RAND and SAGE 1964

The introduction of timesharing on the UT Austin CDC 6600 in 1967, soon after its arrival in 1966, was a student-led initiative that fundamentally changed how the university's computers were used. Instead of originating from faculty or administration, the push for timesharing came from three graduate students, including Forest Baskett, who would eventually run day-to-day aspects of the UTCC systems programming staff. Frustrated by the CDC 6600's primitive batch operating system, the students proposed replacing it with a timesharing system that utilized online terminals. They took their idea to Jim Browne, an early computer science faculty member, who supported the project and got the Computation Center's approval. [1][2]

Baskett drew inspiration from a summer job in 1964 at the System Development Corporation. Spun off from RAND Santa Monica in 1956 to handle the unprecedented software demands of the SAGE project, SDC is widely considered the world's first independent computer software company. The SDC facility originally required an air-conditioning system powerful enough to cool 20,000 homes to offset the heat generated by its early vacuum-tube systems. In this environment, operators monitored radar scopes in dimly lit rooms, surrounded by massive walls of neon bulbs displaying the state of the machine's logic gates. This summer job was while Baskett was an undergrad at Rice University in Houston and already involved with interesting computer research. He was working for a chemistry professor, running simulations of the molecules in a gas and making movies of the results. They had a cathode ray tube with a 16-millimeter film camera attached to it. It could put dots on the screen, take a picture, clear the screen, and advance the film by one click. During this period in the early sixties, Baskett was fortunate enough to experience the SAGE system at SDC.

SAGE, initially designed in the fifties as a military command-and-control system for Soviet bomber defense, featured pioneering real-time processing and early timesharing capabilities. The machine Baskett interacted with specifically was the AN/FSQ-32, commonly referred to as the Q-32, a transistorized prototype that succeeded the massive, vacuum-tube-based machines originally built for the SAGE air-defense network. The Q-32 occupies a unique and somewhat ironic place in computing history. Its cancellation as a military asset is exactly what allowed it to become a pioneering testbed for modern interactive computing.

The Q-32 was originally commissioned by the Air Defense Command to solve the glaring vulnerability of the massive, above-ground AN/FSQ-7 SAGE blockhouses. It was designed to be installed in hardened, underground nuclear bunkers capable of withstanding 200 psi of blast overpressure, called Super Combat Centers. By 1960 the Department of Defense realized that the rapidly increasing yields of Soviet nuclear weapons and the shift toward Intercontinental Ballistic Missiles rendered even these underground bunkers vulnerable. As a result, the Super Combat Center program was cancelled, and the Q-32's military career was terminated before series production could begin, leaving the single completed prototype at the SDC headquarters in Santa Monica.

Because it was no longer needed for active air defense, the Advanced Research Projects Agency, under the guidance of Joseph Licklider, repurposed the Q-32 prototype to research multi-user interactive computing. SDC engineers built the Time-Sharing System for the machine, which achieved its fluid, conversational terminal interactions by utilizing a round-robin scheduling algorithm. The system rapidly swapped active user programs between the machine's 65,000-word core memory and high-speed magnetic drums, allowing it to support upwards of 30 simultaneous users via remote terminals routed through a PDP-1 interface. 

This was the specific architecture that allowed Baskett to sit at a terminal and interact with the machine. It demonstrated that a computer could be an immediate, conversational medium for mathematical exploration. Given the unstructured nature of his summer job, Baskett used the time to teach himself John McCarthy’s Lisp from a textbook and wrote a custom Lisp interpreter directly on the SAGE machine. This hands-on experience became his mental model for how computing should ideally operate when he later encountered the CDC 6600's restrictive, punch-card-based SCOPE batch system. The Q-32's influence extended far beyond Baskett's individual career. In October 1965, the Q-32 in Santa Monica was directly linked via a dedicated dial-up telephone line to the TX-2 computer at MIT's Lincoln Laboratory. This connection marked the first successful transcontinental exchange of data between two independent operating systems, successfully proving the viability of wide-area distributed computing and serving as a direct precursor to the ARPANET. [3]

Understanding this context highlights exactly why Baskett found UT's CDC 6600 so frustrating just a few years later. While the Q-32 at SDC was designed for real-time command, control, and multi-user interaction, the CDC 6600 was engineered purely for maximum scalar floating-point performance. The manufacturer-supplied SCOPE operating system was strictly batch-oriented to keep the central processor constantly fed with scientific simulations. When Baskett and his fellow graduate students proposed building a timesharing system, they were essentially attempting to graft the interactive, user-friendly philosophy he had experienced at SDC onto the raw, unyielding computational power of a machine designed solely to crunch numbers. The students' frustration with the SCOPE system was entirely justified. SCOPE was engineered purely for batch processing, completely isolating the user from the machine. To fix even a minor bug, researchers were forced to submit physical decks of punch cards to operators and wait hours for printed results. The system enforced counterintuitive, rigid rules, such as requiring users to define their maximum runtime in octal seconds, capping execution at exactly 77777 octal seconds, or about nine hours.

When Baskett and his two fellow graduate students approached Jim Browne with their radical idea, Browne's response was enthusiastically pragmatic: "Hmm, that could be fun. Let's try". Browne's backing was the critical catalyst for the project. He had to navigate the university's administrative hierarchy to convince the Computation Center to allow a small group of students to completely replace the core software of a $5.9 million supercomputer. In addition to his work in systems software, Browne served as a Principal Investigator for the Conduit project at UT Austin, working alongside Charles Warlick and George Culp to test, evaluate, and distribute computer-based curriculum materials across different universities. Ultimately, his early experiences supporting timesharing and multi-institutional resource sharing shaped his later career, and Browne went on to become a major proponent of national high-speed computer networks. [2]

Once Browne secured the Computation Center's approval, Baskett and his team ingeniously repurposed the CDC 6600's unique hardware to solve the software bottlenecks. By programming the mainframe's ten independent Peripheral Processors to handle the input/output operations of remote interactive terminals, they freed the central processor to execute user programs in rapid, multiplexed time slices. The trust that Jim Browne and the Computation Center placed in these students yielded extraordinary results. The initial system was up and running within a year and a half, and its subsequent revisions proved so stable that it remained in active production at the university for a remarkable ten years. Browne also went on to serve as Baskett's doctoral thesis advisor, supporting his groundbreaking mathematical proofs on system scheduling and queuing theory that emerged from the project.

