Austrian skydiver Felix Baumgartner made it seem like all you need is a daring jump to get back to Earth from the edge of space. However, he wasn’t actually in space, at least not yet. Heading home from somewhere higher is far more complicated than just going down in a blaze of glory. The most dangerous part of any modern astronaut’s journey requires a lot of steps, each crucial in getting them home safely. So let's find out exactly how an astronaut gets back to earth from outer space.
Felix Baumgartner's supersonic freefall from 128k' - Mission Highlights by Red Bull Each return trip home is determined by first knowing the best course and steps for an optimal return trajectory. Earth constantly rotates, and every other orbiting body has its own motion relative to it. To give you an idea on how this is generally done, if a space capsule is scheduled to return home to Earth from the ISS:
Step 1: Experts on the ground need to prepare beforehand by taking into account the current orbit of the station, its speed, and the current orientation of the planet.
Step 2: They then calculate the capsule's trajectory that will enable it to land within the target destination and re-enter the earths atmosphere without burning up or bouncing off.
Step 3: Once the location has been determined, survey teams are then dispatched that will scout the actual validity of the area. The team needs to observe whether the location is flat or calm enough for a safe landing, or if there will be meteorological complications that might hamper the return trip. Once the course and trajectory has been determined, all onboard systems are given one last round of checking and testing. In the event of a certain malfunction, the course will be adjusted to compensate for time required to resume the return trip. It's important to note that the re-entry window doesn’t just involve place, but also time as the Earth spins, and as the vehicle orbits. With that, the time required to test the systems itself, and any subsequent related actions will also be taken into account.
The next step is to orient the vehicle into its Trans-Earth Injection window. For vehicles docked onto a space station or Shuttle, like the Soyuz or Dragon capsule, proper undocking procedures are carried out first. Separation is then usually done manually by pushing the capsule into a higher orbit, creating a speed gap between the station and vehicle, so that they don't collide at the point where their orbits intersect. For vehicles not docked or connected to another vehicle or stationary body, such as an Apollo capsule, the procedure typically skips to directional orientation and the jettison of non-essential components.
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The remaining portion of the vehicle will then perform a course correction burn. The thrusters are fired to orient the vehicle towards its re-entry angle. This is a delicate step to ensure that the heat-shielded part of the returning module faces the Earth’s atmosphere. Most heat-shields are usually placed at the underside of the returning module, so it should be the side facing the atmosphere as it falls down, or the whole module and the astronauts inside it will disintegrate.
Then, the vehicle performs a de-orbit burn, a procedure that further decreases the speed of the vehicle, in order to break its orbit enough for the atmosphere itself to act as a brake. The de-orbit burn’s duration depends on preliminary calculations, though it typically lasts more than 4 minutes. The de-orbit burn is usually set at a curved, angular path that both reduces re-entry speed and allows penetration through the atmosphere. Too steep, and the vehicle turns in to a fireball and-or exerts too many Gs on the astronauts inside that they won't survive. Too shallow, and the spacecraft bounces off, like a rock skipping onto water. Exactly the angle you need depends on the shape and size of the craft, but generally its about 40 degrees. A streamlined craft can more easily penetrate at a shallow angle, but a blunt shape can survive the heat more easily.
Just before re-entering the earth's atmosphere, often after the de-orbit burn procedure, any final few non-essential components are separated using impact-less separation. Only the descent module will make it back to earth, as the others will burn up in the atmosphere.
Once the vehicle has made contact with the Earth’s atmosphere, it begins experiencing further deceleration, thanks in part to the dense air pushing onto the craft. This is also where the vehicle starts to heat up, due to the massive friction it experiences as it pushes through atmospheric layers.
In fact, it gets so hot, that the air around the craft is literally ionized into plasma, the glowing gaseous stuff of stars. This produces another side effect. Because of the surrounding charged particles, ionization blackout occurs. This means electromagnetic signals get disrupted, and communication with the spacecraft becomes impossible, at least until it gets further down and slows enough for the surrounding plasma to eventually dissipate. One important thing to note during atmospheric entry is trajectory maintenance. Though already calculated during the preparation phase, tiny adjustments in position and direction are often made as the vehicle falls further into the atmosphere. This is mainly due to the differing densities, speeds and directions of wind hitting the vehicle. It can do this by rotating, as rotating in one direction increases lift on the capsule, while rotating in the opposite way decreases lift. Without these tiny adjustments, the vehicle could dangerously veer of course, potentially moving significantly far off from the intended landing destination.
