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STS-73
Spacelab Module LM1 in Columbia's payload bay, serving as the United States Microgravity Laboratory
Mission typeMicrogravity research
OperatorNASA
COSPAR ID1995-056A Edit this at Wikidata
SATCAT no.23688Edit this on Wikidata
Mission duration15 days, 21 hours, 53 minutes, 16 seconds
Distance travelled10,600,000 kilometres (6,600,000 mi)
Orbits completed255
Spacecraft properties
SpacecraftSpace Shuttle Columbia
Payload mass15,250 kilograms (33,620 lb)
Crew
Crew size7
Members
Start of mission
Launch date20 October 1995, 13:53:00 (1995-10-20UTC13:53Z) UTC
Launch siteKennedy, LC-39B
End of mission
Landing date5 November 1995, 11:45:21 (1995-11-05UTC11:45:22Z) UTC
Landing siteKennedy, SLF Runway 33
Orbital parameters
Reference systemGeocentric
RegimeLow Earth
Perigee altitude241 kilometres (150 mi)
Apogee altitude241 kilometres (150 mi)
Inclination39.0 degrees
Period89.7 min

Left to right - Seated: Sacco, Rominger, Lopez-Alegria; Standing: Coleman, Bowersox, Leslie, Thornton
← STS-69 (71)
STS-74 (73) →

STS-73 was a Space Shuttle program mission, during October–November 1995, on board the Space Shuttle Columbia. The mission was the second mission for the United States Microgravity Laboratory. The crew, who spent 16 days in space, were broken up into 2 teams, the red team and the blue team. The mission also included several Detailed Test Objectives or DTO's.

Crew

[edit]
Position Astronaut
Commander Kenneth D. Bowersox Member of Red Team
Third spaceflight
Pilot Kent V. Rominger Member of Red Team
First spaceflight
Mission Specialist 1 Catherine G. Coleman Member of Blue Team
First spaceflight
Mission Specialist 2
Flight Engineer 		Michael López-Alegría Member of Blue Team
First spaceflight
Mission Specialist 3 Kathryn C. Thornton Member of Red Team
Fourth and last spaceflight
Payload Specialist 1 Fred W. Leslie Member of Blue Team
Only spaceflight
Payload Specialist 2 Albert Sacco Jr. Member of Red Team
Only spaceflight
Member of Blue Team Member of Blue Team
Member of Red Team Member of Red Team

Backup crew

[edit]
Position Astronaut
Payload Specialist 1 R. Glynn Holt
Only spaceflight
Payload Specialist 2 David H. Matthiesen
Only spaceflight

Crew seat assignments

[edit]
Seat[1] Launch Landing
Seats 1–4 are on the flight deck.
Seats 5–7 are on the mid-deck.
1 Bowersox
2 Rominger
3 Coleman Thornton
4 Lopez-Alegria
5 Thornton Coleman
6 Leslie
7 Sacco

Mission highlights

[edit]
Launch of STS-73
Attempt Planned Result Turnaround Reason Decision point Weather go (%) Notes
1 28 Sep 1995, 9:35:00 am Scrubbed — Technical 28 Sep 1995, 4:00 am ​(T−03:30:00) 60[2] Hydrogen leak in SSME no. 1.[3][4]: 4 
2 5 Oct 1995, 9:40:00 am Scrubbed 7 days 0 hours 5 minutes Weather 4 Oct 1995, 2:00 pm ​(T−11:00:00 hold) 30[5] Strong winds and rain forecasted due to Hurricane Opal.[6]
3 6 Oct 1995, 9:40:00 am Scrubbed 1 day 0 hours 0 minutes Technical 6 Oct 1995, 3:05 am 30[7] Problem with hydraulic system no. 1.[8]
4 7 Oct 1995, 9:41:00 am Scrubbed 1 day 0 hours 1 minute Technical 7 Oct 1995, 10:00 am ​(T−00:20:00 hold) 60 Master events controller problem.[9]
5 14 Oct 1995, 9:46:00 am Scrubbed 7 days 0 hours 5 minutes Technical 13 Oct 1995, 3:32 pm ​(T−11:00:00 hold) 80[10] Examinations of the SSME were required due to an oxidizer leak in a test engine.[11]
6 15 Oct 1995, 10:46:00 am Scrubbed 1 day 1 hour 0 minutes Weather 15 Oct 1995, 1:25 pm ​(T−00:05:00) 20[12] Poor weather at KSC and RTLS.[13][14]: 2 
7 20 Oct 1995, 9:53:00 am Success 4 days 23 hours 7 minutes 40[15] Countdown held at T−5 minutes due to range safety problem.[16]

The second United States Microgravity Laboratory (USML-2) Spacelab mission was the prime payload on STS-73.[14]: 1 [17] The 16-day flight continued a cooperative effort of the U.S. government, universities and industry to push back the frontiers of science and technology in "microgravity", the near-weightless environment of space.