The primary goal of the new UT system was to make the computer easier to use, more enjoyable, and highly productive for its target audience of faculty researchers and graduate students. Through data analysis of user habits, Baskett deliberately aimed to optimize the system to minimize customer complaints. The system initially used Teletype terminals and relied on the existing compilers supplied by CDC, ensuring the operating system maintained all the interfaces that users were already accustomed to. Baskett implemented a job-scheduling method using round-robin timeslicing, similar to the one he had experienced on the SDC Q-32, keeping the time slices as small as possible while remaining consistent with system overhead. 

Tasks were kept memory-resident and managed via the 6600's base and bounds registers, which provided memory protection on a per-job basis. Because the CDC 6600 completely lacked hardware paging, segmentation, or virtual memory mapping, user programs were forced to reside in contiguous physical blocks within the central memory. The base and bounds registers provided strict per-job memory protection so users couldn't maliciously or accidentally corrupt each other's data. To effectively multiplex dozens of users with round-robin timeslicing, the system had to swap these memory blocks rapidly. The team achieved this by leveraging Extended Core Storage. When a user's time slice expired, the TAURUS scheduler initiated an extremely fast block transfer, copying the user's entire contiguous address space into ECS and immediately swapping the next active user's program into central memory.

During this period, Baskett encountered Seymour Cray and asked the legendary architect to modify the 6600 hardware so that privileged instructions in user mode would cause an exception rather than a no-op. This was essentially a plea for hardware-level virtualization. Cray’s succinct refusal "No, I don’t think so" illustrated the persistent gap between architectural vision and hardware implementation that Baskett would spend his career bridging. As he assumed leadership of the twenty-five-person systems staff at the computation center, he balanced these practical infrastructure challenges with the theoretical rigor that would define his doctoral dissertation. Between 1971 and 1982, his career exemplified a unique industrial-academic synthesis, bridging the gap between national laboratories and corporate research. He led the Demos operating system for the Cray-1 at Los Alamos National Laboratory, which was notable for its use of software-based property tags, an early precursor to modern object-oriented systems. Simultaneously, he conducted VLSI research at Xerox PARC.

The initial timesharing service, known as RESPOND, was officially initiated on the 6600 in March 1967. It proved to be an astounding success, with the system and its subsequent revisions remaining in production for a decade. RESPOND was later replaced by a more advanced system called TAURUS (Texas Anthropocentric Ubiquitous Responsive User System), which operated as an integral part of the UT-2D dual operating system, managing both the CDC 6600 and 6400. Ultimately, the UT Austin students' project was highly influential in the broader computing industry. It demonstrated the viability of timesharing on the CDC 6600, prompting both Control Data Corporation and the Lawrence Livermore National Laboratory to realize the need for such systems and launch their own competing efforts.

SAGE terminal with interactive radar display and light pen.

SAGE terminal.

SAGE AN/FSQ-7 computer. The Q-32 in Santa Monica was a follow-on transistorized version.

[1] CHM Oral History Interview with Forest Baskett 

[2] Jim Browne 

[3] By June 1963 the Time-Sharing System Model Zero was demonstrated after magnetic drums were added to the time-sharing. Each user was given a priority-based time slice, measured in milliseconds, when the user's program was written from the magnetic drums into much higher speed memory, processed, and then written back to the magnetic drums with any computational changes that had occurred. It was influenced by early experiments at Bolt, Beranek, and Newman, and the CTSS project and Project MAC at MIT. Terminals included several Teletype Model 33 ASRs. In October 1965 Lincoln Labs' used a TX-2 solid-state computer tied to the Q-32 prototype for the first telecommunication of time packets. https://en.wikipedia.org/wiki/AN/FSQ-32#Time-sharing 

CDC 6600 Checkout Testing (Space Wars)

Where there were computers, there were computer games. Even the original CDC 6600 checkout engineers famously used the 6600's innovative CRT monitors for early games like Space Wars, Lunar Lander, and Baseball as a way to test the machine. Because it was among the first commercial computers to feature an interactive cathode-ray tube display console instead of just glowing lights and typewriter text, it became the perfect sandbox for early coders. CDC's checkout and maintenance engineers needed a fast, highly visual way to ensure that all parts of the multi-million dollar system, especially the graphics consoles and peripheral processors, were firing correctly under heavy stress. To do this, they programmed a suite of highly advanced, real-time diagnostic games. [1]

While Spacewar was originally coded on the MIT PDP-1 in 1962, the CDC 6600 Space Wars version took full advantage of the supercomputer's relatively immense processing speed. It featured two vector-graphics spaceships maneuvering in real-time, firing torpedoes at each other while being pulled by the gravity of a central star. Lunar Lander was an early, real-time precursor to the text-based and arcade lander games that would explode in popularity in the seventies. Players had to precisely calculate thrust and fuel consumption using the console controls to safely descend a spacecraft onto a jagged vector-graphics moon landscape without crashing. Baseball was a unique vector-graphic sports game. A pitcher would throw a pitch, and the batter would have to swing with strict timing to hit the ball out into a digitally rendered diamond. Some historical legal documents from Magnavox patent lawsuits in the seventies point to this exact CDC game as a precursor to early video arcade sports games.

CDC engineers openly admitted that the games became the primary incentive for getting the temperamental machines operational. If a newly assembled CDC 6600 could smoothly run Space Wars or Baseball without freezing or crashing, it meant the entire system architecture was completely sound. Because these games utilized the console screens long before commercial video games existed, they can be considered among the first computer games to use graphical displays.

Possibly a checkout engineer?

