SpaceX Dragon 2 Updates and Discussion - Thread 3

[Lars-J]

None of those principals are in dispute but no one is answering (and perhaps no one here is able to answer) my question
Yes the Dracos and Super Dracos use the same propellants.
Yes they share propellant distribution and storage systems.
Yes  Cargo Dragon will use same parachute design as Crew Dragon.
But there is no reason to add three tons of propellant that Cargo Dragon cannot burn.
Edit: Yes darkenfast: “that amount COULD be left off the mission.”
One of the advantages of storable propellants ( that weighs against their toxicity) is that they can be metered and don’t boil off. It would be simple to stop the fueling 2500 kg or do short of full.

Yes, we cannot answer all that. But I still want to know the source of YOUR assertion here, that there are 3 tons of propellant that the Cargo dragon cannot burn. You just admitted that they share the same propellant system and tanks, so why is the "abort propellant" not usable for a cargo dragon mission? What is the source of that claim??

[r8ix]

None of those principals are in dispute but no one is answering (and perhaps no one here is able to answer) my question
Yes the Dracos and Super Dracos use the same propellants.
Yes they share propellant distribution and storage systems.
Yes  Cargo Dragon will use same parachute design as Crew Dragon.
But there is no reason to add three tons of propellant that Cargo Dragon cannot burn.
Edit: Yes darkenfast: “that amount COULD be left off the mission.”
One of the advantages of storable propellants ( that weighs against their toxicity) is that they can be metered and don’t boil off. It would be simple to stop the fueling 2500 kg or do short of full.

Yes, we cannot answer all that. But I still want to know the source of YOUR assertion here, that there are 3 tons of propellant that the Cargo dragon cannot burn. You just admitted that they share the same propellant system and tanks, so why is the "abort propellant" not usable for a cargo dragon mission? What is the source of that claim??

Not to speak for the other poster, but I think the implication was that if you use the propellant for abort, you don't need it for RCS, and if you don't abort, you use it for RCS, so either way, you need about the same amount.

[Lars-J]

None of those principals are in dispute but no one is answering (and perhaps no one here is able to answer) my question
Yes the Dracos and Super Dracos use the same propellants.
Yes they share propellant distribution and storage systems.
Yes  Cargo Dragon will use same parachute design as Crew Dragon.
But there is no reason to add three tons of propellant that Cargo Dragon cannot burn.
Edit: Yes darkenfast: “that amount COULD be left off the mission.”
One of the advantages of storable propellants ( that weighs against their toxicity) is that they can be metered and don’t boil off. It would be simple to stop the fueling 2500 kg or do short of full.

Yes, we cannot answer all that. But I still want to know the source of YOUR assertion here, that there are 3 tons of propellant that the Cargo dragon cannot burn. You just admitted that they share the same propellant system and tanks, so why is the "abort propellant" not usable for a cargo dragon mission? What is the source of that claim??

Not to speak for the other poster, but I think the implication was that if you use the propellant for abort, you don't need it for RCS, and if you don't abort, you use it for RCS, so either way, you need about the same amount.

Exactly, that is what I have been arguing. The propellant is used either for abort or RCS. Never both. So I'm just trying to understand where this 3 tons comes from.

[whitelancer64]

None of those principals are in dispute but no one is answering (and perhaps no one here is able to answer) my question
Yes the Dracos and Super Dracos use the same propellants.
Yes they share propellant distribution and storage systems.
Yes  Cargo Dragon will use same parachute design as Crew Dragon.
But there is no reason to add three tons of propellant that Cargo Dragon cannot burn.
Edit: Yes darkenfast: “that amount COULD be left off the mission.”
One of the advantages of storable propellants ( that weighs against their toxicity) is that they can be metered and don’t boil off. It would be simple to stop the fueling 2500 kg or do short of full.

Yes, we cannot answer all that. But I still want to know the source of YOUR assertion here, that there are 3 tons of propellant that the Cargo dragon cannot burn. You just admitted that they share the same propellant system and tanks, so why is the "abort propellant" not usable for a cargo dragon mission? What is the source of that claim??

Not to speak for the other poster, but I think the implication was that if you use the propellant for abort, you don't need it for RCS, and if you don't abort, you use it for RCS, so either way, you need about the same amount.

Exactly, that is what I have been arguing. The propellant is used either for abort or RCS. Never both. So I'm just trying to understand where this 3 tons comes from.

Since Cargo Dragon 2 has no Super Dracos and thus cannot abort, there is no reason for it to carry the reserves of fuel that is needed on the Crew Dragon 2 for abort.

