After triumphantly wrapping up its second eight-launch month, SpaceX looks ahead to a busy June, with CRS-28—the next Cargo Dragon mission to the International Space Station (ISS) under the Commercial Resupply Services contract with NASA—set to fly from historic Pad 39A at Florida’s Kennedy Space Center (KSC) no sooner than 12:35 p.m. EDT Saturday. Assuming an on-time launch, CRS-28 will autonomously dock at the space-facing (or “zenith”) port of the station’s Harmony node around 5:36 a.m. EDT Monday, for a month-long stay.
Most visible among CRS-28’s haul of payloads are the third pair of Boeing-built ISS Roll-Out Solar Arrays (iROSAs), to be installed on 9 and 15 June during two 6.5-hour sessions of Extravehicular Activity (EVA) by Expedition 69 spacewalks Steve Bowen and Warren “Woody” Hoburg. These arrays will augment a pair of existing legacy solar arrays on the station’s starboard side: Power Channel 1A on the S-4 truss and 1B on the S-6 truss.
Both power channels received iROSA “modification kits” on a pair of Expedition 68 EVAs by Koichi Wakata and Nicole Mann earlier this spring and cables and insulation in support of this work were laid by Expedition 69’s Bowen and Sultan Al-Neyadi—the first United Arab Emirates (UAE) spacewalker—during the most recent U.S. EVA on 28 April. After CRS-28 arrives next week, the new iROSAs will be robotically extracted from the cargo ship’s unpressurized “trunk” by means of the 57.7-foot-long (17.6-meter) Canadarm2 robotic arm and temporarily emplaced onto the station’s expansive truss to await installation by Bowen and Hoburg.
This will be the third pair of iROSAs to overlay, and “shadow”, six of the eight legacy ISS solar arrays in support of future expansion and customers’ burgeoning payload needs by increasing the station’s total electrical output by more than 30 percent, from around 160 kilowatts to as much as 215 kilowatts. Two pairs of iROSAs were installed onto the station’s port-side P-6 truss during a three-EVA marathon by Expedition 65 spacewalkers Shane Kimbrough and Thomas Pesquet in June 2021, followed by two others onto the starboard-side S-4 truss and the port-side P-4 truss during a triplet of EVAs by Expedition 68’s Josh Cassada and Frank Rubio last November-December.
Original plans identified six of the eight 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 derive greatest benefit from enhanced iROSA capabilities. Power Channels 2A on the P-4 truss and 1B on the S-6 truss were not initially earmarked for iROSA modification, but last fall NASA “re-evaluated power draws” on all channels and “reallocated” its installation plan.
Left unmodified under the new plan were Power Channels 2A on the P-4 truss and 3B on the S-6 truss. When fully deployed, the third and fourth iROSAs to be installed by Bowen and Hoburg will measure 60 feet (18.2 meters) in length by 20 feet (6 meters) wide and shadow a little more than half of the legacy arrays, each generating about 20 kilowatts of electrical power.
Although the fifth and sixth iROSAs take pride of place in CRS-28’s trunk, the Cargo Dragon’s pressurized section is lifting a wide range of research payloads, experiments and supplies uphill for the Expedition 69 crew.
The Plant Habitat-3 (PH-3) investigation will create a second generation of space-grown plants using seeds previously produced in orbit and returned to Earth. Led by researchers at the University of Florida, it seeks to assess if plants grown in space can transfer genetic adaptations to the next generation and if any observed changes continue or stabilize. PH-3 will use the station’s Advanced Plant Habitat (APH) to cultivate two generations of Arabadopsis thaliana, a model organism plant, which will be photographed and monitored over a three-month period, before the samples are returned to Earth.
Elsewhere, Genes in Space-10 will test techniques for measuring the length of “telomeres”, genetic structures which protect human chromosomes and are known to shorten with age-related wear. NanoRacks’ Educational Space Science and ENgineering CubeSat Experiment Mission (NanoRacks-ESSENCE) will be deployed to observe arctic ice, permafrost thaw, forests and Canada’s northernmost extremities using a fisheye camera, as well as investigating the effects of solar storms and testing new spacecraft algorithms to furnish greater functional control. NanoRacks’ IRIS CubeSat will observe the weathering of geological samples from direct solar and cosmic background radiation to assess the visibility of changes over short time scales.
And the European Space Agency (ESA) is providing its Thor-Davis experiment to observe thunderstorm activity, with specific emphasis upon the inception, frequency and altitude of recently discovered blue discharges. Particularly intense thunderstorms in the tropics and subtropics are difficult to study, but the relatively low orbital altitude of the ISS makes it an ideal platform to conduct long-term optical-band observations that are not possible from ground-based instruments due to atmospheric absorption.
Weather conditions for the opening pair of CRS-28 launch attempts on Saturday and Sunday are predicted to climb no higher than 40-percent-favorable, as a surface low meanders across the eastern Gulf of Mexico into the latter half of the week and over the weekend. “Deep tropical moisture spreading into the Spaceport will bring numerous showers and storms each day,” noted the 45th Weather Squadron at Patrick Space Force Base in a Wednesday update.
It added that the National Hurricane Center (NHC) is assessing risks. “There is uncertainly in what happens with this surface low going into the upcoming weekend,” the 45th added, “with the NHC monitoring the feature for potential tropical development.”
In any case, weather around Saturday’s midday launch window is expected to be “unsettled”, with “periods of showers and storms” that could violate the Thick Cloud Layer Rule, the Flight Through Precipitation Rule and the Disturbed Weather Rule. And although the low is expected have moved east of Florida by Sunday, it should still be close enough for showers and storms to continue, with drier air and a brighter outlook of 60-percent favorability anticipated by Monday 5th.
CRS-28 will kick off a busy June, after SpaceX triumphantly wrapped up its second eight-flight month in May, following Tuesday’s 11:02 p.m. PDT launch of a 14-times-used Falcon 9 booster from Space Launch Complex (SLC)-4E at Vandenberg Space Force Base, Calif. Laden with 52 Starlinks, Tuesday’s mission brought May to a close by launching a total of 185 of these flat-packed low-orbiting internet satellites, together with a dual-stacked payload for Iridium NEXT and OneWeb, Saudi Arabia’s powerful Arabsat-7B geostationary communications satellite and AxiomSpace, Inc.’s all-private Ax-2 mission to the ISS, which concluded with a safe return to Earth late Tuesday night.