SpaceX Falcon 9 / Dragon 2 : SpX-DM2 : May 30, 2020 : DISCUSSION

[OnWithTheShow]

My impression is that solar cells, even space used solar cells, have lifetimes in decades not weeks....

[AU1.52]

I hear the issue is with how atomic oxygen reacts with the cells, while is not an issue on the ground.

[daedalus1]

I hear the issue is with how atomic oxygen reacts with the cells, while is not an issue on the ground.

The ISS panels have been in orbit for nearly two decades.

[karanfildavut]

The material you use for solar cell construction can have enormous impacts in terms of chemical stability, especially with aggressive oxidants such as atomic oxygen. IIRC the ISS solar cells are GaAs which makes them $$$ but have very long lifetimes. SpaceX and other use Si based solar cells which are much more degradation prone under oxidative conditions.

[russianhalo117]

I hear the issue is with how atomic oxygen reacts with the cells, while is not an issue on the ground.

The ISS panels have been in orbit for nearly two decades.

ISS solar arrays have 30 year max rated design life as do the rest of the station with a 10 year minimum certification which is continuously monitored and annually recertified with 5 year extensions (5 year extensions are projected to end at 30 years).

[thirtyone]

The material you use for solar cell construction can have enormous impacts in terms of chemical stability, especially with aggressive oxidants such as atomic oxygen. IIRC the ISS solar cells are GaAs which makes them $$$ but have very long lifetimes. SpaceX and other use Si based solar cells which are much more degradation prone under oxidative conditions.

Any sources on which spacecraft might have used Si-based cells? My understanding was that at traditional spacecraft price points and cost / kg the extra efficiency of III-V cells is almost always worth it and virtually all spacecraft use III-V instead of Si because of the higher efficiency despite cost concerns. SpaceX would of course be the one company which I could imagine *might* have decided to spend the effort trying to make cheaper cells work.

To give you an idea - even OneWeb, which also had relatively aggressive cost targets, used III-V cells in their satellites (just happened to be guesstimating their total power production to see if they had the budget for a GPS-like application...)
https://digitalcommons.usu.edu/cgi/viewcontent.cgi?filename=0&article=4225&context=smallsat&type=additional

I guess it's quite likely some of the very small smallsats use Si-based cells, though.

[edit]
I see sources saying that ISS actually has silicon cells? https://www.nasa.gov/mission_pages/station/structure/elements/solar_arrays.html

In fact, it sounds like the ISS might be one of the few active spacecraft that's still using silicon solar cells?

[karanfildavut]

https://www.solarpowerworldonline.com/2016/03/kind-solar-panels-nasa-use/

I was using this article as my reference. I seem to have misread, the ISS panels are indeed silicon based but are hardened against radiation and radicals via some type of coating.

Ill note they also allude to SpaceX using more off-the-shelf terrestrial type solar cells.

[Norm38]

When are they doing the 4-person camp out in the Dragon?  Are they planning any NASA-TV coverage for that?

[PahTo]

I saw in a related thread that power generation for Dragon gives them some 114 days or more on orbit.  This reminds me to ask:
does Dragon (and the new mating adapters) have SSiPTs capability (I think that was the acronym used during STS-era) whereby power generated by station can be used by VV?  I know said power transfer extended on-orbit capability for Discovery and Endeavour (Atlantis did not have SSPiT).

[Lars-J]

I saw in a related thread that power generation for Dragon gives them some 114 days or more on orbit.  This reminds me to ask:
does Dragon (and the new mating adapters) have SSiPTs capability (I think that was the acronym used during STS-era) whereby power generated by station can be used by VV?  I know said power transfer extended on-orbit capability for Discovery and Endeavour (Atlantis did not have SSPiT).

Yes, while docked the VV are powered by the station. The power generation issue is for when Dragon departs and has to have enough power to fly independently for a few hours before de-orbit. And this is due to these early solar panels gradually losing the ability to generate power, not some on-board consumable. (Shuttle used fuel cells, not solar panels)

The next flight will have the improved solar panels certified for 200+ days.

[AnalogMan]

I saw in a related thread that power generation for Dragon gives them some 114 days or more on orbit.  This reminds me to ask:
does Dragon (and the new mating adapters) have SSiPTs capability (I think that was the acronym used during STS-era) whereby power generated by station can be used by VV?  I know said power transfer extended on-orbit capability for Discovery and Endeavour (Atlantis did not have SSPiT).

As Lars-J noted, power is supplied to the VV (Visiting Vehicle).

Requirement is that the VV draw no more than 500 W continuous from ISS, or consume no more than 1 kW of peak power for 2 hours continuously, once per week.

(However, there is another requirement that the vehicle be capable of receiving 3 kW, but I assume this might be to allow for special contingencies.)

[IntoTheVoid]

in this Video from around 0:50 are a few video sequences from the habitability test on dragon:

Just got around to watching this short space to ground. It also features a quick pic of the 13 member record habitation of ISS in 2009 when STS-127 docked. Some faces looked familiar, as this flight also included current occupants Chris Cassidy, and Doug Hurley on their first spaceflights.

[eeergo]

Chris stated during the Apollo/Soyuz PAO event that a first week in August return is looking likely for Dragon

Interesting they keep moving the landing forward. Prelaunch, estimates for mission duration were between 30 and 119 days, which was later curtailed down to 30-90 days. With the "better than expected" quoted performance obtained, especially regarding solar array degradation not taking place as fast as feared, shouldn't DM-2 be prolonged, rather than shortened to barely 62 days?

