhead, which currently consumes about 27% of available crew time (including both crew and cargo operations), and which detracts from other crew time (e.g., time available for utilization and research, which NASA wants to maximize).
IIRC the minimum NDS design cycle count is ~50, but I can't find a reference. Do you have a reference? If ~50 is the right number, and assuming all cargo and crew missions use NDS (unlikely IMHO), then at 6/yr (4 cargo + 2 crew), that would be > 8 years--assuming they all use the same port (extremely unlikely)--or by the time CCtCap and CRS-2 are in effect, around 2026 before the nominal life of a single port is exhausted.
The due date for the proposals for CRS2 has been pushed back to December 2nd (it was previously November 14th). This was announced yesterday. I don't know if this is related to yesterday's accident on Orbital's CRS-3 flight. http://procurement.jsc.nasa.gov/crs2/
Orbital noted that their CRS2 proposal had Antares with its new engine (Rd180, I believe), so if NK-33 is implicated, it may not affect their CRS2 bid as much as you might think.
@pbdesOrbital Sciences: If our negs w/ ULA for access to Russian RD-180 engine fail, we can refile our antitrust lawsuit against ULA.
The replacement engine is likely to be an RD181 not ULA's RD180. Almost same engine as far I know. There was a Russian website article (early this year) stated they will be supplying RD181s to Orbital in 2016.
Plus, no CCiCap competitor offered more than 16m³ of volume. Enhanced Cygnus (the 3-segment pressurized module version that would fly from CRS-4 onwards), is 26m³, and the proposed "SuperCygnus" version (with 4 segment pressurized module) would have 33.5m³. Of course either Atlas V 501, Delta IV M+(5,2) or even Falcon 9 v1.1 could fit within existing fairing and with a lot of mass margin. They could take up to 4 tonnes of cargo per trip with that configuration. With that they could cover their CRS1 contract in just five launches. The nice thing of flying Cygnus on Atlas V is that ISS would be fully redundant on crew and cargo but still get a nice level of orders for each system. I guess it would require 3 Cargo Dragon, 1 Crew Dragon, 2 Cygnus and 1 CST-100. That's 4 x Falcon 9 per year and 3 x Atlas V. They could get a nice discount on that. Specially since its contracted through commercial means and thus SpaceX, Orbital and Boeing will fight for the best price.
