SpaceX F9 : CRS SpX-20 : March 6/7, 2020 : Discussion

[ugordan]

Beautiful, clear views of the launch from Hilton Head Island! Had a wonderful interaction with some random bystanders enjoying a toke and stroll as well as a man and his father who were also out on the beach for the launch.
Was stage separation up high enough to be in sunlight or was it too late for that, because we had clear views of the second stage and first stage plumes interacting as well as the second stage jellyfish.

That lightshow was plasma physics due to rarefied, but high speed gas collisions rather than direct illumination by a celestial body.

[ZachS09]

When I saw that boostback burn phenomenon from the Embry-Riddle Daytona Beach campus, I was like, "Holy s***!"

It was only the second time I ever saw that in person.

[Rocket Science]

When I saw that boostback burn phenomenon from the Embry-Riddle Daytona Beach campus, I was like, "Holy s***!"

It was only the second time I ever saw that in person.

Incoming!!

[Comga]

When I saw that boostback burn phenomenon from the Embry-Riddle Daytona Beach campus, I was like, "Holy s***!"

It was only the second time I ever saw that in person.

I share your enthusiasm, if not your generation’s way of expressing being overwhelmed by the beauty of the fluid and radiant plume impingement. 😉

I am a little jealous that you got to see it in person.
The photos and videos are marvelous, but we know launches are better observed by eye.

[ZachS09]

When I saw that boostback burn phenomenon from the Embry-Riddle Daytona Beach campus, I was like, "Holy s***!"

It was only the second time I ever saw that in person.

I share your enthusiasm, if not your generation’s way of expressing being overwhelmed by the beauty of the fluid and radiant plume impingement. 😉

I am a little jealous that you got to see it in person.
The photos and videos are marvelous, but we know launches are better observed by eye.

I used to film launches and/or Falcon booster landings for fun, but I stopped doing it because of the slightly low-res quality on my camera. I think it’s better to see it with my own eyes.

[CorvusCorax]

Is there no post launch press conference this time? Did I miss it?

[scr00chy]

Is there no post launch press conference this time? Did I miss it?

They've stopped doing those some time ago.

[daveglo]

A rare glimpse of CRS-20's Dragon performing a post-separation maneuver from a Stage 2 camera via the SpaceX webcast.

[JimO]

Wasn't that the sep maneuver observed from the Netherlands?

[mmonce]

Serious layman's question. Using the Canadarm to grasp Dragon has been working well for years. Dragon 2 will direct dock. But what are the trade-off between the two methods? Seems obvious that they wouldn't switch to direct docking unless that is considered an improvement. Is it safety? Time? Wear and tear on the grasping arm?

Genuinely curious.

[Nomadd]

When I saw that boostback burn phenomenon from the Embry-Riddle Daytona Beach campus, I was like, "Holy s***!"

It was only the second time I ever saw that in person.

I share your enthusiasm, if not your generation’s way of expressing being overwhelmed by the beauty of the fluid and radiant plume impingement. 😉

I am a little jealous that you got to see it in person.
The photos and videos are marvelous, but we know launches are better observed by eye.

I used to film launches and/or Falcon booster landings for fun, but I stopped doing it because of the slightly low-res quality on my camera. I think it’s better to see it with my own eyes.

Tim Dodd and I agreed on that. He just hoped all his cameras were good for the Hopper launch, because neither of us were going to watch that on a display.

[CorvusCorax]

Serious layman's question. Using the Canadarm to grasp Dragon has been working well for years. Dragon 2 will direct dock. But what are the trade-off between the two methods? Seems obvious that they wouldn't switch to direct docking unless that is considered an improvement. Is it safety? Time? Wear and tear on the grasping arm?

Genuinely curious.

Capture with the arm is work intensive and imposes quite a number of additional constraints.

1. You need crew on the station. The crew needs to be available (time, sleep-schedule)
2. That means you also lose valuable science time for berthing maneuvers
3. You need favorable visual conditions to capture for astronauts to see.
4. The robotic arm needs to be working and operational. There is only one arm, if its offline, no vehicle can visit. (Which prevents supplying spare parts for said arm)
5. The procedure takes longer than docking.
6. The process is more error prone (Getting the capsule safely and drifting with zero vector in the capture position is actually slightly harder than an automated docking approach from a guidance and control point of view. As the capsule ends up in free drift in very close proximity to the station, velocity vector needs to match with extreme precision to not drift too far during capture operation)

In contrast, the biggest advantage of berthing is the wider hatch, allowing easy transfer of bulky items. The IDA - especially being at the end of the former shuttle adapters - is pretty narrow and everything has to be transported through an oddly-shaped access tunnel. Bringing entire science racks through there to be installed on the station isn't possible. (But if needed, they can be brought up on Cygnus and brought and returned on Dreamchaser)

[Welsh Dragon]

Serious layman's question. Using the Canadarm to grasp Dragon has been working well for years. Dragon 2 will direct dock. But what are the trade-off between the two methods? Seems obvious that they wouldn't switch to direct docking unless that is considered an improvement. Is it safety? Time? Wear and tear on the grasping arm?

