ORUs Return - Discussion of Potential

[manboy]

Why would one need to enlarge the side hatch?
Why not simply hold the Dragon capsule with the Canadarm2 in about 1.5 meter distance from the station. One can open the hatch at the top and together with the second person they can maneuver the ORU through the hatch and secure [it] inside with as example straps?

Also, can the Dragon avionics work in a vacuum?

I don't believe so.

[mlindner]

Would also need to make sure they don't depend on convection for electronics cooling.

No convection in zero g. Along those lines, forced air, fans maybe, but that would just dump the heat into the cabin. I don't know Dragons thermal design... cooling loops, cold plates, pumps, valves, radiators. O God here we go again!

That was what I was saying...

[Jim]

Would also need to make sure they don't depend on convection for electronics cooling.

That is my point.

[darkenfast]

While I don't believe that it's worth the trouble and risk to bring back one of these units, it does bring up the interesting point: during the design of the Dragon, did they make it possible for the spacecraft to be depressurized, either for an unforeseen circumstance such as this, or with an eye to later manned operations that might include an EVA in the manner of the Apollo Command Module? It does seem to be something that has to be allowed for in the initial design process. My uneducated guess is that they didn't, but it would be interesting to find out.

[CuddlyRocket]

Although bringing back the unit in one piece is ideal; short of ideal is often worth doing - so can they dismantle the unit and bring back some of the salient parts in a Dragon?

[Prober]

Although bringing back the unit in one piece is ideal; short of ideal is often worth doing - so can they dismantle the unit and bring back some of the salient parts in a Dragon?

getting back parts that fail is good science for long term spaceflight.    Seen NASA funds wasted on other projects.   This would be on my list as a sound expense. 
 

[MP99]

Edit: apologies for mis-quote - was intended to be a response to this message:-

Although bringing back the unit in one piece is ideal; short of ideal is often worth doing - so can they dismantle the unit and bring back some of the salient parts in a Dragon?

getting back parts that fail is good science for long term spaceflight.    Seen NASA funds wasted on other projects.   This would be on my list as a sound expense. 

I'd say that would be engineering rather than science, but I take your the point.

However, given the hassle just dealing with the QD's through spacesuit gloves, I just don't see how they could dismantle an ORU that was never designed for it.



Might be possible for future designs of ORU, but that would seem to massively increase the complexity of the design, probably leading to a higher failure rate in the first place.

cheers, Martin

[Xspace_engineerX]

It's actually been stated somewhere that they can attach an external Flow Control Valve to salvage this ORU. No need for return

[douglas100]

Why would one need to enlarge the side hatch?
Why not simply hold the Dragon capsule with the Canadarm2 in about 1.5 meter distance from the station. One can open the hatch at the top and together with the second person they can maneuver the ORU through the hatch and secure [it] inside with as example straps?

Ah the S word! (My bold.) If the Dragon is held on the arm then it is not available  to move either a person or the ORU. That makes things less simple. Better to have the Dragon docked or berthed to the Station.

I agree about the vacuum electronics problem discussed earlier. It was one of the things I had in mind when I said the modifications would neither be simple nor cheap. (This difficulty goes right back to Voskhod 2.)  A motorized enlarge side hatch, emulating the action of the Shuttles payload bay doors would probably be needed as well. Having sufficient volume to return the ORU in question is a given, of course. So is the point about centre of gravity placement made earlier.

I proposed this scenario to see what the general opinion was about how important ORU recovery is. I get the impression that a number of members think it's not worth doing. I tend to agree with that opinion.

[guckyfan]

I proposed this scenario to see what the general opinion was about how important ORU recovery is. I get the impression that a number of members think it's not worth doing. I tend to agree with that opinion.

I agree, it won't come cheap and fast, if and when needed. But it would not cost that huge an amount also. Probably it is not that urgent to get an ORU back. But they may want to place experiments outside and retrieve them without going through the station.

For that scenario NASA would have to contract that capability. And the retrieval flight would not need to be expensive beside the one time develoment cost. If the flight can be used for pressurized station resupply, the down capacity comes virtually free. Once the present backlog of downmass freezers and equipment from inside the station is cleared they may be able to dedicate flights for external downmass without needing to send a separate flight for the purpose.

[Norm38]

I've not heard of any modern COTS electronics, besides pressure sensors/gas analysis sensors, that break when exposed to vacuum

Lots of modern electronics still have electrolytic capacitors, and those will vent and fail in vacuum.  As ceramics can't match them for volumetric density, may still be in use on space hardware.
Point is, there are details to check, don't assume anything.

