Author Topic: Should SpaceX Vehicles Have Androgynous Docking Ports?  (Read 10834 times)

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #20 on: 03/31/2020 08:37 pm »
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.
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Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #21 on: 03/31/2020 08:44 pm »
And if we were serious about building a foundation for spacefaring and operational flexibility, we’d include standard fuel transfer capability, too. That’s much harder than just including passive capability, though.
« Last Edit: 03/31/2020 08:57 pm by Robotbeat »
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Offline indaco1

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Re: Re: SpaceX Dragon XL
« Reply #22 on: 03/31/2020 08:46 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...”


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.


Pretty OT, but is an EVA crew transfer (spacewalk to another veichle) possible for a rescue mission?
« Last Edit: 03/31/2020 08:47 pm by indaco1 »
Non-native English speaker and non-expert, be patient.

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #23 on: 03/31/2020 08:48 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...”


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.


Pretty OT, but is an EVA crew tranfer (spacewalk to another veichle) possible for a rescue mission?
Good idea. Why even put docking ports on the lander, then? Just EVA over to it from Orion! Only need rendezvous, then. ;)
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Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #24 on: 03/31/2020 09:01 pm »
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?

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #25 on: 03/31/2020 09:29 pm »
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.
« Last Edit: 03/31/2020 09:31 pm by Robotbeat »
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Online DigitalMan

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Re: Re: SpaceX Dragon XL
« Reply #26 on: 03/31/2020 09:30 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...”

It isn't sane for the contractor to add requirements to NASA contracts.  It will already be an intense and costly development effort. Anything you add will likely spiral into a testing effort you would regret.

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #27 on: 03/31/2020 09:37 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...”

It isn't sane for the contractor to add requirements to NASA contracts.  It will already be an intense and costly development effort. Anything you add will likely spiral into a testing effort you would regret.
Right. NASA as the customer ought to insist on it.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline whitelancer64

Re: Re: SpaceX Dragon XL
« Reply #28 on: 03/31/2020 09:41 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...”

It isn't sane for the contractor to add requirements to NASA contracts.  It will already be an intense and costly development effort. Anything you add will likely spiral into a testing effort you would regret.
Right. NASA as the customer ought to insist on it.

I know the USA is -particularly- bad about this, but why even have international standards if we're not going to build to them....
"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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Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #29 on: 03/31/2020 10:05 pm »
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.

Well, just keep in mind that sending an adapter isn't much different from sending the Dragon XL, and you only do it once.

Adding 100 lbm or more for a passive capability that may never be used, for every landing and ascent from the moon represents orders of magnitude more mass at liftoff.  Or that much less capability to land on the moon.

It's not quite this simple, but the docking drogue or cone on the Apollo Lunar Lander weighed 18-20 lbs.  That's it.  A modern docking system can weight several hundred pounds.  Not quite apples to apples, but it gives a sense of scale.

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #30 on: 03/31/2020 10:28 pm »
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.

Well, just keep in mind that sending an adapter isn't much different from sending the Dragon XL, and you only do it once.

Adding 100 lbm or more for a passive capability that may never be used, for every landing and ascent from the moon represents orders of magnitude more mass at liftoff.  Or that much less capability to land on the moon.

It's not quite this simple, but the docking drogue or cone on the Apollo Lunar Lander weighed 18-20 lbs.  That's it.  A modern docking system can weight several hundred pounds.  Not quite apples to apples, but it gives a sense of scale.
100lb or more for a passive capability? I find that hard to believe, but I’ll take your word for it.

If we’re not using the advantages of a modern docking system, we should go back to a drogue and cone system and save even more weight.
« Last Edit: 03/31/2020 10:29 pm by Robotbeat »
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Offline matthewkantar

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Re: Re: SpaceX Dragon XL
« Reply #31 on: 03/31/2020 10:48 pm »
This is the sort of thing that arises from extreme mass constrictions to orbit and a stubborn refusal to develop on-orbit fuel transfer. If those two things are sorted out, no one would be so silly as to have anything other than androgynous docking gear.

Online TheRadicalModerate

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Re: Re: SpaceX Dragon XL
« Reply #32 on: 03/31/2020 11:12 pm »
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.

Well, just keep in mind that sending an adapter isn't much different from sending the Dragon XL, and you only do it once.

Adding 100 lbm or more for a passive capability that may never be used, for every landing and ascent from the moon represents orders of magnitude more mass at liftoff.  Or that much less capability to land on the moon.

It's not quite this simple, but the docking drogue or cone on the Apollo Lunar Lander weighed 18-20 lbs.  That's it.  A modern docking system can weight several hundred pounds.  Not quite apples to apples, but it gives a sense of scale.
100lb or more for a passive capability? I find that hard to believe, but I’ll take your word for it.

If we’re not using the advantages of a modern docking system, we should go back to a drogue and cone system and save even more weight.

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.

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.

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?

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.

So you have two options:

1) You have separate active and passive docking ports on the Gateway, which is just dumb.

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).

I assume that active-active really means that one side decides to be passive and leaves its SCS retracted, and that side is the passive recipient of the active hard-capture hooks.  By that logic, HLS will be and active-active system (i.e., capable of being either active or passive).

All that said, and in a feeble attempt to remain vaguely on-topic, that would mean that the DXL could just have a vanilla-flavored active-passive NDS, to dock with the passive Gateway port.  But if you ever wanted to use a DXL and a D2 in some mated configuration (which is definitely not a NASA requirement, but I think was how we wound up down this particular rabbit hole), SpaceX would have to implement active-active functionality on both vehicles.

How badly have I misunderstood this?

Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #33 on: 03/31/2020 11:54 pm »
100lb or more for a passive capability? I find that hard to believe, but I’ll take your word for it.

