SpaceX - US Deorbit Vehicle (for ISS)

[AmigaClone]

Attitude control during the deorbit burns is done solely by the 32 attitude control Dracos (16 on the capsule and 16 on the deorbit section).

Meaning the Russian segment thrusters and ISS CMG's are not used

It was mentioned right after "No gimballing" for the main 30 deorbit thrusters.

Well aware of that.

The initial requote / bolding was responding to Dan regarding the 4 forward nosecone thrusters which are obstructed by the IDA post docking.

Without those 4 thrusters, there are only 12 usable dracos during the deorbit burns (after docking) on cargo dragon (vs the full 16). The context of the debate is the alternate / unlikely paths to free the thrusters up and make the statement reconcile.

Would the Russian segment thrusters and ISS CMG's be used either prior to the initial deorbit burn or between two deorbit burns?

[StraumliBlight]

Would the Russian segment thrusters and ISS CMG's be used either prior to the initial deorbit burn or between two deorbit burns?

At 42:17 in the teleconference, she said the Russian thrusters will continue to be primary for normal attitude control, debris avoidance on the way down, possible altitude lowering depending on fuel remaining and finally as a contingency option if there are multiple failures on the USDV.

[Norm38]

What is driving the requirement to be docked for a year before deorbit?  For what purpose?
And why design the capsule to separate and re-enter for “momentos”?

Wouldn’t those already be packed up?  Or send a dedicated cargo capsule for that.

[Remes]

What is mementos? I haven't seen any plans to depart the usdv. That sounds far too much like fun for NASA.

The crew will leave 6 month before splashdown. So if they dock 1 year earlier, they only have 6 month for scheduling around a limited number of docking ports, do all the check out, tests, etc.

I would assume they will make a few tests with slowing down the station, looking at dynamics, deactivating the existing control system, etc. Those things are not done in a day. Those six month should give them enough time to test and adapt procedures, software, models, ...

A few other thoughts:
- docking earlier: exposes the most vulnerable side of the usdv to the direction of flight. Will there be any removable micro meteorite protection for the trunk?
- docking 1year or later before splashdown: what if something like the launcher has a mishap and the launcher gets grounded? What if the usdv doesn't make it? Will they send up an engineering model or build a second one?

When I heard SpaceX is responsible to deorbit the ISS in 2030 I thought: "nice, ISS will be around till 33/34/...".
And the second thought: "I would have never thought that those words would ever find a place in my brain, but I wish Boeing would have won the contract".

[AmigaClone]

What is driving the requirement to be docked for a year before deorbit?  For what purpose?
And why design the capsule to separate and re-enter for “momentos”?

Wouldn’t those already be packed up?  Or send a dedicated cargo capsule for that.

I suspect most "momentos" will have been returned to Earth by the time the deorbit vehicle has docked. Most would make the return trip in either a Cargo Dragon or Dream chaser but I can see some returning in a crewed vehicle. There might even be an uncrewed Soyuz involved for some Russian "momentos".

[tea monster]

They may want to return the Dragon simply because it's reusable and it's a bit silly to drop it into the ocean.

The irony!

[Jim]

And why design the capsule to separate snip?

Where is that stated?

[Jim]

They may want to return the Dragon simply because it's reusable

it is not after this

[dgmckenzie]

Besides NASA will have bought the Dragon to do with as they want.

[DanClemmensen]

What is driving the requirement to be docked for a year before deorbit?  For what purpose?
And why design the capsule to separate and re-enter for “momentos”?

Wouldn’t those already be packed up?  Or send a dedicated cargo capsule for that.

The USDV is a just an existing Dragon capsule mated to a new-design "trunk". It therefore inherits pretty much all of Dragon's design features, even those it will not use. It will not detach and deorbit separately even though it might have inherited this capability. The deorbit mission requires that it remain attached. It is unlikely that the capsule can separate from the trunk or that is has a heat shield.

There was no mention that the "momentos" would be returned in the USDV. They will be returned in the last crew and cargo vehicles.