Baseball [2]

[1] Mention of the checkout testing games https://www.cisl.ucar.edu/ncar-supercomputing-history/cdc6600 

[2] Baseball photo 

[3] One reason that the following link is so interesting is that have met an original european CDC sales rep. He's a prominent art dealer, gallery owner, and respectable old gentleman of Frankfurt. Was there to meet family for their art opening in October 2024. His home was over the gallery, and during the dinner after the event, quite magically we had a conversation about CDC. Just one of those unforgettable things. CDC 6600 arrives at CERN in 1965 

CDC at UT Austin and IBM at Exxon Houston

There's a curious parallel between UT Austin's CDC hardware and Exxon Houston's IBM hardware during the sixties and seventies, bookended by a shared IBM era in the fifties and a shared Cray era in the eighties. CDC and Cray were members of a family of Minnesota companies (ERA, CDC, Cray) that, along with its UNIVAC relatives, was a vigorous competitor to IBM in the engineering, scientific, national lab, and cryptography fields. In a sense, UT Austin moved from IBM to the ERA tradition in the sixties, and Exxon Houston followed in the eighties. UT Austin's early move was due to David Young's being firmly in the ERA tradition from his work at Ramo-Wooldridge (TRW) in the fifties. He arrived at UT in 1958 and led the acquisition of the CDC 1604 in 1960 and CDC 6600 in 1966. The CDC Cyber hardware that UT acquired in the seventies was essentially updated versions of the CDC 6600, based on the same 60-bit architecture and running similar code.

There were multiple important connections between computing at UT Austin, Exxon, Rice, and Houston. A sign of these connections was the story of how, in 1958, Humble Oil in Houston (now Exxon) donated its IBM Card-Programmed Electronic Calculator to UT Austin. UT’s Al Matsen was a consultant for Exxon Houston and New Jersey for over thirty-five years. The CPC was a landmark gift and a direct result of Matsen’s extensive ties. To bypass bureaucratic paperwork, Matsen, his graduate students, and other faculty physically carried the heavy machine components into Welch and installed it themselves. Exxon had acquired the CPC in 1952 and used it to implement ground-breaking subsurface reservoir simulations and the beginnings of the ADI Alternating Direction Implicit techniques for Finite Difference Methods. This work put Exxon, Rice University, and Houston in a leading position for subsurface modeling and computational engineering and science.

ADI was forged in late 1953 out of urgent commercial necessity by Peaceman, Rachford, and Douglas. Driven by the pragmatic need to simulate oil reservoirs for high-stakes drilling decisions, they bypassed academic idealism in favor of industrial utility. Rather than chasing elegant theorems, they engineered ADI as a brilliant, gritty algorithmic hack, splitting complex multi-dimensional problems into a sequence of cheap, one-dimensional coordinate sweeps to circumvent both the memory bottlenecks of early hardware and the finicky tuning required by SOR. The alignment of Exxon with IBM, and David Young’s association with UNIVAC and Control Data Corporation, mirrors the structural, financial, and philosophical divides of the early computing era. [1]

The IBM CPC was not a computer in the modern sense. It was a hybrid electro-mechanical system. It consisted of an IBM 402 or 417 Accounting Machine (the printer/controller) connected to an IBM 604 Electronic Calculating Punch (the arithmetic unit) and an electromechanical storage unit. It functioned as a decentralized network of specialized units rather than a unified stored-program architecture and was fundamentally incapable of holding both the data and the instructions required for the Simplex Method. Consequently, the program existed not as a digital state within the machine, but as a physical sequence of punched cards. This required the operator to function as a manual control unit, physically re-entering card decks to execute the iterative loops essential for finding an optimal solution within a linear system. 

The development of the CPC itself actually originated from clandestine, user-driven engineering at Northrop Aircraft rather than inside IBM's own research labs. In late 1946, a specialized computing group at Northrop led by engineers Greg Toben, Bill Woodbury, and Rex Rice was tackling complex aerospace calculations, such as jet propulsion and guided missile trajectories, which vastly outstripped the capacity of standard accounting machines.

Because true stored-program computers were not yet available, the Northrop team decided to build their own hardware solver by merging two leased IBM machines: the new IBM 603 Electronic Multiplier, which was fast but lacked sequencing control, and the older IBM 405 Accounting Machine, which was slow at math but had excellent card-reading and printing capabilities. In direct violation of their IBM rental agreements, the Northrop engineers took the protective covers off the machines, exposed their internal wiring, and physically linked the two units together. They affectionately dubbed their makeshift, hybrid creation the poor man's ENIAC.

This prototype, which the engineers nicknamed Betsy, was remarkably powerful but suffered from physical instabilities. The multiplier section would occasionally freeze mid-operation, trapping card decks inside. To clear the jam, the operators often resorted to physical force. In one famous incident, an engineer was told to "Kick it, Gib", and his literal kick drove a heavy metal cover directly into a 60-ampere fuse block, causing a massive, hazardous shower of sparks. When Northrop's founder, Jack Northrop, reached out to IBM's CEO Thomas Watson to demand manufacturing support and standard parts for their modified system, IBM realized the commercial potential of the hybrid concept. IBM immediately flew Woodbury and his colleague George Fenn to New York to present their 603 and 405 combo. IBM's engineers then standardized the physical interfaces, replaced the 603 with the newer 604 calculating punch, and officially announced the commercial Card-Programmed Electronic Calculator in May 1949.

Even after the commercial release, Northrop continued to drive the CPC's evolution. Early users struggled because instruction cards had to point to highly specific, hardwired microprograms on a physical plugboard, making it almost impossible to share programs. To break this hardware bottleneck, Northrop's Rex Rice engineered a general-purpose control panel. By wiring a generalized set of logical pathways and math routing systems directly into the board, programmers could write various mathematical applications entirely on standard card decks without needing to manually rewire the plugboard for every new problem.

The CPC can even be traced a few years further back, to 1943 Los Alamos and the race to build the atomic bomb. All of the pieces that would become the CPC three years later were already being brought together at Los Alamos and even earlier at Columbia University, and it’s extremely likely that some of the Northrop researchers had been present at Los Alamos and possibly Columbia. Here's a description of the arrival at Los Alamos of the pieces of what soon would become known as the CPC, and Richard Feynman’s reaction.