Yes, the "abort" fuel is also used for RCS, however, since Dragon 2 was originally designed to propulsively land - after using RCS fuel on a nominal mission - then does it not still carry to landing a large load of otherwise not needed fuel?

Or has SpaceX now removed the landing fuel reserves from Dragon 2?

IIRC Elon Musk has said it could still propulsively land, in theory, even though SpaceX has ceased development on doing so. This implies that Dragon 2 still carries sufficient fuel reserves for landing.

AIUI, the main question is, does Cargo Dragon 2 still carry those reserves even though it lacks Super Dracos completely?

[Lars-J]

Exactly, that is what I have been arguing. The propellant is used either for abort or RCS. Never both. So I'm just trying to understand where this 3 tons comes from.

Since Cargo Dragon 2 has no Super Dracos and thus cannot abort, there is no reason for it to carry the reserves of fuel that is needed on the Crew Dragon 2 for abort.

Yes, the "abort" fuel is also used for RCS, however, since Dragon 2 was originally designed to propulsively land - after using RCS fuel on a nominal mission - then does it not still carry to landing a large load of otherwise not needed fuel?

Or has SpaceX now removed the landing fuel reserves from Dragon 2?

The "landing fuel reserves" have certainly been removed, it would be shocking if otherwise. And I think it happened many years ago, when propulsive landing was rejected. The idea that would still be holding on to those fuel reserves when the feature no longer exists is absurd. (talk about intentionally reducing your payload)

So again... The 3 extra tons of fuel. @Comga, where is it coming from?

IIRC Elon Musk has said it could still propulsively land, in theory, even though SpaceX has ceased development on doing so. This implies that Dragon 2 still carries sufficient fuel reserves for landing.

It implies no such thing, if those propellant reserves have been allocated to increased capability or Crew Dragon has grown in mass since the original estimate.

[whitelancer64]

Exactly, that is what I have been arguing. The propellant is used either for abort or RCS. Never both. So I'm just trying to understand where this 3 tons comes from.

Since Cargo Dragon 2 has no Super Dracos and thus cannot abort, there is no reason for it to carry the reserves of fuel that is needed on the Crew Dragon 2 for abort.

Yes, the "abort" fuel is also used for RCS, however, since Dragon 2 was originally designed to propulsively land - after using RCS fuel on a nominal mission - then does it not still carry to landing a large load of otherwise not needed fuel?

Or has SpaceX now removed the landing fuel reserves from Dragon 2?

The "landing fuel reserves" have certainly been removed, it would be shocking if otherwise. And I think it happened many years ago, when propulsive landing was rejected. The idea that would still be holding on to those fuel reserves when the feature no longer exists is absurd. (talk about intentionally reducing your payload)

So again... The 3 extra tons of fuel. @Comga, where is it coming from?

Then any talk of Dragon 2 still being "theoretically" capable of propulsive landing is nonsense. Good to know.

[Lars-J]

Then any talk of Dragon 2 still being "theoretically" capable of propulsive landing is nonsense. Good to know.

What I'm trying to get across is that just because Elon once said it supports in theory does NOT mean that it supports it practice, right now. (this is your leap of logic) One does not imply the other at all, after years of development.

Do you really think that they would launch with landing propellant when A) NASA rejected propulsive landing years ago, and B) they could use that for extra cargo margin instead, and C) needlessly make the re-entry much more unsafe with tons of extra propellant (3 tons?) as "ballast"?

[John Santos]

None of those principals are in dispute but no one is answering (and perhaps no one here is able to answer) my question
Yes the Dracos and Super Dracos use the same propellants.
Yes they share propellant distribution and storage systems.
Yes  Cargo Dragon will use same parachute design as Crew Dragon.
But there is no reason to add three tons of propellant that Cargo Dragon cannot burn.
Edit: Yes darkenfast: “that amount COULD be left off the mission.”
One of the advantages of storable propellants ( that weighs against their toxicity) is that they can be metered and don’t boil off. It would be simple to stop the fueling 2500 kg or do short of full.

Yes, we cannot answer all that. But I still want to know the source of YOUR assertion here, that there are 3 tons of propellant that the Cargo dragon cannot burn. You just admitted that they share the same propellant system and tanks, so why is the "abort propellant" not usable for a cargo dragon mission? What is the source of that claim??

Not to speak for the other poster, but I think the implication was that if you use the propellant for abort, you don't need it for RCS, and if you don't abort, you use it for RCS, so either way, you need about the same amount.

Exactly, that is what I have been arguing. The propellant is used either for abort or RCS. Never both. So I'm just trying to understand where this 3 tons comes from.

