SpaceX’s Dragon returns to Earth following successful ISS mission

by Chris Bergin

SpaceX’s Dragon unberthed from the International Space Station (ISS) early on Thursday, ahead of its final hours in space. Following a successful re-entry, splashdown off the coast of California was recorded at 08:42 local time . The nominal End Of Mission (EOM) – coupled with a good post flight review – will clear the way for Dragon to begin Commercial Resupply Services (CRS) missions later this year.

Dragon’s ISS Mission:

This mission has already provided the required breakthrough for Dragon, SpaceX, and indeed NASA, with a successful rendezvous and berthing allowing for the main C3 objectives of the test flight to be fulfilled, justifying the decision to combine what was originally two final COTS missions prior to the opening CRS-1 flight.

While reviews are ongoing, including evaluations into the performance of Falcon 9 that launched Dragon uphill earlier this month, a large number of firsts have been achieved by Dragon, including those carried out during the ISS element of the mission.

One of those goals involved the requirement to offload Dragon’s cargo in a timely manner, a goal that was achieved within one day by the ISS crew, who praised the layout and planning for what will be a regular operation during the upcoming Dragon missions.

Although this Dragon only brought 660kg of supplies with it, given this is a test flight, the cargo operations did create a number of historic firsts, not least marking the first time astronauts had ingressed the spacecraft whilst on orbit. It is hoped that in less than five years time, Dragon astronauts will be seen egressing the spacecraft on to the ISS.

The Dragon was also greeted by one of the ISS’ team from outside of the Station, as the Canadian robot Dextre – or the SPDM (Special Purpose Dexterous Manipulator) – was moved from its staging point by the Space Station Remote Manipulator System (SSRMS) to demonstrate the robotics required from the removal of cargo from the trunk on the aft of Dragon. No cargo flew in the trunk on this test mission.

Preliminary results show the robotic operation enjoyed the expected results seen via simulations – based on clearances and lighting conditions – while a survey of Dragon’s exterior condition also showed no items of concern.

“Dragon Imagery Surveys: The SPDM (Special Purpose Dexterous Manipulator) on the SSRMS was used to get an imagery survey of the Dragon exterior and trunk/interior on May 27,” added notes via the Dragon C2+ Robotic Updates (L2 – Link).

“The survey request was completed with another survey of the Dragon external surfaces by external cameras on the truss on May 30. The imagery team (KX) will coordinate imagery reviews with the requesting parties.”

With late stow items placed aboard the Dragon ahead of hatch closure, another demonstration will be carried out – despite it not being a key C2+ objective – as the SpaceX team aim to recover the Dragon from its splasdown location, transport the spacecraft to Texas, and unload the late stow items within 48 hours.

Dragon Departure:

First up for the EOM day, Dragon needs to safely depart the ISS in what will be a near-reverse procedure to that of its arrival.

The spacecraft was removed from the Node 2 Nadir Port by the SSRMS, taking place at 4:07am Eastern, prior to being translated out to the unberth position. The event was marked at nine days and 23 minutes into the mission, equating to Dragon spending five days, 16 hours and five minutes on Station.

Canadarm2 kept a firm grip on the Dragon for a few hours, ahead of the GO to release the spacecraft at 4:45am Central, prior to the official release, that came four minutes later at 4:49am Central.

Dragon then edged away from the Station, with two small thruster firings to push down the R-Bar. A larger burn was then conducted to send Dragon outside of the approach ellipsoid, at which point SpaceX took full control of the mission.

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Only one related issue – one which has been worked for the past number of weeks – was noted on the ISS side ahead of unberthing, relating to the Station’s Space Integrated GPS/Inertial Navigation Unit (SIGI), one of two GPS units required for Dragon’s Relative GPS (RGPS) navigation. However, this will not provide a problem for Dragon’s farewell.

“GPS1 (Global Position System) Lockup – GPS 1 (aka SIGI 1) locked up this morning,” noted the ISS Status Updates via L2’s ISS Section – LINK. “The GNC community has reviewed the signature and found while the Attitude Determination and State Determination were not updating, the GPS1 continued to receive GAD (GNC Ancillary Data) data and was coined a “dynamic lockup”.

“The signature is somewhat similar to the failure signature observed before the GPS1 R&R, but the output of GAD data shows that the box is still functioning. A power cycle was performed and returned the box to normal functionality. Teams have collected additional bus error data to add to their understanding of the signature.

“Note, GPS lockups happen somewhat frequently and no impact is anticipated to plans for Dragon release and departure.”

Dragon Entry:

Dragon’s preparations for re-entry involved the unlatch/close/latch of the GNC door, prior to a 10 minute deorbit burn using the spacecraft’s Draco thrusters. With the vehicle heading towards Entry Interface, the Dragon trunk was jettisoned, allowing for it to burn up in the atmosphere.

The spacecraft then relied on its PICA-X heat shield – a Thermal Protection System (TPS) based on a proprietary variant of NASA’s phenolic impregnated carbon ablator (PICA) material – designed to protect the capsule during Earth atmospheric re-entry, and is even robust to protect Dragon from the high return velocities from Lunar and Martian destinations.

Entry was tracked via a NASA P3 aircraft, as previously used on some Shuttle missions, while tracking was enabled via GPS systems onboard Dragon.

Once at the required velocity and altitude, Dragon’s drogue parachutes were successfully deployed, followed by Dragon’s main parachutes, easing the vehicle to a splashdown in the Pacific ocean at 8:42am Central.

Three main recovery boats soon arrived on station, with fast boats racing to meet the Dragon shortly after it hits the water, allowing for the recovery procedures to begin. The vehicle was powered down and then be hooked up to the recover assets. 

Dragon was transported to the port of Los Angeles, prior to a trip to Texas for cargo removal.

Refer to the Live Update thread for FD10/EOM on the SpaceX forum section for minute-by-minute updates.

(Images: via L2’s SpaceX Dragon C2+ Mission Special Section – Containing presentations, videos, images(800mb of unreleased hi res images from the mission), interactive high level updates and more, with additional images via NASA). 

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