Feynman, frustrated, turned to Nicholas Metropolis, a mustached Greek mathematician who later became an authority on computation and numerical methods, and said, “Let’s learn about these damned things and not have to send them to Burbank.” (Feynman grew a temporary mustache, too.) They spent hours taking apart new and old machines for comparative diagnosis; learned where the jams and slippages began; and hung out a shingle advertising, “Computers Repaired.” Bethe was not amused at this waste of his theoreticians’ time. He finally ordered a halt to the tinkering. Feynman complied, knowing that within weeks the shortage of machines would change Bethe’s mind. Escalation of the computation effort came in the fall of 1943 with an order to IBM for business machines to be delivered to an unknown location: three 601 multipliers, one 402 tabulator, one reproducer-summary punch, one verifier, one keypunch, one sorter, and one collator. Astronomers at Columbia had been experimenting with punch-card computing before the war. A multiplier, an appliance the size of a restaurant stove, could process calculations in large batches. Electrical probes found the holes in the cards, and operations could be configured by plugging groups of wires into a patchboard. Among the computation-minded at Los Alamos, the prospect of such machines caused excitement. Even before they arrived, one of the theorists, Stanley Frankel, set about devising improvements: for example, tripling the output by rearranging the plugs so that three sets of three- or four-digit numbers could be multiplied in a single pass. Having requisitioned the machines, the scientists now also requisitioned a maintenance man—an IBM employee who had been drafted into the army. They were gaining adroitness at military procurement. The crates arrived two days before the repairman; in those two days Feynman and his colleagues managed to get the machines unpacked and assembled, after a fashion, with the help of nothing but a set of wiring blueprints. [6] 

Exxon donated its IBM CPC to UT in 1958. The CDC Cyber was essentially an updated CDC 6600. By the eighties, both UT and Exxon were in the ERA tradition with Cray hardware.

Is this Seymour Cray during installation of the CDC 6600 in 1966? Genuine question, as it does seem at least possible.

Official event for the CDC 6600 in 1966. David Young is at the very top center, somewhat less visible because of lack of contrast against the background. Curiously, Al Matsen seems not to be present in this photo. Both Young and Matsen are variously described as founders and heads of the UT Computation Center.

[1] SOR Successive Over-Relaxation and the work of David Young at TRW were prominently applied to fluid and heat flows for atmospheric reentry vehicles. At the same time, ADI Alternate Direction Implicit was being applied to fluid and heat flows for the oil industry in Houston. This was all in the mid and late fifties, and among the most important early applications of computers in modeling and simulation, alongside Dantzig's work on Simplex at RAND.

[2] For more about Exxon Houston, A Personal Retrospection of Reservoir Simulation, Donald Peaceman 

[3] The photos above related to the CDC 6600 are thanks to the Briscoe Center 

[4] Here's an excellent new post about the IBM CPC from Ken Shirriff.

[5] Notes about the post 6600 CDC hardware in Austin. UTCC upgraded to systems like the Cyber 170/750 and 175, which maintained compatibility with the older 6000 series code but introduced crucial magnetic-core and semiconductor memory enhancements to support operational runs on much larger scales. The Cyber 170/750 was a critical high-performance resource managed by the UT Computation Center. While the university's primary, general-access academic mainframes such as the original CDC 6600 and early Cyber systems were famously housed in an underground facility beneath the East Mall on the main campus, the Cyber 170/750 was deployed differently. The university utilized facilities at the Balcones Research Center, now known as the Pickle Research Campus, to host high-performance systems like the Cyber 170/750. At this off-campus site, the 170/750 was dedicated to handling specialized research and mathematically intensive data analysis tasks. Researchers also utilized a CDC Cyber 175 during the late seventies and eighties. At the time, the Cyber 175 was one of Control Data Corporation’s top-tier, high-speed scalar processors, and it was used intensively for complex finite element and alternating-direction method simulations to solve the types of convection-diffusion problems that frequently appear in reservoir engineering and geology.

[6] James Gleick, Genius: The Life and Science of Richard Feynman (New York: Pantheon Books, 1992)

Oldest Computer On Campus (But Not The First)

The first computer on campus was the chemistry department’s 1955 IBM 650 Magnetic Drum Data Processing Machine, acquired using specific research grant funds secured by Al Matsen. The 650 was in Welch, the chemistry building, and was the first real computer on campus. It was a very early mass-produced computer, and Matsen and colleagues used it to compute the Quantum Chemistry Integrals and Tables, which provided the computational foundation for molecular orbital calculations across the field. Although the machine was purchased for his own work, Matsen established a precedent of shared usage at the university by allowing faculty members and researchers from other academic disciplines to utilize the computer. In one legendary exchange, the university president complained to Matsen that the "computer center" did not have long enough open hours and help was not always available. Matsen informed the president that UT actually had no official computer center and was merely using his grant-funded machine, but emphasized that the university desperately needed to build a centralized facility.

The oldest computer arrived second, in 1958, when Humble Oil in Houston (now Exxon) donated an IBM Card-Programmed Electronic Calculator to the university. Matsen was a consultant for Exxon Houston and New Jersey for over thirty-five years. In his Reminiscences he relates a story “Amusingly, I had been lecturing at an unnamed university on the unitary group formulation of the many-body theory. I apparently went way over the listeners' heads since the only question I got was, What possible use could you be to Exxon?” The CPC was a landmark gift and a direct result of Matsen’s extensive ties. To bypass bureaucratic paperwork, Matsen, his graduate students, and other faculty physically carried the heavy machine components into Welch and installed it themselves.

Exxon acquired that CPC in 1952, at the same time that Dantzig was implementing Simplex on a CPC at Rand in Santa Monica. The Exxon CPC was used to implement ground-breaking subsurface reservoir simulations and the beginnings of the ADI Alternating Direction Implicit techniques for Finite Difference Methods and Finite Element Methods. This work by Rachford, Peaceman, and Douglas put Exxon, Rice University, and Houston in the lead position for subsurface modeling and computational engineering and science. [1]

The 1952 IBM CPC at Humble / Exxon Production Research in Houston must be the one donated to Al Matsen in 1958 and carried into Welch by his grad students. 

Components of the IBM CPC. The iceboxes each contained sixteen ten-digit numbers in electromechanical counter wheels, like the odometer on a car. One could open the top and actually read out the numbers during debugging.

