SpaceX F9 / Crew Dragon : Crew-2 : 22 April 2021 - DISCUSSION

[kdhilliard]

Can I ask about the bracelets the crew are wearing? They look like hospital bracelets but I’m not sure, the previous crew also wore them? But soyuz crews don’t? Does anyone know why they are worn?

All four crew members are wearing them on their right wrist, including the Commander Shane Kimbrough who also wears his watch on the right.  The best shot I got was of Thomas Pesquet at 3:11 of the "Watch SpaceX Crew-2's on-orbit tour of Crew Dragon Endeavour" video.

My best, fully uninformed guess is that they are radiation dosimeters.

Edited to add link to DM-2 image showing Doug & Bob with their bracelets.
I'm still guessing dosimeter, but I've still not seen one from any angle showing an additional thickness to support that.

[Svenry]

I'm watching a replay and, during the lead-up to the launch, the commentators got all excited about a highly magnified view of "the space station".  Here's an enhanced version of that shot.

Ummmm...the station looks a lot like Jupiter to me.

Good eye! Yep, that is Jupiter. I don't think anyone was waving back, unfortunately. Video at 3:50:09

[OneSpeed]

Here is a comparison of the launch telemetry from the Crew-1 and Crew-2 missions.

1. The Crew-2 telemetry has reverted to the usual SpaceX altitude resolution of a single decimal point below 100km and none above.
2. The Crew-2 telemetry has reverted to the usual SpaceX update rate of 25 per second, and hence gives a much smoother acceleration plot.
3. Ignoring the spikes in the Crew-1 acceleration, the profiles are otherwise very similar.

[Kiwi53]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

[Jansen]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

Phasing

[Rossco]

Great achievement.

Looking forward to a decent picture of both Dragons docked - bet that'll be one for the office wall at hawthorne!

[Life_Support_32]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

Soyuz docking is either 2-orbit "express" or 34-orbit (about 51 hours) "regular". The 8 hours you mention was a 4-orbit mode that was replaced with the 2-orbit.

[cscott]

And one difference is that AIUI it takes ISS fuel to manuveur for an "express" rendezvous, and they usually want to conserve ISS fuel. The decision is not all about spacecraft capabilities.

[TJL]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

Another reason is that SpaceX prefers to have a "rest period" for the crew prior to linking up with ISS after a very long day.

[Norm38]

11 people on ISS right now thanks to Dragon. What a great photo.

SpaceX has launched 10 people into orbit and 8 are in that shot.

[allio]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

If I remember correctly it has something to do with Russian ground monitoring stations.

Scott Manley has an excellent video about It.

[Lars-J]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

From a physics POV, nothing prevents Dragon from doing the same, but taking longer is due to two issues:
- phasing (basically where ISS is in the same orbit at launch, how much “chasing” Dragon has to do to catch up, some launch days have better “phasing” than others)
- crew rest concerns (it had already been a long day for them so why push it)

[hektor]

https://twitter.com/Thom_astro/status/1385998235005751297?s=20

[Jorge]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

https://forum.nasaspaceflight.com/index.php?topic=53087.msg2193888#msg2193888

[kdhilliard]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'? ...

https://forum.nasaspaceflight.com/index.php?topic=53087.msg2193888#msg2193888

Yep, it's all about phase angle and whether it is worth coordinating an ISS reboost to enable a fast rendezvous on a particular launch date.

Crew-1 launched on 15 November 2020 and docked to ISS 27.5 hours later, but had it launch on 14 November as had been expected at one point, it would have flown an 8.5 hour rendezvous.

Here's the Chris G tweet with the detailed timeline for a 14 November launch, and here's my post from back then with an attached PDF of that timeline.

[Kiwi53]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

Thank you, the answers have been both educational and helpful
 

[SPKirsch]

https://twitter.com/SpaceXFleet/status/1386067579912048645

The SpaceX fleet is about to have a very busy week...

- OCISLY w/ B1061-2 en-route to Florida (ETA Monday-ish)
- JRTI en-route to the Starlink LZ
- GO Searcher stationed for Atlantic Crew-1 splashdown in, Navigator in Gulf
- GO Quest and Shelia Bordelon preparing for Starlink

[WannaWalnetto]

Has any more information been shared / discovered / posted anywhere about “the close approach of that surprise object” that hurriedly put the crew back into their flight suits?  I’m wondering just what the surprise really was.

A new object that nobody knew about, or a known object that wasn’t a threat ... until it was?

[CuddlyRocket]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

Another reason is that SpaceX prefers to have a "rest period" for the crew prior to linking up with ISS after a very long day.

If I was on the crew I'd probably enjoy the chance to chill out and admire the view for an extended period. A Dragon with four astronauts is a lot more comfortable than a Soyuz with three. Keep your customers happy!

[mandrewa]

Why does Crew Dragon take pretty much a day to dock with the ISS, when Soyuz can do it in around three hours 'express' or about eight hours 'regular'?

Sorry if this is a dumb question

https://forum.nasaspaceflight.com/index.php?topic=53087.msg2193888#msg2193888

To elaborate a bit more, Baikonur Cosmodrome is under the ISS's orbit in a way that Cape Canaveral simply isn't.  Baikonur's alignment means it could make an express launch every single day if it wanted to while Cape Canaveral only has opportunities once or twice a month.

And since each three hour rendezvous means the ISS has to expend propellant to line itself precisely for the meeting, weather also has a big impact on all of this.  Cape Canaveral's weather is far less predictable than Baikonur's.  That means that if NASA did attempt short journeys using one of its occasional opportunities, there's a much higher risk that the propellant expenditure on the ISS would be wasted because weather might cancel the whole thing at the last minute.