During atmospheric entry, all vehicles typically start at almost 30,000 km/h, that's more than 20 times the speed of sound. After about 8 minutes of descent, the atmosphere will be able to decelerate the vehicle to just about 1,000 km/h. This is still way too fast for a gentle touchdown though, so a series of parachutes are deployed. The first parachute usually provides preliminary deceleration, with the main parachutes deploying later to ease the capsule all the way towards touchdown. The capsule is suspended below the parachute at a specific angle relative to the ground to help dissipate heat gained through its re-entry.
With a controlled descent, returning spacecraft are usually able to minimize the G-forces experienced by the astronauts as much as possible, usually to around 4Gs, which is a relatively smooth ride compared to the 6Gs they experienced during lift-off. However, emergency re-entry procedures may force them to experience much higher Gs. This was the case during the re-entry of the Soyuz TMA-10 in 2007, as it was forced into an unexpected ballistic descent of almost 9Gs, after its equipment was damaged. Miraculously, all astronauts survived.
Expedition 37/38 Crew Welcomed into the Space Station by NASA The final stages of the operation occur when the vehicle is only about 5 km above ground. The somewhat-cooled-down-but-still-very-hot heat-shield is finally jettisoned away. At this point, the initial parachutes have been jettisoned, and the main parachutes have been working for several minutes, but an extra set of retro rockets, positioned below the spacecraft behind the heat-shield, prepare for firing in order to further decrease the speed of the vehicle as needed. The vehicle then internally adjusts to orient the astronauts upwards, to reduce the impact as the crews seats have shock absorbers. Then, just as it reaches approximately a meter off the ground, the rockets fire in order to slow the capsule down to around 5 kilometers per hour.
Though the capsule keeps moving downwards, the crews seats are cushioned by their shock absorbers. Outside the vehicle, flotation mechanisms may be deployed shortly before the last few seconds to help the vehicle stay afloat and upright in the event of a splashdown.
But other, more sophisticated landing procedures, like propulsive landings, are being developed as a third final touchdown method, particularly for SpaceX’s Dragon 2 capsule. Think of those rocket sci-fi films landing down on alien planets. Basically the boosters would not just act as minor retro rockets, but will be ignited and used from a significantly higher altitude, all the way down to its target destination.
Dragon 2 Propulsive Hover Test by SpaceX Though some plans were scrapped in June last year, it remains as an alternative method of providing deceleration for the a manned spacecraft’s final descent in the future. And that is generally how we get astronauts home today from space. However, several of these steps may differ depending on the vehicle used and the profile of the mission. This is especially true when the configurations of such vehicles are significantly different from what would typically be considered the bread and butter capsule or module type. The most common example is the standard Space Shuttle. Orientation and de-orbit procedures aside, the Space Shuttle’s plane like form factor lets it use a combination of standard deceleration procedures and aircraft maneuvers in order to land. After a de-orbit burn, it falls down on its underside, and then flies like an ordinary airplane, until it reaches the runway where it lands. Parachutes then help it further decelerate.
Landing of a Space Shuttle Full HD! by XXDTOBIXXD Another special case is the Dragon 2 capsule. As mentioned briefly earlier, it's designed to use an active, powered landing system via boosters, completely ditching the use of parachutes during its lower atmospheric descent. This was initially due to the fact that its designed to land not just on Earth, but on destinations where parachutes may be ineffective, such as the thin and non-existent atmospheres of Mars and our Moon respectively. Another special mention when it comes to landing spacecraft is SpaceShipOne, and its current version SpaceShipTwo. Technically, this space-plane isn’t capable of orbital distances similar to that of other manned capsules. However, it does demonstrate its “feathered landing” procedure, a method of controlled descent by tilting the wings down during free fall, slowing down the craft enough to not require heat shielding, much like a shuttlecock. This method is optimal for the craft due to its lower reentry speed and lower altitude, though it's also only effective for similar sub-orbital “jump shot” launches.
Watch SpaceshipTwo's glide flight and landing at Spaceport America by VideoFromSpace
Developing these techniques to get our astronauts back home safely has cost the worlds space programs billions, but it continues to be one of the most challenging parts of any trip to space. I hope you were amazed at how astronauts get home from space! Thanks for reading.
