EVA presented us with surprises. From the experience of Gemini 4 in June 1965, EVA was not seen as exceptionally difficult. On that flight, Ed White egressed the spacecraft with a tether and an umbilical for all necessary services. He floated outside and moved around with a hand held thruster device, using pressurized nitrogen. It seemed relatively easy. However, one year later, the Gemini 9 EVA was an eye-opener in terms of how quickly events deteriorated to a life threatening condition facing Gene Cernan. The next EVA on Gemini 10 was relatively easy by comparison and then the Gemini 11 EVA was once again a very demanding chore for Dick Gordon. By Gemini 12, the provisioning of restraints for hands, feet, and body and water-tank training allowed Gemini to finish with a much better understanding of the necessary techniques for weightless EVAs.
The Flight Dynamics Team Tackles Gemini
The task confronting the Flight Dynamics Team as Gemini approached was immense. The question was how to use these flight vehicles to achieve orbit, rendezvous, docking, docked maneuvers, reentry, and accurate landings. These vehicles were a significant step up in technology and capability over the Mercury ship. The Trench had to understand the trajectory and orbital mechanics to master the necessary capabilities. They had to determine how to use the guidance and propulsion capabilities within the flight elements. They had to figure how to turn all that understanding into an MCC capability that can direct and support these phases in real time. They also had to smoothly fit their discipline into the operation of the overall MCC team and the flight crews. Starting in early 1963, before the last Mercury flight flew, we began to grapple with these subjects. As we did, the MCC Flight Dynamics team grew to include a third position, the guidance officer.
Expanding the Launch Phase Capabilities
The Titan launch vehicle had some major new capabilities compared to the Atlas used for Mercury. There was the capability to switchover to backup guidance from the Gemini spacecraft and/or hydraulics within the Titan. It would be reasonable to ask how we trained these young folks to perform this work. Perhaps the best way to explain is by example. Charley Parker came to the group from a long line of Texans in June of 1963. He was obviously observant. When he asked, “Well, Glynn how much travel should I expect?” My reply was, “Not very much.” My reply was based on the fact that things had changed since Mercury. The MCC was now in Houston and the Goddard computer complex was replaced by real time computing complex in the MCC. Both of the facilities, MCC and the RTCC, were right here at home in Houston. However, Charley was looking at my briefcase that had the remains of three years of airline baggage tickets on it. As it turned out, travel did not turn out to be as big a burden for us as it was in Mercury.
When Charley arrived, we were powering up for Gemini that brought a number of new features to manage. Gemini had a digital computer – new to our spacecraft repertoire – and with a launch vehicle guidance capability. A redundant set of hydraulics within the Titan launch vehicle and the ability to actually guide the launch vehicle through the launch phase added to our complexity. We also had to plan for rendezvous, docking, docked propulsion burns and reentry maneuvers. We had already decided to add a guidance officer position to the other two positions.
Without knowing the strength of Charley’s capability, we had the guidance officer role as a blank sheet, and assigned the whole package to Charley. For the first task of monitoring the Titan launch vehicle for either guidance or hydraulics switchover, we knew that we needed another console. For it, we envisioned a bank of strip charts to evaluate the guidance signals and the hydraulics response of the engine actuators for each of two first stage engines. That was about as far as Cliff and I got in definition and turned it over to Charley.
Charley accepted that assignment with little or no comment and moved right into the definition of the specifics for the console. He always seemed clear-headed and sure of what he was doing – always answering questions intelligently. But, it was when he sat down at the console for his first simulation that he really impressed all of us. Charley was slender of build and he had the habit of sitting with the right knee over the left one and snaking his right leg around the left leg, as if it were made out of rubber. Cigarette in hand, he was ready to go.
And he seemed to read the mind of that Titan launch vehicle. Cliff accused him of “doing a mind-meld with the Titan.” He read the vital signs of the rocket and could diagnose any guidance or control problems in very short order. After our first day of simulations, Cliff and I looked at each other, and I observed, “Well, it looks like we got ourselves a real guidance officer.” Charley was trained by taking on a big job and mastering it himself. Somewhere in these early days, Cliff tagged Charley as “the fox” and it is still a favorite handle, even today.
Once the early Gemini flights were accomplished, Charley turned to understanding how to use the on-board Gemini computer to control the attitude and propulsion capabilities. These capabilities were targeted to accomplish the maneuvers calculated by FIDO, Retro or in some cases by the onboard computer. So, in answer to the valid question about how we trained him, the answer is: “We did not train him, he invented the position, prepared and trained himself.”
We were always learning something from Chris that we could apply to our world. By example, he taught us, “Give them a big job and any help they ask for – let them do it – test them and satisfy yourself about their abilities – and then trust them to perform.” Sounds simple, and this story repeated itself many times as young men stepped up to big challenges. There were things like, how do we manage launch windows, rendezvous maneuvers, docking, maneuvers mated with the Agena target vehicle, and reentry for landing with the Gemini ship. And in Apollo, how did we use the new Saturn V, the command service module, the Lunar module, their prime and backup computers, targeting for the injection maneuver to the moon, midcourse maneuvers, the placing of the vehicle into lunar orbit, the lunar landing challenge, lunar module ascent and rendezvous with the command ship, return to earth and eventually reentry and recovery. While all of the nominal missions were being examined, understood, and mastered, it was also necessary to maintain a return to earth and abort capabilities throughout the mission phases, even with various degrees of degraded onboard systems.