[1] A Personal Retrospection of Reservoir Simulation, Donald Peaceman

[2] An interesting comparison of ADI with contemporary Soviet methods, including a discussion of the CDC 6600 versus the BESM-6. https://vixra.org/pdf/2601.0025v1.pdf 

[3] The photo at the top of the post shows Henry Rachford using the Humble/Exxon CPC. From 1951 onwards, Rachford, Peaceman, and Jim Douglas, became the founders of reservoir modeling. They very soon became deeply associated with Rice University, a few miles from the Exxon offices, and this was the beginning of a long tradition connecting Exxon, Rice, and UT Austin.

[4] The iceboxes were designed to be fixed-point integer. Rachford and Peaceman rewired the machine for floating-point. Two floating-point operations per card.

Laser Ranging From The Chihuahuan Desert

Laser ranging played a core role in the birth of modern space geodesy, and during the seventies the McDonald Observatory in West Texas established a virtual hegemony over these types of observations, beginning with the transformation of the moon into a high-precision geodetic reference target. In space geodesy, the Earth is understood as a highly dynamic system rather than a rigid sphere. Calculating the highly precise round-trip travel time of a laser pulse to the moon or an artificial satellite requires an extraordinarily accurate mathematical model. To isolate the distance measurement, researchers must account for a vast array of Earth's rotational dynamics, including its overall rotation rate, precession, nutation, and polar motion. With the placement of the first laser retro-reflector arrays on the lunar surface, particularly during the Apollo program, researchers were able to revolutionize lunar distance measurement. The Apollo era retro-reflectors enabled centimeter-level measurements from McDonald, replacing radar uncertainties of 0.7 miles during the sixties, and early laser experiments from 1965 that achieved only 180 meter accuracy.

The moon was a difficult target for laser ranging because of both its distance and the relative speeds involved. The phenomenon of velocity aberration dictated that smaller retro-reflector cubes would provide higher intensity for a single ground-based receiver, so that arrays of smaller cubes were preferable. These physical constraints necessitated a permanent tracking station capable of capturing the few photons available after the enormous losses compared to retro-reflectors on near-Earth satellites. The small signal called for a large telescope, and this was one of the key motivations for NASA to fund construction of the new 107 inch telescope at McDonald in support of the Apollo program. The 107 inch telescope served as the world’s only routine lunar ranging facility for over fifteen years, achieving its first successful returns on August 19, 1969. 

During the seventies, satellite laser ranging at the McDonald Observatory developed in parallel with the lunar laser ranging program. While the 107 inch telescope is most famous for its post-Apollo lunar tracking, its observing time was also shared with artificial-satellite ranging. UT Austin's Center for Space Research utilized the SLR data collected to make pioneering advances in precision orbit determination and geophysical measurement. Key satellite missions and SLR milestones included the GEOS-3 Geodynamics Experimental Ocean Satellite which was used to study precision orbit determination and to develop regional gravity models. With LAGEOS in 1976, a high-density passive reflector in medium Earth orbit, CSR researchers were among the first to demonstrate that SLR could be used to measure tectonic plate motion. SLR tracking of LAGEOS also allowed CSR to provide definitive results for Earth's polar motion, calculate the value of Earth's mass, and make the first measurements of climate-induced time-variable gravity. And with the early Earth-observing satellite SeaSat in 1978, CSR led the precision orbit determination team, using tracking data to support radar altimetry processing for accurate ocean surface topography and gravity measurements. 

As the demand for artificial satellite tracking grew, the engineering and operational footprint at McDonald Observatory expanded. In the late seventies, UT Austin developed and tested the first Transportable Laser Ranging System at the McDonald site, validating coordinate determination algorithms and demonstrating the viability of mobile laser tracking. This effort evolved into the dedicated McDonald Laser Ranging Station, sited near the 107 inch. Furthermore, starting in 1979, various NASA-supplied Earth satellite ranging stations began operating continuously at the observatory.

The connection between the Transit satellite system and McDonald Observatory as a geodetic station was made in the computational modeling at UT’s CSR and ARL. These models combined Transit's radio-frequency Doppler tracking with the optical SLR networks anchored at McDonald Observatory, creating an early end-to-end tie between the celestial frame, terrestrial frame, and the Earth’s position and rotation. In some sense CSR was tying together McDonald and McMurdo via UT's TRANET Station 019. The Transit satellites continuously broadcasted two coherent carrier frequencies at 150 MHz and 400 MHz to allow ground receivers to eliminate first-order ionospheric refraction. The global tracking network supporting these geodetic investigations, TRANET, consisted of stations equipped with ultrastable rubidium or cesium frequency standards. UT Austin served as a vital institutional node linking this Doppler-based satellite network with high-precision laser ranging. ARL developed specialized mathematical packages to compute ionospheric and tropospheric refraction corrections for the TRANET network. To standardize geodetic data archiving and coordinate exchange, ARL developed the FICA Floating Integer Character ASCII format, which served as the standard for geodetic GPS and Transit data before the universal adoption of RINEX.

The direct operational connection between the Transit system and McDonald Observatory was forged through modeling and orbital synthesis at CSR. Precision orbit determination for major oceanographic altimetry missions required integrating data from the 48 station TRANET network with optical tracking data. CSR researchers merged the TRANET Doppler measurements with SLR data collected by McDonald and similar observatories. To resolve scale discrepancies, CSR executed precise coordinate ties between the TRANET receivers and the SLR network. This synthesis successfully tied Doppler-determined geocentric coordinates to the highly accurate SLR reference system, defined by targets such as LAGEOS, reducing radial orbit errors to approximately 20 cm. ARL and CSR also evaluated prototype GPS geodetic receivers by comparing GPS pseudorange and phase observations against legacy Transit integrated Doppler phase accumulations. These field tests demonstrated sub-meter baseline measurements, validating the transition from Transit-based datums to the modern WGS 84 World Geodetic System and the ITRF International Terrestrial Reference Frame, a framework to which McDonald Observatory continuously contributed.

