Heading Back to Earth—An Astronaut's Perspective
Science Buddies' founder, Kenneth Hess, was an astronaut on Blue Origin's NS-25 suborbital spaceflight. Follow along as he recounts the minutes of descent and rapid changes in g-force before touching back down on Earth—and explore science projects students can do to experiment with the physics of spacecraft design and landing.
In previous posts, Ken shared an overall account of his flight and then described in detail preparing for suborbital flight and his experience with the rocket's launch, ascent, and time in flight. In this final post in this series, Ken shares his experience as he and the other astronauts aboard NS-25 headed back to Earth.
The 30-second warning buzzer to get back into our seats broke the silence of space. Despite all my preparation, my two and a half minutes in space had passed as if time had been accelerated. In disbelief that it was time to get back in my seat, I began to slip back under my shoulder straps and tighten the 5-point harness.
At that moment, at an altitude above 200,000 feet, in what was still almost a vacuum outside, I heard a subtle and pure musical tone (D 6th octave, I later identified). The capsule literally began to whistle its way back to Earth. As it slipped through the thin upper atmosphere at a speed passing through Mach 3 (three times the speed of sound), the high velocity of the supersonic flow compensated for the lack of air density, creating a resonance on some part of the structure, probably the reaction control system (RCS). The sound carried through to the capsule interior. Fifteen seconds later, having fallen approximately 10 miles during that brief interval, the sky ever so slightly began to brighten. The whistle was swallowed by what sounded like a rapidly building storm as the atmosphere thickened and the wind noise became audible and grew.
A space capsule's blunt cone shape is purposefully designed to be non-aerodynamic because it was found in research during the 1950s that the resulting shockwave carries much of the re-entry heat away from the vehicle. The blunt shape also slows the vehicle more quickly than one that is streamlined, creating stronger peak G-forces. Our G-forces began to build along with the aerodynamic noise outside; in just 30 seconds, we went from zero-G to the maximum for the entire flight of 5.2 Gs as the thickening atmosphere rapidly slowed our capsule.
Because we were in reclined seats, the G-forces in the New Shepard crew capsule were primarily through the chest, from front to back, called the x-direction (or Gx). These forces are like having someone sitting on your chest. They make it more and more difficult to breathe as the Gx force increases, but they are still easier to tolerate than G forces in other directions. I had been trained in the proper breathing techniques during 2021 training in the high-G centrifuge at NASTAR outside Philadelphia, and I instinctively began using those techniques as the Gx forces rose—inhaling deeply and pursing my lips together to increase pressure in my lungs, forcing oxygen into the bloodstream and keeping my chest inflated.
Absent the steadying inertia and guidance system of the aerodynamic booster, which is many times the size of the crew capsule, our vehicle was like a shuttlecock in the wind. Constantly jostled and gently shook, not jerked or tossed, descent contrasted with the smooth ride up. The RCS began firing to keep the capsule properly oriented just as the plateau in aerodynamic noise coincided with the max G-forces. The sound level was approximately the same as the aerodynamic noise at max Q during ascent, but far below the sound level of launch.
As quickly as they had arrived, the high G-forces were gone—we were only above 3 Gs for 20 seconds. The aerodynamic noise also subsided as the atmosphere slammed on the brakes, slowing us from Mach 3.4 to subsonic in just over half a minute. At 55,000 feet, the sky was bright, and the RCS thrusters fired in rapid succession as descent continued.
For 90 seconds, we continued to fall, approaching a terminal velocity of about 220 mph and a G-force just above 1, Earth's normal gravitational force. The noise level was about the same as the cabin of an airliner. The capsule communicator in mission control (CAPCOM) told us that our booster had safely landed.
During the early stages of descent, even when velocity reached 2,383 mph, there was no sense or visual clue of falling from space. As we passed through clouds, we could see the ground. We continued falling. We knew we were falling.
With the ground appearing closer and closer, I was still on a high from being in space, not anxious, not apprehensive, but certainly prepared to be appreciative when the chutes opened. After all the amazing, state-of-the-art technology that enabled the flight to this juncture, my life then depended on some nylon fabric and string! I knew that a Soviet flight had been lost when the parachutes did not open. CAPCOM crackled over the radio, "Standby drogues. Standby drogues."