#Jim: No.

They need MUCH more fuel for an abort than they would for normal orbital maneuvering (including rendezvous, docking, and de-orbiting).  Like 10 to 20 times as much.  On a crewed flight, if there isn't a Super Draco-propelled ascent abort, there is tons of excess fuel on board once they reach orbit.  This is an issue with EDL and the parachute system design; it has to handle this excess mass, or dump the excess fuel before (or after but before the parachutes open) re-entry.  This subject came up during Demo-1 and Demo-2, but I don't think either SpaceX or NASA supplied a clear answer.  I THINK they decided to keep the fuel on board and land with it (which might have been part of the reason for all the attention they paid to possible fuel vapor around the capsule when Demo-2 landed.)

Anyway, with no Super Dracos, it would take many minutes to burn off all the extra propellant through the regular Dracos, and I haven't heard of any plans to do this.  They could, in theory, maybe, boost the payload capacity of cargo Dragon-2 by launching it into a suborbital trajectory and then using the Dracos to boost it the rest of the way to orbit, much like the shuttle used the OMS burn to do the same thing after dropping the ET.  I doubt this method would net much additional payload mass, given gravity losses and the low thrust of the Dracos (despite their much higher ISP than the Super Dracos.)  However, according to many sources, the cargo Dragon is volume-limited, not mass-limited so doesn't need this anyway.

My guess is they have removed (i.e. never installed) the Super Dracos and associated valves and plumbing, capped off the SD pipes, and will short-fill the tanks with only as much propellant as they will need, with some margin, of course.

[Comga]

Then any talk of Dragon 2 still being "theoretically" capable of propulsive landing is nonsense. Good to know.

What I'm trying to get across is that just because Elon once said it supports in theory does NOT mean that it supports it practice, right now. (this is your leap of logic) One does not imply the other at all, after years of development.

Do you really think that they would launch with landing propellant when A) NASA rejected propulsive landing years ago, and B) they could use that for extra cargo margin instead, and C) needlessly make the re-entry much more unsafe with tons of extra propellant (3 tons?) as "ballast"?

We might be "in violent agreement".
In the very beginning, Crew Dragon had integral abort motors that would be used for propulsive landing at the end of a nominal mission.
The fuel was either used for abort or for ground landing, which were mutually exclusive on any single flight.
There was and is a single propellant system shared by Dracos for maneuvering and Super Dracos for abort or landing.
Because Crew Dragon does just as much on-orbit maneuvering as Cargo Dragon, the propellant system was designed to carry both allotments. 
We don't need to rehash how and why propulsive landing was abandoned.
The systems remain in place on Crew Dragon to provide launch abort capability.
The Super Dracos are not installed on Cargo Dragon 2.
While some amount of propellants are needed for on orbit maneuvering, it much less than needed for aborting.
White Lancer and Lars-J agreed above that it makes no sense for SpaceX to load all that propellant that won't be used.
(I do not recall the source of the 3 ton value I wrote above. However, we can be sure it's a substantial mass.)
That's all this was about.
Cargo Dragon should have much less mass than Crew Dragon, ECLSS aside, because of the lack of Super Dracos and the propellants needed for an abort.

[whitelancer64]

Then any talk of Dragon 2 still being "theoretically" capable of propulsive landing is nonsense. Good to know.

What I'm trying to get across is that just because Elon once said it supports in theory does NOT mean that it supports it practice, right now. (this is your leap of logic) One does not imply the other at all, after years of development.

Do you really think that they would launch with landing propellant when A) NASA rejected propulsive landing years ago, and B) they could use that for extra cargo margin instead, and C) needlessly make the re-entry much more unsafe with tons of extra propellant (3 tons?) as "ballast"?

It's not a leap of logic. IIRC Elon Musk has said fairly recently that propulsive landing was still possible. IIRC this was said sometime shortly after the switch to burst disks, so not that long ago. This implies that Dragon 2 still carries reserves of landing fuel, or at the very least, has the tank capacity to do so.

If neither is the case, then propulsive landing is no longer even theoretically possible.

I agree (and always have) that it makes sense to not load the fuel tanks with excess fuel.

[russianhalo117]

How many more hours or days of email notifications of this back and forth shooting the breeze will I continue to receive. Just find the tweet and post it and be done of the squabbling and please move on to another non derailed topic.

[AS-503]

Then any talk of Dragon 2 still being "theoretically" capable of propulsive landing is nonsense. Good to know.

What I'm trying to get across is that just because Elon once said it supports in theory does NOT mean that it supports it practice, right now. (this is your leap of logic) One does not imply the other at all, after years of development.

