SpaceX COTS Demo 2/3 Updates (THREAD 2)

[LegendCJS]

In layman’s terms, Dragon is likely to carry around 1,000lbs of various supplies – such as clothes and food – to the crew of the International Space Station.

I'm surprised they're sending lots of empty bags and only 1000 lbs of stuff. Why not fill the empty bags with jugs of water?

Volume constraints matter as well.  Apparently only a few (less than 4 iirc) of these empty, folded up bags can fit inside a regular bag/ cargo slot.  They need the empty bags for stuffing full of trash to make the best use of upcoming mass disposal opportunities from visiting vehicles.

[RocketJack]

In layman’s terms, Dragon is likely to carry around 1,000lbs of various supplies – such as clothes and food – to the crew of the International Space Station.

I'm surprised they're sending lots of empty bags and only 1000 lbs of stuff. Why not fill the empty bags with jugs of water?

If they don't carry max payload, then they have a much greater fuel margin.  In the event that orbital insertion is a bit off for some reason, that could be the difference between making it to the ISS or not.
It's a demo mission.  If all they bring up is a bag of M&Ms, but it does get there, then they hit all their performance goals for this flight.

I also figure their ideal down mass isn't maxed out either.

How do you know this isn't flying "max payload"?

At a guess, the reason for believing that C2/3 will be flying light is simply becaues of the nature of the mission.  The objective is to rendezvous and berth with the ISS, not deliver the maximum payloayd to the station.  Because of that, you will want to maximise your chances of reaching the ISS and being able to carry out the required proximity ops.  That means maximum margin on launcher and RCS delta-v and that means low-mass.

I have no doubt that, as they gain confidence with the vehicle, the mass numbers will go up towards the nominal maximums, but not before Merlin-1d is in service.

I don't think we know what the payload capability is. The website says 6000 kilograms. However, on this flight we had Orbcomm being deployed above, then below, then off. New trajectory software was needed. Then the discussion about "special ISS conditions" for plane and altitude. Now there is a reduced cargo. Does SpaceX stick with the 6000kg to ISS? There is a big difference between 6000 and 450 (i am assuming the 1000 lbs stated above is correct, i haven't seen it documented). That is what, 7.5% of stated payload capability? It will be interesting to see if the COTS agreement specified number of flights or kilos to orbit...

[deltaV]

Apparently only a few (less than 4 iirc) of these empty, folded up bags can fit inside a regular bag/ cargo slot.  They need the empty bags for stuffing full of trash to make the best use of upcoming mass disposal opportunities from visiting vehicles.

You can fit several hundred ordinary plastic trash bags on a compact roll that's smaller than a single full bag. Why does NASA need such bulky bags for trash disposal?

[Jim]

Trash bags outgas
Trash bags don't contain decomposition gases
Trash bags don't hold shape
Trash bags can't hold heavy objects

[Jim]

Trash bags rip
Trash bags don't fit in the cargo restraint systems

[Antares]

It will be interesting to see if the COTS agreement specified number of flights or kilos to orbit...

See for yourself
http://www.nasa.gov/centers/johnson/news/contracts/cots.html

[neilh]

Apparently only a few (less than 4 iirc) of these empty, folded up bags can fit inside a regular bag/ cargo slot.  They need the empty bags for stuffing full of trash to make the best use of upcoming mass disposal opportunities from visiting vehicles.

You can fit several hundred ordinary plastic trash bags on a compact roll that's smaller than a single full bag. Why does NASA need such bulky bags for trash disposal?

Sorry DeltaV, i know you actually do pay attention but this is a 'Nuspace amazing people' post that impressively represents an entire genre of posts in only 2 sentences. Yet it contains:
-1.false and irrelevant parallel between everyday life and spaceflight (kitchen trashbags=/=cargo bags. Not on a ship, airliner, ambulance, or any other kind of professional transport.)
-2.assumption that traditional spaceflight is overengineered for no real good reason. Bags have to be tough, properly secured, and weight distributed reasonably so that attitude control and spacecraft dynamics are within capability of GNC/RCS to keep it smooth IVO station and for deorbit.
3. Rhetorical question that implies NASA is kloo-less and hidebound. No, NASA sets standards such that a few hundred dollars worth of (reusable possibly) cargo bags to ensure a 100 millions$ spacecraft doesn't destroy a $100 billion spacestation. Standards that Bigelow Aerospace would likely also require, BTW.

Huh, maybe we read it differently, but I thought it was an honest question. I was glad to have read Jim's informative answer.

