After 30 days in space and 28 days berthed to the International Space Station, SpaceX’s first ever reused Dragon capsule has unberthed from the Station ahead of a Monday afternoon reentry and splashdown in the Pacific Ocean for recovery. Over the course of its month-long stay, Dragon delivered several thousand pounds of scientific experiments and equipment to the Space Station – some of which were so time sensitive that they had to be performed in the past 28 days so they could return with Dragon today.
Dragon departure and splashdown:
Originally scheduled to depart the ISS and splashdown in the Pacific Ocean off the coast of Baja California on Sunday, 2 July, Dragon’s homecoming was delayed one day due to unfavorable weather conditions in the Eastern Pacific.
Dragon has performed flawlessly during her mission while the three person ISS crew has spent the last 28 days unloading the capsule, performing the time sensitive experiments that are due to return on it, and removing external payloads for the Station from Dragon’s trunk to either attach them on ISS or to perform test objectives on them.
The mission holds a historic place for SpaceX being the first re-flight of a Dragon capsule that had already flown to space once prior.
Previously, the Dragon capsule used for CRS-11 had flown the CRS-4 mission in September-October 2014.
The reuse of this Dragon capsule marks the first time a private spaceflight company has reused a spacecraft and also marked the first time that a reused spacecraft arrived at the International Space Station since the conclusion of the Space Shuttle Program in 2011.
With Dragon’s first reflight now set to conclude, the three person reduced crew aboard the International Space Station began robotic preparations for the vehicle’s released by grappling Dragon with the Space Station Remote Manipulator System (Station arm or SSRMS) over the weekend ahead of final hatch closer on Sunday.
Firmly held in the snares of the Latching End Effector (LEE) on the end of the SSRMS, bolts securely fastening Dragon to the nadir (Earth-facing) Common Berthing Mechanism of Node-2 Harmony were driven to the retract position, freeing Dragon from its berthing port on the Station.
The Station crew then maneuvered Dragon on the end of the SSRMS away from the main structure of the ISS to its release point 10 meters from the orbital lab.
With a release time of 02:41 EDT on Monday, 3 July, astronauts Peggy Whitson and Jack Fischer – working in the Cupola lab of the ISS – commanded the release of the LEE snares holding Dragon.
The exact time of release was subject to change from the announced plan due to lighting conditions, communications coverage, and day-of timeline activities.
Once the LEE snares released, Whitson and Fischer backed the SSRMS away from Dragon as the craft held its position at the 10m mark.
Once the Station’s arm was cleared to a safe distance, Dragon was conducted through a series of three small thruster firing departure burns that moved the capsule down the R-Bar (Radial Vector) and away from the International Space Station toward Earth (when viewed in relation to ISS orientation and Dragon movements with respect to Earth).
During the initial stage of departure, Dragon was under the control of its own computer programming, with Whitson and Fischer aboard the International Space Station and controllers at Mission Control Houston in Texas for NASA having primary control over the spacecraft.
As Dragon pushed down the R-Bar, the largest of the three thruster departure burns imparted enough Delta Velocity (Delta-V) change to Dragon to push it outside of the approach ellipsoid.
The approach ellipsoid is a 4 km by 2 km oval-shaped region around the International Space Station that extends 2 km in front of and 2 kilometers behind the ISS along the velocity vector (V-Bar) and 1 km above and 1 km below the Station along the R-Bar.
Once Dragon cleared the approach ellipsoid 1 km below the ISS, primary control of the vehicle shifted from NASA to SpaceX controllers in Hawthorne, California.
Dragon performed roughly five hours of free flight activities as controllers at Mission Control SpaceX prepared the vehicle for the end of its mission.
Roughly five hours after departing the Space Station, the Guidance Navigation and Control (GNC) bay door on Dragon was closed, creating a perfect thermal protection seal around the entirety of Dragon for entry.
At the appropriate time, Dragon’s Draco thrusters began a 10-minute firing sequence known as the deorbit burn to slow the capsule and place it on to the proper heading for entry into Earth’s atmosphere.
Following the deorbit burn, the umbilicals between Dragon and her external payload trunk were severed ahead of the trunk’s separation from Dragon itself.
Dragon then reoriented, with its heat shield out in front in preparation for Entry Interface (EI) – the moment Dragon reached the first traces of Earth’s upper atmosphere.
Once EI occurred, Dragon’s Thermal Protection System (TPS) protected it from the searing hot temperatures of reentry formed as the air molecules around Dragon are instantly heated and turned to plasma under the friction created by Dragon’s high velocity.
Dragon’s primary heat shield, called PICA-X, is based on a proprietary variant of NASA’s Phenolic Impregnated Carbon Ablator (PICA) material and is designed to protect Dragon during atmospheric re-entry.
PICA-X is robust enough to protect Dragon not only during ISS return missions but also during high velocity returns from Lunar and Martian destinations.
Unlike the Dragon capsule, the Dragon trunk destructively burned up in Earth’s atmosphere.
Once safely through the plasma stage of reentry, Dragon’s drogue parachutes deployed, followed by the main chutes designed to ease the vehicle to a splashdown in the Pacific Ocean for recovery.