As McDonald developed into a key geodetic reference site across the seventies, the nature of its West Texas geology was crucial. For one thing, it is onboard one of the major cratons that have played major roles across geologic deep time, though near a margin or boundary zone, rather than in an ultra-stable core region. In other words, it is in a fairly stable and ancient continental plate region. Likewise, it's sitting on deeply stable rock, at the opposite end of the spectrum from a site on top of subsurface reservoirs which can expand and contract. The Davis Mountains represent the largest contiguous volcanic remnant of the mid-Tertiary Trans-Pecos Magmatic Province, a massive alkalic volcanic field formed over forty million years of tectonic reorganization. Between 39 and 35 million years ago, a violent series of caldera collapses and explosive eruptions buried the region in vast sheets of ash-flow tuffs and flood rhyolites. The resulting stratigraphic architecture produced a landscape characterized by low-viscosity, high-temperature silicic magmas that cooled into exceptionally dense, structurally rigid igneous rocks. These precise geomechanical properties served as the foundational bedrock for the world-class optical and geodetic instrumentation at the McDonald Observatory.

The volcanic rocks supporting Mount Locke and Mount Fowlkes are highly fractured. Rainwater rapidly seeps deep into these fractures, accumulating as "rock moisture" within the unsaturated zone. During heavy monsoon seasons, the increased water mass within the fractured trachyte and tuff increases the local gravitational pull. This localized subsurface water storage mimics the gravimetric signature of actual tectonic crustal subsidence. The deep infiltration of water into the observatory's bedrock plays a critical role in the broader regional hydrogeology of Far West Texas. The precipitation that falls on the Davis Mountains percolates underground, migrating through highly porous volcanic pathways and underlying Cretaceous limestone layers to recharge artesian desert spring systems, most notably the San Solomon Springs in Balmorhea. While the continuous baseflow of these springs originates distally from the Salt Basin Bolsons to the west, the system is augmented multifold by local stormflow recharge moving through the subsurface from the Davis Mountains. The fractured volcanic layers, particularly the basal conglomerate of the Huelster Formation and associated vesicular lavas, act as rapid transport conduits, though some volcanic layers may also retain water and release it slowly over months, sustaining the springs long after precipitation events.

While the interior of the Davis Mountains is relatively stable, the region is bounded by major active fault zones associated with the Rio Grande Rift and the Texas Lineament, a major crustal boundary separating the stable North American craton from the active Chihuahuan borderlands. The persistent seismic risk of the subsurface was demonstrated by the 1931 Valentine Earthquake, the largest in Texas history, centered just 25 miles west-southwest of the observatory. Although the dense, consolidated volcanic sequences of Mount Locke and Mount Fowlkes act as a rigid, dampening block that mitigates catastrophic ground failure, the continuous, low-frequency seismic stress of the basin-and-range faults must be continuously accounted for in the observatory's geodetic and astronomical measurements. McDonald Observatory’s enduring scientific legacy is inextricably linked to its geology and subsurface environment. In recognition of this intrinsic connection, its mission has evolved to include geological, hydrological, and ecological research across its 650 acres of Chihuahuan Desert terrain. [1]

The telescope site’s geomechanical stability was paramount. High-precision astronomical instrumentation requires structural foundations entirely decoupled from wind shear, thermal expansion, and human-induced vibrations. The Mount Locke Formation, restricted to a 93 meter thick flow of coarse, highly porphyritic metaluminous trachyte, provided an exceptionally dense and unyielding bedrock. By anchoring the 107 inch telescope’s massive 160 ton structure directly into this rigid volcanic substrate, engineers achieved the absolute dimensional stability necessary to isolate the optical path from environmental noise. The rigid bedrock of the Mount Locke Formation provided the exceptional load-bearing strength necessary for the telescope's foundations and allowed for the site’s calibration to the International Terrestrial Reference Frame and the International Celestial Reference Frame with zero margin for error. The seventies data boom allowed for the first empirical measurements of Earth Orientation Parameters and the determination that the North American Plate drifts southwestward across the mantle.

The data boom resulting from the network of lunar reflectors and the unyielding trachyte foundation of Mount Locke allowed McDonald’s LLR measurements to serve as a highly stable anchor for the ITRF, ICRF, and IERS. Through continuous tracking, researchers successfully utilized the LLR data to empirically measure Earth Orientation Parameters, including polar motion, nutation, and variations in the length of day. By definitively linking terrestrial coordinates to the Earth's center of mass, the observatory tracked the continuous drift of the North American Plate across the mantle, validating the mechanics of plate tectonics and cementing the site's legacy in the geosciences. McDonald Observatory and the Center for Space Research were the first laser ranging group to provide operational observations of these Earth Orientation Parameters, notably polar motion and length of day. Through the accumulation of SLR and LLR data, researchers have been able to isolate variations in the Earth's principal figure axis and key geopotential coefficients across timescales ranging from sub-daily to decadal.

Along with SLR, researchers tracked the precise distances between different global ground stations. Over time, these inter-station baseline rates reveal the slow, continuous drift of the Earth's tectonic plates with a precision of better than one centimeter. McDonald Observatory played a critical role in this endeavor and accumulated a continuous legacy of providing reference positions that accurately tracked the motion of the North American Plate from the seventies onwards. These measurements are a cornerstone of the ITRF for tracking the dynamic movement of the Earth's crust.

Understanding continental motion is an absolute prerequisite for accurately measuring global sea levels. CSR led the Precision Orbit Determination efforts for satellites monitoring variations in sea surface height using radar altimeters such as the TOPEX/Poseidon and Jason series missions. These altimeters measured the distance between the satellite and the ocean surface. To determine the actual height of the sea, CSR tracked the satellite's exact altitude and position in space relative to the center of the Earth. This required tracking the satellite from ground stations. Because these ground stations are constantly moving due to tectonic drift, their exact coordinates must be continuously updated using the ITRF. If continental motion were not accounted for, the changing position of the ground stations would introduce significant errors into the satellite's orbit calculations, which would in turn corrupt the sea level measurements. While altimeter missions track the total height and volume of the continental and ocean surfaces, CSR has also led efforts to directly track subsurface and oceanic mass variations.