On October 26, through pre-recorded video, Mission Commander Ken Bowersox threw out the first pitch for Game 5 of the 1995 World Series between the Cleveland Indians and the Atlanta Braves from orbit.[18]

Some of the experiments carried on the USML-2 payload were suggested by the results of the first USML mission that flew aboard Columbia in 1992 during STS-50. The USML-1 mission provided new insights into theoretical models of fluid physics, the role of gravity in combustion and flame spreading, and how gravity affects the formation of semiconductor crystals. Data collected from several protein crystals grown on USML-1 enabled scientists to determine the molecular structures of those proteins.

USML-2 built on that foundation. Technical knowledge gained was incorporated into the mission plan to enhance procedures and operations. Where possible, experiment teams refined their hardware to increase scientific understanding of basic physical processes on Earth and in space, as well as to prepare for more advanced operations aboard the International Space Station and other future space programs.

The landing of STS-73.

USML-2 Flight controllers and experiment scientists directed science activities from NASA's Spacelab Mission Operations Control facility at the Marshall Space Flight Center. In addition, science teams at several NASA centers and universities monitored and supported operations of a number of experiments.

Other payloads on board included the Orbital Acceleration Research Experiment (OARE), Space Acceleration Measurement System (SAMS), Three Dimensional Microgravity Accelerometer (3DMA), Suppression of Transient Accelerations By Levitation Evaluation (STABLE) and the High-Packed Digital Television Technical Demonstration system.

Launch was originally scheduled for 25 September 1995 but endured six scrubbed launch attempts before its 20 October 1995 lift off. STS-73 and STS-61C both carry the distinction of being tied for the most scrubbed launches, each having launched on their seventh attempt.[19]

After the mission, five of the crew members, namely, Bowersox, Coleman, Thornton, Leslie, and Sacco appeared on the 13 February 1996 episode of Home Improvement, "Fear of Flying", on a segment of Tool Time.[20] It was Bowersox's second time on the show.

See also

[edit]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

STS-73

View on Grokipedia
from Grokipedia
STS-73 was the 72nd mission of NASA's and the second flight of the Microgravity Laboratory (USML-2), launched aboard the orbiter Columbia on October 20, 1995, at 9:53 a.m. EDT from Kennedy Space Center's Launch Complex 39A. The mission focused on conducting over a dozen microgravity experiments in fields including fluid physics, , , combustion science, and commercial processing, while also supporting secondary objectives like the Orbital Acceleration Research Experiment (OARE). It marked the second dedicated microgravity laboratory flight, building on USML-1 from in 1992, and aimed to gather extensive data—over 60 terabits and 750 video tapes—on phenomena altered by the absence of gravity. The seven-member crew, divided into red and blue teams for 24-hour operations, was commanded by Kenneth D. Bowersox, with Kent V. Rominger as pilot, Kathryn C. Thornton as payload commander, and mission specialists Catherine G. Coleman, Michael E. Lopez-Alegria, Fred W. Leslie, and Albert Sacco Jr. Despite multiple pre-launch delays caused by a hydrogen leak in the orbiter's auxiliary power unit, hydraulic fluid issues, and Hurricane Opal's weather impacts, the mission proceeded successfully after a 14-day postponement. In orbit, the crew managed the Spacelab module in Columbia's payload bay, performing tasks such as growing over 1,500 protein crystals for pharmaceutical research and studying crystal growth in advanced materials. The flight lasted 15 days, 21 hours, 52 minutes, and 21 seconds, concluding with a landing on Runway 33 at Kennedy Space Center on November 5, 1995, after 256 orbits. Notable in-flight challenges included a water spray boiler freeze-up, failures in reaction control system thrusters, and a failed forward experiment set heater, but these did not compromise the primary scientific goals. Overall, STS-73 advanced NASA's understanding of microgravity effects, contributing foundational data for future long-duration spaceflight research, including preparations for the International Space Station.

