Rendezvous

This is the art and science of getting two orbiting object together. It is required for Docking with the ISS, repairing and retrieving satellites. To perform a successful rendezvous, the Space Shuttle crew must match the orbits and position of the ISS (or the target object, like the Hubble, etc.).

The Shuttle crew matches the orbits and location through a series of OMS/NC burns which match the Apogee and Perigee of the Shuttle and the target vehicle (The ISS or a satellite). After the burns series is completed, the last phase of the final “approach” of the rendezvous and docking with the ISS (or grappling a certain object in space) is performed manually, assisted by the radar guidance system and various cameras (and also by visually following the target through the Space Shuttle windows).

Rendezvous in SSM2007

Correction burns

First stage of the rendezvous is figuring out where is the target object and how to match it's orbit to yours. This is pre-calculated by the GC weeks before the launch. In fact, the launch window in set according to those calculations.

The base if for all of these maneuvers is that lower orbits have faster “lap time”. They circle the earth faster allowing the intercepting object “catch up” with the target object. in our case the interceptor is the Space Shuttle while the target is a satellite or the ISS.
The Shuttle is launched to a lower orbit and every few orbits the peregee is raised by a few miles those “slowing” the closure rate (to raise the orbit you actually speed up), depends on the target orbit it usually takes three to five burns to get the orbits aligned.

All NC burns are made using the OMS engines.

FIXME

Star Tracker & KU band

After the NC burns are complete the Shuttle and the Target are a few miles from each other on very similar orbits. In SSM2007 the magic number is about 45Kft (or 13.5km, or 7.3NM). The Shuttle is on a slightly lower orbit, thus catching up with the target (mostly the ISS) because of its higher orbital velocity. In order to fine tune the rendevous the Shuttle needs exact information on the whereabouts of the target. To give the crew this information the Shuttle is using two systems, the Star Tracker and the KU band Radar. Both controlled from CRT4 in the R11 panel.

Star Tracker

OPS202 SPEC22 - Star Tracker

In addition for its duties and a navigational aid the Star tracker can help determine the location of other orbiting objects. It just needs to be activated to do so by the crew. The star tracker controls are available in the OPS2 Mode of the The GPC under the SPEC22 display.

In order to load a target TGT TRK needs to be enabled on both Y and Z axis, this is done by selecting ITEM 5 (Y) & ITEM 6 (Z). After setting the star tracker to the correct mode - targets can be loaded using ITEM 11 and ITEM 12 one per axis. The correct syntax for loading a target includes the target ID in the The GPC - so you are actually typing ITEM 11+2 EXEC (or in GPC free-speech “Load -Y target No.2 - GO”)

Loading the target allows the Star tracker to calculate azimuth and elevation as well as give a rough range estimate. This information is then fed to the KU-band radar.

KU-Band Radar

Ku-Band antenna controls on A1U panel OPS202 SPEC33 - KU band The KU-band antenna is usually used for high-Bandwidth transmissions back to earth. But it is also used as a radar antenna. The KU-band controls are available in the OPS2 Mode of the The GPC under the SPEC33 display. In order to function for the rendezvous it should be activated in RNDZ NAV mode (ITEM 1).

The computer will automatically try and aim the antenna at the target selected by the Star-tracker. This is the software side of the work. The antenna itself should be allowed to track and the radar should be turned on. This is done from the A1U panel.

The KU-band Power should be moved to the ON position and the KU-band mode selection rotary dial should be set to Auto Track

LOS System

LOS indicator (A2 Panel) The final most important part of the rendezvous is done with the Line-Of-Sight indicator (LOS). This indicator displays the information supplied by the KU-Band Radar. it allows the crew to have range, closure rate, elevation and azimuth offset and drift rates all displayed in a relative simple matter. The indicator is found on the A2 panel. LOS contains two indicators a Digital readout and an Analog display.

The LOS work mode is set by two switches.

  • DIGI DIS SELECT - allows the crew to display either Range and Range Rates (R/R) or Elevation and Azimuth deviations (EL/AZ).
  • PNTR SCALE - changes the sensitivity of the analog display - it shows the drift rate of the target in relation to your line of sight. Means, if you are translating left, the target will -in your view- drift to the left.

It is important to understand how the thrusters of the RCS will work. For this understanding it is mandatory to know the different axes of the Shuttle. upload.ssm-fans.info_images_axis.jpg For most rendevous and docking you will look out of the overhead windows, your chest facing the aft controls. That means, you will look into the -Z direction. To tell the Shuttle that you have now a new line-of-sight alignment you must switch on the FLT CNTRL Power on the left side of the A6U panel and flip the SENSE switch to –Z. Forward is now –Z, -Y is right and +X is up. This makes your THC inputs easier.

upload.ssm-fans.info_images_rbar.jpg In order to rendevous with your target you should make sure that you are closing in, done by translational thrust toward the target. Closing in means you have a negative number on your lower digital read out when DIGI DIS R/R is selected. In SSM2007 this rate (velocity) should be kept at >3.00 to meet your target in time. Another task will be to get the Shuttle aligned with the so called R-Bar. That is an imaginary line that connects the target with the center of the earth. With your DIGI DIS SELECT switch in EL/AZ position you can see how high/low and how far right/left your target is in relation to your -Z axis. If you have positive numbers on your digital readout you have to translate up and/or right and vice versa. When both readouts are 0, you are on the R-Bar. Click on the drawing right.

Go on with docking

FIXME

Video Tutorials

Rendezvous Video Tutorial

Same Video Tutorial on Youtube:
Part 1 Part 2 Part 3 Part 4 Part 5

rendezvous.txt · Last modified: 2011/10/05 11:02 by uri_ba
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