I would hope that most NASA fans have played around with ISS Live! by now (simply go to http://spacestationlive.nasa.gov/). ISS Live! truly is an unprecedented public relations tool for NASA spaceflight. In summary, the application (online and available as a mobile app) gives the public access to live and detailed information from the ISS – including daily crew timelines and system telemetry. I imagine it’s a nice resource for hardcore space geeks and some educators. But in my opinion, a huge part of the potential of ISS Live! is lost if the public does not know exactly what ISS is doing and how to interpret the data being shown. That’s why I’ve written this blog post. It’s an experiment.

Tomorrow morning HTV3 will rendezvous with ISS at about 7:00 AM CDT. The standard way for space fans to follow along with an event like this is to turn on NASA TV and listen to the public affairs officer describe the events. But let’s face it, that can be boring. What if I describe to you what flight controllers are doing to configure the space station for HTV3 rendezvous so you can watch major milestones as they occur in the ISS telemetry?

Friday 1:00 AM

For the real insomniacs, ISS systems start changing tonight at about 1 AM. That’s about 2 hours away as I write this post. at 1 AM the power system officer, Spartan, will be directing ISS flight controllers around the world to power down certain systems to conserve ISS battery power. This is being done because the solar arrays will have to be positioned for attitude control on thrusters. The solar arrays will no longer be allowed to track the sun.

Friday 2:30 AM

The solar array positioning is the first milestone you can easily track in ISS live. AT 2:30 AM the Spartan officer will be commanding both SARJs (solar alpha rotary joints) to a parked mode. In ISS live on page 1 of the Spartan displays, the SARJ angles are given in degrees. When they are sent to park you may see those numbers reverse direction (but not always) as they head to the commanded position. Then they will reach the commanded angle and stop moving.

Friday 4:00 AM

After solar array parking, not much happens – that I know of – in ISS systems until the attitude maneuver to capture attitude at about 4 AM. At this time the guidance system will be commanded to stop using only CMGs (control moment gyroscopes) and instead will use the Russian Segment thrusters to initiate the maneuver. Thruster control will continue for 3 more hours until HTV is just a few meters from ISS ready for capture.

To monitor the maneuver to HTV capture attitude, go to the ADCO displays and start on page 2. On the upper right it says “GNC Mode – CMG Thruster Assist” and “Control Type – Mom Mgmt” (which stands for momentum management). When ADCO commands the new control mode and maneuver the control type will change to “Att Hold” and you will be able to see the Commanded Attitude update on the lower part of the display. Watch the current attitude change as the space station maneuvers in attitude to the new position. The attitude error should reduce, of course, as it gets closer.

Friday 4-7 AM

During the next 3 hours HTV will be doing its final approach up the R-bar (the line drawn from the ISS down towards the Earth). On NASA TV HTV will become visible in the camera views during this time. Not much ISS configuration is done. We sit and wait in the capture attitude for HTV to arrive.

Friday 7 AM

If everything goes to plan, HTV will arrive at the “capture point” about 10 meters below ISS and wait for the ISS astronauts to grab it with the space station robot arm. Some final commands are sent by the ground teams to get ready for capture. ADCO will send a command to enable “attitude maneuver”, for instance. This is a command needed so that the ISS crew can do the next step.

Friday 7:03 AM

The planned times are rather precise. Go for capture is expected at 7:03. Once that happens, the ISS crew is in charge and ground teams just watch. This is when you want to be on the ADCO displays again, but this time on page 3. Under “momentum” watch the “desaturation request” field. The astronauts are going to hit a button onboard ISS that will set that parameter to “inhibit”. This effectively stops any thruster firings so that the SSRMS can approach HTV. We do not allow thruster firings when the SSRMS is close to HTV because the sudden impulses could be a collision hazard. Once they have confirmed desaturation requests are inhibited, the astronaut flying the SSRMS will move “into the box” and try to grapple HTV.

Friday 7:04 AM

Capture should occur only a minute or two after the final configurations are in place. Once desaturations are inhibited, attitude control is again on CMGs only. Watch the “momentum percentage” on ADCO display page 3. This value will slowly creep up. The astronauts only have until this value reaches 100% to capture HTV, otherwise ISS will have lost attitude control, and contingency procedures will be executed.

Friday 7:08 AM

If HTV is successfully captured, ground teams will take back control of the ISS guidance system. At 7:08 ADCO will command ISS back into a mode that allows thruster firings. At this time you will see “desaturation request” go back to “enable”.

Friday 7:25 AM

The day isn’t over. Ground teams and the ISS crew still need to work as a team to get HTV berthed on the Node 2 nadir common berthing mechanism. At 7:25 ADCO will initiate an attitude maneuver to a new attitude that is most optimal for the new center of mass of ISS with HTV onboard. Watch the “attitude” section on ADCO display page 2.

Friday 8:00 AM

After the maneuver, ADCO will prepare to go back to a momentum management control mode. This activation will occur at about 8:00 and you will see the control type change on ADCO display page 2.

After returning to momentum management, ADCO will again need to inhibit thruster firings because HTV will be very close to Node 2 getting ready for berthing. Again, “desaturation request” will go to “inhibit”.

Friday 8:35 AM

While HTV berthing is ongoing, the power officer will be reconfiguring his system post-rendezvous. The solar arrays will be taken back to autotrack at about 8:35. Go back to the Spartan display and you will see the SARJ joints start moving again.

And those are all the key milestones that you can follow on ISS Live! Obviously other important things will be going on related to rendezvous, but not everything is easily viewed in the available telemetry. I hope that at least one person will follow along on ISS Live! while watching NASA TV and maybe learn something new. Let me know if you do!