The experience of seeing Charley blossom into a competent, trusted operator was repeated many times as our young men grappled with the unknowns of Gemini and Apollo.
Moving to Rendezvous
John Mayer’s organization had developed its usual group of technical wizards for many of these subjects. People like Ed Lineberry, Ken Young, Bob Becker and Bob Regelbrugge stand out as aces on the rendezvous subject. Several people in the Gemini program office had also begun to explore this subject and were making progress. Jim Chamberlain from Avro was the program manager for Gemini, but, in our work, we dealt with Dick Carley, also of Avro, and Jim Rose from Langley. Both of these men worked in the Gemini program office (GPO) and had started on their own understanding of rendezvous.
We soon realized that the problem could best be understood in three separate segments. First, the two vehicles have to be in the same orbital plane. Think of the orbital plane as a flat surface and round like a plate. The spacecraft traverses the outer edge of the plate, but the plane is fixed in inertial space relative to the stars. Think of a plate inclined to the equator at about thirty degrees but the plane or plate stays fixed and the earth rotates underneath the plane. The spacecraft flies around the edge of the plate to traverse one orbit in about ninety minutes. If you plotted the geographical position of the spacecraft over time, it would look like a sine wave passing over the earth, but displaced to the West each time around by the distance the earth has turned in the ninety minutes of orbital traverse. Assume the launches are due east from the pads in Florida as that is the most fuel-efficient direction. Then the maximum latitude above and below the equator of the sine wave is essentially the latitude of the launch site.
In one orbit or ninety minutes after launch of the target
vehicle, a second spacecraft launch due east will come very close to being in the same plane as the original target spacecraft. The sine waves of each spacecraft would overlay each other. Because they are very close to the same plane, it takes only a relatively small amount of launch vehicle fuel to steer the second vehicle into the same plane as the target. Usually, because of inaccuracies and other difficulties, there is some small plane change correction yet to be made by either one of the spacecraft once in orbit to make the vehicles co-planar. And this became the approach for the first segment of the Gemini rendezvous problem. Actually, like all things in our business, there are often second or third order effects and there is one here which makes it a little more complicated than I just described. The earth’s oblateness and the initial differences in altitudes between the target vehicle and the chasing spacecraft create small perturbations, resulting in differential nodal regression, to the inertial planes such that a correction must be made to the yaw steering of the launch vehicle to match the planes at the planned intercept rather than the initial insertion into orbit.
The second segment of the rendezvous is called phasing. At orbital insertion, the vehicles are now in about the same plane, but displaced from one another on the edge of the plate. Typically this might have the chase vehicle trailing the target vehicle by five hundred to one thousand miles. There are many sequences of maneuvers that can bring the two ships together and we examined many of them. The chase vehicle with lower altitudes than the target’s is traveling faster and therefore catching up. The rate of catch-up can be controlled by altitude adjustments during this phasing period.
But, we were missing a part of the puzzle without knowing “the best way to bring the ships finally together.” This was resolved when Buzz Aldrin arrived at JSC. He had just completed his PhD, and his dissertation treated how best to approach a target vehicle in order to facilitate a consistent approach for a crewmember to monitor and provide visible cues as to how the closing part of the approach is going. To locate the final braking geometry, Buzz selected an approach in darkness, from below the target and slightly in front of it. This creates a line of sight to the target, which should be inertially fixed relative to the star field behind the target. Any relative motion of the target, against the star field indicates an error to be zeroed out by the approaching ship. The scale here is such that the distance to the target would be about ten miles when this condition applies. There is also a fore and aft correction that needs to be calculated or measured by radar. This amounts to a braking of about 30-40 feet per second as seen by the crew in the chase vehicle. Zeroing out this closing velocity occurs as the chase vehicle gets within a few miles or closer of the target vehicle. All nulling of relative motion is complete when the chase vehicle is within about the last hundred feet of the target. Manual crew control is then based on visual cues and is called station-keeping. The lighting is selected so that both vehicles are now out in the daylight for the station-keeping phase. The contribution of Buzz’s work coupled with a clear understanding of the orbital mechanics developed by Ed Lineberry and his team completed the picture.
This approach with the third segment provides the end point for the phasing maneuvers in the second segment. Buzz recommended that the chase vehicle fly in a lower co-elliptic orbit than the target vehicle with an altitude differential of about ten to fifteen miles. The crew can track or see the target vehicle from this closing position and at a known elevation angle to the target, perform a small propulsion maneuver of about thirty to forty fps to create an intercept path that will meet the conditions described in segment three. So the early maneuvers are calculated to set up this ultimate braking geometry. This all seems so apparent now, but there were a lot of possibilities and mysteries to fathom before we got there.
And this technique continued to evolve. For Apollo, some plans were for a fairly rapid rendezvous sequence, completing on the first orbit. It continues to be modified today because of the scale of the Shuttle and Space Station vehicles. It is less of a fighter plane intercept and more of a berthing of a large ship to a larger ship. So, in modern rendezvous sequence, the final approach is set up to approach the space station from below and by traveling up the earth radius vector (called r-bar). The orbital mechanics are such that the shuttle is beginning to slow down relative to the ISS and falls to a condition of zero relative motion at the ISS, at which point the Shuttle would fall back down the earth radius vector away from the target if no further propulsive maneuver was performed. To match the ISS conditions, the Shuttle adds energy (versus braking) to achieve identical orbital conditions. This acceleration maneuver also directs the plume from the thrusters to the rear of the shuttle and away from the Space Station with its many appendages. This is a more benign approach scheme for avoiding any contamination damage or disruption from the thruster plumes on the ISS target vehicle.
This all came about four decades later as a more suitable variant for the final approach to the target. And, as in Gemini, the desired final conditions for intercept determine the intervening sequence of phasing maneuvers, although the time between launch and actual rendezvous is measured in days rather than a few hours in order to allow the crew to adjust to zero-G. We conducted a terminal phase similar to the Apollo scheme on Gemini 11 with the first rendezvous and experimented with a variation to slow down the relative speeds on a re-rendezvous called the “standoff” technique. These exercises were very helpful in tailoring the sequence to new conditions and constraints in the future.
And Using a Guided Reentry to Landing Point
Gemini did have a small Lift/Drag ratio (L/D), established by an offset of the center of gravity. This small amount of lift was then modulated by rolling the vehicle during reentry to provide the correct amount of lift in plane to reach the target. Once our team got comfortable with this guidance scheme and the control system to achieve it, they added some simulator time to see it all in action. This capability quickly became a known and comfortable staple for the Retros and Guidos.
The first two Gemini flights were unmanned. The objectives of GT-1 on April 8, 1964, were to validate loads on a spacecraft shell and the combined structure of the spacecraft and launch vehicle. The vehicle was guided into a one hundred by two hundred mile orbit with an early planned reentry, which occurred on sixty-fourth orbit. During its time on the pad, GT-2 was subject to some lighting strikes in the area that caused a delay. Then, there were two delays due to the threats of two hurricanes, Cleo and then Dora, resulting in a destack of the vehicle. Back on the pad on December ninth, there was a pad shutdown at T+ one second. After resolving the problem, GT-2 finally launched on a short suborbital flight on January 19, 1965 with a duration of only nineteen minutes. These two flights were monitored by Cliff and me, John Llewellyn and Jerry Bostick as Retros and the “fox,” Charley Parker.
As we prepared for GT-3 that flew on March 22, 1965, the first manned Gemini was crewed by Gus Grissom and John Young. Cliff, John and Charley were the flight dynamics operators. It had been decided to “flight-follow” the MCC at the Cape with the new MCC in Houston. In my new role as a Flight Director in training, I and Jerry Bostick as FIDO and Retro, and Arnie Aldrich as the Gemini systems expert were in the Houston MCC as backup. For the next flight GT-4, we reversed locations and were on backup duty at the Cape. We enjoyed making an occasional offer to take over for any problems at the other MCC.
The flight was such a technical success that the coverage degenerated into the “ham sandwich” crisis as John Young had smuggled an unauthorized sandwich in his suit pocket. Much ado about not much, except that the configuration system that controlled what was in the spacecraft was strengthened, but even then, not enough. This subject came back to bite NASA much later during the Apollo XV stamp cover fiasco, which was an acknowledged violation of common sense standards if not an actual legal transgression. At the time of Apollo XV, Chris Kraft was Center Director at JSC and spent the best part of a year dealing with the fallout from that issue.
Back to GT-3, we were all especially pleased that this flight went so well after the loss of the MR-4 spacecraft when Gus almost drowned. Most of us were very supportive and proud of Gus and happy in this success for him. As a measure of NASA and Deke Slayton’s confidence in him, Gus flew the first Gemini and was scheduled to fly the first Apollo.
Right after GT-3, Cliff informed me about the possibility of a space walk. The EVA activity was being considered for GT-4 but was still under wraps pending completion of certain certification tests. This was a big step for all of us even thought the Flight dynamics team was mostly an observer of EVAs. Mercury did not have an EVA capability and it was believed that we had to exercise EVA in Gemini before we got to the moon, where so much depended on a successful walk on the moon. The EVA was approved for flight only ten days before the mission, when the necessary tests on the EVA equipment were successfully completed. The four-day mission was also a big step in flight duration from Mercury (one and a half days on MA-9) and three orbits on GT-3. GT-4 launched on June 3, 1965, with Jim McDivitt and Ed White as the crew. The orbit was nominal and, after separation, Jim attempted to station keep with the Titan second stage. As he came out of the night pass, he recommended the cessation of the station keeping exercise because it was causing excessive fuel usage. Chris at MCC agreed. This was an early indication that orbital mechanics played a big role in station keeping if the chase vehicle was very far away from the target, more than several hundreds of feet.
Highways Into Space: A first-hand account of the beginnings of the human space program Page 11