[Mike_1179]

An honest question would have involved a "question" such as "Why are such large bags needed and not something more lightweight like a common kitchen trash bag?"  When asked the way it was, it implies all that cuddihy states - that those who currently build and operate rockets and spacecraft have no common sense and spend money without regard. 

[subzero788]

I don't think we know what the payload capability is. The website says 6000 kilograms. However, on this flight we had Orbcomm being deployed above, then below, then off. New trajectory software was needed. Then the discussion about "special ISS conditions" for plane and altitude. Now there is a reduced cargo. Does SpaceX stick with the 6000kg to ISS? There is a big difference between 6000 and 450 (i am assuming the 1000 lbs stated above is correct, i haven't seen it documented). That is what, 7.5% of stated payload capability? It will be interesting to see if the COTS agreement specified number of flights or kilos to orbit...

In addition to what others here have said about the constraints of volume and the need for performance margin for the demo flight, the total (claimed) payload capacity of 6,000 kg = pressurized cargo + unpressurised cargo capacity. Obviously, no unpressurised cargo will be transported in the C2/3 demo mission.

[Comga]

In addition to what others here have said about the constraints of volume and the need for performance margin for the demo flight, the total (claimed) payload capacity of 6,000 kg = pressurized cargo + unpressurised cargo capacity. Obviously, no unpressurised cargo will be transported in the C2/3 demo mission.

Which brings up an excellent point.  Although it can  probably be found in the COTS documentation, does anyone know when SpaceX is supposed to demonstrate carrying external cargo to the ISS?  Some of my hardware is supposed to ride in the Trunk, but I have seen almost nothing (except a CAD image on this forum) about mounting or retrieving hardware from the Trunk.  One would think that demonstrating this would be a COTS milestone, one that would have superseded the whole Orbcomm-on-COTS-2/3 idea. 

[ChefPat]

Which brings up an excellent point.  Although it can  probably be found in the COTS documentation, does anyone know when SpaceX is supposed to demonstrate carrying external cargo to the ISS?  Some of my hardware is supposed to ride in the Trunk, but I have seen almost nothing (except a CAD image on this forum) about mounting or retrieving hardware from the Trunk.  One would think that demonstrating this would be a COTS milestone, one that would have superseded the whole Orbcomm-on-COTS-2/3 idea. 

I'm curious how much more difficult it could be retrieving cargo from Dragon's trunk than it could have been constructing the ISS in the first place?

[Lurker Steve]

Which brings up an excellent point.  Although it can  probably be found in the COTS documentation, does anyone know when SpaceX is supposed to demonstrate carrying external cargo to the ISS?  Some of my hardware is supposed to ride in the Trunk, but I have seen almost nothing (except a CAD image on this forum) about mounting or retrieving hardware from the Trunk.  One would think that demonstrating this would be a COTS milestone, one that would have superseded the whole Orbcomm-on-COTS-2/3 idea. 

I'm curious how much more difficult it could be retrieving cargo from Dragon's trunk than it could have been constructing the ISS in the first place?

Those assembly flights had the benefit of the shuttle's RMS, and the SSRMS to hand off items from the external cargo bay to an external stowage location. There is only 1 RMS now, so it't going to be trickier to move things around. The SSRMS can grab an item from the trunk, but it can't really translate to another position on the station without letting go of the item it took out of the trunk. The procedures to move something from the Trunk to the opposite side of the station from where the Dragon is docked might be challenging.

[deltaV]

Thanks for your answers Jim & Cuddihy.

[Jim]

Which brings up an excellent point.  Although it can  probably be found in the COTS documentation, does anyone know when SpaceX is supposed to demonstrate carrying external cargo to the ISS?  Some of my hardware is supposed to ride in the Trunk, but I have seen almost nothing (except a CAD image on this forum) about mounting or retrieving hardware from the Trunk.  One would think that demonstrating this would be a COTS milestone, one that would have superseded the whole Orbcomm-on-COTS-2/3 idea. 

I'm curious how much more difficult it could be retrieving cargo from Dragon's trunk than it could have been constructing the ISS in the first place?

