The vehicles were on autopilot, testing the “new and improved” automated docking and rendezvous system that NASA had been working on since the space-shuttle days. Gone was the day of the astronaut “rocket jockey” controlling every spacecraft movement with a throttle and stick. Of course, the “rocket jockeys” themselves didn’t agree with the move, and the general public typically liked the notion of the superheroic space-pilot astronauts. However, the guys with the software had won the technical arguments and determined that having the pilot “out of the loop” was by far a safer approach. Or so their calculations indicated.
The massive aluminum-and-composite EDS had been launched just hours previously by the mighty Ares V rocket. Measuring over ninety feet long and containing enough fuel to carry four people, a lunar lander, and all the supplies needed for a week’s stay on the Moon, the EDS appeared to be dead, floating effortlessly two hundred and ten kilometers above the Earth. The over-one-hundred-forty-ton behemoth moved around the Earth at nearly seventeen thousand miles per hour. The Orion was closing in on it, moving with about the same speed, adding only enough velocity to catch up with the EDS in order for the two spacecraft to dock.
And the distance was closing—rapidly. Too rapidly. The first warning bell sounded in mission control at 2:58 p.m., local time. Nobody was particularly alarmed by the bell.
“Bill, we’ve got an anomaly with the Orion’s close rate on the EDS,” Marianne Thomas said calmly from her console near the back right corner of Constellation Mission Control at the Johnson Space Center in Houston. The anomaly had been simulated in training, but she hadn’t expected it to happen during the test. But that was why they trained. “Orion’s laser ranging indicates they’re closing faster than programmed and faster than the onboard computer says it’s going.” There was only objectivity in her voice and not a trace of the anxiety that she was starting to experience in her gut.
“Roger that,” Mission Commander and Blue Team’s Flight Controller Bill Stetson responded automatically—again, thanks to the training. “Do we have confirmation of the closure rate from GPS?”
The onboard differential GPS system was supposed to be able to resolve the relative positions of the two spacecraft and calculate relative motion based on successive position measurements. Stetson was set to command the next flight—the one that would actually carry people to the Moon—and was in charge of this portion of the final flight test. Up to this point, everything had gone fairly smoothly, and this was just fine with Bill Stetson.
“Bill…” Thomas hesitated, a pause that was noticed by all in the room, including Stetson. “Looks like we have no data from GPS.” Her eyes were scanning the display in front of her, desperately trying to find out why there was no data and simultaneously not believing that she would be the one with the flight anomaly. She pursed her lips and repeated her last words for clarity. “We have no data from GPS. I’m trying to find out why.”
Throughout mission control, those on console were verifying and reverifying the data scrolling across their screens, hoping to have some bit of information to provide that would help all in the room understand the situation. Only a minute had passed since Thomas’ announcement, but to those responsible for the success of the test flight, it seemed like an eternity. Finally, the technician monitoring the Orion’s propulsion system saw something and spoke up.
“Orion propellant is showing lower than predicted,” the console tech said. He then hesitated a moment before continuing. “It’s not enough to trigger an alert, but it is lower than it should be.” The technician, known to his comrades and friends as “Stubborn Stu” due to his alleged inflexibility in virtually all things, might also have been called “Meticulous Stu” for his attention to detail. Whatever the nickname might have been, when he spoke, his colleagues always listened.
“Roger that, Stu.” Bill thought about the data briefly. He knew that less propellant in the tank could mean that more propellant was being used than predicted. And that could account for the Orion moving too fast. If the engines were burning for even a fraction of a second too long, then they would consume more propellant. And if they were consuming too much propellant, then the spacecraft was accelerating faster than expected. That wouldn’t be good.
Of course, there could also be other explanations. In this case, the specific reason why the propellant was low was not of immediate concern. But Bill was certain that the fact the propellant level was too low was all the confirmation he needed to conclude what his next step ought to be.
“Marianne, what rate does laser tell us we’re dealing with here?”
“Hold on.” Thomas tapped some keys on her console without hesitation and then replied. “According to laser, we now have a delta-vee excess of slightly over five meters per second and accelerating. No confirmation from GPS.”
“Sheesh,” Bill muttered to himself. Five meters per second was just a little more than fifteen feet per second. All in the room understood the implications. The Orion and EDS were designed to soft dock with one another. In other words, their rate of closure would gradually decrease to only a fraction of a meter per second when they finally made contact. If they were to collide moving tens of feet per second, not only would the docking maneuver fail but it might result in a crash, with the loss of both the Orion and the EDS being a real possibility. And that was simply not acceptable to NASA, mission control, or Bill Stetson.
“Abort options?” Stetson hated to ask the question, but mission procedures gave him no option. A safe abort and potential retry in a few orbits was simply the right course of action to consider. Lives were not at stake, but billions of dollars and months, perhaps years, of schedule were. And Bill Stetson didn’t want a test-flight failure to set back the date for his flight to the Moon. Who knew how the press would handle another NASA failure? The evening news report of a disaster in space might be enough to halt the Moon mission altogether.
The technician who reported the excess propellant usage had on his screen an algorithm that constantly told him what propellant would be required to perform an abort and an estimate of the trajectory and time required to recover from the abort so that another attempt could be made. Bill knew that the console tech was ready for his question.
“Well, Bill,” Stubborn Stu started, “if laser ranging data is correct and we have to perform a burn to take out that velocity and then fly around a few orbits to try again, we will be at the minimum propellant margin for the rendezvous. But it still won’t meet mission-success criteria. The EDS will have been on-station too long. Propellant boil-off will exceed TLI commit.”
Though never actually uttered, virtually everyone in the room heard the expletive that Stetson thought to himself. Bill pulled his headset free for a second and adjusted his thinning hair while making a motorboat sound with his lips. Not being able to do a TLI, or Trans-Lunar Injection, burn of the rocket engines would mean not going to the Moon. The longer the EDS had to wait, the more propellant would evaporate—reducing the total burn-time possible for the engine. They had to fire before too much had boiled off.
The EDS was powered by one of the most energetic rocket fuels known—liquid hydrogen. When combined with an oxidizer, in this case the ultimate oxidizer, liquid oxygen, the combustion produced the rocket thrust that would propel the EDS toward the Moon. It was these same propellants that powered the three main engines of the old space shuttle, producing much of the cloud of steam that was the hallmark of a successful launch.