Mission background

Development and planning

STS-73 was designated as the Microgravity Laboratory-2 (USML-2) mission, serving as the successor to USML-1, which flew aboard in 1992. This second dedicated microgravity laboratory flight aimed to advance research in areas such as fluid physics, , , combustion science, and commercial space processing by leveraging extended-duration operations in . Planning for STS-73 began in the early 1990s as part of NASA's ongoing commitment to microgravity science, with the mission originally targeted for launch on September 25, 1995, from Kennedy Space Center's Pad 39B. However, the countdown experienced six scrubs due to a combination of weather and technical issues, including a hydrogen leak in the No. 1 main engine's fuel valve leading to a scrub on September 28, impacts from Hurricane Opal delaying proceedings on October 5, inadvertent drainage of hydraulic fluid on October 6, a master events controller failure on October 7, and low clouds and rain on October 15. The launch on October 20 was delayed three minutes by a range computer glitch. These setbacks pushed the liftoff to October 20, 1995. The mission utilized (OV-102) for its 14th flight, with the orbiter undergoing preparations at , including integration of the 23-foot long module into the payload bay to support microgravity experiments. The primary payload bay configuration accommodated the module alongside various facilities and instruments, enabling continuous scientific operations. Overall mission parameters called for a planned duration of 16 days, encompassing 256 orbits at a 150-nautical-mile altitude and 39-degree inclination, for a total distance of approximately 6.6 million miles; the actual flight lasted 15 days, 21 hours, 52 minutes, and 21 seconds.

Scientific objectives

The STS-73 mission, as the second flight of the Microgravity Laboratory (USML-2), aimed to advance scientific understanding of microgravity effects across multiple disciplines, including fluid physics, , , combustion science, and commercial space processing. These objectives sought to investigate how the absence of gravitational forces influences physical and biological processes, providing data to refine theoretical models and support the development of space-based technologies. In fluid physics, the mission focused on studying behaviors such as thermocapillary flows, fluid surface configurations, and droplet dynamics in low-gravity environments, using experiments like the Space Technology Experiments (STDCE) and the Drop Physics Module to explore principles without sedimentation or interference. Materials science objectives centered on for semiconductors and other compounds, employing facilities such as the Crystal Growth Furnace and Zeolite Crystal Growth Furnace to assess how microgravity improves crystal quality and uniformity, with potential applications in and electronics. Biotechnology efforts included plant investigations, such as the Astroculture experiment examining growth and development, alongside extensive protein studies involving over 1,500 samples to enhance structural analysis for pharmaceuticals. Combustion science goals targeted droplet combustion dynamics through the Fiber Supported Droplet Combustion experiment, aiming to characterize stability and in microgravity. The payload, housed in the long module, comprised the Microgravity Payload-2 (USMP-2), which encompassed 14 major experiments and numerous supporting investigations, including the Advanced Protein Crystallization Facility for commercial bioprocessing with over 200 experiments. Broader mission goals emphasized testing microgravity's impact on fundamental processes to validate theories, foster innovations for future applications like high-quality materials production, and promote commercial ventures in manufacturing by demonstrating feasible processing techniques.