Unless of course they want to speed up USCV-1 and need a minimum time for debriefing - or there are other undisclosed issues.

[Vettedrmr]

Chris stated during the Apollo/Soyuz PAO event that a first week in August return is looking likely for Dragon

Interesting they keep moving the landing forward. Prelaunch, estimates for mission duration were between 30 and 119 days, which was later curtailed down to 30-90 days. With the "better than expected" quoted performance obtained, especially regarding solar array degradation not taking place as fast as feared, shouldn't DM-2 be prolonged, rather than shortened to barely 62 days?

Unless of course they want to speed up USCV-1 and need a minimum time for debriefing - or there are other undisclosed issues.

I interpret it more as Bob & Doug's work on ISS is moving along well, as is USCV preparations.  The earlier they can get back, the sooner they can the final test points verified/validated to get USCV-1 cleared for flight.  And I expect USCV's crew has a lot more work they can get done on ISS.

Certainly haven't heard of any issues cropping up on either DM-2 or USCV-1.

Have a good one,
Mike

[eeergo]

Chris stated during the Apollo/Soyuz PAO event that a first week in August return is looking likely for Dragon

Interesting they keep moving the landing forward. Prelaunch, estimates for mission duration were between 30 and 119 days, which was later curtailed down to 30-90 days. With the "better than expected" quoted performance obtained, especially regarding solar array degradation not taking place as fast as feared, shouldn't DM-2 be prolonged, rather than shortened to barely 62 days?

Unless of course they want to speed up USCV-1 and need a minimum time for debriefing - or there are other undisclosed issues.

I interpret it more as Bob & Doug's work on ISS is moving along well, as is USCV preparations.  The earlier they can get back, the sooner they can the final test points verified/validated to get USCV-1 cleared for flight.  And I expect USCV's crew has a lot more work they can get done on ISS.

Certainly haven't heard of any issues cropping up on either DM-2 or USCV-1.

Have a good one,
Mike

I haven't either, doesn't mean they don't exist. It's certainly possible it's just a matter of wanting 2 extra crewmembers with a more ISS-oriented training than just stretching out the current DM-2 crew, who might well have put more focus during training on the S/C-centric mission than ISS utilization, as should be the case for a test mission.

Guess I'm just used to the regular modus operandi in the space sector - when a nominal mission duration is announced, it usually means at least that, plus perhaps extensions if at all possible.

[abaddon]

DM-2 mission extension length has been noted multiple times as being driven primarily by USCV-1 timing and minimizing the gap between.  Moving forward suggests certification is going better than expected.

[Robotbeat]

https://www.solarpowerworldonline.com/2016/03/kind-solar-panels-nasa-use/

I was using this article as my reference. I seem to have misread, the ISS panels are indeed silicon based but are hardened against radiation and radicals via some type of coating.

Ill note they also allude to SpaceX using more off-the-shelf terrestrial type solar cells.

SpaceX uses Silicon cells from Sunpower, or at least they did for some of the Dragon Cargo vehicles.

And the radiation-resistant coating is cover glass. Just a thin piece of glass over the cells. It is already normal to cover solar panels in a glass sheet, so it's not much different to terrestrial panels, fundamentally.

[Tomness]

https://www.solarpowerworldonline.com/2016/03/kind-solar-panels-nasa-use/

I was using this article as my reference. I seem to have misread, the ISS panels are indeed silicon based but are hardened against radiation and radicals via some type of coating.

Ill note they also allude to SpaceX using more off-the-shelf terrestrial type solar cells.

SpaceX uses Silicon cells from Sunpower, or at least they did for some of the Dragon Cargo vehicles.

And the radiation-resistant coating is cover glass. Just a thin piece of glass over the cells. It is already normal to cover solar panels in a glass sheet, so it's not much different to terrestrial panels, fundamentally.

I thought they built them in house since I thought it was weird they didn't get them through Tesla Energy aka SolarCity

[cppetrie]

Via Twitter:
Eric Berger
@SciGuySpace
·
5m
NASA is currently targeting 2:35 p.m. ET (18:35 UTC) on Sunday, August 2, 2020 for the landing of the Dragonship Endeavour mission.

    *Behnken joined his fellow SpaceX Crew Dragon crewmate Doug Hurley and began packing for their return to Earth and splashdown in the Gulf of Mexico on Aug. 2.*
https://blogs.nasa.gov/spacestation/2020/07/22/crew-awaits-cargo-works-science-and-departure-following-spacewalk/

Gulf of Mexico? I thought the primary splashdown site was the Atlantic off the eastern shore of the cape? Is this a weather related change or a misprint?

[NX-0]

Via Twitter:
Eric Berger
@SciGuySpace
·
5m
NASA is currently targeting 2:35 p.m. ET (18:35 UTC) on Sunday, August 2, 2020 for the landing of the Dragonship Endeavour mission.

    *Behnken joined his fellow SpaceX Crew Dragon crewmate Doug Hurley and began packing for their return to Earth and splashdown in the Gulf of Mexico on Aug. 2.*
https://blogs.nasa.gov/spacestation/2020/07/22/crew-awaits-cargo-works-science-and-departure-following-spacewalk/

Gulf of Mexico? I thought the primary splashdown site was the Atlantic off the eastern shore of the cape? Is this a weather related change or a misprint?

Maybe concerns over TS Gonzalo? Current track has it between Dominca and Aruba on Monday.