Author Topic: Should SpaceX Vehicles Have Androgynous Docking Ports?  (Read 10803 times)

Offline pochimax

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1) Anyone care to speculate/confirm whether a Dragon 2 can dock to a Dragon XL?
maybe, you can have a problem with the nose cap of Crew Dragon. Independently of ports compatiblity.

Edit. Maybe DragonXL has been exactly calculated to avoid this problem?



« Last Edit: 04/02/2020 03:13 am by gongora »

Offline Zed_Noir

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Re: Re: SpaceX Dragon XL
« Reply #1 on: 03/31/2020 10:34 am »
If DragonXL does a slow transfer to NRHO (months), how did SpaceX comply with the unique capability of a fast transfer to Gateway (<30 days)? If NASA request this unique capability.

The standard DragonXL launch and travel is not a fully expendable Falcon Heavy? And the fast transit is a fully expendable?

I' m a little bit lost.

Can you point to the specific requirement for a <30 days transfer to Gateway? I can't seem to find it.

File: Attachment_01_GLS_SOW.pdf
5.0 MISSION UNIQUE CAPABILITIES (SUBCLIN 103) [pages 29-30]

Fast Transit to Gateway: Provide end-to-end cargo delivery services withcargo transit time of 30 days or less. NASA shall have the ability to order this capability within the time defined in the GLS Space System Architecture contract attachment.


Perfect! Thank you. It is sometimes challenging to find specifics when an RFP has a kazillion attachments ;)

It is a mission unique capability. Here is the first paragraph, which basically explains it all:

Quote from: Attachment_01_GLS_SOW
5.0 MISSION UNIQUE CAPABILITIES (SUBCLIN 103)

The contractor shall provide Mission Unique Capabilities for requirements over and above
logistic service requirements obtained under subCLINs 101 and 102.

These capabilities may be added throughout the life of the contract or they may be incorporated in
response to specific task order requirements.


So, these are non-standard capabilities which MAY be - someday - required by NASA. As such, they are not part of the baseline solution offered by SpaceX.
What I think (but I'll have to check with my sources) is that SpaceX is perfectly capable of sending Dragon XL on an expedited trajectory to Gateway, but at the cost of reduced cargo up-mass.

Another solution would probably be to to fly FH in fully expendable mode. Which will result in the launch being more expensive to NASA and thus the total number of launches under the fixed price cost cap decreasing.

If NASA get over their aversion to Earth orbit rendezvous. SpaceX could just assembled and pre-positioned a large vehicle stack in LEO with enough hypergolic propellants for a fast transfer from LEO to the Gateway. The Dragon XL flies up on a Falcon 9 and docked with vehicle stack then head for the Moon.

Maybe the vehicle stack could be a modified Dragon XL variant only carrying hypergolic propellants with a vacuum optimized de-rated SuperDraco in place of the docking port on the bottom and a docking collar on the top.

Offline Zed_Noir

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Re: Re: SpaceX Dragon XL
« Reply #2 on: 03/31/2020 10:59 am »
<snip>
I do wonder how many other customers there would be for this kind of thing.  Surely the creation of a class of small, temporary and private space station(s) in LEO would help SpaceX fund SS/SH development?

1) Anyone care to speculate/confirm whether a Dragon 2 can dock to a Dragon XL?
2) Could it be done autonomously? (e.g. so crew of two could just be payload specialists, or spaceflight participants).
3) Just because Dragon XL is not designed to re-enter the atmosphere need not make it "expendable" if it could be reused by multiple visiting vehicles.
4) If Dragon XL is being designed to host a Canadarm, could it retrieve payloads from the trunk of a visiting Dragon 2?
5) Would it be possible to use the visiting Dragon 2 as an airlock (i.e. shut the hatch between D2 and Dragon XL and open and close the main side hatch)?
....

@jarmumd posted up thread regarding your 1) query
If it is supposed to transfer both pressurized and unpressurized cargo, how could it have docking at both ends?

Also, SpaceX would need to build their own IDSS passive docking port.  Contrary to popular belief, the current system does not have the equipment to act as a passive for other vehicles to dock (ie not androgynous)....
Citation needed. The standard specifies it must be androgynous (at least for active side). If it's not androgynous, it's not IDSS.

For Crew Dragon, androgyny is a safety consideration as well to allow rescue. Doubtful that they'd change the spec for Dragon XL as that'd require more certification.

If you're right, then you should be able to provide a reference. If you're just supposing, then you should say so.

I'm the citation, I work on docking systems.

Also, if you look at any high resolution picture of the SpaceX docking system, there are no passive strikers or hooks, so there is nothing to soft or hard capture to.

Offline rakaydos

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Re: Re: SpaceX Dragon XL
« Reply #3 on: 03/31/2020 11:39 am »
<snip>
I do wonder how many other customers there would be for this kind of thing.  Surely the creation of a class of small, temporary and private space station(s) in LEO would help SpaceX fund SS/SH development?

1) Anyone care to speculate/confirm whether a Dragon 2 can dock to a Dragon XL?
2) Could it be done autonomously? (e.g. so crew of two could just be payload specialists, or spaceflight participants).
3) Just because Dragon XL is not designed to re-enter the atmosphere need not make it "expendable" if it could be reused by multiple visiting vehicles.
4) If Dragon XL is being designed to host a Canadarm, could it retrieve payloads from the trunk of a visiting Dragon 2?
5) Would it be possible to use the visiting Dragon 2 as an airlock (i.e. shut the hatch between D2 and Dragon XL and open and close the main side hatch)?
....

@jarmumd posted up thread regarding your 1) query
If it is supposed to transfer both pressurized and unpressurized cargo, how could it have docking at both ends?

Also, SpaceX would need to build their own IDSS passive docking port.  Contrary to popular belief, the current system does not have the equipment to act as a passive for other vehicles to dock (ie not androgynous)....
Citation needed. The standard specifies it must be androgynous (at least for active side). If it's not androgynous, it's not IDSS.

For Crew Dragon, androgyny is a safety consideration as well to allow rescue. Doubtful that they'd change the spec for Dragon XL as that'd require more certification.

If you're right, then you should be able to provide a reference. If you're just supposing, then you should say so.

I'm the citation, I work on docking systems.

Also, if you look at any high resolution picture of the SpaceX docking system, there are no passive strikers or hooks, so there is nothing to soft or hard capture to.
How hard would it be to retrofit passive elements to an existing design? Is the lack of strikers or hooks a critical design flaw, or is it something that can be rectified if SpaceX actually cared?

Offline pochimax

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Re: Re: SpaceX Dragon XL
« Reply #4 on: 03/31/2020 01:18 pm »
Quote
Also, if you look at any high resolution picture of the SpaceX docking system, there are no passive strikers or hooks, so there is nothing to soft or hard capture to.

Is it true? I thought an APAS can act as active or passive as needed.



« Last Edit: 03/31/2020 01:48 pm by Carl G »

Offline woods170

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Re: Re: SpaceX Dragon XL
« Reply #5 on: 03/31/2020 01:29 pm »
Quote
Also, if you look at any high resolution picture of the SpaceX docking system, there are no passive strikers or hooks, so there is nothing to soft or hard capture to.

Is it true? I thought an APAS can act as active or passive as needed.

<removed image. PLEASE, do NOT embed images. Attach only>


That's the thing: it's not an APAS. It is based on NDS, which is NASA's implementation of the IDSS.

IF the docking system was built to the letter, as specified in IDSS
THAN the docking system is androgynous (Meaning that it can dock to a duplicate of itself)
ELSE it cannot dock to a duplicate of itself.

However:
SpaceX did NOT build their version of the IDSS to the letter. They only included the ACTIVE side latches into the system. The passive latches are missing.
In other words: two SpaceX docking systems can NOT dock to each other, because they are not fully androgynous. The active hooks on one side would find NO passive hooks on the other side to latch onto.


« Last Edit: 03/31/2020 02:03 pm by woods170 »

Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #6 on: 03/31/2020 04:10 pm »
How hard would it be to retrofit passive elements to an existing design? Is the lack of strikers or hooks a critical design flaw, or is it something that can be rectified if SpaceX actually cared?

I think you are missing the point.  Everything is built to the minimum that meets requirements.  Every extra thing, passive docking components, airlocks, it's not just the hardware, it's the money to build it, test it, the documentation to certify it.  I know many people on this forum think it's easy, and sure it's not that hard to get the machinists to build it.  But certifying it is probably more the double the cost and more critically, the time.