Observations from McDonald Observatory and the global geodetic network reveal that Earth's rotation is altered by three primary mechanisms: external gravitational torques, internal mass redistribution, and the transfer of angular momentum between the solid Earth and its fluid layers. The gravitational attraction of the Sun and Moon generate oceanic and solid-body tides, and the friction from these tides causes the Earth's rotation rate to slowly decrease. To conserve the total angular momentum of the Earth-Moon system, this deceleration forces the Moon to spiral away from the Earth at a rate of approximately 3.8 centimeters per year.

As the Earth displaces its mass, its moment of inertia changes, subsequently altering its spin rate and the position of its poles. Variations in the Earth's length of day on decadal scales are heavily influenced by the internal structure of the planet. Gravitational and hydrodynamic coupling between the fluid outer core, the solid inner core, and the mantle exerts torques at the boundaries of these layers, leading to persistent oscillations in Earth's rotation rate. The precision of LLR is so extraordinary that even biospheric cycles are detectable. As tree sap rises or falls seasonally in the heavily forested Northern Hemisphere, the corresponding change in Earth's moment of inertia minutely alters the planet's rotation rate, a signature captured in the ranging data. A certain young astronomy undergrad was in the audience when Pete Shelus described this research in 1987 during one of Harlan Smith's weekly astronomy seminars. Tying tree sap to continental plates, subsurface reservoirs, satellites, the moon, and the stars was an extremely effective lecture, needless to say.

[1] Chihuahuan Desert Nature Center in Fort Davis.

McMurdo Sound Antarctica And Austin

UT Austin operated the Transit satellite system TRANET Station 019 at McMurdo Sound Antarctica for much of the seventies. This was the critical polar node for the Transit system, the predecessor to modern GPS. Because Transit satellites were in polar orbits, high-latitude tracking data from McMurdo was essential for accurately determining the satellites' inclination, nodal progression, and overall global orbital models. A hallmark of the McMurdo station was that it was staffed and operated by two-person teams consisting of a grad student and an undergrad, usually from electrical engineering. These students lived in extreme cold, maintained complex Doppler receivers, managed HF radio communication links, and ensured continuous data collection. [1] 

Gear inside TRANET Station 019 operated by UT Austin at McMurdo for much of the 1970s.

The Transit system was driven by the US Navy’s need for high-precision navigational updates for its submarine fleet. To ensure the accuracy of inertial guidance systems onboard submarines, the Transit satellite system was deployed, utilizing Doppler frequency measurements to provide all-weather positioning. The first Transit satellite was launched into orbit on 13 April 1960. Among other information, it provided confirmation of the Earth's asymmetrical shape and highlighted the inadequacies of contemporary knowledge of the Earth's gravitational field for the prediction of satellite orbits and other important near-Earth ballistic trajectories. Such prediction was essential for Transit's navigational role, in which receivers would determine their own position by monitoring the Doppler shift from a satellite of known orbit.

Already in May 1961 it was noted that “Meeting the ultimate program goals for Transit thus requires considerable improvement in the present knowledge of these factors (roughly the shape and mass distribution of the earth). This is the primary remaining development challenge of the Transit program.” Navigators have always relied on the stars for the purposes of terrestrial positioning. Artificial satellites revolutionized this paradigm by providing radio signals, available day and night and regardless of weather conditions. However, this shift introduced a significant challenge. Unlike the natural stars, these artificial stars are moving rapidly and are subject to complex orbital perturbations. 

A satellite is essentially a body in free fall influenced by forces such as gravity anomalies, atmospheric drag, and solar radiation pressure. Variations in the Earth’s gravitational field mean that the satellite’s trajectory is a direct reflection of the planet's irregular mass distribution. The concept of using satellites as test particles for probing the Earth’s gravitational field quickly developed and the Center for Space Research at UT Austin was on the frontier of this research. The convergence of astrodynamics and geophysics established a computational grand challenge, where the requirements of gravity modeling and subsurface modeling drove a new scale of computing problems. Through the lens of computational geodesy, the satellite serves as a remote sensor for the Earth's interior, linking orbital mechanics to subsurface exploration and the management of global resources.

Transit system accuracy. UT Austin played important roles in these results. Note that the time span fits exactly with our 1958 to 1982 focus.

[1] Tracking operations at McMurdo (initially designated as Station 019) began on February 5, 1965, within a National Science Foundation building, and were originally managed by New Mexico State University's Physical Science Laboratory (PSL). After PSL withdrew in December 1966 due to administrative issues, the University of Texas at Austin's Applied Research Laboratories (ARL:UT) officially reopened the station on October 10, 1968. ARL:UT maintained continuous management of the site for a quarter-century.

Welch Hall 1958, Benedict Hall 1960

Two threads in the story of early computing at UT Austin are of special interest because of their links with the subsurface and outer space. There’s Exxon Houston’s 1958 donation of an IBM CPC to the chemistry department in Welch Hall, representing the pragmatism of the oil industry and its ties with Al Matsen. And there’s the 1960 purchase of a CDC 1604 for the math department in Benedict Hall on the South Mall, representing the systems thinking of the aerospace industry and its ties with David Young. Both Matsen and Young are variously described as founders and first directors of the UT Computation Center from 1958 up through roughly 1970, and it seems likely that they collaborated in UTCC’s early days and blended together the influences of their respective industries and technical fields. A curious fact is that when the CDC 6600 arrived in its underground home in 1966, it was located roughly midway between Welch Hall to the north and Benedict Hall to the south. The 1966 Computation Center sub-terrace building and million dollar 6600 were a landmark for the end of the early days, symbolizing the onset of computing maturity, and how computers and software had grown larger than particular industries and departments.

One of the interesting aspects of this very early period is the clear differentiation between IBM and CDC hardware. There’s no question that at the time Exxon and the oil industry in Houston were using IBM hardware and that this heavily influenced the chemistry department at UT, which also ended up having two IBM machines. Meanwhile, David Young was associated with TRW Los Angeles, which was a UNIVAC shop. CDC was a spinoff from UNIVAC, and when Young arrived at UT, CDC hardware followed soon after. There was clearly an important contrast between the oil and aerospace industries at work here, and between the nature of IBM and CDC and their customers.