Recovery will be attained by three main recovery vessels which will be positioned near Dragon’s return location.
Fast recovery vessels were deployed to begin collecting Dragon’s parachutes as recovery of the capsule itself was conducted by the primary recovery assets.
Once safely aboard the recovery vessel, Dragon is being transported to the Port of Los Angeles and then shipped to Texas for cargo removal.
Currently, Dragon is the only resupply vessel capable of returning experiments and equipment from the International Space Station as the three other in-service resupply vehicles (Progress, Cygnus, and the H-II Transfer Vehicle) all perform destructive reentries into Earth’s atmosphere.
Under the second Commercial Resupply Services (CRS-2) contract award, Sierra Nevada’s Dream Chaser spaceplane will join Dragon as only the second uncrewed vehicle capable of returning equipment and experiments from the Station.
With the conclusion of CRS-11, NASA’s next commercial resupply mission to the International Space Station will be SpaceX’s CRS-12 flight, which is currently targeting liftoff from SLC-39A at the Kennedy Space Center on 10 August 2017 at 14:07 EDT.
The science of CRS-11:
In addition to the 524 kg (1,155 lb) of crew supplies, vehicle hardware, spacewalk equipment, and computer resources aboard Dragon, the craft delivered a crucial 1,069 kg (2,356.7 lb) of internal science experiments to the Station.
Among these experiments were some that had to be performed/started quickly when Dragon arrived at the Station, as those experiments had to return aboard Dragon for landing Monday.
Specifically, two of the experiments are related to the biological sciences, one using fruit flies and one using mice.
Fruit Fly Lab:
Fruit Fly Lab-02 (FFL-02) follows three previous fruit fly experiments: Fungal Pathogenesis, Tumorigenesis, and Effects of Host Immunity in Space, which flew aboard Shuttle Discovery on the STS-121 second Return To Flight mission in 2006; NanoRacks-HEART FLIES, which was launched on SpaceX CRS-3 in 2014; and Fruit Fly Lab-01 (FFL-01), which launched to the Station on CRS-5 in 2015.
Specifically for FFL-02, the experiment studies the underlying mechanisms responsible for adverse effects of prolonged exposure to microgravity on the heart.
To this end, the experiment uses fruit flies (scientifically known as Drosophila melanogaster), as their well-known genetic make-up and very rapid aging make them good models for studying heart function.
According to NASA, a fruit fly’s heart “develops and functions in a fashion remarkably similar to that of the human heart, and is an excellent model to study the molecular-genetic basis of cardiac development as the underlying molecular pathways and cellular functions are fundamentally conserved even to humans.”
Moreover, fruit fly hearts have been used to determine fundamental causes of cardiac dysfunction, such as arrhythmias (a group of conditions in which the heartbeat is irregular, too fast, or too slow) and cardiomyopathies (diseases of the heart muscles), which can lead to heart failure and death in humans.
For FFL-02, “the development of a microgravity heart model in the fruit fly, which is more genetically tractable and faster aging than vertebrate hearts, could represent a potentially significant advancement in the study of how spaceflight affects the cardiovascular system and may facilitate the development of countermeasures to prevent the adverse effects of microgravity in astronauts.”
To this end, FFL-02 is comprised of six Vented Fly Boxes, each containing triplicate samples of five different fruit fly strains.
Once Dragon was launched into space, the ground-born flies developed to adulthood and reproduced.
The space-born flies then went through their life cycle – the formative parts of which all took placed in microgravity – before coming back on Dragon, at which point the space-born fruit fly hearts are compared to control ground-born fruit fly hearts.
Furthermore, the effects of microgravity are “compared between samples composed of control fly strains and those composed of mutant flies that are genetically predisposed to two types of heart dysfunction: arrhythmia and cardiac dilation.”
Direct application of this experiment for astronauts and future spaceflights include the development of a microgravity heart model which could significantly advance the study of spaceflight effects on the cardiovascular system and facilitate the development of measures to prevent the adverse effects of space travel on astronauts.
Ground-based applications – for those of us not lucky enough to fly into space – of FFL-02 include additions to the growing body of research on fruit flies as models for human heart health and improving efforts to use fly studies to develop new cardio therapies.
Systemic Therapy of NELL-1 for Osteoporosis – Rodent Research 5:
Rodent Research 5 (RR-5) continues the study of bone density loss (osteoporosis) in space while also testing new applications and drugs that can rebuild bone and prevent further bone loss on orbit.
In short, RR-5 is an experiment to study the potential for a new drug, NELL-1, to slow and/or reverse bone loss during spaceflight.
According to NASA’s coverage of the experiment, “exposure to the spaceflight environment results in significant and rapid effects on the skeletal system, similar to what occurs in certain bone wasting diseases, as well as aging, on earth.
“Studying accelerated bone loss in space provides insight into disease mechanisms, confirms potential new drug targets, and enables the preclinical evaluation of a candidate therapeutic targeted to such disease.”
To carry out RR-5, 40 mice – all females between the ages of 30-40 weeks, with 32 week old female mice being preferred – were launched in the CRS-11 Dragon.
