I do not know if Samantha loved to catch butterflies as a child… but I am sure she never dreamt of catching a Dragon with a robotic arm!
That is exactly what is going to happen today: she is in charge of grappling the SpaceX Dragon-6 cargo ship from her favourite spot in the Space Station: the Cupola. It is the first time that this task is been given to an Italian astronaut. Samantha assisted her NASA colleague Terry Virts for the last SpaceX docking. If you are curious she wrote about it extensively it in her logbook (link).
The Dragon spaceships perform a “stop and go” dance as they approach the Space Station: it’s all about the team play between the crew onboard and the Control Centres on Earth. After many miles travelled this part of its journey is very delicate. Dragon left Earth on Wednesday. Just ten minutes after launch the cargo spaceship reaches its first orbit and from there it starts its slow approach to the Space Station which lasts a couple of days.
Credits: NASA
When the spaceship starts to ”see” the Space Station is time for the Control Centres (NASA’s one in Houston and the SpaceX’s one in Hawtorne, USA) to fire the engines and gently push the cargo up to 250 metres from the Station’s docking port. Now the Dragon’s eyes are important: a radar system (that works with visible-light wavelength) and an infrared camera. The data from its ‘eyes’ are compared and allow the spaceship’s systems to know precisely its position and speed in relation to the Station. Meanwhile, Dragon and the Space Station are communicate via UHF band. From this moment on, the astronauts operate the SpaceX cargo remotely with the support of the Control Centres on the Ground.
The first stop is at 50 metres from the orbital outpost. Once the OK to proceed comes from ground control the spaceship can move closer. From this point the Dragon enters the so-called “Keep-Out Sphere”. Sounds like science-fiction but it is nothing more than a term to make sure even more caution is heeded: nobody wants a Dragon to collide with the Space Station!
The crew will the bring the Dragon spaceship to within 30 metres and then at 10 metres from the Space Station. Stop and ground control (Hi there Major TomJ)… this is where Samantha’s real work starts today: she will grapple the cargo vessel with the Canadarm robotic arm and… tame the Dragon!
Stefano Sandrelli
17/04/2015