Preliminary results are showing SpaceX’s Falcon 9 enjoyed a nominal ride uphill – with no issues – prior to deploying the Dragon spacecraft on orbit. So as not to let down its ride, Dragon then passed several major – and new – milestones, including the deployment of both solar arrays, and the opening of its GNC door, as the vehicle now chases its prize, a date with the ISS.
From a Falcon 9 perspective, the third flight of what is still a new vehicle was highly successful, per the quick look overview into the vehicle’s performance.
Lift off at 3:44am from Cape Canaveral Air Force Station (CCAFS) in Florida was only the second attempt to get off the ground for this mission, some achievement in itself, given the near-instantaneous launch window.
The first launch attempt was scrubbed at T-0.5 seconds – with the engines firing – due to a problem with a nitrogen purge valve on Engine 5, an issue SpaceX later claimed would not have caused a problematic launch, as much as the flight computer did the right thing by aborting the “trending high” parameter on the Merlin engine’s chamber pressure readings.
With the valve replaced at the pad, with plenty of time to spare until the next opportunity on Tuesday morning, SpaceX’s team indirectly proved one of its strengths, with its “in house” engineering team not being delayed by having to consult and debate with numerous external vendors, an issue that could sometimes be seen with other vehicles such as shuttle, as much as the shuttle was a far more complex vehicle by nature.
With a smooth countdown, suffering from no issues relating to SpaceX’s hardware, the clock once again ticked down to the ignition of the nine Falcon 9 engines, this time resulting in a lift-off and a nominal first stage flight through the key stages of achieving the correct trajectory, and passing through MaxQ.
A nominal staggered shutdown (MECO) of Falcon 9’s engines was followed by a clean staging and ignition of the single Merlin engine (MVac), again with nominal performance through to the injection of Dragon into the desired orbit, as much as it was slightly off the pre-published orbital target.
Dragon was then tasked with some immediate firsts, all required mission objectives to allow Dragon to proceed towards the ultimate goal of berthing with the International Space Station (ISS).
The first came just a few minutes after the end of the powered flight, as both solar arrays came to life and deployed. With video coverage still available, images of both arrays successfully deployed was greeted by loud cheers by the gathered SpaceX team outside the Mission Control Center (MCC) in Hawthorne, California.
This event was a mission first for SpaceX, with the arrays providing life blood to the Dragon for its longest mission to date. However, they were not out of the woods yet, per the list of immediate requirements of potentially completing both the C2 and C3 mission objectives.
That next milestone came with the opening of the GNC door on the spacecraft, a requirement to allow Dragon to navigate in space with its Light Detection and Ranging, or LIDAR hardware. The LIDAR system aboard the Dragon spacecraft is known as DragonEye, and is used for ranging and direction finding during Dragon’s approach to the ISS.
That procedure was success, as the door opened and importantly latched into a fixed position, a milestone that also exposed the grapple fixture that the Space Station Remote Manipulator System (SSRMS) will grab hold of, to allow the “big arm” to carefully translate the spacecraft towards its berthing point on the orbital outpost.
And that date with history is now fast approaching, as Dragon enters a stage of the flight known as far field phasing. However, Dragon still has a lot of work to complete ahead of being allowed to get close to the Station, with numerous testing requirements under the C2 portion of the test flight.
During this period, Dragon will perform Free Drift, and Abort Demos, while conducting checks on its Absolute GPS (AGPS) system.
Per L2 information (L2 Link), Free Drift is performed in this early mission timeframe for spacecraft efficiency, but is not required until Dragon reaches the capture point. However, the AGPS and Abort tests are required prior to the Go/No-Go for the HA2/CE2 burn pair, a burn pair that will take Dragon to 2.5 km below ISS – a distance chosen as acceptable in relation to posing no risk to the Station in the event of a problem.
This early phase of the mission is full of objectives as part of the flight rules, ensuring Dragon is capable of carrying out the requirements, prior to actually arriving at the ISS.
“Abort: Demonstrate both types of abort burns, large on axis and small pulsed off axis. Confirmation of expected delta V and attitude error are within bounds,” listed the objectives on the mission walkthrough (L2). “AGPS: Confirmation that Dragon position and velocity is accurate within error bounds. Based on comparison of Dragon dissimilar navigation measurements.
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“Recover from Free Drift: Confirmation that Dragon mode changes to and from Free Drift. Verification that required system inhibits are put in place prior to free drift and removed when Dragon recovers from free drift. Confirmation that recovery attitude error is within bounds and Dragon remains in that attitude.”
Completing these objectives will provide the required confidence in allowing Dragon to move on to the next phase of testing, whilst in the ISS’ back yard.
Those events will occur on Flight Day 3, as the Dragon makes a flyby of the ISS at a distance of 2.5 kilometres (1.3 nautical miles, 1.6 statute miles). During this flyby, tests of the Relative Global Positioning System (RGPS) and COTS UHF Communications Unit (CUCU) will be conducted.
For the interim, and for most of Flight Day 2, the mission will be dedicated to orbit phasing, as the the Dragon first circularising its orbit, and subsequently raising itself towards the orbit of the ISS, all leading towards Friday’s historic berthing.
(Images: NASA, SpaceX and via L2’s SpaceX Dragon C2+ Mission Special Section – Containing presentations, videos, images, interactive high level updates and more, with additional images via NASA, SpaceX).
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