Those assembly flights had the benefit of the shuttle's RMS, and the SSRMS to hand off items from the external cargo bay to an external stowage location. There is only 1 RMS now, so it't going to be trickier to move things around. The SSRMS can grab an item from the trunk, but it can't really translate to another position on the station without letting go of the item it took out of the trunk. The procedures to move something from the Trunk to the opposite side of the station from where the Dragon is docked might be challenging.

there are separate end effectors on the MBS just for this purpose

[Space Pete]

there are separate end effectors on the MBS just for this purpose

But not all FRAM-type payloads will have FRGFs for the MBS POA to grapple. Most likely, the SPDM (on the end of the SSRMS based on the Node 2 PDGF) will remove the FRAM-type payload from the Dragon Trunk via the FRAM's micro-fixture, then the SSRMS will place the SPDM onto an MBS PDGF, change base itself to an MBS PGDF, then grapple the SPDM again, following which the MBS/MT will translate to the payload install site (likely an ELC).

[Jim]

there are separate end effectors on the MBS just for this purpose

But not all FRAM-type payloads will have FRGFs for the MBS POA to grapple. Most likely, the SPDM (on the end of the SSRMS based on the Node 2 PDGF) will remove the FRAM-type payload from the Dragon Trunk via the FRAM's micro-fixture, then the SSRMS will place the SPDM onto an MBS PDGF, change base itself to an MBS PGDF, then grapple the SPDM again, following which the MBS/MT will translate to the payload install site (likely an ELC).

Most handling is done grapple fixtures.  The SPDM is not used for this type of task

[Space Pete]

Most handling is done grapple fixtures.  The SPDM is not used for this type of task

Yes, it is - unless the FRAM payload/ORU in the Trunk has its own FRGF/PDGF, and has an EVA crew to climb inside the Trunk to release the FRAM with a PGT - which I doubt (SPDM would be much easier).

[cuddihy]

Apparently only a few (less than 4 iirc) of these empty, folded up bags can fit inside a regular bag/ cargo slot.  They need the empty bags for stuffing full of trash to make the best use of upcoming mass disposal opportunities from visiting vehicles.

You can fit several hundred ordinary plastic trash bags on a compact roll that's smaller than a single full bag. Why does NASA need such bulky bags for trash disposal?

Sorry DeltaV, i know you actually do pay attention but this is a 'Nuspace amazing people' post that impressively represents an entire genre of posts in only 2 sentences. Yet it contains:
-1.false and irrelevant parallel between everyday life and spaceflight (kitchen trashbags=/=cargo bags. Not on a ship, airliner, ambulance, or any other kind of professional transport.)
-2.assumption that traditional spaceflight is overengineered for no real good reason. Bags have to be tough, properly secured, and weight distributed reasonably so that attitude control and spacecraft dynamics are within capability of GNC/RCS to keep it smooth IVO station and for deorbit.
3. Rhetorical question that implies NASA is kloo-less and hidebound. No, NASA sets standards such that a few hundred dollars worth of (reusable possibly) cargo bags to ensure a 100 millions$ spacecraft doesn't destroy a $100 billion spacestation. Standards that Bigelow Aerospace would likely also require, BTW.

Huh, maybe we read it differently, but I thought it was an honest question. I was glad to have read Jim's informative answer.

Maybe I was being too hasty.

[Antares]

the total (claimed) payload capacity of 6,000 kg = pressurized cargo + unpressurised cargo capacity.

Looking at the Dragon page on spacex.com, I think 6Mg is to "LEO" not to ISS.  And, as noted above, I think that's evenly split between capsule and trunk, given that advertised downmass is 3Mg.

From their CRS contract p.6 at http://www.nasa.gov/centers/johnson/pdf/418857main_sec_nnj09ga04b.pdf

• Pricing assumes that final Task Order award ATP is a minimum of 21 months prior to the launch due to the unique nature of CRS-specific deliverables and mission requirements.  The following pricing scheme is applicable if more rapid call up is required: launches ordered from L-20 to L-18 require a l5% expedite fee; Launches from L-17 to L-12 require a 25% expedite fee. Less than 12month call up is to be negotiated on a case by case basis.
• All per kilogram pricing assumes cargo mass capacity fully utilized (3310 kg upmass and 3310 kg dowumass).
• Cargo load is variable and could be volume rather than mass limited. Because pricing is based on mass- per mission pricing is applicable for volume limited missions.
• There is a volume constraint of 14m3 unpressurized cargo and 11.2m3 of pressurized cargo (up or down).
• Maximum combined pressurized downmass and unpressurized downmass is 3,310 kg, which can be all unpressurized disposal mass or up to 2,500 kg of return (cargo or disposal mass). Pressurized downmass is driven by parachute limitations.
• Maximum combined pressurized and unpressurized upmass is 3,310 kg, which can be all pressurized, all unpressurized or anywhere in between.

[yg1968]

Video of the wet dress test: