Author Topic: Should SpaceX Vehicles Have Androgynous Docking Ports?  (Read 10754 times)

Offline kkattula

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Re: Re: SpaceX Dragon XL
« Reply #40 on: 04/01/2020 04:14 am »
So then surely it would make sense for the Gateway modules to have androgynous docking adapters, so they can do both passive with active Orion & Dragon XL, and do active with passive HLS?

Online TheRadicalModerate

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Re: Re: SpaceX Dragon XL
« Reply #41 on: 04/01/2020 05:49 am »
I'm getting really confused here. 

I thought that the difference between an active and a passive IDSS-compliant system is that the active system (of which NDS is an implementation) has the extendable soft-capture system, which has latches that engage with the passive system's petals.  Then, once the soft-capture system retracts, active hooks on the active system engage with passive hooks on the passive system.

generally correct.
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I can't see how a passive system would be heavier.  Maybe some of the confusion is that the ISS's IDA is actually an adapter to make APAS IDSS-compliant?  You wouldn't need that if you were to implement an IDSS passive system from scratch.

To be androgynous, the Active needs additional structure, passive hooks, wiring, strikers, back structure to support docking loads, as well as sensors.  A pure passive would not be heavier.
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IDSS allows for active-active systems, doesn't it?  So the real question is whether NDS has implemented active-active, or whether it's only able to be the active component of an active-passive system.  Which is it?

NDS Block 1 is active-passive (CST-100 to IDA/ISS).  I don't know about Block 2, I think it might be fully androgynous (Orion/Gateway).  Neither has flown yet, B1 will fly on the first CST-100 mission, as far as I know.
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There has to be a plan that makes sense here, because HLS without a Gateway is going to have to dock with Orion (an active NDS system), which would require HLS to be passive if NDS is only active-passive.  But Orion is also going to have to dock with the Gateway, and if it's only active-passive, then the dock at the Gateway would have to be passive.  But then HLS can't dock at the gateway.
See previous posts about HLS appendix and possible gateway adapter (if I understand it right)
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So you have two options:

1) You have separate active and passive docking ports on the Gateway, which is just dumb.
I realize it seems dumb, but if they did do that, it's a question of cost.  Cost of an active is much much greater than a passive.  Also time to actually build.  (as I understand it, I might have that wrong).  If you want to send up the gateway Hab as soon as possible, makes more sense to build passives and send up adapters, than sit on it while an active gets built?  maybe?
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2) The HLS has to be able to work in both active-active mode (for docking with Orion) and active-passive mode (for docking with the GW).

...

How badly have I misunderstood this?

Not too bad!

Thanks for the info.  So passive would be the lightest, active-only would be heavier, and active-active would be heavier still?

Is the D2 docking port not an NDSB1 implementation?

Offline russianhalo117

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Re: Re: SpaceX Dragon XL
« Reply #42 on: 04/01/2020 06:03 am »
So then surely it would make sense for the Gateway modules to have androgynous docking adapters, so they can do both passive with active Orion & Dragon XL, and do active with passive HLS?
Increases mass and cost to have all ports be active. I would only expect the end cone ports to be active as they will be along the velocity vector when initially docking. When moved by arm to their final spot they can be berthed passive mode like a CBM. The IDSS specs did account for active-active and passive-passive configurations however nominal dockings will always have one active side in passive mode.

On ISS only one of the PMA's were active mode capable because of shuttle station interactions and it has only been used by PMA-1 to dock with FGB. APAS-89 both sides were active capable whereas APAS-95 was strengthened for shuttle thus only the shuttle side was active. PMA-1 and FGB Interfaces were designed APAS-89 with modifications.

Reference this thread: https://forum.nasaspaceflight.com/index.php?topic=5863.0
« Last Edit: 04/01/2020 06:32 am by russianhalo117 »

Online TheRadicalModerate

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Re: Re: SpaceX Dragon XL
« Reply #43 on: 04/01/2020 06:22 am »
So then surely it would make sense for the Gateway modules to have androgynous docking adapters, so they can do both passive with active Orion & Dragon XL, and do active with passive HLS?
Increases mass and cost to have all ports be active. I would only expect the end cone ports to be active as they will be along the velocity vector when initially docking. When moved by arm to their final spot they can be berthed passive mode like a CBM. The IDSS specs did account for active-active and passive-passive configurations however nominal dockings will always have one active side in passive mode.

Who has the hard-dock hooks in a passive-passive docking, even if it's berthed?  I can't see how it would work even in an off-nominal emergency.

Offline woods170

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Re: Re: SpaceX Dragon XL
« Reply #44 on: 04/01/2020 07:34 am »
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.

Emphasis mine.

Which does not apply to Crew Dragon.

When a Crew Dragon gets into trouble either BEFORE docking to the ISS, or AFTER undocking from the ISS, the prudent thing to do is to de-orbit to the safety of the planet surface.

If however such a "into trouble" scenario strands the crew in orbit, without any possibilty of either de-orbiting or docking with the ISS, than they are a lost cause. You see, in no way would SpaceX, or any other launch provider, be able to launch a rescue vehicle within the five days before the ECLSS consumables run out on Crew Dragon.

When Crew Dragon gets into trouble while docked to the ISS the crew can shelter in place aboard the ISS.

As such, there are no scenarios where the docking system on Crew Dragon is required to be fully androgynous. Which is exactly why it IS NOT fully androgynous.

Offline woods170

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Re: Re: SpaceX Dragon XL
« Reply #45 on: 04/01/2020 07:40 am »
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...”

Wrong.

When Crew Dragon launches into orbit, there is no second Crew Dragon on stand-by for a fast rescue launch. Neither is a Starliner standing by. Nor an Orion.
And vice versa.

The scenario where a rescue vehicle was standing by for fast rescue launch only existed in the post-Columbia shuttle era.

Both Orion and the CCP vehicles are required to be robust enough to get themselves out of trouble.

Offline woods170

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Re: Re: SpaceX Dragon XL
« Reply #46 on: 04/01/2020 07:54 am »
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.

I read "HLS_Appendix_H_BAA_2019-10-02c.pdf" page 9, CLIN 009 - Option A: Docking System.  Work on a detachable docking adapter...  As to mean an adapter to make a port on the gateway active instead of passive.  How do you read that?
Ah, you got me.

Looks like NASA is *allowing* HLS offerers to have passive-only on their lander PROVIDED they also build an active-active adapter for the gateway. But I see this as merely allowing the maximum possible options to be considered, whether or not they’re a good idea.

Insane to me that we’re actually talking about building a separate chunk of flight hardware as a kludge to avoid building the adapter fully to the androgynous spec of IDSS.

That means that you have less redundancy as you cannot swap Orion and the lander’s docking ports.

I pray that whatever bean counter you work with that is insisting on doing this kludge instead of building androgynous capability right the first time changes their mind.

Same for SpaceX.

Really, NASA ought to be insisting on androgynous capability at least for everything that needs to be active plus the lander. I means seriously, adding an extra docking adapter just to avoid making the lander or Orion androgynous! Insane.

That’s just my personal opinion, though.

Jarmund's original point was about the current CCP vehicles not having fully androgynous docking systems.

That says exactly NOTHING about the nature of the docking system that will be on Dragon XL.

What DOES have influence on the docking system on Dragon XL is the requirements laid down by NASA. And currently NASA only requires Dragon XL to have an active docking system. Because Gateway, like the ISS, is designated the passive vehicle in a docking. Gateway, like ISS, wil have fully androgynous IDSS compliant docking systems. But the visiting vehicles are not required to have those as well. Only the active part.

If you find fault in that, than it is not the right thing to "hope" that SpaceX will come to its senses. You should complain to NASA for laying down "incomplete" requirements.

Remember, SpaceX builds this stuff exclusively for NASA, to fit NASA requirements. Adding extras, which are not required by NASA, is usually not done in the aerospace industry. Not even by SpaceX. The one exception being the port-a-potty on Crew Dragon.

Offline woods170

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Re: Re: SpaceX Dragon XL
« Reply #47 on: 04/01/2020 07:57 am »
It’s impossible to use dragon XL as a mission-extending mini-station as supposed here if it doesn’t have an androgynous (or passive) docking capability.

You said it: "as supposed here".

SpaceX is not seriously considering using Dragon XL as a mission-extending mini-station. That is just an idea floated here by NSF members. Not rooted in reality.

Offline kevinof

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Re: Re: SpaceX Dragon XL
« Reply #48 on: 04/01/2020 08:15 am »
Yeah I think we tend to get carried away here on NSF with "oh you could do this or that and this also". Dragon XL is an interim , stop-gap offering to Nasa. It's not on the long term path for SpaceX and as soon as Starship is viable, they would dump Dragon XL and go just with SS.

This is a minimum viable product for SpaceX. It's doing a little as necessary to fulfill the needs of Nasa while keeping costs down and not distracting from SS. Adding bells and whistles to DragonXL is great for us here on NSF but does not make sense to SpaceX given the requirements and also the direction they want to go in.


It’s impossible to use dragon XL as a mission-extending mini-station as supposed here if it doesn’t have an androgynous (or passive) docking capability.

You said it: "as supposed here".

SpaceX is not seriously considering using Dragon XL as a mission-extending mini-station. That is just an idea floated here by NSF members. Not rooted in reality.

Offline tyrred

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Re: Re: SpaceX Dragon XL
« Reply #49 on: 04/01/2020 09:05 am »
I think some of the younger people also may succumb to KSP syndrome, where every module with a docking port can dock to every other module with a docking port of the same size.  Rockets aren't LEGO Elements. 

Why can't my Yaris dock with Dragon XL?  Oh, yeah nobody wants to launch my Yaris into orbit except for me  8)

It looks like that's not happening, so I guess SpaceX is planning on going to resupply the Gateway instead.

Offline baldusi

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Re: Re: SpaceX Dragon XL
« Reply #50 on: 04/01/2020 09:09 am »
Do not want to beat a dead horse, but Revision E of the IDSS standard also adds the retroreflectors to the passive side for final navigation and alignment. So that's another set of things that you would have to add if you wanted fully androgynous interface. Just saying that it's not that easy to do.
« Last Edit: 04/01/2020 09:09 am by baldusi »

Offline mikelepage

Re: Re: SpaceX Dragon XL
« Reply #51 on: 04/01/2020 09:20 am »
Fully agreed btw.  The format of my post floating the idea was simply:
1) Can it be done? (D2 to DXL docking)
2) if so, potential revenue opportunity in the form of LEO operations.

I'm optimistic about Starship/Superheavy being ready for cargo in near future.  Human-rating it seems like it has ample opportunity to take considerably longer and be considerably more expensive than projected.

Dragon XL to Gateway is one way to use proven hardware/processes to generate revenue in that eventuality.  It seemed like a natural progression to use that hardware to do other revenue-generating activities as well. 

Yeah I think we tend to get carried away here on NSF with "oh you could do this or that and this also". Dragon XL is an interim , stop-gap offering to Nasa. It's not on the long term path for SpaceX and as soon as Starship is viable, they would dump Dragon XL and go just with SS.

This is a minimum viable product for SpaceX. It's doing a little as necessary to fulfill the needs of Nasa while keeping costs down and not distracting from SS. Adding bells and whistles to DragonXL is great for us here on NSF but does not make sense to SpaceX given the requirements and also the direction they want to go in.


It’s impossible to use dragon XL as a mission-extending mini-station as supposed here if it doesn’t have an androgynous (or passive) docking capability.

You said it: "as supposed here".

SpaceX is not seriously considering using Dragon XL as a mission-extending mini-station. That is just an idea floated here by NSF members. Not rooted in reality.
« Last Edit: 04/01/2020 09:21 am by mikelepage »

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #52 on: 04/01/2020 10:31 am »
It’s impossible to use dragon XL as a mission-extending mini-station as supposed here if it doesn’t have an androgynous (or passive) docking capability.

You said it: "as supposed here".

SpaceX is not seriously considering using Dragon XL as a mission-extending mini-station. That is just an idea floated here by NSF members. Not rooted in reality.
Welcome to NSF! Always glad to have new members. 😂
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Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #53 on: 04/01/2020 10:32 am »
I think some of the younger people also may succumb to KSP syndrome, where every module with a docking port can dock to every other module with a docking port of the same size.  Rockets aren't LEGO Elements. 

Why can't my Yaris dock with Dragon XL?  Oh, yeah nobody wants to launch my Yaris into orbit except for me  8)

It looks like that's not happening, so I guess SpaceX is planning on going to resupply the Gateway instead.
Spacecraft aren’t LEGOs when they’re specifically engineered not to be.
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Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #54 on: 04/01/2020 10:32 am »
Do not want to beat a dead horse, but Revision E of the IDSS standard also adds the retroreflectors to the passive side for final navigation and alignment. So that's another set of things that you would have to add if you wanted fully androgynous interface. Just saying that it's not that easy to do.
Well understood by all.
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Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #55 on: 04/01/2020 10:35 am »
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...”

Wrong.

When Crew Dragon launches into orbit, there is no second Crew Dragon on stand-by for a fast rescue launch. Neither is a Starliner standing by. Nor an Orion.
And vice versa.

The scenario where a rescue vehicle was standing by for fast rescue launch only existed in the post-Columbia shuttle era.

Both Orion and the CCP vehicles are required to be robust enough to get themselves out of trouble.
If Dragon or Starliner has a problem detected with their landing system when near ISS but cannot dock, another visiting vehicle could dock with them.
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Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #56 on: 04/01/2020 10:37 am »
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...”

Wrong.

When Crew Dragon launches into orbit, there is no second Crew Dragon on stand-by for a fast rescue launch. Neither is a Starliner standing by. Nor an Orion.
And vice versa.

The scenario where a rescue vehicle was standing by for fast rescue launch only existed in the post-Columbia shuttle era.

Both Orion and the CCP vehicles are required to be robust enough to get themselves out of trouble.
If Dragon or Starliner has a problem detected with their landing system when near ISS but cannot dock, another visiting vehicle could dock with them if there was true androgynous capability.

Of course I understand rockets aren’t Legos. But these aren’t rockets, they’re spacecraft with standard interfaces, interfaces explicitly standardized (originally) with the idea of the possibility of rescue by different vehicles in mind. So incompatibility is a design decision by the customer (NASA).
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Offline soltasto

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Re: Re: SpaceX Dragon XL
« Reply #57 on: 04/01/2020 10:38 am »
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...”

Wrong.

When Crew Dragon launches into orbit, there is no second Crew Dragon on stand-by for a fast rescue launch. Neither is a Starliner standing by. Nor an Orion.
And vice versa.

The scenario where a rescue vehicle was standing by for fast rescue launch only existed in the post-Columbia shuttle era.

Both Orion and the CCP vehicles are required to be robust enough to get themselves out of trouble.
If Dragon or Starliner has a problem detected with their landing system when near ISS but cannot dock, another visiting vehicle could dock with them.
Ehm, it doesn't make any sense.  Either your are able to or you are not.

Offline danneely

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Re: Re: SpaceX Dragon XL
« Reply #58 on: 04/01/2020 11:14 am »
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.

Only the hubble repair mission had a second shuttle ready to go for an emergency.  Everything else was an ISS flight, and the emergency plan was to hang out there for a few months if the shuttle broke.

Online rakaydos

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Re: Re: SpaceX Dragon XL
« Reply #59 on: 04/01/2020 11:37 am »
There's no rescue mission set up for crewed flights to the ISS, because in a crisis the iss itself functions as the rescue vehical. And other than the last few shuttle missions, there hasnt been any crewed flights that were NOT to the ISS, not since the second shuttle exploded.

But with Artemis, Gateway, and Mars all on the horizon, that will shortly no longer be the case.


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