[MP99]

I've not heard of any modern COTS electronics, besides pressure sensors/gas analysis sensors, that break when exposed to vacuum

Lots of modern electronics still have electrolytic capacitors, and those will vent and fail in vacuum.  As ceramics can't match them for volumetric density, may still be in use on space hardware.
Point is, there are details to check, don't assume anything.

It looks to me like this may just be a matter of the casing being optimised for atmospheric pressure.

Is it possible to get them with tougher casings which are strong enough to withstand a vacuum? If so, it would seem to be a sensible precaution to use these in spacecraft electronics, even if intended for use in a pressurised section.

cheers, Martin

[Jim_LAX]

Tantalum capacitors have replaced the older borax and water electrolytic capacitors for any military applications.  They have even better capacitance to volume ratio and are available in metal cans with glass seals for very long life. No doubt they are available in vacuum rated versions too.
Even the pressurized section of a capsule may need to be vacuum rated in case an EVA becomes necessary.

[rst]

I've not heard of any modern COTS electronics, besides pressure sensors/gas analysis sensors, that break when exposed to vacuum

Lots of modern electronics still have electrolytic capacitors, and those will vent and fail in vacuum.  As ceramics can't match them for volumetric density, may still be in use on space hardware.
Point is, there are details to check, don't assume anything.

It looks to me like this may just be a matter of the casing being optimised for atmospheric pressure.

Is it possible to get them with tougher casings which are strong enough to withstand a vacuum? If so, it would seem to be a sensible precaution to use these in spacecraft electronics, even if intended for use in a pressurised section.

But then the circuit boards that include these capacitors are no longer COTS ("commercial, off the shelf").  And if, as some of us have been assuming, use of COTS components is part of SpaceX's cost-reduction strategy, your avionics costs just went up, possibly by a fairly large amount.  Even vacuum-qualifying COTS components that you expect to work could be a distraction.

It's worth remembering that this discussion started with the idea of using a "previously flown" Dragon, with the idea that it would be a cheap mission.  In that context, particularly given the strapped state of NASA's budget (with data analysis for Cassini and Curiosity on the chopping block), it's not likely they'd consider something like this unless it saved them money that they'd have to spend otherwise.  And in that context, every extra dollar spent tells.  So, unless the Dragon systems have been vacuum-rated already (which we wouldn't necessarily know), this is still worth talking about.

[Joffan]

Potentially the requirement for redesign could be reduced to a new hatch for external equipment return. The mission could otherwise be a normal cargo resupply/return, but with an adapted  hatch that allows for fitting and covering an ORU inside an additional shaped enclosure protruding into the body of the craft. The outer cover could either bleed slowly to ambient pressure (vacuum or atmospheric) or hold vacuum at some greater cost and risk.

The internal working volume, both up and return, would be reduced by the enclosure plus enough to allow the hatch to move with the internally-protruding enclosure.

Certainly not a cost-free option but perhaps fewer impacts on the internal status of Dragon working.

A reusable nosecap, in discussion on another thread, would allow a different protected external volume for this sort of proposed requirement.

[MP99]

I've not heard of any modern COTS electronics, besides pressure sensors/gas analysis sensors, that break when exposed to vacuum

Lots of modern electronics still have electrolytic capacitors, and those will vent and fail in vacuum.  As ceramics can't match them for volumetric density, may still be in use on space hardware.
Point is, there are details to check, don't assume anything.

It looks to me like this may just be a matter of the casing being optimised for atmospheric pressure.

Is it possible to get them with tougher casings which are strong enough to withstand a vacuum? If so, it would seem to be a sensible precaution to use these in spacecraft electronics, even if intended for use in a pressurised section.

But then the circuit boards that include these capacitors are no longer COTS ("commercial, off the shelf").  And if, as some of us have been assuming, use of COTS components is part of SpaceX's cost-reduction strategy, your avionics costs just went up, possibly by a fairly large amount.  Even vacuum-qualifying COTS components that you expect to work could be a distraction.

It's worth remembering that this discussion started with the idea of using a "previously flown" Dragon, with the idea that it would be a cheap mission.  In that context, particularly given the strapped state of NASA's budget (with data analysis for Cassini and Curiosity on the chopping block), it's not likely they'd consider something like this unless it saved them money that they'd have to spend otherwise.  And in that context, every extra dollar spent tells.  So, unless the Dragon systems have been vacuum-rated already (which we wouldn't necessarily know), this is still worth talking about.

ISTM that COTS does not mean lowest quality / price components, just not rad hardened.

As I speculated, and per Jim LAX's comment, it's possible that the avionics are already vacuum rated, to deal with contingencies.

Cheers, Martin

[Jim]

Even the pressurized section of a capsule may need to be vacuum rated in case an EVA becomes necessary.

Not if the capsule never intends to support EVA.