Every time you add something, you need to think about "what if".  What if something fails, then something else fails, or combinations of other failures.  Every "what if" is analysis and documentation and meetings.  Now multiply that by every component - the work load becomes exponential.  Minimum Viable Product is the name of the game.

Online Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #7 on: 03/31/2020 05:30 pm »
How hard would it be to retrofit passive elements to an existing design? Is the lack of strikers or hooks a critical design flaw, or is it something that can be rectified if SpaceX actually cared?

I think you are missing the point.  Everything is built to the minimum that meets requirements.  Every extra thing, passive docking components, airlocks, it's not just the hardware, it's the money to build it, test it, the documentation to certify it.  I know many people on this forum think it's easy, and sure it's not that hard to get the machinists to build it.  But certifying it is probably more the double the cost and more critically, the time.

Every time you add something, you need to think about "what if".  What if something fails, then something else fails, or combinations of other failures.  Every "what if" is analysis and documentation and meetings.  Now multiply that by every component - the work load becomes exponential.  Minimum Viable Product is the name of the game.
It's interesting, because lack of passive capability reduces safety of the IDSS design. One of the main features of an androgynous design (over probe and drogue, for instance) is ability to rescue and overall operational flexibility and contingency.
« Last Edit: 03/31/2020 05:30 pm by Robotbeat »
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Offline Coastal Ron

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Re: Re: SpaceX Dragon XL
« Reply #8 on: 03/31/2020 05:53 pm »
When RFP's are put out for systems that are needed and you've got one, two, or three options you are pretty much stuck with those options.

That is the same no matter if the custom product is for the government or a commercial company. So it has no bearing to this discussion.

Quote
For big contracts engineers are utilized and a better sense of value can be determined. However, when there is limited competion you have to pick from the options available.

I realize you are new to NSF, and it is good you are engaging in discussions. But many of us have seen how the NASA competitive procurement process works on programs like the Commercial Cargo and Commercial Crew programs, so we have seen how NASA evaluated and justified their choices.

For instance, Look at the Selection Statement for the Commercial Crew Integrated Capability (CCiCap) contract award and you'll see how NASA evaluated the bids.

Quote
Even if an option is "overpriced" for what is being done...

When you are talking about something highly technical that has never been done, the term "overpriced" can't be justified or quantified. Instead the government, through the President and Congress, determine what they are willing to pay, and then they solicit quotes to see what the contractors are willing to charge.

If the bids come back within the range the government was expecting, then they can proceed with determining the winning bidder. If the pricing comes in higher than what the government wanted, then they will work with the bidding companies to determine what is driving the prices higher than desired. If they can't work it out the government may cancel the program, or they may restructure it. That didn't happen with this program.

Quote
Also just as a side note, regardless of the capability of the individuals that work for the government they are hindered by the system that moves slow and inefficiently.

That is the same for the private sector too, so again that has no bearing on this discussion.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #9 on: 03/31/2020 05:53 pm »
It's interesting, because lack of passive capability reduces safety of the IDSS design. One of the main features of an androgynous design (over probe and drogue, for instance) is ability to rescue and overall operational flexibility and contingency.

In general, you aren't wrong, but where we are today it doesn't matter.  For instance, to your points on rescue, operational flexibility, contingency....     how?  Rescue what?

What would the scenario have to be to have Orion or CST-100 dock to a Dragon (if it was equipped)?  In any contingency you might be thinking of, the existing spacecraft must have enough redundancies and equipment to make it back to earth safely.  Why design for something that is so far out of the fault space?  There is no reasonable circumstance in which you could launch a rescue spacecraft in time to do anything.  The exception to this is if one is already docked to the ISS.

And if you are already at the ISS, what's the point? 

If a spacecraft is so damaged it cannot return to earth, are you sure it could even be docked to?

In case my tone comes across wrong, understand that I do agree with you in principal, but once you go down the rabbit hole, you'll see there just isn't a credible reason now to have this capability, and I haven't seen a reasonable need to have it in the future, specifically for commercial crew or cargo resupply.
« Last Edit: 03/31/2020 05:57 pm by jarmumd »

Online Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #10 on: 03/31/2020 05:58 pm »
It's interesting, because lack of passive capability reduces safety of the IDSS design. One of the main features of an androgynous design (over probe and drogue, for instance) is ability to rescue and overall operational flexibility and contingency.

In general, you aren't wrong, but where we are today it doesn't matter.  For instance, to your points on rescue, operational flexibility, contingency....     how?  Rescue what?

What would the scenario have to be to have Orion or CST-100 dock to a Dragon (if it was equipped)?  In any contingency you might be thinking of, the existing spacecraft must have enough redundancies and equipment to make it back to earth safely.  Why design for something that is so far out of the fault space?  There is no reasonable circumstance in which you could launch a rescue spacecraft in time to do anything.  The exception to this is if one is already docked to the ISS.

And if you are already at the ISS, what's the point?  And if things were so bad that you needed to go from one spacecraft to the other, wouldn't it make more sense to just open the hatches, throw a line and go across?  Or, why would you be docking two healthy spacecraft in this scenario?  If one is so damaged it cannot return to earth, are you sure it could even be docked to?

In case my tone comes across wrong, understand that I do agree with you in principal, but once you go down the rabbit hole, you'll see there just isn't a credible reason now to have this capability, and I haven't seen a reasonable need to have it in the future, specifically for commercial crew or cargo resupply.

The Russians have docked to spacecraft that were inactive. It's tough, but it can be done. The main argument is to give flexibility where otherwise there'd be none. For instance, imagine a LEO servicing mission gone awry: Heatshield or parachute system damaged.
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Offline whitelancer64

Re: Re: SpaceX Dragon XL
« Reply #11 on: 03/31/2020 06:39 pm »
It's like the Shuttle Columbia rescue scenario - fast-track another Shuttle to launch to rescue the crew - but imagine if there had been something like Dragon or Starliner that could have docked to the Shuttle.

And while Starliner and Dragon are currently going to ISS, the ISS will be splashed someday. Or maybe one is flying some independent tourists, or to a private space station.

Missions that find themselves in danger are almost always failures of imagination. Not allowing for the possibility of being able to be docked to in an emergency situation IMO is a failure of imagination as well.
"One bit of advice: it is important to view knowledge as sort of a semantic tree -- make sure you understand the fundamental principles, ie the trunk and big branches, before you get into the leaves/details or there is nothing for them to hang on to." - Elon Musk
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Online Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #12 on: 03/31/2020 06:42 pm »
Another one was Dragon autonomously docking to Orion with orion serving as a passive side because its AR&D wasn’t finished, yet. This was one possibility considered for getting a 2020 trip around the Moon with people in orion.
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Offline Khadgars

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Re: Re: SpaceX Dragon XL
« Reply #13 on: 03/31/2020 06:46 pm »
It's interesting, because lack of passive capability reduces safety of the IDSS design. One of the main features of an androgynous design (over probe and drogue, for instance) is ability to rescue and overall operational flexibility and contingency.

In general, you aren't wrong, but where we are today it doesn't matter.  For instance, to your points on rescue, operational flexibility, contingency....     how?  Rescue what?

What would the scenario have to be to have Orion or CST-100 dock to a Dragon (if it was equipped)?  In any contingency you might be thinking of, the existing spacecraft must have enough redundancies and equipment to make it back to earth safely.  Why design for something that is so far out of the fault space?  There is no reasonable circumstance in which you could launch a rescue spacecraft in time to do anything.  The exception to this is if one is already docked to the ISS.

And if you are already at the ISS, what's the point? 

If a spacecraft is so damaged it cannot return to earth, are you sure it could even be docked to?

In case my tone comes across wrong, understand that I do agree with you in principal, but once you go down the rabbit hole, you'll see there just isn't a credible reason now to have this capability, and I haven't seen a reasonable need to have it in the future, specifically for commercial crew or cargo resupply.

It's a good point.  The only way I see it working is how they did it with shuttle at the end, with every manned U.S space launch, a secondary option must be ready to launch within a given time frame (48/72 hours?).  With Orion, Starliner and Crew Dragon, we have the options.
« Last Edit: 03/31/2020 06:47 pm by Khadgars »
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Online Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #14 on: 03/31/2020 07:17 pm »
Imagine how dumb you’d look if you had one of these scenarios happen where the crew could’ve been rescued but they can’t.

“I thought you said the port was androgynous?”
“Well, see the thing is...”
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Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #15 on: 03/31/2020 07:25 pm »
Another one was Dragon autonomously docking to Orion with orion serving as a passive side because its AR&D wasn’t finished, yet. This was one possibility considered for getting a 2020 trip around the Moon with people in orion.

There currently isn't such a thing as autonomous docking between spacecraft.  Only autonomous docking to ISS, and hopefully gateway.  There are no passive reflectors which exist on any spacecraft other than the IDA/ISS.  And some spacecraft use telemetry from the ISS to dock, using reflectors for backup.  As such two spacecraft docking would be a manual process.  An automated process might be years of development.  Again, not the hardware, it's the certification.

Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #16 on: 03/31/2020 07:36 pm »
It's like the Shuttle Columbia rescue scenario - fast-track another Shuttle to launch to rescue the crew - but imagine if there had been something like Dragon or Starliner that could have docked to the Shuttle.

And while Starliner and Dragon are currently going to ISS, the ISS will be splashed someday. Or maybe one is flying some independent tourists, or to a private space station.

Missions that find themselves in danger are almost always failures of imagination. Not allowing for the possibility of being able to be docked to in an emergency situation IMO is a failure of imagination as well.

I don't think there is any credible scenario where a spacecraft is "fast-tracked" to launch a rescue.  For the foreseeable future, all spacecraft are visiting a space station.  Maybe there is a scenario where you can't dock to the station, but another capsule can dock to you?  Maybe.  But what if Shuttle were putting up a satellite or going to Hubble?  There just isn't the fuel for a capsule to go and rescue them, starting at the ISS.  So apply that to anything coming in the future.  I just don't think there is such a thing as a capsule going to rescue another capsule.  Maybe some form of proximity operations at a station, but then you probably also have other options.

I'll caveat that to say that I do think that we would need an androgynous docking system if we had multiple commercial lunar landers.  But even then, weight is so critical to lunar operations, I think you would explore every other option in fault space before taking a large amount of useless mass with you.  If you only have a single lander, then it's the same as the ISS.  And if you were to have an "Active" on an Orion, and a "Passive" on a lander, well then you have contingencies at gateway because you could do Orion->Lander or Orion->Gateway->Lander, so there still isn't a need for androgyny.

Offline whitelancer64

Re: Re: SpaceX Dragon XL
« Reply #17 on: 03/31/2020 08:02 pm »
It's like the Shuttle Columbia rescue scenario - fast-track another Shuttle to launch to rescue the crew - but imagine if there had been something like Dragon or Starliner that could have docked to the Shuttle.

And while Starliner and Dragon are currently going to ISS, the ISS will be splashed someday. Or maybe one is flying some independent tourists, or to a private space station.

Missions that find themselves in danger are almost always failures of imagination. Not allowing for the possibility of being able to be docked to in an emergency situation IMO is a failure of imagination as well.

I don't think there is any credible scenario where a spacecraft is "fast-tracked" to launch a rescue.  For the foreseeable future, all spacecraft are visiting a space station.  Maybe there is a scenario where you can't dock to the station, but another capsule can dock to you?  Maybe.  But what if Shuttle were putting up a satellite or going to Hubble?  There just isn't the fuel for a capsule to go and rescue them, starting at the ISS.  So apply that to anything coming in the future.  I just don't think there is such a thing as a capsule going to rescue another capsule.  Maybe some form of proximity operations at a station, but then you probably also have other options.

I'll caveat that to say that I do think that we would need an androgynous docking system if we had multiple commercial lunar landers.  But even then, weight is so critical to lunar operations, I think you would explore every other option in fault space before taking a large amount of useless mass with you.  If you only have a single lander, then it's the same as the ISS.  And if you were to have an "Active" on an Orion, and a "Passive" on a lander, well then you have contingencies at gateway because you could do Orion->Lander or Orion->Gateway->Lander, so there still isn't a need for androgyny.

Both Starliner and Dragon are largely reusable, so after a couple years of ISS crew rotations they both will have several spacecraft in various states of readiness, probably with long periods where launch-ready (or nearly so) spacecraft are simply waiting on the next mission. Both providers are launching on a more or less steady cadence and so would have LVs available. SpaceX, in particular, would be capable of pulling a launch vehicle out of rotation, or out of its stockpile, on short notice.