The three drogue parachutes are small, intended to stabilize the capsule and shave about 70 mph off its velocity, reducing the strain on the main parachutes (which they help to pull out) when they open about 15 seconds later. Leaving nothing to chance, the drogues are blasted out by mortars. The explosion from the small cannons breaks the drogue storage compartment covers into hundreds of tiny shards, visible through our windows, then snap—the drogues jerked us to attention as they opened at 6,500 ft above ground level.
Almost immediately, the CAPCOM announced, "Standby mains. Standby mains."
Seconds later, the three main parachutes blasted from their compartments as we passed through an altitude of 3,700 feet. The mains are reefed when they first open. A cord wrapped around the canopy keeps them from fully inflating until moments later, softening the deceleration, a more prolonged jolt than for the drogues.
We floated down in a welcome anticlimax to the sensory overload of everything that preceded. The quiet was broken twice as the RCS's compressed nitrogen tank vented leftover gas with a loud hiss. What people on the ground knew but my crewmates and I did not was that one of the reef cords didn't release, so we only had two out of three fully inflated main parachutes. We were coming in hot.
Normal terminal velocity while under the main parachutes is about 17 mph—we were descending at 21 or 22 mph. A retrorocket of compressed gas fires several feet above the ground to shed some of that speed before touchdown. Two backup systems also protect the crew. The first is a sacrificial ring of aluminum honeycomb material at the base of the crew capsule that crushes to absorb energy under a strong impact. Likewise, each crew seat is on a scissor mechanism that collapses under the most extreme conditions. We hit the desert floor in what sounded like an automobile crash. Pushed into our seats by the impact before bouncing up to the extent our five-point harnesses allowed, then finally falling to rest, we all clapped and shouted! None of us had any idea anything was wrong, and we felt complete exhilaration at the successful fulfillment of a long-anticipated endeavor.
My wife Connie was there to greet me on landing with a hug and a kiss and the question, "Did you know that you only had two parachutes?" A short time later, I was reunited with the thirteen other family members who watched my flight, including my daughter Amber and her three boys. Amber was arguably the most worried about my flight, and we had an emotional reunion.
Following in the footsteps of my pioneer ancestors, going to space was my baby step contribution to opening the space frontier, an expansion of humanity's geography that will evolve in fits and starts over a timespan measured in centuries, typical for a new world. For a few brief moments, with a flood of new sensations, my trip arcing into the frontiers of space allowed me to experience life on the tip of the spear.
Student Project: Experiment with Parachutes for Safe Landing
In Ken's account of the landing of NS-25, he explains the system of parachutes and how they are deployed. Until they landed, he and the other astronauts were not aware that only two parachutes had fully deployed, which made them land at a greater velocity than expected. In the How Does the Number of Parachutes Affect Terminal Velocity? project, students experiment to see how the number of parachutes affects the terminal velocity.
Other Student Projects
Students interested in the physics of a spacecraft's descent and landing can conduct related experiments with projects like these:
- Build a Model Planetary Lander with micro:bit: Use micro:bit to build a "lander" vehicle with a sensor that can measure distance to the ground, allowing programmed outputs like blinking lights or an audible alarm.
- Build a Model Planetary Lander with Arduino: Use Arduino to make a model planetary lander that uses a distance sensor and automatically deploys landing gear before impact.
- Make a Model Rocket Land Vertically: Explore the physics behind designing a rocket for a vertical landing and experiment with reversing the aerodynamic stability of a basic model rocket.
- Rocket Catcher Challenge: Explore the idea of reusable rockets and design a paper-based rocket-catching device to enable a vertical landing.
A Firsthand Account of Suborbital Spaceflight—From Pre-flight Training to Landing
This post is part of a series of posts about Ken's experience as an astronaut on Blue Origin's NS-25 suborbital spaceflight. This series breaks space flight into individual segments, including pre- and post-flight, and connects Ken's first-hand account with space science projects for students.
Other posts in this series:
- A Firsthand Account of Suborbital Spaceflight - An Astronaut's Perspective
- Preparing to Go to Space! - An Astronaut's Perspective
- The Thrill of a Rocket's Launch & Ascent - An Astronaut's Perspective
"Going to space was my baby step contribution to opening the space frontier, an expansion of humanity's geography that will evolve in fits and starts over a timespan measured in centuries, typical for a new world."
Kenneth Hess, Science Buddies Founder
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