After liftoff and separation from stage one of the Falcon 9 rocket, the SpaceX Dragon capsule must successfully perform several functions to get ready to dock with the ISS. A few minutes after the Dragon separates from the second stage of the Falcon, at about T+12:00, the sequence to activate the solar arrays starts. Try to recall the COTS 2/3 mission webcast, there was cheering from SpaceX employees after the solar arrays deployed. While SpaceX employees have a right to cheer about every aspect of the Falcon and Dragon, the solar arrays are unique. Most spacecraft similar to Dragon only use battery power.
The solar arrays provide primary power for the sensors, heating and cooling, and communication systems aboard the Dragon. When in the shadow of the sun the Dragon is powered by the onboard batteries. When in full sun the solar arrays add charge to the batteries. This method of generating power is what will allow the Dragon to go on longer missions into deep into space. The “life boat” version of the Dragon [slide 30], that could stay attached to the ISS for up to a year, would not have solar arrays, there is enough power in the batteries to power electrical systems to get back to Earth.
This begs the question: Are the onboard batteries a redundancy system for the solar panel arrays? We’ve reached out to SpaceX to confirm if the systems only work together or if the systems are a redundancy set up. So, in a scenario that the arrays do not deploy, can the Dragon still make it to ISS? Can the Dragon still complete it’s full mission duration or will it have to be truncated? Or possibly the spacecraft would need to sit in orbit until able to return to Earth. We will post the response from SpaceX as soon as we get it, so stay tuned.
Each array is constructed of four panels and each array measures twenty-one feet long. The arrays can draw up to 5,000 watts of power which is enough power to light about 85 light bulbs. They are stowed in the unpressurized trunk of the Dragon and are covered by protective fairings. When the fairings jettison. the automated deployment of the arrays is triggered. On the way back to Earth the trunk is jettison and it, along with the arrays, burn up in the atmosphere.