Genuinely curious.

Manned craft always dock rather than berth (better for emergency departures IIRC) and Dragon 2 is fundamentally a manned craft that happens to also be used as a crago craft.

[starbase]

Serious layman's question. Using the Canadarm to grasp Dragon has been working well for years. Dragon 2 will direct dock. But what are the trade-off between the two methods? Seems obvious that they wouldn't switch to direct docking unless that is considered an improvement. Is it safety? Time? Wear and tear on the grasping arm?

Genuinely curious.

Upside: Docking needs less crew time, Dragon 2 has more pressurized/unpressurized cargo volume available plus more slots for powered experiment payloads (freezers)
Downside: Narrow hatch allows only less bulky cargo items

[starbase]

Any info yet on when Bartolomeo extraction/installation will happen?

[Nomadd]

Serious layman's question. Using the Canadarm to grasp Dragon has been working well for years. Dragon 2 will direct dock. But what are the trade-off between the two methods? Seems obvious that they wouldn't switch to direct docking unless that is considered an improvement. Is it safety? Time? Wear and tear on the grasping arm?

Genuinely curious.

Capture with the arm is work intensive and imposes quite a number of additional constraints.

1. You need crew on the station. The crew needs to be available (time, sleep-schedule)
2. That means you also lose valuable science time for berthing maneuvers
3. You need favorable visual conditions to capture for astronauts to see.
4. The robotic arm needs to be working and operational. There is only one arm, if its offline, no vehicle can visit. (Which prevents supplying spare parts for said arm)
5. The procedure takes longer than docking.
6. The process is more error prone (Getting the capsule safely and drifting with zero vector in the capture position is actually slightly harder than an automated docking approach from a guidance and control point of view. As the capsule ends up in free drift in very close proximity to the station, velocity vector needs to match with extreme precision to not drift too far during capture operation)

In contrast, the biggest advantage of berthing is the wider hatch, allowing easy transfer of bulky items. The IDA - especially being at the end of the former shuttle adapters - is pretty narrow and everything has to be transported through an oddly-shaped access tunnel. Bringing entire science racks through there to be installed on the station isn't possible. (But if needed, they can be brought up on Cygnus and brought and returned on Dreamchaser)

A bigger factor than not being able to get on would be not being able to get off, if the arm wasn't an option for any reason.

[CorvusCorax]

 A bigger factor than not being able to get on would be not being able to get off, if the arm wasn't an option for any reason.

I think that is an issue that could worse case be mitigated with a spacewalk, or even with the capsule's (or even the station's)  thrusters. The bolts can all be loosened from the inside. The only thing the arm is needed is to pull the capsule away and drop it off right next to the station so it can maneuver away. I think, if the arm was unavailoable and Dragon1 HAD to leave, an improvised mitigation could be found.

The needed precision for unmating is much lower than the needed precision for mating.

It's a bigger issue for crewed vehicles, which need to be able to undock during a station evacuation with no one on board to loosen the bolts.

[mmonce]

Great answers, and all make sense. Glad I asked.

[tbellman]

In contrast, the biggest advantage of berthing is the wider hatch, allowing easy transfer of bulky items. The IDA - especially being at the end of the former shuttle adapters - is pretty narrow and everything has to be transported through an oddly-shaped access tunnel. Bringing entire science racks through there to be installed on the station isn't possible. (But if needed, they can be brought up on Cygnus and brought and returned on Dreamchaser)

But that's a limitation of the docking adaptor, right?  Not inherent to whether the spacecraft docks autonomously or is brought in using an arm on the station.

Is there anything preventing a visiting spacecraft from performing a docking operation to the berthing position on ISS without using the Canadarm?

[Lars-J]

Is there anything preventing a visiting spacecraft from performing a docking operation to the berthing position on ISS without using the Canadarm?

In theory, yes, but in practice, no. The docking adapters have springs to dampen impact as two spacecraft dock and connect, but the berthing mechanism does not. It has to be very careful aligned and connected, which is why the arm is used.

Could a spacecraft use super precise thruster firings to do the same? In theory, yes, but... I don't believe any current (or planned) visiting vehicles have that level of fine grained thruster control. I could be wrong.