Crew and training

Crew composition

The STS-73 mission, the second flight of the United States Microgravity Laboratory (USML-2), featured a seven-member crew comprising NASA astronauts in the roles of commander, pilot, payload commander, and two mission specialists, along with two payload specialists selected for their expertise in microgravity research. This structure supported the mission's focus on extended-duration experiments in materials science, biotechnology, combustion, and fluid physics aboard the Space Shuttle Columbia. The crew members and their assignments were as follows:
NameRoleFlight NumberBrief Background
Kenneth D. BowersoxCommander3rdU.S. Navy captain and naval aviator with over 5,000 flight hours; selected as NASA astronaut in 1987; prior flights included STS-50 (pilot, USML-1) and STS-61 (pilot, Hubble servicing).
Kent V. RomingerPilot1stU.S. Navy commander and test pilot with over 7,000 flight hours in more than 35 aircraft types; selected as NASA astronaut in 1992; expertise in aeronautical engineering (M.S., 1987).
Kathryn C. ThorntonPayload Commander / Mission Specialist 34thCivilian physicist (Ph.D., University of Virginia, 1979); selected as NASA astronaut in 1984; prior flights included STS-33, STS-49 (first EVA by a woman), and STS-61, with over 21 hours of EVA experience.
Catherine G. ColemanMission Specialist 11stU.S. Air Force captain and research chemist (Ph.D. in polymer science, University of Massachusetts, 1991); selected as NASA astronaut in 1992; specialized in materials science and microgravity surface analysis.
Michael E. Lopez-AlegriaMission Specialist 21stU.S. Navy lieutenant commander and naval aviator with over 5,700 flight hours; B.S. in systems engineering (U.S. Naval Academy, 1980) and M.S. in aeronautical engineering (1988); selected as NASA astronaut in 1992. Born in Madrid, Spain, he was the first Spanish-born person to travel to space, holding dual U.S. and Spanish citizenship; this distinguishes him from Pedro Duque, who was the first astronaut representing Spain in 1998.
Fred W. LesliePayload Specialist 11stNASA research scientist at Marshall Space Flight Center (Ph.D. in meteorology/fluid mechanics, University of Oklahoma, 1979); chief of Fluid Dynamics Branch; principal investigator for microgravity fluid experiments, including crystal growth.
Albert Sacco Jr.Payload Specialist 21stChemical engineering professor at Worcester Polytechnic Institute (Ph.D., MIT, 1977); principal investigator for zeolite crystal growth in microgravity; served as backup payload specialist for USML-1 (STS-50) due to prior involvement in similar zeolite research.
Crew seating assignments for launch placed Bowersox in seat 1 (commander), Rominger in seat 2 (pilot), Coleman in seat 3, Lopez-Alegria in seat 4, Thornton in seat 5, Leslie in seat 6, and Sacco in seat 7; landing assignments were similar, with adjustments for Thornton to seat 2.

Preparation and roles

The STS-73 crew underwent an intensive regimen spanning approximately two years, developed under NASA's in collaboration with contractors like Teledyne Brown Engineering, to prepare for the United States Microgravity Laboratory-2 (USML-2) mission. This program emphasized hands-on simulations at the , including practice in mockups to familiarize the team with experiment procedures and hardware operations, such as high-temperature furnaces for research. incorporated interactive systems with video, , and role-playing scenarios to simulate microgravity conditions and payload handling, ensuring proficiency in scientific and operational tasks. To support continuous 24-hour operations for the 14 major experiments aboard, the seven-member crew was organized into two alternating 12-hour shifts: the , consisting of Commander Kenneth D. Bowersox, Pilot Kent V. Rominger, Payload Commander Kathryn C. Thornton, and Albert Sacco Jr.; and the Blue Team, comprising Catherine G. Coleman, Michael E. Lopez-Alegria, and Fred W. Leslie. The payload specialists led science-specific tasks, while flight crew members managed vehicle systems during off-shift periods to maintain overall mission efficiency. Specific responsibilities were assigned based on crew expertise: Bowersox, as , oversaw all vehicle operations, navigation, and decision-making for the Orbiter Columbia. Rominger, the Pilot, focused on ascent, entry, landing maneuvers, and attitude control during orbital adjustments. Thornton, serving as Payload Commander, coordinated experiment timelines, resource allocation, and interactions with ground-based principal investigators across disciplines like fluid physics and . Coleman and Lopez-Alegria, as Mission Specialists, handled systems monitoring, in-flight maintenance, and support for contingency procedures, including readiness for extravehicular activities that were not ultimately required. Leslie and Sacco, the Payload Specialists, concentrated on executing and troubleshooting USML-2 experiments in , combustion science, and commercial processing, drawing on their scientific backgrounds. Pre-flight preparations included standard protocols for crew health, such as a quarantine period to minimize risks and baseline biomedical monitoring for detailed supplementary objectives like immunological assessments conducted before and after the mission. These measures ensured optimal physical condition for the 16-day flight, with medical supporting ongoing health research.

