SpaceX Dragon 2 Updates and Discussion - Thread 3

[Danderman]

Question: the Dragon specs say that an extension to the trunk can be flown, but has one actually flown? What is the mass penalty for flying the extension?

[woods170]

Question: the Dragon specs say that an extension to the trunk can be flown, but has one actually flown? What is the mass penalty for flying the extension?

No trunk extension has flown to date. NASA has had no need for extended trunks so far.

[RoadWithoutEnd]

Here's a fun thought regarding the application of Dragon 2: With Demo-2 and Crew-1, SpaceX is technically on an exponential growth curve for the metric people/year (2 astronauts, then 4).  All they have to do to maintain that growth rate is launch two 4-person flights in 2021 (one is already scheduled NET March), and average to a quarterly flight in 2022 (which may be doable regardless of the NASA schedule if private flights commence).

If that happens, it would be challenging to continue the trend past 12 people per year unless Starship is flying with crew by then, but 2023 sounds reasonable for that if Elon Musk's statements aren't too optimistic.  Especially if SpaceX flies Dragon 2 and Starship in parallel while the latter is developing.

[Vettedrmr]

I think you'll find the overall throttle to crew rate to/from ISS to be the ISS itself.

[RoadWithoutEnd]

I think you'll find the overall throttle to crew rate to/from ISS to be the ISS itself.

That only necessarily throttles NASA missions.  Nothing says a Dragon has to take people to ISS.  It's a spacious craft even by itself. 

Also, even before Starship is equipped to launch humans, it may be equipped to serve as habitable volume in-space for Dragons to dock to.  Though this is speculative, since I haven't seen anything discussed about it. 

[Vettedrmr]

That only necessarily throttles NASA missions.  Nothing says a Dragon has to take people to ISS.  It's a spacious craft even by itself.

Yeah, that's my bad.  I assumed that you were discussing ISS flights; clearly you weren't.  It's going to be a very interesting transition when private orbital flights commence (regardless of going to ISS or not).

I hope to see a private space station in the next 10 years or so.

Have a good one,
Mike

[cohberg]

Some photos of the 2 fin cargo trunk

[Danderman]

Some photos of the 2 fin cargo trunk

It looks like there is plenty of room in the trunk for an extended module. Unfortunately, the Nanoracks module is constrained by the available volume at the end of Node 3.

[docmordrid]

No trunk extension has flown to date. NASA has had no need for extended trunks so far.

It looks like there is plenty of room in the trunk for an extended module.

Huh, I had never bothered to compare the D1 and D2 trunk dimensions. I was wondering why Bishop looked so spacious in D2 trunk vs D1 trunk. Do we have official sources for the dimensions on both trunks?
>

From the DragonLab datasheet, Dragon 1 had a Standard Trunk of 14 cu/meters and an Extended Trunk option of 34 cu/meters.

https://web.archive.org/web/20110104010401if_/http://www.spacex.com/downloads/dragonlab-datasheet.pdf

SpaceX's current Dragon 2 page lists a Trunk volume of 37 cu/meters, so it's received quite a stretch.

https://www.spacex.com/vehicles/dragon/

[cohberg]

SpaceX's current Dragon 2 page lists a Trunk volume of 37 cu/meters, so it's received quite a stretch.

I don't think that you can compare volumes (of the D1 extended trunk and D2's trunk) and conclude that D1's extended trunk is longer.

Remember that the D1 trunk diagrams had the huge keep out envelope for the S2 that wasn't observed (see BEAM / Bishop) and the solar panel mounts cut into the cylinder sides. D2's trunk is actually fully cylindrical.

[joseph.a.navin]

I am surprised that the Cargo Dragon V2 does not have extra TPS where the SuperDracos would be on a Crew Dragon.

[Asteroza]

Wait, is a D2 trunk extension even being offered? We know that Elon in the past offered a D1 extended trunk publicly if anyone needed it.

[Alexphysics]

I am surprised that the Cargo Dragon V2 does not have extra TPS where the SuperDracos would be on a Crew Dragon.

That TPS is only there for the Super Dracos. Without the TPS, they would likely end up burning through the structure... not a desirable outcome

[russianhalo117]

Wait, is a D2 trunk extension even being offered? We know that Elon in the past offered a D1 extended trunk publicly if anyone needed it.

AFAIU it is a long lead option. Before IROSA they were studying an extension to fly replacement SAW's as a unit. When retracted and locked the Blanket boxes supposedly could be R&R'd through releasing from the mast canister. I don't have the file anymore but might still exist. Cygnus ULC version was the alternative delivery and disposal method flying 2 channels of SAW's at a time one on each side of the ULC. Would have required a 5m fairing for the later option.

[docmordrid]

SpaceX's current Dragon 2 page lists a Trunk volume of 37 cu/meters, so it's received quite a stretch.

I don't think that you can compare volumes (of the D1 extended trunk and D2's trunk) and conclude that D1's extended trunk is longer.

Remember that the D1 trunk diagrams had the huge keep out envelope for the S2 that wasn't observed (see BEAM / Bishop) and the solar panel mounts cut into the cylinder sides. D2's trunk is actually fully cylindrical.

ISTM all those specs were listing net usable volume. Why would they change it between D1 and D2?

[yg1968]

https://twitter.com/genejm29/status/1334980748009484288

[cohberg]

Finally got around counting solar cells on D2's trunk to answer the question "why do they need fins on the cargo dragon".

Crew Dragon has 1810 cells
Cargo Dragon has 1822 cells
Cargo Dragon (with no fins [theoretical]) would have 1680 cells

So, an theoretical un-finned D2 has ~8% less solar cells. Additionally, the cells on the fin have the smallest solar zenith angle in sun pointing mode so presumably the net power generation loss would be over 8%.

[intrepidpursuit]

Have we determined why Dragon 2 Falcon landed on a drone ship? Is it heavy enough to cross the threshold where that is required, or flying the shallow profile of the crew dragon for better passive abort options? Dragon flights were always a great chance to see a land landing (which are spectacular) so if those are a thing of the past it will be sad.

[gongora]

It's heavy.  Dragon doesn't fly a shallow profile.

[yg1968]

See below:

NASA says SpaceX is now on the hook for nine CRS-2 missions, three more than the guaranteed minimum of six.

NASA signed a new cargo delivery contract with SpaceX for at least six upgraded Cargo Dragon space station flights in 2016. A NASA spokesperson said in November that the resupply contract has been extended to cover nine Cargo Dragon missions.

https://twitter.com/StephenClark1/status/1335678224253263876