The chemistry department acquired an IBM 650 Magnetic Drum Data Processing Machine in 1955 using specific research grant funds secured by Al Matsen [1]. The 650 was almost certainly in Welch (always and for all time The Chemistry Building) and the first real computer on campus. Though note that there's evidence of IBM hardware up at DRL/ARL [4]. The 650 was a very early mass-produced computer, and at least somewhat comparable to the LGP-30 of The Story of Mel fame [2]. Matsen and colleagues used the 650 to compute the seminal Quantum Chemistry Integrals and Tables, which provided the computational foundation for molecular orbital calculations across the field. Although the machine was purchased for his own work, Matsen established a precedent of shared usage at the university by allowing faculty members and researchers from other academic disciplines to utilize the computer. In one legendary exchange, the university president complained to Matsen that the "computer center" did not have long enough open hours and help was not always available. Matsen informed the president that UT actually had no official computer center and was merely using his grant-funded machine, but emphasized that the university desperately needed to build a centralized facility.

A second transformative event occurred in 1958 when Humble Oil in Houston (now Exxon) donated an IBM Card-Programmed Electronic Calculator to the university. Matsen was a consultant for Exxon Houston and New Jersey for over thirty-five years. In his Reminiscences he relates a story “Amusingly, I had been lecturing at an unnamed university on the unitary group formulation of the many-body theory. I apparently went way over the listeners' heads since the only question I got was, What possible use could you be to Exxon?” The CPC was a landmark gift and a direct result of Matsen’s extensive ties. To bypass bureaucratic paperwork, Matsen, his graduate students, and other faculty physically carried the heavy machine components into Welch and installed it themselves.

The IBM CPC was not a computer in the modern sense, and in fact was a major step backwards from the IBM 650, but it was useful in the Welch Hall of 1958. The CPC will always be legendary as the machine that George Dantzig implemented the Simplex method on at RAND in 1952. It was a hybrid electro-mechanical system. It consisted of an IBM 402 or 417 Accounting Machine (the printer/controller) connected to an IBM 604 Electronic Calculating Punch (the arithmetic unit) and an electromechanical storage unit. It functioned as a decentralized network of specialized units rather than a unified stored-program architecture and was fundamentally incapable of holding both the data and the instructions required for Simplex. Consequently, the program existed not as a digital state within the machine, but as a physical sequence of punched cards. This required the operator to function as a manual control unit, physically re-entering card decks to execute the iterative loops essential for finding an optimal solution within a linear system. 

IBM CPC Card-Programmed Electronic Calculator 1949 

In 1958 David Young moved to UT from TRW and the Los Angeles aerospace environment. He was tasked with founding the Computation Center and serving as its first director. When Young arrived, the Computation Center was "almost non-existent," consisting of Young, his colleague Robert Gregory, and a secretary sharing a single office next to the IBM 650. Within 18 months, Young leveraged his formidable reputation to secure a $400,000 NSF grant for the CDC 1604, and in 1966, he secured the first $1,000,000 NSF grant towards the purchase of the CDC 6600 supercomputer. Emphasizing that this was a personal triumph for Young rather than a political favor, Gregory stated: "I could not have done this, you could not have done this, but David Young did it." [3]

I joined David at UT six months after he arrived there in Fall 1958. At that time the Computation Center was almost non-existent. They had acquired an IBM 650 and David, I, and a secretary shared a single office next to the computer room. Within 18 months David, on the basis of his reputation alone, got the first $400,000 grant from NSF towards the purchase of a CDC 1604, the first transistorized computer. It beat the IBM 7090 into production by one month. Thus, UT went from nothing to a first class Computation Center in one big jump. Then in 1966, after acquiring a building to house the CDC 1604, and after it became saturated with users, David (again on his reputation alone) got the first $1,000,000 grant from NSF towards the purchase of a CDC 6600. This, again, put UT at the front of the line as far as University Computing Centers go. UT was the first university to have a 6600 and this put them ahead of Berkeley, Stanford, MIT, Harvard and all the rest.

Benedict Hall, the old home of the math department and probably of the Numerical Computation Center and the CDC 1604 in 1960. Pearce Hall (the old Law building, replaced by GSB around 1975) was to its east, which may help explain why it had a remote job entry point in the early seventies. 

A nice view of Welch for those of us who spent years working in ESB and saw the same daily.

[1] https://utphysicshistory.net/FrederickAMatsen.html 

[2] The Royal McBee Librascope LGP-30 and the IBM 650 represent two contrasting architectural philosophies in early 1950s computing, both leveraging magnetic-drum memory but targeting distinct operational paradigms. The IBM 650 emerged as the world’s first mass-produced mainframe, utilizing a power-intensive architecture of roughly 2,000 vacuum tubes and employing a unique "one-plus-one" addressing scheme to optimize instruction timing on a high-speed drum. In stark contrast, the LGP-30 pioneered the concept of the desk-sized minicomputer by prioritizing hardware minimalism; it utilized only 113 vacuum tubes, required no specialized cooling, and relied on low-cost paper tape input. While the IBM 650 dominated high-throughput corporate and institutional markets through punched-card workflows and faster drum rotation speeds, the LGP-30 democratized decentralized scientific computing by offering an affordable, single-user system that could operate seamlessly within a standard office environment. The IBM 650 was the world's first mass-produced computer and a massive financial success, renting or selling for upwards of $100,000+. The LGP-30 was aimed at a cheaper, scientific market segment, retailing around $40,000.

[3] Robert Todd Gregory, testimonial letter, August 24, 1982, quoted in David R. Kincaid, Legacy of a Giant: The Career of David M. Young (Austin: Archives of American Mathematics, Center for American History, The University of Texas at Austin).

[4] After the end of hostilities, the name was changed to Military Physics Research Laboratory and the group moved to the site of the Wartime Magnesium Plant. later to be named the Off-Campus Research Center, a little later the Balcones Research Center (a name suggested by Jim Han. the first Chancellor of UT), and more recently the J. J. Pickle Research Campus. MPRL continued to work with the Texas Tester and exterior ballistics for some years. It was the first group in Austin to use large mainframe IBM computers. ln time, the program decreased in size and in 1964, at their request, they merged with DRL. https://utphysicshistory.net/ARLOriginsMcKinney.html