Falcon 9 Block 4 debut a success, Dragon arrives for Station berthing

by Chris Gebhardt

After launching right on time in a rare single day launch window on Monday afternoon, SpaceX’s Dragon capsule for the SpX-12/CRS-12 mission arrived at the International Space Station and completed rendezvous and berthing operations.  The mission is delivering thousands of pounds of scientific experiments to the Station for what promises to be a busy month of science aboard the world’s orbital laboratory.

Block 4 debuts – another perfect launch and landing for Falcon 9:

Since launch on Monday afternoon from the Kennedy Space Center, Dragon has enjoyed an issue-free orbital trip to the International Space Station (ISS).

Cruising to orbit on her Falcon 9 Block 4 first and second stages, the SpX-12 Dragon slipped into her preliminary orbit after a flawless launch into a thankfully clear Florida afternoon summer sky.

As has seemingly become the usual mode of operation, following completion of first stage flight, the Falcon 9 first stage successfully flew itself back to the Cape Canaveral Air Force Station and Landing Zone 1 (LZ-1) for a successful RTLS (Return To Launch Site) landing.

This was the 6th Falcon 9 RTLS landing and the 14th overall successful landing of the Falcon 9 first stage – a feat made even more remarkable considering the first successful landing was slightly less than 20 months ago and includes a five month stand down period following the AMOS-6 pad conflagration.

Moreover, since the first successful landing, only three landing attempts have failed – with no landing attempt failures since Eutelsat 117 West B & ABS-2A on 15 June 2016.

Notable for SpX-12, however, is its importance to the overall goal of introducing upgrades to the Falcon 9 that will culminate next year in the so-called Block 5 iteration.

While both the first and second stage Block 5 variants will make their debut on the uncrewed Demo-1 flight of the crew Dragon capsule in February 2018, intermediate advancements from the upgraded Full Thrust variant have now taken to the skies and pushed a payload to orbit.

The inaugural flight of the Block 4 appears from all accounts to have been a tremendous success – delivering Dragon to her intended orbit while also allowing landing and recovery of the first stage.

This first stage recovery will allow SpaceX engineers to comb through the first flight-proven Block 4, examining the first stage’s performance and post-flight condition.

While this first Block 4 curiously did not fly with the new titanium grid fins, which debuted earlier this year on the June launch of Iridium Next 11-20 from Vandenberg, the first Block 4 did make use of increased-thrust Merlin 1D engines.

The thrust increase of the Merlin 1Ds is also incremental, with a final thrust increase set to debut on the Block 5.

These incremental performance upgrades to the eventual Block 5 design are crucial to SpaceX’s desire to achieve an ability to land, refuel, and launch a Falcon 9 first stage with minimal refurbishment and to further lower the cost of access to space.

However, per current vehicle assignments, the next Falcon 9 will not be a Block 4 but rather an upgraded Full Thrust variant tasked with launching Taiwan’s extremely lightweight Formosat-5 satellite on 24 August from SLC-4E at Vandenberg Air Force Base, California.

The second flight of the new Block 4 will occur two flights from now on the OTV-5 mission, the fifth flight of the X-37B spaceplane for the U.S. Air Force – a mission that will launch from LC-39A at the Kennedy Space Center No Earlier Than (NET) 7 September.

SpX-12 – rendezvous and berthing:

Following orbit insertion Monday afternoon, Dragon performed a series of trajectory adjustment burns over the capsule’s slightly less than two-day chase with the ISS to properly align itself 6 km from the Station on Wednesday morning for final approach operations.

(NOTE: All times listed below are per NASA’s SpX-12 approach timeline. It is common for Dragon to perform better than anticipated and arrive at its various approach milestones earlier than predicted.

The detailed approach timeline, including time and duration of all thruster firings and associated delta-V (velocity) changes, is available for download on L2.)

Following approval from NASA, SpaceX controllers commanded Dragon to begin its final approach sequence with the HA4 Approach Initiation burn around 04:16 EDT – at which time the six-person ISS crew began actively monitoring Dragon’s approach to the orbital outpost.

During final approach, Dragon maintains proper alignment with the ISS through its Relative Navigation System – which was developed by SpaceX and debuted on CRS-3’s approach on 20 April 2014.

Specifically, the HA4 burn is designed to pulse Dragon up toward the ISS to its 350 m (1,148.3 ft) hold point.

Dragon initially approaches the Station from behind and underneath, and the HA4 burn starts the craft’s trip up the Radial velocity vector, or R-bar, toward the ISS.

Once Dragon arrived at the 350 m hold point, the craft fired its thrusters to hold relative position with the Station – at which time controllers at SpaceX’s Mission Control Center (MCC-X) in Hawthorne, CA, commanded Dragon to perform a 180° Yaw maneuver so the craft was oriented to its proper position for grappling by the Space Station Remote Manipulator System (SSRMS, or Station Arm) at the end of the approach sequence.