When Dragon berthed to the ISS on 5 June, the mice were transferred to Rodent Habitats aboard the Station.
There, they were divided into two groups: control (“vehicle only” injection and bone marker) and experimental (“NELL1 injection” and bone marker).
The first round of injections occurred at Launch +1 (L+1) week, with the 20 control mice receiving vehicle injections and the 20 experimental mice receiving NELL1.
After this first round, dual-energy X-ray Analysis (DXA) scans were performed on all of the mice.
From this point, a subsequent injection series occurred at L+3 weeks (± 1 day).
This weekend, just prior to hatch closure and Dragon departure, 10 control mice and 10 experimental mice were randomly chosen for Live Animal Return (LAR) and were transported back into Dragon for a return trip to Earth.
The remaining 20 mice (10 control and 10 experimental) will now remain aboard the ISS, receiving a third and fourth round of injections at L+5 weeks and L+7 weeks.
At L+9 weeks, a third DXA scan will be performed (the second having occurred at L+5 weeks).
At this point, the final blood samples will be obtained from all the remaining mice, and those blood samples will then be wrapped in aluminum foil and stored at -80˚C or colder until return on CRS-12.
The RR-5 investigations are expected to increase understanding of ground-based diseases, disorders, and injuries affecting millions of people globally and aid in the development of new therapeutics and strategies to treat such conditions.
Specifically, this research holds the potential to lead to new treatments for bone loss associated with immobilization, stroke, cerebral palsy, muscular dystrophy, spinal cord injury, and jaw resorption after tooth loss.
Other major science experiments on CRS-11:
In addition to FFL-02 and RR-5, numerous other experiments launched aboard CRS-11, including: Microbial Tracking-2, Seedling Growth-3, Advanced Plant Experiments -02-2, and Advanced Colloids Experiment – Temperature -6.
Microbial Tracking-2 (MT-2) is part of a Microbial Tracking series that seeks to better characterize the microbial communities present on the Station using cutting edge molecular analysis techniques.
Specifically, MT-2 will study how microbial communities on the ISS and short-living viruses in a closed habitat have an adverse influence on crew health.
MT-2 will help fully characterize microbes and viruses present on three different crew members and in the environment during consecutive expeditions.
To accomplish this, crew members will take saliva, mouth, and body samples at various points in the consecutive expeditions so their respective microbiomes can be fully assessed and compared to ground baseline samples from before and after their flights.
Additionally, crew members will obtain air and surface microbial samples from inside U.S. modules.
In this manner, MT-2 will not only describe the microbial and viral communities of the Station and the crew, but will also seek to distinguish whether these biological signatures are of any concern to crew health and engineering systems.
According to NASA, “All microbial and viral data generated by the investigation will be hosted by GeneLab and will be available to the scientific community and NASA to compare population dynamics to baseline standards and enable more accurate assessments of crew health associated with a given mission and future mission planning.”
Seedling Growth-2 and Advanced Plant Experiments -02-2:
Seedling Growth-3 (SG-3) is the third of the Seedling Growth Experiment series and uses the plant Arabidopsis thaliana (more commonly known as the thale cress or mouse-ear cress).
SG-3 specifically investigates the effects of gravity on the cellular signaling mechanisms of light sensing in plants (phototropism) and investigates cell growth and proliferation responses to light stimulation under microgravity conditions.
The results could provide improvements in agricultural biotechnology and can contribute to increased production, lessened environmental impact, and sustainability of agricultural production.
The European Space Agency (ESA) leads this experiment, which will be performed in the European Modular Cultivation System (EMCS) in the Columbus Module.
Separately, the Advanced Plant Experiments -02-2 (APEX 02-2) will collect quantitative measurements of radiation damage to yeast DNA exposed to space radiation.
APEX 02-2 will represent the first time a highly powered genome-wide analysis of mechanisms of radiation damage in space can be conducted – made possible by “state of the art technologies”.
Specifically, APEX 02-2 uses a genome-wide series of deletion clones of Baker’s Yeast to determine the quantity of radiation damage during spaceflight in comparison to ground controls.
While performed on the ISS, APEX-02-2 holds both space-based and ground-based applications – providing potential simple approaches to enhancing space-based and clinical radiation damage.
Advanced Colloids Experiment – Temperature -6:
Advanced Colloids Experiment – Temperature -6 (ACE T-6) is an investigation which aims to study the microscopic behavior of colloids in gels and creams.
Colloids are suspensions of microscopic particles in a liquid commonly found in products ranging from milk to fabric softener.
Consumer products often use colloidal gels to distribute specialized ingredients throughout a liquid or semi-liquid medium.
However, these gels must serve two opposite purposes: disperse the active ingredient and maintain an even distribution so the product does not spoil.
To this end, coarsening (to make or become rough) is an issue with colloids that can limit the shelf life of many products that use them.
As such, ACE T-6 seeks to provide new insight into colloid coarsening in an effort to better understand the mechanism behind it – with an aim toward improving shelf life in consumer products.
(Images: NASA, SpaceX, and L2 artist Nathan Koga – The full gallery of Nathan’s (SpaceX Dragon to MCT, SLS, Commercial Crew and more) L2 images can be *found here*)