If we’re not using the advantages of a modern docking system, we should go back to a drogue and cone system and save even more weight.

It's probably not that much, I dunno probably somewhere around 20-80?  It's passive hooks, thick Bellevue washer springs, back structure to support the hooks, passive hook explosive bolts for contingency release, wiring, strikers mounted somewhere to something and associated back structure, docking alignment cross, reflectors, ship to ship telemetry.... 

Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #34 on: 04/01/2020 12:06 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.
Quote

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.
Quote

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.
Quote

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)
Quote

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?
Quote


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!

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #35 on: 04/01/2020 12:15 am »
A problem with the active-active adapter for Gateway is it's going to compromise the rigidity and strength of the whole Gateway/visiting-vehicle stack. There's already a mass limit on Gateway-docking visiting vehicles, and having to use an adapter would theoretically reduce that allowable limit (longer moment arm for an already-long vehicle, additional flex which reduces the fundamental frequency and makes control harder, etc) besides adding more things that can fail and reducing inherent redundancy. I'm not sure that's captured by the requirements fully in a way that allows fair scoring, so that could be one area where the non-androgynous approach ends up penny-wise but pound-foolish.
« Last Edit: 04/01/2020 12:20 am by Robotbeat »
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Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #36 on: 04/01/2020 12:26 am »
A problem with the active-active adapter for Gateway is it's going to compromise the rigidity and strength of the whole Gateway/visiting-vehicle stack. There's already a mass limit on Gateway-docking visiting vehicles, and having to use an adapter would theoretically reduce that allowable limit (longer moment arm for an already-long vehicle, additional flex which reduces the fundamental frequency and makes control harder, etc) besides adding more things that can fail and reducing inherent redundancy. I'm not sure that's captured by the requirements fully in a way that allows fair scoring, so that could be one area where the non-androgynous approach ends up penny-wise but pound-foolish.

why wouldn't it stay attached to the gateway?

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #37 on: 04/01/2020 12:28 am »
A problem with the active-active adapter for Gateway is it's going to compromise the rigidity and strength of the whole Gateway/visiting-vehicle stack. There's already a mass limit on Gateway-docking visiting vehicles, and having to use an adapter would theoretically reduce that allowable limit (longer moment arm for an already-long vehicle, additional flex which reduces the fundamental frequency and makes control harder, etc) besides adding more things that can fail and reducing inherent redundancy. I'm not sure that's captured by the requirements fully in a way that allows fair scoring, so that could be one area where the non-androgynous approach ends up penny-wise but pound-foolish.

why wouldn't it stay attached to the gateway?
I didn’t say it wouldn’t. It still compromises the Gateway/VV stack.
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Offline jarmumd

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Re: Re: SpaceX Dragon XL
« Reply #38 on: 04/01/2020 12:37 am »
A problem with the active-active adapter for Gateway is it's going to compromise the rigidity and strength of the whole Gateway/visiting-vehicle stack. There's already a mass limit on Gateway-docking visiting vehicles, and having to use an adapter would theoretically reduce that allowable limit (longer moment arm for an already-long vehicle, additional flex which reduces the fundamental frequency and makes control harder, etc) besides adding more things that can fail and reducing inherent redundancy. I'm not sure that's captured by the requirements fully in a way that allows fair scoring, so that could be one area where the non-androgynous approach ends up penny-wise but pound-foolish.

why wouldn't it stay attached to the gateway?
I didn’t say it wouldn’t. It still compromises the Gateway/VV stack.

Wouldn't affect mass limit if it stays attached

bending moment ... nah...  but you couldn't really know that.  Just consider that docking is bounded by shuttle's off center CG, capsules don't put nearly the moment in.

can't be lower than the ISS fundamental frequency, lol

reducing redundancy more than a ISS made up of CBM's and other docking ports?  See also frequency through all those ports.

Just isn't an issue.  You aren't wrong that all those things detract, just not as much as you think.  And in the grand scheme, nothing in comparison to saving mass on a lander.

Offline Robotbeat

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Re: Re: SpaceX Dragon XL
« Reply #39 on: 04/01/2020 12:53 am »
A problem with the active-active adapter for Gateway is it's going to compromise the rigidity and strength of the whole Gateway/visiting-vehicle stack. There's already a mass limit on Gateway-docking visiting vehicles, and having to use an adapter would theoretically reduce that allowable limit (longer moment arm for an already-long vehicle, additional flex which reduces the fundamental frequency and makes control harder, etc) besides adding more things that can fail and reducing inherent redundancy. I'm not sure that's captured by the requirements fully in a way that allows fair scoring, so that could be one area where the non-androgynous approach ends up penny-wise but pound-foolish.

why wouldn't it stay attached to the gateway?
I didn’t say it wouldn’t. It still compromises the Gateway/VV stack.

Wouldn't affect mass limit if it stays attached

bending moment ... nah...  but you couldn't really know that.  Just consider that docking is bounded by shuttle's off center CG, capsules don't put nearly the moment in.

can't be lower than the ISS fundamental frequency, lol

reducing redundancy more than a ISS made up of CBM's and other docking ports?  See also frequency through all those ports.

Just isn't an issue.  You aren't wrong that all those things detract, just not as much as you think.  And in the grand scheme, nothing in comparison to saving mass on a lander.
From what I understand, the Gateway’s mass limit is for any visiting vehicle and is driven by PPE’s control authority which is limited (and sure, ISS is worse, but PPE is not designed for torquing ISS around, just the Gateway stack). I’m not talking about lander performance or launch vehicle limits.

And yeah, ISS always has redundant CBMs and NDSes and probe&drogues. It has a lot more redundancy.
« Last Edit: 04/01/2020 01:02 am by Robotbeat »
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