After the yaw maneuver, MCC-X and MCC Houston (MCC-H) controllers confirmed the health of Dragon’s systems, after which the spacecraft departed the 350 m hold point – at ~05:11 EDT.

The next hold point for Dragon was 250 m (820.2 ft) below the ISS. Here, controllers once again confirmed Dragon’s health and the craft’s orientation before giving a “go” to press ahead toward capture.

Importantly, at any point – at a scheduled hold point or otherwise – ground controllers and the Station crew have the ability to manually abort Dragon’s approach through the Commercial Orbital Transportation Services Ultra High-Frequency Communication Unit (CUCU) if an off-nominal condition presents itself.

Dragon’s onboard computers also have the ability to abort the approach sequence at any point if they sense an off-nominal situation – be that drifting off course or a misalignment/miscommunication of the guidance and navigation systems.

These off nominal situations are exceedingly rare, but can/do happen. The SpX-10/CRS-10 Dragon suffered just such a fate on its first attempt at rendezvous in February 2017; berthing was aborted that day and proceeded nominally the following day.

While such an event is not expected for SpX-12’s arrival, should it occur, NASA and SpaceX will review the reason for the abort and NASA will have a conversation with Roscosmos – the Russian federal space agency – to determine how best to realign the scheduled Thursday EVA (spacewalk) of Russian ISS crewmembers Fyodor Yurchikhin and Sergey Ryazanskiy as Thursday is the day Dragon would likely re-attempt a rendezvous (depending on the reason for an abort) with the ISS due to a need to be berthed to the Station before that spacewalk.

In this situation, with Dragon on orbit carrying time-sensitive science experiments, it would be advantageous – in the event of an aborted rendezvous Wednesday – to get Dragon berthed to the ISS before the Russian EVA if possible.

The Russian EVA is to deploy five nanosatellites, including the first 3D printed CubeSat, into Earth orbit – and that deployment would prevent Dragon from approaching the ISS – if deployment occurs before Dragon’s berthing – due to the need to calculate and concretely define those nanosats’ orbits and trajectories to ensure they do not pose a collision danger to Dragon as it approaches the Station.

Nonetheless, for SpX-12’s nominal approach this morning, once a “go” to proceed from the 250 m hold point was given by both MCC-X and MCC-H, Dragon continued its approach.

Shortly thereafter, Dragon crossed the 200 m mark from ISS and entered the Keep Out Sphere (KOS) around the Station.

At this point, MCC-X handed off primary ground control/decision making to NASA controllers at MCC-H.

Dragon then arrived at the 30 m (98.4 ft) hold point where teams performed final assessments of Dragon’s readiness to close to the Capture Point 10 m (32.8 ft) below the ISS.

Once Dragon arrived at the Capture Point, ISS Flight Engineers Jack Fischer and Paolo Nespoli – working in the Robotic Work Station in the Cupola lab – extended the SSRMS toward Dragon’s grapple fixture.

After receiving a “Go for Capture” from MCC-H, Fischer and Nespoli used the SSRMS’s camera on the Latching End Effector (as overviewed in a detailed presentation available in L2) to precisely move the Station Arm to grapple posture.

At this point, Fischer and Nespoli “inhibited” the Station’s thrusters and Dragon was commanded to “free drift” mode.

Fischer and Nespoli will moved the SSRMS over Dragon’s grapple fixture pin and triggered the capture sequence.

Fischer and Nespoli captured Dragon at 06:52 EDT.

After capture, a series of post-grapple checkouts occurred before Fischer and Nespoli carefully translated Dragon to its pre-install position 3.5 m away from Node-2 Harmony’s nadir port.

Once at the pre-install position, Station crewmembers took photos and videos of Dragon for post-launch engineering evaluation.

Fischer and Nespoli then moved Dragon 1.5 m from Node-2, at which point they waited for the final “go for berthing” call to connect Dragon to the Common Berthing Mechanism (CBM) interface and secure the spacecraft to the Station.

Under the current plan, the CRS-12 Dragon will remain berthed to the ISS for slightly more than one month, with release scheduled for 17 September – at which point Dragon will reenter Earth’s atmosphere and splashdown for recovery in the Pacific Ocean.

Under the current ISS Visiting Vehicle manifest, the next cargo resupply mission is Orbital ATK’s OA-8E Cygnus on 11 October 2017 from the MARS (Mid Atlantic Regional Spaceport) in Wallops, Virginia, on the company’s Antares rocket.

(Images: NASA, SpaceX, and L2 artist Nathan Koga – The full gallery of Nathan’s (Falcon Heavy to Dragon to Starliner, MCT, SLS, Commercial Crew and more) L2 images can be *found here*)

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