Do you really think that they would launch with landing propellant when A) NASA rejected propulsive landing years ago, and B) they could use that for extra cargo margin instead, and C) needlessly make the re-entry much more unsafe with tons of extra propellant (3 tons?) as "ballast"?

It's not a leap of logic. IIRC Elon Musk has said fairly recently that propulsive landing was still possible. IIRC this was said sometime shortly after the switch to burst disks, so not that long ago. This implies that Dragon 2 still carries reserves of landing fuel, or at the very least, has the tank capacity to do so.

If neither is the case, then propulsive landing is no longer even theoretically possible.

I agree (and always have) that it makes sense to not load the fuel tanks with excess fuel.

Don't forget that the movable ballast sled that would be required for changing center of gravity from offset (for re-entry) to centered\symmetric (for landing) would be required for propulsive landing and is almost certainly not in any of these latest Dragon 2 vehicles. 

[whitelancer64]

Don't forget that the movable ballast sled that would be required for changing center of gravity from offset (for re-entry) to centered\symmetric (for landing) would be required for propulsive landing and is almost certainly not in any of these latest Dragon 2 vehicles.

I'm aware of that.

There's a solid source for mass of Dragon capsule at re-entry and that's

https://www.nasa.gov/feature/top-10-things-to-know-for-nasa-s-spacex-demo-2-return

"After trunk separation and the deorbit burn are complete, the Crew Dragon capsule weighs approximately 21,200 pounds." which is 9,615 kg.

[whitelancer64]

None of those principals are in dispute but no one is answering (and perhaps no one here is able to answer) my question
Yes the Dracos and Super Dracos use the same propellants.
Yes they share propellant distribution and storage systems.
Yes  Cargo Dragon will use same parachute design as Crew Dragon.
But there is no reason to add three tons of propellant that Cargo Dragon cannot burn.
Edit: Yes darkenfast: “that amount COULD be left off the mission.”
One of the advantages of storable propellants ( that weighs against their toxicity) is that they can be metered and don’t boil off. It would be simple to stop the fueling 2500 kg or do short of full.

Yes, we cannot answer all that. But I still want to know the source of YOUR assertion here, that there are 3 tons of propellant that the Cargo dragon cannot burn. You just admitted that they share the same propellant system and tanks, so why is the "abort propellant" not usable for a cargo dragon mission? What is the source of that claim??

Not to speak for the other poster, but I think the implication was that if you use the propellant for abort, you don't need it for RCS, and if you don't abort, you use it for RCS, so either way, you need about the same amount.

Exactly, that is what I have been arguing. The propellant is used either for abort or RCS. Never both. So I'm just trying to understand where this 3 tons comes from.

The "3 tons" number might come from the in-flight abort Environmental Assessment.

"Dragon would contain approximately 5,650 pounds [2.835 US tons) of hypergolic propellant, including approximately 3,500 pounds of dinitrogen tetroxide (NTO) and 2,150 pounds of monomethylhydrazine (MMH). Dragon would contain approximately 2,400 pounds of residual propellant after the abort test."

[Lars-J]

The "3 tons" number might come from the in-flight abort Environmental Assessment.

"Dragon would contain approximately 5,650 pounds [2.835 US tons) of hypergolic propellant, including approximately 3,500 pounds of dinitrogen tetroxide (NTO) and 2,150 pounds of monomethylhydrazine (MMH). Dragon would contain approximately 2,400 pounds of residual propellant after the abort test."

Thanks for that, a great find! 

That does suggest, however, that the abort propellant use is far lower than what most of us expect, if it uses ~60% of the available propellant. It does suggest that the on-orbit draco use is more than than the abort use (presumably they size the tanks for max use scenario). I did not expect that.

[dglow]

How many more hours or days of email notifications of this back and forth shooting the breeze will I continue to receive. Just find the tweet and post it and be done of the squabbling and please move on to another non derailed topic.

This isn’t an updates-only thread. If you feel you’re receiving too many email notifications, either 1) turn them off for this thread, or 2) switch to daily updates.

[whitelancer64]

I've been looking at the new interior photos of cargo Dragon 2 and wanted to peer review some observations

*snip*

New cargo rack layout

Dragon 2 appears to be a radical departure in design from Dragon 1's cargo racks. Instead of 4 racks and a central column, D2 is just 2 racks.

Due to that, D2 looks significantly easier to load with effectively just a couple levels to load (under floor, under rack (level where the workers are kneeling), rack level, and late load) verses the D1 which was many layers for each rack per side.

