4 comments

• Icepilot

  October 8, 2020 at 4:28 pm

  For the two dozen exoplanets, two questions (likely for the future):
  Are they double-planets like Earth-Luna?
  What is the metallicity (or generation) of each star?
  Both may be critical factors regarding the initiation of life.
• mkent

  December 22, 2020 at 9:11 pm

  Robert: I don’t know if you’ll see this comment, since it’s on a post on page 13 of your blog (I’m a bit behind on listening to your Batchelor show podcasts (absolutely great podcasts, by the way)), but I wanted to add some information about the ISS that wasn’t apparent from the podcast itself.

  First, Zvezda (also known as the Service Module) was the third ISS module launched (behind the FGB and Node 1), but that’s a minor nit. More important is the possibility of separating the two halves of the ISS into separate space stations.

  You were correct when you hinted that the ISS is really two separate space stations joined at the FGB. The American side (known as the USOS (the United States Operating Segment)) can’t function long without the Russian side (known as the ROS (the Russian Operating Segment)). While the USOS now has its own life support, crew return vehicle, gyroscopic attitude control, electrical generation, heat rejection, communications, and command and control, it lacks the propulsive attitude control and orbital reboost capability provided by the Service Module.

  While the Control Moment Gyros (CMGs) on the Z-1 truss can provide attitude control for quite some time, unbalanced torques will eventually saturate the CMGs, requiring them to be desaturated while the thrusters on the Service Module fire. In addition, without the Service Module, the ISS has no orbital reboost capability, so it will re-enter the atmosphere about 1-2 years after separation.

  I think the proposed Axiom module can provide both of those functions, but don’t quote me on that.

  It’s not all rosy on the ROS either. The FGB is actually owned by the Americans (it was paid for by the U. S. taxpayers), so after separation they would be cut off from their own Docking and Stowage module attached to it. Perhaps worse, the ROS relies on the USOS for most of its power. *Each* of the four solar array trusses on the USOS provides about ten times the electrical power as the Service Module. As part of the giant barter system that is the ISS program, the ROS draws most of its power from the USOS.

  So while the Russians *say* they’re going to separate their modules from the ISS and go their own way (and they probably really want to), they can’t do it any more than we can. And if the Russian science module’s 20-year journey to the launch site shows anything, it’s that the U. S. can develop and build new space station modules a whole lot faster than the Russians.
• Robert Zimmerman

  December 22, 2020 at 9:29 pm

  mkent: Interesting engineering details, most of which I had read years past but had forgotten.

  Overall, it does appear the Russians are in a weaker position than the U.S. They can’t get anything new built and don’t have the cash to do it even if they could. We have an increasingly thriving commercial space industry that is building things fast, and making money in the process. Even if ISS is approaching its wear date, the U.S. is well positioned to replace its capabilities, while Russia is not.
• Robert Zimmerman

  December 22, 2020 at 9:30 pm

  PS. All new comments show up on my feed, when they happen, regardless of the post they are sent to. And they also show up in the “most-recent comments” section in the right column when they are posted, irrelevant to the post itself.