Quote
There just isn't the fuel for a capsule to go and rescue them, starting at the ISS.

Start from the ground.

Quote
I just don't think there is such a thing as a capsule going to rescue another capsule.

And there can't be, if they aren't capable of being docked to.

But the IDSS standard was specifically designed with that in mind. It is androgynous, or it's supposed to be.
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Online Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #18 on: 03/31/2020 08:22 pm »
It's like the Shuttle Columbia rescue scenario - fast-track another Shuttle to launch to rescue the crew - but imagine if there had been something like Dragon or Starliner that could have docked to the Shuttle.

And while Starliner and Dragon are currently going to ISS, the ISS will be splashed someday. Or maybe one is flying some independent tourists, or to a private space station.

Missions that find themselves in danger are almost always failures of imagination. Not allowing for the possibility of being able to be docked to in an emergency situation IMO is a failure of imagination as well.

I don't think there is any credible scenario where a spacecraft is "fast-tracked" to launch a rescue.  For the foreseeable future, all spacecraft are visiting a space station.  Maybe there is a scenario where you can't dock to the station, but another capsule can dock to you?  Maybe.  But what if Shuttle were putting up a satellite or going to Hubble?  There just isn't the fuel for a capsule to go and rescue them, starting at the ISS.  So apply that to anything coming in the future.  I just don't think there is such a thing as a capsule going to rescue another capsule.  Maybe some form of proximity operations at a station, but then you probably also have other options.

I'll caveat that to say that I do think that we would need an androgynous docking system if we had multiple commercial lunar landers.  But even then, weight is so critical to lunar operations, I think you would explore every other option in fault space before taking a large amount of useless mass with you.  If you only have a single lander, then it's the same as the ISS.  And if you were to have an "Active" on an Orion, and a "Passive" on a lander, well then you have contingencies at gateway because you could do Orion->Lander or Orion->Gateway->Lander, so there still isn't a need for androgyny.
This latter sentence seems false. For instance:

Original plan is Gateway goes up first. Both lander and Orion need active systems to dock to the passive gateway. But! Current plan is to skip Gateway and dock directly to each other for the first mission, and then *later* go back to the original plan (so that the lander ascent stage can be docked to Gateway between missions for reuse). So, given NASA's current plans, the lander at least MUST be androgynous if we're to keep its configuration the same.
« Last Edit: 03/31/2020 08:24 pm by Robotbeat »
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Offline whitelancer64

Re: Re: SpaceX Dragon XL
« Reply #19 on: 03/31/2020 08:28 pm »
It's interesting, because lack of passive capability reduces safety of the IDSS design. One of the main features of an androgynous design (over probe and drogue, for instance) is ability to rescue and overall operational flexibility and contingency.

In general, you aren't wrong, but where we are today it doesn't matter.  For instance, to your points on rescue, operational flexibility, contingency....     how?  Rescue what?

What would the scenario have to be to have Orion or CST-100 dock to a Dragon (if it was equipped)?  In any contingency you might be thinking of, the existing spacecraft must have enough redundancies and equipment to make it back to earth safely.  Why design for something that is so far out of the fault space?  There is no reasonable circumstance in which you could launch a rescue spacecraft in time to do anything.  The exception to this is if one is already docked to the ISS.

And if you are already at the ISS, what's the point? 

If a spacecraft is so damaged it cannot return to earth, are you sure it could even be docked to?

In case my tone comes across wrong, understand that I do agree with you in principal, but once you go down the rabbit hole, you'll see there just isn't a credible reason now to have this capability, and I haven't seen a reasonable need to have it in the future, specifically for commercial crew or cargo resupply.

It's a good point.  The only way I see it working is how they did it with shuttle at the end, with every manned U.S space launch, a secondary option must be ready to launch within a given time frame (48/72 hours?).  With Orion, Starliner and Crew Dragon, we have the options.

I think it wouldn't hurt to consider that as a possibility. NASA did indeed make it the regular practice on the last dozen Shuttle flights. It wouldn't be too great of a burden on SpaceX, would be a much greater burden for Starliner.
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