A lengthy session of Extravehicular Activity (EVA) by Expedition 65 spacewalkers Aki Hoshide and Mark Vande Hei has been postponed, reportedly due to a crew medical issue. NASA on Monday announced that Tuesday’s planned U.S. EVA-77—the 77th station-based excursion conducted in U.S.-built Extravehicular Mobility Units (EMUs), without the presence of the Space Shuttle—will now occur after this weekend’s launch of the SpaceX CRS-23 Dragon cargo mission and a pair of critical Russian spacewalks early next month to commence outfitting the newly-arrived Nauka (“Science”) lab.
Original plans called for Hoshide (designated “EV1”, with red stripes on his suit for identification) and Vande Hei (“EV2”, clad in a pure white ensemble) to depart the Quest airlock of the International Space Station (ISS) around 8:30 a.m. EDT Tuesday for six hours and 50 minutes. Their primary task was to install a Modification Kit at the base of the P-4 truss in readiness for next year’s arrival of a third ISS Roll-Out Solar Array (iROSA).
Additionally, Hoshide and Vande Hei—who already boast seven previous EVAs and 48 hours and 3 minutes of spacewalking time between them—would Remove & Replace (R&R) a Floating Potential Measurement Unit (FPMU) to measure the accumulation of electrical charges across the station’s solar arrays.
But in a clipped statement on Monday, NASA revealed that U.S. EVA-77 is postponed, “due to a minor medical issue involving Vande Hei”. The agency stressed that the incident does not constitute “a medical emergency” and the spacewalk’s objectives are by no means time-critical. Indeed, responding to an AmericaSpace question at a recent pre-flight news conference ahead of Northrop Grumman Corp.’s NG-16 Cygnus cargo mission, ISS Program Manager Joel Montalbano explained that the “Mod Kit” was being installed early in order to circumvent problems down the road. The iROSA array itself is not due to be delivered until next spring, tentatively aboard SpaceX’s CRS-25 Dragon.
As previously reported by AmericaSpace, the Boeing-led iROSA concept promises to furnish an electrical power hike of 20-30 percent for the station to support future commercial and payload requirements.
Although trade studies for improved power-generation functionality have been in the works for several years, it was only around 2016 that in-depth discussions began on the roll-out arrays. Just last January, NASA and Boeing announced their intent to equip the USOS with six new arrays over the next couple of years. When fully implemented, the iROSA hardware will overlay and “shadow” six of the station’s eight legacy Solar Array Wings (SAWs) and increase its total power output from approximately 160 kilowatts to as high as 215 kilowatts.
This much-needed increase in robustness is expected to meet power demands which were not even dreamed about when the ISS entered service in the late 1990s. These demands include the European Space Agency’s (ESA) Bartolomeo platform, AxiomSpace, Inc.’s plans for a pressurized suite of research and habitation modules and an ever-growing backlog of payload customers.
In its present form, the station’s football-field-sized Integrated Truss Structure (ITS)—delivered, installed and activated by ten Space Shuttle crews between October 2000 and March 2009—supports the legacy arrays and their associated hardware for power storage, distribution and cooling. But more than a decade of service and expected degradation in the arrays gradually and progressively took its toll. In June 2017, SpaceX’s CRS-11 Dragon cargo mission evaluated a prototype Roll-Out Solar Array (ROSA) and though it encountered some problems on-orbit the concept was sufficiently well-proven to be expanded into a major ISS hardware upgrade.
“Removing the original arrays was unnecessary, because [they] still produce electricity and are useful to the ISS power grid,” said Rick Golden, Boeing’s iROSA project manager, in comments provided to AmericaSpace. “That process would also be very complex and not worth the effort since they are still quite effective, just degraded over time. We looked at other power-generation options, such as adding additional arrays and utilizing different design solutions. But those options were more difficult and costly to implement.”
As part of its ongoing analysis of ISS systems, structures and operational parameters as the station’s prime contractor, Boeing identified six power channels—2B and 4B on the P-6 truss, 4A on the P-4 truss, 1A and 3A on the S-4 truss and 3B on the S-6 truss—which would benefit most from the additional power afforded by the iROSA arrays. However, Mr. Golden noted that the final decision on applying those analysis lay with NASA.
Power Channels 2A on the P-4 truss and 1B on the S-6 truss are not presently earmarked for iROSA arrays, although Mr. Golden told us that it remains “NASA’s decision” on whether to upgrade that hardware at a later date.
But NASA has so far ruled out an upgrade of the final pair of power channels. “Only six of the eight solar arrays required augmentation to provide enough power and a reasonable but non-excessive amount of margin and redundancy,” said NASA’s Gary Jordan. “Eight new arrays would provide more power than is required at increased cost. Augmenting six of eight channels provides the best balance between cost and the anticipated power-need.”
In July 2020, Expedition 63 spacewalkers Chris Cassidy and Bob Behnken prepared for the arrival of the first iROSA modification kit on the P-6 truss, which carries the oldest set of solar arrays, having been delivered and installed more than two decades ago.