Launch

Pre-launch preparations

The pre-launch preparations for STS-73 commenced with the first countdown initiation at T-43 hours on September 25, 1995, but were immediately disrupted by a leak in the main fuel valve of Space Shuttle Main Engine No. 1, necessitating replacement of the valve and rescheduling the launch attempt. Subsequent efforts on October 5 were postponed to due to adverse weather from , which brought high winds and heavy rain to ; the countdown was then scrubbed prior to external tank loading after was inadvertently drained from system 1. On October 7, the attempt halted at T-20 seconds owing to a in Master Events Controller 1 core B, prompting its replacement and additional vehicle verifications. Further delays arose from ongoing inspections, including checks of the oxidizer ducts following a crack discovered in a ground test , and replacement of a faulty general purpose computer; these pushed the next window to October 14, with the countdown on October 15 scrubbed at T-5 minutes due to low clouds and rain violating launch weather constraints. Launch was tentatively reset for October 19 pending clearance from an rocket launch on October 18, but the Atlas delay shifted STS-73 to October 20; upper-level winds exceeding limits also factored into weather-related holds during preparations. The successful countdown for the October 20 liftoff began at T-43 hours on October 17, incorporating standard holds such as a 3-hour pause at T-9 hours for final weather assessments and a 4-hour hold at T-6 hours to load the external tank with cryogenic propellants. Comprehensive vehicle inspections verified the condition of the Solid Rocket Boosters (BI-075), External Tank (ET-73), and Space Shuttle Main Engines (SSMEs 2037, 2031, and 2038), while payload integration in Columbia's payload bay—housing the United States Microgravity Laboratory-2 (USML-2) Spacelab module and associated experiments—was confirmed operational prior to bay doors closure. Range safety evaluations ensured compliance with trajectory and abort parameters throughout. Approximately three hours prior to liftoff, the seven-member crew departed the for final briefings and suiting in the crew quarters, then proceeded to Pad 39B for ingress into the orbiter at T-2.5 hours. The final go/no-go polls, involving approvals from Mission Management Team, launch director, and control, were executed at T-31 seconds, confirming readiness for main engine start; a minor three-minute delay occurred due to a range computer processing but did not impact overall proceedings.

Liftoff and orbital insertion

The lifted off from Launch Pad 39B at NASA's on October 20, 1995, at 9:53:00 a.m. EDT, marking the start of the STS-73 mission after a series of pre-launch holds. The three Space Shuttle Main Engines ignited approximately 6.6 seconds prior to liftoff, followed by ignition of the two Solid Rocket Boosters at T-0, generating the thrust needed to clear the tower and begin the ascent phase. The ascent followed a nominal , with the Solid Rocket Boosters separating from the External Tank at T+2:05, allowing the main engines to continue the burn unassisted. Main Engine Cutoff occurred at 511.3 seconds mission elapsed time, after which the External Tank was jettisoned at T+8:32. The orbiter then coasted into a preliminary characterized by an altitude of 296 x 306 km and an inclination of 28.45 degrees. To achieve circularization, the engines performed the OMS-1 burn, raising the orbit to a nominal 300 km altitude. At orbital insertion, Columbia attained a of 7.8 km/s, with no major anomalies noted during the ascent phase. Post-insertion activities included the deployment of the vehicle's radiators for thermal control, the opening of the payload bay doors to facilitate heat dissipation and payload access, and comprehensive verification of onboard systems to ensure operational readiness. These checks confirmed the orbiter's stable configuration in the initial orbit.

In-flight activities

Payload deployment and operations

Following orbital insertion, the crew initiated Spacelab activation within the first 24 hours of flight, powering up the module and conducting checkouts of environmental control systems, including Freon coolant loops positioned for thermal management, as well as data recorders and support subsystems. This process ensured stable conditions for the Microgravity Laboratory-2 (USML-2) housed in the module within the payload bay. Payload bay operations commenced shortly after launch with the opening of the bay doors at approximately 00:01:35 mission elapsed time (MET), initially positioning the port door at 62 degrees to reduce micrometeorite exposure before fully opening for Spacelab condensate dumping and experiment setup around 04:23:50 MET. Key experiments were deployed and activated, including the Commercial Protein Crystal Growth (CPCG) facility in the Spacelab module for crystal growth studies and the Middeck Glovewater System (MGS) in the orbiter's middeck for middeck-based fluid physics investigations. These setups involved securing hardware, initializing power and cooling interfaces, and verifying instrument functionality to support microgravity operations. Daily routines were structured around two 12-hour shifts for the seven-member —divided into and teams—to monitor major USML-2 experiments continuously, with tasks including real-time adjustments, , and downlink transmissions to ground stations via the Ku-band system. Sample handling was a key element, such as tending to the five potato plants in the Advanced Astroculture (ADVASC) unit located in the module, which required periodic environmental checks and growth medium maintenance to sustain plant development under microgravity conditions. Orbiter systems provided essential support for payload operations, including attitude holds such as the bottom-Sun orientation maintained for over eight hours to meet thermal conditioning requirements for specific experiments. Thruster firings using the (RCS) ensured orbit maintenance despite isolated anomalies, like the temporary failure of the F1F thruster early in the mission, while biomedical monitoring of the crew tracked physiological responses to extended microgravity exposure via onboard devices. Available consumables supported up to 70 additional hours of operations at 19.5 kW power levels beyond the planned 16-day mission, thereby maximizing the science return from the .

Key experiments and results

The STS-73 mission, as part of the Microgravity Laboratory-2 (USML-2), conducted extensive experiments in fluid physics, focusing on the Surface Tension Driven Convection Experiment-2 (STDCE-2), which investigated oscillatory thermocapillary flow in 2 cSt silicone oil using cylindrical containers of varying diameters under reduced gravity conditions. Observations revealed the onset of unexpected oscillations in confined fluids, with viscous-dominated flows near the transition point and documented patterns and frequencies that challenged the rigid surface assumption in traditional Marangoni convection models while confirming numerical predictions for free surface deformations. These findings advanced understanding of thermocapillary instabilities, with implications for defect reduction in crystal and metal processing on . In , the mission emphasized protein crystal to enhance for , utilizing hardware like the Vapor Diffusion Apparatus (VDA), Protein Crystallization Apparatus for Microgravity (PCAM), and Diffusion-controlled Crystallization Apparatus for Microgravity (DCAM). For , microgravity yielded larger, higher-quality crystals with improved resolution (1.5 Å compared to 1.7 Å for Earth-grown samples), 30% better efficiency, and reduced mosaicity (0.020° versus 0.048°), enabling suspended growth free of imperfections. crystals also showed slightly higher efficiency and resolution than ground controls, though some degradation occurred due to pre-launch delays, providing insights into pharmaceutical applications despite these challenges. Combustion science experiments on STS-73 included the Fiber Supported Droplet Combustion-2 (FSDC-2), which ignited over 25 fuel droplets suspended on ceramic wires in ambient shuttle air (21% oxygen, 1 bar pressure) to study burning characteristics in microgravity. Results demonstrated extended burn times up to 10 times longer than in gravity, along with larger flame diameters and confirmation of microgravity-specific formation and combustion byproducts, validating theoretical models like Spalding's 1979 framework for buoyancy-free flames and informing designs for and terrestrial applications. Biotechnology and plant growth investigations featured the Astroculture facility, where five tubers developed from axillary buds over the 16-day flight, forming mature structures similar to Earth-grown ones but with a higher proportion of smaller grains and reduced activity of ADP-glucose pyrophosphorylase, indicating altered patterns under microgravity. These outcomes highlighted potential adaptations for space agriculture, demonstrating viable edible crop production in orbit while revealing metabolic shifts relevant to long-duration missions. Commercial experiments encompassed in the , successfully crystallizing four types (A, X, Beta, and Silicalite) to produce larger, more defect-free structures in higher yields than achievable on , supporting applications in and technologies. Additionally, LED lighting tests within the Astroculture setup for growth proved effective for controlled illumination, leading to commercial hardware availability and adaptations for Earth-based plant nurseries to optimize energy-efficient cultivation.

Landing

Deorbit and reentry

Preparations for deorbit commenced on flight day 16 with the shutdown of ongoing operations and reconfiguration of the bay, beginning approximately 24 hours prior to the burn to ensure a safe reentry configuration. The Ku-band antenna was stowed at 308:23:05 GMT (015:09:12 mission elapsed time, or MET), and final checks confirmed the readiness of systems for . The bay doors were successfully closed and latched at 309:08:15 GMT (015:18:22 MET), securing all experiments and equipment. The deorbit burn was executed using the Orbiter Maneuvering System (OMS) Pod 2 engine on orbit 255 at 309:10:46:40 GMT (015:20:53:40 MET), equivalent to 5:46 a.m. EST on November 5, 1995. The burn lasted 162.5 seconds and imparted a velocity change of 270 ft/s (approximately 82 m/s), targeting the for reentry interface at 400,000 feet altitude. Columbia reached entry interface at 309:11:13:19 GMT (015:21:20:19 MET), entering the sensible atmosphere at approximately Mach 25. The reentry profile maintained a nominal 45-degree during the peak heating phase to optimize drag and heat distribution, resulting in a plasma sheath formation that caused a lasting about 15 minutes. Guidance and control during reentry relied on the (RCS) for precise roll maneuvers to adjust the flight path and manage heating loads. Crew and ground teams monitored thermal protection system performance, with tile temperatures peaking at 1,650°C in critical areas such as the nose cap and wing leading edges. In-flight RCS thruster issues, including intermittent failures in units R5R, R5D, L3D, and R3D, had been resolved through prior to entry, allowing nominal operation. Post-blackout, communications were reacquired via S-band links with ground stations and the Tracking and Data Relay Satellite System, enabling real-time telemetry and voice contact as the orbiter descended.

Touchdown and recovery

The final approach for STS-73 transitioned to the Terminal Area Energy Management (TAEM) phase at 309:11:39:09 G.m.t., corresponding to an altitude of approximately 23,000 feet. The autopilot was handed over to the pilot at 10,000 feet to initiate the manual landing segment. Columbia executed a precise approach to Kennedy Space Center's Shuttle Landing Facility Runway 33, touching down at 6:45:21 a.m. EST on November 5, 1995, after completing 256 orbits. Performance during landing was nominal, with the main making contact at 214 knots and a low sink rate. The nose gear subsequently touched down at 58 knots, followed by a rollout distance of 9,038 feet with no reported issues. The drag chute deployed shortly after main gear contact and was jettisoned prior to wheels stop, resulting in a total rollout time of 55.6 seconds. The orbiter's landing weight was 230,200 pounds, and peak pressures remained within acceptable limits. Recovery operations commenced immediately after wheels stop, including of toxic fumes from the propulsion systems to ensure safe access, with post-landing vacuum vent line temperatures ranging from 59 to 73°F and nozzle temperatures from 100 to 157°F. The egressed via the orbiter's crew access hatch with assistance from the ground recovery team. Orbiter safing procedures followed, encompassing shutdown 18 minutes 46.5 seconds after and nominal hydraulic system load tests. The total mission duration stood at 15 days, 21 hours, 52 minutes, and 21 seconds. The landing occurred under favorable weather conditions at KSC, featuring clear skies and 10-knot winds that precluded any need for a divert to . Post-, the received evaluations to assess their condition following the extended microgravity exposure and conducted a media debrief to review mission outcomes.

Post-flight analysis

Mission accomplishments

The STS-73 mission, as the second flight of the Microgravity Laboratory (USML-2), achieved significant scientific yield by processing over 1,500 protein crystal growth samples across three dedicated experiments, yielding crystals of enhanced quality that advanced microgravity research in and . These results validated theoretical models of crystal formation in low-gravity environments and provided new datasets that contributed to subsequent peer-reviewed publications on protein structures and their applications in pharmaceutical development. Additionally, the mission processed 38 zeolite samples and grew eight crystals, further expanding knowledge in materials processing under microgravity. The mission was planned for 16 days plus two contingency days and lasted 15 days, 21 hours, 52 minutes, and 21 seconds, during which the orbiter traveled approximately 6.6 million miles while completing 256 orbits, enabling continuous experimentation in a stable microgravity environment. Technological advances from STS-73 included improved techniques for , such as using a liquid bridge method in the Crystal Growth Furnace, which produced crystals with fewer defects than ground-based counterparts and informed enhancements in Earth-based manufacturing processes for semiconductors and pharmaceuticals. Plant growth experiments in the Astroculture facility successfully cultivated five small tubers, providing insights into hydroponic systems and informing the development of 's advanced life support technologies for long-term space habitation. The mission's broader impact was amplified through international collaboration, with payload elements including the European Space Agency's Glovebox Facility—contributed by partners from and —for seven biotechnology experiments, fostering global data sharing and cooperation in microgravity science. These efforts paved the way for subsequent USMP missions by establishing protocols for extended microgravity research and international payload integration. Quantitative achievements underscored the mission's success, with a 100% completion rate for all primary experiments and the collection of over 41,000 gigabits (approximately 5 terabytes) of scientific data, including more than 750 video tapes and 300 high-resolution images.

Anomalies and lessons learned

During the STS-73 mission, the Reaction Control Subsystem (RCS) experienced several anomalies affecting attitude control. The forward primary thruster F1F failed to achieve nominal chamber pressure (reaching only 17 psia) during the first Orbital Maneuvering Subsystem trim burn due to a blockage in the PC tube orifice; this was addressed through thruster reselection and subsequent hot-fire verification, with no recurrence. Additionally, aft vernier thrusters R5R and R5D failed off a total of eight times, linked to an intermittent command path issue in the RCS module of mass memory (MOM S/N 121) and remote joint drive (RJD S/N 20); contingency procedures, including thruster reconfiguration and manual attitude holds, maintained vehicle control without impacting primary objectives. Communications systems encountered temporary S-band forward-link dropouts on the lower right antenna, occurring intermittently and traced to a potential path issue between the antenna and switch; these were mitigated via ground-commanded antenna handovers to the (TDRS) system, ensuring no loss of critical data relay. Among payload operations, the Orbital Acceleration Research Experiment (OARE) showed minor and an electronic bias shift during Z-axis scale factor in the C-range, consistent with prior missions but confined to non-data-collection periods; this introduced negligible noise (estimated 30-60 nano-g error) without affecting overall microgravity measurements or experiment outcomes. Post-flight inspections confirmed no critical Thermal Protection System (TPS) tile damage, despite 147 micrometeoroid/orbital debris impacts, including 26 exceeding 1 inch in diameter—the highest lower fuselage heating observed to date—none of which compromised reentry safety. Crew members experienced typical minor space adaptation syndrome symptoms, including motion sickness, but achieved full operational productivity throughout the mission. Key lessons learned emphasized enhancing RCS command path redundancy through electronics upgrades and pre-flight testing protocols to prevent intermittent failures, as the affected units were replaced without identifying a root cause. Recommendations also included refined antenna cabling inspections and switch diagnostics for S-band reliability, contributing to broader Shuttle program improvements in communication links. These insights, along with successful in-flight maintenance like cathode ray tube (CRT) swaps for display glitches, informed contingency planning for future long-duration missions.

References

  1. https://ntrs.nasa.gov/api/citations/19970001426/downloads/19970001426.pdf
  2. https://www.nasa.gov/mission/sts-73/
  3. https://www.nasa.gov/wp-content/uploads/2016/01/bowersox_kenneth_0.pdf
  4. https://www.nasa.gov/wp-content/uploads/2016/01/rominger_kent.pdf
  5. https://www.nasa.gov/wp-content/uploads/2016/01/thornton_kathryn.pdf
  6. https://www.nasa.gov/wp-content/uploads/2023/05/coleman.pdf
  7. https://www.nasa.gov/wp-content/uploads/2021/11/lopez-alegria_michael_0.pdf
  8. https://www.axiomspace.com/astronaut/michael-lopez-alegria
  9. https://sutusummit.com/speakers/michael-lopez-alegria/
  10. https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/ESA_astronaut_Pedro_Duque_appointed_to_new_Spanish_government
  11. https://www.nasa.gov/wp-content/uploads/2016/01/leslie.pdf
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  19. https://apps.dtic.mil/sti/tr/pdf/ADA353128.pdf
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  21. https://ntrs.nasa.gov/citations/19990018874
  22. https://ntrs.nasa.gov/api/citations/20000021513/downloads/20000021513.pdf
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  27. https://ntrs.nasa.gov/api/citations/19820015617/downloads/19820015617.pdf
  28. https://aviation.stackexchange.com/questions/21981/how-does-the-space-shuttle-slow-down-during-re-entry-descent-and-landing
  29. https://www.researchgate.net/figure/Fig-1-Re-entry-trajectories-and-blackout-range-for-Space-Shuttle-RAM-C-and-ARD_fig1_228651596
  30. https://www.faa.gov/sites/faa.gov/files/about/office_org/headquarters_offices/avs/III.4.1.7_Returning_from_Space.pdf
  31. https://ntrs.nasa.gov/api/citations/19970009811/downloads/19970009811.pdf
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