I'm assuming that the GLACIER's (2 or 4) are going to go in the "top level" (outlined in blue and purple). I'm basing this on:

The top shelf is reinforced with the supports (GLACIER's look heavier than normal CTB density) Is there a max weight for powered lockers similar to the max density numbers for CTBs?
The area around that is perforated for air circulation as the units reject heat into the atmosphere.
There are what appear to be power / data cables available.

Also any ideas on these studs? I'm thinking either a removable rack shelf panel that spans the 2 racks for more cargo (those black vertical supports look super over engineered otherwise).

Late load cargo

As there would presumably be cargo in the way of the GLACIER's (opposite side of the side hatch) I'm thinking that the entire red worker handhold / hatch protector gets removed and additional powered lockers gets installed in its place. This would be similar to D1's hatch late load items.

Also, does anyone want to speculate on the black X gridded boxes closest to the side hatch?

Floor

It looks like the 2 floor panels swing open (outlined in green and orange). Based on their size I think that 4 lockers can fit in each of the sections.

Additionally it looks like the black triangles are a latch release that allows the panel to swing open left or right

Lockers look to have displaced (relative to the crewed version) some of the ECLSS items. I'm thinking that of the 4 air / nitrox tanks from the crewed version only 1-2 needed to remain and were moved to the left. Obviously the CO2 scrubbing LIOH array can be removed as well as all the toilet systems.

I'm speculating that the dehumidifier was moved to the right as there is far more plumbing in the picture on the right. Additionally on the crewed version the vacuum lines, valves, etc.  for the dehumidifier are on the right

This has been commented on elsewhere, though I can't recall exactly where.

The largest ISS standard cargo bags can't fit through the IDSS compliant docking hatch. Therefore the largest bags cannot be loaded into Cargo Dragon 2, which changes the packing arrangements. I am of the understanding that (all else being equal) this results in more cargo being able to fit into Dragon 2 than the original Dragon.

All late load cargo will be through the side hatch while Dragon is vertical at the pad.

[cohberg]

This has been commented on elsewhere, though I can't recall exactly where.

I had posted about it upthread, not sure if you are referring to that.

The largest ISS standard cargo bags can't fit through the IDSS compliant docking hatch. Therefore the largest bags cannot be loaded into Cargo Dragon 2, which changes the packing arrangements. I am of the understanding that (all else being equal) this results in more cargo being able to fit into Dragon 2 than the original Dragon.

I agree that the M01 stack being removed likely influenced the new rack arrangement. I don't think that simply removing the central stack and rearranging within the D1 rack design lead to more volume being available. Those side racks left significant pressurized volume inaccessible between the rear of the rack and the pressure vessel wall. 

Sidenote: I have not been able to find any literature on allowable CTB stacking weight / height etc. There must have been a reason that SpaceX went with the 4 sided multi tiered rack layout with complex loading procedure.

Between the "open layout" of the new 2 rack layout (primary volume gain) and the other items that I had covered earlier (secondary / minor) is where most of the volume is regained.

All late load cargo will be through the side hatch while Dragon is vertical at the pad.

Agree and included in the earlier post. My point was more speculation on if SpaceX is going to continue to utilize the side hatch area for late load cargo (specifically powered + cryogenic payloads) like D1. The area above the hatch is "dead" space as the top hatch needs that area for actuation: curious to see how they utilize it.

[cohberg]

Occasionally I will check in on the latest flight packages from the JSC VR Lab for insights on hardware happening for the ISS.

With the latest Stage_63-3_v10 release, CRS-21's model is now updated to a Dragon 2 cargo model. It appears to show a trunk with only 2 fins (vs 4 on the crewed version for aborts)

This makes sense because there are solar panels on those fins. Deleting those fins would reduce the amount of solar generation capability.

This could be a low fidelity mockup that omitted the additional fins, but with the SSRMS is close proximity to the trunk I believe that they would have modeled the additional fins to verify that all planned robotic operations had sufficient clearance.

Additional screenshots are linked. You can also request access to the DOUG (Dynamic Onboard Ubiquitous Graphics) software via the link.

[cohberg]

Interesting thread with someone representing themselves as a SpaceX employee.

Takeaways (all unconfirmed but logical):

Pressure vessel assignments
CRS-21 - C208
CRS-22 - C209
Crew-3 - C210

There is a elevated tray that sits on the pins to span that “walkway” where the techs are in the photo. This explains the super heavy duty black column supports and makes loading and unloading easier.

The rear section opposite to the side hatch (the black grid with square cutouts) is for "accessories" (apparently for mounting cargo off the stack)