Last October, the kit itself arrived aboard Northrop Grumman Corp.’s NG-14 Cygnus cargo ship and earlier this spring Expedition 64 spacewalkers Kate Rubins, Victor Glover and Soichi Noguchi installed it during a pair of challenging EVAs. And the first two iROSA arrays were delivered by SpaceX’s CRS-22 Dragon cargo ship in early June and installed onto Power Channels 2B and 4B on the P-6 truss by Expedition 65 spacewalkers Thomas Pesquet and Shane Kimbrough during a three-EVA marathon later that month.
“The first iROSAs…began drawing power immediately, during the first orbital daylight, post-deployment, and are performing well,” Mr. Jordan told AmericaSpace. “Ground teams will continue to collect data on performance and compare to last year’s information, calculating the total power gained.”
With the first two of the eventual six iROSA sets thus installed, Hoshide and Vande Hei will tend to Power Channel 4A on the port-side P-4 truss. This houses the second-oldest set of U.S. solar arrays, having been delivered and installed by the STS-115 shuttle crew, way back in September 2006. Two weeks ago, Northrop Grumman’s NG-16 Cygnus arrived at the station, carrying the 330-pound (150 kg) modification kit.
The delay to U.S. EVA-77 is unfortunate, not least in view of how much work the Expedition 65 crew and ground teams have devoted to its preparation. Earlier this month, Hoshide and Vande Hei began resizing and servicing their suits, assembling tools, preparing safety and waist tethers and scrubbing coolant loops. Just last week, the astronauts undertook computer-based training with Virtual Reality (VR) hardware and the Dynamic On-Board Ubiquitous Graphics (DOUG) software.
On 17 August, they were joined by Expedition 65 crewmates Pesquet and Megan McArthur for a fully-suited On-Orbit Fit-Check Verification (OFV) in the airlock. And the following day, U.S. astronaut Shane Kimbrough—currently the United States’ fifth most experienced spacewalker—unpacked the modification kit from Cygnus and stowed its hardware into an 8-foot-long (2.4-meter) EVA Bag for transfer outside.
“Teams are assessing the next available opportunity to conduct the spacewalk,” NASA continued in its Monday update, “following the SpaceX CRS-23 cargo resupply launch planned for 28 August and upcoming Russian spacewalks.” Following CRS-23’s launch on Saturday and anticipated docking on Sunday, Russian cosmonauts Oleg Novitsky and Pyotr Dubrov are set to make two EVAs on 2 and 8 September to configure the Nauka lab for science operations. Last week, the cosmonauts gathered tools, studied paths toward their external work sites and checked out their Orlan space suits.
This would appear to indicate a delay of several weeks, possibly until mid-September, before Hoshide and Vande Hei can now perform their own EVA.
And although no further detail has been provided as to the issue which affected Vande Hei, it is certainly not the first time that illnesses or medical ailments have caused spacewalks to be delayed, canceled or jeopardized. Way back in March 1969, Apollo 9 spacewalker Rusty Schweickart was tasked with a critical “all-up” test of the Apollo lunar surface suit in low-Earth orbit. But shortly after launch, Schweickart suffered “space sickness” and there existed very real fears that his EVA might be canceled.
“Throwing up inside a pressure suit,” wrote fellow astronaut Deke Slayton in his memoir Deke, co-authored with historian Michael Cassutt, “would not only be unpleasant as hell, it might be fatal.” As circumstances transpired, Schweickart recovered thanks to an avoidance of sudden head movements and anti-nausea medication and his spacewalk went ahead without incident.
Four years later, in the summer of 1973, astronauts Al Bean, Jack Lousma and Owen Garriott arrived at America’s Skylab space station for a planned two-month stay. But their first few days were marred by space sickness, a situation exacerbated by the enormous internal volume of the station itself.
Breakfasts went uneaten, rest-days were moved forward on the timeline and the crew’s first EVA—scheduled only a few days after their arrival—was twice postponed. Tasked with installing film cassettes into the Apollo Telescope Mount (ATM) and deploying a backup sunshade for the ailing station, it was particularly critical, and although it was later conducted without incident the troubles of Skylab 3 brought the issue of space sickness to the forefront of many minds.
In November 1982, astronauts Bill Lenoir and Joe Allen were set to perform the first EVA of the Space Shuttle program. Launched aboard Columbia, alongside STS-5 Commander Vance Brand and Pilot Bob Overmyer, it was intended that Lenoir and Allen would spend around three hours outside the shuttle, putting their suits through their paces and running through a series of exercises and tasks.
Unfortunately, both Lenoir and Overmyer suffered a severe dose of space sickness. Lenoir later described it as like “a low-grade hangover”, but lauded Overmyer’s tenacious capacity to work even after throwing up. In the event, Lenoir and Overmyer recovered, but the EVA was eventually canceled thanks to an issue with the suits themselves and the first shuttle spacewalk was rescheduled for a later mission.
Subsequent shuttle flights also suffered from canceled or rescheduled EVAs, including STS-80 in late 1996, when a stuck hatch on the airlock precluded a pair of spacewalks by astronauts Tammy Jernigan and Tom Jones. And in February 2008, as the STS-122 crew prepared to install and activate Europe’s Columbus lab on the ISS, German astronaut Hans Schlegel was replaced by Stan Love for one EVA, “due to a crew medical issue”. It did not impair Schlegel for long and a couple days later he went outside on another spacewalk. But it furnished yet another reminder that crew-related medical issues in the hostile environment of low-Earth orbit cannot be ignored.