[seb21051]

Interesting Stokes-like arrangement of Draco thrusters at the business end of the USDV:

https://spacenews.com/enhanced-dragon-spacecraft-to-deorbit-the-iss-at-the-end-of-its-life/

[Norm38]

And why design the capsule to separate snip?

Where is that stated?

It was a comment upthread, I was replying to that.  The only formal requirement I was questioning was the 1 year loiter time.

[Norm38]

The crew will leave 6 month before splashdown. So if they dock 1 year earlier, they only have 6 month for scheduling around a limited number of docking ports, do all the check out, tests, etc.

So what is the requirement to wait 6 months after the crew departs?  If something goes wrong and the crew isn't there to fix it, deorbit may have to happen sooner.  So why wait?  What is driving that requirement?

[matthewkantar]

The crew will leave 6 month before splashdown. So if they dock 1 year earlier, they only have 6 month for scheduling around a limited number of docking ports, do all the check out, tests, etc.

So what is the requirement to wait 6 months after the crew departs?  If something goes wrong and the crew isn't there to fix it, deorbit may have to happen sooner.  So why wait?  What is driving that requirement?

Just a guess, six months of drag on station will give the delta v available from the deorbit vehicle more authority.

[Jim]

The crew will leave 6 month before splashdown. So if they dock 1 year earlier, they only have 6 month for scheduling around a limited number of docking ports, do all the check out, tests, etc.

So what is the requirement to wait 6 months after the crew departs?  If something goes wrong and the crew isn't there to fix it, deorbit may have to happen sooner.  So why wait?  What is driving that requirement?

it is letting the orbit decay naturally, which reduces propellant required.  There is "nothing" to break on the ISS.   The USDV will be in full control.

[DanClemmensen]

The crew will leave 6 month before splashdown. So if they dock 1 year earlier, they only have 6 month for scheduling around a limited number of docking ports, do all the check out, tests, etc.

So what is the requirement to wait 6 months after the crew departs?  If something goes wrong and the crew isn't there to fix it, deorbit may have to happen sooner.  So why wait?  What is driving that requirement?

it is letting the orbit decay naturally, which reduces propellant required.  There is "nothing" to break on the ISS.   The USDV will be in full control.

Conceivably, there is one thing that might fail and that might be important. If ISS loses pressure, it becomes less  rigid and it also cannot tolerate as much thrust from the USDV. This is a purely theoretical observation since I have no insight into the structural analyses of the ISS as a system. I started thinking about it when I found the reference in the IDSS spec that the IDSS port must be able to handle 100,000 N in tension but only 10,000 N in compression, after Garmund pointed out the tension that comes from the atmospheric presssure. Depressurization will almost certainly affect the harmonic oscillation modes of ISS as it becomes "floppier" if depressurized. The professionals will have already analyzed this and will make the proper adjustments to the control software.

[Jim]

Conceivably, there is one thing that might fail and that might be important. If ISS loses pressure

all the hatches will sealed

[Norm38]

The crew will leave 6 month before splashdown. So if they dock 1 year earlier, they only have 6 month for scheduling around a limited number of docking ports, do all the check out, tests, etc.

So what is the requirement to wait 6 months after the crew departs?  If something goes wrong and the crew isn't there to fix it, deorbit may have to happen sooner.  So why wait?  What is driving that requirement?

it is letting the orbit decay naturally, which reduces propellant required.  There is "nothing" to break on the ISS.   The USDV will be in full control.

Is there a reason they can't simply skip the last Progress reboost?  Or, can Progress also "deboost" the station instead, giving the same drop in altitude?

[Yellowstone10]

Conceivably, there is one thing that might fail and that might be important. If ISS loses pressure

all the hatches will sealed

Once the internal hatches are closed, is there any way to route atmosphere from the NORS tanks in the airlock to other modules?

[DanClemmensen]

Conceivably, there is one thing that might fail and that might be important. If ISS loses pressure

all the hatches will sealed

Once the internal hatches are closed, is there any way to route atmosphere from the NORS tanks in the airlock to other modules?

In the unlikely event that pressurization actually matters, the effect becomes increasingly less important as the modules get farther away from the USDV. That's good because the historically leakiest modules are the farthest away.