Mike Mullane - Riding Rockets

Astronauts have great faith in the OMS engines. They are the essence of simplicity. They have no spinning turbo-pumps to worry us, not even an igniter to fail and jeopardize our lives. The fuel and oxidizer are pushed into the combustion chamber by helium pressure, and their chemical composition causes them to ignite on contact. No spark needed. Getting stuck in orbit would ruin your whole day, so having a deorbit engine that was as foolproof as possible eased one of our perennial worries.

At time-zero the cockpit shuddered under the hammer of the two engines. Small bits of food crumbs, which had escaped our cleanup, drifted to the back wall. Hoot and Guy watched the computer displays of helium pressures, temperatures, and other indications of engine performance. They were all nominal.

The burn, and its acceleration on our bodies, ended. We were back in weightlessness. Hoot checked the residuals, which indicated the error of the maneuver. They were negligible. Whatever fate awaited us, we were now irrevocably committed. The OMS deorbit burn had clipped 200 miles per hour from our speed and changed our orbit so its low point was into the Earth’s atmosphere. There was no way we could climb back up to the temporary sanctuary of orbit.

According to the checklist I should have been strapped into the mid-deck seat, but there was nothing to do or see down there, so I had asked Hoot if I could hang out on the flight deck and shoot some video of the early part of reentry. I would get into my seat before the Gs got too high.

During the next twenty-five minutes we fell across the Indian Ocean, across the darkened continent of Australia, and shot into the night sky of the great Pacific basin. In our dive toward perigee, Atlantis gained back the velocity lost in the deorbit burn and added more. Shuttles achieved their peak speed on reentry, not ascent. The ride was as smooth and silent as oil on glass. The machine was on autopilot, with only her rear thruster jets active. Those were holding Atlantis ’s nose 40 degrees high and presenting her wounded belly to the approaching atmosphere. Her aerodynamic control surfaces, the elevons on the wings and rudder on the tail, wouldn’t be able to hold her in attitude until we were much deeper into the atmosphere. If the rear thrusters failed, we would slowly drift out of attitude, tumble, and die. But an RCS system failure was far down on our lists of worries. The thruster jets were just smaller versions of the OMS engines, using a simple blow-down helium pressure feed system with propellants that burned on contact.

Hoot called the descent. “Mach 25.1…340,000 feet…Guidance looks great.” We were slightly faster than 25 times the speed of sound and at an altitude of 64 miles. Our little green bug was tracking perfectly down the center energy line. We were on course for Edwards AFB, still 5,000 miles away.

The atmosphere had thickened enough to become an obstacle to our hypersonic sled. Compression against Atlantis ’s belly heated the air to a white-hot glow now visible from the front windows. I wondered what was happening underneath us. I had visions of molten aluminum being smeared backward like rain on a windshield. None of our instruments or computer displays showed Atlantis ’s skin temperature. Only Houston had that data. I wondered if they would call us if they saw it rising. I hoped not. Such a call would definitely have us all tensed up as we died. Even Hoot wouldn’t be able to laugh away that MCC call. I looked at our displays and meters, not sure which would be the first to reveal a heat-shield problem. They were all in the green. Hoot would later tell me his eyes were never long from the elevon position indicators, certain a left-right split in those instruments would be the first hint the right wing was melting.

With the nominal displays I was happy to consider that our worries might have been misplaced. Maybe we had been alarmists. Maybe the damage was minor, as MCC had indicated. I still couldn’t believe that, but I prayed it was the case. I would have no problem offering the flight director, the CAPCOM, and everybody else an apology for having questioned their judgment.

“Three hundred ten thousand feet…still holding Mach 25…some Gs starting to build.”

Hoot didn’t have to tell me about the Gs. Dressed in my LES I had added more than sixty pounds to my body. My zero-G-acclimated muscles were finding it difficult to bear that weight against even a small G-load.

I looked upward through the top windows. As I had seen on STS-41D a snake of plasma flickered over us and slithered into the black. Periodically it would pulsate in incandescent-bright flashes that filled the cockpit like camera flashes. I wished I had paid more attention to the reentry light show during my Discovery mission. Wasn’t this plasma ribbon brighter? Weren’t those flashes more frequent? Was it Atlantis ’s vaporized skin enhancing the show? There were no calls of distress from Hoot or Guy and the radios were mute. If the heat was dissolving Atlantis ’s belly, the damage had yet to reach a system sensor.

At 240,000 feet and Mach 24.9 the guidance system commanded Atlantis into a 75-degree right bank. She was high on energy and the autopilot was pulling her off course to increase the distance to landing. In that extra distance we would have more time to descend. We trusted the autopilot to turn us back toward the Edwards AFB runway at the appropriate time. It was impossible for a shuttle pilot to look out the window at a featureless ocean from 45 miles high while still 3,000 miles from the runway and manually modulate the orbiter’s energy state. We had to trust the wizardry of accelerometers in Atlantis ’s inertial measuring units to do that.

The plasma vortex intensified in brightness. I wondered how many earthlings were watching the celestial spectacle. The trail of superheated air would glow for many minutes after our passage. We were painting a white-hot arc from horizon to horizon to take away the breath of anybody watching, be they jungle island shaman or the crew of a supertanker.

The horizon came into view from Guy’s window. The Earth’s limb was tinted with the indigo of an impending sunrise.

“Mach 22 at 220,000 feet, a half-G.”

I wasn’t going to be able to stand much longer. My leg muscles were quivering. I had to get down the ladder to my seat. Before I left the flight deck, though, I craned my neck to see the Earth. The Sun had risen and painted a broken layer of clouds in flamingo pink. Just when I thought I had seen every “wow” scene in space, I was treated with a new feast for the eye. We were still traveling at a couple miles per second but had dropped to within forty miles of the cloud tops. The illusion was that we were accelerating, not slowing down. The clouds appeared to skim by at science-fiction speeds. The sight was a narcotic and I watched it until my zero-G-weakened legs couldn’t take my weight any longer and I collapsed to the floor. It was beyond time to get to my seat. I crawled to the mid-deck ladder like a wounded infantryman and felt with my feet for the ladder rungs. In slow, deliberate movements I worked my way downward and into my seat. By the time I was strapped in, I felt as if I had just descended the Hillary Step with a Sherpa on my back. I was exhausted from working in a G-force that was one half of the Earth’s pull.

I hated being downstairs. I was staring at a wall of lockers. There were no windows, no instruments. I felt claustrophobic. I could not imagine anything more terrifying than being in this room and hearing the death throes of a disintegrating shuttle while simultaneously having the lights and intercom go off, as had Ron McNair, Greg Jarvis, and Christa McAuliffe on Challenger. If the lights went dark and my intercom failed, I resolved to unstrap from my seat and try to climb upward so at least I could die looking out a window. There would be no reason to go to the side hatch and try our new bailout system. If I jumped out during aerodynamic heating, my body would be vaporized as quickly as a mosquito in a bug lamp.